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   150363篇
  免费   12886篇
  国内免费   6397篇
电工技术   8574篇
技术理论   16篇
综合类   9636篇
化学工业   24887篇
金属工艺   8160篇
机械仪表   9419篇
建筑科学   11762篇
矿业工程   4387篇
能源动力   4301篇
轻工业   9356篇
水利工程   2670篇
石油天然气   8233篇
武器工业   1107篇
无线电   18629篇
一般工业技术   18636篇
冶金工业   7820篇
原子能技术   1761篇
自动化技术   20292篇
  2024年   677篇
  2023年   2526篇
  2022年   4298篇
  2021年   5845篇
  2020年   4568篇
  2019年   3778篇
  2018年   4326篇
  2017年   4866篇
  2016年   4289篇
  2015年   5757篇
  2014年   7274篇
  2013年   8940篇
  2012年   9487篇
  2011年   10032篇
  2010年   8842篇
  2009年   8430篇
  2008年   8392篇
  2007年   7793篇
  2006年   7982篇
  2005年   6963篇
  2004年   4834篇
  2003年   4330篇
  2002年   4088篇
  2001年   3822篇
  2000年   3685篇
  1999年   4033篇
  1998年   3398篇
  1997年   2934篇
  1996年   2704篇
  1995年   2232篇
  1994年   1792篇
  1993年   1372篇
  1992年   1118篇
  1991年   854篇
  1990年   701篇
  1989年   572篇
  1988年   464篇
  1987年   332篇
  1986年   253篇
  1985年   202篇
  1984年   127篇
  1983年   96篇
  1982年   109篇
  1981年   79篇
  1980年   58篇
  1979年   43篇
  1978年   32篇
  1977年   35篇
  1976年   63篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A modified CIECAM02 colour appearance model, named CIECAM02‐m2, is proposed to enable CIECAM02 to predict the simultaneous contrast effect. The structure of the CIECAM02‐m2 is a development from CIECAM02, and contains two different procedures for modifying the reference white; one is for lightness and the other is for hue. The model was tested using a data set accumulated in this study and the LUTCHI data. The CV values for three colour attributes between predictions and experimental data were used to evaluate the accuracy of the model. The low CV values obtained show the performance of the CIECAM02‐m2 model to predict the simultaneous contrast effect satisfactorily. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 121 – 129, 2007  相似文献   
992.
The research literature has seen a number of studies aimed at understanding customer attitudes towards banking technologies, and thereby providing implications for developmental planning and marketing. However, even though banking technologies have a significant amount of information systems (IS) component to them, there is a paucity of research that considers them from the IS perspective. In this paper, we fill this gap by considering three constructs, namely usefulness, ease of use and usage, that are all rooted in the IS literature. We study user’s perceptions of these constructs, as well as the relationships among them, for both online and telephone banking.  相似文献   
993.
994.
Barium strontium titanate glass-ceramics were successfully produced with one major crystalline phase when Al2O3 was added to the melt. A dielectric constant of 1000 and a breakdown strength of 800 kV/cm was achieved; however the energy density was only measured to be 0.3–0.9 J/cm3. These energy density values were lower than anticipated due to the presence of dendrites and pores in the microstructure. Using BaF2 as a refining agent improved the microstructure and doubled the energy density for BST 80/20 samples. However, no refining agent reduced the increasing amount of hysteresis that developed with increasing applied electric field. This phenomenon is believed to be due to interfacial polarization.  相似文献   
995.
996.
Strains of Bacteroides fragilis associated with diarrheal disease (enterotoxigenic B. fragilis) produce a 20-kDa zinc-dependent metalloprotease toxin (B. fragilis enterotoxin; BFT) that reversibly stimulates chloride secretion and alters tight junctional function in polarized intestinal epithelial cells. BFT alters cellular morphology and physiology most potently and rapidly when placed on the basolateral membrane of epithelial cells, suggesting that the cellular substrate for BFT may be present on this membrane. Herein, we demonstrate that BFT specifically cleaves within 1 min the extracellular domain of the zonula adherens protein, E-cadherin. Cleavage of E-cadherin by BFT is ATP-independent and essential to the morphologic and physiologic activity of BFT. However, the morphologic changes occurring in response to BFT are dependent on target-cell ATP. E-cadherin is shown here to be a cellular substrate for a bacterial toxin and represents the identification of a mechanism of action, cell-surface proteolytic activity, for a bacterial toxin.  相似文献   
997.
Crystal structures of the murine cytokine-inducible nitric oxide synthase oxygenase dimer with active-center water molecules, the substrate L-arginine (L-Arg), or product analog thiocitrulline reveal how dimerization, cofactor tetrahydrobiopterin, and L-Arg binding complete the catalytic center for synthesis of the essential biological signal and cytotoxin nitric oxide. Pterin binding refolds the central interface region, recruits new structural elements, creates a 30 angstrom deep active-center channel, and causes a 35 degrees helical tilt to expose a heme edge and the adjacent residue tryptophan-366 for likely reductase domain interactions and caveolin inhibition. Heme propionate interactions with pterin and L-Arg suggest that pterin has electronic influences on heme-bound oxygen. L-Arginine binds to glutamic acid-371 and stacks with heme in an otherwise hydrophobic pocket to aid activation of heme-bound oxygen by direct proton donation and thereby differentiate the two chemical steps of nitric oxide synthesis.  相似文献   
998.
HREM and FEG TEM were emphasized and extensively used to follow the most subtle changes in the structure and composition of ball-milled Cu, Fe-Cu, and thermally decomposed Fe60Cu40. Some significant results are obtained and summarized as follows: HREM shows that the deformation of ball-milled copper proceeds mainly by twinning and shear bands (SBs) formation. The nano-grains formed during ball milling (BM) contain a high density of dislocations. The grain boundaries (GBs) of nanocrystalline (NC) Cu prepared by BM are ordered, curved, and strained, but disordering, lattice distortion, and nanovoids in local regions were frequently observed. Nanoscale composition analysis on mechanically alloyed Fe16Cu84 shows that the average Fe content in both the interior of grains and the GBs is close to the designed composition, which proves that a supersaturated solid solution has really formed. However, the Fe content is rather inhomogeneous between the larger and smaller grains, which infers the inhomogeneous mixing of Fe and Cu during mechanical alloying (MA). NC structure and the mechanical force-enhanced fast diffusion are the reasons of the formation of supersaturated solid solutions in immiscible systems with positive enthalpy of mixing. HREM observations carried out with the thermally decomposed Fe60Cu40 solid solution show that the Nishiyama (N-W) or Kurdyumov-Sachs (K-S) orientation relationships exist between alpha-Fe and Cu. Energy dispersive X-ray spectra (EDXS) results show that the Cu content in these alpha-Fe grains reaches as high as 9.5 at.% even after heating to 1,400 degrees C, which is even higher than the maximum solubility of Cu in gamma-Fe at 1,094 degrees C.  相似文献   
999.
对线材制品从连续化、自动化、高速化等方面与国外企业生产状况进行了分析比较,提出了实现生产过程的连续化、高速化、自动化是发展我国线材制品的必由之路的观点。  相似文献   
1000.
分析了真空离子镀的基本原理,研究了NbFeB永磁合金表面离子镀Cu-Al-In三元仿金合金的新工艺。合金镀层晶粒较小,均匀美观,光泽柔和;合理的工艺条件为:偏压200V,主弧电流5A±0.25A,间距120mm,加热功率11kW,氩气分压1.33Pa~0.0133Pa,时间30min。  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