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   26602篇
  免费   1541篇
各国政治   1069篇
工人农民   982篇
世界政治   2174篇
外交国际关系   839篇
法律   17354篇
中国共产党   3篇
中国政治   155篇
政治理论   5322篇
综合类   245篇
  2020年   502篇
  2019年   546篇
  2018年   660篇
  2017年   764篇
  2016年   811篇
  2015年   647篇
  2014年   694篇
  2013年   2695篇
  2012年   635篇
  2011年   741篇
  2010年   798篇
  2009年   790篇
  2008年   677篇
  2007年   682篇
  2006年   720篇
  2005年   601篇
  2004年   580篇
  2003年   611篇
  2002年   553篇
  2001年   1005篇
  2000年   885篇
  1999年   732篇
  1998年   415篇
  1997年   350篇
  1996年   296篇
  1995年   323篇
  1994年   375篇
  1993年   323篇
  1992年   505篇
  1991年   544篇
  1990年   483篇
  1989年   528篇
  1988年   475篇
  1987年   465篇
  1986年   484篇
  1985年   480篇
  1984年   432篇
  1983年   444篇
  1982年   346篇
  1981年   330篇
  1980年   277篇
  1979年   366篇
  1978年   239篇
  1977年   210篇
  1976年   187篇
  1975年   175篇
  1974年   199篇
  1973年   175篇
  1972年   155篇
  1971年   144篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
In the forensic science laboratory, the recovery of spermatozoa from vaginal swabs, or vaginal cells from penile swabs, can help determine if sexual intercourse may have taken place. There are several methods used to recover spermatozoa and cells from the swabs before visualisation on a microscope slide and most of these methods use water. Phosphate buffered saline (PBS) is a non-toxic solution used in many biological laboratories. Unlike water, PBS prevents cells rupturing or shrivelling up due to osmosis. This study demonstrates that PBS can be used for the extraction of spermatozoa and cells from swabs and that PBS does not affect subsequent DNA profiling.  相似文献   
172.
Bioaerosol data is often used in cases of building mold infestation alleging damage or adverse health effects upon occupants, despite the lack of consistent sampling and analytical protocols and numerical health-based standards. The most fundamental problem in these scenarios is defining a “significant” difference between a suspect indoor environment and the reference environment, regardless of the type of sampling and analysis utilized. Data interpretation focused upon differences in absolute numerical concentrations of fungi is subject to wide differences in expert opinion. On the other hand, an objective quantification of differences can be expressed in terms of probability and better meets criteria established in evidentiary rules.  相似文献   
173.
Der Begriff der Landeskultur umfasst alle Maßnahmen zur Verbesserung der land- und forstwirtschaftlichen Nutzung des Bodens einschließlich der Erhaltung der Kulturlandschaft. Landeskultur ist somit alles Planen und Handeln mit dem Ziel, die Umwelt als gegebenes Naturraumpotential, insbesondere Wasser, Boden, Luft und die dazugehörigen Natur-, Kultur- und Sachgüter optimal zu erhalten, gestalten und rationell zu nutzen sowie dieses Potential mit bestmöglicher Qualität als natürliche und kulturelle Lebensgrundlage für die Allgemeinheit nachhaltig zu sichern. Landeskultur dient somit auch der Belebung und Werterhöhung der gebauten und gepflanzten Umwelt. Dies schließt auch und gerade die kulturelle Seite einschließlich Kulturlandschaften mit ein. Dabei ist es bis zur Überprüfung durch das BVerfG noch hinnehmbar, dass der Begriff „Landeskultur“ in Art. 89 Abs. 3 GG wegen der Mischkompetenz von Bund und Land vom BVerwG enger ausgelegt wird als in anderen Rechtsvorschriften.  相似文献   
174.
175.
176.
A 6-month-old girl died suddenly without any previous symptoms of heart failure. Autopsy examination showed cardiomegaly (97 g) with a severely fibrotized myocardium. The left coronary artery was originating from the pulmonary artery. Histologically, the myocardium showed myocardial infarcts of different ages, as well as grossly thickened arterial branches due to increased flow in left-right shunt. We suggest that rare anomalies of the coronary arteries should be considered in the autopsies of suspected sudden infant death syndrome cases.  相似文献   
177.
The impact of high temperatures (24 to 39 degrees C) and low to moderately high humidities (20 to 70%) on the applicability of TLC systems for drug identification was studied during a 6 month climatologic cycle in Burkina Faso (West Africa). In general, the Rf values as observed on the plates were found to be substantially affected as compared with values obtained at temperate climates. Some TLC systems were more affected than others and the largest deviations of up to 30 Rf units were at low humidities. Tropical conditions also had a negative effect on the reproducibility of Rf values. However, when an Rf-correction procedure was applied, using reference mixtures of known drugs on each plate, accuracy as well as reproducibility of the resulting Rfc values were drastically improved and data thus corrected were found to be compatible with existing TLC data bases developed under moderate climatological conditions. The impact of high to extremely high humidities (70 to 100%) remains to be investigated.  相似文献   
178.
Washington University v. Catalona revolves around ownership of tissue samples provided by patients for research purposes, raising significant ethical and legal questions concerning patient rights, current human research practices, and the treatment of samples as capital resources by the research institution.  相似文献   
179.
Here we consider two ways that nanomedicine might be disruptive. First, low-end disruptions that are intrinsically unpredictable but limited in scope, and second, high end disruptions that involve broader societal issues but can be anticipated, allowing opportunity for ethical reflection.  相似文献   
180.
In this study, a new method was developed for the impurity profiling of illicit MDMA tablets. The extraction efficiency, linearity, repeatability and reproducibility of the method were evaluated. Eighty two MDMA tablets coming from presumed unrelated large seizures in 2004 (n >500 tablets) were analyzed by gas chromatography mass spectrometry (GC-MS) in order to assess the discrimination power of the method. The latter was found to be practical, robust, relatively easy to perform, highly discriminative and yielding good chromatography. In addition, some new impurities were detected and identified. Their chemical structures and mass spectra are reported.  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