全文获取类型
收费全文 | 2613篇 |
免费 | 594篇 |
国内免费 | 178篇 |
专业分类
化学 | 523篇 |
晶体学 | 9篇 |
力学 | 287篇 |
综合类 | 54篇 |
数学 | 884篇 |
物理学 | 1628篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 50篇 |
2021年 | 45篇 |
2020年 | 50篇 |
2019年 | 52篇 |
2018年 | 71篇 |
2017年 | 87篇 |
2016年 | 91篇 |
2015年 | 66篇 |
2014年 | 161篇 |
2013年 | 194篇 |
2012年 | 172篇 |
2011年 | 199篇 |
2010年 | 161篇 |
2009年 | 187篇 |
2008年 | 195篇 |
2007年 | 180篇 |
2006年 | 160篇 |
2005年 | 140篇 |
2004年 | 142篇 |
2003年 | 118篇 |
2002年 | 117篇 |
2001年 | 106篇 |
2000年 | 90篇 |
1999年 | 72篇 |
1998年 | 88篇 |
1997年 | 59篇 |
1996年 | 61篇 |
1995年 | 47篇 |
1994年 | 22篇 |
1993年 | 29篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有3385条查询结果,搜索用时 46 毫秒
61.
Stefan Langer 《International Journal of Computational Fluid Dynamics》2013,27(3):131-150
For unstructured finite volume methods, we present a line implicit Runge–Kutta method applied as smoother in an agglomerated multigrid algorithm to significantly improve the reliability and convergence rate to approximate steady-state solutions of the Reynolds-averaged Navier–Stokes equations. To describe turbulence, we consider a one-equation Spalart–Allmaras turbulence model. The line implicit Runge–Kutta method extends a basic explicit Runge–Kutta method by a preconditioner given by an approximate derivative of the residual function. The approximate derivative is only constructed along predetermined lines which resolve anisotropies in the given grid. Therefore, the method is a canonical generalisation of point implicit methods. Numerical examples demonstrate the improvements of the line implicit Runge–Kutta when compared with explicit Runge–Kutta methods accelerated with local time stepping. 相似文献
62.
Bill Domoney 《Research in Mathematics Education》2013,15(1):53-67
Previous research has shown that secondary school students’ understanding of fractions is dominated by the part-whole concept to the possible detriment of their understanding of a fraction as a number in its own right. The present paper reports on an investigation into the understanding of intending primary teachers in this area. Four representatives of a cohort of sixty students on a PGCE course specialising in the lower primary age range were asked detailed questions probing their knowledge of fractions. The conclusion was that the part-whole concept dominates. All of the students were familiar with the numerical concept from their work on the PGCE course, but they reverted to the more familiar part-whole ideas in attempting to solve problems. 相似文献
63.
64.
Cannibalization is a major concern for a firm when designing a product line. In addition, external options from outside the firm’s product line may also play a significant role. In this paper, we investigate the impact of external options, represented by reservation utility, on product line design and introduction sequence. We find that: (a) heterogeneous reservation utility defines the relative attractiveness of segments and corresponding product line; (b) reservation utility makes it more favorable to introduce products sequentially rather than simultaneously; (c) aggregating segments is an effective way to mitigate cannibalization when it becomes too difficult to manage with different values of reservation utility across multiple segments; and (d) introducing products in a non-monotone order of quality can improve profit from simultaneous introduction when the value of reservation utility of a middle segment is particularly high. 相似文献
65.
María-Teresa Celis Luis H. Garcia-Rubio 《Journal of Dispersion Science and Technology》2013,34(1-3):293-299
In emulsion polymerization, the formation of particles has an important effect on the rate of reaction and on the final properties of the latex. To investigate particle nucleation mechanisms in emulsion polymerization it is necessary to establish the initial conditions of the emulsified system before the reaction takes place. This research reports on a technique to continuously monitor the droplet size distribution of liquid-liquid emulsions using spectroscopy. The on-line particle characterization methodology is based on an integrated sampling and dilution strategy combined with spectroscopy methods. It is shown that the sampling system integrated with a multiwavelength turbidity detector provides reliable estimates of droplet populations as function of the dispersed phase concentration in emulsions of saturated hydrocarbons. The results provide not only the groundwork necessary for the elucidation of particle nucleation during emulsion polymerization process but also suggests the potential of this combined technology to further our understanding of liquid-liquid emulsions. 相似文献
66.
Irene Maijó Núria Fontanals Francesc Borrull Christian Neusüß Marta Calull Carme Aguilar 《Electrophoresis》2013,34(3):374-382
The use of SPE coupled in‐line to CE using electrospray MS detection (in‐line SPE‐CE‐ESI‐MS) was investigated for the preconcentration and separation of four UV filters: benzophenone‐3, 2,2‐dihydroxy‐4‐methoxybenzophenone, 2,4‐dihydroxybenzophenone and 2‐phenylbenzimidazole‐5‐sulphonic acid. First, a CE‐ESI‐MS method was developed and validated using standard samples, obtaining LODs between 0.06 μg/mL and 0.40 μg/mL. For the in‐line SPE‐CE‐ESI‐MS method, three different sorbents were evaluated and compared: Oasis HLB, Oasis MCX, and Oasis MAX. For each sorbent, the main parameters affecting the preconcentration performance, such as sample pH, volume, and composition of the elution plug, and sample injection time were studied. The Oasis MCX sorbent showed the best performance and was used to validate the in‐line SPE‐CE‐ESI‐MS methodology. The LODs reached for standard samples were in the range between 0.01 and 0.05 ng/mL with good reproducibility and the developed strategy provided sensitivity enhancement factors between 3400‐fold and 34 000‐fold. The applicability of the developed methodology was demonstrated by the analysis of UV filters in river water samples. 相似文献
67.
68.
69.
We prove in this paper an existence result for frequency modes coupling seismic waves and vibrating tall buildings. The derivation from physical principles of a set of equations modeling this phenomenon was done in previous studies. In this model all vibrations are assumed to be anti-plane and time harmonic so the two dimensional Helmholtz equation can be used. A coupling frequency mode is obtained once we can determine a wavenumber such that the solution of the corresponding Helmholtz equation in the lower half plane with relevant Neumann and Dirichlet conditions at the interface satisfies a specific integral equation at the base of an idealized tall building. Although numerical simulations suggest that such wavenumbers should exist, as far as we know, to date, there is no theoretical proof of their existence. This is what this present study offers to provide. 相似文献
70.
From Crofton's formula for Minkowski tensors we derive stereological estimators of translation invariant surface tensors of convex bodies in the n‐dimensional Euclidean space. The estimators are based on one‐dimensional linear sections. In a design based setting we suggest three types of estimators. These are based on isotropic uniform random lines, vertical sections, and non‐isotropic random lines, respectively. Further, we derive estimators of the specific surface tensors associated with a stationary process of convex particles in the model based setting. 相似文献