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   403668篇
  免费   5407篇
  国内免费   1354篇
电工技术   7575篇
综合类   314篇
化学工业   59698篇
金属工艺   16443篇
机械仪表   13526篇
建筑科学   8364篇
矿业工程   2154篇
能源动力   11577篇
轻工业   28508篇
水利工程   4267篇
石油天然气   7915篇
武器工业   17篇
无线电   49365篇
一般工业技术   83164篇
冶金工业   75054篇
原子能技术   9188篇
自动化技术   33300篇
  2022年   2332篇
  2021年   3930篇
  2020年   2986篇
  2019年   3837篇
  2018年   6531篇
  2017年   6534篇
  2016年   6968篇
  2015年   4336篇
  2014年   7176篇
  2013年   20089篇
  2012年   11446篇
  2011年   15320篇
  2010年   12180篇
  2009年   13740篇
  2008年   14084篇
  2007年   13843篇
  2006年   12437篇
  2005年   11135篇
  2004年   10521篇
  2003年   10441篇
  2002年   9847篇
  2001年   9745篇
  2000年   9145篇
  1999年   9537篇
  1998年   24350篇
  1997年   16723篇
  1996年   12812篇
  1995年   9532篇
  1994年   8373篇
  1993年   8394篇
  1992年   6055篇
  1991年   5696篇
  1990年   5684篇
  1989年   5322篇
  1988年   5045篇
  1987年   4426篇
  1986年   4303篇
  1985年   4812篇
  1984年   4423篇
  1983年   3997篇
  1982年   3655篇
  1981年   3732篇
  1980年   3432篇
  1979年   3330篇
  1978年   3338篇
  1977年   3756篇
  1976年   4858篇
  1975年   2853篇
  1974年   2663篇
  1973年   2732篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
141.
A series of 2-phenyloxazoles bearing an amide group at position 4 were designed and synthesized for evaluation as potential inhibitors of human recombinant monoamine oxidases (hrMAOs). Results of kinetics experiments demonstrated that all compounds behave as competitive MAO inhibitors, with good selectivity toward the MAO-B isoform. The most potent and selective derivatives are characterized by inhibition constant (Ki) values in the sub-micromolar range and a good selectivity index (Ki MAO-A/Ki MAO-B>50). Some derivatives were also found to be able to inhibit MAO activity in nerve growth factor (NGF)-differentiated PC12 cells, taken as a model of neuronal cells. In particular, 2-(2-hydroxyphenyl)-N-phenyloxazole-4-carboxamide (compound 4 a ) may be a promising new scaffold, exerting the highest selectivity and inhibitory effect toward MAOs in NGF-differentiated PC12 cell lysates, without compromising cell viability. Molecular docking analysis allowed a rationalization of the experimentally observed binding affinity and selectivity.  相似文献   
142.
Theoretical Foundations of Chemical Engineering - Using chemical and XRD phase analysis, along with electron microscopy, the hydrolytic processing of metallic bismuth into high-purity citrate has...  相似文献   
143.
The potential energy profile of the reaction between dimethyl disulfide and OH? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10?10?cm3?molecule?1?s?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH3S?(OH)SCH3 decomposing rapidly to yield CH3S?+CH3SOH.  相似文献   
144.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.  相似文献   
145.
146.
147.
148.
149.
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite.  相似文献   
150.
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