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   261552篇
  免费   2929篇
  国内免费   545篇
电工技术   4759篇
综合类   320篇
化学工业   42196篇
金属工艺   10213篇
机械仪表   7953篇
建筑科学   5942篇
矿业工程   1450篇
能源动力   5667篇
轻工业   26337篇
水利工程   2665篇
石油天然气   5247篇
武器工业   33篇
无线电   27303篇
一般工业技术   48275篇
冶金工业   50774篇
原子能技术   6278篇
自动化技术   19614篇
  2021年   2236篇
  2019年   2161篇
  2018年   3692篇
  2017年   3625篇
  2016年   3907篇
  2015年   2398篇
  2014年   4159篇
  2013年   10916篇
  2012年   6593篇
  2011年   8962篇
  2010年   7035篇
  2009年   7784篇
  2008年   8200篇
  2007年   8354篇
  2006年   7448篇
  2005年   6677篇
  2004年   6346篇
  2003年   6165篇
  2002年   6259篇
  2001年   6140篇
  2000年   5933篇
  1999年   5840篇
  1998年   14470篇
  1997年   10125篇
  1996年   7767篇
  1995年   5953篇
  1994年   5262篇
  1993年   5192篇
  1992年   3981篇
  1991年   3681篇
  1990年   3893篇
  1989年   3775篇
  1988年   3556篇
  1987年   3121篇
  1986年   3144篇
  1985年   3603篇
  1984年   3395篇
  1983年   3070篇
  1982年   2903篇
  1981年   3011篇
  1980年   2901篇
  1979年   2771篇
  1978年   2816篇
  1977年   3194篇
  1976年   4143篇
  1975年   2474篇
  1974年   2343篇
  1973年   2479篇
  1972年   2047篇
  1971年   1927篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.  相似文献   
52.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
53.
The criterion for crack growth instability in an elastic-softening material that is subjected to displacement control loading conditions is examined. A theoretical analysis of the model of a solid containing two symmetrically situated deep cracks and with tensile loading of the remaining ligament, defines the criterion for crack growth instability. The criterion is expressed in terms of the material's softening characteristics and the solid's geometrical parameters. The analysis covers the complete spectrum of material behaviour from the case where the softening zone is very small to the case where instability does not occur until the softening zone traverses the ligament between the crack tips.  相似文献   
54.
The DQA1 and DQB1 alleles of 258 rhesus monkeys (Macaca mulatta) of different origin were typed by PCR-RFLP. Five novel MamuDQA1 and five novel -DQB1 alleles were detected and 15 Mamu-DQA1-DQB1 haplotypes were identified. Haplotype analysis confirmed the conservation of the DQA1*01-DQB1 *06 haplotypes in evolution. The most conspicuous finding was the tight linkage between the Mamu-DQA1 and -DQB1 alleles. Almost in every case the Mamu-DQA1 allele was linked to only one particular Mamu-DQB1 allele. Although there also are constraints in the formation of DQ haplotypes in humans, such tight linkages are not observed. These findings support the hypothesis of some kind of co-evolution between DQA1 and DQB1 alleles and may reflect a stronger force of natural selection in macaques than in humans.  相似文献   
55.
The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing.  相似文献   
56.
57.
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow.  相似文献   
58.
Functional Properties and Food Applications of Rapeseed Protein Concentrate   总被引:1,自引:0,他引:1  
Rapeseed protein concentrate (RC), prepared with 2% hexameta-phosphate, was tested for its functionality and performance in some foods. The RC had good nitrogen solubility, fat absorption, emulsification, and whipping capacities but poor water absorption and gelling properties. It increased the emulsion stability, and protein but lowered the fat content of wieners. It also increased the cooking yield, reduced the shrinkage and tenderized meat patties. Results were similar to soybean isolate except for the poorer color and flavor. The cooking yield of RC supplemented wieners was less than the all-meat control and soybean-supplemented wieners. A 9% RC dispersion mixed with an equal volume of eggwhite produced a meringue of comparable stability and texture to that of eggwhite alone.  相似文献   
59.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
60.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained.  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