全文获取类型
收费全文 | 130979篇 |
免费 | 9888篇 |
国内免费 | 7596篇 |
专业分类
电工技术 | 8333篇 |
技术理论 | 6篇 |
综合类 | 12234篇 |
化学工业 | 21872篇 |
金属工艺 | 9947篇 |
机械仪表 | 4849篇 |
建筑科学 | 5474篇 |
矿业工程 | 1896篇 |
能源动力 | 4323篇 |
轻工业 | 8165篇 |
水利工程 | 2321篇 |
石油天然气 | 5849篇 |
武器工业 | 1105篇 |
无线电 | 13544篇 |
一般工业技术 | 19863篇 |
冶金工业 | 4672篇 |
原子能技术 | 2608篇 |
自动化技术 | 21402篇 |
出版年
2024年 | 222篇 |
2023年 | 1079篇 |
2022年 | 1593篇 |
2021年 | 2104篇 |
2020年 | 2592篇 |
2019年 | 2500篇 |
2018年 | 2473篇 |
2017年 | 2678篇 |
2016年 | 3194篇 |
2015年 | 3865篇 |
2014年 | 6248篇 |
2013年 | 7310篇 |
2012年 | 6902篇 |
2011年 | 7546篇 |
2010年 | 5954篇 |
2009年 | 7589篇 |
2008年 | 7475篇 |
2007年 | 8293篇 |
2006年 | 7664篇 |
2005年 | 6375篇 |
2004年 | 5469篇 |
2003年 | 5334篇 |
2002年 | 5165篇 |
2001年 | 4090篇 |
2000年 | 4344篇 |
1999年 | 3857篇 |
1998年 | 3299篇 |
1997年 | 3099篇 |
1996年 | 3112篇 |
1995年 | 3178篇 |
1994年 | 2855篇 |
1993年 | 1772篇 |
1992年 | 1781篇 |
1991年 | 1256篇 |
1990年 | 954篇 |
1989年 | 859篇 |
1988年 | 719篇 |
1987年 | 423篇 |
1986年 | 274篇 |
1985年 | 411篇 |
1984年 | 459篇 |
1983年 | 460篇 |
1982年 | 360篇 |
1981年 | 427篇 |
1980年 | 292篇 |
1979年 | 119篇 |
1978年 | 118篇 |
1977年 | 75篇 |
1975年 | 60篇 |
1974年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
IP电话的实现及其关键技术 总被引:1,自引:0,他引:1
IP电话在推出后短短十年的时间以其低价、高效、灵活的特点迅速发展起来。本文介绍了IP电话的基本结构,比较了IP电话与普通电话的优缺点,讨论了IP电话的相关协议及关键技术,在这些基础上进一步指出IP电话的发展趋势,相信IP将成为未来信息通信的主导技术。 相似文献
992.
993.
近年来,大电流的监测成了人们十分关心的问题,这是由于大电流有强磁、高压、电流大等一系列的直接监测所不能克服的问题。这就需要把高压大电流的强电信号,经过提取后变成能在实验室中直接观测的弱电信号。为此,如何从高压大电流的信号中提取出随实时信号变化而实时变化的小信号就变成了一个关键问题。详细介绍了监测信号提取的光收发电路原理和后续信号处理电路,分析了各部分的作用,给出了必要的分析结果。 相似文献
994.
Piero Villaggio 《Journal of Engineering Mathematics》2003,46(3-4):409-416
The diffusion of contact stresses between an elastic bar, bonded to an elastic half-plane and loaded longitudinally, requires the integration of a singular integral equation. The solution of this equation is not available in closed form, but only by a series expansion of the contact tangential force mutually transmitted between the stiffener and the plate. Since forty years it has been realized that the expansion of the solution in terms of Chebyshev polynomials is its most convenient method of representation. The procedure can also be extended to treat the brittle detachments of the tips of the stiffener when, according to Griffith's criterion of fracture, a balance can be virtually established between the increase of strain energy due to a propagation of cracks and the surface energy created. 相似文献
995.
L. Pamela Cook Emeka Nwankwo Gilberto Schleiniger Bryan Wood 《Journal of Engineering Mathematics》2003,45(3-4):269-282
A general formulation for capillary flow of two miscible fluids – one a dilute plug of polymer fluid inserted into a fully developed Poiseuille flow of the other, a Newtonian stream – is examined for its long time behavior. Phenomenologically, the system evolves from an initial state, that of a plug within the boundaries of sharp, well defined fronts inside a Newtonian stream, to a more homogenized state in the very long time scale. This problem was addressed by G.I. Taylor but with regard to a system of two Newtonian fluids, leading to the well-known results commonly described as `Taylor axial dispersion'. In this paper, a general and systematic perturbation analysis is presented from which Taylor's result is recovered as a special case of a more general solution which applies to fluids incorporating elastic properties. In particular, the influence of viscoelasticity and (polymer) diffusivity on the observed pressure profile in the capillary conduit is examined. This effect is clearly separated out for small Peclet number flows using asymptotic and numerical analysis. The results identify the influence of fluid viscosity, elasticity, and diffusivity on the observed pressure profile and form the basis for the improved characterization of polymeric elasticity using capillaries – a finding that is of significant scientific and commercial interest. These results were obtained by the authors as a class of observations resulting from the perturbation analysis of forced-flow capillary devices in viscoelastic fluid property investigation. 相似文献
996.
Rui Morimoto Chisato Yokomori Akiko Kikkawa Akira Izumi Hideki Matsumura 《Thin solid films》2003,430(1-2):230-235
In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiNx films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O2 oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiNx prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiNx films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm−1 of OFF leakage current and ON/OFF ratio of 107–108 are realized, i.e. the devices can operate similarly to conventional thermal CVD process. 相似文献
997.
998.
999.
1000.
防治畜类寄生线虫的又一阿维菌素类化合物--道拉菌素 总被引:4,自引:2,他引:2
道拉菌素是利用生物突变合成方法得到的新型阿维菌素族广谱杭寄生虫药。它的化学结构和作用机制与依维菌素相似。试验证实道拉菌素在低剂量下对多种体内外寄生虫具有良好的防治效果。 相似文献