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   996篇
  免费   31篇
各国政治   66篇
工人农民   66篇
世界政治   83篇
外交国际关系   46篇
法律   460篇
中国政治   53篇
政治理论   245篇
综合类   8篇
  2023年   7篇
  2022年   6篇
  2021年   11篇
  2020年   26篇
  2019年   31篇
  2018年   36篇
  2017年   33篇
  2016年   36篇
  2015年   22篇
  2014年   31篇
  2013年   157篇
  2012年   25篇
  2011年   23篇
  2010年   22篇
  2009年   26篇
  2008年   28篇
  2007年   21篇
  2006年   27篇
  2005年   21篇
  2004年   21篇
  2003年   28篇
  2002年   23篇
  2001年   16篇
  2000年   25篇
  1999年   21篇
  1998年   13篇
  1997年   12篇
  1996年   12篇
  1995年   16篇
  1994年   16篇
  1993年   15篇
  1992年   12篇
  1991年   14篇
  1990年   14篇
  1989年   11篇
  1988年   9篇
  1987年   14篇
  1986年   11篇
  1985年   17篇
  1984年   12篇
  1983年   13篇
  1982年   17篇
  1981年   9篇
  1980年   6篇
  1979年   5篇
  1978年   5篇
  1977年   7篇
  1976年   11篇
  1975年   6篇
  1968年   4篇
排序方式: 共有1027条查询结果,搜索用时 15 毫秒
141.
A solid-phase microextraction-gas chromatographic-mass spectrometric (SPME-GC-MS) method has been developed and validated for measuring four club drugs in human urine. These drugs include gamma-hydroxybutyrate (GHB), ketamine (KET), methamphetamine (MAMP), and methylenedioxymethamphetamine (MDMA). These drugs are referred to as 'club drugs' because of their prevalence at parties and raves. Deuterium labeled internal standards for each of the four drugs was included in the assay to aid in quantitation. The drugs were spiked into human urine and derivatized using pyridine and hexylchloroformate to make them suitable for GC-MS analysis. The SPME conditions of extraction time/temperature and desorption time/temperature were optimized to yield the highest peak area for each of the four drugs. The final SPME parameters included a 90 degrees C extraction for 20min with a 1min desorption in the GC injector at 225 degrees C using a splitless injection. All SPME work was done using a 100microm PDMS fiber by Supelco. The ratio of pyridine to hexylchloroformate for derivatization was also optimized. The GC separation was carried out on a VF-5ht column by Varian (30m, 0.25mm i.d., 0.10microm film thickness) using a temperature program of 150-270 degrees C at 10 degrees C/min. The instrument used was a ThermoFinnigan Trace GC-Polaris Q interfaced with a LEAP CombiPal autosampler. The data was collected by using extracted ion chromatograms of marker m/z values for each drug from the total ion chromatograms (TIC) (full scan mode). Calibration curves with R(2)>0.99 were generated each day using the peak area ratios (peak area drug/peak area internal standard) versus concentration. The validated method resulted in intra-day and inter-day precision (% R.S.D.) of less than 15% and a % error of less than 15% for four concentrations in the range of 0.05-20microg/mL (MAMP) and 0.10-20microg/mL (GHB, KET, and MDMA). This method has the advantage of an easy sample preparation with acceptable accuracy and precision for the simultaneous quantification of these four drugs of abuse and shows no interference from the urine matrix.  相似文献   
142.
This article examines the contract design decisions of three federal agencies—the Departments of Health and Human Services, Defense, and Homeland Security—using five years of data from the Federal Procurement Data System. Three basic contract design elements are charted—type (fixed price versus cost reimbursement), length, and value—across simple to complex products. All three agencies use short‐term, fixed‐price contracts for the majority of the purchases that they make. This basic contract design allows agencies to tap the benefits of competition: innovation and cost‐efficiency. However, the Departments of Defense and Homeland Security often dramatically increase the length and value of contracts through modifications to initial agreements. This approach forgoes the benefits of competition and may expose the agency to the risk of cost overruns, delivery delays, and diminished product quality.  相似文献   
143.
As the challenges of maintaining (or, in the US case, attaining) affordable universal coverage multiply, the debate about what constitutes "real" reform intensifies in Western health care systems. The reality of reform, however, lies in the eyes of myriad beholders who variously enshrine consumer responsibility, changes in payment systems, reorganization, and other strategies -- or some encompassing combination of all of the above -- as the essential ingredient(s). This debate, increasingly informed by the agendas of health services researchers and health policy analysts, arguably serves as much or more to becloud as to clarify the practical options policy makers face and remains severely imbalanced with respect to the institutional sectors on which it concentrates, the fields of knowledge on which it draws, and the roles it envisions for markets and the state.  相似文献   
144.
正Dear Readers,Forum is a column that provides a space for varying perspectives on contemporary Chinese society.We invite you to submit personal viewpoints on past and current topics(in either English or Chinese).yanwei@bjreview.com Please provide your name and address along with your comments Deng Xiaoping’s role as the father of reform in modern China is historically secure.In his vast biography of the Chinese leader published in 2011,American academic  相似文献   
145.
146.

