全文获取类型
收费全文 | 1422140篇 |
免费 | 28941篇 |
国内免费 | 10273篇 |
专业分类
化学 | 722053篇 |
晶体学 | 20755篇 |
力学 | 77171篇 |
综合类 | 295篇 |
数学 | 250214篇 |
物理学 | 390866篇 |
出版年
2021年 | 14551篇 |
2020年 | 16823篇 |
2019年 | 17066篇 |
2018年 | 15027篇 |
2017年 | 13329篇 |
2016年 | 29915篇 |
2015年 | 22184篇 |
2014年 | 31942篇 |
2013年 | 76772篇 |
2012年 | 43251篇 |
2011年 | 42828篇 |
2010年 | 40443篇 |
2009年 | 42231篇 |
2008年 | 40488篇 |
2007年 | 36606篇 |
2006年 | 40775篇 |
2005年 | 33489篇 |
2004年 | 33669篇 |
2003年 | 31147篇 |
2002年 | 31764篇 |
2001年 | 31461篇 |
2000年 | 26817篇 |
1999年 | 23742篇 |
1998年 | 21724篇 |
1997年 | 21626篇 |
1996年 | 21786篇 |
1995年 | 19700篇 |
1994年 | 19167篇 |
1993年 | 18726篇 |
1992年 | 18946篇 |
1991年 | 19062篇 |
1990年 | 18217篇 |
1989年 | 18214篇 |
1988年 | 17795篇 |
1987年 | 17694篇 |
1986年 | 16649篇 |
1985年 | 23006篇 |
1984年 | 24088篇 |
1983年 | 20185篇 |
1982年 | 21798篇 |
1981年 | 21031篇 |
1980年 | 20343篇 |
1979年 | 20644篇 |
1978年 | 21835篇 |
1977年 | 21452篇 |
1976年 | 21164篇 |
1975年 | 19858篇 |
1974年 | 19511篇 |
1973年 | 19923篇 |
1972年 | 14442篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The anisotropic g-values of defects in hydrogenated microcrystalline silicon prepared by hot-wire chemical vapour deposition have been measured as a function of crystalline volume fraction at room temperature. The defect has been identified as a silicon-dangling bond existing on the surface of crystalline grain. Their anisotropic g-values are discussed in the light of theoretical calculations by Ishii et al. and Ishii and Shimizu. The defect density is also discussed as a function of crystalline volume fraction. 相似文献
992.
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. 相似文献
993.
We consider the problem of determining the stress distributionin a finite rectangular elastic layer containing a Griffithcrack which is opened by internal shear stress acting alongthe length of the crack. The mode III crack is assumed to belocated in the middle plane of the rectangular layer. The followingtwo problems are considered: (A) the central crack is perpendicularto the two fixed lateral surfaces and parallel to the othertwo stress-free surfaces; (B) all the lateral surfaces of therectangular layer are clamped and the central crack is parallelto the two lateral surfaces. By using Fourier transformations,we reduce the solution of each problem to the solution of dualintegral equations with sine kernels and a weight function whichare solved exactly. Finally, we derive closed-form expressionsfor the stress intensity factor at the tip of the crack andthe numerical values for the stress intensity factor at theedges of the cracks are presented in the form of tables. 相似文献
994.
A MCSCF-method for minimization of the variance yielding an optimal basisset of variance minimizing orbitals in analogy to Löwdin's natural orbitals for minimal energy is developed. 相似文献
995.
996.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
997.
998.
999.
Electrohydrodynamic instability in homeotropically oriented nematic samples of 4'-n-octyl-4-cyano-biphenyl and 4'n-alkyloxy-4-cyanobiphenyl, (n = 8.9) have been studied in an a.c. electric field. The domain patterns during the instability in these compounds in a very low frequency a.c. field are very similar to those in a d.c. field. The domain patterns observed at higher frequencies have been identified as 'maltese crosses' or 'crossed isogyres'. The electro-convective 'isotropic' flows near the electrode play an important role in the observed instability. 相似文献
1000.
W M Niessen M A de Kraa E R Verheij P J Bergers G F La Vos U R Tjaden J van der Greef 《Rapid communications in mass spectrometry : RCM》1989,3(1):1-4
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL. 相似文献