首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   327篇
  免费   2篇
专业分类
各国政治   30篇
工人农民   5篇
世界政治   3篇
外交国际关系   1篇
法律   264篇
中国政治   12篇
政治理论   13篇
综合类   1篇
出版年
  2024年   39篇
  2023年   151篇
  2021年   36篇
  2020年   3篇
  2018年   1篇
  2017年   5篇
  2016年   3篇
  2015年   3篇
  2013年   21篇
  2012年   9篇
  2011年   8篇
  2010年   11篇
  2009年   10篇
  2008年   6篇
  2007年   2篇
  2006年   4篇
  2005年   1篇
  2004年   3篇
  2001年   1篇
  2000年   2篇
  1998年   1篇
  1997年   2篇
  1991年   3篇
  1989年   1篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
排序方式： 共有329条查询结果，搜索用时 15 毫秒
71.
    
Optical tweezers have a wide range of uses for mechanical manipulation of objects in the microscopic range. This includes both living and static cells in a variety of biomedical and research applications. Single-focus optical tweezers, formed by focusing a laser beam through a high numerical aperture immersion objective, create a significant force, which enables controlled transport of a variety of different cell types and morphologies in three dimensions. Optical tweezers have been previously reported to capture and separate spermatozoa from a reconstituted simulated postcoital sample. We report herein the development of a simplified, more efficient cell transfer protocol that can separate and isolate both spermatozoa as well as leukocytes, with similar efficiencies as those previously reported. The new cell transfer method was used to separate sperm cells from a reconstituted mixture of spermatozoa and vaginal epithelial cells, with complete STR profiles developed from 50 cells with little evidence of contribution from the female contributor to the mixture. This modified protocol was then used to separate 21 samples of enriched leukocytes, with trapped cells ranging from 5 to 22 cells. Complete STR profiles were developed from as few as 10 leukocytes. Thus, with minimal sample preparation and a short trapping time, this method has the potential to provide an alternative to traditional differential extraction methods for separation of sperm:nonsperm mixtures while also providing versatility for separation of cells with differing morphologies.  相似文献   
72.
    
Ketamine deemed as a psychoactive substance has gained popularity for recreational use owing to its hallucinogenic and dissociative effects. Understanding the synthetic processes of ketamine can provide essential clues for law enforcement officers against illicit ketamine manufacturing. In this case report, a chemical company was being monitored by law enforcement officers due to its importation of precursors and materials that could be used for the synthesis of illicit drugs. After materials and products seized from this chemical company were employed for analyses using gas chromatography–mass spectrometry, liquid chromatography–high-resolution mass spectrometry, and nuclear magnetic resonance analyses, ketamine, hydroxylamine, 2-chlorophenyl cyclopentyl ketone, and cyclopentanone p-toluenesulfonylhydrazone were identified. In addition, a novel process for the synthesis of ketamine precursor 2-chlorophenyl cyclopentyl ketone from cyclopentanone p-toluenesulfonylhydrazone and 2-chlorobenzaldehyde was validated. This is the first report to uncover this novel process for the synthesis of 2-chlorophenyl cyclopentyl ketone and can be used to increase awareness among law enforcement officers and forensic practitioners about these novel starting materials for the synthesis of ketamine.  相似文献   
73.
    
Forensic firearm examination provides the court of law with information about the source of fired cartridge cases. We assessed the validity of source decisions of a computer‐based method and of 73 firearm examiners who compared breechface and firing pin impressions of 48 comparison sets. We also compared the computer‐based method's comparison scores with the examiners' degree‐of‐support judgments and assessed the validity of the latter. The true‐positive rate (sensitivity) and true‐negative rate (specificity) of the computer‐based method (for the comparison of both the breechface and firing pin impressions) were 94.4% and at least 91.7%, respectively. For the examiners, the true‐positive rate was at least 95.3% and the true‐negative rate was at least 86.2%. The validity of the source decisions improved when the evaluations of breechface and firing pin impressions were combined and for the examiners also when the perceived difficulty of the comparison decreased. The examiners were reluctant to provide source decisions for \"difficult\" comparisons even though their source decisions were mostly correct. The correlation between the computer‐based method's comparison scores and the examiners' degree‐of‐support judgments was low for the same‐source comparisons to negligible for the different‐source comparisons. Combining the outcomes of computer‐based methods with the judgments of examiners could increase the validity of firearm examinations. The examiners' numerical degree‐of‐support judgments for their source decisions were not well‐calibrated and showed clear signs of overconfidence. We suggest studying the merits of performance feedback to calibrate these judgments.  相似文献   
74.
    
