全文获取类型
收费全文 | 8736篇 |
免费 | 268篇 |
国内免费 | 301篇 |
专业分类
化学 | 1317篇 |
晶体学 | 51篇 |
力学 | 67篇 |
综合类 | 15篇 |
数学 | 6624篇 |
物理学 | 1231篇 |
出版年
2023年 | 49篇 |
2022年 | 98篇 |
2021年 | 25篇 |
2020年 | 56篇 |
2019年 | 222篇 |
2018年 | 249篇 |
2017年 | 118篇 |
2016年 | 78篇 |
2015年 | 87篇 |
2014年 | 263篇 |
2013年 | 630篇 |
2012年 | 307篇 |
2011年 | 520篇 |
2010年 | 423篇 |
2009年 | 579篇 |
2008年 | 637篇 |
2007年 | 556篇 |
2006年 | 481篇 |
2005年 | 330篇 |
2004年 | 287篇 |
2003年 | 272篇 |
2002年 | 210篇 |
2001年 | 227篇 |
2000年 | 225篇 |
1999年 | 242篇 |
1998年 | 229篇 |
1997年 | 177篇 |
1996年 | 227篇 |
1995年 | 230篇 |
1994年 | 215篇 |
1993年 | 197篇 |
1992年 | 128篇 |
1991年 | 53篇 |
1990年 | 29篇 |
1989年 | 31篇 |
1988年 | 26篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 54篇 |
1984年 | 67篇 |
1983年 | 47篇 |
1982年 | 57篇 |
1981年 | 60篇 |
1980年 | 44篇 |
1979年 | 42篇 |
1978年 | 51篇 |
1977年 | 34篇 |
1976年 | 26篇 |
1975年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有9305条查询结果,搜索用时 15 毫秒
11.
A.K. Tashmukhamedova I.A. Stempnevskaya 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(2):91-98
The effect of the nature of the substituent in the monosubstituted derivatives of dibenzo-18-crown-6 on the reactivity and direction of the electrophilic substitution reaction of the unsubstituted benzene ring has been determined. This transfer is carried out via the macrocycle and therefore is called transannular transmission. The possible mechanism of this transmission is discussed. 相似文献
12.
J. Czarnowska 《Periodica Mathematica Hungarica》1993,26(2):101-110
To 80th birthday of Paul Erds 相似文献
13.
Riddhi Shah 《Monatshefte für Mathematik》1993,115(3):191-213
For any locally compact groupG, we show that any locally tight homomorphism from a real directed semigroup intoM
1
(G) (semigroup of probability measures onG) has a shift which extends to a continuous one-parameter semigroup. IfG is ap-adic algebraic group then the above holds even iff is not locally tight. These results are applied to give sufficient conditions for embeddability of some translate of limits of sequences of the form {v
n
kn
} and M
1
(G) such that ()=
M
, for somek>1 and AutG (cf. Theorems 2.1, 2.4, 3.7). 相似文献
14.
Existence and uniqueness of semimartingale reflecting Brownian motions in an orthant 总被引:1,自引:0,他引:1
Summary This work is concerned with the existence and uniqueness of a class of semimartingale reflecting Brownian motions which live in the non-negative orthant of
d
. Loosely speaking, such a process has a semimartingale decomposition such that in the interior of the orthant the process behaves like a Brownian motion with a constant drift and covariance matrix, and at each of the (d-1)-dimensional faces that form the boundary of the orthant, the bounded variation part of the process increases in a given direction (constant for any particular face) so as to confine the process to the orthant. For historical reasons, this pushing at the boundary is called instantaneous reflection. In 1988, Reiman and Williams proved that a necessary condition for the existence of such a semimartingale reflecting Brownian motion (SRBM) is that the reflection matrix formed by the directions of reflection be completely-L. In this work we prove that condition is sufficient for the existence of an SRBM and that the SRBM is unique in law. It follows from the uniqueness that an SRBM defines a strong Markov process. Our results have potential application to the study of diffusions arising as approximations tomulti-class queueing networks.Research supported in part by NSF Grants DMS 8657483, 8722351 and 9023335, and a grant from AT&T Bell Labs. In addition, R.J. Williams was supported in part during the period of this research by an Alfred P. Sloan Research Fellowship 相似文献
15.
JIANG Qi-Jun 《结构化学》2005,24(10):1140-1144
1 INTRODUCTION The electron-transfer reaction of C60 derivatives, especially light-induced electron-transfer reaction, has been an active research field for a long time. Many researches are focused on the long-live charge- separated state caused by electron-transfer[1]. And several electron-transfers between electron donor and C60 or intramolecular electron-transfer have been confirmed. As an example, TTF-C60 is proved to be a short-live charge-separated compound[2].Due to the excelle… 相似文献
16.
N. N. Yusubov 《Russian Chemical Bulletin》1996,45(6):1433-1436
The reactions of ()-alkylthioalkyl)phenols with formaldehyde and secondary amines afforded the corresponding aminomethyl derivatives, in which the dimethylamino group may be replaced by the alkylthio group.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1504–1507, June, 1996. 相似文献
17.
B. Gyires 《Periodica Mathematica Hungarica》1978,9(1-2):109-113
This paper contains applications of theorems of [1] for quadratic statistics which have constant regression on linear statistics. Two theorems are proved. The first is a sufficient condition which assumes that the characteristic function of a sample is an entire function. The second gives a new characterization of the normal distribution. 相似文献
18.
R. J. Williams 《Journal of Optimization Theory and Applications》1980,30(4):569-582
Mixed strategy -equilibrium points are given forN-person games with cost functions consisting of quadratic, bilinear, and linear terms and strategy spaces consisting of closed balls in Hilbert spaces. The results are applied to linear-quadratic differential games with no information and quadratic integral constraints on the control functions.This work was supported by a Commonwealth of Australia, Postgraduate Research Award. 相似文献
19.
Shie-Shien Yang 《Annals of the Institute of Statistical Mathematics》1981,33(1):463-470
Summary Let (X
1,Y
1), (X
2,Y
2),…, (X
n,Y
n) be i.i.d. as (X, Y). TheY-variate paired with therth orderedX-variateX
rn is denoted byY
rn and terms the concomitant of therth order statistic. Statistics of the form
are considered. The asymptotic normality ofT
n is established. The asymptotic results are used to test univariate and bivariate normality, to test independence and linearity
ofX andY, and to estimate regression coefficient based on complete and censored samples. 相似文献
20.
Frank J.S. Wang 《Stochastic Processes and their Applications》1977,5(2):173-193
Consider a population consisting of one type of individual living in a fixed region with area A. In [8], we constructed a stochastic population model in which the death rate is affected by the age of the individual and the birth rate is affected by the population density PA(t), i.e., the population size divided by the area A of the given region. In [8], we proposed a continuous deterministic model which in general is a nonlinear Volterra type integral equation and proved that under appropriate conditions the sequence PA(t) would converge to the solution P(t) of our integral equation in the sense that .In this paper, we obtain a “central limit theorem” for the random element √A(PA(t)?P(t)). We prove that under appropriate conditions √A(PA(t)?P(t)) will converge to a Gaussian process. (See Theorem 3.4 for the explicit formula of this Gaussian process.) 相似文献