全文获取类型
收费全文 | 15010篇 |
免费 | 853篇 |
国内免费 | 899篇 |
专业分类
化学 | 7958篇 |
晶体学 | 78篇 |
力学 | 745篇 |
综合类 | 146篇 |
数学 | 3360篇 |
物理学 | 4475篇 |
出版年
2023年 | 138篇 |
2022年 | 364篇 |
2021年 | 351篇 |
2020年 | 304篇 |
2019年 | 348篇 |
2018年 | 302篇 |
2017年 | 327篇 |
2016年 | 350篇 |
2015年 | 312篇 |
2014年 | 453篇 |
2013年 | 858篇 |
2012年 | 508篇 |
2011年 | 535篇 |
2010年 | 485篇 |
2009年 | 751篇 |
2008年 | 843篇 |
2007年 | 871篇 |
2006年 | 765篇 |
2005年 | 553篇 |
2004年 | 510篇 |
2003年 | 499篇 |
2002年 | 532篇 |
2001年 | 452篇 |
2000年 | 423篇 |
1999年 | 358篇 |
1998年 | 351篇 |
1997年 | 233篇 |
1996年 | 165篇 |
1995年 | 158篇 |
1994年 | 149篇 |
1993年 | 157篇 |
1992年 | 241篇 |
1991年 | 126篇 |
1990年 | 99篇 |
1989年 | 80篇 |
1988年 | 88篇 |
1987年 | 92篇 |
1986年 | 73篇 |
1985年 | 74篇 |
1984年 | 81篇 |
1982年 | 111篇 |
1981年 | 304篇 |
1980年 | 312篇 |
1979年 | 314篇 |
1978年 | 326篇 |
1977年 | 246篇 |
1976年 | 261篇 |
1974年 | 76篇 |
1973年 | 183篇 |
1972年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
车前子中多糖含量的测定 总被引:12,自引:1,他引:11
采用蒽酮-硫酸法比色测定,用精制车前子多糖测得车前子多糖对葡萄糖的换算因子,对我国同属不同品种的车前子不同采集时间及炮制前后其多糖含量进行了比较研究。结果表明:此测定方法简便可行。供试液在8h内显色稳定,重现性较好,平均回收率为97.8%,RSD=1.41%(n=5)。江西吉安产大粒车前子生品多糖含量在9.15%~9.83%之间,炮制后其多糖含量在6.29%~6.81%之间;南昌新祺周车前GAP标准基地的大粒车前子生品多糖含量为7.85%~8.38%,炮制后其多糖含量为6.01%~6.64%;东北产的小粒车前子生品多糖含量为6.61%,炮制后其多糖含量为6.45%。 相似文献
32.
Miklós Csörgő 《Periodica Mathematica Hungarica》2005,50(1-2):1-27
Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks. 相似文献
33.
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
34.
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
35.
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
36.
37.
38.
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
39.
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
40.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献