全文获取类型
收费全文 | 2975篇 |
免费 | 298篇 |
国内免费 | 192篇 |
专业分类
化学 | 2120篇 |
晶体学 | 34篇 |
力学 | 128篇 |
综合类 | 15篇 |
数学 | 265篇 |
物理学 | 903篇 |
出版年
2023年 | 49篇 |
2022年 | 59篇 |
2021年 | 72篇 |
2020年 | 119篇 |
2019年 | 104篇 |
2018年 | 78篇 |
2017年 | 65篇 |
2016年 | 122篇 |
2015年 | 104篇 |
2014年 | 119篇 |
2013年 | 191篇 |
2012年 | 201篇 |
2011年 | 232篇 |
2010年 | 129篇 |
2009年 | 121篇 |
2008年 | 162篇 |
2007年 | 146篇 |
2006年 | 100篇 |
2005年 | 108篇 |
2004年 | 86篇 |
2003年 | 90篇 |
2002年 | 99篇 |
2001年 | 82篇 |
2000年 | 63篇 |
1999年 | 64篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 34篇 |
1995年 | 24篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 40篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 22篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 24篇 |
1974年 | 20篇 |
1973年 | 18篇 |
1972年 | 18篇 |
排序方式: 共有3465条查询结果,搜索用时 15 毫秒
971.
Photofabrication of periodic microstructures in azodye-doped polymers by interference of laser beams 总被引:4,自引:0,他引:4
Volume holographic gratings and two-dimensional periodic microstructures in azodye-doped polymethylmethacrylate were fabricated,
respectively, by interference of two coherent beams of a femtosecond laser and by interference of three coherent beams of
a nanosecond laser. The dependence of the first-order Bragg diffraction efficiency and the photoinduced refractive-index modulation
of the gratings on the intensity of the writing light was investigated. The measurements of the absorption spectra before
and after irradiation with the writing light suggest that the photoinduced gratings were refractive-index-modulated gratings,
which arose from a photoinduced decomposition reaction of the azodye molecules through multiphoton absorption. In the experiments
involving the interference of three beams, the period of the two-dimensional periodic microstructures was changed by adjusting
the angle between the three writing beams.
Received: 10 July 2002 / Revised version: 5 September 2002 / Published online: 20 December 2002
RID="*"
ID="*"Corresponding author. Fax: +81-774/955206, E-mail: jhsi@photon.jst.go.jp 相似文献
972.
Ohyabu N Ida K Morisaki T Narihara K Komori A Watanabe K Narushima Y Nagayama Y Shoji M Ashikawa N Emoto M Funaba H Goto M Idei H Ikeda K Inagaki S Inoue N Isobe M Khlopenkov K Kobuchi T Kostrioukov A Kubo S Kumazawa R Liang Y Masuzaki S Minami T Miyazawa J Morita S Muto S Mutoh T Murakami S Nakamura Y Nakanishi H Nishimura K Noda N Notake T Ohkubo K Ohdachi S Oka Y Osakabe M Ozaki T Peterson BJ Sakamoto R Sakakibara S Sagara A Saito K Sasao M Sato K Sato M Seki T Shimozuma T Sudo S Suzuki H 《Physical review letters》2002,88(5):055005
In the Large Helical Device plasma discharges, the size of an externally imposed island with mode number ( n/m = 1/1) decreases substantially when the plasma is collisionless ( nu(*)< approximately 1) and the beta is finite ( > approximately 0.1%) at the island location. For the collisional plasmas with finite beta, on the other hand, the size of the island increases. However, there is a threshold in terms of the vacuum island size below which the island enlargement is not seen. 相似文献
973.
Experiments in heavy-fermion metals and related theoretical work suggest that critical local-moment fluctuations can play an important role near a zero-temperature phase transition. We study such fluctuations at the quantum critical point of a Kondo impurity model in which the density of band states vanishes as /epsilon/(r) at the Fermi energy (epsilon=0). The local spin response is described by a set of critical exponents that vary continuously with r. For 0相似文献
974.
Psilocin analogs having either a formyl group (9-12) or a bromine atom (13-18) at the 5- or 7-position have been prepared for the first time. Syntheses of 5- and 7-bromo derivatives of 4-hydroxy- (23, 24, 28) and 4-benzyloxyindole-3-carbaldehyde (19, 25, 29, 30), 4-benzyloxyindole-3-acetonitriles (20, 31), and 4-benzyloxy-N,N-dimethyltryptamine (32, 34, 35) have also been established. 相似文献
975.
We report the synthesis of alpha-AlReSi and show that it is a 1/1-cubic approximant phase of the icosahedral quasicrystal with a = 12.9 A. The trend of the resistivity of the new approximant phase shows a nonmetallic character, similar to those seen in the stable icosahedral phases. The resistivity depends sensitively on the Re concentration and the nonmetallic transport is observed only at the Re concentration close to 17.4 at. %, where the transition metal sites in the icosahedral cluster are exclusively occupied by Re atoms. In view of a recent ab initio calculation, the present result suggests strongly the formation of the virtual bound states, or confinement of electrons, in the icosahedral clusters of transition metal atoms. 相似文献
976.
54-fs, 10-GHz soliton generation from a polarization-maintaining dispersion-flattened dispersion-decreasing fiber pulse compressor 总被引:2,自引:0,他引:2
A 10-GHz train of nearly transform-limited 54-fs soliton pulses was generated by adiabatic compression of the output of a mode-locked fiber laser with a polarization-maintaining dispersion-flattened dispersion-decreasing fiber. The peak-to-pedestal ratio exceeded 23 dB. At high input powers, the pulse width was reduced to as short as 43 fs, although the wings of the pulse were degraded and the jitter increased. The compression properties are different for the two polarization axes, owing to their different dispersion characteristics. The output polarization exhibits no drift. 相似文献
977.
Experimental tie-line data have been determined for the ternary system water + methyl tert-butyl ether + tert-amyl methyl ether and the quaternary systems water + methanol + methyl tert-butyl ether + tert-amyl methyl ether, and water + ethanol + methyl tert-butyl ether + tert-amyl methyl ether at 25°C and ambient pressure. The experimental results have been satisfactorily correlated using the modified UNIQUAC and extended UNIQUAC models with ternary and quaternary, in addition to binary parameters. 相似文献
978.
979.
基于新近提出的具有最佳超收敛阶的单元能量投影(EEP)超收敛算法,提出用具有最佳超收敛阶的EEP超收敛解对有限元解进行误差估计,用均差法进行网格划分,用拟有限元解进行多次遍历而不反复求解有限元真解,形成一套新型的一维有限元自适应求解策略.该法理论上简明清晰,算法上高效可靠,对于大多数问题,一步自适应迭代便可给出按最大模度量逐点满足误差限的有限元解答.以二阶椭圆型常微分方程模型问题为例,介绍了该法的基本思想、实施策略及具体算法,并给出具有代表性的数值算例,以展示该法的优良性能和效果. 相似文献
980.
The norm convergence of the Trotter–Kato product formula with error bound is shown for the semigroup generated by that operator sum of two nonnegative selfadjoint operators A and B which is selfadjoint.An erratum to this article can be found at 相似文献