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   7183篇
  免费   479篇
各国政治   336篇
工人农民   228篇
世界政治   473篇
外交国际关系   241篇
法律   5055篇
中国政治   35篇
政治理论   1257篇
综合类   37篇
  2020年   158篇
  2019年   169篇
  2018年   181篇
  2017年   218篇
  2016年   214篇
  2015年   199篇
  2014年   180篇
  2013年   745篇
  2012年   158篇
  2011年   174篇
  2010年   207篇
  2009年   228篇
  2008年   164篇
  2007年   157篇
  2006年   174篇
  2005年   160篇
  2004年   177篇
  2003年   158篇
  2002年   137篇
  2001年   310篇
  2000年   252篇
  1999年   225篇
  1998年   97篇
  1997年   66篇
  1996年   69篇
  1995年   80篇
  1994年   86篇
  1993年   88篇
  1992年   153篇
  1991年   157篇
  1990年   146篇
  1989年   156篇
  1988年   123篇
  1987年   138篇
  1986年   124篇
  1985年   132篇
  1984年   102篇
  1983年   116篇
  1982年   84篇
  1981年   78篇
  1980年   56篇
  1979年   108篇
  1978年   69篇
  1977年   59篇
  1976年   50篇
  1975年   47篇
  1974年   56篇
  1973年   55篇
  1972年   45篇
  1968年   40篇
排序方式: 共有7662条查询结果,搜索用时 15 毫秒
231.
A 55-year-old man complained of sudden onset of severe neck pain. This was followed by prompt loss of consciousness and death. Autopsy revealed rupture of a saccular aneurysm, which was considered to have resulted from enlargement of the remaining ductal tissue, and was located on the medial aspect of the uppermost portion of the descending aorta. Dense blood extravasation was noted in the posterior mediastinum and extending to the strap muscles of the neck and larynx. Histological examination of the rupture site revealed disappearance of the medial elastic fibers and thickened intima covered with dense fibrous tissue. Spontaneous ductus arteriosus aneurysm in adults is a rare finding, but widespread use of imaging technologies has revealed that it develops more frequently than previously recognized. Fatal complications may occur even when the aneurysm is relatively small. Therefore, pathologists should be aware of this aneurysm as a potential cause of sudden death.  相似文献   
232.
Objectives

While block randomized designs have become more common in place-based policing studies, there has been relatively little discussion of the assumptions employed and their implications for statistical analysis. Our paper seeks to illustrate these assumptions, and controversy regarding statistical approaches, in the context of one of the first block randomized studies in criminal justice—the Jersey City Drug Market Analysis Project (DMAP).

Methods

Using DMAP data, we show that there are multiple approaches that can be used in analyzing block randomized designs, and that those approaches will yield differing estimates of statistical significance. We develop outcomes using both models with and without interaction, and utilizing both Type I and Type III sums-of-squares approaches. We also examine the impacts of using randomization inference, an approach for estimating p values not based on approximations using normal distribution theory, to adjust for possible small N biases in estimating standard errors.

Results

The assumptions used for identifying the analytic approach produce a comparatively wide range of p values for the main DMAP program impacts on hot spots. Nonetheless, the overall conclusions drawn from our re-analysis remain consistent with the original analyses, albeit with more caution. Results were similar to the original analyses under different specifications supporting the identification of diffusion of benefits effects to nearby areas.

Conclusions

The major contribution of our article is to clarify statistical modeling in unbalanced block randomized studies. The introduction of blocking adds complexity to the models that are estimated, and care must be taken when including interaction effects in models, whether they are ANOVA models or regression models. Researchers need to recognize this complexity and provide transparent and alternative estimates of study outcomes.

