全文获取类型
收费全文 | 837703篇 |
免费 | 7951篇 |
国内免费 | 2531篇 |
专业分类
化学 | 425053篇 |
晶体学 | 11805篇 |
力学 | 41764篇 |
综合类 | 23篇 |
数学 | 120285篇 |
物理学 | 249255篇 |
出版年
2021年 | 6585篇 |
2020年 | 7247篇 |
2019年 | 8238篇 |
2018年 | 14302篇 |
2017年 | 14498篇 |
2016年 | 17258篇 |
2015年 | 9268篇 |
2014年 | 14518篇 |
2013年 | 35511篇 |
2012年 | 28538篇 |
2011年 | 37765篇 |
2010年 | 26323篇 |
2009年 | 26204篇 |
2008年 | 34717篇 |
2007年 | 36386篇 |
2006年 | 27720篇 |
2005年 | 27511篇 |
2004年 | 24215篇 |
2003年 | 22254篇 |
2002年 | 21211篇 |
2001年 | 21620篇 |
2000年 | 17064篇 |
1999年 | 13150篇 |
1998年 | 11332篇 |
1997年 | 11263篇 |
1996年 | 10740篇 |
1995年 | 9668篇 |
1994年 | 9516篇 |
1993年 | 9406篇 |
1992年 | 10003篇 |
1991年 | 10499篇 |
1990年 | 10033篇 |
1989年 | 9936篇 |
1988年 | 9793篇 |
1987年 | 9476篇 |
1986年 | 9131篇 |
1985年 | 11963篇 |
1984年 | 12514篇 |
1983年 | 10404篇 |
1982年 | 11077篇 |
1981年 | 10456篇 |
1980年 | 9982篇 |
1979年 | 10560篇 |
1978年 | 11142篇 |
1977年 | 10804篇 |
1976年 | 10973篇 |
1975年 | 10261篇 |
1974年 | 10231篇 |
1973年 | 10764篇 |
1972年 | 7555篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Let Ψ(x,y) (resp. Ψm(x,y)) denote the number of integers not exceeding x that are y-friable, i.e. have no prime factor exceeding y (resp. and are coprime to m). Evaluating the ratio Ψm(x/d,y)/Ψ(x,y) for 1≤slantd≤slantx, m≥slant 1, x≥slant y≥slant 2, turns out to be a crucial step for estimating arithmetic sums over friable integers. Here, it is crucial to obtain formulae with a very wide range of validity. In this paper, several uniform estimates are provided for the aforementioned ratio, which supersede all previously known results. Applications are given to averages of various arithmetic functions over friable integers which in turn improve corresponding results from the literature. The technique employed rests mainly on the saddle-point method, which is an efficient and specific tool for the required design.2000 Mathematics Subject Classification: Primary—11N25; Secondary—11K65, 11N37 相似文献
992.
993.
Analysis of amlodipine in human plasma by gas chromatography 总被引:3,自引:0,他引:3
994.
995.
D. K. Kulshrestha 《The Journal of the Operational Research Society》1987,38(5):447-452
Consider a finite set of demand points which exist anywhere on the boundary of a rectangle contained in the two-dimensional Euclidean space. This paper considers the problem of finding an optimal location (on the boundary of the rectangle) which minimizes the maximum average Euclidean distance to the demand points. The method presented is independent of the number of demand points. 相似文献
996.
In this paper the performances of inhomogeneous dielectric slabs as solar light collectors for both illumination and solar energy applications are analysed. 相似文献
997.
R. Salomon 《Zeitschrift für Physik B Condensed Matter》1989,73(4):519-527
The diffusion constant and the diagonal conductivity for non-interacting electrons in a two-dimensional, disordered system are studied. A homogeneous magnetic field perpendicular to the electron system is assumed. For weak short-range random potentials and high fields the Landau quantum numbern can be used as expansion parameter. In the limit of high Landau levels the system shows metallic behaviour. Corrections for finiten decrease the conductivity and indicate localized states in the whole energy band. A breakdown of the expansion and stronger localization are observed only for the lowest Landau levels if the typical experimental length scale of the quantized Hall effect is used. 相似文献
998.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
999.
Calculations are performed, using a basis of two-center functions described previously, for excited states of the following three-and four-electron compounds: H2
–, He2
+, He2, Li2
+2. High efficiency is demonstrated for the frozen ionic core approximation and the nonorthogonal orbital method in such calculations. For four-electron systems the practical feasibility of the frozen hybrid core approximation is demonstrated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 53–56, August, 1987. 相似文献
1000.
S. S. Dragomir 《Acta Mathematica Hungarica》2005,109(4):331-345
Summary General divergence measures for probability distributions are introduced and their main properties established. Connections
with f-divergence corresponding to a convex function fare explored. 相似文献