全文获取类型
收费全文 | 15726篇 |
免费 | 2655篇 |
国内免费 | 1317篇 |
专业分类
化学 | 3426篇 |
晶体学 | 236篇 |
力学 | 4379篇 |
综合类 | 191篇 |
数学 | 2907篇 |
物理学 | 8559篇 |
出版年
2024年 | 40篇 |
2023年 | 154篇 |
2022年 | 435篇 |
2021年 | 465篇 |
2020年 | 460篇 |
2019年 | 409篇 |
2018年 | 422篇 |
2017年 | 556篇 |
2016年 | 652篇 |
2015年 | 576篇 |
2014年 | 816篇 |
2013年 | 1320篇 |
2012年 | 917篇 |
2011年 | 1047篇 |
2010年 | 879篇 |
2009年 | 948篇 |
2008年 | 1030篇 |
2007年 | 1105篇 |
2006年 | 985篇 |
2005年 | 867篇 |
2004年 | 704篇 |
2003年 | 709篇 |
2002年 | 589篇 |
2001年 | 542篇 |
2000年 | 505篇 |
1999年 | 419篇 |
1998年 | 419篇 |
1997年 | 292篇 |
1996年 | 216篇 |
1995年 | 190篇 |
1994年 | 194篇 |
1993年 | 143篇 |
1992年 | 115篇 |
1991年 | 94篇 |
1990年 | 84篇 |
1989年 | 50篇 |
1988年 | 46篇 |
1987年 | 51篇 |
1986年 | 45篇 |
1985年 | 55篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 8篇 |
1976年 | 17篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
42.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献
43.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
44.
溃坝问题的间断有限元方法 总被引:2,自引:0,他引:2
本文研究90年代初提出的Runge-Kutta间断Galerkin有限元方法,给出该方法的精度分析,通过经典算例验证该方法处理间断问题、捕捉锐利波形的能力,并将其推广到求解浅水问题.针对坝底无摩擦,无坡度的理想情形进行讨论,给出方溃坝和圆溃坝问题的数值模拟结果. 相似文献
45.
46.
本文采用高分辨率格式和多块多网格方法求解雷诺平均Navier-Stokes方程,数值模拟多排叶片内的三维粘性流动;使用数值激盘模拟叶片排的存在,研究叶片排与非轴对称排气部件之间的相互作用以及复杂的内部流动。文中描述了数值方法,给出了NASA透平导叶和单级透平内部流场的数值结果及其与相应实验结果的对比,也给出了多级透平内部流场的数值结果,以及透平与排气部件之间的耦合流场的结果。 相似文献
47.
E. de A. Gonçalves V. M. de Oliveira A. Rosas P. R.A. Campos 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):127-132
Adaptation of populations takes place with the occurrence and subsequent fixation of mutations that confer some selective
advantage
to the individuals which acquire it. For this reason, the study of the process of fixation of advantageous mutations has a
long history
in the population genetics literature. Particularly, the previous investigations aimed to find out the main evolutionary forces
affecting the strength of natural selection in the populations.
In the current work, we investigate the dynamics of fixation of beneficial mutations in a subdivided population. The subpopulations
(demes)
can exchange migrants
among their neighbors, in a migration network which is assumed to have either a random graph or a scale-free topology. We
have observed that the migration rate
drastically affects the dynamics of mutation fixation, despite of the fact that the probability of fixation is invariant on
the
migration rate, accordingly to
Maruyama's conjecture. In addition, we have noticed a topological dependence of the adaptive evolution of the population when
clonal interference
becomes effective. 相似文献
48.
J. Schulte 《Journal of statistical physics》1993,70(5-6):1343-1347
The thermodynamic stability of4He4–13 at 3.2 K is investigated with the classical Monte Carlo method, with the semiclassical path-integral Monte Carlo (PIMC) method, and with the semiclassical all-order many-body method. In the all-order many-body simulation the dipole-dipole approximation including short-range correction is used. The resulting stability plots are discussed and related to recent TOF experiments by Stephens and King. It is found that with classical Monte Carlo of course the characteristics of the measured mass spectrum cannot be resolved. With PIMC, switching on more and more quantum mechanics. by raising the number of virtual time steps results in more structure in the stability plot, but this did not lead to sufficient agreement with the TOF experiment. Only the all-order many-body method resolved the characteristic structures of the measured mass spectrum, including magic numbers. The result shows the influence of quantum statistics and quantum mechanics on the stability of small neutral helium clusters. 相似文献
49.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation. 相似文献
50.