全文获取类型
收费全文 | 317085篇 |
免费 | 2739篇 |
国内免费 | 1244篇 |
专业分类
化学 | 152915篇 |
晶体学 | 4395篇 |
力学 | 16381篇 |
综合类 | 2篇 |
数学 | 57938篇 |
物理学 | 89437篇 |
出版年
2020年 | 1771篇 |
2019年 | 2042篇 |
2018年 | 12535篇 |
2017年 | 12306篇 |
2016年 | 9700篇 |
2015年 | 3394篇 |
2014年 | 4161篇 |
2013年 | 11403篇 |
2012年 | 11652篇 |
2011年 | 20008篇 |
2010年 | 11925篇 |
2009年 | 12259篇 |
2008年 | 15261篇 |
2007年 | 17444篇 |
2006年 | 8551篇 |
2005年 | 9036篇 |
2004年 | 8418篇 |
2003年 | 8068篇 |
2002年 | 7083篇 |
2001年 | 7411篇 |
2000年 | 5604篇 |
1999年 | 4332篇 |
1998年 | 3700篇 |
1997年 | 3687篇 |
1996年 | 3470篇 |
1995年 | 3240篇 |
1994年 | 3016篇 |
1993年 | 3086篇 |
1992年 | 3345篇 |
1991年 | 3389篇 |
1990年 | 3190篇 |
1989年 | 3155篇 |
1988年 | 3218篇 |
1987年 | 3084篇 |
1986年 | 2982篇 |
1985年 | 4031篇 |
1984年 | 4185篇 |
1983年 | 3435篇 |
1982年 | 3791篇 |
1981年 | 3684篇 |
1980年 | 3562篇 |
1979年 | 3594篇 |
1978年 | 3811篇 |
1977年 | 3625篇 |
1976年 | 3829篇 |
1975年 | 3403篇 |
1974年 | 3528篇 |
1973年 | 3841篇 |
1972年 | 2344篇 |
1971年 | 1793篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
R. L. Moreira P. Saint-Grgoire M. Lopez M. Latour 《Journal of Polymer Science.Polymer Physics》1989,27(3):709-722
The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed. 相似文献
75.
Agrachev A. A. Gamkrelidze R. V. 《Proceedings of the Steklov Institute of Mathematics》2006,253(1):S4-S12
Proceedings of the Steklov Institute of Mathematics - 相似文献
76.
T. Yu. Gumerov A. F. Dobrynina R. A. Yusupov V. P. Barabanov 《Russian Journal of Applied Chemistry》2006,79(12):1935-1939
The behavior of real disperse systems with organic impurities was examined under conditions of destabilization by inorganic coagulants. A number of physicochemical methods of analysis and a simulation method were used to identify the character and type of the complexes formed and to calculate their stability constants. 相似文献
77.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found. 相似文献
78.
For fairly high concentrations, the effective arsenic diffusioncoefficient is known to grow linearly with the concentration.In this paper, we consider the strongly enhanced diffusion ofarsenic by asymptotic methods, and extend the results of a previouspaper (King & Please, 1987) in three ways: we characterizean additional (low-concentration) region; we consider the influenceof the initial data; and we consider the case of constant surfaceconcentration. 相似文献
79.
R. Jayakumar Y.‐S. Lee S. Nanjundan 《Journal of polymer science. Part A, Polymer chemistry》2003,41(18):2865-2878
The calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HEEP)2 and poly(ethylene glycol) (PEG300 or PEG400) with di‐n‐butyltin dilaurate as a catalyst. A series of calcium‐containing PUEs of different compositions were synthesized with Ca(HEEP)2/PEG300 (or PEG400)/diisocyanate (HMDI or TDI) molar ratios of 2:2:4, 3:1:4, and 1:3:4 so that the coating properties of the PUEs could be studied. Blank PUEs without calcium‐containing ionic diols were also prepared by the reaction of PEG300 or PEG400 with HMDI or TDI. The PUEs were well characterized by Fourier transform infrared, 1H and 13C NMR, solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as top coats on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, such as the tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2865–2878, 2003 相似文献
80.
The aim of this paper is to introduce a new functional in thestudy of swelling porous elastic soils saturated by a fluid.This new functional is a useful tool; it allows us to provethe existence of solutions in the case of a compressible fluid.We also prove the stability of solutions and the exponentialdecay in the case of an incompressible fluid. We study as wellthe continuous dependence with respect to the initial time. 相似文献