全文获取类型
收费全文 | 5782篇 |
免费 | 506篇 |
国内免费 | 230篇 |
专业分类
化学 | 1586篇 |
晶体学 | 13篇 |
力学 | 369篇 |
综合类 | 187篇 |
数学 | 2458篇 |
物理学 | 1905篇 |
出版年
2024年 | 4篇 |
2023年 | 41篇 |
2022年 | 199篇 |
2021年 | 208篇 |
2020年 | 139篇 |
2019年 | 165篇 |
2018年 | 166篇 |
2017年 | 264篇 |
2016年 | 275篇 |
2015年 | 231篇 |
2014年 | 304篇 |
2013年 | 472篇 |
2012年 | 266篇 |
2011年 | 329篇 |
2010年 | 261篇 |
2009年 | 313篇 |
2008年 | 335篇 |
2007年 | 359篇 |
2006年 | 261篇 |
2005年 | 251篇 |
2004年 | 236篇 |
2003年 | 185篇 |
2002年 | 158篇 |
2001年 | 147篇 |
2000年 | 108篇 |
1999年 | 109篇 |
1998年 | 109篇 |
1997年 | 71篇 |
1996年 | 76篇 |
1995年 | 80篇 |
1994年 | 55篇 |
1993年 | 46篇 |
1992年 | 44篇 |
1991年 | 33篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 26篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有6518条查询结果,搜索用时 31 毫秒
951.
为实现大型物理实验现场复杂多样的仪器控制,分析了物理实验的特点、过程、环境及仪器控制功能需求,利用虚拟仪器技术、计算机网络技术和数据库技术,建立了一套集成硬件和软件的综合控制管理信息系统,实现记录系统中示波器状态远程批量设置及波形数据自动采集、控制探测系统的高压电源并发加压或退压、保障各测试项目间测试仪器之间时间关联、监控UPS电量和远端现场图片或视频状态。给出了系统的关键的设计思路,列举了某型示波器控制的通用控制代码。结果表明,系统达到了一人总控或多人分权控制实验过程中多种多台仪器的目标,方便快捷地实现不同品牌不同类型示波器的相同功能。 相似文献
952.
953.
Phillips KM Wolf WR Patterson KY Sharpless KE Holden JM 《Analytical and bioanalytical chemistry》2007,389(1):219-229
Over a 6.5-year period a total of 2554 values were reported by nine laboratories for 259 certified or reference nutrient concentrations
in 26 certified reference materials (CRM) submitted to contract laboratories, blinded, as part of the qualifying process for
analytical contracts and in the routine sample stream as part of the National Food and Nutrient Analysis Program. Each value
was converted to a Z′-score, reflecting the difference from the assigned value related to the combined expected analytical uncertainty plus the
uncertainty in the CRM value. Z′-scores >|3.0| were considered unacceptable. For some nutrients (Na, folate, dietary fiber, pantothenic acid, thiamin, tocopherols,
carotenoids, monounsaturated, and polyunsaturated fatty acids), >20% of Z′-scores were >|3.0|. For total fat, vitamin C, and niacin >25% of Z′-scores were >|2.0|. Components for which CRM data were
best (more than 90% of Z′-scores <|2.0|) were Mg, P, Mn, Se, and vitamin B12. In some cases deviations from assigned values were not uniform across
laboratories and materials. For Na almost all high Z′-scores were for low-Na matrices, suggesting analytical problems related to concentration.
Figure Z′-scores for vitamins in certified reference materials
Disclaimer: Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental
procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute
of Standards and Technology, or the United States Department of Agriculture, nor is it intended to imply that the materials
or equipment identified are necessarily the best available for the purpose. 相似文献
954.
By using the unit-cube decomposition to the frequency spaces, we study the Cauchy problem for the nonlinear Schrödinger equation and the nonlinear Klein-Gordon equation. Some global well posedness results are obtained for the small Cauchy data in some modulation spaces . 相似文献
955.
The convergences of three L1 spline methods for scattered data interpolation and fitting using bivariate spline spaces are studied in this paper. That is, L1 interpolatory splines, splines of least absolute deviation, and L1 smoothing splines are shown to converge to the given data function under some conditions and hence, the surfaces from these three methods will resemble the given data values. 相似文献
956.
Nakao Hayashi Elena I. Kaikina 《Journal of Mathematical Analysis and Applications》2007,334(2):1400-1425
We study the nonlinear damped wave equation
(0.1) 相似文献
957.
Standard thermodynamic properties of minerals and phases of ternary systems Ag-Au-X (X = S, Se, Te) are determined by measuring the EMF in the cells with a common gas space and Ag4RbI5 as the solid electrolyte. By this means, thermodynamic functions of the following minerals and phases are determined: Au2S, Ag3AuS2 (uytenbogaardtite), AgAuS (petrovskaite), Ag2Se (naumannite), AuSe, Ag3AuSe2 (fischesserite), and Ag5Te3 (stuetzite). Thermodynamics of a pyrite-pyrrhotite equilibrium in the Ag-Fe-S system is studied in a cell with a solid electrolyte based on silver iodide at 500–730 K and atmospheric pressure. 相似文献
958.
A. Guilloux 《Mathematical Methods of Statistics》2007,16(3):202-216
In a population of individuals, where the random variable (r.v.) σ denotes the birth time and X the lifetime, we consider the case, where an individual can be observed only if its life-line
(σ, X) = {(σ + y, y), 0 ≤ y ≤ X} intersects a given Borel set S in ℝ × ℝ+. Denoting by σ
S and X
S the birth time and lifetime for the observed individuals, we point out that the distribution function (d.f.) F
S of the r.v. X
S suffers from a selection bias in the sense that F
S = ∝ w d F/μ
S, where w and μ
S depend only on the distribution of σ and on F, the d.f. of X. Assuming in addition that the r.v. X
S is randomly right-censored as soon as the individual is selected, we construct a productlimit estimator
for the d.f. F
S and a nonparametric estimator ŵ for the weight function w. We prove a consistency result for ŵ and a weak convergence result for
. We establish in addition an exponential bound for
.
相似文献
959.
Nicolas G. Fournier 《Journal of Heuristics》2007,13(6):587-639
A new analytical tool is presented to provide a better understanding of the search space of k-sat. This tool, termed the local value distribution , describes the probability of finding assignments of any value q′ in the neighbourhood of assignments of value q. The local value distribution is then used to define a Markov model to model the dynamics of a corresponding stochastic local
search algorithm for k-sat. The model is evaluated by comparing the predicted algorithm dynamics to experimental results. In most cases the fit of the
model to the experimental results is very good, but limitations are also recognised. 相似文献
960.
Likelihood estimation of the extremal index 总被引:1,自引:0,他引:1
Mária Süveges 《Extremes》2007,10(1-2):41-55
The article develops the approach of Ferro and Segers (J.R. Stat. Soc., Ser. B 65:545, 2003) to the estimation of the extremal index, and proposes the use of a new variable decreasing the bias of the likelihood based
on the point process character of the exceedances. Two estimators are discussed: a maximum likelihood estimator and an iterative
least squares estimator based on the normalized gaps between clusters. The first provides a flexible tool for use with smoothing
methods. A diagnostic is given for condition , under which maximum likelihood is valid. The performance of the new estimators were tested by extensive simulations. An
application to the Central England temperature series demonstrates the use of the maximum likelihood estimator together with
smoothing methods.
相似文献