全文获取类型
收费全文 | 252664篇 |
免费 | 2959篇 |
国内免费 | 867篇 |
专业分类
电工技术 | 4807篇 |
综合类 | 193篇 |
化学工业 | 36114篇 |
金属工艺 | 9506篇 |
机械仪表 | 7544篇 |
建筑科学 | 6072篇 |
矿业工程 | 880篇 |
能源动力 | 7225篇 |
轻工业 | 21098篇 |
水利工程 | 2202篇 |
石油天然气 | 3230篇 |
武器工业 | 15篇 |
无线电 | 34277篇 |
一般工业技术 | 49967篇 |
冶金工业 | 48534篇 |
原子能技术 | 5075篇 |
自动化技术 | 19751篇 |
出版年
2021年 | 2169篇 |
2020年 | 1560篇 |
2019年 | 1916篇 |
2018年 | 3270篇 |
2017年 | 3308篇 |
2016年 | 3399篇 |
2015年 | 2217篇 |
2014年 | 3955篇 |
2013年 | 11472篇 |
2012年 | 6233篇 |
2011年 | 8572篇 |
2010年 | 6904篇 |
2009年 | 7884篇 |
2008年 | 8402篇 |
2007年 | 8294篇 |
2006年 | 7363篇 |
2005年 | 6498篇 |
2004年 | 6282篇 |
2003年 | 6554篇 |
2002年 | 6036篇 |
2001年 | 6513篇 |
2000年 | 5973篇 |
1999年 | 6388篇 |
1998年 | 16480篇 |
1997年 | 11408篇 |
1996年 | 8792篇 |
1995年 | 6606篇 |
1994年 | 5901篇 |
1993年 | 5842篇 |
1992年 | 4131篇 |
1991年 | 4020篇 |
1990年 | 3857篇 |
1989年 | 3648篇 |
1988年 | 3559篇 |
1987年 | 3017篇 |
1986年 | 2941篇 |
1985年 | 3206篇 |
1984年 | 2926篇 |
1983年 | 2829篇 |
1982年 | 2636篇 |
1981年 | 2542篇 |
1980年 | 2461篇 |
1979年 | 2305篇 |
1978年 | 2107篇 |
1977年 | 2604篇 |
1976年 | 3562篇 |
1975年 | 1764篇 |
1974年 | 1729篇 |
1973年 | 1665篇 |
1972年 | 1465篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
932.
933.
934.
935.
We study the nonlinear propagation of light in optical fibers in the strong nonlinearity limit. In this limit, the transverse guiding properties are altered and cannot be decoupled from the longitudinal part of the wave equation. We consider a refractive index profile with no bound modes at low intensities and show that stable self-guiding occurs at a critical intensity. This critical intensity is a property of the guide and can be made much lower than the threshold for unstable self-focusing. We consider a particular design for which self-guiding occurs at three orders of magnitude lower than the self-focusing threshold. 相似文献
936.
Blair J.D. Correale A. Jr. Cranford H.C. Dombrowski D.A. Erdelyi C.K. Hoffman C.R. Lamphere J.L. Lang K.W. Lee J.K. Mullen J.M. Norman V.R. Oakland S.F. 《Solid-State Circuits, IEEE Journal of》1989,24(6):1647-1655
The authors describe a 9.02×9.02-mm chip built in 1-μm CMOS with two levels of metal and an additional mask level for fabricating capacitors. It contains both analog and digital circuits and has provisions for self-test. The function includes the transmitter, receiver, protocol handler, an microprocessor, as well as interfaces for RAM/ROM storage, IBM PC bus, IBM PS/2 bus, IBM 3174 bus, and Motorola 68000 bus. The physical design terrains are formed by 24K circuits of standard cell gates, a 10K-circuit equivalent hand-honed custom microprocessor, and an analog macro. The chip operates from a single 5-V supply, and the power consumption is 0.8 W nominal at 16 Mb/s. The chip can also be operated at 4 Mb/s 相似文献
937.
938.
V. N. Serebryany A. Ya. Kochubei S. F. Kurtasov K. E. Mel’nikov 《Russian Metallurgy (Metally)》2007,(1):73-78
Quantitative texture analysis is used to study texture formation in an MA2-1 magnesium alloy subjected to axisymmetric upsetting at temperatures of 250–450°C and strain rates of 10?4–100 ?1. The deformed structure is examined by optical microscopy, and the results obtained are used to plot the structural-state diagram of the alloy after 50% upsetting. The experimental textures are compared with the textures calculated in terms of a thermoactivation model. 相似文献
939.
The viscometric, turbidimetric and potentiometric properties of copolymers of acrylamide (AM) with 2-acrylamido-2-methylpropanedimethylammonium chloride (AMPDAC) were studied in aqueous solutions. The AMPDAC polymers exhibit poor salt tolerance and large, negative viscosity/temperature coefficients. Furthermore, the polymers were found to be sensitive to changes in pH. The AMPDAC polymers undergo phase separation in the presence of dianions as a function of temperature and AMPDAC composition. 相似文献
940.
K W Brown K C Donnelly J C Thomas P Davol B R Scott 《The Science of the total environment》1985,41(2):173-186
A chemical and biological testing protocol was employed to evaluate the mutagenic potential of the organic compounds extracted from three agricultural soils. The analytical procedures used included bioassays with Salmonella typhimurium and Aspergillus nidulans for the detection of point mutations and a gas chromatography/mass spectrometry/computer system to identify major organic constituents. The extracts of all three soils exhibited mutagenic response in the bioassays. At a dose level of 1000 micrograms per plate, the organic extract of the Bastrop clay induced 434 net revertants; while at the same dose level the Norwood sandy clay and the Sassafrass sandy loam induced 35 and 178 net revertants, respectively, in the Salmonella assay with metabolic activation. In the Aspergillus assay, the extract of the Norwood and Bastrop soils induced a positive response without metabolic activation; this effect was reduced or eliminated in the presence of metabolic activation. Chemical analysis identified a variety of initiators, promotors, inhibitors, and cocarcinogens; however, there were no mutagenic compounds identified in any of the soil extracts. The results of this combined testing protocol indicate that the agricultural soils tested had an inherent level of mutagenic activity, which was not detected by GC/MS analysis alone, and this activity may be related to the past history of agricultural practices, including biocide applications, fertilization, and cultivation. 相似文献