全文获取类型
收费全文 | 360174篇 |
免费 | 3911篇 |
国内免费 | 1087篇 |
专业分类
化学 | 188966篇 |
晶体学 | 5536篇 |
力学 | 15476篇 |
综合类 | 13篇 |
数学 | 41105篇 |
物理学 | 114076篇 |
出版年
2021年 | 2805篇 |
2020年 | 3197篇 |
2019年 | 3368篇 |
2018年 | 4457篇 |
2017年 | 4439篇 |
2016年 | 6798篇 |
2015年 | 4340篇 |
2014年 | 6372篇 |
2013年 | 15853篇 |
2012年 | 12687篇 |
2011年 | 15110篇 |
2010年 | 10519篇 |
2009年 | 10318篇 |
2008年 | 14095篇 |
2007年 | 13912篇 |
2006年 | 13440篇 |
2005年 | 12067篇 |
2004年 | 11035篇 |
2003年 | 9841篇 |
2002年 | 9471篇 |
2001年 | 11509篇 |
2000年 | 8728篇 |
1999年 | 6724篇 |
1998年 | 5127篇 |
1997年 | 5222篇 |
1996年 | 4946篇 |
1995年 | 4592篇 |
1994年 | 4485篇 |
1993年 | 4222篇 |
1992年 | 5042篇 |
1991年 | 4944篇 |
1990年 | 4774篇 |
1989年 | 4531篇 |
1988年 | 4499篇 |
1987年 | 4559篇 |
1986年 | 4175篇 |
1985年 | 5448篇 |
1984年 | 5658篇 |
1983年 | 4600篇 |
1982年 | 4772篇 |
1981年 | 4601篇 |
1980年 | 4477篇 |
1979年 | 4785篇 |
1978年 | 4934篇 |
1977年 | 4916篇 |
1976年 | 4897篇 |
1975年 | 4575篇 |
1974年 | 4546篇 |
1973年 | 4640篇 |
1972年 | 2995篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
D. Yu. Gladilov S. Yu. Nekhaevskii A. V. Ochkin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(12):1934-1939
Various methods for describing the distribution of water in the H2O-tributyl phosphate (TBP) system were considered. An equation for describing the deviations from the Henry law was proposed. A three-parameter equation for calculating the distribution of water in H2O-TBP-solvent systems was derived. It is based on the additive solubility model and allows for the dependence of the activity coefficients on the TBP concentration. Based on the published data, the parameters of the equation for a number of systems were calculated. 相似文献
92.
93.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
94.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
95.
Evstafyeva I. T. Bozhenkov G. V. Aizina Ya. A. Rozenzveig I. B. Ermakova T. G. Levkovskaya G. G. Mirskova A. N. 《Russian Journal of Organic Chemistry》2002,38(8):1178-1182
1H-Pyrazoles, triazoles, and imidazoles in reaction with ethoxycarbonylimine and arylsulfonylimines of chloral yield addition products, corresponding 1-(1-amidotrichloroethyl)azoles. Derivatives of 1-alkylpyrazoles and pyrazolones react with chloral 4-chlorophenylsulfonylimine to furnish products of C-amidotrichloroethylation into position 4 of the azole ring. 相似文献
96.
In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the differential quadrature (DQ) method. The vorticity‐stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 104 to 106 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are critical to the patterns of flow and thermal fields. The present study suggests that a critical aspect ratio may exist at high Rayleigh number to distinguish the flow and thermal patterns. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
97.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
98.
Electron mobility has been calculated in a number of binary II–VI compound semiconductors using a displaced Maxwellian distribution function and taking the various scattering mechanisms into consideration at different lattice temperatures and for various amounts of ionized impurity concentrations. It is observed that the low field mobility values can be expressed by a cubic power relationship with lattice temperature and with ionized impurity concentration using a least mean square fit technique with an accuracy better than 5 per cent. Similarly, the field dependence of mobility can also be expressed as a power series of the applied electric field. It is suggested that these equations can be profitably used for a quick estimation of mobility values as a check on experiments and also as sufficiently accurate formulae for simulation and modelling purposes. 相似文献
99.
100.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献