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   319703篇
  免费   3670篇
  国内免费   1573篇
电工技术   5921篇
综合类   1550篇
化学工业   47135篇
金属工艺   13377篇
机械仪表   10417篇
建筑科学   7839篇
矿业工程   2163篇
能源动力   7336篇
轻工业   24381篇
水利工程   3614篇
石油天然气   6849篇
武器工业   54篇
无线电   39230篇
一般工业技术   63523篇
冶金工业   55382篇
原子能技术   7846篇
自动化技术   28329篇
  2022年   4314篇
  2021年   5577篇
  2020年   4141篇
  2019年   5228篇
  2018年   4603篇
  2017年   4307篇
  2016年   4232篇
  2015年   2808篇
  2014年   4680篇
  2013年   12690篇
  2012年   7567篇
  2011年   11196篇
  2010年   8733篇
  2009年   10080篇
  2008年   9757篇
  2007年   9819篇
  2006年   8559篇
  2005年   8152篇
  2004年   9092篇
  2003年   8694篇
  2002年   8588篇
  2001年   8301篇
  2000年   7456篇
  1999年   7581篇
  1998年   17145篇
  1997年   12309篇
  1996年   9455篇
  1995年   7286篇
  1994年   6563篇
  1993年   6476篇
  1992年   4802篇
  1991年   4496篇
  1990年   4380篇
  1989年   4473篇
  1988年   4099篇
  1987年   3631篇
  1986年   3738篇
  1985年   4029篇
  1984年   3637篇
  1983年   3484篇
  1982年   3268篇
  1981年   3233篇
  1980年   3172篇
  1979年   2940篇
  1978年   3062篇
  1977年   3396篇
  1976年   4288篇
  1975年   2610篇
  1974年   2530篇
  1973年   2496篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
1.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
2.
3.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  相似文献   
4.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
5.
6.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  相似文献   
7.
8.
9.
10.
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