全文获取类型
收费全文 | 172606篇 |
免费 | 15174篇 |
国内免费 | 8104篇 |
专业分类
电工技术 | 10845篇 |
技术理论 | 12篇 |
综合类 | 12309篇 |
化学工业 | 27895篇 |
金属工艺 | 9410篇 |
机械仪表 | 10917篇 |
建筑科学 | 13607篇 |
矿业工程 | 4987篇 |
能源动力 | 4667篇 |
轻工业 | 12831篇 |
水利工程 | 3362篇 |
石油天然气 | 8460篇 |
武器工业 | 1459篇 |
无线电 | 20731篇 |
一般工业技术 | 20077篇 |
冶金工业 | 8069篇 |
原子能技术 | 2177篇 |
自动化技术 | 24069篇 |
出版年
2024年 | 693篇 |
2023年 | 2769篇 |
2022年 | 5237篇 |
2021年 | 7023篇 |
2020年 | 5298篇 |
2019年 | 4244篇 |
2018年 | 4837篇 |
2017年 | 5475篇 |
2016年 | 4770篇 |
2015年 | 6674篇 |
2014年 | 8678篇 |
2013年 | 10600篇 |
2012年 | 11675篇 |
2011年 | 12404篇 |
2010年 | 11206篇 |
2009年 | 10686篇 |
2008年 | 10569篇 |
2007年 | 10009篇 |
2006年 | 9654篇 |
2005年 | 8314篇 |
2004年 | 5783篇 |
2003年 | 4657篇 |
2002年 | 4207篇 |
2001年 | 3830篇 |
2000年 | 3875篇 |
1999年 | 4072篇 |
1998年 | 3247篇 |
1997年 | 2859篇 |
1996年 | 2576篇 |
1995年 | 2142篇 |
1994年 | 1696篇 |
1993年 | 1348篇 |
1992年 | 1054篇 |
1991年 | 808篇 |
1990年 | 638篇 |
1989年 | 538篇 |
1988年 | 420篇 |
1987年 | 300篇 |
1986年 | 208篇 |
1985年 | 172篇 |
1984年 | 107篇 |
1983年 | 79篇 |
1982年 | 91篇 |
1981年 | 68篇 |
1980年 | 63篇 |
1979年 | 40篇 |
1978年 | 25篇 |
1977年 | 27篇 |
1976年 | 41篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
实时可视决策系统在渤海湾旅大油田开发中的应用 总被引:4,自引:1,他引:3
实时可视决策系统可以将接收到的现场数据实时传输到陆地,井眼轨迹和随钻测井资料可实时在三维地质油藏模型中显示,供钻完井和地质油藏专家综合分析、判断并及时下达指令指导现场施工。旅大油田运用实时可视决策系统成功钻成了6口水平井和4口水平分支井,实现了不钻领眼、井眼轨迹在最佳油层内成功着陆,并使水平井段尽可能沿着油层最佳位置钻进。例如在LD10—1-A25m水平分支井段的钻井过程中,利用实时可视决策系统,控制水平井眼轨迹在油层最佳位置钻进,获得了日产810M^3。的高产油气流。 相似文献
992.
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
993.
县级小型电视台没有电视转播车,很难对一些重要的新闻事件或文艺演出等进行现场直播,作者通过多年的实践探索出一套简单实用的方法,在现场直播中,视音频信号处理及传送、导播通信是很关键的环节,对这两个问题进行重点分析并提出具体的解决方案。 相似文献
994.
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
995.
996.
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
997.
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
998.
BR Crane AS Arvai DK Ghosh C Wu ED Getzoff DJ Stuehr JA Tainer 《Canadian Metallurgical Quarterly》1998,279(5359):2121-2126
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
999.
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
1000.
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