全文获取类型
收费全文 | 12107篇 |
免费 | 1078篇 |
国内免费 | 1446篇 |
专业分类
化学 | 783篇 |
晶体学 | 17篇 |
力学 | 696篇 |
综合类 | 322篇 |
数学 | 10741篇 |
物理学 | 2072篇 |
出版年
2024年 | 16篇 |
2023年 | 127篇 |
2022年 | 139篇 |
2021年 | 200篇 |
2020年 | 255篇 |
2019年 | 312篇 |
2018年 | 270篇 |
2017年 | 314篇 |
2016年 | 349篇 |
2015年 | 277篇 |
2014年 | 534篇 |
2013年 | 794篇 |
2012年 | 492篇 |
2011年 | 702篇 |
2010年 | 648篇 |
2009年 | 849篇 |
2008年 | 939篇 |
2007年 | 962篇 |
2006年 | 798篇 |
2005年 | 755篇 |
2004年 | 551篇 |
2003年 | 637篇 |
2002年 | 541篇 |
2001年 | 427篇 |
2000年 | 491篇 |
1999年 | 423篇 |
1998年 | 399篇 |
1997年 | 328篇 |
1996年 | 230篇 |
1995年 | 133篇 |
1994年 | 135篇 |
1993年 | 83篇 |
1992年 | 64篇 |
1991年 | 60篇 |
1990年 | 46篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 40篇 |
1984年 | 38篇 |
1983年 | 17篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
871.
The characteristics of ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7. This has been used to evaluate the extraction characteristics (accel-decel system) to generate an ion beam with low beam emittance and high brightness. The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target. Also, a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus. 相似文献
872.
We consider derivation of the effective potential for a scalar field in curved space-time within the physical regularization scheme, using two sorts of covariant cut-off regularizations. The first one is based on the local momentum representation and Riemann normal coordinates and the second is operatorial regularization, based on the Fock-Schwinger-DeWitt proper-time representation. We show, on the example of a self-interacting scalar field, that these two methods produce equal results for divergences, but the first one gives more detailed information about the finite part. Furthermore, we calculate the contribution from a massive fermion loop and discuss renormalization group equations and their interpretation for the multi-mass theories. 相似文献
873.
A.D. Ribeiro 《Physics letters. A》2011,375(4):812-816
The semiclassical formula for the coherent-state propagator is written in terms of complex classical trajectories of an equivalent classical system. Depending on the parameters involved, more than one trajectory may contribute to the calculation. Eventually, however, two contributing trajectories coalesce, characterizing what is called phase space caustic. In this case, the usual semiclassical formula for the propagator diverges, so that a uniform approximation is required to avoid this singularity. In this Letter, we present a non-trivial numerical application illustrating this scenario, showing the accuracy of the uniform formula that we have previously derived. 相似文献
874.
We investigate the role of Casimir energy as a mechanism for brane stability in five-dimensional models with the fifth dimension compactified on an S1/Z2 orbifold, which includes the Randall–Sundrum two brane model (RS1). We employ a ζ-function regularization technique utilizing the Schwinger proper time method and the Jacobi theta function identity to calculate the one-loop effective potential. We show that the combination of the Casimir energies of a scalar Higgs field, the three generations of Standard Model fermions and one additional massive non-SM scalar in the bulk produces a non-trivial minimum of the potential. In particular, we consider a scalar field with a coupling in the bulk to a Lorentz violating vector particle localized to the compactified dimension. Such a scalar may provide a natural means of fine tuning needed for stabilization of the brane separation. Finally, we briefly review the possibility that Casimir energy plays a role in generating the currently observed epoch of cosmological inflation by examining a simple five-dimensional anisotropic metric. 相似文献
875.
876.
We investigate the geometry of the moduli space of N vortices on line bundles over a closed Riemann surface Σ of genus g>1, in the little explored situation where 1≤N<g. In the regime where the area of the surface is just large enough to accommodate N vortices (which we call the dissolving limit), we describe the relation between the geometry of the moduli space and the complex geometry of the Jacobian variety of Σ. For N=1, we show that the metric on the moduli space converges to a natural Bergman metric on Σ. When N>1, the vortex metric typically degenerates as the dissolving limit is approached, the degeneration occurring precisely on the critical locus of the Abel–Jacobi map of Σ at degree N. We describe consequences of this phenomenon from the point of view of multivortex dynamics. 相似文献
877.
878.
The piecewise continuous function space is an important state space in various nonlinear problems. In this paper, we establish some new fixed point theorems for the perturbed contraction operators in piecewise continuous function spaces. Our results can be applied to various integral operators. Some previous results are improved in this literature. As applications, the existence and uniqueness of solutions of impulsive anti‐periodic boundary value problems and the Lasota–Wazewska models with delays are exhibited at last two sections. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
879.
Serhii Gryshchuk Massimo Lanza de Cristoforis 《Mathematical Methods in the Applied Sciences》2014,37(12):1755-1771
Let be a bounded open domain of . Let denote the outward unit normal of . We assume that the Steklov problem Δu = 0 in and on has a simple eigenvalue of . Then we consider an annular domain obtained by removing from a small‐cavity size of ε > 0, and we show that under proper assumptions there exists a real valued and real analytic function defined in an open neighborhood of (0,0) in and such that is a simple eigenvalue for the Steklov problem Δu = 0 in and on for all ε > 0 small enough, and such that . Here denotes the outward unit normal of , and δ2,2 ≡ 1 and δ2,n ≡ 0 if n ≥ 3. Then related statements have been proved for corresponding eigenfunctions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
880.
Ahmed Alsaedi Mohammed S. Alhothuali Bashir Ahmad Sebti Kerbal Mokhtar Kirane 《Mathematical Methods in the Applied Sciences》2014,37(13):2009-2016
Sobolev type nonlinear equations with time fractional derivatives are considered. Using the test function method, limiting exponents for nonexistence of solutions are found. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献