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   302219篇
  免费   4001篇
  国内免费   848篇
电工技术   5199篇
综合类   175篇
化学工业   48975篇
金属工艺   12381篇
机械仪表   9233篇
建筑科学   7374篇
矿业工程   1850篇
能源动力   7218篇
轻工业   27333篇
水利工程   3242篇
石油天然气   7126篇
武器工业   16篇
无线电   33099篇
一般工业技术   59751篇
冶金工业   53398篇
原子能技术   7709篇
自动化技术   22989篇
  2021年   2405篇
  2019年   2253篇
  2018年   4020篇
  2017年   4031篇
  2016年   4375篇
  2015年   2862篇
  2014年   4808篇
  2013年   13032篇
  2012年   7596篇
  2011年   10191篇
  2010年   8311篇
  2009年   9334篇
  2008年   9630篇
  2007年   9389篇
  2006年   8319篇
  2005年   7750篇
  2004年   7226篇
  2003年   6957篇
  2002年   6968篇
  2001年   6779篇
  2000年   6427篇
  1999年   6482篇
  1998年   15277篇
  1997年   11412篇
  1996年   8816篇
  1995年   6724篇
  1994年   6123篇
  1993年   5979篇
  1992年   4618篇
  1991年   4565篇
  1990年   4408篇
  1989年   4443篇
  1988年   4354篇
  1987年   3672篇
  1986年   3689篇
  1985年   4285篇
  1984年   4074篇
  1983年   3698篇
  1982年   3504篇
  1981年   3640篇
  1980年   3495篇
  1979年   3446篇
  1978年   3524篇
  1977年   4012篇
  1976年   5153篇
  1975年   3226篇
  1974年   3053篇
  1973年   3086篇
  1972年   2681篇
  1971年   2499篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
A membrane reactor containing different types of ZSM-5/porous SS membranes was used to perform the xylene isomerization reaction. The parent Na-ZSM-5 layer was synthesized by secondary growth on top of porous stainless steel tubes. The xylene isomerization reaction was carried out at different temperatures in the membrane reactor and in a fixed-bed reactor of identical geometry for comparison. Two different kinds of membranes were prepared by ion exchange: a Pt/H-ZSM-5 catalytic membrane and two Ba-ZSM-5 composites with different Ba2+ concentration. The p-xylene production using 100% exchanged Ba-membrane was about 28% higher than the fixed-bed reactor at 370 °C, when m-xylene was fed.  相似文献   
162.
The photoelectric parameters of silicon solar cells degraded under the action of 60Co gamma-radiation can be partly restored using an ultrasonic treatment (UST). The growth of the maximum output power of solar cells after the UST is related to a redistribution of the radiation defects and an increase in the homogeneity of a semiconductor crystal structure.  相似文献   
163.
This research supports the hypothesis that the Trust Vector model can be modified to fit the CyberCraft Initiative, and that there are limits to the utility of historical data. This research proposed some modifications and expansions to the Trust Model Vector, and identified areas for future research.  相似文献   
164.
The results of a computational experiment with a neural-net model simulating the effect of the chemical composition on the plastic properties of ÉP-450 steel are presented. It is shown that computer-aided development of reactor steel with prescribed properties is, in principle, possible.  相似文献   
165.
166.
We present here the results of a study of the separation process in the extraction matrix of a novel high-intensity magnetic separator (HIMS). The matrix uses an ordered array of grooved plates (replacing conventional collectors, which are generally made of wires). Only experimental results are available for grooved plates in the literature, but here we propose a new theoretical approach. We report on the particles' behavior, the existence of a percolation phenomenon, and the filtration efficiency, in order to analyze and compare the performance of matrix structures (Lenoir's and Jones'). We discuss the causes of the percolation phenomenon and its effect on filtration efficiency. Correspondence between the theory and the experiments is good. We suggest appropriate uses of each matrix structure according to the property of the processed particles.  相似文献   
167.
168.
169.
The biological decolorization of two industrial, spent textile reactive dyebaths was investigated using a suspended-growth, halophilic mixed culture fed with glucose. Dyebath I contained mainly Reactive Blue 19 (RB19), an anthraquinone dye, whereas dyebath II contained mainly Reactive Blue 21 (RB21), a phthalocyanine dye. Batch assays under anaerobic conditions with the two neutralized dyebaths resulted in 87 and 37% extent of decolorization for dyebaths I and II, respectively. The rate of glucose utilization and the extent of acetate production were impacted in the presence of each dyebath as compared to the control culture. However, dyebath decolorization occurred despite moderate culture inhibition. Reuse of a biologically renovated RB19-containing dyebath in the dyeing process resulted in reproducible but not identical cotton fabric shades as compared to a standard dyeing (i.e., control) using fresh water. This difference is attributed to a variable degree of RB19 aggregation during the dyeing process and is not related to the efficiency of the biodecolorization process. Further improvement of the redyeing efficiency will lead to the development of an in-plant, closed-loop decolorization system resulting in significant water conservation and minimization of textile pollutants such as salt and dyes.  相似文献   
170.
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