全文获取类型
收费全文 | 698445篇 |
免费 | 9197篇 |
国内免费 | 2128篇 |
专业分类
化学 | 366299篇 |
晶体学 | 10132篇 |
力学 | 31212篇 |
综合类 | 23篇 |
数学 | 90591篇 |
物理学 | 211513篇 |
出版年
2021年 | 6384篇 |
2020年 | 6953篇 |
2019年 | 7586篇 |
2018年 | 9946篇 |
2017年 | 9954篇 |
2016年 | 14964篇 |
2015年 | 9474篇 |
2014年 | 14293篇 |
2013年 | 33619篇 |
2012年 | 26111篇 |
2011年 | 31359篇 |
2010年 | 22418篇 |
2009年 | 22086篇 |
2008年 | 28452篇 |
2007年 | 28194篇 |
2006年 | 25984篇 |
2005年 | 23104篇 |
2004年 | 21412篇 |
2003年 | 18847篇 |
2002年 | 18657篇 |
2001年 | 20610篇 |
2000年 | 15797篇 |
1999年 | 12415篇 |
1998年 | 10381篇 |
1997年 | 9994篇 |
1996年 | 9693篇 |
1995年 | 8481篇 |
1994年 | 8528篇 |
1993年 | 8204篇 |
1992年 | 9008篇 |
1991年 | 9132篇 |
1990年 | 8777篇 |
1989年 | 8484篇 |
1988年 | 8318篇 |
1987年 | 8276篇 |
1986年 | 7840篇 |
1985年 | 10115篇 |
1984年 | 10314篇 |
1983年 | 8349篇 |
1982年 | 8528篇 |
1981年 | 8287篇 |
1980年 | 7842篇 |
1979年 | 8448篇 |
1978年 | 8526篇 |
1977年 | 8423篇 |
1976年 | 8368篇 |
1975年 | 7854篇 |
1974年 | 7745篇 |
1973年 | 7766篇 |
1972年 | 5492篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
In this paper, the detailed asymptotic behaviour of the solutions of a kinetic equation for quantum particles is studied. It is shown that this behaviour is sensitive not only to the total mass of the initial data but also to its precise behaviour near the origin. In some cases, solutions develop a Dirac mass at the origin for long times in a self-similar manner that is analysed in detail. 相似文献
982.
M Gubinelli 《Journal of Functional Analysis》2004,216(1):86-140
We formulate indefinite integration with respect to an irregular function as an algebraic problem which has a unique solution under some analytic constraints. This allows us to define a good notion of integral with respect to irregular paths with Hölder exponent greater than 1/3 (e.g. samples of Brownian motion) and study the problem of the existence, uniqueness and continuity of solution of differential equations driven by such paths. We recover Young's theory of integration and the main results of Lyons’ theory of rough paths in Hölder topology. 相似文献
983.
J. M. Martínez‐Burgos R. Benavente E. Prez M. L. Cerrada 《Journal of Polymer Science.Polymer Physics》2003,41(11):1244-1255
Several composites were prepared on the basis of an ethylene homopolymer and different copolymers of ethylene and 1‐hexene, synthesized with a metallocene catalyst, as matrices and a content of a 5 wt % of short glass fiber. The effect of the fiber incorporation on the structure and mechanical and viscoelastic behaviors was analyzed for the different samples. The glass fibers induced a slightly higher crystallinity, and the crystallite morphology significantly changed (long spacings and crystal orientation). The incorporation of fibers did not reinforce the different matrices under study at this low content; consequently, the mechanical parameters, such as Young's modulus, yielding stress, and microhardness, were lower in the composites as compared with those values found in the neat polyolefins. The location and apparent activation energies of distinct relaxation processes are also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1244–1255, 2003 相似文献
984.
Gregory S. Constable Alan J. Lesser E. Bryan Coughlin 《Journal of Polymer Science.Polymer Physics》2003,41(12):1323-1333
An in situ ultrasonic spectroscopy technique was used to study the ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by bis(tricyclohexylphosphine)benzylidene ruthenium dichloride. A reaction cell employing a flexible poly(ethylene terephthalate) window for pulse echo ultrasonic spectroscopy was used to monitor the polymerization. The changes in the density, wave speed, acoustic modulus, and attenuation were all simultaneously monitored. In comparison with Fourier transform infrared (FTIR) spectroscopy data, the changes in the density, velocity, and modulus only accurately measured the rate constant for the metathesis of the cyclopentyl unsaturation. The ultrasonic values were within 6% of the values determined by FTIR. The activation energy for metathesis of the cyclopentyl unsaturation was 84 kJ mol?1, following first‐order kinetics. Rate constants for the polymerization of the norbornyl unsaturation could not be determined by ultrasound. The gel point, vitrification, and qualitative information about the reaction rate could be determined from the change in the attenuation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1323–1333, 2003 相似文献
985.
The identification of incomplete signal re-setting of optically stimulated luminescence signals in sedimentary quartz is a vitally important step in the continued improvement of optical dating. It is shown that narrow spectrum (blue-green) laboratory partial bleaching of aliquots of natural sedimentary quartz has a significant effect on equivalent dose (measured using a single aliquot procedure) calculated as a function of measurement time (De(t)). The blue-green stimulation spectrum mimics that found underwater and the results suggest that incomplete re-setting of waterlain sediments may be possible using the De(t) method. 相似文献
986.
M. D. Srinivas 《Pramana》2003,60(6):1137-1152
We derive an optimal bound on the sum of entropic uncertainties of two or more observables when they are sequentially measured
on the same ensemble of systems. This optimal bound is shown to be greater than or equal to the bounds derived in the literature
on the sum of entropie uncertainties of two observables which are measured on distinct but identically prepared ensembles
of systems. In the case of a two-dimensional Hilbert space, the optimum bound for successive measurements of two-spin components,
is seen to be strictly greater than the optimal bound for the case when they are measured on distinct ensembles, except when
the spin components are mutually parallel or perpendicular 相似文献
987.
988.
On the Application of the Auxiliary Problem Principle 总被引:6,自引:0,他引:6
The auxiliary problem principle (APP) derives from a general theory on decomposition-coordination methods establishing a comprehensive framework for both one-level and two-level methods. In this paper, the results of the two-level methods of APP are specialized for an efficient application to some engineering problems. 相似文献
989.
V. Balek T. Mitsuhashi I.M. Bountseva H. Haneda Z. Malek J. Šubrt 《Journal of Sol-Gel Science and Technology》2003,26(1-3):185-189
The diffusion structural analysis (DSA) was used to characterize microstructure changes of hydrous titania gel films under in situ conditions of heating. TG and DTA were used in order to elucidate the processes controlling the formation of anatase film during heating of hydrous titania gel film. The annealing of porosity and near surface structure defects of the dehydrated titania films was indicated by DSA in the temperature range 255–700°C as the decrease of radon release rate. It was demonstrated that the annealing was enhanced on heating in oxygen in comparison with heating in argon. The DSA experimental results were compared with model curves describing the radon diffusion mobility and the annealing of radon diffusion paths. 相似文献
990.
Stuart S. Antman 《Journal of Elasticity》2003,70(1-3):55-64
The introduction of artificial viscosity into the partial differential equations of mechanics is often useful for both analytic and numerical studies. The traditional forms of artificial viscosity, originally designed to treat problems for fluids, when applied to problems for solids often lead to equations describing material properties that are not invariant under rigid motions. Consequently, for rapidly rotating bodies, artificial viscosity could produce serious errors. In this paper it is shown how to introduce artificial viscosity in a properly invariant way, and that the resulting systems have a rich and attractive structure, which beckons analysis. 相似文献