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   18270篇
  免费   835篇
  国内免费   208篇
管理学   2646篇
劳动科学   2篇
民族学   63篇
人才学   4篇
人口学   352篇
丛书文集   905篇
理论方法论   550篇
综合类   8461篇
社会学   937篇
统计学   5393篇
  2024年   21篇
  2023年   154篇
  2022年   200篇
  2021年   260篇
  2020年   403篇
  2019年   519篇
  2018年   585篇
  2017年   742篇
  2016年   611篇
  2015年   625篇
  2014年   1028篇
  2013年   2446篇
  2012年   1305篇
  2011年   1178篇
  2010年   967篇
  2009年   953篇
  2008年   1055篇
  2007年   1036篇
  2006年   947篇
  2005年   799篇
  2004年   677篇
  2003年   563篇
  2002年   515篇
  2001年   413篇
  2000年   282篇
  1999年   221篇
  1998年   119篇
  1997年   121篇
  1996年   88篇
  1995年   76篇
  1994年   75篇
  1993年   47篇
  1992年   53篇
  1991年   50篇
  1990年   32篇
  1989年   24篇
  1988年   28篇
  1987年   14篇
  1986年   15篇
  1985年   15篇
  1984年   13篇
  1983年   14篇
  1982年   11篇
  1981年   4篇
  1980年   1篇
  1979年   4篇
  1978年   2篇
  1977年   1篇
  1975年   1篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
991.
BOOST-PFC电路反馈环节的优化设计   总被引:1,自引:0,他引:1  
介绍了平均电流控制BOOST─PFC电路的原理,建立了电流环和电压环的小信号简化模型,讨论了双环反馈环节的设计原则和方法,提出最优设计的思想和数学模型,并以一种BOOST─PFC电路为例进行优化设计,计算模拟结果显示优化后有关指标好于优化前。  相似文献   
992.
Explicit expressions for Bayes invariant quadratic estimates, biased and unbiased, are presented and proved to cover the entire class of admissible estimates in the considered classes. An unbalanced genetic model is studied for demonstration.  相似文献   
993.
具有共轭复数重特征值的系统(A,B,C)经状态变换为模式系统(M,B~,C~)且公式地写出eMt。在此基础上,导出了系统的观控性判据,从而有效地避免了不必要地把系统化为对角型或Jordan标准型来决定观控性。且暗示出一种把系统(A,B,C),特别是无论特征值相同或相重与否,也无论同一个特征值组成多个Jordan块与否的对角型或Jordan标准型状态变换为模式系统(M,B~,C~的方法  相似文献   
994.
A system of predictors for estimating a finite population variance is defined and shown to be asymptotically design-unbiased (ADU) and asymptotically design-consistent (ADC) under probability sampling. An asymptotic mean squared error (MSE) of a generalized regression-type predictor, generated from the system, is obtained. The suggested predictor attains the minimum expected variance of any design-unbiased estimator when the superpopulation model is correct. The generalized regression-type predictor and the predictor suggested by Mukhopadhyay (1990) are compared.  相似文献   
995.
通过库诺特模型可以说明,“假象”的存在将改变均衡结果:如果信息获取是无成本的,那么“假象”将使信息占优一方的均衡利润增加,其对手的均衡利润可能减少,也可能增加;如果获取对手的信息是有代价的,根据我们给出的信息投资的边界条件,当获取信息的代价大于这一边界条件时,获取对手信息是有必要的,反之,应该放弃对信息的投资。  相似文献   
996.
