全文获取类型
收费全文 | 779篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 407篇 |
晶体学 | 42篇 |
力学 | 40篇 |
数学 | 95篇 |
物理学 | 204篇 |
出版年
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 24篇 |
2013年 | 57篇 |
2012年 | 35篇 |
2011年 | 38篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 19篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1990年 | 6篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1972年 | 9篇 |
1970年 | 7篇 |
1964年 | 6篇 |
排序方式: 共有788条查询结果,搜索用时 15 毫秒
51.
52.
The 4-hydroxy buteneolide terminus 3, applicable to mucocin 1 and related annonaceous acetogenins, was prepared in an expeditious manner from the selenocarbonate 2 via an intramolecular acyl radical cyclization followed by an enantioselective Lewis-acid catalyzed Keck-allylation reaction. 相似文献
53.
N.Sreedhara Murthy N.S. Bapat T. Manisekaran 《Journal of Quantitative Spectroscopy & Radiative Transfer》1983,30(4):381-383
A method is proposed for estimation of the vibrational anharmonicity constants ωeχe of diatomic molecules. The procedure involves fitting of the potential energy curve obtained by the RKRV method with that obtained by using the 5-parameter Hulburt-Hirschfelder potential function. We have predicted values of ωeχe for alkali halides for which accurate data are not available. 相似文献
54.
55.
56.
The quantum-mechanical methods (EHT and CNDO /2) have been applied to the homoallylic cation. Both methods successfully predict that the ion need not be represented as a nonclassical structure. 相似文献
57.
A careful discussion is given of the definitions of “target asymmetry” and “effective neutron polarization” in the reaction with polarized deuterons. The connection between the analyzing powers, Tqk of the reaction and the target asymmetry, T is established taking into account the method of preparation of the polarized target. It is further shown that the concept of effective neutron polarization Peff is valid only in a very approximate way, even when the target deuteron is purely vector polarized. 相似文献
58.
The overall Kaplan-Meier estimate of the survival curve underlying a study population does not individually account for the ages at which patients were first seen and thence followed up in the study. Since the number of patients in these age-specific subgroups varies quite arbitrarily for a given study, the overall Kaplan-Meier curve which assumes that all patients were seen from the beginning of the study usually either overestimates or underestimates the survival probability, depending on the varying sample sizes. In this paper, we therefore propose an estimate of the overall survival curve underlying a study population based on the individual age-specific Kaplan-Meier estimates and the probability distribution of the age at which patients were first seen in the study. In the particular case when there is no censoring, it is shown that the usual overall Kaplan-Meier survival curve which assumes that all patients irrespective of their age at entry into the study were followed from the beginning of the study is identical with the proposed estimate. This result does not seem to necessarily hold good in the presence of arbitrary censoring. Further, the estimate is unbiased and consistent, a property which the Kaplan-Meier estimate also enjoys. The efficiency of the proposed estimate relative to the Kaplan-Meier estimate is being investigated and will be reported along with results of its application in a separate communication. 相似文献
59.
Recent experiments on quantum Hall bilayers near total filling factor 1 have demonstrated that they support an imperfect two-dimensional superfluidity, in which there is nearly dissipationless transport at nonvanishing temperature observed both in counterflow resistance and interlayer tunneling. We argue that this behavior may be understood in terms of a coherence network induced in the bilayer by disorder, in which an incompressible, coherent state exists in narrow regions separating puddles of dense vortex-antivortex pairs. A renormalization group analysis shows that it is appropriate to describe the system as a vortex liquid. We demonstrate that the dynamics of the nodes of the network leads to a power law temperature dependence of the tunneling resistance, whereas thermally activated hops of vortices across the links control the counterflow resistance. 相似文献
60.
Murthy G 《Physical review letters》2000,84(2):350-353
It is well known that the nu = 2/5 state is unpolarized at zero Zeeman energy, while it is fully polarized at large Zeeman energies. A novel state with a charge/spin density wave order for composite fermions is proposed to exist at intermediate values of the Zeeman coupling for nu = 2/5. This state has half the maximum possible polarization, and can be extended to other incompressible fractions. A Hartree-Fock calculation based on the new approach for all fractional quantum Hall states developed by R. Shankar and the author is used to demonstrate the stability of this state to single-particle excitations and to compute gaps. A very recent experiment shows direct evidence for this state. 相似文献