全文获取类型
收费全文 | 6803篇 |
免费 | 805篇 |
国内免费 | 329篇 |
专业分类
化学 | 1983篇 |
晶体学 | 60篇 |
力学 | 642篇 |
综合类 | 134篇 |
数学 | 2720篇 |
物理学 | 2398篇 |
出版年
2024年 | 12篇 |
2023年 | 62篇 |
2022年 | 106篇 |
2021年 | 175篇 |
2020年 | 164篇 |
2019年 | 158篇 |
2018年 | 142篇 |
2017年 | 225篇 |
2016年 | 265篇 |
2015年 | 166篇 |
2014年 | 345篇 |
2013年 | 620篇 |
2012年 | 336篇 |
2011年 | 381篇 |
2010年 | 319篇 |
2009年 | 379篇 |
2008年 | 450篇 |
2007年 | 415篇 |
2006年 | 347篇 |
2005年 | 341篇 |
2004年 | 275篇 |
2003年 | 258篇 |
2002年 | 203篇 |
2001年 | 210篇 |
2000年 | 176篇 |
1999年 | 205篇 |
1998年 | 167篇 |
1997年 | 121篇 |
1996年 | 102篇 |
1995年 | 117篇 |
1994年 | 76篇 |
1993年 | 78篇 |
1992年 | 70篇 |
1991年 | 52篇 |
1990年 | 53篇 |
1989年 | 36篇 |
1988年 | 36篇 |
1987年 | 38篇 |
1986年 | 26篇 |
1985年 | 50篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有7937条查询结果,搜索用时 31 毫秒
41.
BAHADURASYMPTOTICEFFICIENCYINASEMIPARAMETRICREGRESSIONMODEL¥LIANGHUA;CHENGPINGAbstract:TheauthorSgiveMLEθ1MLofθ1inthemodelY=θ... 相似文献
42.
从非线性自回归模型Xt+1=-αXtλ+1+βXt+γ出发,通过变量替换Xt=aYt,推出三参数混沌动力学系统模型Yt+1=kYt(1-Ytλ)+c;采用线性回归与非线性回归相结合的改进的混合法,对模型参数作了估计;实际研究表明,该模型可以用于对国内生产总值GDP增长的研究. 相似文献
43.
A scheme for vehicle density and velocity estimation in a stretch of highway based on a modified cell transmission model [C.
F. Daganzo, Transportation Research, Part B, 28B(4),269–287, 1994. Elsevier is presented. The scheme is intended for use with on-ramp metering control algorithms, providing
local knowledge of densities and velocities that is helpful to improve on-ramp metering control performance. Estimation of
density is obtained by nonlinear estimators, while velocity estimation is obtained by gradient algorithms. There is one density–velocity
estimator for free traffic flow and other for congested traffic flow. Both estimator schemes work in parallel. The final estimation
of density and velocity results from a convex combination of the predictions of the two estimators. This combination depends
on occupancy or density measurements at the boundaries of the stretch and is produced by a fuzzy inference system. Stability
and convergence of the density and velocity estimation scheme is proved by Lyapunov based techniques. Simulation results comparing
measured and estimated traffic data are presented. They confirm good performance of the estimators.
Research sponsored by grants UNAM PAPIIT IN110403 and CONACYT 47583. 相似文献
44.
We study two estimators of the long-range parameter of a covariance stationary linear process. We show that one of the estimators
achieve the optimal semiparametric rate of convergence, whereas the other has a rate of convergence as close as desired to
the optimal rate. Moreover, we show that the estimators are asymptotically normal with a variance, which does not depend on
any unknown parameter, smaller than others suggested in the literature. Finally, a small Monte Carlo study is included to
illustrate the finite sample relative performance of our estimators compared to other suggested semiparametric estimators.
More specifically, the Monte-Carlo experiment shows the superiority of the proposed estimators in terms of the Mean Squared
Error.
The first author research was funded by the Economic and Social Research Council (ESRC) reference number: R000238212. The
second author research was funded by the Ministry of Education, Culture, Sports and Technology of Japan, reference number:
09CE2002 and B(2)10202202. 相似文献
45.
We propose objectives consisting of two mirrors with central holes for passage of a light beam. The optical layout ensures
multiple reflection of rays from both mirrors. We consider several approaches to calculating the design parameters for which
three and four aberrations do not occur. The objectives can be used in optical devices operating in the UV and IR regions
of the spectrum.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 267–270, March–April, 2007. 相似文献
46.
47.
文章讨论无界区域上GBBM方程的Cauchy问题,对方程的解进行了先验估计,并证明了在H1弱拓扑中整体吸引子的存在性. 相似文献
48.
The paper is devoted to statistical nonparametric estimation of multivariate distribution density. The influence of data pre-clustering
on the estimation accuracy of multimodal density is analyzed by means of the Monte Carlo method. It is shown that the soft
clustering is more advantageous than the hard one. While a moderate increase in the number of clusters also increases the
calculation time, it considerably reduces the estimation error. 相似文献
49.
Supply Chain Management (SCM) is an important activity in all producing facilities and in many organizations to enable vendors,
manufacturers and suppliers to interact gainfully and plan optimally their flow of goods and services. To realize this, a
dynamic modelling approach for characterizing supply chain activities is opportune, so as to plan efficiently the set of activities
over a distributed network in a formal and scientific way. The dynamical system will result so complex that it is not generally
possible to specify the functional forms and the parameters of interest, relating outputs to inputs, states and stochastic
terms by experiential specification methods. Thus the algorithm that will presented is Data Driven, determining simultaneously
the functional forms, the parameters and the optimal control policy from the data available for the supply chain. The aim
of this paper is to present this methodology, by considering dynamical aspects of the system, the presence of nonlinear relationships
and unbiased estimation procedures to quantify these relations, leading to a nonlinear and stochastic dynamical system representation
of the SCM problem. Moreover, the convergence of the algorithm will be proved and the satisfaction of the required statistical
conditions demonstrated. Thus SCM problems may be formulated as formal scientific procedures, with well defined algorithms
and a precise calculation sequence to determine the best alternative to enact. A “Certainty equivalent principle” will be
indicated to ensure that the effects of the inevitable uncertainties will not lead to indeterminate results, allowing the
formulation of demonstrably asymptotically optimal management plans. 相似文献
50.
N. A. Gasviani M. Sh. Khutsishvili L. M. Abazadze 《Russian Journal of Electrochemistry》2006,42(9):931-937
Electrochemical reduction of sodium metavanadate in an equimolar KCl-NaCl melt and the effect of acid-base properties of environment on this process are studied by a voltammetry method on a stationary platinum electrode. It is established that the limiting current of the NaVO3 electroreduction process has a kinetic nature. The process proceeds via an autoinhibition scheme and its rate is limited by an acid-base reaction conjugated with an irreversible charge transfer reaction. A substantial role of cationic composition of the melt is revealed experimentally. Following acidification of the KCl-NaCl-NaVO3 melt by Mg2+ (from MgCl2), the process passes from an irreversible kinetic regime into a reversible diffusion (quasi-diffusion) process. Values of stability constants for vanadates produced with the aid of acid-base titration of vanadium pentoxide by oxygen ions in experimental conditions are presented. These values are taken into account when calculating kinetic parameters of the NaVO3 electroreduction. 相似文献