全文获取类型
收费全文 | 18708篇 |
免费 | 493篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 226篇 |
综合类 | 14篇 |
化学工业 | 2562篇 |
金属工艺 | 229篇 |
机械仪表 | 335篇 |
建筑科学 | 895篇 |
矿业工程 | 42篇 |
能源动力 | 452篇 |
轻工业 | 1941篇 |
水利工程 | 262篇 |
石油天然气 | 28篇 |
无线电 | 1704篇 |
一般工业技术 | 2375篇 |
冶金工业 | 5388篇 |
原子能技术 | 144篇 |
自动化技术 | 2621篇 |
出版年
2023年 | 65篇 |
2022年 | 114篇 |
2021年 | 265篇 |
2020年 | 135篇 |
2019年 | 199篇 |
2018年 | 266篇 |
2017年 | 247篇 |
2016年 | 272篇 |
2015年 | 252篇 |
2014年 | 387篇 |
2013年 | 657篇 |
2012年 | 678篇 |
2011年 | 916篇 |
2010年 | 634篇 |
2009年 | 663篇 |
2008年 | 697篇 |
2007年 | 672篇 |
2006年 | 567篇 |
2005年 | 553篇 |
2004年 | 505篇 |
2003年 | 466篇 |
2002年 | 427篇 |
2001年 | 343篇 |
2000年 | 320篇 |
1999年 | 438篇 |
1998年 | 1941篇 |
1997年 | 1177篇 |
1996年 | 795篇 |
1995年 | 481篇 |
1994年 | 465篇 |
1993年 | 459篇 |
1992年 | 201篇 |
1991年 | 201篇 |
1990年 | 192篇 |
1989年 | 191篇 |
1988年 | 195篇 |
1987年 | 128篇 |
1986年 | 130篇 |
1985年 | 182篇 |
1984年 | 140篇 |
1983年 | 99篇 |
1982年 | 106篇 |
1981年 | 111篇 |
1980年 | 84篇 |
1979年 | 93篇 |
1978年 | 80篇 |
1977年 | 133篇 |
1976年 | 147篇 |
1975年 | 78篇 |
1974年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Ideally selective diisocyanate building blocks: New perspectives for dendrimers and coating binders 总被引:3,自引:0,他引:3
R. A. T. M. van Benthem A. Hofland H. W. I. Peerlings E. W. Meijer 《Progress in Organic Coatings》2003,48(2-4):164-176
Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial ones like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanate-functional coating resins. Without any increase in polydispersity, a hydroxyl-functional polyester can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings. 相似文献
103.
Noise modeling for RF CMOS circuit simulation 总被引:2,自引:0,他引:2
Scholten A.J. Tiemeijer L.F. van Langevelde R. Havens R.J. Zegers-van Duijnhoven A.T.A. Venezia V.C. 《Electron Devices, IEEE Transactions on》2003,50(3):618-632
The RF noise in 0.18-/spl mu/m CMOS technology has been measured and modeled. In contrast to some other groups, we find only a moderate enhancement of the drain current noise for short-channel MOSFETs. The gate current noise on the other hand is more significantly enhanced, which is explained by the effects of the gate resistance. The experimental results are modeled with a nonquasi-static RF model, based on channel segmentation, which is capable of predicting both drain and gate current noise accurately. Experimental evidence is shown for two additional noise mechanisms: 1) avalanche noise associated with the avalanche current from drain to bulk and 2) shot noise in the direct-tunneling gate leakage current. Additionally, we show low-frequency noise measurements, which strongly point toward an explanation of the 1/f noise based on carrier trapping, not only in n-channel MOSFETs, but also in p-channel MOSFETs. 相似文献
104.
A semi-empirical mathematical model for the acid-oxygen pressure leaching of Ni–Cu matte is presented, based on data from batch leaching experiments. The primary controlling factor in the leaching process is found to be galvanic inhibition of the more highly oxidized copper and nickel sulfide species by less oxidized species, particularly Ni alloy and Ni3S2. The leaching rate of many species is greatly reduced by the presence of one or both of these phases, and others will not commence leaching until neither is present. The mathematical model is based on first-order chemical reaction controlled rate expressions, as the reactions occurring are electrochemical in nature. Mass transfer effects are included only empirically. Some possibly diffusion-related phenomena are noted, although the model is not extended to incorporate these effects on a fundamental level. The model is verified and extended by the inclusion of several different factors that were tested experimentally. The effects of variations in O2 flow rate and partial pressure, initial particle size, reaction pulp density and initial acid concentration were all studied, and included in the model. Variations in O2 flow rate and partial pressure are found to affect the reaction rates via the dissolved oxygen concentration in the solution phase. 相似文献
105.
We introduce optical local-area network (LAN) architectures based on multimode optical fiber and components, short wavelength lasers and detectors, and the widely used fast Ethernet protocol. These architectures are designed to lower the costs associated with passive optical LAN implementation. Further reduction in overall cost is achieved through decreased network downtime, lower maintenance cost, extended geometrical spans, and larger headroom for future capacity increase. These optically transparent networks represent a novel approach for implementing fiber-to-the-desk. 相似文献
106.
The crystal structure of CaMgGeO4 is described. CaMgGeO4, Mr = 200.9, orthorhombic, Pnam, A = 11.285(5) Å, B = 5.016(2) Å, C = 6.435(2) Å, V = 364.36 Å3, Dx = 3.664 Mg/m3.λ(MoKa = 0.71069 Å, F(000) = 384, room temperature, final R = 0.045 for 1752 observed reflections. The structure is isomorphous with CaMgSiO4 (monticellite). 相似文献
107.
Bushman Brad J.; Bonacci Angelicca M.; van Dijk Mirjam; Baumeister Roy F. 《Canadian Metallurgical Quarterly》2003,84(5):1027
Laboratory analog studies investigated the theory that narcissism and reactance contribute to causing rape. In Study 1, narcissism correlated positively with rape-supportive beliefs and negatively with empathy for rape victims. In Study 2, narcissists reported more enjoyment than other men of film depictions that presented consensual, affectionate activity followed by rape (but not in response to either affection or rape alone). In Study 3, narcissists were more punitive than other men toward a female confederate who refused to read a sexually arousing passage aloud to them. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
109.
110.