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   369681篇
  免费   6056篇
  国内免费   1231篇
化学   201411篇
晶体学   4713篇
力学   14479篇
综合类   12篇
数学   46586篇
物理学   109767篇
  2021年   2168篇
  2020年   2714篇
  2019年   2514篇
  2018年   2690篇
  2017年   2597篇
  2016年   5347篇
  2015年   4373篇
  2014年   5701篇
  2013年   16864篇
  2012年   13020篇
  2011年   15968篇
  2010年   9925篇
  2009年   9604篇
  2008年   14843篇
  2007年   14941篇
  2006年   14361篇
  2005年   13153篇
  2004年   11702篇
  2003年   10224篇
  2002年   9951篇
  2001年   11150篇
  2000年   8685篇
  1999年   6807篇
  1998年   5511篇
  1997年   5341篇
  1996年   5548篇
  1995年   5073篇
  1994年   4904篇
  1993年   4764篇
  1992年   5253篇
  1991年   4836篇
  1990年   4594篇
  1989年   4370篇
  1988年   4587篇
  1987年   4280篇
  1986年   4103篇
  1985年   6009篇
  1984年   6066篇
  1983年   4985篇
  1982年   5370篇
  1981年   5413篇
  1980年   5155篇
  1979年   5236篇
  1978年   5250篇
  1977年   5194篇
  1976年   5110篇
  1975年   5001篇
  1974年   4835篇
  1973年   4971篇
  1972年   2782篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
31.
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   
32.
33.
34.
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions.  相似文献   
35.
36.
37.
38.
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   
39.
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