全文获取类型
收费全文 | 2205篇 |
免费 | 97篇 |
国内免费 | 214篇 |
专业分类
化学 | 183篇 |
晶体学 | 4篇 |
力学 | 88篇 |
综合类 | 32篇 |
数学 | 1859篇 |
物理学 | 350篇 |
出版年
2024年 | 3篇 |
2023年 | 28篇 |
2022年 | 25篇 |
2021年 | 20篇 |
2020年 | 36篇 |
2019年 | 54篇 |
2018年 | 27篇 |
2017年 | 52篇 |
2016年 | 51篇 |
2015年 | 36篇 |
2014年 | 80篇 |
2013年 | 180篇 |
2012年 | 85篇 |
2011年 | 99篇 |
2010年 | 99篇 |
2009年 | 106篇 |
2008年 | 109篇 |
2007年 | 147篇 |
2006年 | 113篇 |
2005年 | 107篇 |
2004年 | 91篇 |
2003年 | 104篇 |
2002年 | 91篇 |
2001年 | 71篇 |
2000年 | 100篇 |
1999年 | 71篇 |
1998年 | 84篇 |
1997年 | 69篇 |
1996年 | 45篇 |
1995年 | 27篇 |
1994年 | 37篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 27篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有2516条查询结果,搜索用时 31 毫秒
121.
Mutual mass diffusion and thermal diffusion has been investigated in poly(dimethylsiloxane)/ poly(ethylmethylsiloxane) (PDMS/PEMS) polymer blends of equal weight fractions. Molar masses ranged from below 1 to over 20 kg/mol. Both the mutual mass (D) and the thermal diffusion (DT) coefficient contain a thermally activated factor with an activation temperature of 1415 K. The molar mass dependence of DT is due to an end-group effect of the local friction coefficient. The thermal diffusion coefficient in the limit of long chains and infinite temperature is DT0, = - 1.69×10-7cm2(sK)-1. The Soret coefficient ST of blends far enough away from a critical point is proportional to the static structure factor S(q = 0). 相似文献
122.
The aim of our study is the development of a method for calculating the interface of dimerization of protein-protein complexes based on simplified medium-resolution structures. In particular, we wished to evaluate if the existing concepts for the computation of the Solvent-Accessible Surface Area (SASA) of macromolecules could be applied to medium-resolution models. Therefore, we selected a set of 140 protein chains and computed their reduced representations by topological analysis of their electron density maps at 2.85 A crystallographic resolution. This procedure leads to a limited number of critical points (CPs) that can be identified and associated to backbone and side-chain parts. To evaluate the SASA and interfaces of dimerization of the reduced representations, we chose and modified two existing programs that calculate the SASA of atomic representations, and tested (1) several radii tables of amino acids, (2) the influence of the backbone and side-chain points, and (3) the radius of the solvent molecule, which rolls over the surface. The results are shown in terms of relative error compared to the values calculated on the corresponding atomic representations of the proteins. 相似文献
123.
IP Wai-Cheung WONG Heung XIE Zhongjie & LUAN YihuiDepartment of Applied Mathematics Hong Kong Polytechnic University Hong Kong China Department of Probability Statistics Peking University Beijing China 《中国科学A辑(英文版)》2004,47(1):52-64
The main purpose of this paper is to investigate the detection of jump points of a discontinuous function in the presence of a noise by the wavelet approach. A computing algorithm of our method is proposed and then applied to the daily exchange rate of US Dollar against Deutsche Mark. All the points detected by our method reflect very strong economic and political impacts. Other statistical methods to detect jump points have also been applied to the same exchange rate data. Our proposed method has produced more convincing empirical results than others. 相似文献
124.
For problems in the calculus of variations with
isoperimetric side constraints, we provide in this paper a set of
points whose emptiness, independently of nonsingularity assumptions,
is equivalent to the nonnegativity of the second variation along
admissible variations. The main objective of introducing a
characterization of this condition should be, of course, to obtain a
simpler way of verifying it. There are two other sets of points
available in the literature, introduced by Loewen and Zheng (1994)
and Zeidan (1996), for which this necessary condition implies their
emptiness. However, we show that verifying membership of these sets
may be more difficult than checking directly if that condition
holds. Contrary to this behavior, we prove that the desired
objective of characterizing that condition is achieved by means of
the set introduced in this paper. 相似文献
125.
Juan F. Mena-Jurado Francisco Montiel-Aguilera 《Journal of Mathematical Analysis and Applications》2004,289(1):30-34
In this note, we characterize nice operators in a class of Banach spaces, which includes spaces and L1(μ), as those operators that preserve extreme points. 相似文献
126.
Fred J. Hickernell Ian H. Sloan Grzegorz W. Wasilkowski. 《Mathematics of Computation》2004,73(248):1903-1911
We prove that for every dimension and every number of points, there exists a point-set whose -weighted unanchored discrepancy is bounded from above by independently of provided that the sequence has for some (even arbitrarily large) . Here is a positive number that could be chosen arbitrarily close to zero and depends on but not on or . This result yields strong tractability of the corresponding integration problems including approximation of weighted integrals over unbounded domains such as . It also supplements the results that provide an upper bound of the form when .
127.
W.A. Kirk 《Journal of Mathematical Analysis and Applications》2003,277(2):645-650
Let be a contractive gauge function in the sense that φ is continuous, φ(s)<s for s>0, and if f:M→M satisfies d(f(x),f(y))?φ(d(x,y)) for all x,y in a complete metric space (M,d), then f always has a unique fixed point. It is proved that if T:M→M satisfies
128.
In this paper, we introduce a new class of vector quasi-equilibrium problems with set-valued maps. Almost all the vector equilibrium models of the Blum-Oettli type in the literature are special cases of our new class of equilibrium problems under consideration. Moreover, a number of C-diagonal quasiconvexity properties are proposed for set-valued maps, which are natural generalizations of the -diagonal quasiconvexity for real functions. Together with an application of continuous selection and fixed-point theorems, these conditions enable us to prove unified existence results of solutions for such vector equilibrium problems. 相似文献
129.
Zbigniew Jelonek 《Proceedings of the American Mathematical Society》2003,131(5):1361-1367
Let be a polynomial of degree . Assume that the set there is a sequence s.t. and is finite. We prove that the set of generalized critical values of (hence in particular the set of bifurcation points of ) has at most points. Moreover, We also compute the set effectively.
130.
Petra Sindelá rová 《Proceedings of the American Mathematical Society》2003,131(7):2089-2096
We show that there is a continuous map of the unit interval into itself of type which has a trajectory disjoint from the set of recurrent points of , but contained in the closure of . In particular, is not closed. A function of type , with nonclosed set of recurrent points, was found by H. Chu and J. Xiong [Proc. Amer. Math. Soc. 97 (1986), 361-366]. However, there is no trajectory contained in , since any point in is eventually mapped into . Moreover, our construction is simpler.
We use to show that there is a continuous map of the interval of type for which the set of recurrent points is not an set. This example disproves a conjecture of A. N. Sharkovsky et al., from 1989. We also provide another application of .