Aluminum (Al) powders are commonly used in improvised explosive devices as metallic fuels, a component of explosive mixtures. These powders can be obtained readily from industrial‐scale and consumer products, and produced using unsophisticated “kitchen chemistry” techniques. This research demonstrates the potential of automated particle micromorphometry for comparisons between known source and questioned Al powders recovered from IEDs, as well as for insight into the method of Al powder manufacture. Al powder samples were obtained from legitimate manufacturers, and 56 samples were produced “in‐house” from Al‐containing spray paints and ball‐milled Al foils. Transmitted light microscope images of Al powder particles were acquired using an automated stage with automated z‐focus; 17 size and shape parameters were measured for all particles. Approximately 37,000–2,500,000 particles/sample were analyzed using an open‐source statistical package with customized code. Dimensionality reduction was required for processing the large datasets: eight of the 17 measured variables were selected based on inspection of the correlation matrix. Data from four subsamples from each of the 56 samples produced using “in‐house” methods were analyzed using ANOVA to assess the within‐ and between‐sample variation. High within‐sample variation was noted; however, ANOVA and post‐hoc Tukey's honestly significant difference (HSD) tests demonstrated that the between‐sample variation was substantially larger than the within‐sample variation. Each sample could be differentiated from all other samples in the test set. Future experiments will focus on ways to reduce the within‐sample variation, and additional statistical and microanalytical methods to classify sources and confidently constrain the method of Al powder manufacture.  相似文献   
75.
    
Homicide by stab wound is common worldwide. However, the use of unusual edged weapons is rarely reported in the forensic literature. Here, we report two cases of homicide involving a Japanese sword, or katana, and a sickle. Both of these weapons can create either stab or incised wounds with some particularities. In our cases, characteristics of the external wounds, internal injuries, and the depth of penetration raised the possibility of an unusual weapon. Meticulous forensic examination of these injuries (morphological characteristics, depth of penetration, trajectories, and cut marks in the bone) may allow the forensic expert to determine the type of weapon used.  相似文献   
76.
    
Testing for drugs in hair raises several difficulties. Among them is the interpretation of the final concentration(s). In a post‐mortem case, analyses revealed the presence of furosemide (12 ng/mL) in femoral blood, although it was not part of the victim's treatment. The prosecutor requested our laboratory to undertake an additional analysis in hair to obtain information about the use of furosemide. A specific method was therefore developed and validated to identify and quantify furosemide in hair by UHPLC‐MS/MS. After decontamination of 30 mg of hair, incubation in acidic condition, extraction with ethyl acetate, the samples were analyzed by UHPLC‐MS/MS. Furosemide was found in the victim's hair at 225 pg/mg. However, it was not possible to interpret this concentration due to the absence of data in the literature. Therefore, the authors performed a controlled study in two parts. In order to establish the basis of interpretation, several volunteers were tested (four after a single 20 mg administration and twenty‐four under daily treatment). The first part indicated that a single dose is not detectable in hair using our method. The second part demonstrated concentrations ranging from 5 to 1110 pg/mg with no correlation between dosage and hair concentrations. The decedent's hair result was interpreted as repeated exposures. In the case of furosemide analysis, hair can provide information about its presence but cannot give information about dosage or frequency of use.  相似文献   
77.
    
