全文获取类型
收费全文 | 1682篇 |
免费 | 59篇 |
国内免费 | 8篇 |
专业分类
化学 | 1027篇 |
晶体学 | 11篇 |
力学 | 47篇 |
数学 | 275篇 |
物理学 | 389篇 |
出版年
2022年 | 14篇 |
2021年 | 15篇 |
2020年 | 35篇 |
2019年 | 22篇 |
2018年 | 26篇 |
2017年 | 13篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 47篇 |
2013年 | 78篇 |
2012年 | 92篇 |
2011年 | 94篇 |
2010年 | 52篇 |
2009年 | 42篇 |
2008年 | 84篇 |
2007年 | 76篇 |
2006年 | 78篇 |
2005年 | 93篇 |
2004年 | 64篇 |
2003年 | 67篇 |
2002年 | 47篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 36篇 |
1998年 | 20篇 |
1997年 | 10篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 28篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1988年 | 9篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1974年 | 17篇 |
1973年 | 26篇 |
1969年 | 9篇 |
1904年 | 11篇 |
排序方式: 共有1749条查询结果,搜索用时 15 毫秒
1.
2.
3.
We present a method that formally calculates exact frequency shifts of an electromagnetic field for arbitrary changes in the refractive index. The possible refractive index changes include both anisotropic changes and boundary shifts. Degenerate eigenmode frequencies pose no problems in the presented method. The approach relies on operator algebra to derive an equation for the frequency shifts, which eventually turn out in a simple and physically sound form. Numerically the equations are well-behaved, easy implementable, and can be solved very fast. Like in perturbation theory a reference system is first considered, which then subsequently is used to solve another related, but different system. For our method precision is only limited by the reference system basis functions and the error induced in frequency is of second order for first-order basis set error. As an example we apply our method to the problem of variations in the air-hole diameter in a photonic crystal fiber. 相似文献
4.
5.
The mechanism of ozone formation has been studied using 16O and 18O2. High-resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end-on-addition. 相似文献
6.
Martin E. V. Pedersen Lars S. Rishøj Henrik Steffensen Sanshui Xiao Niels Asger Mortensen 《Optical and Quantum Electronics》2007,39(10-11):903-911
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals is theoretically studied. Using a scattering-matrix approach and the Wigner–Smith delay time concept, we show that optical absorbance benefits both from slow-light phenomena as well as a high filling factor of the energy residing in the liquid. Utilizing strongly dispersive photonic crystal structures, we numerically demonstrate how liquid-infiltrated photonic crystals facilitate enhanced light–matter interactions, by potentially up to an order of magnitude. The proposed concept provides strong opportunities for improving existing miniaturized absorbance cells for optical detection in lab-on-a-chip systems. 相似文献
7.
This paper investigates the mathematical well‐posedness of the variational model of quasi‐static growth for a brittle crack proposed by Francfort and Marigo in [15]. The starting point is a time discretized version of that evolution which results in a sequence of minimization problems of Mumford and Shah type functionals. The natural weak setting is that of special functions of bounded variation, and the main difficulty in showing existence of the time‐continuous quasi‐static growth is to pass to the limit as the time‐discretization step tends to 0. This is performed with the help of a jump transfer theorem which permits, under weak convergence assumptions for a sequence {un} of SBV‐functions to its BV‐limit u, to transfer the part of the jump set of any test field that lies in the jump set of u onto that of the converging sequence {un}. In particular, it is shown that the notion of minimizer of a Mumford and Shah type functional for its own jump set is stable under weak convergence assumptions. Furthermore, our analysis justifies numerical methods used for computing the time‐continuous quasi‐static evolution. © 2003 Wiley Periodicals, Inc. 相似文献
8.
This paper analyses the implications of persistent growth upon the stability properties of dynamic models. Besides the traditional concept of asymptotic stability, new stability criteria-strong/weak absolute, strong/weak relative, strong/weak logarithmic stability-are introduced, and global stability conditions for satisfying these criteria are stated for general first-order autonomous differential equations. The conflict between rapidity of growth and the degree of stability is demonstrated. Economic applications of the stability theorems are illustrated within the growth models of Harrod and Solow. 相似文献
9.
10.
Wu DY Hayes K Perl ML Barklow T Boyarski A Burchat PR Burke DL Dorfan JM Feldman GJ Gladney L Hanson G Hollebeek RJ Innes WR Jaros JA Karlen D Klein SR Lankford AJ Larsen RR LeClaire BW Lockyer NS Lüth V Ong RA Richter B Riles K Yelton JM Abrams G Amidei D Baden AR Boyer J Butler F Gidal G Gold MS Goldhaber G Golding L Haggerty J Herrup D Juricic I Kadyk JA Levi ME Nelson ME Rowson PC Schellman H Schmidke WB Sheldon PD Trilling GH Wood DR Schaad T 《Physical review D: Particles and fields》1990,41(7):2339-2342