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:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5737篇
  免费   119篇
各国政治   238篇
工人农民   226篇
世界政治   456篇
外交国际关系   207篇
法律   3586篇
中国政治   49篇
政治理论   1077篇
综合类   17篇
  2021年   41篇
  2020年   69篇
  2019年   103篇
  2018年   131篇
  2017年   116篇
  2016年   118篇
  2015年   68篇
  2014年   118篇
  2013年   583篇
  2012年   141篇
  2011年   151篇
  2010年   122篇
  2009年   138篇
  2008年   167篇
  2007年   155篇
  2006年   140篇
  2005年   129篇
  2004年   155篇
  2003年   124篇
  2002年   100篇
  2001年   312篇
  2000年   277篇
  1999年   193篇
  1998年   79篇
  1997年   79篇
  1996年   52篇
  1995年   54篇
  1994年   48篇
  1993年   38篇
  1992年   121篇
  1991年   139篇
  1990年   131篇
  1989年   126篇
  1988年   113篇
  1987年   125篇
  1986年   100篇
  1985年   95篇
  1984年   96篇
  1983年   83篇
  1982年   57篇
  1981年   73篇
  1980年   35篇
  1979年   73篇
  1978年   43篇
  1975年   37篇
  1974年   49篇
  1973年   54篇
  1972年   39篇
  1971年   34篇
  1970年   29篇
排序方式: 共有5856条查询结果,搜索用时 15 毫秒
101.
Abstract: This study evaluates the use of polydimethylsiloxane polymer composites (PDMS, Fe–PDMS) as a passive sampling media to preconcentrate analytes found in environmental settings. Samplers were made using commercially available silicone products. The composite samplers were assessed for their sorption properties using Atrazine and Irgarol 1051 as model compounds. The initial study assessed the utility of PDMS sheets as adsorption material by following analyte depletion from spiked water samples by solid‐phase microextraction gas chromatography/mass spectrometry (GC/MS). Follow‐up studies conducted at high and low concentrations using lab manufactured iron‐ PDMS rods (Fe–PDMS) showed effective uptake at differential rates from concentrations ranging between 1 μg/L and 10 μg/L. Adsorption mechanism was reversible, and compounds were recovered from the exposed materials and analyzed by liquid–liquid extraction‐GC/MS. Both composites showed better affinity for Irgarol 1051, 100% removal, than for Atrazine, 30% removal, likely representing their KOW differences, 3.6 and 2.6, respectively. This “proof of concept” study demonstrates the positive implications for the use of silicon polymer composites as a monitoring tool for environmental forensic purposes.  相似文献   
102.
Abstract: The proper identification of illicit plants such as Papaver somniferum L (opium poppy) is important for law enforcement agencies. The identification of opium poppy was presently tested using 10 genetic markers that are universal for all plants or specific to a few poppy plants. The genetic distances of universal markers such as nuclear internal transcribed spacer (ITS), 18S rRNA, plastid rbcL, and trnL‐trnF intergenic spacer (IGS) of 14 species included in the Papaveraceae and Fumariaceae family were acquired by sequence comparisons. Both the ITS region and trnL‐trnF IGS showed high levels of interspecific divergence. Six Papaver genera‐specific markers were developed from coding regions involved in morphine biosynthesis. Three markers (TYDC, NCS, and BBE) produced amplicons only in opium poppy, providing a presence/absence test for opium poppy, while three additional markers (CYP80B1, SAT, and COR) were genus specific. These 10 markers might be useful for the forensic DNA analysis of opium poppy.  相似文献   
103.
Although gunshot is by far the most common means of homicide in the United States, significant numbers of homicides are also perpetrated by other means. Blunt-force injuries are produced by a variety of objects, including hands and feet and many different weapons. Some of these objects produce distinctive patterns of injury of potential evidentiary value. This paper presents a series of 20 consecutive blunt-force homicides in adults. Seventy percent (14 cases) of the victims were men. Thirty percent (six cases) followed an argument or altercation. A number of the weapons used were "weapons of opportunity" seized in the course of the incidents. Sixty-nine percent (nine cases) of known assailants were acquainted with their victims. Few characteristic patterned injuries were seen. Not surprisingly, craniocerebral trauma was the most common cause of death. One half (10 cases) the victims survived their assaults for varying periods of time. Homicides due to blunt-force injury still pose a significant challenge for the forensic pathologist, who must obtain a complete and accurate history of the fatal incident, interpret patterns of injury and other findings at autopsy, and correlate all of the findings to make an accurate ruling of the cause and manner of death.  相似文献   
104.
