全文获取类型
收费全文 | 1486496篇 |
免费 | 26940篇 |
国内免费 | 7846篇 |
专业分类
电工技术 | 35348篇 |
技术理论 | 5篇 |
综合类 | 7391篇 |
化学工业 | 271724篇 |
金属工艺 | 64520篇 |
机械仪表 | 42067篇 |
建筑科学 | 46351篇 |
矿业工程 | 11777篇 |
能源动力 | 50317篇 |
轻工业 | 112358篇 |
水利工程 | 14948篇 |
石油天然气 | 38327篇 |
武器工业 | 367篇 |
无线电 | 196715篇 |
一般工业技术 | 280006篇 |
冶金工业 | 146147篇 |
原子能技术 | 33926篇 |
自动化技术 | 168988篇 |
出版年
2021年 | 16017篇 |
2020年 | 12087篇 |
2019年 | 14802篇 |
2018年 | 15285篇 |
2017年 | 14587篇 |
2016年 | 21199篇 |
2015年 | 17798篇 |
2014年 | 29133篇 |
2013年 | 88429篇 |
2012年 | 35785篇 |
2011年 | 47988篇 |
2010年 | 42961篇 |
2009年 | 51329篇 |
2008年 | 44970篇 |
2007年 | 42220篇 |
2006年 | 45296篇 |
2005年 | 39516篇 |
2004年 | 41196篇 |
2003年 | 41026篇 |
2002年 | 40318篇 |
2001年 | 36851篇 |
2000年 | 35482篇 |
1999年 | 34060篇 |
1998年 | 39145篇 |
1997年 | 35851篇 |
1996年 | 33071篇 |
1995年 | 29352篇 |
1994年 | 27733篇 |
1993年 | 27588篇 |
1992年 | 25987篇 |
1991年 | 22938篇 |
1990年 | 23311篇 |
1989年 | 22381篇 |
1988年 | 20923篇 |
1987年 | 19191篇 |
1986年 | 18531篇 |
1985年 | 21874篇 |
1984年 | 22259篇 |
1983年 | 20186篇 |
1982年 | 19179篇 |
1981年 | 19280篇 |
1980年 | 17841篇 |
1979年 | 18479篇 |
1978年 | 17695篇 |
1977年 | 17115篇 |
1976年 | 17742篇 |
1975年 | 15957篇 |
1974年 | 15509篇 |
1973年 | 15553篇 |
1972年 | 13044篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well 相似文献
942.
A 3-wave longitudinal design was used to examine the relationships among emotional restraint, peer drug associations, and gateway drug use in a sample of 1,256 middle school students. Structural equation modeling was used to compare 3 models: (1) One model viewed drug use as a consequence of emotional restraint and peer variables; (2) 1 viewed drug use as a cause of restraint and peer variables; and (3) 1 included reciprocal effects. All 3 models fit the data fairly well. However, the reciprocal model fit the data significantly better than either of the others. Within this model, low emotional restraint was significantly related to subsequent increases in gateway drug use among boys. In contrast, peer drug models and peer pressure were not related to subsequent changes in gateway drug use. Changes in peer drug models were, however, predicted by previous levels of gateway drug use. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
943.
K Alanko L Kanerva B Mohell-Talolahti R Jolanki T Estlander 《Canadian Metallurgical Quarterly》1996,35(4):647-648
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data. 相似文献
944.
945.
946.
Butyl, hexyl, and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl)-2,2-dichloroethene, hexyl and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl) ketone, and the hexyl diester of 1,1-bis(5-carboxyl-2-furyl)methane were synthesized from furfural and evaluated for their plasticizing abilities toward PVC, by the application of dynamic mechanical thermal analysis and [di(2-ethylhexyl) phthalate] as a standard of reference. © 1995 John Wiley & Sons, Inc. 相似文献
947.
Shamachary Sathish John H. Cantrell William T. Yost 《Journal of the American Ceramic Society》1996,79(1):209-212
Scanning acoustic microscopy of SCS-6 silicon carbide fiber reveals large radial variations in acoustic reflectivity associated with the chemical composition and microstructure of a given fiber region. Rayleigh wave fringe patterns observed in each of five subregions are used to calculate the average Young modulus of that subregion. The Young modulus is found to increase monotonically from 40 GPa in the carbon core to a value of 413 GPa in the stoichiometric SiC region. The effective Young modulus of the fiber as a whole is estimated from the moduli of the individual regions and it is compared with mechanical measurements reported in the literature. 相似文献
948.
V. M. Yakovenko M. V. Burtyka I. V. Yakovenko 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(3):559-568
The theory of interaction of charged particle beams with 2D electron gas, located in the field of the delta-like potential wallU(y) =U oδ(y) has been developed. The kinetic equation for plasmons in 2D electron gas was obtained; the conditions of arising of their instability are given and the corresponding expressions for the increment of plasmons are found. 相似文献
949.
通过氟塑料-石墨板式换热器在化纤生产中高温强腐蚀换热工况中的实际应用,并与常规换热器的使用情况的对比分析,阐述了这种新型换热设备的特点。 相似文献
950.
Maher M. Osman Mounir M. Abd El-Malek Aida B. Tadros Atef M. Michael 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,62(1):46-52
4-Amino-3-thio-1,24-triazolidine (L1) and 4-amino-5-thio-1,3,4-thiadiazole (LII) as well as their metal complexes of the general formulae MLI·2H2O and MLIICl (M; Pb(II), Cd(II) and Zn(II)) were prepared. With Sn(II), we obtained Sn(LI)2·2H2O and SnLIICl, respectively. The structures of the compounds were identified through elemental analysis, and IR and UV spectra measurements, in addition to thermal analysis in case of the metal complexes. The antifouling properties of the compounds were tested by their incorporation into paint formulations which were applied to PVC substrates and tested in water from Alexandria western harbour. When the compounds were added at 17·5% by volume, the coated panels were fouled after 3 months of immersion. The addition of 6·7% by volume of tributyltin oxide to 15·8% of the prepared compounds in one formulation elevated the paint efficiency and prevented fouling for 11 months. Paint containing solely tributyltin oxide at the same concentration was inactive against algae. 相似文献