首页 | 官方网站   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   1405573篇
  免费   23901篇
  国内免费   6874篇
工业技术   1436348篇
  2021年   15387篇
  2020年   11667篇
  2019年   14426篇
  2018年   13659篇
  2017年   12832篇
  2016年   20118篇
  2015年   17030篇
  2014年   28400篇
  2013年   87235篇
  2012年   32391篇
  2011年   42990篇
  2010年   40019篇
  2009年   49084篇
  2008年   40833篇
  2007年   37476篇
  2006年   42205篇
  2005年   36438篇
  2004年   39151篇
  2003年   39279篇
  2002年   38718篇
  2001年   34939篇
  2000年   33832篇
  1999年   32081篇
  1998年   29807篇
  1997年   30117篇
  1996年   29400篇
  1995年   27224篇
  1994年   26018篇
  1993年   25936篇
  1992年   25269篇
  1991年   22165篇
  1990年   22626篇
  1989年   21699篇
  1988年   20149篇
  1987年   18562篇
  1986年   17850篇
  1985年   21218篇
  1984年   21819篇
  1983年   19797篇
  1982年   18930篇
  1981年   18986篇
  1980年   17549篇
  1979年   18178篇
  1978年   17431篇
  1977年   16532篇
  1976年   16370篇
  1975年   15758篇
  1974年   15304篇
  1973年   15362篇
  1972年   12846篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
114.
115.
116.
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined.  相似文献   
117.
 A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation. The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest. Sponsored by The Research Council of Norway, project number 125676/410 Dedicated to the memory of Prof. Mike Crisfield, a respected colleague  相似文献   
118.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture.  相似文献   
119.
This study investigates the citation patterns in the journal, Medical Principles and Practice from its inception in 1989 through 2000 (volumes 1-9). The data set includes 4740 references appended to the 221 original research articles. All of the citations were entered into a ProCite database for analysis. Specifically, this study addresses: (1) bibliometric patterns of cited works in terms of publication format, subject scatter, authorship characteristics, age of citations, geographic distribution, and language distribution; (2) productivity of journal titles; (3) the role of self-citation; and (4) how selected bibliometric indicators apply. Some of the findings include: journal articles are most frequently cited; English language publications dominate the literature; there is a trend of multiple authorship; and the pattern of aging is below the norm for medical literature. The results of the study can provide a benchmark to measure the user behavior of a particular group of researchers as well as for the provision of collection development and management decisions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
120.
The purpose of this paper is to introduce a new I DDQ measurement technique based on active successive approximations, called ASA-I DDQ. This technique has unique features facilitating a speed-up in I DDQ measurement. Experimental results suggest that a significant speed-up factor (up to 4) can be obtained over the QuiC-Mon technique. Such a speed-up is a key element in the replacement of single-threshold I DDQ testing since it amplifies the effectiveness of post-processing techniques.  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-23

京公网安备 11010802026262号