  相似文献   
233.
Document examiners sometimes eliminate writers on the basis of differences which are given too much weight. This article is an attempt to explain some conditions whereby differences in the writing of one individual are misinterpreted as significant differences, when they are actually caused by conditions which are unknown to the examiner.  相似文献   
234.
Postmortem stability of DNA   总被引:11,自引:0,他引:11  
High-molecular-weight DNA was recovered postmortem in sufficient quantities from various human organ tissues as well as from blood, although not all organs were equally well suitable. Good DNA stability was found in brain cortex, lymph nodes and psoas muscle over a period of three weeks postmortem. Spleen and kidney showed good DNA stability up to five days postmortem but after longer periods, rapid degradation was observed. Yields of DNA from blood were not consistent because of the non homogeneity of samples. Blood clots were rich with DNA. Generally, the amount of degraded DNA correlated directly with the duration of the postmortem period. However in some cases, DNA degradation was already prominent after a short period. However in some cases, DNA degradation was already prominent after a short period. Case histories showed that high environmental temperature at the site of death and/or infectious diseases prior to death were the main factors for rapid autolysis. Gradual disappearance to complete loss of the long fragments (15-23 kb) was observed in DNA fingerprinting using the minisatellite probe 33.15. No extra-bands were noted, thus excluding erroneous conclusions. However, evidentiary value of older samples was lower.  相似文献   
235.
Hopelessness is implicated in multiple psychological disorders. Little is known, however, about the trajectory of hopelessness during adolescence or how emergent future orientation may influence its trajectory. Parallel process latent growth curve modelling tested whether (i) trajectories of future orientation and hopelessness and (ii) within-individual change in future orientation and hopelessness were related. The study was comprised of 472 adolescents [52% female, 47% Caucasian, 47% received free lunch] recruited at ages 12–13 who completed measures of future orientation and hopelessness at five annual assessments. The results indicate that a general decline in hopelessness across adolescence occurs quicker for those experiencing faster development of future orientation, when controlling for age, sex, low socio-economic status in addition to stressful life events in childhood and adolescence. Stressful childhood life events were associated with worse future orientation at baseline and negative life events experienced during adolescence were associated with both an increase in the trajectory of hopelessness as well as a decrease in the trajectory of future orientation. This study provides compelling evidence that the development of future orientation during adolescence is associated with a faster decline in hopelessness.  相似文献   
236.
Adolescent self-regulation is increasingly seen as an important predictor of sexual risk-taking behaviors, but little is understood about how changes in self-regulation affect later sexual risk-taking. Family financial stress may affect the development of self-regulation and later engagement in sexual risk-taking. We examined whether family financial stress influences self-regulation in early adolescence (age 13) and growth in self-regulation throughout adolescence (from age 13–17 years). We then assessed the effects of family financial stress, baseline self-regulation, and the development of self-regulation on adolescent sexual risk-taking behaviors at age 18 years. Using a curve-of-factors model, we examined these relationships in a 6-year longitudinal study of 470 adolescents (52% female) and their parents from a large northwestern city in the United States. Results indicated that family financial stress was negatively associated with baseline self-regulation but not with growth in self-regulation throughout adolescence. Both baseline self-regulation and growth in self-regulation were predictive of decreased likelihood of engaging in sexual risk-taking. Family financial stress was not predictive of later sexual risk-taking. Intervening to support the development of self-regulation in adolescence may be especially protective against later sexual risk-taking.  相似文献   
237.
An extensive body of research documents how governing parties generally suffer electoral defeats. Varying explanations have been offered, most of which touch upon the liabilities of policy responsibility. Although media coverage is generally acknowledged as one of these liabilities, few empirical studies have examined how news content affect government support. Based on the fact that voters get their information about politics, policies and societal issues from the media, this article studies how the constant stream of negative news influences incumbent support over a 20-year period in Denmark. Modeling a previously untested argument on the cost of ruling, it shows that the accumulation of bad news throughout tenure exerts a substantial effect on government support.  相似文献   
238.
There is an ongoing debate among practitioners and scholars about the security consequences of transnational migration. Yet, existing work has not, so far, fully taken into account the policy instruments states have at their disposal to mitigate these risks, and reliable evidence is lacking for the effectiveness of such measures. This article addresses both shortcomings as whether and to what extent national migration policies affect the diffusion of terrorism via population movements are analysed. Spatial analyses report robust support for a moderating influence of states’ policies: while terrorism can travel from one country to another via larger migration populations, this only applies to target countries with extremely lax regulations and control mechanisms. This research sheds new light on the security implications of population movements, and it crucially adds to our understanding of governments’ instruments for addressing migration challenges as well as their effectiveness.  相似文献   
239.
Innovating upon previous field experiments and theories of identity‐based discrimination, we test whether public officials are using searches (“identity‐questing”) to profile citizens and acting on latent biases. Pairs of “institutional” and “noninstitutional” requesters send lower and moderate burden freedom of information (FOI) requests—providing no identity cues apart from undistinctive names, e‐mails, and ID numbers—to nearly 700 of Brazil's largest municipalities. Results show institutional requesters receive one‐fifth more responses than noninstitutional comparators. For moderate versus lower burden requests, noninstitutional requesters are 11% less likely to receive a compliant response than their institutional comparators. The only plausible explanation for these results is identity‐questing, a phenomenon that has far‐reaching policy implications. Most of the world's FOI laws, for example, contain vague ID obligations, which translate incoherently from laws to regulation and practice. Results enjoin public service providers to protect the identities of citizens by default or upon request.  相似文献   
240.
Amidst calls for more scrutiny of the failure of infrastructure public–private partnerships (PPPs), uncertainty about how we can measure failure remains, and little systematic evidence illuminates its likelihood. Our mixed‐methods design explores the notion of failure and identifies the conditions under which it happens. The first phase of our research employs documentary analysis and semistructured expert interviews, and identifies project cancellation as capturing the most severe occurrences of failure. A second phase statistically analyzes a unique World Bank data set capturing the provisions of over 4,000 infrastructure PPPs launched between 1990 and 2015 in 89 countries. We find robust evidence supporting the theoretical claim that PPPs are less likely to be canceled in countries with more veto points among their political institutions to restrain politicians from intervening in policy implementation. Cancellation is a rare, but valid indicator of failure, and the importance of veto players clarifies how political risk operates in this context.  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