全文获取类型
收费全文 | 27379篇 |
免费 | 5383篇 |
国内免费 | 2284篇 |
专业分类
化学 | 6147篇 |
晶体学 | 552篇 |
力学 | 5138篇 |
综合类 | 342篇 |
数学 | 6098篇 |
物理学 | 16769篇 |
出版年
2024年 | 52篇 |
2023年 | 255篇 |
2022年 | 541篇 |
2021年 | 631篇 |
2020年 | 802篇 |
2019年 | 718篇 |
2018年 | 789篇 |
2017年 | 926篇 |
2016年 | 1084篇 |
2015年 | 1118篇 |
2014年 | 1705篇 |
2013年 | 2149篇 |
2012年 | 1626篇 |
2011年 | 1829篇 |
2010年 | 1630篇 |
2009年 | 1752篇 |
2008年 | 1706篇 |
2007年 | 1728篇 |
2006年 | 1722篇 |
2005年 | 1544篇 |
2004年 | 1428篇 |
2003年 | 1304篇 |
2002年 | 1127篇 |
2001年 | 935篇 |
2000年 | 906篇 |
1999年 | 735篇 |
1998年 | 653篇 |
1997年 | 577篇 |
1996年 | 447篇 |
1995年 | 368篇 |
1994年 | 341篇 |
1993年 | 252篇 |
1992年 | 268篇 |
1991年 | 220篇 |
1990年 | 190篇 |
1989年 | 156篇 |
1988年 | 118篇 |
1987年 | 103篇 |
1986年 | 91篇 |
1985年 | 85篇 |
1984年 | 61篇 |
1983年 | 36篇 |
1982年 | 61篇 |
1981年 | 44篇 |
1980年 | 44篇 |
1979年 | 41篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1971年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
151.
We propose iteration methods for solving the Dirichlet problem in domains with involved geometry. Such problems arise in relation to the problem of optimizing quantum dot and antidot infrared detectors. We estimate the deviation of an approximate solution from the exact solution. 相似文献
152.
Ledzewicz U. Nowakowski A. Schättler H. 《Journal of Optimization Theory and Applications》2004,122(2):345-370
It is shown that, if a parametrized fämily of extremals F can be stratified in a way compatible with the flow map generated by F, then those trajectories of the family which realize the minimal values of the cost in F are indeed optimal in comparison with all trajectories which lie in the region R covered by the trajectories of F. It is not assumed that F is a field covering the state space injectively. As illustration, an optimal synthesis is constructed for a system where the flow of extremals exhibits a simple cusp singularity. 相似文献
153.
构造了第孙中禹种强度不等的非对称三态叠加多模叠加态光场|ψ1(ABC)〉q.利用多模压缩态理论研究了态|ψ1(ABC)〉q第一正交分量高次和压缩.结果发现:①当构成态|ψ1(ABC)〉q的三个多模相干态光场的强度不相等时,在一定条件下,态|ψ1(ABC)〉q的第一正交分量可出现任意幂次的高次和压缩.②当上述的三个多模相干态光场强度相等时,态|ψ1(ABC)〉q的第一正交分量的高次和压缩现象消失.在这种情况下,态|ψ1(ABC)〉q的第一正交分量恒处于NH最小测不准态. 相似文献
154.
活动标形法的论述首推苏步青译,佐佐木重夫著《微分几何学》,还有的著作从外微分形式引入活动标形,本文论证取曲面的正交曲率网为参数网时,曲面论的基本公式就是活动标形的微分形式,并用其分析了点啮合齿轮传动误差. 相似文献
155.
This work is concerned with the maximum principle for optimal control problem governed by magnetohydrodynamic equations, which describe the motion of a viscous incompressible conducting fluid in a magnetic field and consist of a subtle coupling of the Navier-Stokes equation of viscous incompressible fluid flow and the Maxwell equation of electromagnetic field. An integral type state constraint is considered. 相似文献
156.
Yasumitsu Matsuo Takehiko Ijichi Hironori Yamada Junko Hatori Seiichiro Ikehata 《Central European Journal of Physics》2004,2(2):357-366
We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and
investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current
at around the coercive electric fieldE
c
of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET)
based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than
that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such
devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the
organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the
initial drain current ofE
G
=0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E
c
). From these results, it is suggested that the PEN-FET becomes a memory device. 相似文献
157.
本文就欧氏空间和球面中紧致子流形的Yang-Mills场进行了讨论.得到了一类不稳定性结果. 相似文献
158.
We show that there is a threshold in energy for the onset of chaos in cosmology for the Universe described as a dynamical system derived from the Einstein equations of General Relativity (GR). In the case of the mixmaster model (homogeneous and anisotropic cosmology with a Bianchi IX metric), the chaos occurs precisely at the prescribed necessary value H
vac=0 of the GR for the energy of the Universe while the system is found to be regular for H<0 and chaotic for H>0 with respect to its pure vacuum part. In the case of generalized scalar tensor theories within the Bianchi IX model, we show using the ADM formalism and a conformal transformation that the energy of the dynamical system as compared to vacuum lies below the zero energy threshold. The system is thus not exhibiting chaos and the conclusion still holds in the presence of ordinary matter as well. The suppression of chaos occurs in a similar way for stiff matter alone. 相似文献
159.
Sergey Chervon 《General Relativity and Gravitation》2004,36(7):1547-1553
A new strategy of exact solutions construction in inflationary cosmology within the self-interacting scalar field theory is proposed. It is shown that inflationary models have no restrictions dictated by the slow-roll approximation on the self-interacting potential. The suggested approach makes it possible to compute precisely the e-folds numbers in inflationary scenarios. The scalar field with a logarithmic evolution in time is analyzed in details. Other possible types of scalar field evolution are discussed. 相似文献
160.
A. López-Ortega 《General Relativity and Gravitation》2004,36(6):1299-1319
We show that the Dirac equation is separable in the circularly symmetric metric in three dimensions and when the background spacetime is de Sitter we find exact solutions to the radial equations. Using these results we show that the de Sitter horizon has a cross section equal to zero for the massless Dirac field, as in the case of the scalar field. Also, using the improved brick wall model we calculate the fermionic entropy associated with the de Sitter horizon and we compare it with some results previously published. 相似文献