全文获取类型
收费全文 | 16033篇 |
免费 | 1462篇 |
国内免费 | 1055篇 |
专业分类
化学 | 6568篇 |
晶体学 | 78篇 |
力学 | 979篇 |
综合类 | 216篇 |
数学 | 5399篇 |
物理学 | 5310篇 |
出版年
2023年 | 160篇 |
2022年 | 405篇 |
2021年 | 404篇 |
2020年 | 399篇 |
2019年 | 409篇 |
2018年 | 355篇 |
2017年 | 437篇 |
2016年 | 468篇 |
2015年 | 379篇 |
2014年 | 643篇 |
2013年 | 1079篇 |
2012年 | 664篇 |
2011年 | 741篇 |
2010年 | 677篇 |
2009年 | 956篇 |
2008年 | 1007篇 |
2007年 | 1025篇 |
2006年 | 886篇 |
2005年 | 657篇 |
2004年 | 587篇 |
2003年 | 612篇 |
2002年 | 602篇 |
2001年 | 503篇 |
2000年 | 456篇 |
1999年 | 417篇 |
1998年 | 387篇 |
1997年 | 248篇 |
1996年 | 185篇 |
1995年 | 185篇 |
1994年 | 176篇 |
1993年 | 168篇 |
1992年 | 244篇 |
1991年 | 130篇 |
1990年 | 104篇 |
1989年 | 91篇 |
1988年 | 94篇 |
1987年 | 97篇 |
1986年 | 73篇 |
1985年 | 80篇 |
1984年 | 82篇 |
1983年 | 48篇 |
1982年 | 96篇 |
1981年 | 175篇 |
1980年 | 183篇 |
1979年 | 182篇 |
1978年 | 165篇 |
1977年 | 102篇 |
1976年 | 108篇 |
1973年 | 77篇 |
1972年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
22.
Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
23.
Kurt Majewski 《Queueing Systems》2005,50(2-3):199-230
We consider multiclass feedforward queueing networks under first in first out and priority service disciplines driven by long-range dependent arrival and service time processes. We show that in critical loading the normalized workload, queue length and sojourn time processes can converge to a multi-dimensional reflected fractional Brownian motion. This weak heavy traffic approximation is deduced from a deterministic pathwise approximation of the network behavior close to constant critical load in terms of the solution of a Skorokhod problem. Since we model the doubly infinite time interval, our results directly cover the stationary case.AMS subject classification: primary 90B15, secondary 60K25, 68M20 相似文献
24.
Some new oscillation criteria are established for a second order neutral delay differential equations. These results improve oscillation results of Y.V. Rogo-vchenko for the retarded delay differential equations. The relevance of our theorems is illustrated with two carefully selected examples. 相似文献
25.
Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR. 相似文献
26.
27.
28.
Lahcne Mezrag 《Mathematische Nachrichten》2004,266(1):60-67
In [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Ka?in cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
29.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
30.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献