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   307340篇
  免费   5013篇
  国内免费   824篇
电工技术   5435篇
综合类   233篇
化学工业   49687篇
金属工艺   12470篇
机械仪表   9093篇
建筑科学   7862篇
矿业工程   1964篇
能源动力   7050篇
轻工业   28744篇
水利工程   3313篇
石油天然气   7115篇
武器工业   16篇
无线电   32845篇
一般工业技术   62636篇
冶金工业   51829篇
原子能技术   7695篇
自动化技术   25190篇
  2021年   2540篇
  2019年   2310篇
  2018年   4445篇
  2017年   4378篇
  2016年   4773篇
  2015年   3145篇
  2014年   5117篇
  2013年   13703篇
  2012年   7877篇
  2011年   10449篇
  2010年   8602篇
  2009年   9606篇
  2008年   10037篇
  2007年   9841篇
  2006年   8585篇
  2005年   7935篇
  2004年   7306篇
  2003年   7070篇
  2002年   7132篇
  2001年   6922篇
  2000年   6541篇
  1999年   6504篇
  1998年   14973篇
  1997年   11264篇
  1996年   8762篇
  1995年   6696篇
  1994年   6081篇
  1993年   5924篇
  1992年   4604篇
  1991年   4557篇
  1990年   4371篇
  1989年   4389篇
  1988年   4331篇
  1987年   3688篇
  1986年   3674篇
  1985年   4354篇
  1984年   4135篇
  1983年   3742篇
  1982年   3542篇
  1981年   3685篇
  1980年   3537篇
  1979年   3451篇
  1978年   3536篇
  1977年   3997篇
  1976年   5111篇
  1975年   3245篇
  1974年   3069篇
  1973年   3098篇
  1972年   2680篇
  1971年   2507篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
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   
4.
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   
5.
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   
6.
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   
7.
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   
8.
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   
9.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
10.
Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions.  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