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   679666篇
  免费   11563篇
  国内免费   1987篇
电工技术   11822篇
综合类   517篇
化学工业   105623篇
金属工艺   26126篇
机械仪表   20699篇
建筑科学   15937篇
矿业工程   3726篇
能源动力   17923篇
轻工业   57474篇
水利工程   7197篇
石油天然气   13060篇
武器工业   37篇
无线电   75257篇
一般工业技术   134633篇
冶金工业   128996篇
原子能技术   14452篇
自动化技术   59737篇
  2021年   6696篇
  2020年   5222篇
  2019年   6396篇
  2018年   11176篇
  2017年   11071篇
  2016年   11945篇
  2015年   7794篇
  2014年   12243篇
  2013年   33414篇
  2012年   19606篇
  2011年   25174篇
  2010年   20275篇
  2009年   22447篇
  2008年   23095篇
  2007年   22399篇
  2006年   19617篇
  2005年   17788篇
  2004年   16747篇
  2003年   16488篇
  2002年   15767篇
  2001年   15229篇
  2000年   14369篇
  1999年   14922篇
  1998年   39496篇
  1997年   27792篇
  1996年   21149篇
  1995年   15646篇
  1994年   13869篇
  1993年   13825篇
  1992年   9815篇
  1991年   9398篇
  1990年   9275篇
  1989年   8990篇
  1988年   8700篇
  1987年   7457篇
  1986年   7432篇
  1985年   8427篇
  1984年   7821篇
  1983年   7088篇
  1982年   6687篇
  1981年   6839篇
  1980年   6428篇
  1979年   6204篇
  1978年   6306篇
  1977年   7425篇
  1976年   9907篇
  1975年   5504篇
  1974年   5165篇
  1973年   5323篇
  1972年   4478篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a...  相似文献   
12.
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   
13.
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   
14.
Water Resources Management - The water evaluation and planning (WEAP) approach and the invasive weed optimization algorithm (IWOA) are herein employed to determine the optimal operating policies in...  相似文献   
15.
Photoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light-responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials-driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials-based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials.  相似文献   
16.
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   
17.
The constructive analysis of Madrid's old timber-framed collective courtyard buildings, whether demolished, preserved intact, or enlarged, has achieved the dating of relevant case studies. New parameters established in this study set a chronology based on front sector original projects: old (1737–1788), pre-modern (1788–1847) and modern (1847–1892). The on-site inspection and archival research point to ongoing misleading construction in the historic Southern area. Some modern corralas erected on top of pre-existing buildings confirm the initial hypothesis. First dimensioning rules for new façades and the stability required in old ones before adding new storeys, maintaining the original masonry or double-layered system, are discovered. Undated buildings suggest their possible origin a la malicia and a later transformation into transitional corralas. Finally, an analysis of the demolished courtyards narrows down the dating and points to new conjectures in some preserved by showing their uneven layout, old features, and structural discordances in each sector.  相似文献   
18.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy...  相似文献   
19.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
20.
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   
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