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   17997篇
  免费   523篇
  国内免费   18篇
电工技术   237篇
综合类   9篇
化学工业   3549篇
金属工艺   280篇
机械仪表   310篇
建筑科学   1099篇
矿业工程   109篇
能源动力   505篇
轻工业   1381篇
水利工程   158篇
石油天然气   194篇
武器工业   1篇
无线电   1064篇
一般工业技术   2876篇
冶金工业   4167篇
原子能技术   162篇
自动化技术   2437篇
  2022年   120篇
  2021年   213篇
  2020年   170篇
  2019年   223篇
  2018年   265篇
  2017年   259篇
  2016年   319篇
  2015年   238篇
  2014年   380篇
  2013年   1101篇
  2012年   663篇
  2011年   870篇
  2010年   674篇
  2009年   662篇
  2008年   858篇
  2007年   870篇
  2006年   685篇
  2005年   719篇
  2004年   559篇
  2003年   569篇
  2002年   509篇
  2001年   329篇
  2000年   300篇
  1999年   303篇
  1998年   312篇
  1997年   300篇
  1996年   299篇
  1995年   333篇
  1994年   267篇
  1993年   303篇
  1992年   272篇
  1991年   164篇
  1990年   237篇
  1989年   283篇
  1988年   204篇
  1987年   215篇
  1986年   211篇
  1985年   265篇
  1984年   258篇
  1983年   227篇
  1982年   217篇
  1981年   213篇
  1980年   172篇
  1979年   187篇
  1978年   176篇
  1977年   177篇
  1976年   147篇
  1975年   178篇
  1974年   165篇
  1973年   133篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
961.
962.
963.
Insoluble polymer bound photosensitizers, useful for the conversion of norbornadiene (1) to quadricyclene (2), have been synthesized. An acetophenone analogue was produced by Friedel-Crafts acylation of polystyrene resin while treatment of chloromethylated resin with salicyladehyde and triethylamine produced an anlogue of benzyloxybenzaldehyde. Reaction of lithio---polystyrene resin with methyl 4-(N,N-dimethylamino)benzoate gave a ketone equivalent to 4-(N,N-dimethylamino)benzophenone (3). Quantum yields for the conversion of 1 and 2 using the polymer bound sensitizers were generally comparable to, but slightly lower than, the analogous compound in homogeneous solution. The quantum yield of polymer bound 3 was less solvent dependent than that of the homogeneous counterpart. The advantages of isolating the photosensitizer to the photochemical reactor stage of a photochemical solar energy storage device are discussed. Efficient sensitization by polymer bound photosensitizers demonstrates the feasibility of this approach.  相似文献   
964.
965.
GRIP (GeneRal Interactive Processor) is a problem-oriented language which establishes a powerful and convenient communication linkage between engineer and computer. GRIP is implemented in a set of programs which provide its capabilities for command translation, on-line programming and small database management. The GRIP application program, written using the grammer of the language, provides access to one or more task specific programs and to utility resources such as numerical methods and interactive graphics packages. This paper describes the structure and function of GRIP applications which support chemical engineering education and research activities.  相似文献   
966.
Some Practical System Availability Calculations   总被引:1,自引:0,他引:1  
The usefulness of a recent result in system availability is displayed and discussed. Methods are presented for solving some problems which arise in the practical implementation of this result. Specifically, equations are provided for calculating the availability of a series system in which one or more components may have a surge or an installed spare. Finally, a manufacturing line efficiency model is described which has system (line) availability as one of its principal factors.  相似文献   
967.
Performed 3 experiments on small groups (n = 2-6) of thirsty Carworth female albino rats. Cool water suppressed water intake. The suppression was apparent from the 1st min of drinking. Suppression occurred for both short (20-min) and long (100-min) daily drinking sessions, and occurred whether the water was available from a sipper tube or a bowl. When cellular hydration was delayed by giving Ss isotonic saline instead of water, the suppression by cooling was enhanced. Cool-water suppression of water intake appears to be a short-latency satiety mechanism that anticipates cellular and extracellular hydration. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
968.
Research in the 1960s demonstrated the capabilities of infants and the demand characteristics of their behavior. These data, together with the failure of studies directed exclusively to parent effects on children, have led to a reformulation of socialization theory to encompass the reciprocal influences of parent and offspring. The cognitive capabilities, knowledge, and attitudes of parents assume a more important role in this theory. New research approaches are now available that can isolate parent and child effects, thus providing the foundation needed for identifying reciprocal influences. If research fills in the outline of this new perspective, and the viewpoint is communicated to parents, it should facilitate parent–child interaction. Previous theories, all too often given extreme expression in the mass media, have adversely affected the functioning of parents, either causing them to feel too much responsibility for their children's development, or leading them to mistake permissiveness for parental involvement and commitment. The reformulation should attenuate these extreme formulations, because neither of the latter is consistent with the concept of reciprocal influences. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
969.
The Ellis withdrawal theory is shown to be a eubstantial improvement for predicting film thickness as compared to the previous theory for pseudo-plastic fluids. The two-term Ellis power-law theory ie shown to be a good approximation to the Ellis theory. The relative deviations between data and Ellis theory become larger at lower speeds.  相似文献   
970.
Use of nonfatty raw materials for the production of a variety of new aliphatic chemical derivatives are discussed, including petroleumderived olefins, which are converted by Armour Industrial Chemical Co. to so-called “β-Amines.”  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