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   354342篇
  免费   4492篇
  国内免费   989篇
电工技术   7286篇
综合类   1596篇
化学工业   54232篇
金属工艺   12705篇
机械仪表   10933篇
建筑科学   9592篇
矿业工程   1484篇
能源动力   9073篇
轻工业   33245篇
水利工程   3192篇
石油天然气   4885篇
武器工业   20篇
无线电   45477篇
一般工业技术   66373篇
冶金工业   61129篇
原子能技术   5907篇
自动化技术   32694篇
  2022年   4441篇
  2021年   5852篇
  2020年   4367篇
  2019年   5560篇
  2018年   4731篇
  2017年   4196篇
  2016年   3969篇
  2015年   2967篇
  2014年   4884篇
  2013年   15207篇
  2012年   8092篇
  2011年   11864篇
  2010年   9261篇
  2009年   10636篇
  2008年   10546篇
  2007年   10456篇
  2006年   9419篇
  2005年   8933篇
  2004年   9833篇
  2003年   9444篇
  2002年   9348篇
  2001年   9128篇
  2000年   8217篇
  1999年   8391篇
  1998年   18379篇
  1997年   13477篇
  1996年   10611篇
  1995年   8280篇
  1994年   7727篇
  1993年   7304篇
  1992年   5658篇
  1991年   5338篇
  1990年   5220篇
  1989年   5185篇
  1988年   4989篇
  1987年   4121篇
  1986年   4348篇
  1985年   5029篇
  1984年   4486篇
  1983年   4338篇
  1982年   3857篇
  1981年   3951篇
  1980年   3574篇
  1979年   3538篇
  1978年   3443篇
  1977年   4065篇
  1976年   5021篇
  1975年   2982篇
  1974年   2814篇
  1973年   2771篇
排序方式: 共有10000条查询结果,搜索用时 8 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