全文获取类型
收费全文 | 217篇 |
免费 | 10篇 |
国内免费 | 9篇 |
专业分类
化学 | 48篇 |
力学 | 8篇 |
综合类 | 3篇 |
数学 | 43篇 |
物理学 | 134篇 |
出版年
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 34篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
131.
M. S. DE GROOT I. A. M. HESSELMANN J. SCHMIDT J. H. VAN DER WAALS 《Molecular physics》2013,111(1):31-43
Experiments have been performed to determine the path of entry into and exit from the phosphorescent triplet state T0 of quinoxaline in a durene host. First of all the decay of phosphorescence after flash excitation was followed at 4.2 and 1.34 °K. It was found that for both perdeutero- and perhydroquinoxaline the lifetime is shortened by a factor of about three when the temperature is lowered from 4.2 to 1.34 °K. At 1.34 °K relaxation between the spin components (i.e. re-orientation of the triplet spin angular momentum) is slow relative to the decay, and the observed reduction in lifetime indicates that entry into and exit from T0, are through the same spin component. Similar decay experiments were then carried out at 1.34 °K in a 10 kG magnetic field or in a somewhat weaker field so chosen that the effect of microwave saturation of one of the E.S.R. transitions between the components could be observed. From the results it follows that on intersystem crossing the molecules enter the manifold T0 through the top zero-field component and thus initially have their spins aligned. Decay departs almost exclusively from the same component, even in the case of perhydroquinoxaline, where at least 45 per cent of it must be radiationless. The decay route agrees with out-of-plane polarization of phosphorescence for the free molecule. Finally, spin alignment on intersystem crossing is discussed from the theoretical point of view. It appears that the phenomenon is clear-cut only in molecules such as those of the aza-aromatics, where strong spin-orbit coupling of the atomic type occurs betwen ππ? and nπ? states. 相似文献
132.
Directional wave field decomposition can be accomplished with the aid of pseudo-differential operators. A fast numerical scheme
requires sparse matrix representations of these operators. This paper focuses on designing sparse matrices for the propagator
while keeping the accuracy high at the cost of ignoring critical-angle phenomena. The matrix representation follows from a
rational approximation for the square root operator and the derivatives. The parameterization thus introduced lends itself
to an overall optimization procedure that minimizes the errors for a chosen discretization rate. As such, the approach leads
to an accurate propagator up to the (local) critical angle on a coarse numerical grid.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
133.
本文提出并实现了一种新的穆斯堡尔谱——时间相关穆斯堡尔谱。这是利用两步衰变119mTe→119Sb→119Sn而获得的。测量了110keV 119mTe加1015稳定Te/cm2注入并经600℃退火的样品在不同测量时间内的穆斯堡尔谱,分析了各谱线随ξ的变化。这里ξ是我们定义的参量,它等于ΦTe/Φ总,由退火时刻ta关键词: 相似文献
134.
135.
Abstract— The photosensitization of some biomolecules by proflavine was studied using the technique of electron paramagnetic resonance. It was shown that this process is directly influenced by the relative molar concentration of dye and substrate. For some values of these concentrations, a singlet associated with a radical form of proflavine is observed. The appearance of this signal is discussed in terms of electron transfer from an ionized proflavine molecule directly to another neutral dye molecule or via a molecule of substrate as an intermediate. It is shown that this transfer is facilitated by stacking. These results were compared with radiolysis of the same kind of complexes in frozen aqueous solution. 相似文献
136.
J.M. Weiss G.S. Abrams M.S. Alam C.A. Blocker A. Blondel A.M. Boyarski M. Breidenbach D.L. Burke W.C. Carithers W. Chinowsky M.W. Coles S. Cooper W.E. Dieterle J.B. Dillon J. Dorenbosch J.M. Dorfan M.W. Eaton G.J. Feldman H. Zaccone 《Physics letters. [Part B]》1981,101(6):439-443
We have searched 1.4 × 106e+e? annihilation events for particles with 1–3 GeV/c2 mass and charge from the processes e+e?→qX and e+e? → q. Upper limits of RQ ~ 10?4 for each process are presented which improve the previous limits on free quark production in electromagnetic interactions by 2 orders of magnitude. 相似文献
137.
D.L. Scharre G.H. Trilling G.S. Abrams M.S. Alam C.A. Blocker A. Blondel A.M. Boyarski M. Breidenbach D.L. Burke W.C. Carithers W. Chinowsky M.W. Coles S. Cooper W.E. Dieterle J.B. Dillon J. Dorenbosch J.M. Dorfan M.W. Eaton H. Zaccone 《Physics letters. [Part B]》1980,97(2):329-332
We have observed a radiative transition from the ψ to a state decaying into KSK±π?, with mass M = 1.44?0.015+0.01 GeV/c2 and width Γ = 0.05?0.02+0.03 GeV/c2. We tentatively identify this state as the E(1420). Assuming that this state is an isospin singlet, we have determined the branching fraction product . 相似文献
138.
139.
A Note on Sampling from Combinations of Distributions 总被引:1,自引:0,他引:1
A rejection technique is described for sampling from a combinationof distributions with negative weights for some of the components. 相似文献
140.
In this paper, it is demonstrated how a direct stiffness method for wavepropagation in multilayered saturated poroelastic media, based on integraltransform techniques, can be modified to account for a small amount of gasin the pores. Unsaturated media with small gas fractions can be treatedusing Smeulders extension of Biots poroelastic theory. The effect of thepresence of gas bubbles on the fluid bulk modulus and the dispersioncharacteristics of a water-saturated sand of Mol is demonstrated. Thedirect stiffness method is illustrated with a numerical example wheretransient wave propagation in a dry, saturated and unsaturated halfspaceis considered. 相似文献