全文获取类型
收费全文 | 3807篇 |
免费 | 139篇 |
国内免费 | 45篇 |
专业分类
化学 | 2494篇 |
晶体学 | 28篇 |
力学 | 136篇 |
综合类 | 2篇 |
数学 | 565篇 |
物理学 | 766篇 |
出版年
2023年 | 23篇 |
2022年 | 29篇 |
2021年 | 49篇 |
2020年 | 48篇 |
2019年 | 43篇 |
2018年 | 43篇 |
2016年 | 74篇 |
2015年 | 69篇 |
2014年 | 96篇 |
2013年 | 193篇 |
2012年 | 249篇 |
2011年 | 266篇 |
2010年 | 137篇 |
2009年 | 141篇 |
2008年 | 231篇 |
2007年 | 219篇 |
2006年 | 220篇 |
2005年 | 193篇 |
2004年 | 174篇 |
2003年 | 149篇 |
2002年 | 112篇 |
2001年 | 95篇 |
2000年 | 99篇 |
1999年 | 58篇 |
1998年 | 58篇 |
1997年 | 34篇 |
1996年 | 75篇 |
1995年 | 53篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 46篇 |
1991年 | 37篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 47篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 21篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1973年 | 19篇 |
排序方式: 共有3991条查询结果,搜索用时 109 毫秒
991.
We demonstrate continuous-wave cascaded optical parametric oscillation in which the signal field of the primary parametric oscillator internally pumps the secondary parametric oscillator. Wavelength tuning is achieved with temperature tuning and a fan-out grating structure of a dual-grating periodically poled lithium niobate crystal. Above the secondary threshold the primary signal power is clamped, and all the other output powers increase linearly with the input pump power, in accordance with theory. Cascaded parametric oscillation offers a convenient and efficient way to generate multiple tunable outputs. 相似文献
992.
Fu-Hsiang Wong Shiueh-Ling Yu Cheh-Chih Yeh Wei-Cheng Lian 《Applied Mathematics Letters》2006,19(12):1293-1299
The purpose of this work is to establish the timescale version of Lyapunov’s inequality as follows: Let be a nontrivial solution of satisfying . Then, under suitable conditions on , , and , we have where and satisfies if . Here is a timescale (see below). 相似文献
993.
As a chromatographic column, the high-speed counter-current chromatography system was equipped with a preparative HPLC series, enabling the successful isolation of hydrolysable tannins from the fruits of Terminalia chebula, a traditional Chinese medicine. The two-phase solvent system was composed of n-hexane-ethyl acetate-methanol-water (1:20:1:20 v/v). As a result, 33.2 mg chebulagic and 15.8 mg chebulinic acids were obtained in one step from 300 mg of crude extract. Their purities were determined by HPLC to be 95.3 and 96.1%, respectively. The chemical structures were identified by their MS and 1H NMR spectra. 相似文献
994.
We investigate the formation of ringlike deposits in drying drops of DNA. In analogy with the colloidal "coffee rings," DNA is transported to the perimeter by the capillary flow. At the droplet edge, however, DNA forms a lyotropic liquid crystal (LC) with concentric chain orientations to minimize the LC elastic energy. During the final stages of drying, the contact line retracts, and the radial stress causes undulations at the rim that propagate inward through the LC and form a periodic zigzag structure. We examine the phenomenon in terms of a simple model based on LC elasticity. 相似文献
995.
Uniform asymptotic formulas are obtained for the Stieltjes-Wigert polynomial, the q−1-Hermite polynomial and the q-Laguerre polynomial as the degree of the polynomial tends to infinity. In these formulas, the q-Airy polynomial, defined by truncating the q-Airy function, plays a significant role. While the standard Airy function, used frequently in the uniform asymptotic formulas for classical orthogonal polynomials, behaves like the exponential function on one side and the trigonometric functions on the other side of an extreme zero, the q-Airy polynomial behaves like the q-Airy function on one side and the q-Theta function on the other side. The last two special functions are involved in the local asymptotic formulas of the q-orthogonal polynomials. It seems therefore reasonable to expect that the q-Airy polynomial will play an important role in the asymptotic theory of the q-orthogonal polynomials. 相似文献
996.
P. H. Kropholler S. J. Pride W. A. M. Othman K. B. Wong P. C. Wong 《Semigroup Forum》2010,81(1):172-186
In this paper, we study some properties of semigroups with presentation 〈a,b ; a
p
=b
r
,a
q
=b
s
〉. We will also study their potential as platforms for the Diffie-Hellman key exchange protocol. 相似文献
997.
Ravi P. Agarwal Said R. Grace Patricia J. Y. Wong 《Journal of Applied Mathematics and Computing》2010,32(1):189-203
Some new criteria for the oscillation of third order nonlinear difference equations $$\begin{array}{l}\Delta^{2}\bigl(\frac{1}{a(k)}(\Delta x(k))^{\alpha}\bigr)+q(k)f(x[g(k)])=0\quad\mbox{and}\\[6pt]\Delta^{2}\bigl(\frac{1}{a(k)}(\Delta x(k))^{\alpha}\bigr)=q(k)f(x[g(k)])+p(k)h(x[\sigma(k)])\end{array}$$ are established. 相似文献
998.
Yuming Wei Patricia J.Y. Wong 《Journal of Computational and Applied Mathematics》2010,233(9):2189-2199
In this paper, we consider the existence of countably many positive solutions to a boundary value problem of a nonlinear delay differential equation with countably many singularities on infinite interval
999.
Is it possible to obtain an objective and quantifiable measure of risk backed up by choices made by some specific groups of rational investors? To answer this question, in this paper we establish some behavior foundations for various types of VaR models, including VaR and conditional-VaR, as measures of downside risk. In this paper, we will establish some logical connections among VaRs, conditional-VaR, stochastic dominance, and utility maximization. Though supported to some extents with unanimous choices by some specific groups of expected or non-expected-utility investors, VaRs as profiles of risk measures at various levels of risk tolerance are not quantifiable – they can only provide partial and incomplete risk assessments for risky prospects. 相似文献
1000.
The purpose of assessing past performances and setting future targets for an organisation such as a bank branch is to find where the branch stands in comparison to its peers within the bank branch network and how to improve the efficiency of its operations relatively when compared to the best practice branches. However, future performance targets may be set arbitrarily by the head-office and thus could be unrealistic and not achievable by a branch. A hybrid minimax reference point-data envelopment analysis (HMRP-DEA) approach is investigated to incorporate the value judgements of both branch managers and head-office directors and to search for the most preferred solution (MPS) along the efficient frontier for each bank branch. The HMRP-DEA approach is composed of three minimax models, including the super-ideal point model, the ideal point model and the shortest distance model, which share the same decision and objective spaces, are different from each other only in their reference points and weighting schema, and are proven to be equivalent to the output-oriented DEA dual models. These models are examined both analytically and graphically in this paper using a case study, which provides the unprecedented insight into integrated efficiency and trade-off analyses. The HMRP-DEA approach uses DEA as an ex-post-facto evaluation tool for past performance assessment and the minimax reference point approach as an ex-ante planning tool for future performance forecasting and target setting. Thus, the HMRP-DEA approach provides an alternative means for realistic target setting and better resource allocation. It is examined by a detailed investigation into the performance analysis for the fourteen branches of an international bank in the Greater Manchester area. 相似文献