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   588064篇
  免费   5645篇
  国内免费   1378篇
化学   296209篇
晶体学   8689篇
力学   29281篇
综合类   10篇
数学   77054篇
物理学   183844篇
  2020年   5255篇
  2019年   5994篇
  2018年   8033篇
  2017年   8126篇
  2016年   11478篇
  2015年   6511篇
  2014年   10918篇
  2013年   25201篇
  2012年   19886篇
  2011年   23964篇
  2010年   17504篇
  2009年   17685篇
  2008年   22575篇
  2007年   22561篇
  2006年   21028篇
  2005年   18668篇
  2004年   17381篇
  2003年   15793篇
  2002年   15875篇
  2001年   16821篇
  2000年   13116篇
  1999年   10091篇
  1998年   8757篇
  1997年   8496篇
  1996年   8160篇
  1995年   7367篇
  1994年   7219篇
  1993年   7039篇
  1992年   7541篇
  1991年   7816篇
  1990年   7554篇
  1989年   7386篇
  1988年   7399篇
  1987年   7161篇
  1986年   6778篇
  1985年   8874篇
  1984年   9194篇
  1983年   7641篇
  1982年   8192篇
  1981年   7921篇
  1980年   7443篇
  1979年   8054篇
  1978年   8123篇
  1977年   8293篇
  1976年   8305篇
  1975年   7956篇
  1974年   7701篇
  1973年   8032篇
  1972年   5662篇
  1971年   4698篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
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   
92.
Russian Journal of General Chemistry - The main sources of emissions of industrial nitrogen oxides have been reviewed. A promising method for the absorption of nitrogen monoxide by a reusable...  相似文献   
93.
94.
Russian Journal of General Chemistry - 8-Phenyltetrazolo[5,1-b][1,3,4]thiadiazepine was obtained as a result of intermolecular cyclization of 1-amino-1H-tetrazole-5-thiol and 3-phenyl-2-propynal....  相似文献   
95.
96.
97.
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   
98.
99.
100.
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   
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