全文获取类型
收费全文 | 5546篇 |
免费 | 280篇 |
国内免费 | 53篇 |
专业分类
电工技术 | 78篇 |
综合类 | 13篇 |
化学工业 | 1151篇 |
金属工艺 | 125篇 |
机械仪表 | 164篇 |
建筑科学 | 121篇 |
矿业工程 | 29篇 |
能源动力 | 292篇 |
轻工业 | 462篇 |
水利工程 | 59篇 |
石油天然气 | 42篇 |
无线电 | 634篇 |
一般工业技术 | 1257篇 |
冶金工业 | 545篇 |
原子能技术 | 66篇 |
自动化技术 | 841篇 |
出版年
2024年 | 24篇 |
2023年 | 117篇 |
2022年 | 287篇 |
2021年 | 436篇 |
2020年 | 264篇 |
2019年 | 295篇 |
2018年 | 311篇 |
2017年 | 267篇 |
2016年 | 260篇 |
2015年 | 174篇 |
2014年 | 221篇 |
2013年 | 429篇 |
2012年 | 256篇 |
2011年 | 284篇 |
2010年 | 190篇 |
2009年 | 159篇 |
2008年 | 151篇 |
2007年 | 135篇 |
2006年 | 117篇 |
2005年 | 85篇 |
2004年 | 65篇 |
2003年 | 79篇 |
2002年 | 61篇 |
2001年 | 52篇 |
2000年 | 49篇 |
1999年 | 64篇 |
1998年 | 154篇 |
1997年 | 128篇 |
1996年 | 98篇 |
1995年 | 73篇 |
1994年 | 61篇 |
1993年 | 56篇 |
1992年 | 36篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 25篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 29篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 23篇 |
1973年 | 8篇 |
1972年 | 8篇 |
排序方式: 共有5879条查询结果,搜索用时 0 毫秒
1.
2.
3.
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
4.
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
5.
6.
7.
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
8.
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
9.
10.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献