全文获取类型
收费全文 | 337645篇 |
免费 | 2769篇 |
国内免费 | 886篇 |
专业分类
化学 | 161835篇 |
晶体学 | 5036篇 |
力学 | 16556篇 |
综合类 | 2篇 |
数学 | 50613篇 |
物理学 | 107258篇 |
出版年
2020年 | 1766篇 |
2019年 | 2037篇 |
2018年 | 10976篇 |
2017年 | 11783篇 |
2016年 | 7782篇 |
2015年 | 3435篇 |
2014年 | 4009篇 |
2013年 | 11272篇 |
2012年 | 12247篇 |
2011年 | 22149篇 |
2010年 | 13530篇 |
2009年 | 13500篇 |
2008年 | 19310篇 |
2007年 | 22855篇 |
2006年 | 8550篇 |
2005年 | 14616篇 |
2004年 | 10404篇 |
2003年 | 9531篇 |
2002年 | 7508篇 |
2001年 | 7356篇 |
2000年 | 5660篇 |
1999年 | 4248篇 |
1998年 | 3592篇 |
1997年 | 3595篇 |
1996年 | 3455篇 |
1995年 | 3230篇 |
1994年 | 3030篇 |
1993年 | 3072篇 |
1992年 | 3359篇 |
1991年 | 3401篇 |
1990年 | 3211篇 |
1989年 | 3172篇 |
1988年 | 3245篇 |
1987年 | 3108篇 |
1986年 | 2996篇 |
1985年 | 4062篇 |
1984年 | 4244篇 |
1983年 | 3476篇 |
1982年 | 3828篇 |
1981年 | 3720篇 |
1980年 | 3594篇 |
1979年 | 3643篇 |
1978年 | 3882篇 |
1977年 | 3627篇 |
1976年 | 3864篇 |
1975年 | 3435篇 |
1974年 | 3555篇 |
1973年 | 3898篇 |
1972年 | 2363篇 |
1971年 | 1807篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
Summary This paper is concerned with the problem of developing numerical integration algorithms for differential equations that, when
viewed as equations in some Euclidean space, naturally evolve on some embedded submanifold. It is desired to construct algorithms
whose iterates also evolve on the same manifold. These algorithms can therefore be viewed as integrating ordinary differential
equations on manifolds. The basic method “decouples” the computation of flows on the submanifold from the numerical integration
process. It is shown that two classes of single-step and multistep algorithms can be posed and analyzed theoretically, using
the concept of “freezing” the coefficients of differential operators obtained from the defining vector field. Explicit third-order
algorithms are derived, with additional equations augmenting those of their classical counterparts, obtained from “obstructions”
defined by nonvanishing Lie brackets. 相似文献
152.
A. E. Dorokhov 《Czechoslovak Journal of Physics》2002,52(3):C79-C90
Nonperturbative nolocal structure of QCD vacuum is well described by instanton model. Specific helicity and flavor structure of zero modes of quarks, in instanton field allows simultaneously to explain some important features of low-and high-energy hadron phenomemology. The basic characteristics of hadron spectrum, partonic sum rules, heavyquark potential etc within the instanton liquid model are briefly discussed. 相似文献
153.
154.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
155.
Using an integral theory of grating diffraction we calculate efficiencies greater than 100% if a coating with gain is taken into account. A connection with guided modes is conjectured. The application in optical computing seems to be possible. 相似文献
156.
R. F. Bikbaev 《Theoretical and Mathematical Physics》1989,80(3):1004-1006
Physics and Mathematics Division with Computational Center of the Bashkir Branch of the USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 80, No. 3, pp. 470–473, September, 1989. 相似文献
157.
158.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献
159.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
160.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献