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   303609篇
  免费   4613篇
  国内免费   824篇
电工技术   5351篇
综合类   234篇
化学工业   48999篇
金属工艺   12377篇
机械仪表   9010篇
建筑科学   7637篇
矿业工程   1936篇
能源动力   6991篇
轻工业   28456篇
水利工程   3289篇
石油天然气   7106篇
武器工业   16篇
无线电   32445篇
一般工业技术   61193篇
冶金工业   52006篇
原子能技术   7663篇
自动化技术   24337篇
  2021年   2443篇
  2019年   2223篇
  2018年   4236篇
  2017年   4168篇
  2016年   4552篇
  2015年   2974篇
  2014年   4910篇
  2013年   13277篇
  2012年   7616篇
  2011年   10174篇
  2010年   8361篇
  2009年   9367篇
  2008年   9748篇
  2007年   9603篇
  2006年   8413篇
  2005年   7811篇
  2004年   7201篇
  2003年   6957篇
  2002年   7046篇
  2001年   6822篇
  2000年   6468篇
  1999年   6454篇
  1998年   15001篇
  1997年   11252篇
  1996年   8750篇
  1995年   6711篇
  1994年   6082篇
  1993年   5929篇
  1992年   4608篇
  1991年   4539篇
  1990年   4375篇
  1989年   4370篇
  1988年   4334篇
  1987年   3686篇
  1986年   3678篇
  1985年   4323篇
  1984年   4122篇
  1983年   3716篇
  1982年   3515篇
  1981年   3679篇
  1980年   3523篇
  1979年   3452篇
  1978年   3544篇
  1977年   4013篇
  1976年   5110篇
  1975年   3248篇
  1974年   3086篇
  1973年   3098篇
  1972年   2690篇
  1971年   2518篇
排序方式: 共有10000条查询结果,搜索用时 804 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.
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed.  相似文献   
4.
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   
5.
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   
6.
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   
7.
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   
8.
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   
9.
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   
10.
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