The bruise dating can have important medicolegal implications in family violence and violence against women cases. However, studies show that the medical specialist has 50% accuracy in classifying a bruise by age, mainly due to the variability of the images and the color of the bruise. This research proposes a model, based on deep convolutional neural networks, for bruise dating using only images, by age ranges, ranging from 0–2 days to 17–30 days, and images of healthy skin. A 2140 experimental bruise photograph dataset was constructed, for which a data capture protocol and a preprocessing procedure are proposed. Similarly, 20 classification models were trained with the Inception V3, Resnet50, MobileNet, and MnasNet architectures, where combinations of learning transfer, cross‐validation, and data augmentation were used. Numerical experiments show that classification models based on MnasNet have better results, reaching 97.00% precision and sensitivity, and 99.50% specificity, exceeding 40% precision reported in the literature. Also, it was observed that the precision of the model decreases with the age of the bruise.  相似文献   
78.
    
Performing point‐of‐care urine drug screen testing at autopsy by a forensic pathologist may provide an early indication of the presence of analytes of interest during autopsy. An evaluation for the screening of 14 classes of common drugs of abuse in postmortem urine by the point‐of‐care screening device, Alere iCup DX 14, is presented. One hundred ninety postmortem urine samples were screened with the iCup occurring at autopsy by the forensic pathologist. Positive and negative results obtained from the screening kit were evaluated against confirmatory test results obtained using routine forensic toxicology analyses that employed LC‐MS/MS and GC‐MS to detect a combination of over 85 common drugs of abuse and medications. Sensitivity for each respective iCup drug class ranged from 66% (buprenorphine) to 100% (methadone, tricyclic antidepressants). Specificity for each respective iCup drug class ranged from 89% (benzodiazepines) to 100% (amphetamines, barbiturates, buprenorphine, 3,4‐methylenedioxymethamphetamine, methadone). Positive predictive values ranged from 44% (benzodiazepines) to 100% (amphetamines, barbiturates, buprenorphine, methylenedioxymethamphetamine, methadone), while negative predictive values ranged from 96% (methamphetamine) to 100% (barbiturates, methadone, tricyclic antidepressants). A high false‐positive rate was yielded by the benzodiazepine class. The lack of fentanyl screening in the point‐of‐care device is a significant limitation considering its prolific prevalence in forensic casework. The results obtained in the study should be acknowledged when considering the use of the Alere iCup DX 14 in the context of postmortem casework to help indicate potential drug use contemporaneously with autopsy and when requiring such preliminary results prior to the release of a final forensic toxicology report.  相似文献   
79.
    
This is the first report on development of a library search‐based screening system for 3,4‐methylenedioxymethamphetamine (MDMA) in ecstasy tablets using a portable near‐infrared (NIR) spectrometer. The spectrum library consisted of spectra originating from standard substances as well as mixtures of MDMA hydrochloride (MDMA‐HCl) and diluents. The raw NIR spectra were mathematically pretreated, and then, a library search was performed using correlation coefficient. To enhance the discrimination ability, the wavelength used for the library search was limited. Mixtures of MDMA‐HCl and diluents were used to decide criteria to judge MDMA‐positive or MDMA‐negative. Confiscated MDMA tablets and medicinal tablets were used for performance check of the criteria. Twenty‐two of 27 MDMA tablets were truly judged as MDMA‐positive. Five false‐negative results may be caused by compounds not included in the library. No false‐positive results were obtained for medicinal tablets. This system will be a useful tool for on‐site screening of MDMA tablets.  相似文献   
80.
人力资源管理思想:三个里程碑及其在中国的升华   总被引：2，自引：0，他引：2  
人力资源管理实践历程中三个标志性实验成果昭示了人力资源管理思想演变的客观规律,是人力资源管理思想嬗变过程中的三大里程碑。科学管理实验使人力资源管理从自发管理走向自觉管理、科学管理和制度管理;霍桑实验系统发现了提高生产效率的社会心理因素,使人力资源管理从技术管理走向社会管理、行为管理和心理管理;职业生涯实验显示员工职业发展也是现代企业管理目标,现代企业目标和员工职业发展目标共存共长。三次实验的思想脉络、理论构造、功能机制有机对接、联动传承并推向纵深,成为人力资源管理历史上三个具有划时代意义的丰碑。科学人才观提出的"以人为本"的思想和理念是人力资源管理思想在当代中国的发展和升华。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号