全文获取类型
收费全文 | 16502篇 |
免费 | 1594篇 |
国内免费 | 1089篇 |
专业分类
化学 | 1808篇 |
晶体学 | 153篇 |
力学 | 1297篇 |
综合类 | 283篇 |
数学 | 12073篇 |
物理学 | 3571篇 |
出版年
2024年 | 35篇 |
2023年 | 137篇 |
2022年 | 170篇 |
2021年 | 257篇 |
2020年 | 413篇 |
2019年 | 426篇 |
2018年 | 416篇 |
2017年 | 472篇 |
2016年 | 513篇 |
2015年 | 382篇 |
2014年 | 659篇 |
2013年 | 1406篇 |
2012年 | 647篇 |
2011年 | 824篇 |
2010年 | 806篇 |
2009年 | 936篇 |
2008年 | 1079篇 |
2007年 | 1067篇 |
2006年 | 916篇 |
2005年 | 805篇 |
2004年 | 741篇 |
2003年 | 739篇 |
2002年 | 719篇 |
2001年 | 589篇 |
2000年 | 543篇 |
1999年 | 469篇 |
1998年 | 401篇 |
1997年 | 336篇 |
1996年 | 298篇 |
1995年 | 200篇 |
1994年 | 205篇 |
1993年 | 157篇 |
1992年 | 154篇 |
1991年 | 132篇 |
1990年 | 106篇 |
1989年 | 87篇 |
1988年 | 93篇 |
1987年 | 65篇 |
1986年 | 73篇 |
1985年 | 87篇 |
1984年 | 111篇 |
1983年 | 65篇 |
1982年 | 75篇 |
1981年 | 73篇 |
1980年 | 53篇 |
1979年 | 65篇 |
1978年 | 48篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
n阶矩阵A称为完全正的,如果A有分解:A=BBT,其中B为元素非负矩阵,B的最小可能列数称为A的分解指数.本文考察低阶双非负矩阵在整数环上的完全正分解及其分解指数. 相似文献
72.
73.
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
74.
映象方程多解问题的某些研究 总被引:1,自引:0,他引:1
本文用fp-同伦方法,在一定的技巧和变换的配合下,在紧性条件支持下,研究了赋范线性空间中一类集值映象方程的多解问题。还给出所得理论结果的一个应用。 相似文献
75.
We develop a production policy that controls work-in-process (WIP) levels and satisfies demand in a multistage manufacturing system with significant uncertainty in yield, rework, and demand. The problem addressed in this paper is more general than those in the literature in three aspects: (i) multiple products are processed at multiple workstations, and the capacity of each workstation is limited and shared by multiple operations; (ii) the behavior of a production policy is investigated over an infinite-time horizon, and thus the system stability can be evaluated; (iii) the representation of yield and rework uncertainty is generalized. Generalizing both the system structure and the nature of uncertainty requires a new mathematical development in the theory of infinite-horizon stochastic dynamic programming. The theoretical contributions of this paper are the existence proofs of the optimal stationary control for a stochastic dynamic programming problem and the finite covariances of WIP and production levels under the general expression of uncertainty. We develop a simple and explicit sufficient condition that guarantees the existence of both the optimal stationary control and the system stability. We describe how a production policy can be constructed for the manufacturing system based on the propositions derived. 相似文献
76.
77.
In the present article, we aim at treating the existence of fundamental solutions of linear partial differential operators with constant coefficients from the viewpoint of setting up explicit formulae yielding fundamental solutions. 相似文献
78.
Many biological and medical studies have as a response of interest the time to occurrence of some event, such as the occurrence of a particular symptom or disease, remission, relapse, death due to some specific disease, or simply death. In this paper we study the problem of assessing the effect of potential risk factors on the outcome event of interest through a parametric or semi-parametric frailty model where the lifetimes have a reason to be considered dependent. This dependence may arise because of multiple endpoints within the same individual or because, when studying a single endpoint, there are natural groupings between study subjects. The objective of this paper is to extend both parametric and semi-parametric approaches to regression analysis in which the lifetimes of individuals in a group are effected by the same random frailty which follows a positive stable distribution. Some comparisons of the properties of this frailty distribution with other frailty distributions are made and an example which assesses the effect of a treatment in a litter-matched tumorigenesis study is presented. 相似文献
79.
本文以fp 同伦方法为工具,借助于一些适当的变换,研究有序的(B)空间中的集值映象方程的多正解问题;在文中的有关工作中,还使用了集值映象的拟导数的某些性质. 相似文献
80.
Liquid-liquid phase equilibria of aqueous two-phase systems containing salts and polyethylene glycol 总被引:2,自引:0,他引:2
Liquid-liquid phase equilibria of the ternary systems: (a) polyethylene glycol - ammonium sulfate- water and (b) polyethylene glycol - sodium carbonate -water have been determined experimentally at 15°, 25°, 35° and 45°C and for two different molecular weights of the polymer (Avg. M.W. 1000 and 2000). Details of the glass cell and of the equilibration and analytical procedures used are described. Equilibrium data along with phase diagrams are presented. Finally the effect of temperature and of the molecular weight of the polymer are also discussed. 相似文献