全文获取类型
收费全文 | 4812篇 |
免费 | 408篇 |
国内免费 | 158篇 |
专业分类
化学 | 627篇 |
晶体学 | 3篇 |
力学 | 358篇 |
综合类 | 92篇 |
数学 | 3126篇 |
物理学 | 1172篇 |
出版年
2024年 | 5篇 |
2023年 | 65篇 |
2022年 | 87篇 |
2021年 | 112篇 |
2020年 | 104篇 |
2019年 | 93篇 |
2018年 | 74篇 |
2017年 | 147篇 |
2016年 | 158篇 |
2015年 | 106篇 |
2014年 | 258篇 |
2013年 | 396篇 |
2012年 | 301篇 |
2011年 | 269篇 |
2010年 | 213篇 |
2009年 | 307篇 |
2008年 | 309篇 |
2007年 | 285篇 |
2006年 | 217篇 |
2005年 | 185篇 |
2004年 | 148篇 |
2003年 | 144篇 |
2002年 | 112篇 |
2001年 | 118篇 |
2000年 | 102篇 |
1999年 | 101篇 |
1998年 | 118篇 |
1997年 | 77篇 |
1996年 | 88篇 |
1995年 | 71篇 |
1994年 | 52篇 |
1993年 | 49篇 |
1992年 | 35篇 |
1991年 | 37篇 |
1990年 | 45篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 59篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有5378条查询结果,搜索用时 62 毫秒
71.
72.
73.
A. Meister 《Mathematical Methods of Statistics》2007,16(1):63-76
This paper addresses the statistical problem of density deconvolution under the condition that the density to be estimated
has compact support. We introduce a new estimation procedure, which establishes faster rates of convergence for smooth densities
as compared to the optimal rates for smooth densities with unbounded support. This framework also allows us to relax the usual
condition of known error density with non-vanishing Fourier transform, so that a nonparametric class of densities is valid;
therefore, even the shape of the noise density need not be assumed. These results can also be generalized for fast decaying
densities with unbounded support. We prove optimality of the rates in the underlying experiment and study the practical performance
of our estimator by numerical simulations.
相似文献
74.
Characterization of semiconductor laser frequency chirp based on signal distortion in dispersive optical fiber 总被引:1,自引:0,他引:1
P. Krehlik 《Opto-Electronics Review》2006,14(2):119-124
In the paper, the simple method of laser chirp parameters estimation is presented. It is based on measuring time-domain distortions
of chirped signal transmitted through dispersive fiber and finding laser chirp parameters by matching measured distortions
to calculated ones. Experiments undertaken with 1.55 μm telecommunication grade distributed feedback (DFB) lasers and standard
single-mode fiber are described, together with some practical remarks on measurement setup and main conclusions. 相似文献
75.
本文对广义风险过程中的渐近方差作了非参数估计,得出并证明了两个定理,为广义风险过程中破产概率的区间估计作了理论准备. 相似文献
76.
Wanpracha Art Chaovalitwongse Oleg A. Prokopyev Panos M. Pardalos 《Annals of Operations Research》2006,148(1):227-250
Epilepsy is among the most common brain disorders. Approximately 25–30% of epilepsy patients remain unresponsive to anti-epileptic
drug treatment, which is the standard therapy for epilepsy. In this study, we apply optimization-based data mining techniques
to classify the brain's normal and epilepsy activity using intracranial electroencephalogram (EEG), which is a tool for evaluating
the physiological state of the brain. A statistical cross validation and support vector machines were implemented to classify
the brain's normal and abnormal activities. The results of this study indicate that it may be possible to design and develop
efficient seizure warning algorithms for diagnostic and therapeutic purposes.
Research was partially supported by the Rutgers Research Council grant-202018, the NSF grants DBI-980821, CCF-0546574, IIS-0611998,
and NIH grant R01-NS-39687-01A1. 相似文献
77.
Klaus Ziegler 《Journal of multivariate analysis》1997,62(2):233-272
Functional central limit theorems for triangular arrays of rowwise independent stochastic processes are established by a method replacing tail probabilities by expectations throughout. The main tool is a maximal inequality based on a preliminary version proved by P. Gaenssler and Th. Schlumprecht. Its essential refinement used here is achieved by an additional inequality due to M. Ledoux and M. Talagrand. The entropy condition emerging in our theorems was introduced by K. S. Alexander, whose functional central limit theorem for so-calledmeasure-like processeswill be also regained. Applications concern, in particular, so-calledrandom measure processeswhich include function-indexed empirical processes and partial-sum processes (with random or fixed locations). In this context, we obtain generalizations of results due to K. S. Alexander, M. A. Arcones, P. Gaenssler, and K. Ziegler. Further examples include nonparametric regression and intensity estimation for spatial Poisson processes. 相似文献
78.
Optimization of plate buckling resistance is very complicated, because the in-plane stress resultants in the prebuckled state of a plate are functions of thickness distribution. This paper discusses the problem of finding the optimum thickness distribution of isotropic plate structures, with a given volume and layout, that would maximise the buckling load. A simple numerical method using the finite-element analysis is presented to obtain the optimum thickness distribution. Optimum designs of compression-loaded rectangular plates with different boundary conditions and plate aspect ratios are obtained by using the proposed method. Optimum designs from earlier studies and the methods of buckling analysis used to attain these results are discussed and compared with the designs from the proposed method. This paper also examines the reliability of the optimality criterion generally used for plate buckling optimization, which is based on the uniform strain energy density. 相似文献
79.
K. Najim L. Pibouleau M. V. Le Lann 《Journal of Optimization Theory and Applications》1990,64(2):331-347
Optimization techniques are finding increasingly numerous applications in process design, in parallel to the increase of computer sophistication. The process synthesis problem can be stated as a largescale constrained optimization problem involving numerous local optima and presenting a nonlinear and nonconvex character. To solve this kind of problem, the classical optimization methods can lead to analytical and numerical difficulties. This paper describes the feasibility of an optimization technique based on learning systems which can take into consideration all the prior information concerning the process to be optimized and improve their behavior with time. This information generally occurs in a very complex analytical, empirical, or know-how form. Computer simulations related to chemical engineering problems (benzene chlorination, distillation sequence) and numerical examples are presented. The results illustrate both the performance and the implementation simplicity of this method.Nomenclature
c
i
penalty probability
-
cp
precision parameter on constraints
-
D
variation domain of the variablex
-
f(·)
objective function
-
g(·)
constraints
-
i,j
indexes
-
k
iteration number
-
N
number of actions
-
P
probability distribution vector
-
p
i
ith component of the vectorP as iterationk
-
r
number of reactors in the flowsheet
-
u(k)
discrete value or action chosen by the algorithm at iterationk
-
u
i
discrete value of the optimization variable in [u
min,u
max]
-
u
min
lowest value of the optimization variable
-
u
max
largest value of the optimization variable
-
Z
random number
-
x
variable for the criterion function
-
xp
precision parameter on criterion function
-
W(k)
performance index unit output at iterationk
-
0, 1
reinforcement scheme parameters
-
p
sum of the probability distribution vector components 相似文献
80.
Let
l
be the critical exponent associated with the probability thatl independentN-step ordinary random walks, starting at nearby points, are mutually avoiding. Using Monte Carlo methods combined with a maximum-likelihood data analysis, we find that in two dimensions 2=0.6240±0.0005±0.0011 and 3=1.4575±0.0030±0.0052, where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second error bar represents statistical error (classical 95% confidence limits). These results are in good agreement with the conformal-invariance predictions 2=5/8 and 3=35/24. 相似文献