全文获取类型
收费全文 | 44311篇 |
免费 | 1866篇 |
国内免费 | 1472篇 |
专业分类
化学 | 32310篇 |
晶体学 | 336篇 |
力学 | 819篇 |
综合类 | 10篇 |
数学 | 6060篇 |
物理学 | 8114篇 |
出版年
2023年 | 342篇 |
2022年 | 683篇 |
2021年 | 886篇 |
2020年 | 795篇 |
2019年 | 776篇 |
2018年 | 846篇 |
2017年 | 838篇 |
2016年 | 1629篇 |
2015年 | 1318篇 |
2014年 | 1421篇 |
2013年 | 2978篇 |
2012年 | 3236篇 |
2011年 | 3551篇 |
2010年 | 2077篇 |
2009年 | 2093篇 |
2008年 | 2762篇 |
2007年 | 2689篇 |
2006年 | 2353篇 |
2005年 | 2262篇 |
2004年 | 2264篇 |
2003年 | 1645篇 |
2002年 | 1513篇 |
2001年 | 902篇 |
2000年 | 754篇 |
1999年 | 597篇 |
1998年 | 488篇 |
1997年 | 389篇 |
1996年 | 469篇 |
1995年 | 350篇 |
1994年 | 301篇 |
1993年 | 354篇 |
1992年 | 302篇 |
1991年 | 218篇 |
1990年 | 206篇 |
1989年 | 168篇 |
1988年 | 168篇 |
1987年 | 164篇 |
1986年 | 153篇 |
1985年 | 243篇 |
1984年 | 220篇 |
1983年 | 172篇 |
1982年 | 150篇 |
1981年 | 151篇 |
1980年 | 121篇 |
1979年 | 120篇 |
1978年 | 104篇 |
1977年 | 100篇 |
1976年 | 93篇 |
1975年 | 90篇 |
1973年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
94.
Generally, in homotopy theory a cylinder object (or, its dual, a path object) is used to define homotopy between morphisms,
and a cone object is used to build exact sequences of homotopy groups. Here, an axiomatic theory based on a cone functor is
given. Suspension objects are associated to based objects and cofibrations, obtaining homotopy groups referred to an object
and relative to a cofibration, respectively. Exact sequences of these groups are built. Algebraic and particular examples
are given. We point out that the main results of this paper were already stated in [3], and the purpose of this article is
to give full details of the foregoing. 相似文献
95.
E. Liénard G. Ban J. Blieck D. Durand F. Duval X. Fléchard M. Herbane M. Labalme Y. Lemière F. Mauger A. Méry O. Naviliat-Cuncic D. Rodríguez J. C. Thomas 《Hyperfine Interactions》2006,172(1-3):29-33
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller
decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The
6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to
deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this
experiment. Up to 105 coincidences were recorded during a second run in 2006. 相似文献
96.
Summary The gas chromatographic behaviour of crosslinked macroporous 2-hydroxyethyl methacrylate grafted with 2-methyloxazoline was
investigated and the range of applicability of the copolymer was assessed. Retention index values were measured on this copolymer
and compared with those obtained on the terpolymer 2-hydroxyethyl methacrylate-ethylene dimethacrylate-acrylonitrile. Rohrschneider
constants and efficiency data for selected sorbates are given. The use of this type of polymer in the separation of various
types of compounds is documented by various examples. 相似文献
97.
Some curvature conditions about the geodesics emanating from a submanifold are obtained. These conditions are used to to study the topological and geometric properties of the ambient spaces which admit some minimal submanifolds. 相似文献
98.
Luis Anchordoqui María Teresa Dova Thomas McCauley Stephen Reucroft 《Annals of Physics》2004,314(1):145-207
The properties of cosmic rays with energies above 106 GeV have to be deduced from the spacetime structure and particle content of the air showers which they initiate. In this review we summarize the phenomenology of these giant air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra high energies, and discuss the prospects for insights into forward physics at the LHC. We also describe the main electromagnetic processes that govern the longitudinal shower evolution, as well as the lateral spread of particles. Armed with these two principal shower ingredients and motivation from the underlying physics, we provide an overview of some of the different methods proposed to distinguish primary species. The properties of neutrino interactions and the potential of forthcoming experiments to isolate deeply penetrating showers from baryonic cascades are also discussed. We finally venture into a terra incognita endowed with TeV-scale gravity and explore anomalous neutrino-induced showers. 相似文献
99.
María G. Armentano Ricardo G. Durn 《Numerical Methods for Partial Differential Equations》2003,19(5):653-664
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003 相似文献
100.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel. 相似文献