全文获取类型
收费全文 | 10986篇 |
免费 | 2003篇 |
国内免费 | 1020篇 |
专业分类
化学 | 7420篇 |
晶体学 | 87篇 |
力学 | 683篇 |
综合类 | 89篇 |
数学 | 1262篇 |
物理学 | 4468篇 |
出版年
2024年 | 26篇 |
2023年 | 251篇 |
2022年 | 425篇 |
2021年 | 411篇 |
2020年 | 447篇 |
2019年 | 444篇 |
2018年 | 367篇 |
2017年 | 349篇 |
2016年 | 536篇 |
2015年 | 503篇 |
2014年 | 574篇 |
2013年 | 781篇 |
2012年 | 962篇 |
2011年 | 1060篇 |
2010年 | 667篇 |
2009年 | 695篇 |
2008年 | 705篇 |
2007年 | 594篇 |
2006年 | 556篇 |
2005年 | 452篇 |
2004年 | 353篇 |
2003年 | 290篇 |
2002年 | 268篇 |
2001年 | 215篇 |
2000年 | 226篇 |
1999年 | 213篇 |
1998年 | 215篇 |
1997年 | 199篇 |
1996年 | 151篇 |
1995年 | 199篇 |
1994年 | 169篇 |
1993年 | 128篇 |
1992年 | 104篇 |
1991年 | 89篇 |
1990年 | 92篇 |
1989年 | 67篇 |
1988年 | 45篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 22篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
1 Besicovitch Inner ProductIll this paper, we consider Dirichlet serie8where an, tL = 1, 2,' ', are complex nunlbers. They are Besicovitch almost periodic functionsWe see the 8ystenl {e.(t); e.(t) = e--it Iog 1l, 71 = l, 2,' .} fOrnis a1l orthollor11la1 systelll witl1respect to tI1e BesicovitcI1 iIl1ler productThell we call fOrm the gelleralized trigouolnetrical polynolIlialsAccording to tl1e idea developed il1 [l],[2], auy Dirichlet seriesis weakly convergent over K witll respect to … 相似文献
994.
本文概述了长春物理研究所为人民大会堂研制的交流(AC)、直流(DC)电致发光(EL)矩阵大屏幕会务信息显示的结果。其中,ACEL矩阵屏幕尺寸为2.5×3m2,由30块0.46×0.46m2的单元屏拼接而成。平均亮度20尼特,对比度10:1;DCEL矩阵屏幕为:1m2,行列数120×144,平均亮度45尼特,对比度大于10:1。在环境照度60lux条件下,观察距离分别为65m、20m。并从分析EL矩阵的显示特性出发,阐明了显示系统的设计要点,控制、匹配电路和亮度、对比度的关系;还给出了部分驱动电路结构和系统的应用结果。 相似文献
995.
996.
A mathematical model is developed to study periodic-impact motions and bifurcations in dynamics of a small vibro-impact pile driver. Dynamics of the small vibro-impact pile driver can be analyzed by means of a three-dimensional map, which describes free flight and sticking solutions of the vibro-impact system, between impacts, supplemented by transition conditions at the instants of impacts. Piecewise property and singularity are found to exist in the Poincaré map. The piecewise property is caused by the transitions of free flight and sticking motions of the driver and the pile immediately after the impact, and the singularity of map is generated via the grazing contact of the driver and the pile immediately before the impact. These properties of the map have been shown to exhibit particular types of sliding and grazing bifurcations of periodic-impact motions under parameter variation. The influence of piecewise property, grazing singularities and parameter variation on the performance of the vibro-impact pile driver is analyzed. The global bifurcation diagrams for the impact velocity of the driver versus the forcing frequency are plotted to predict much of the qualitative behavior of the actual physical system, which enable the practicing engineer to select excitation frequency ranges in which stable period one single-impact response can be expected to occur, and to predict the larger impact velocity and shorter impact period of such response. 相似文献
997.
This paper is concerned with optimal harvesting policy for an age-dependent n-dimensional food chain model. The existence and uniqueness of non-negative solution of the system are proved using the fixed point theorem. By Mazur's theorem, the existence of optimal control strategy is demonstrated and optimality conditions derived by means of normal cone. 相似文献
998.
999.
Optical properties of silver nanobowtie with anisotropic topology, which is separated with nanogap that is horizontal (Y direction)
and vertical (Z direction) to the line between the two constituent triangles (i.e., the bowtie axis), are studied. A discrete
dipole approximation (DDA) method is used to determine the extinction efficiency and the electric field (E-field) distribution,
then the corresponding enhancement factor (EF) and the full width half maximum (FWHM) of the E-field are obtained and analyzed.
Our results show that the wavelength of localized surface plasmon resonance (LSPR)-induced blue-shifts and the maximum EF
decrease were observed with increasing gap size for the parallel polarized (Z-polarized) excitation. It is also found that
the light spot at the “hot spot” in the gap becomes larger and deviates from the rectangular pattern with the increase of
the gap in the Z direction (Z-gap), and the FWHM in the Z direction of the localized E-field in the gap broadens with either
an increase in the gap in the Y direction (Y-gap) or the Z-gap. These behaviors are due to the decrease of the coupling efficiency
of near-field plasmon coupling. In contrast, the wavelength of the LSPR and the maximum EF excited by the perpendicularly
polarized (Y-polarized) light show less dependence on the gap size than that of the Y-polarized light.
PACS 73.20.Mf; 78.67.-n 相似文献
1000.
This paper considers the expected residual minimization (ERM) method proposed by Luo and Lin (J. Optim. Theory Appl. 140:103–116,
2009) for a class of stochastic variational inequality problems. Different from the work mentioned above, the function involved
is assumed to be nonlinear in this paper. We first consider a quasi-Monte Carlo method for the case where the underlying sample
space is compact and show that the ERM method is convergent under very mild conditions. Then, we suggest a compact approximation
approach for the case where the sample space is noncompact.
This work was supported in part by Project 10771025 supported by NSFC and SRFDP 20070141063 of China. 相似文献