Twenty-four-hour recall data from the Continuing Survey of Food Intake by Individuals (CSFII) are frequently used to estimate dietary exposure for risk assessment. Food frequency questionnaires are traditional instruments of epidemiological research; however, their application in dietary exposure and risk assessment has been limited. This article presents a probabilistic method of bridging the National Health and Nutrition Examination Survey (NHANES) food frequency and the CSFII data to estimate longitudinal (usual) intake, using a case study of seafood mercury exposures for two population subgroups (females 16 to 49 years and children 1 to 5 years). Two hundred forty-nine CSFII food codes were mapped into 28 NHANES fish/shellfish categories. FDA and state/local seafood mercury data were used. A uniform distribution with minimum and maximum blood-diet ratios of 0.66 to 1.07 was assumed. A probabilistic assessment was conducted to estimate distributions of individual 30-day average daily fish/shellfish intakes, methyl mercury exposure, and blood levels. The upper percentile estimates of fish and shellfish intakes based on the 30-day daily averages were lower than those based on two- and three-day daily averages. These results support previous findings that distributions of "usual" intakes based on a small number of consumption days provide overestimates in the upper percentiles. About 10% of the females (16 to 49 years) and children (1 to 5 years) may be exposed to mercury levels above the EPA's RfD. The predicted 75th and 90th percentile blood mercury levels for the females in the 16-to-49-year group were similar to those reported by NHANES. The predicted 90th percentile blood mercury levels for children in the 1-to-5-year subgroup was similar to NHANES and the 75th percentile estimates were slightly above the NHANES.  相似文献   
997.
Interdependency analysis in the context of this article is a process of assessing and managing risks inherent in a system of interconnected entities (e.g., infrastructures or industry sectors). Invoking the principles of input-output (I-O) and decomposition analysis, the article offers a framework for describing how terrorism-induced perturbations can propagate due to interconnectedness. Data published by the Bureau of Economic Analysis Division of the U.S. Department of Commerce is utilized to present applications to serve as test beds for the proposed framework. Specifically, a case study estimating the economic impact of airline demand perturbations to national-level U.S. sectors is made possible using I-O matrices. A ranking of the affected sectors according to their vulnerability to perturbations originating from a primary sector (e.g., air transportation) can serve as important input to risk management. For example, limited resources can be prioritized for the "top-n" sectors that are perceived to suffer the greatest economic losses due to terrorism. In addition, regional decomposition via location quotients enables the analysis of local-level terrorism events. The Regional I-O Multiplier System II (RIMS II) Division of the U.S. Department of Commerce is the agency responsible for releasing the regional multipliers for various geographical resolutions (economic areas, states, and counties). A regional-level case study demonstrates a process of estimating the economic impact of transportation-related scenarios on industry sectors within Economic Area 010 (the New York metropolitan region and vicinities).  相似文献   
998.
Alon Tal  Igor Linkov 《Risk analysis》2004,24(5):1243-1248
During the 21st century, environmental challenges are likely to intensify across the world and possibly lead to violent conflicts. Strategies for conflict avoidance will be incomplete unless they recognize, discuss, and mitigate regional environmental stress factors. Comparative risk assessment (CRA) is one of the most critical tools emerging to influence modern environmental policies and is increasingly used to create a common language to help reconcile competing interests in development and environmental disputes around the world. This article considers the environmental challenges facing the Middle East in light of their "transboundary" nature and proposes CRA as a framework for setting environmental priorities and reducing tensions in the region.  相似文献   
999.
集团军山地进攻作战减员预计模型   总被引:2,自引:0,他引:2  
收集了我军以往作战军减员的经验数据,建立军减员率的时间序列模型,提出计算机模拟的方法。在此基础上,着重分析影响减员的多种因素,对交战双方武器装备数量及技术等级,作战地区的地形和气候条件等因素进行了定量描述。运用专家咨询方法筛选了社会经济行为等"软"指标,用群体层次分析法确定各指标的权重,建立了量化指标体系,并运用该指标体系对我军今后主要作战对象进行了量化。结合以上因素对计算机模拟生成的数据进行修正,建立相应的调整算法。  相似文献   
1000.
在对金融系统中货币供应量的预测进行相关研究的基础上,介绍了符合金融系统预测规律的灰色系统动态预测法,并根据中国货币供应量的实际数据进行了实证的预测检验。结果显示,这种方法简单,不需要借助于其他任何时间序列数据,需要数据量少,预测精确度高,对于近期预测尤其准确,也可进行中长期预测;实证预测结果也符合我国金融系统中货币供应量预测的实际。  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