Objectives

The present study examines how individuals’ sanction risk perceptions are shaped by neighborhood context.

Methods

Using structural equation modeling on data from waves 6 and 7 of the National Youth Survey, we assess the direct and indirect relationships between adverse neighborhood conditions and two dimensions of sanction risk perceptions: the certainty of punishment and perceived shame. In addition, the role of shame as a mediator between neighborhood context and certainty of punishment is also investigated.

Results

The results indicate that adverse neighborhood conditions indirectly affect both forms of sanction risk perceptions, and additional results show that perceived shame fully mediates the effect of neighborhood conditions on perceptions of the certainty of punishment.

Conclusions

The perceptual deterrence/rational choice perspective will need to be revised to accommodate more explicitly the role of neighborhood context in shaping sanction risk perceptions.  相似文献   
147.
Forensic fractographic features of bone reliably establish crack propagation in perimortem injuries. We investigated if similar fracture surface features characterize postmortem fractures. Experimentally induced peri- and postmortem fractures were used to assess if fractographic features vary as bone elasticity decreases during the postmortem interval (PMI). Thirty-seven unembalmed, defleshed human femoral shafts from males and females aged 33–81 years were fractured at varying PMIs with a drop test frame using a three-point bending setup and recorded with a high-speed camera. Vital statistics, cause of death, PMI length, temperature, humidity, collagen percentage, water loss, fracture energy, and fractography scores were recorded for each sample. Results showed that fractographic features associated with perimortem fractures were expressed in PMIs up to 40,600 accumulated degree hours (ADH), or 60 warm weather days. Hackle was the most consistently expressed feature, occurring in all fractures regardless of ADH. The most variable characteristics were wake features (78.4%) and arrest ridges (70.3%). Collagen percentage did not correlate strongly with ADH (r = −0.04, p = 0.81); however, there was a strong significant correlation between ADH and water loss (r = 0.74, p < 0.001). Multinomial logistic regression showed no association between fractographic feature expression and ADH or collagen percentage. In conclusion, forensic fractographic features reliably determine initiation and directionality of crack propagation in experimentally induced PMIs up to 40,600 ADH, demonstrating the utility of this method into the recent postmortem interval. This expression of reliable fractographic features throughout the early PMI intimates these characteristics may not be useful standalone features for discerning peri- versus postmortem fractures.  相似文献   
148.
149.
150.
ABSTRACT

As one of many scholars who have situated their research in terms of nonviolence (a mode of action) rather than pacifism (a philosophical position), I ask, what do we gain instead by adopting an explicitly pacifist stance, especially as a response to forms of violent extremism? First, I respond to three common dismissals of pacifism, interrogating the misguided assumptions about violence/nonviolence upon which they depend. Second, exploring recent violent encounters between white nationalist and antifa activists in the US, as well as insights from Ruddick’s “maternal thinking,” I argue that taking a principled stance against collective violence (1) has practical utility, including a protective effect, (2) forces us to wrestle with the humanity of our adversaries and our inability to ever fully control them, and (3) enables radical inclusion by requiring sustained attention to difference but also resistance to the forms of injustice and oppression this “difference” might entail. The pacifism that emerges here is messy and power laden, demanding that we continually wrestle not only with one another but with the tensions inherent in human interaction, difference, and conflict.  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