全文获取类型
收费全文 | 4590篇 |
免费 | 812篇 |
国内免费 | 141篇 |
专业分类
化学 | 2185篇 |
晶体学 | 11篇 |
力学 | 486篇 |
综合类 | 32篇 |
数学 | 494篇 |
物理学 | 2335篇 |
出版年
2024年 | 19篇 |
2023年 | 72篇 |
2022年 | 101篇 |
2021年 | 99篇 |
2020年 | 146篇 |
2019年 | 136篇 |
2018年 | 134篇 |
2017年 | 179篇 |
2016年 | 179篇 |
2015年 | 198篇 |
2014年 | 243篇 |
2013年 | 322篇 |
2012年 | 339篇 |
2011年 | 331篇 |
2010年 | 243篇 |
2009年 | 250篇 |
2008年 | 285篇 |
2007年 | 300篇 |
2006年 | 240篇 |
2005年 | 249篇 |
2004年 | 196篇 |
2003年 | 193篇 |
2002年 | 157篇 |
2001年 | 97篇 |
2000年 | 130篇 |
1999年 | 107篇 |
1998年 | 73篇 |
1997年 | 71篇 |
1996年 | 75篇 |
1995年 | 52篇 |
1994年 | 54篇 |
1993年 | 40篇 |
1992年 | 52篇 |
1991年 | 48篇 |
1990年 | 27篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有5543条查询结果,搜索用时 15 毫秒
51.
Yirang Yuan 《Numerical Methods for Partial Differential Equations》2003,19(5):665-681
For the coupled system of multilayer fluid dynamics in porous media, the modified characteristic finite difference fractional steps method applicable to parallel arithmetic is put forward and two‐dimensional and three‐dimensional schemes are used to form a complete set. Some techniques, such as calculus of variations, energy method, piecewise biquadratic interpolation, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L2 norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of multilayer fluid dynamics in porous media. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 665–681, 2003. 相似文献
52.
A Tandem Queue with Coupled Processors: Computational Issues 总被引:2,自引:0,他引:2
In Resing and Örmeci [16] it is shown that the two-stage tandem queue with coupled processors can be solved using the theory of boundary value problems. In this paper we consider the issues that arise when calculating performance measures like the mean queue length and the fraction of time a station is empty. It is assumed that jobs arrive at the first station according to a Poisson process and require service at both stations before leaving the system. The amount of work that a job requires at each of the stations is an independent, exponentially distributed random variable. When both stations are nonempty, the total service capacity is shared among the stations according to fixed proportions. When one of the stations becomes empty, the total service capacity is given to the nonempty station. We study the two-dimensional Markov process representing the numbers of jobs at the two stations. The problem of finding the generating function of the stationary distribution can be reduced to two different Riemann-Hilbert boundary value problems, where both problems yield a complete analytical solution. We discuss the similarities and differences between the two problems, and relate them to the computational aspects of obtaining performance measures. 相似文献
53.
注入控制铜蒸气激光方向性时间过程测量 总被引:1,自引:0,他引:1
实验研究了注入控制对铜蒸气激光非稳腔输出光束质量的影响,从输出光发散角时间分辨过程的测量结果说明注入加速被注入腔内激光发散角的减小过程。由于被注入腔内放大自发辐射的存在,为得到较好的注入控制效果,注入光的脉宽和进入被注入腔的延时必须恰当。 相似文献
54.
We consider a composite material composed of fibres included in a resin which becomes solid when it is heated up (reaction of reticulation). The mathematical modelling of the cure process is given by a kinetic equation describing the evolution of the reaction of reticulation coupled with the heat equation. In this paper, we are interested in the computation of approximate solutions. We propose a family of discretized problems depending on two parameters (β1, β2) ε [0, 1]2 which split the linear and non‐ linear terms in implicit and explicit parts. We prove the stability and convergence of the discretization for any (β1, β2) ε [½, 1 ] × [0, 1]. We present also some numerical results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
55.
A quick sample preparation method was used for the determination of sulphur and trace metals in oil and oily products by the ICP with a minitorch. Stable aqueous emulsions of oils and oil products were made by using two kinds of emulsifiers (one with low sulphur content, the other sulfonated). Aqueous standard solutions can be used for the preparation of calibration solutions. The contents of S, Al, Cr, Cu, Fe, Mg, Ni and Pb in aqueous emulsions were determined and the results were in good agreement with the composition of oil standard solutions used for control analysis procedure. 相似文献
56.
57.
58.
59.
The mechanism of the slowly opened Q-switch operation was investigated thoroughly. Maximum energy extraction from the resonator
could be optimized, and the smallest output beam divergence could be achieved. In this article, we present a detailed analysis
that has numerically verified the mode-selection mechanism in the slowly opened Q-switch operation, and the degree of the
smaller output laser beam divergence that has been achieved. The mechanism of the slowly opened Q-switch operation is the
inherent advantage of the passive saturable absorber in this operation. We can use the maximum energy extraction and the smallest
output beam divergence results of the slowly opened Q-switch operation to design and optimize various passive saturable absorbers:
plastic dye sheets, LiF:F2− color center crystals, Cr4+: YAG crystals, RG1000 color glass filters, and the single crystal semiconductor saturable absorber wafers that are in developed
in our microchip laser systems. 相似文献
60.
Hee Seok Choi Young Han Kim Shun Myung Shin 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2428-2439
An in‐line monitoring device using a quartz crystal resonator for thin film polymerization was proposed, and its performance has been evaluated by implementing in the UV polymerization of 2‐hydroxyethyl methacrylate with a photoinitiator of 1‐chloroanthraquinone. Because the variation of resonant resistance of the resonator is proportional to the square root of viscosity change that is closely related to the polymerization degree, the resistance can be used as a measure of the polymerization degree. The resistance measurements were compared with the outcome of instrumental analyses of polymerization degree using an FTIR spectrometer and a gel permeation chromatograph. The experimental results showed that the resistance measurements were consistent with the experimental outcome of the instrumental analyses, and this indicates the effectiveness of the proposed device. Owing to the simplicity and availability of the resonator system, its wide utilization in the monitoring of a variety of film polymerization processes, including photoresistor application, is expected. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2428–2439, 2006 相似文献