全文获取类型
收费全文 | 10400篇 |
免费 | 488篇 |
国内免费 | 26篇 |
专业分类
化学 | 7444篇 |
晶体学 | 77篇 |
力学 | 220篇 |
数学 | 1410篇 |
物理学 | 1763篇 |
出版年
2023年 | 89篇 |
2022年 | 71篇 |
2021年 | 157篇 |
2020年 | 198篇 |
2019年 | 182篇 |
2018年 | 222篇 |
2017年 | 190篇 |
2016年 | 424篇 |
2015年 | 313篇 |
2014年 | 351篇 |
2013年 | 765篇 |
2012年 | 690篇 |
2011年 | 806篇 |
2010年 | 410篇 |
2009年 | 346篇 |
2008年 | 692篇 |
2007年 | 685篇 |
2006年 | 577篇 |
2005年 | 542篇 |
2004年 | 404篇 |
2003年 | 372篇 |
2002年 | 346篇 |
2001年 | 230篇 |
2000年 | 218篇 |
1999年 | 136篇 |
1998年 | 116篇 |
1997年 | 105篇 |
1996年 | 131篇 |
1995年 | 82篇 |
1994年 | 80篇 |
1993年 | 105篇 |
1992年 | 89篇 |
1991年 | 62篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 39篇 |
1986年 | 45篇 |
1985年 | 81篇 |
1984年 | 69篇 |
1983年 | 45篇 |
1982年 | 56篇 |
1981年 | 50篇 |
1980年 | 33篇 |
1979年 | 18篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
In single-objective optimization it is possible to find a global optimum, while in the multi-objective case no optimal solution is clearly defined, but several that simultaneously optimize all the objectives. However, the majority of this kind of problems cannot be solved exactly as they have very large and highly complex search spaces. Recently, meta-heuristic approaches have become important tools for solving multi-objective problems encountered in industry as well as in the theoretical field. Most of these meta-heuristics use a population of solutions, and hence the runtime increases when the population size grows. An interesting way to overcome this problem is to apply parallel processing. This paper analyzes the performance of several parallel paradigms in the context of population-based multi-objective meta-heuristics. In particular, we evaluate four alternative parallelizations of the Pareto simulated annealing algorithm, in terms of quality of the solutions, and speedup. 相似文献
32.
Rafael Tiedra de Aldecoa 《Annales Henri Poincare》2006,7(1):105-124
Although many physical arguments account for using a modified definition of time delay in multichannel-type scattering processes,
one can hardly find rigorous results on that issue in the literature. We try to fill in this gap by showing, both in an abstract
setting and in a short-range case, the identity of the modified time delay and the Eisenbud-Wigner time delay in waveguides.
In the short-range case we also obtain limiting absorption principles, state spectral properties of the total Hamiltonian,
prove the existence of the wave operators and show an explicit formula for the S-matrix. The proofs rely on stationary and commutator methods.
Communicated by Yosi Avron
submitted 12/04/05, accepted 13/05/05 相似文献
33.
34.
A new way of expounding analytical properties based on their mutual dependence (complementary and contradictory relationships) and their unequivocal connection with analytical quality facets is presented. To this end, the paper provides answers to the obvious questions that arise in dealing with the subject: why?, how?, when? and where to teach analytical properties in the Analytical Chemistry curriculum? 相似文献
35.
M. T. Crespo J. M. Los Arcos C. E. Granados M. L. Aceña 《Journal of Radioanalytical and Nuclear Chemistry》1989,130(1):99-110
A new method of analysis of the efficiency of four filters of MnO2 in series which takes into account the reactions induced in plutonium by the sorbent is described. The system of differential equations describing the behaviour of plutonium in water as it passes through the filters is solved and the parameters of the filters are determined for a best fitting of the solutions corresponding to the experimental uncertainties. The method is checked by numerical simulation and then applied to water solutions with a known plutonium concentration and to some experimental results given by other authors. In all occassions the results are consistent with the possibility of determining the contents of plutonium in sea and continental waters with uncertainties of the order of 10%. 相似文献
36.
Rafael Ortega 《Journal of Dynamics and Differential Equations》1992,4(4):651-665
This paper gives sufficient conditions for the existence of periodic solutions of twist type of a time-dependent differential equation of the second order. The concept of periodic solution of twist type is defined in terms of the corresponding Birkhoff normal form and, in particular, implies that the solution is Lyapunov stable. Some applications to nonlocal problems are given. 相似文献
37.
In this work we show that the energy associated to the linear three-dimensional magneto-elastic system decays polynomially to zero as time goes to infinity, provided the initial data is smooth enough. 相似文献
38.
C. Torres O. Alejos C. de Francisco J.M. Muñoz P. Hernández-Gómez 《Applied Physics A: Materials Science & Processing》2003,77(3-4):543-547
This paper describes a robust and fast fitting procedure applicable for relaxing processes that cannot be understood as a discrete sum of single processes but require an activation energy distribution. The method is based on a set of closed-form expressions that allow the computation of the relaxation parameters directly from the isochronal curves obtained experimentally. The usefulness of this method is checked by analyzing the isochronal curves given by a theoretical energy distribution and the magnetic disaccommodation spectra observed in yttrium iron garnet (YIG) samples. PACS 02.60.Ed; 75.60.Lr; 75.50.Gg 相似文献
39.
40.
Algebraic Formulation of Quantum Decoherence 总被引:1,自引:0,他引:1
An algebraic formalism for quantum decoherence in systems with continuous evolution spectrum is introduced. A certain subalgebra, dense in the characteristic algebra of the system, is defined in such a way that Riemann–Lebesgue theorem can be used to explain decoherence in a well defined final pointer basis. 相似文献