全文获取类型
收费全文 | 81602篇 |
免费 | 458篇 |
国内免费 | 398篇 |
专业分类
化学 | 26640篇 |
晶体学 | 820篇 |
力学 | 6863篇 |
数学 | 32285篇 |
物理学 | 15850篇 |
出版年
2022年 | 256篇 |
2021年 | 197篇 |
2020年 | 145篇 |
2019年 | 134篇 |
2018年 | 10538篇 |
2017年 | 10339篇 |
2016年 | 6196篇 |
2015年 | 986篇 |
2014年 | 440篇 |
2013年 | 602篇 |
2012年 | 3990篇 |
2011年 | 10701篇 |
2010年 | 5750篇 |
2009年 | 6159篇 |
2008年 | 6705篇 |
2007年 | 8883篇 |
2006年 | 323篇 |
2005年 | 1416篇 |
2004年 | 1593篇 |
2003年 | 2031篇 |
2002年 | 1066篇 |
2001年 | 310篇 |
2000年 | 336篇 |
1999年 | 207篇 |
1998年 | 215篇 |
1997年 | 169篇 |
1996年 | 237篇 |
1995年 | 155篇 |
1994年 | 101篇 |
1993年 | 123篇 |
1992年 | 85篇 |
1991年 | 102篇 |
1990年 | 68篇 |
1989年 | 78篇 |
1988年 | 85篇 |
1987年 | 83篇 |
1986年 | 83篇 |
1985年 | 84篇 |
1984年 | 65篇 |
1983年 | 59篇 |
1982年 | 63篇 |
1981年 | 49篇 |
1980年 | 74篇 |
1979年 | 65篇 |
1978年 | 61篇 |
1977年 | 45篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
We prove that three automorphisms of the rooted binary tree defined by a certain 3-state automaton generate a free non-Abelian
group of rank 3.
Both authors are supported by the NSF grants DMS-0308985 and DMS-0456185. Yaroslav Vorobets is supported by a Clay Research
Scholarship. 相似文献
192.
K A Dowsland M Gilbert G Kendall 《The Journal of the Operational Research Society》2007,58(4):429-438
This paper is concerned with the development of a customized circle packing algorithm for a manufacturer of sprockets for the motor cycle industry. Practical constraints mean that the problem differs somewhat from those tackled elsewhere in the literature. In particular, the layouts need to conform to a given structure. This is achieved by using a local search algorithm with an appropriate starting solution and a series of neighbourhoods designed to preserve the layout structure. Empirical evidence based on real data shows that the quality of the resulting solutions closely matches that of cutting patterns currently produced by human experts. Computation times average around 20–30?s per order as compared to several hours for an equivalent manual solution. 相似文献
193.
Gu-Qiang Li 《Theoretical and Mathematical Physics》2007,151(1):586-589
We use the Parikh-Wilczek method to treat Hawking radiation as a tunneling process across the event horizon and calculate
the emission rate of a Gibbons-Maeda dilaton black hole. We show that if self-gravitation is taken into account, then the
radiation deviates from the purely thermal spectrum, and the corrected spectrum is consistent with an underlying unitary theory.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 1, pp. 172–175, April, 2007. 相似文献
194.
In this paper we investigate the electrostatic problem of determining conductivity profiles from the knowledge of boundary
currents and voltages. We obtain an improved estimate for the voltage potential of a two-dimensional conductor having finitely
many circular inclusions and piecewise constant conductivity profile. We derive an asymptotic expansion for the voltage potential
in terms of the reference voltage potential and the location, size, and conductivity of the inhomogeneities. This representation
is used to formulate the nonlinear least squares problem for estimating the location and size of the inhomogeneities. Required
boundary data for the voltage potential are generated numerically by solving a system of integral equations. Computational
experiments are presented to demonstrate the effectiveness of our identification procedure. 相似文献
195.
Semyon Alesker 《Geometric And Functional Analysis》2007,17(4):1321-1341
This is a non-technical survey of a recent theory of valuations on manifolds constructed in [A10], [A11], [AF] and [A12],
and actually a guide to this series of articles. We also review some recent related results obtained by a number of people.
Received: February 2006, Revision: June 2006, Accepted: June 2006 相似文献
196.
197.
M. Niyaz Khan 《国际化学动力学杂志》1991,23(7):561-566
The effects of the concentrations of LiCl, NaCl, KCl, CsCl, Na2CO3, BaCl2, and Me4NCl on the rates of reactions of hydroxide ion with ionized N-hydroxyphthalimide (NHP) at 30°C and in a H2O–MeCN solvent containing 98%, v/v, H2O reveal a nonlinear increase in observed rate constants with increase in salt concentrations. The observed rate constants are highly sensitive to the valence state of cations and almost insensitive to the valence state of anions of the salts. These observations are explained in terms of ion-pair formation between cations and NHP?. 相似文献
198.
199.
200.
A well-known problem of prediction in linear regression models is to find a confidence interval for the random value of the dependent variable when the values of the independent variables are given. Such a situation may arise in economic quality control models when the independent variables are costly inputs and the dependent variable is some measure of quality or production. In such a circumstance, an important control objective may be to find values for the inputs that will maximize the lower limit of the prediction confidence interval for a fixed budget, or alternatively, to minimize the cost of the inputs for a fixed lower limit of the confidence interval. In this paper, we shall show that global optima can be found using known algorithms. The special case of simple linear regression is discussed and an illustrative example is provided. 相似文献