全文获取类型
收费全文 | 465543篇 |
免费 | 4208篇 |
国内免费 | 1441篇 |
专业分类
化学 | 248801篇 |
晶体学 | 7118篇 |
力学 | 20506篇 |
综合类 | 11篇 |
数学 | 54300篇 |
物理学 | 140456篇 |
出版年
2020年 | 3556篇 |
2019年 | 3999篇 |
2018年 | 5142篇 |
2017年 | 5060篇 |
2016年 | 7669篇 |
2015年 | 4894篇 |
2014年 | 7539篇 |
2013年 | 20120篇 |
2012年 | 14828篇 |
2011年 | 18227篇 |
2010年 | 12577篇 |
2009年 | 12200篇 |
2008年 | 16672篇 |
2007年 | 16959篇 |
2006年 | 15674篇 |
2005年 | 14420篇 |
2004年 | 13062篇 |
2003年 | 11723篇 |
2002年 | 11669篇 |
2001年 | 12945篇 |
2000年 | 9898篇 |
1999年 | 7739篇 |
1998年 | 6683篇 |
1997年 | 6657篇 |
1996年 | 6286篇 |
1995年 | 5832篇 |
1994年 | 5836篇 |
1993年 | 5651篇 |
1992年 | 6279篇 |
1991年 | 6276篇 |
1990年 | 6044篇 |
1989年 | 5938篇 |
1988年 | 6079篇 |
1987年 | 5878篇 |
1986年 | 5613篇 |
1985年 | 7521篇 |
1984年 | 7967篇 |
1983年 | 6628篇 |
1982年 | 7016篇 |
1981年 | 6885篇 |
1980年 | 6760篇 |
1979年 | 6771篇 |
1978年 | 7181篇 |
1977年 | 7051篇 |
1976年 | 7252篇 |
1975年 | 6616篇 |
1974年 | 6769篇 |
1973年 | 7206篇 |
1972年 | 4780篇 |
1971年 | 3875篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
The state of the art in the Internet information resources for biosensors is considered, and the classification of the websites is given 相似文献
952.
Spenta R Wadia 《Pramana》1997,49(1):71-80
We report some progress on the quark confinement problem in 2 + 1 dim. pure Yang-Mills theory, using Euclidean instanton methods.
The instantons are regularized Wu-Yang ‘monopoles’, whose long range Coulomb field is screened by collective effects. Such
configurations are stable to small perturbations unlike the case of singular, undressed monopoles. Using exact non-perturbative
results for the 3-dim. Coulomb gas, where Debye screening holds for arbitrarily low temperatures, we show in a self-consistent
way that a mass gap is dynamically generated in the gauge theory. The mass gap also determines the size of the monopoles.
We also identify the disorder operator of the model in terms of the Sine-Gordon field of the Coulomb gas and hence obtain
a dual representation whose symmetry is the centre ofSU(2). 相似文献
953.
R. R. Kerswell 《Physica D: Nonlinear Phenomena》1997,100(3-4):355-376
Based on earlier studies by Hopf (1941), Doering and Constantin (1992, 1994, 1995) have recently formulated a new “background” technique for obtaining upper bounds on turbulent fluid flow quantities. This method produces upper bounds on the limit supremum of long time averages, making no statistical assumptions about the flow in contrast to the well-known Howard-Busse approach. The full optimisation problems posed by this method for the momentum transport in turbulent Couette flow and the heat transport (with zero background flow) in turbulent Boussinesq convection are solved here for the first time at asymptotically large Reynolds number and Rayleigh number within Busse's multiple boundary layer approximation to extract the best (lowest) possible upper bounds available. Intriguingly, the original bounds isolated by Busse (1969, 1970) within the confines of statistical stationarity are recovered exactly using this new formalism. The optimal background velocity profile for turbulent Couette flow is found to be shearless in the interior thus differing from Busse's “
” mean shear result. In the convective case, an interesting degeneracy in the formulation of the background variational problem leads to an indeterminacy in the optimal background temperature profile. Only for one special choice is the isothermal core feature of Busse's mean profile recovered. 相似文献
954.
955.
G. O. Balabanyan 《Theoretical and Mathematical Physics》1991,89(1):1106-1119
Moscow Institute of Electronic Engineering. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 89, No. 1, pp. 132–150, October, 1991. 相似文献
956.
A. L. Itkin E. G. Kolesnichenko 《Journal of Applied Mechanics and Technical Physics》1991,32(4):580-581
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 122–123, July–August, 1991. 相似文献
957.
958.
Summary Global average temperatures from 1860 to 1989 were analysed with a simple fitting procedure. The temperature records can be
fitted with a rising exponential up to 1946 and with the same exponential minus an increasing cooling action from 1946 to
1989. It is shown that the results are compatible with the hypothesis of an albedo increase caused by SO2 emissions. This hypothesis gives satisfactory explanations of the temperature drop in the years 1940–1970, of the different
warming of the northern and southern hemispheres and of the slower warming observed over North America. The results give an
indication that the greenhouse warming in the next years could be faster than predicted until now.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
959.
A new microscopic model of anomalous muonium for the elemental semiconductors is proposed. The relevant configuration consisting
of both a diamagrentic molecule Si−Mu and an unpaired orbital e− is contained into a semivacancy of the real lattice. By using the unrestricted Hartree-Fock computational method the principal
properties of the system are established. A dynamical version of the model together with a question on the formation of such
system are discussed. 相似文献
960.
A random-medium model which is a correlated distribution of points (particles) randomly positioned in the 3-dimensional space
is considered. The construction of the medium starts from a noncorrelated (Poisson) distribution of parent particles, each
of them initiates a finite Markov chain of its descendants. The complete collection of correlation functions of all orders
within the scope of the model have been obtained. The use of the 3-dimensional stable law (Lévy law) as a transition probability
allows us to present the correlation function in an explicit form.
Proceedings of the XVII Seminar on Stability Problems for Stochastic Models, Kazan, Russian, 1995, Part II. 相似文献