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   376651篇
  免费   5543篇
  国内免费   1015篇
电工技术   7537篇
综合类   1644篇
化学工业   59150篇
金属工艺   13106篇
机械仪表   11304篇
建筑科学   10973篇
矿业工程   1541篇
能源动力   9672篇
轻工业   35001篇
水利工程   3349篇
石油天然气   5012篇
武器工业   23篇
无线电   47081篇
一般工业技术   70431篇
冶金工业   64618篇
原子能技术   6047篇
自动化技术   36720篇
  2022年   4760篇
  2021年   6362篇
  2020年   4740篇
  2019年   5986篇
  2018年   5283篇
  2017年   4678篇
  2016年   4680篇
  2015年   3572篇
  2014年   5616篇
  2013年   16569篇
  2012年   9243篇
  2011年   13372篇
  2010年   10338篇
  2009年   11601篇
  2008年   11708篇
  2007年   11589篇
  2006年   10404篇
  2005年   9719篇
  2004年   10582篇
  2003年   10068篇
  2002年   9960篇
  2001年   9493篇
  2000年   8585篇
  1999年   8737篇
  1998年   18705篇
  1997年   13789篇
  1996年   10915篇
  1995年   8588篇
  1994年   8018篇
  1993年   7608篇
  1992年   5938篇
  1991年   5504篇
  1990年   5447篇
  1989年   5402篇
  1988年   5183篇
  1987年   4340篇
  1986年   4543篇
  1985年   5230篇
  1984年   4668篇
  1983年   4501篇
  1982年   4024篇
  1981年   4091篇
  1980年   3703篇
  1979年   3674篇
  1978年   3562篇
  1977年   4156篇
  1976年   5117篇
  1975年   3078篇
  1974年   2891篇
  1973年   2847篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
2.
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   
3.
4.
5.

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   
6.
7.
Pinhão seed is an unconventional source of starch and the pines grow up in native forests of southern Latin America. In this study, pinhão starch was adjusted at 15, 20 and 25% moisture content and heated to 100, 110 and 120 °C for 1 h. A decrease in λ max (starch/iodine complex) was observed as a result of increase in temperature and moisture content of HMT. The ratio of crystalline to amorphous phase in pinhão starch was determined via Fourier transform infra red by taking 1045/1022 band ratio. A decrease in crystallinity occurred as a result of HMT. Polarised light microscopy indicated a loss of birefringence of starch granules under 120 °C at 25% moisture content. Granule size distribution was further confirmed via scanning electron microscopy which showed the HMT effects. These results increased the understanding on molecular and structural properties of HMT pinhão starch and broadened its food and nonfood industrial applications.  相似文献   
8.

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   
9.
10.
Food Analytical Methods - The habanero pepper (Capsicum chinense Jacq.) is very aromatic and is the hottest pepper in the world. In this study, a headspace solid-phase microextraction/gas...  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