全文获取类型
收费全文 | 6777篇 |
免费 | 374篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 94篇 |
综合类 | 19篇 |
化学工业 | 1404篇 |
金属工艺 | 159篇 |
机械仪表 | 228篇 |
建筑科学 | 177篇 |
矿业工程 | 31篇 |
能源动力 | 382篇 |
轻工业 | 565篇 |
水利工程 | 65篇 |
石油天然气 | 56篇 |
无线电 | 796篇 |
一般工业技术 | 1497篇 |
冶金工业 | 611篇 |
原子能技术 | 73篇 |
自动化技术 | 1060篇 |
出版年
2024年 | 27篇 |
2023年 | 158篇 |
2022年 | 350篇 |
2021年 | 516篇 |
2020年 | 322篇 |
2019年 | 375篇 |
2018年 | 390篇 |
2017年 | 324篇 |
2016年 | 325篇 |
2015年 | 221篇 |
2014年 | 295篇 |
2013年 | 525篇 |
2012年 | 307篇 |
2011年 | 359篇 |
2010年 | 224篇 |
2009年 | 221篇 |
2008年 | 191篇 |
2007年 | 175篇 |
2006年 | 157篇 |
2005年 | 108篇 |
2004年 | 86篇 |
2003年 | 93篇 |
2002年 | 85篇 |
2001年 | 63篇 |
2000年 | 64篇 |
1999年 | 70篇 |
1998年 | 166篇 |
1997年 | 140篇 |
1996年 | 114篇 |
1995年 | 81篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 47篇 |
1991年 | 50篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 37篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 32篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 24篇 |
1973年 | 10篇 |
排序方式: 共有7217条查询结果,搜索用时 15 毫秒
1.
A systematic and straightforward procedure is developed for the synthesis and analysis of transformer-isolated power converters. The procedure can be used to determine the ranges of duty-ratio over which the transformer-isolated power converters of a given class can be operated without transformer saturation. The procedure can also be used to study the dependence of the power converter switch stresses on duty-ratios. This information is useful in the selection of the transformer-isolated power converter most suitable for a given application and in the design of this power converter with minimum switch stresses, high power density, and low cost 相似文献
2.
Electroinitiated cationic copolymerisation of indene and styrene was investigated by constant potential electrolysis. Effects of copolymerisation potential and temperature on the copolymer composition and the reactivity ratios are discussed. The reactivity ratios of the monomers were calculated according to the integrated Lewis-Mayo equation. 相似文献
3.
Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable
sample is prepared by adding a mixture of aqueous solutions of 0·5 mol L−1 sodium tungstate, potassium iodate and 1 mol L−1 orthophosphoric acid to aqueous solution of 0·1 mol L−1 zirconium(IV) oxychloride. Its ion exchange capacity for Na+ and K+ was found to be 2·20 and 2·35 meq g−1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier
transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger
at different temperatures has been studied. The analytical importance of the material has been established by quantitative
separation of Pb2+ from other metal ions. 相似文献
4.
In this paper, the test results of liquid injection impact on the performance of new alternative refrigerant mixtures such as: R-410A, R-507, R-407C and R-404A are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various liquid injection ratios. Performance tests were conducted according to the ARI/ASHRAE standards. The performance data demonstrated that as liquid injection ratio increases, compressor head pressure and discharge temperature decrease. This has a positive effect in protecting the compressor. The effect of liquid injection on mixture behaviour varies from one mixture to another depending upon the mixture's composition. Furthermore, liquid injection appears to have a significant influence on R-410A behaviour compared to the other mixtures in question. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
6.
7.
The p53 tumor suppressor gene encodes a phosphoprotein which when overexpressed can induce growth arrest at the G1 and G2/M phases of the cell cycle, promote differentiation and apoptosis. This paper demonstrates that p53 can associate with trk tyrosine kinase. Expression of a murine temperature-sensitive (ts) p53 mutant in PC12 cells overexpressing trk (a model system to analyse cellular differentiation and signal transduction induced by NGF) induces morphological changes in the absence of NGF stimulation at 32 degrees C but not at 37 degrees C. In cells differentiated by p53, trk, but not EGFr, was hyperphosphorylated on tyrosine. Furthermore trk was not phosphorylated when expressed in Saos-2 cells (human osteosarcoma cells that lack expression of both endogenous trk and p53) at either temperature. However, transfection of ts p53 into these cells induces trk phosphorylation at 32 degrees C in the absence of NGF stimulation. Association of trk and p53 can be detected in NIH3T3 and PC12 cells co-expressing trk and the ts p53 mutant, in NIH3T3 and PC12 cells transfected with trk alone, and in untransfected PC12 cells, showing that overexpressed and/or endogenous trk associates with endogenous, low levels of p53. These data suggest a novel function for p53 which involves the stimulation of signal transduction pathways (mediating morphological properties of cells), possibly through association with and hyperphosphorylation of trk. 相似文献
8.
A rare case associated with congenital hematometrocolpos in a circumcised 13 years old Somalian girl is presented. Emphasis on proper history is highlighted. Mutilation caused by bad cultural practice of female circumcision which is although not a problem in Pakistan, is brought into notice for those who may be unaware of perineal appearance of a circumcised female and stitched over vagina. 相似文献
9.
H.U. Khan K.M. Agrawal M. Anwar S.P. Nautiyal B.S. Rawat 《Petroleum Science and Technology》1998,16(1):145-166
Lubricating oil base stocks differ greatly in their chemical composition and consequently in their physical properties and applications. Influence of waxes and various hydrocarbon type constituents viz saturates and aromatic components on the viscosity and shear stress as a function of temperature in different lube oil base stocks has been studied in the present paper. 相似文献
10.