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:      
  示例: 沙坡头地区,人工植被区,变化  检索词用空格隔开表示必须包含全部检索词,用“,”隔开表示只需满足任一检索词即可!
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   20477篇
  免费   62篇
  国内免费   1篇
管理学   2896篇
民族学   93篇
人才学   13篇
人口学   1761篇
丛书文集   90篇
理论方法论   1794篇
综合类   185篇
社会学   9391篇
统计学   4317篇
  2023年   127篇
  2021年   121篇
  2020年   325篇
  2019年   454篇
  2018年   500篇
  2017年   683篇
  2016年   473篇
  2015年   384篇
  2014年   475篇
  2013年   3485篇
  2012年   694篇
  2011年   543篇
  2010年   488篇
  2009年   405篇
  2008年   461篇
  2007年   458篇
  2006年   473篇
  2005年   469篇
  2004年   381篇
  2003年   367篇
  2002年   407篇
  2001年   501篇
  2000年   428篇
  1999年   439篇
  1998年   343篇
  1997年   294篇
  1996年   321篇
  1995年   292篇
  1994年   333篇
  1993年   290篇
  1992年   316篇
  1991年   326篇
  1990年   321篇
  1989年   277篇
  1988年   315篇
  1987年   293篇
  1986年   237篇
  1985年   301篇
  1984年   279篇
  1983年   256篇
  1982年   214篇
  1981年   174篇
  1980年   162篇
  1979年   205篇
  1978年   167篇
  1977年   142篇
  1976年   128篇
  1975年   127篇
  1974年   113篇
  1973年   104篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Differences between plant varieties are based on phenotypic observations, which are both space and time consuming. Moreover, the phenotypic data result from the combined effects of genotype and environment. On the contrary, molecular data are easier to obtain and give a direct access to the genotype. In order to save experimental trials and to concentrate efforts on the relevant comparisons between varieties, the relationship between phenotypic and genetic distances is studied. It appears that the classical genetic distances based on molecular data are not appropriate for predicting phenotypic distances. In the linear model framework, we define a new pseudo genetic distance, which is a prediction of the phenotypic one. The distribution of this distance given the pseudo genetic distance is established. Statistical properties of the predicted distance are derived when the parameters of the model are either given or estimated. We finally apply these results to distinguishing between 144 maize lines. This case study is very satisfactory because the use of anonymous molecular markers (RFLP) leads to saving 29% of the trials with an acceptable error risk. These results need to be confirmed on other varieties and species and would certainly be improved by using genes coding for phenotypic traits.  相似文献   
72.
G = F k (k > 1); G = 1 − (1−F) k (k < 1); G = F k (k < 1); and G = 1 − (1−F) k (k > 1), where F and G are two continuous cumulative distribution functions. If an optimal precedence test (one with the maximal power) is determined for one of these four classes, the optimal tests for the other classes of alternatives can be derived. Application of this is given using the results of Lin and Sukhatme (1992) who derived the best precedence test for testing the null hypothesis that the lifetimes of two types of items on test have the same distibution. The test has maximum power for fixed κ in the class of alternatives G = 1 − (1−F) k , with k < 1. Best precedence tests for the other three classes of Lehmann-type alternatives are derived using their results. Finally, a comparison of precedence tests with Wilcoxon's two-sample test is presented. Received: February 22, 1999; revised version: June 7, 2000  相似文献   
73.
We define a notion of de-initializing Markov chains. We prove that to analyse convergence of Markov chains to stationarity, it suffices to analyse convergence of a de-initializing chain. Applications are given to Markov chain Monte Carlo algorithms and to convergence diagnostics.  相似文献   
74.
The non-parametric maximum likelihood estimators (MLEs) are derived for survival functions associated with individual risks or system components in a reliability framework. Lifetimes are observed for systems that contain one or more of those components. Analogous to a competing risks model, the system is assumed to fail upon the first instance of any component failure; i.e. the system is configured in series. For any given risk or component type, the asymptotic distribution is shown to depend explicitly on the unknown survival function of the other risks, as well as the censoring distribution. Survival functions with increasing failure rate are investigated as a special case. The order restricted MLE is shown to be consistent under mild assumptions of the underlying component lifetime distributions.  相似文献   
75.
In 1997 intense media coverage raised public concerns about germ warfare simulation experiments conducted by the Ministry of Defence during the 1960s, which included the release of bacteria over Dorset. Families in East Lulworth, Dorset, have linked this with allegedly high rates of miscarriages, still-births, congenital malformations, learning and other neurodevelopmental disabilities in their village. The response of the Dorset Health Authority (DHA) included the examination of background information from the Ministry of Defence, national data on congenital malformations in Dorset, health information collected by campaigners and a systematic health survey conducted by the DHA among former and current residents of East Lulworth. The investigation did not confirm the presence of a cluster. It is debatable whether the DHA should have proceeded with their survey when none of the other more immediately available results indicated the presence of a cluster.  相似文献   
76.
Comment   总被引:1,自引:0,他引:1  
  相似文献   
77.
In a searching analysis of the fiducial argument Hacking (1965) proposed the Principle of Irrelevance as a condition under which the argument is valid. His statement of the Principle was essentially non-mathematical and this paper presents a mathematical development of the Principle. The relationship with likelihood inference is explored and some of the proposed counter-examples to fiducial theory are considered. It is shown that even with the Principle of Irrelevance examples of non-uniqueness of fiducial distributions exist.  相似文献   
78.
For two-level factorials, we consider designs in N=2 (mod 4) runs as obtained by adding two runs, with a certain coincidence pattern, to an orthogonal array of strength two. These designs are known to be optimal main effect plans in a very broad sense in the absence of interactions. Among them, we explore the ones having minimum aberration, with a view to ensuring maximum model robustness even when interactions are possibly present. This is done by sequentially minimizing a measure of the bias caused by interactions of successively higher orders.  相似文献   
79.
For much of 1970 and during the early part of 1971 some forty members of the American Statistical Association, working as seven task force groups under the guidance of a special Steering Committee, gave much time and thought to an examination of the objectives and activities of ASA. Their purpose was to try to determine what those objectives should be and how best to accomplish them. After careful review and study by the Board of ASA, the task force and steering committee findings and recommendations were adopted, modified or supplemented and issued as an integrated Board report under the title of A Study of Future Goals of ASA.  相似文献   
80.
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