全文获取类型
收费全文 | 608篇 |
免费 | 60篇 |
国内免费 | 60篇 |
专业分类
化学 | 292篇 |
晶体学 | 1篇 |
力学 | 50篇 |
综合类 | 22篇 |
数学 | 159篇 |
物理学 | 204篇 |
出版年
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 25篇 |
2020年 | 32篇 |
2019年 | 25篇 |
2018年 | 18篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 54篇 |
2012年 | 35篇 |
2011年 | 21篇 |
2010年 | 29篇 |
2009年 | 38篇 |
2008年 | 32篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 19篇 |
2002年 | 22篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有728条查询结果,搜索用时 15 毫秒
51.
A. Narayanan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):13-22
An effective four-level system around the D2 line
of 85Rb at room temperature, is experimentally investigated
by fluorescent studies
under the action of two driving fields L1 and L2.
This system exhibits unique features in fluorescence as a function of frequency
separation between L1 and L2. In particular, at two-photon resonance,
when the Rabi frequency of L1 exceeds that of L2,
signatures of Electromagnetically Induced Transperancy effect (EIT)
arising from the three-level Λ sub-system
is present as a sub-natural dip in fluorescence from the fourth level.
At comparable strengths of L1 and L2
the fluorescence features indicate a regime, where
the effects arising
from optical pumping and EIT effect due to ground hyperfine level coherence
coexist. We see in the coexistence regime, saturation
effects arising from difference frequency crossing (DFC) resonances and optical
pumping around the EIT window. At low strengths of L1, all signs of
coherence vanishes from the system and the fluorescent features result
from incoherent optical pumping through the
Autler-Townes split states of the excited state
hyperfine levels, which are split due to the stronger L2 laser.
The dominant role of the L1 laser in creating a robust transparency signal even
in the presence of an off-resonant excitation is brought out.
The results are supported by density matrix calculations. 相似文献
52.
53.
54.
对沱江流域金堂、简阳、内江三地河流沉积物中重金属Pb和Cd含量及其时空分布特征进行了研究,并结合与沉积物中Fe、Mn和LOI等参数的相关性对河流沉积物中Pb和Cd地球化学性质进行了初步的分析和讨论。结果表明,沱江三地沉积物中Cd、Pb含量不高,平均含量按上、中、下游次序逐渐降低;从垂向分布行为看,Cd在上游金堂地区上部含量高于下部,而中、下游两地则相反,而Pb均随着深度的增加而减少,反映了近年来人类活动所产生Pb污染的加剧;TOC、沉积物性状和上覆水体中的物化性质对于其垂向分布有着较大影响。对于深入揭示水环境中重金属的环境地球化学循环有着重要的指导意义。 相似文献
55.
用密度泛函理论中的UB3LYP方法,对W采用相对论校正赝势基组(SDD),对C、O采用6-311+G(3d)基组,研究了气相中不同自旋态W+活化CO2分解的反应机理.计算结果表明,W+活化CO2分解反应以六重态进入反应通道,经过六重态势能面到四重态势能面的系间窜越(ISC),最后产物WO+和CO以四重态离开反应通道.运用Harvey方法优化出最低能量交叉点(MECP),并计算了MECP处的自旋-轨道耦合(SOC)常数(494.95cm-1),势能面的交叉和在MECP处较强的自旋-轨道耦合作用降低了自旋禁阻反应能垒,为反应提供了一条低能反应路径,反应总放热量为122.33kJ.mol-1. 相似文献
56.
57.
An attempt was made to use thermal analysis (DTA, TG, DTG) for identification of the mineralogical composition of contemporary lake sediments. Sediments were investigated both in the natural state and after ignition at 300°C. Selected fractions of the sediments in the natural state were also studied. The thermoanalytical curves of mollusca shells, reed and plankton were also recorded for use in the interpretation of the thermoanalytical curves of sediments.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
58.
59.
We describe a method of creating an infinite family of crossing‐critical graphs from a single small planar map, the tile, by gluing together many copies of the tile together in a circular fashion. This method yields all known infinite families of k‐crossing‐critical graphs. Furthermore, the method yields new infinite families, which extend from (4,6) to (3.5,6) the interval of rationals r for which there is, for some k, an infinite sequence of k‐crossing‐critical graphs all having average degree r. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 332–341, 2003 相似文献
60.
Haru T. Pinson 《Journal of statistical physics》1994,75(5-6):1167-1177
We compute the various crossing probabilities defined by R. Langlands, P. Pouliot, and Y. Saint-Aubin for the critical percolation on the torus. 相似文献