全文获取类型
收费全文 | 389144篇 |
免费 | 5635篇 |
国内免费 | 2189篇 |
专业分类
电工技术 | 7440篇 |
技术理论 | 5篇 |
综合类 | 3444篇 |
化学工业 | 57229篇 |
金属工艺 | 20288篇 |
机械仪表 | 15532篇 |
建筑科学 | 9441篇 |
矿业工程 | 2807篇 |
能源动力 | 7166篇 |
轻工业 | 29140篇 |
水利工程 | 4736篇 |
石油天然气 | 7442篇 |
武器工业 | 243篇 |
无线电 | 41271篇 |
一般工业技术 | 78366篇 |
冶金工业 | 53911篇 |
原子能技术 | 6764篇 |
自动化技术 | 51743篇 |
出版年
2021年 | 2443篇 |
2019年 | 2105篇 |
2018年 | 22707篇 |
2017年 | 22230篇 |
2016年 | 15974篇 |
2015年 | 3762篇 |
2014年 | 4833篇 |
2013年 | 11549篇 |
2012年 | 12371篇 |
2011年 | 24818篇 |
2010年 | 21493篇 |
2009年 | 19022篇 |
2008年 | 20413篇 |
2007年 | 22967篇 |
2006年 | 8592篇 |
2005年 | 11514篇 |
2004年 | 9214篇 |
2003年 | 8559篇 |
2002年 | 7198篇 |
2001年 | 6460篇 |
2000年 | 6163篇 |
1999年 | 5939篇 |
1998年 | 12903篇 |
1997年 | 9526篇 |
1996年 | 7039篇 |
1995年 | 5486篇 |
1994年 | 5079篇 |
1993年 | 4942篇 |
1992年 | 3921篇 |
1991年 | 3758篇 |
1990年 | 3797篇 |
1989年 | 3721篇 |
1988年 | 3491篇 |
1987年 | 2982篇 |
1986年 | 3015篇 |
1985年 | 3391篇 |
1984年 | 3295篇 |
1983年 | 3042篇 |
1982年 | 2675篇 |
1981年 | 2867篇 |
1980年 | 2624篇 |
1979年 | 2821篇 |
1978年 | 2722篇 |
1977年 | 2827篇 |
1976年 | 3680篇 |
1975年 | 2442篇 |
1974年 | 2281篇 |
1973年 | 2309篇 |
1972年 | 1974篇 |
1971年 | 1776篇 |
排序方式: 共有10000条查询结果,搜索用时 577 毫秒
101.
Journal of Computer and Systems Sciences International - We consider a controlled mechanical system with one degree of freedom described by an angular coordinate. The system is under the action of... 相似文献
102.
103.
104.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献
105.
A. M. Mirzabaev V. P. Kanonerov T. A. Makhkamov O. R. Sytdykov Sh. M. Mirzabekov 《Applied Solar Energy》2018,54(3):224-226
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered. 相似文献
106.
Harrison D. Root Gregory Thiabaud Jonathan L. Sessler 《Frontiers of Chemical Science and Engineering》2020,14(1):19
We report here a water-soluble metal cation sensor system based on the as-prepared or reduced form of an expanded porphyrin, texaphyrin. Upon metal complexation, a change in the redox state of the ligand occurs that is accompanied by a color change from red to green. Although long employed for synthesis in organic media, we have now found that this complexation-driven redox behavior may be used to achieve the naked eye detectable colorimetric sensing of several number of less-common metal ions in aqueous media. Exposure to In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) cations leads to a colorimetric response within 10 min. This process is selective for Hg(II) under conditions of competitive analysis. Furthermore, among the subset of response-producing cations, In(III) proved unique in giving rise to a ratiometric change in the ligand-based fluorescence features, including an overall increase in intensity. The cation selectivity observed in aqueous media stands in contrast to what is seen in organic solvents, where a wide range of texaphyrin metal complexes may be prepared. The formation of metal cation complexes under the present aqueous conditions was confirmed by reversed phase high-performance liquid chromatography, ultra-violet-visible absorption and fluorescence spectroscopies, and high-resolution mass spectrometry. 相似文献
107.
C. G. Prosgolitis S. G. Lambrakos A. D. Zervaki 《Journal of Materials Engineering and Performance》2018,27(10):5102-5113
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size. 相似文献
108.
109.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献
110.