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   325133篇
  免费   5257篇
  国内免费   853篇
电工技术   5633篇
综合类   224篇
化学工业   53606篇
金属工艺   12790篇
机械仪表   9377篇
建筑科学   8582篇
矿业工程   2250篇
能源动力   7566篇
轻工业   29341篇
水利工程   3484篇
石油天然气   7342篇
武器工业   16篇
无线电   33872篇
一般工业技术   64454篇
冶金工业   57247篇
原子能技术   7876篇
自动化技术   27583篇
  2021年   2770篇
  2019年   2521篇
  2018年   4582篇
  2017年   4484篇
  2016年   4949篇
  2015年   3299篇
  2014年   5420篇
  2013年   14767篇
  2012年   8396篇
  2011年   11158篇
  2010年   9120篇
  2009年   10166篇
  2008年   10685篇
  2007年   10500篇
  2006年   9238篇
  2005年   8526篇
  2004年   7810篇
  2003年   7553篇
  2002年   7597篇
  2001年   7220篇
  2000年   6778篇
  1999年   6815篇
  1998年   15270篇
  1997年   11572篇
  1996年   9124篇
  1995年   7061篇
  1994年   6443篇
  1993年   6273篇
  1992年   4958篇
  1991年   4762篇
  1990年   4719篇
  1989年   4708篇
  1988年   4607篇
  1987年   4038篇
  1986年   3962篇
  1985年   4679篇
  1984年   4494篇
  1983年   4062篇
  1982年   3841篇
  1981年   3924篇
  1980年   3764篇
  1979年   3754篇
  1978年   3779篇
  1977年   4184篇
  1976年   5280篇
  1975年   3450篇
  1974年   3242篇
  1973年   3281篇
  1972年   2824篇
  1971年   2594篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
3.
4.
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control.  相似文献   
5.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  相似文献   
6.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
7.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
8.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
9.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
10.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  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