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   28132篇
  免费   704篇
  国内免费   42篇
电工技术   347篇
综合类   16篇
化学工业   6114篇
金属工艺   530篇
机械仪表   480篇
建筑科学   1208篇
矿业工程   333篇
能源动力   669篇
轻工业   1842篇
水利工程   231篇
石油天然气   286篇
武器工业   1篇
无线电   1808篇
一般工业技术   4312篇
冶金工业   6621篇
原子能技术   276篇
自动化技术   3804篇
  2022年   247篇
  2021年   418篇
  2020年   276篇
  2019年   354篇
  2018年   433篇
  2017年   378篇
  2016年   492篇
  2015年   394篇
  2014年   625篇
  2013年   1687篇
  2012年   960篇
  2011年   1263篇
  2010年   956篇
  2009年   1004篇
  2008年   1190篇
  2007年   1097篇
  2006年   1005篇
  2005年   913篇
  2004年   773篇
  2003年   756篇
  2002年   751篇
  2001年   515篇
  2000年   412篇
  1999年   480篇
  1998年   563篇
  1997年   507篇
  1996年   527篇
  1995年   498篇
  1994年   496篇
  1993年   475篇
  1992年   455篇
  1991年   299篇
  1990年   432篇
  1989年   409篇
  1988年   355篇
  1987年   417篇
  1986年   368篇
  1985年   460篇
  1984年   477篇
  1983年   416篇
  1982年   388篇
  1981年   312篇
  1980年   314篇
  1979年   369篇
  1978年   307篇
  1977年   260篇
  1976年   252篇
  1975年   254篇
  1974年   226篇
  1973年   237篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
The total syntheses of 9(Z),12(E)- and 9(E),12(Z)-octadecadienoic acids have been carried out. A useful intermediate in both syntheses, 8-bromo-octanoic acid, recently has become available from commercial sources. This compound has been used to expedite the preparation of these isomers. The remaining carbon atoms were derived from propargyl alcohol along with either 1-heptyne or acetylene and 1-bromopentane. Because the overall yield for each sequence was roughly 15% and there were no extraordinary reaction conditions in any of the synthetic steps, the compounds could be prepared readily in multiple gram quantities. The syntheses of the two compounds were supported by data from a variety of spectroscopic techniques.  相似文献   
33.
K.Y. Wang  R.E. West  F. Kreith  P. Lynn 《Energy》1985,10(10):1165-1175
Alkali-metal carbonate salts meet the requirements for high-temperature solar central receiver systems, but because of their corrosiveness they present special problems in the design of storage tanks. In order to reduce corrosion and temperature sufficiently to retain strength in the storage containing wall, internal and thermal insulation is required. We present design options and operation criteria for sensible-heat, molten-salt storage with internal insulation.  相似文献   
34.
35.
Primer walking of cloned DNA is a standard research tool. It has been used in the past to determine the sequence of individual clones of interest. With the expansion of DNA sequencing capacity the need to be able to walk larger numbers of clones has become necessary. Our laboratory is a mid-sized genomics facility. In conjunction with the Advanced Biomedical Computing Center (ABCC) we have developed methods for automating the primer selection, DNA sequencing, contig assembly and sequence analysis for clones arrayed in microtiter format. This approach has allowed us to walk 475 clones (five microtiter plates) selected from a cDNA library.  相似文献   
36.
Defends the practice of modifying reprints of journal articles to amend typographical and other errors that can affect meaning. A standard should be developed for dealing with such errors by hand writing corrections, including a list of errata, or issuing professionally corrected reprints with the notation that corrections have been made. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
37.
Successful Aging     
This issue's Works in Progress department presents six abstracts for projects that are developing interesting solutions to the elderly's quality of life challenges. The first two abstracts discuss projects that will help provide the elderly with freedom and independence by instrumenting their environments with supportive technology. The next two abstracts discuss projects building specialized user interfaces for addressing some of the challenges associated with aging, such as vision impairment. The final two abstracts present projects that will aid independence for the elderly by providing remote monitoring and assistance.  相似文献   
38.
Almond preferences were produced by giving rats a mixture of almond and sucrose (Experiments 1-4) or saccharin (Experiment 4). A subsequent extinction procedure consisted of either repeated 2-bottle almond versus water tests (Experiment 1) or repeated exposure to almond alone (Experiments 2-4). The main independent variable was whether access to food following a session was given immediately, 30 min later, or 120 min later. No effect of extinction was found in any experiment. An important finding was that varying the delay until food access had no detectable effect. It was concluded that inadvertent flavor-food associations do not maintain preference for the flavor under extinction conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
39.
The Republicans took control of both houses of Congress in November of 1994 for the 1st time in 42 yrs. Although the magnitude of the Clinton Administration's proposed Health Security Act may well have triggered fears of overcontrol, it is clear that the delivery of psychological care will be changed dramatically by the combined forces of federal and state health reform. R. J. Resnick, President of the American Psychological Association, has appointed the Task Force on Education and Training for Work in Organized Delivery Systems to look at how psychological health care is provided in the new and evolving systems, and to examine how current training programs prepare new psychologists to practice in and around organized health care systems. Dr. Resnick is similarly concerned about standardization of training, training in nontraditional areas of competence, and increased federal recognition and funding of training in psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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