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   69691篇
  免费   6432篇
  国内免费   3010篇
电工技术   3886篇
技术理论   3篇
综合类   4008篇
化学工业   12129篇
金属工艺   4103篇
机械仪表   4443篇
建筑科学   5106篇
矿业工程   2064篇
能源动力   2036篇
轻工业   4723篇
水利工程   1112篇
石油天然气   3723篇
武器工业   543篇
无线电   8263篇
一般工业技术   9268篇
冶金工业   3666篇
原子能技术   841篇
自动化技术   9216篇
  2024年   378篇
  2023年   1376篇
  2022年   2362篇
  2021年   3340篇
  2020年   2507篇
  2019年   2196篇
  2018年   2285篇
  2017年   2516篇
  2016年   2279篇
  2015年   2958篇
  2014年   3521篇
  2013年   4244篇
  2012年   4367篇
  2011年   4905篇
  2010年   3940篇
  2009年   3829篇
  2008年   3774篇
  2007年   3414篇
  2006年   3503篇
  2005年   3020篇
  2004年   2077篇
  2003年   1852篇
  2002年   1703篇
  2001年   1470篇
  2000年   1472篇
  1999年   1622篇
  1998年   1420篇
  1997年   1177篇
  1996年   1136篇
  1995年   938篇
  1994年   751篇
  1993年   539篇
  1992年   427篇
  1991年   376篇
  1990年   289篇
  1989年   257篇
  1988年   199篇
  1987年   153篇
  1986年   101篇
  1985年   84篇
  1984年   68篇
  1983年   52篇
  1982年   41篇
  1981年   35篇
  1980年   36篇
  1979年   26篇
  1978年   19篇
  1976年   23篇
  1975年   11篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In this study, the anti-atherosclerotic properties of three marine phospholipids (MPLs) extracts from fishery by-products including codfish roe, squid gonad, and shrimp head are verified. Their effects on key factors involved in atherosclerosis are examined and compared to explore whether the differences in their constitutions lead to the differences in the function. All three MPLs dampen oxidation of low- density lipoproteins (LDL) in vitro. Treating RAW264.7 macrophages and HUVECs endothelial cells with each MPLs ranging 10–100 µg mL−1 does not decrease cell viability, yet ox-LDL caused cytotoxicity of both cells are alleviated by 50 or 100 µg mL−1 MPLs treatment. In addition, the three MPLs reduce ox-LDL induced macrophage foam-like transition, mainly through inhibition of lipid uptake. Of the three MPLs, the one from squid gonad exhibits the best effect. On the other hand, all three MPLs modulate inflammatory responses, equally, by inhibiting the adhesion of monocytes to endothelial cells, and decreasing secretion of pro-inflammatory cytokines IL-6 and MCP-1. Using a high-cholesterol diet induced zebrafish model, it is found that all three MPLs, especially the one from squid gonad, alleviates cholesterol accumulation in early plaques, and decreases total cholesterol as well as lipid peroxide in vivo. Practical Applications: As a way of making the best of the increasingly scarce marine resources, valuable lipid components can be recovered from by-products and wastes from the fishery industry. Here, we tested the anti-atherosclerotic effects and the mechanisms of three MPLs extracted from codfish roe, squid gonad, and shrimp head. Our study provides further evidence that marine phospholipids extracted from fishery by-products could protect against atherosclerosis, and helps to elucidate the structure-function relationship of MPLs.  相似文献   
22.
23.
24.
Amino acid modified polyaspartic acids were evaluated as calcium-scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg-SA-PASP has better scale inhibition and corrosion inhibition performance than His-SA-PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg-SA-PASP is an excellent scale and corrosion inhibitor.  相似文献   
25.
26.
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc.  相似文献   
27.
28.
Peer-to-Peer Networking and Applications -  相似文献   
29.
30.
既有公共建筑能耗中,围护结构节能潜力巨大。以兰州某既有办公建筑为例,采用DeST-C软件模拟围护结构不同材料厚度、窗型,得出系列负荷,通过对数据分析、比较,得出如下结论:外墙外保温适宜材料为50mm的挤塑板,最大热负荷节能率为45.66%;屋面适宜保温材料为65mm的挤塑板,最大热负荷节能率为4.25%;外窗各个朝向全部更换玻璃,推荐选用内张膜中空玻璃(双膜),最大热负荷节能率为7.36%;单独更换南向外窗材料,推荐选用真空镀膜复合中空玻璃,最大热负荷节能率为1.78%。  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