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   350092篇
  免费   4324篇
  国内免费   983篇
电工技术   7235篇
综合类   1592篇
化学工业   53385篇
金属工艺   12620篇
机械仪表   10829篇
建筑科学   9288篇
矿业工程   1477篇
能源动力   8898篇
轻工业   32781篇
水利工程   3104篇
石油天然气   4864篇
武器工业   20篇
无线电   45163篇
一般工业技术   65559篇
冶金工业   60744篇
原子能技术   5874篇
自动化技术   31966篇
  2022年   4398篇
  2021年   5792篇
  2020年   4307篇
  2019年   5490篇
  2018年   4653篇
  2017年   4097篇
  2016年   3885篇
  2015年   2856篇
  2014年   4741篇
  2013年   14897篇
  2012年   7828篇
  2011年   11566篇
  2010年   9062篇
  2009年   10397篇
  2008年   10196篇
  2007年   10195篇
  2006年   9191篇
  2005年   8695篇
  2004年   9651篇
  2003年   9300篇
  2002年   9209篇
  2001年   9044篇
  2000年   8163篇
  1999年   8314篇
  1998年   18339篇
  1997年   13435篇
  1996年   10551篇
  1995年   8237篇
  1994年   7681篇
  1993年   7278篇
  1992年   5629篇
  1991年   5306篇
  1990年   5198篇
  1989年   5149篇
  1988年   4973篇
  1987年   4091篇
  1986年   4327篇
  1985年   4995篇
  1984年   4459篇
  1983年   4312篇
  1982年   3837篇
  1981年   3941篇
  1980年   3574篇
  1979年   3530篇
  1978年   3434篇
  1977年   4057篇
  1976年   5025篇
  1975年   2962篇
  1974年   2803篇
  1973年   2769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