Determination of methamphetamine and amphetamine in hair was performed by gas chromatography/mass spectrometry using stable isotope-labeled internal standards, 2-methylamino-1-phenylpropane-2,3,3,3-d4 and 2-amino-1-phenylpropane-2,3,3,3-d4. Extraction of hair with methanol/5M hydrochloric acid (20:1) using ultrasonication was chosen as the standard method. The calibration curves for amphetamines in the hair were linear from 1 to 100 ng/mg (r greater than 0.99). The detection limit was 0.5 ng/mg at the 95% confidence level. The coefficients of variation (CV) (n = 8) of analysis using the spiked hair with methamphetamine were from 0.7 to 6%. The CV (n = 8) of analysis of the methamphetamine abuser's hair was 17.5%. Sectional analysis of monkey and human hair after methamphetamine ingestion suggested a good correlation between the duration of drug use and drug distribution in the hair.  相似文献   
105.
A simple and sensitive method is described for quantitative analysis of chlorpromazine in blood, serum, urine and tissue homogenate. The chlorpromazine cation radical produced by adding perchloric acid and 2,3-dichloro-5,6-dicyano-p-benzoquinone to the sample can be detected by the ESR method at room temperature. The sensitivity limit is 10 ng, that is, 20 μl of the solution containing 0.5 μg chlorpromazine/ml. The time needed for the measurement is within 10 min. The chlorpromazine radical thus produced is very stable; for example, 95% of the radical was observed after 24 h. The advantage of this method is discussed by comparing with the ordinary spectrophotometry which requires the purification of the sample.  相似文献   
106.
A method has been developed on reverse phase high performance liquid chromatography for simultaneous determination of methyl, ethyl and isopropyl alcohols under refractive index detection using pure water as the mobile phase. A good separation has been achieved between these alcohols. Detector response was linear with a detection limit of 5 mg/100 ml. Recovery studies were performed by adding known amounts of methyl and ethyl alcohols to blood, lung and liver within the range 80–90%. The reproducibility of the results was always >90%. The quantitative distribution of methyl alcohol in postmortem body tissues and fluids has been reported in three cases of poisoning.  相似文献   
107.
This article explores how the concept of enforcement style can be adapted to be more analytically useful in the study of regulatory behavior and its effects in developing countries. In its first part, the article sets forth a dimensional conception of enforcement style and suggests two new dimensions to incorporate the variations in the autonomy and capacity of regulatory agencies that are so significant in developing countries. In its second part, the article uses this analytical framework to compare the enforcement styles of state environmental agencies in two Brazilian states, São Paulo and Pará.  相似文献   
108.
Abstract:  We retrospectively reviewed autopsy records at a statewide medical examiner's office in order to identify and characterize deaths due to child abuse. In a 6-year period in New Mexico, the medical examiner investigated 45 deaths determined to be child abuse-related. Decedents were predominantly male (68.9%), Hispanic White (53.3%), and all were 5 years of age or younger, with a median age of 1 year. Head injuries were the most common cause of death (44.4%), followed by battered baby syndrome (15.6%). Relatives were involved as alleged perpetrators in 80% of the cases, with the father most often implicated (36.1% of cases), and 88.9% of child abuse injuries resulting in death occurred in the family's residence. Toxicology was positive in 26.7% of cases, but only two cases had substances of abuse present. Information on risk factors such as prematurity, parental age, and history of abuse was also collected.  相似文献   
109.
This paper reports results of a study based on a nationally representative sample of U.S. youth (N = 11,549) that asked two questions: (1) How does family structure affect the likelihood of adolescent death beyond that of race/ethnicity, sex, socioeconomic status, personal behavior, and other structural factors and (2) under what conditions might appeals for social justice be warranted for relative mortality statuses and for absolute gains in mortality? The study found that marital instability increases the likelihood of dying when controlling for a variety of other factors including class, race/ethnicity, sex, and unemployment rate in area of residence. The author argues that this finding lends support to social justice arguments to redistribute resources in such a way as to ensure the likelihood of absolute gains in mortality. The study also found, however, that race/ethnicity/sex also accounted for the likelihood of dying independently of family structure when controlling for socioeconomic and other factors. The author argues that this finding lends support to social justice arguments to redistribute resources on the basis of relative mortality statuses.  相似文献   
110.
A simple technique is presented for the longitudinal sectioning of hair samples without the need for any embedding medium. The technique applies to single hair samples that are placed in a groove of a particular depth and can either be scraped or cut to the desired level. Planar sections are obtained that reveal the internal structure of the sample and are ideal for the application of surface analytical techniques for the study of internal transverse and longitudinal distributions of xenobiotics.  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