全文获取类型
收费全文 | 447717篇 |
免费 | 6088篇 |
国内免费 | 1361篇 |
专业分类
化学 | 241333篇 |
晶体学 | 6533篇 |
力学 | 19060篇 |
综合类 | 14篇 |
数学 | 52716篇 |
物理学 | 135510篇 |
出版年
2021年 | 4019篇 |
2020年 | 4513篇 |
2019年 | 4892篇 |
2018年 | 6165篇 |
2017年 | 6004篇 |
2016年 | 9334篇 |
2015年 | 6035篇 |
2014年 | 9013篇 |
2013年 | 20969篇 |
2012年 | 16546篇 |
2011年 | 20327篇 |
2010年 | 14076篇 |
2009年 | 13851篇 |
2008年 | 18378篇 |
2007年 | 18208篇 |
2006年 | 16957篇 |
2005年 | 15174篇 |
2004年 | 14056篇 |
2003年 | 12292篇 |
2002年 | 12090篇 |
2001年 | 13631篇 |
2000年 | 10230篇 |
1999年 | 8072篇 |
1998年 | 6712篇 |
1997年 | 6458篇 |
1996年 | 6227篇 |
1995年 | 5594篇 |
1994年 | 5490篇 |
1993年 | 5292篇 |
1992年 | 5903篇 |
1991年 | 5993篇 |
1990年 | 5725篇 |
1989年 | 5510篇 |
1988年 | 5532篇 |
1987年 | 5417篇 |
1986年 | 5131篇 |
1985年 | 6619篇 |
1984年 | 6737篇 |
1983年 | 5327篇 |
1982年 | 5425篇 |
1981年 | 5405篇 |
1980年 | 4993篇 |
1979年 | 5382篇 |
1978年 | 5529篇 |
1977年 | 5422篇 |
1976年 | 5372篇 |
1975年 | 4938篇 |
1974年 | 4915篇 |
1973年 | 4908篇 |
1972年 | 3466篇 |
排序方式: 共有10000条查询结果,搜索用时 890 毫秒
921.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
922.
923.
In the nineteenth century, field theory brilliantly resolveda number of questions that had taxed mathematicians for centuries;for example, The circle cannot be squared by straightedge and compass, and solving polynomial equations by radicalsis not always possible. These successes have continued to beheld up as superb examples of the power of mathematical thought,and are demonstrated at an undergraduate level. The purposeof this article is to provide another such natural example whichleads to a concrete realisation of the free group on 2 generators. 相似文献
924.
925.
926.
927.
928.
The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare
earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys
has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals
ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of
Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated
for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline
multilayers has been discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
929.
930.
We consider systems of GI/M/1 type with bulk arrivals, bulk service and exponential server vacations. The generating functions of the steady-state probabilities
of the embedded Markov chain are found in terms of Riemann boundary value problems, a necessary and sufficient condition of
ergodicity is proved. Explicit formulas are obtained for the case where the generating function of the arrival group size
is rational. Resonance between the vacation rate and the system is studied. Complete formulas are given for the cases of single
and geometric arrivals.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献