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   3861篇
  免费   72篇
各国政治   122篇
工人农民   116篇
世界政治   171篇
外交国际关系   108篇
法律   2873篇
中国政治   18篇
政治理论   488篇
综合类   37篇
  2023年   35篇
  2021年   25篇
  2020年   40篇
  2019年   44篇
  2018年   60篇
  2017年   51篇
  2016年   76篇
  2015年   39篇
  2014年   61篇
  2013年   322篇
  2012年   99篇
  2011年   141篇
  2010年   89篇
  2009年   78篇
  2008年   123篇
  2007年   137篇
  2006年   119篇
  2005年   96篇
  2004年   133篇
  2003年   122篇
  2002年   122篇
  2001年   161篇
  2000年   138篇
  1999年   115篇
  1998年   25篇
  1993年   31篇
  1992年   69篇
  1991年   92篇
  1990年   91篇
  1989年   99篇
  1988年   98篇
  1987年   90篇
  1986年   78篇
  1985年   78篇
  1984年   70篇
  1983年   61篇
  1982年   25篇
  1981年   26篇
  1979年   33篇
  1978年   34篇
  1977年   25篇
  1976年   28篇
  1975年   28篇
  1974年   39篇
  1973年   37篇
  1972年   35篇
  1971年   37篇
  1970年   38篇
  1969年   33篇
  1968年   28篇
排序方式: 共有3933条查询结果,搜索用时 0 毫秒
941.
The optimal conditions for the isolation of caffeine from human blood by means of acetone extraction are described with special reference to the peculiarities of extraction from aqueous solutions. The possibility of concentration and purification of caffeine from blood plasma using acetone and aceton-chlorophorm mixture (2:8) as the solvents is illustrated. In addition, purification by silica-gel thin layer chromatography is discussed. Thin layer chromatography, UV-spectrophotometry, and high performance liquid chromatography are considered as potential methods for the identification and quantitative determination of caffeine.  相似文献   
942.
The authors consider topical problems pertaining to the performance of forensic medical expertise of the subjects suspected or accused of committing a crime and remaining in custody. The discussion is focused on the organization of expertise and medical examination of such persons with the participation of personnel representing different clinical disciplines. The special emphasis is laid on the absence in the normative-legal basis of the well-specified criteria for the severity of disease, the degree of vital activity limitation, and duration of the treatment in specialized hospitals. The lack of such criteria hampers not only medical certification of the subjects suspected or accused of committing a crime and remaining in custody but also objective forensic medical estimation of their health status. Recommendations for addressing this problem and its resolution are proposed.  相似文献   
943.
944.
945.
Recent information from various sources suggests that a new illicit drug, called "oxi", is being spread across Brazil. It would be used in the smoked form and it would look like to crack cocaine: usually small yellowish or light brown stones. As fully released in the media, "oxi" would differ from crack cocaine in the sense that crack would contain carbonate or bicarbonate salts whereas "oxi" would include the addition of calcium oxide and kerosene (or gasoline). In this context, this work presents a chemical profiling comparative study between "oxi" street samples seized by the Civil Police of the State of Acre (CP/AC) and samples associated with both international and interstate drug trafficking seized by the Brazilian Federal Police in Acre (FP/AC). The outcome of this work assisted Brazilian authorities to stop inaccurate and alarmist releases on this issue. It may be of good use by the forensic community in order to better understand matters in their efforts to guide local law enforcement agencies in case such claims reach the international illicit market.  相似文献   
946.
In response to the guidelines issued by the American Society of Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB-International) to establish traceability and quality assurance in U.S. crime laboratories, a NIST/ATF joint project entitled National Ballistics Imaging Comparison (NBIC) was initialized in 2008. The NBIC project aims to establish a National Traceability and Quality System for ballistics identifications in crime laboratories within the National Integrated Ballistics Information Network (NIBIN) of the U.S. NIST Standard Reference Material (SRM) 2460 bullets and 2461 cartridge cases are used as reference standards. 19 ballistics examiners from 13 U.S. crime laboratories participated in this project. They each performed 24 periodic image acquisitions and correlations of the SRM bullets and cartridge cases over the course of a year, but one examiner only participated in Phase 1 tests of SRM cartridge case. The correlation scores were collected by NIST for statistical analyses, from which control charts and control limits were developed for the proposed Quality System and for promoting future assessments and accreditations for firearm evidence in U.S. forensic laboratories in accordance with the ISO 17025 Standard.  相似文献   
947.
During the winter in 2008, Iowa experienced an increase in sudden unexplained infant deaths (SUIDs). SUIDs and infectious causes of infant deaths generally average 3 monthly (SD = 1.0) in Iowa. However, in January 2008, 9 infant deaths were reported to the Iowa Department of Public Health and the Iowa Office of the State Medical Examiner. Between January and March of 2008, joint investigation of 22 SUIDs was conducted. The investigations required the involvement of multiple medical examiners from various jurisdictions, testing for pathogens at the University Hygienic Laboratory, epidemiologic support from the Iowa Department of Public Health, and consultation with the Centers for Disease Control and Prevention. The preliminary hypotheses for the increase in the infant mortality included viral respiratory disease and/or possible novel respiratory viral infections being the cause. Collaboration between public health and the medical examiner offices resulted in timely assessment of the cases. While no single causative agent was responsible for the increase seen in the number of infant deaths, respiratory pathogens played a role in the deaths of 15 of 22 children.  相似文献   
948.
A morphine to codeine ratio greater than unity (M/C>1) has been suggested as an indicator of heroin use in living individuals. The aim of this study was to examine the morphine to codeine ratio in a large population (N=2438) of forensically examined autopsy cases positive for 6-monoacetylmorphine (6-MAM) and/or morphine in blood and/or urine. Blood and urine concentrations of 6-MAM, morphine and codeine were examined using GC-MS and LC-MS/MS methods. In 6-MAM positive samples, the M/C ratio was greater than unity in 98% (N=917) of the blood samples and 96% (N=665) of the urine samples. Stratification of 6-MAM negative cases by M/C above or below unity revealed similarities in morphine and codeine concentrations in cases where M/C>1 and 6-MAM positive cases. Median blood and urine morphine concentrations were 8-10 times greater than codeine for both groups. Similarly to 6-MAM positive cases, 25-44 year-old men prevailed in the M/C>1 group. In comparison to cases where M/C ≤ 1, the M/C ratio was a hundred times higher in both 6-MAM positive and M/C>1 cases. The range of morphine concentration between the lowest and the highest quintile of codeine in M/C>1 cases was similar to that in 6-MAM positive cases. This range was much higher than for M/C ≤ 1 cases. Moreover, linear regression analyses, adjusted for age and gender, revealed a strong positive association between morphine and codeine in 6-MAM positive and M/C>1 cases. The M/C ratio appeared to be a good marker of heroin use in post-mortem cases. Both blood and urine M/C>1 can be used to separate heroin users from other cases positive for morphine and codeine.  相似文献   
949.
950.
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