全文获取类型
收费全文 | 208583篇 |
免费 | 4013篇 |
国内免费 | 2503篇 |
专业分类
电工技术 | 5424篇 |
技术理论 | 4篇 |
综合类 | 2131篇 |
化学工业 | 24861篇 |
金属工艺 | 14045篇 |
机械仪表 | 11023篇 |
建筑科学 | 5629篇 |
矿业工程 | 1821篇 |
能源动力 | 4433篇 |
轻工业 | 9390篇 |
水利工程 | 2371篇 |
石油天然气 | 4138篇 |
武器工业 | 231篇 |
无线电 | 26252篇 |
一般工业技术 | 45232篇 |
冶金工业 | 32553篇 |
原子能技术 | 2814篇 |
自动化技术 | 22747篇 |
出版年
2023年 | 804篇 |
2022年 | 1472篇 |
2021年 | 2032篇 |
2020年 | 1624篇 |
2019年 | 1488篇 |
2018年 | 11031篇 |
2017年 | 11741篇 |
2016年 | 7015篇 |
2015年 | 2725篇 |
2014年 | 2988篇 |
2013年 | 6348篇 |
2012年 | 7103篇 |
2011年 | 14552篇 |
2010年 | 13196篇 |
2009年 | 12426篇 |
2008年 | 12365篇 |
2007年 | 14625篇 |
2006年 | 5223篇 |
2005年 | 8465篇 |
2004年 | 6082篇 |
2003年 | 5511篇 |
2002年 | 4182篇 |
2001年 | 3776篇 |
2000年 | 3467篇 |
1999年 | 3789篇 |
1998年 | 9932篇 |
1997年 | 6565篇 |
1996年 | 5132篇 |
1995年 | 3491篇 |
1994年 | 3068篇 |
1993年 | 2921篇 |
1992年 | 1787篇 |
1991年 | 1707篇 |
1990年 | 1603篇 |
1989年 | 1381篇 |
1988年 | 1217篇 |
1987年 | 901篇 |
1986年 | 910篇 |
1985年 | 936篇 |
1984年 | 812篇 |
1983年 | 707篇 |
1982年 | 703篇 |
1981年 | 689篇 |
1980年 | 577篇 |
1979年 | 479篇 |
1978年 | 416篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 276篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Examination of the wreckage of a light aircraft revealed that approximately 20 cm was missing from one tip of the aluminum
alloy propeller. Fractographic and metallographic examination of the remaining portion of the propeller revealed extensive
grain-boundary separation in the vicinity of the fracture, and grain edges and corners rounded by corrosion on the fracture
surface. Energy dispersive X-ray analysis (EDXA) revealed fluorine on, and in the vicinity of, the fracture surface. In the
ensuing litigation, it was asserted that the crash occurred because the propeller fractured in flight as the result of intergranular
attack caused by the use of a fluorine-bearing cleaner. 相似文献
52.
M. Kawasaki T. Tsukamoto Y. Kimura T. Iwasaki H. Yamane 《Journal of Materials Science》2003,38(4):739-745
The damage imposed on SiO
x
deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiO
x
layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiO
x
layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiO
x
deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S. 相似文献
53.
54.
The interaction of transient electromagnetic pulse with an air layer in a dielectric medium is formulated in terms of a time-domain integral equation and solved numerically via the method of moments. Previous related works pointed to the inherent inadequacy of the marching-on-in-time method in this case, but suggested no remedy. This paper explains why an implicit modeling scheme would work effectively in this case. It is also noted that the use of an implicit scheme would normally involve a solution of a very large and dense matrix equation. To alleviate this drawback of the implicit scheme, the use of a wavelet-based impedance-matrix-compression technique, which has facilitated in the very recent past solutions of time-domain problems with greater efficiency, is described. 相似文献
55.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
56.
The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented 相似文献
57.
阴,阳离子聚合物地层内凝胶化改善水驱效果的研究 总被引:9,自引:1,他引:8
研究了一杆阴离子聚合物(Ac530)和一种阳离子聚合物(Mb581)在水溶液中形成凝胶的条件和过程、凝胶化学结构、形态、稳定性和力学性能。在模拟地层的二维微观模型内观测了两种聚合物驱替渗流、相逼、形成凝胶、凝胶封堵大孔道的机理。在亲水填砂模型内测定了阴、阳离子聚合物凝胶体系降低渗透率的能力。 相似文献
58.
59.
60.