全文获取类型
收费全文 | 8087篇 |
免费 | 270篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 163篇 |
综合类 | 12篇 |
化学工业 | 1673篇 |
金属工艺 | 226篇 |
机械仪表 | 157篇 |
建筑科学 | 204篇 |
矿业工程 | 31篇 |
能源动力 | 420篇 |
轻工业 | 484篇 |
水利工程 | 37篇 |
石油天然气 | 23篇 |
无线电 | 983篇 |
一般工业技术 | 1720篇 |
冶金工业 | 1068篇 |
原子能技术 | 52篇 |
自动化技术 | 1128篇 |
出版年
2023年 | 88篇 |
2022年 | 157篇 |
2021年 | 240篇 |
2020年 | 181篇 |
2019年 | 190篇 |
2018年 | 258篇 |
2017年 | 234篇 |
2016年 | 195篇 |
2015年 | 145篇 |
2014年 | 226篇 |
2013年 | 563篇 |
2012年 | 319篇 |
2011年 | 429篇 |
2010年 | 316篇 |
2009年 | 322篇 |
2008年 | 310篇 |
2007年 | 287篇 |
2006年 | 252篇 |
2005年 | 249篇 |
2004年 | 198篇 |
2003年 | 190篇 |
2002年 | 159篇 |
2001年 | 145篇 |
2000年 | 117篇 |
1999年 | 128篇 |
1998年 | 254篇 |
1997年 | 194篇 |
1996年 | 149篇 |
1995年 | 118篇 |
1994年 | 149篇 |
1993年 | 135篇 |
1992年 | 120篇 |
1991年 | 92篇 |
1990年 | 73篇 |
1989年 | 69篇 |
1988年 | 83篇 |
1987年 | 78篇 |
1986年 | 71篇 |
1985年 | 92篇 |
1984年 | 87篇 |
1983年 | 74篇 |
1982年 | 67篇 |
1981年 | 71篇 |
1980年 | 57篇 |
1979年 | 44篇 |
1978年 | 44篇 |
1977年 | 50篇 |
1976年 | 66篇 |
1974年 | 36篇 |
1973年 | 37篇 |
排序方式: 共有8381条查询结果,搜索用时 781 毫秒
31.
Sudhir Singh Bhadauria Dr. Mahesh Chandra Gupta 《Canadian Metallurgical Quarterly》2007,21(3):234-239
Reports of failure of existing concrete structures due to a lack of durability, rather than a deficiency in structural strength, has made concrete technologists, engineers, and researchers focus research on the parameters influencing durability performance with respect to time. Systematic performance monitoring, with respect to chosen durability parameters of existing concrete structures, will decide the direction of future research in this area. Inferences based on laboratory simulations and testing need to be confirmed by in situ field measurements and studies. In situ condition rating and performance monitoring surveys have been conducted by many researchers, scientists, and professional associations, and reported in literature. Inferences of few such studies are summarized and discussed. Deterioration of concrete structures constructed in recent times is observed at relatively faster rates, and has been mainly attributed to cracking. Cracking is associated with the use of faster-hydrating portland cements with increased fineness and the tricalcium silicate (C3S) content to support the high speed of modern construction. In the present research, a case study of deteriorated water tank structures situated in the semitropical region of India is presented. Some selected parameters—such as concrete cover, carbonation depth, chloride concentration, compressive strength, etc. which influence long term durability of structures—have been measured. 相似文献
32.
Irvin Roy Hentzel 《Computers & Mathematics with Applications》1991,22(12):61-66
We are interested in deciding if a given nonassociative polynomial h is an identity for a variety of nonassociative algebras. We present an algorithm for constructing a certain homomorphic image of a free nonassociative algebra which is sufficient to answer the question. The algorithm resembles dynamic programming in that the algebra is built by constructing a sequence of subspaces; the basis of each subspace is determined by the basis of previous subspaces. The number of arithmetic operations required to construct the algebra is bounded by a polynomial in the degree of h and the dimension of the resulting algebra. 相似文献
33.
34.
35.
Identification of a specific biomolecular target appropriately sensitive to a wide array of anesthetics has been elusive. At concentrations close to their respective ED50's for anesthesia in man or other species, 18 compounds, differing in potencies up to 66,000 fold, inhibited cytochrome P450 mediated metabolism of aminopyrine, a synthetic substrate, and arachidonic acid (AA), an endogenous substrate, in isolated liver microsomes. There was a highly significant correlation for both substrates between the absolute concentrations required for anesthesia (EC50) and for inhibition of P450 activity (Ki or IC50). The mean Ki/EC50 ratio was 0.97 for inhibition of aminopyrine demethylase. The mean IC50/EC50 ratios were 0.42 and 0.64 for inhibition of two AA-derived products and 2.8 for a third; a mean ratio of 1.4 for inhibition of overall AA metabolism suggests interaction of general anesthetics with a composite of P450 isozymes. The universal cytochrome P450 monooxygenases, in conjunction with other lipid oxygenases (cyclooxygenases and lipoxygenases) participate in the second messenger AA cascade. In nerve cells the sensitivity of these enzymes to hydrophobic neurodepressant drugs may underlie the state of general anesthesia: reversible disruption of intracellular and intercellular signalling without impairment of enzymes vital to cell respiration. 相似文献
36.
Also with the Department of Agronomy. 相似文献
37.
Robert H. Doremus Denis Murphy Narottam P. Bansal William A. Lanford Chandra Burman 《Journal of Materials Science》1985,20(12):4445-4453
When liquid water contacts a zirconium-barium-lanthanum fluoride glass, at least three different processes occur. Barium and zirconium fluoride dissolve into the water, water penetrates into the glass, and zirconium fluoride crystals grow on the glass surface, in static solution. The rate of dissolution, as measured by solution analysis, is possibly controlled by diffusion in the solid surface; surface blockage and surface reactions are other possible kinetic steps involved. Diffusion in solution is not the controlling mechanism. Hydrogen profiles in the glass surface suggest that the penetration rate of water into the glass is controlled by diffusion and a surface reaction. 相似文献
38.
On-body communications around the human torso are considered, using ultra-wideband transmissions. The velocity of the diffracted wave propagating around the body is extracted from frequency- domain spatial correlation analyses. 相似文献
39.
L. J. Singh S. Choudhury S. Singha Roy K. P. Ghatak 《Electrical Engineering (Archiv fur Elektrotechnik)》2005,87(1):1-9
An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs2, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions. 相似文献
40.
Roy S. Berns 《Color research and application》2007,32(4):334-335
The term “color gamut” historically has been associated with color output such as optimal color stimuli and additive and subtractive imaging systems. Recently, this term has been used with input devices such as scanners and digital cameras. It is proposed that the term “color‐gamut rendering” should be used instead of input devices. This clarifies the distinction between input (analysis) and output (synthesis) color systems in terms of the effect of an input system on defining the colorimetric properties of an output system. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 334–335, 2007 相似文献