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   420007篇
  免费   5721篇
  国内免费   1376篇
电工技术   7885篇
综合类   365篇
化学工业   63563篇
金属工艺   16887篇
机械仪表   13864篇
建筑科学   9155篇
矿业工程   2267篇
能源动力   11792篇
轻工业   30859篇
水利工程   4388篇
石油天然气   7935篇
武器工业   17篇
无线电   50217篇
一般工业技术   87342篇
冶金工业   75371篇
原子能技术   9319篇
自动化技术   35878篇
  2022年   2727篇
  2021年   4272篇
  2020年   3268篇
  2019年   4108篇
  2018年   7085篇
  2017年   7071篇
  2016年   7588篇
  2015年   4895篇
  2014年   7824篇
  2013年   21396篇
  2012年   12209篇
  2011年   16223篇
  2010年   12987篇
  2009年   14483篇
  2008年   14891篇
  2007年   14650篇
  2006年   13009篇
  2005年   11546篇
  2004年   10873篇
  2003年   10808篇
  2002年   10230篇
  2001年   10051篇
  2000年   9390篇
  1999年   9721篇
  1998年   24477篇
  1997年   16876篇
  1996年   12947篇
  1995年   9662篇
  1994年   8478篇
  1993年   8467篇
  1992年   6153篇
  1991年   5770篇
  1990年   5744篇
  1989年   5380篇
  1988年   5109篇
  1987年   4480篇
  1986年   4349篇
  1985年   4939篇
  1984年   4572篇
  1983年   4083篇
  1982年   3749篇
  1981年   3851篇
  1980年   3523篇
  1979年   3403篇
  1978年   3416篇
  1977年   3812篇
  1976年   4914篇
  1975年   2930篇
  1974年   2723篇
  1973年   2791篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This is a review of Advances in Electronic Testing: Challenges and Methodologies (edited by Dimitris Gizopoulos), which is part of a series called Frontiers in Electronic Testing. This book can be thought of as a set of advanced tutorials in book form. One of the best things about this book is that several chapters go beyond the what of the subject and into the why. The book is also well integrated, with pointers to other chapters when necessary and with a minimum overlap between chapters.  相似文献   
992.
A simple measurement method for the absolute Raman scattering cross-section of an optical fibre is presented. This method does not require a high power pump laser and it measures the fibre directly. It is also shown that the calculation of the cross-section depends on the fibre structure, such as its refractive index profile and the differential attenuation between the pump wavelength and Raman wavelength.<>  相似文献   
993.
994.
Raw and heat processed peanut flours were found to contain higher in vitro trypsin inhibitor activity and lectin content than similarly processed soy flour. When fed to weanling rats at a level of 10% protein, the response pattern in food consumption, growth, liver function, and serum chemistries was not consistent among or between the groups. It is concluded that the levels of antinutritional factors in legumes do not correlate with their overall biological impact in feeding studies with the rat.  相似文献   
995.
996.
Accuracy and repeatability of complexometric methods for measuring calcium in cheese are limited by titration endpoints that are difficult to recognize. Much of this difficulty results from turbidity during titration. An alternative procedure is described in which 2 to 3 g of cheese are ashed, dissolved in dilute acid, and added calcium chloride is back titrated with ethylenediaminetetraacetic acid using hydroxy naphthol blue as indicator. Samples remain free of turbidity, and the titration endpoint is recognized easily.Recovery of calcium from solutions containing magnesium and phosphate was 100.9 ± .3%, indicating that a portion of sample magnesium (about 12%) also was measured. Error caused by magnesium recovery represented less than 1% of true calcium content.Analyses of 10 Cheddar cheese samples by the proposed method and by atomic emission differed by an average of .010% calcium. Mean values of the 10 samples did not differ significantly (P>.05) between methods. Duplicate analyses of 67 Cheddar cheese samples differed by an average of .008 ± .006% calcium. Similar repeatability was achieved by several inexperienced analysts. The method is applied readily to other dairy products.  相似文献   
997.
The present study was conducted to explore the sterilizing effect of phosphine on Ephestia cautella. Three to four-day old pupae were exposed to 0, 0.007, 0.014, 0.021, 0.028, 0.035, 0.042 and 0.049 mg/l of phosphine for 24 h at room temperature. The normally developed adults of each treatment were pair mated and several physiological and genetical parameters were investigated. The results showed gradual increases with dose in pupal mortality and adult malformation. The crossing results showed no changes in adult longevity and mating frequency. However, consistent reduction was noted in the fecundity and fertility of normally emerged adults. Preliminary data indicated similar levels of inherited sterility in the F1 adults raised from the above mentioned crosses.  相似文献   
998.
999.
Presents an analysis of the attrition dilemma in psychotherapy research and reviews the methods used to compensate for data loss. It is argued that attrition is not ultimately a problem of bias but a problem of lack of information. A reformulation is offered that integrates single-case studies with traditional group comparison methodology in an attempt to find optimal causal relations of treatments to outcomes. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
Management is aware that the value of firms is the ultimate measure of company performance. However, management has been using common accounting measures as an operating guide because the linkage between operational planning and value is vague and complex and, therefore, difficult to apply. Managers need to have clear targets and performance measures to track progress. This paper examines if a set of common accounting performance measures are linked tightly to the overall value of the firm. An abductive learning network (ALN) approach, an artificial intelligence technique, is used in this research because an ALN approach is non-parametric and can capture a subtle dynamic relationship between input and output variables, which is not obvious in linear statistical analysis. Empirical results show that an ALN model is very effective in synthesizing the value of the firm using six common accounting variables. The results also provide four strategic variables that can be used for devising strategic and operating plans to maximize the value of firms.  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