全文获取类型
收费全文 | 4993篇 |
免费 | 465篇 |
国内免费 | 350篇 |
专业分类
化学 | 743篇 |
晶体学 | 10篇 |
力学 | 360篇 |
综合类 | 82篇 |
数学 | 3060篇 |
物理学 | 1553篇 |
出版年
2024年 | 5篇 |
2023年 | 42篇 |
2022年 | 98篇 |
2021年 | 98篇 |
2020年 | 97篇 |
2019年 | 114篇 |
2018年 | 92篇 |
2017年 | 140篇 |
2016年 | 170篇 |
2015年 | 117篇 |
2014年 | 269篇 |
2013年 | 339篇 |
2012年 | 191篇 |
2011年 | 282篇 |
2010年 | 278篇 |
2009年 | 275篇 |
2008年 | 306篇 |
2007年 | 371篇 |
2006年 | 287篇 |
2005年 | 254篇 |
2004年 | 248篇 |
2003年 | 248篇 |
2002年 | 198篇 |
2001年 | 149篇 |
2000年 | 155篇 |
1999年 | 142篇 |
1998年 | 115篇 |
1997年 | 107篇 |
1996年 | 72篇 |
1995年 | 91篇 |
1994年 | 58篇 |
1993年 | 50篇 |
1992年 | 48篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 4篇 |
排序方式: 共有5808条查询结果,搜索用时 15 毫秒
41.
基于错误概率达到最小的原则,该文在罐子模型序贯试验中构造了一种渐近最优设计。在这种设计下,不仅能使病员以较多机会分配到较好的处理,而且能使估计量的统计效率在一定意义下达到最优。 相似文献
42.
43.
Su-Yun Huang Chuhsing Kate Hsiao Ching-Wei Chang 《Annals of the Institute of Statistical Mathematics》2003,55(3):655-670
The article provides a refinement for the volume-corrected Laplace-Metropolis estimator of the marginal likelihood of DiCiccioet al. The correction volume of probability α in DiCiccioet al. is fixed and suggested to take the value α=0.05. In this article α is selected based on an asymptotic analysis to minimize
the mean square relative error (MSRE). This optimal choice of α is shown to be invariant under linear transformations. The
invariance property leads to easy implementation for multivariate problems. An implementation procedure is provided for practical
use. A simulation study and a real data example are presented. 相似文献
44.
45.
Noga Alon Oded Goldreich Johan Hstad Ren Peralta 《Random Structures and Algorithms》1992,3(3):289-304
We present three alternative simple constructions of small probability spaces on n bits for which any k bits are almost independent. The number of bits used to specify a point in the sample space is (2 + o(1)) (log log n + k/2 + log k + log 1/?), where ? is the statistical difference between the distribution induced on any k bit locations and the uniform distribution. This is asymptotically comparable to the construction recently presented by Naor and Naor (our size bound is better as long as ? < 1/(k log n)). An additional advantage of our constructions is their simplicity. 相似文献
46.
离子表面活性剂胶团对阿斯匹林碱水解反应的影响 总被引:3,自引:0,他引:3
离子表面活性剂胶团对阿斯匹林碱水解反应的影响史振民*刘生昆张祝莲巩育军(延安大学化学系延安716000)关键词表面活性剂,阿斯匹林,碱水解反应,胶团,抑制作用1996-05-04收稿,1996-08-12修回阿斯匹林(ASP),学名为乙酰水杨酸,有较... 相似文献
47.
The solvent extraction of cobalt(II), nickel(II) and copper(II) using 2,4-pent-dione (Hacac) and 4-phenyl-2, 4-but-dione (Hbzac)
is carried out by varying the reagent concentration and pH of the aqueous phase. Each of these metals is quantitatively separated
(≈ 98%) from their binary mixtures with monovalent (Ag), divalent (Mn, Zn, Cd, Hg, Mg, Sn, Pb) and trivalent (Cr, Fe) metals.
The extraction constants are calculated from the metal distribution data using linear regression analysis. The extracted species
is MA2 in each case. A most significant result is separation of copper(II) from iron(III) which otherwise interferes when extracted
from the acidic medium. 相似文献
48.
We define a classical probability analogue of Voiculescu's free entropy dimension that we shall call the classical probability entropy dimension of a probability measure on Rn. We show that the classical probability entropy dimension of a measure is related with diverse other notions of dimension. First, it can be viewed as a kind of fractal dimension. Second, if one extends Bochner's inequalities to a measure by requiring that microstates around this measure asymptotically satisfy the classical Bochner's inequalities, then we show that the classical probability entropy dimension controls the rate of increase of optimal constants in Bochner's inequality for a measure regularized by convolution with the Gaussian law as the regularization is removed. We introduce a free analogue of the Bochner inequality and study the related free entropy dimension quantity. We show that it is greater or equal to the non-microstates free entropy dimension. 相似文献
49.
Discrete-time GI/Geo/1 queue with multiple working vacations 总被引:2,自引:0,他引:2
Consider the discrete time GI/Geo/1 queue with working vacations under EAS and LAS schemes. The server takes the original
work at the lower rate rather than completely stopping during the vacation period. Using the matrix-geometric solution method,
we obtain the steady-state distribution of the number of customers in the system and present the stochastic decomposition
property of the queue length. Furthermore, we find and verify the closed property of conditional probability for negative
binomial distributions. Using such property, we obtain the specific expression for the steady-state distribution of the waiting
time and explain its two conditional stochastic decomposition structures. Finally, two special models are presented.
相似文献
50.
Richard F. Serfozo 《Queueing Systems》1989,5(1-3):5-36
A Markovian network process describes the movement of discrete units among a set of nodes that process the units. There is considerable knowledge of such networks, often called queueing networks, in which the nodes operate independently and the routes of the units are independent. The focus of this study, in contrast, is on networks with dependent nodes and routings. Examples of dependencies are parallel processing across several nodes, blocking of transitions because of capacity constraints on nodes, alternate routing of units to avoid congestion, and accelerating or decelerating the processing rate at a node depending on downstream congestion. We introduce a general network process representing the numbers of units at the nodes and derive its equilibrium distribution. This distribution takes the form of a product of functions of vectors in which the arguments of the functions satisfy an interchangeability property. This new type of distribution may apply to other multi-variate processes as well. A basic idea in our approach is a linking of certain micro-level balance properties of the network routing to the processing rates at the nodes. The link is via routing-balance partitions of nodes that are inherent in any network. A byproduct of this approach is a general characterization of blocking of transitions without the restriction that the process is reversible, which had been a standard assumption. We also give necessary and sufficient conditions under which a unit moving in the network sees a time average for the unmoved units (called the MUSTA property). Finally, we discuss when certain flows between nodes in an open network are Poisson processes.This research was sponsored in part by Air Force Office of Scientific Research contract 84-0367. 相似文献