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   411645篇
  免费   4305篇
  国内免费   1100篇
化学   204624篇
晶体学   5920篇
力学   19437篇
综合类   7篇
数学   59520篇
物理学   127542篇
  2020年   1983篇
  2019年   1957篇
  2018年   10975篇
  2017年   11853篇
  2016年   7909篇
  2015年   4155篇
  2014年   4550篇
  2013年   14113篇
  2012年   15032篇
  2011年   25632篇
  2010年   15524篇
  2009年   15446篇
  2008年   22728篇
  2007年   26291篇
  2006年   12392篇
  2005年   18267篇
  2004年   13575篇
  2003年   12175篇
  2002年   10046篇
  2001年   10259篇
  2000年   7983篇
  1999年   6152篇
  1998年   4935篇
  1997年   4753篇
  1996年   4916篇
  1995年   4456篇
  1994年   4192篇
  1993年   4009篇
  1992年   4501篇
  1991年   4358篇
  1990年   4073篇
  1989年   3898篇
  1988年   4203篇
  1987年   3865篇
  1986年   3739篇
  1985年   5396篇
  1984年   5485篇
  1983年   4451篇
  1982年   4825篇
  1981年   4866篇
  1980年   4622篇
  1979年   4752篇
  1978年   4765篇
  1977年   4672篇
  1976年   4651篇
  1975年   4554篇
  1974年   4401篇
  1973年   4603篇
  1972年   2595篇
  1971年   1897篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
31.
32.
33.
Profiling engineered data with robust mining methods continues attracting attention in knowledge engineering systems. The purpose of this article is to propose a simple technique that deals with non-linear multi-factorial multi-characteristic screening suitable for knowledge discovery studies. The method is designed to proactively seek and quantify significant information content in engineered mini-datasets. This is achieved by deploying replicated fractional-factorial sampling schemes. Compiled multi-response data are converted to a single master-response effectuated by a series of distribution-free transformations and multi-compressed data fusions. The resulting amalgamated master response is deciphered by non-linear multi-factorial stealth stochastics intended for saturated schemes. The stealth properties of our method target processing datasets which might be overwhelmed by a lack of knowledge about the nature of reference distributions at play. Stealth features are triggered to overcome restrictions regarding the data normality conformance, the effect sparsity assumption and the inherent collapse of the ‘unexplainable error’ connotation in saturated arrays. The technique is showcased by profiling four ordinary controlling factors that influence webpage content performance by collecting data from a commercial browser monitoring service on a large scale web host. The examined effects are: (1) the number of Cascading Style Sheets files, (2) the number of JavaScript files, (3) the number of Image files, and (4) the Domain Name System Aliasing. The webpage performance level was screened against three popular characteristics: (1) the time to first visual, (2) the total loading time, and (3) the customer satisfaction. Our robust multi-response data mining technique is elucidated for a ten-replicate run study dictated by an L9(34) orthogonal array scheme where any uncontrolled noise embedded contribution has not been necessarily excluded.  相似文献   
34.
35.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
36.
37.
38.
39.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs.  相似文献   
40.
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