全文获取类型
收费全文 | 378571篇 |
免费 | 3408篇 |
国内免费 | 1144篇 |
专业分类
化学 | 164769篇 |
晶体学 | 5374篇 |
力学 | 15531篇 |
综合类 | 7篇 |
数学 | 38464篇 |
物理学 | 109746篇 |
无线电 | 49232篇 |
出版年
2021年 | 3510篇 |
2020年 | 3777篇 |
2019年 | 4244篇 |
2018年 | 5721篇 |
2017年 | 5871篇 |
2016年 | 8060篇 |
2015年 | 4368篇 |
2014年 | 7657篇 |
2013年 | 17086篇 |
2012年 | 13092篇 |
2011年 | 15664篇 |
2010年 | 11960篇 |
2009年 | 12444篇 |
2008年 | 15110篇 |
2007年 | 15626篇 |
2006年 | 14510篇 |
2005年 | 12756篇 |
2004年 | 11901篇 |
2003年 | 10689篇 |
2002年 | 10592篇 |
2001年 | 12293篇 |
2000年 | 9545篇 |
1999年 | 7633篇 |
1998年 | 6594篇 |
1997年 | 6403篇 |
1996年 | 5921篇 |
1995年 | 5219篇 |
1994年 | 5137篇 |
1993年 | 4979篇 |
1992年 | 5406篇 |
1991年 | 5515篇 |
1990年 | 5232篇 |
1989年 | 4959篇 |
1988年 | 4638篇 |
1987年 | 4424篇 |
1986年 | 4111篇 |
1985年 | 5140篇 |
1984年 | 5181篇 |
1983年 | 4311篇 |
1982年 | 4315篇 |
1981年 | 4019篇 |
1980年 | 3907篇 |
1979年 | 4151篇 |
1978年 | 4122篇 |
1977年 | 4114篇 |
1976年 | 4062篇 |
1975年 | 3878篇 |
1974年 | 3776篇 |
1973年 | 3816篇 |
1972年 | 2730篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The energy levels and oscillator strengths for dipole transitions between the levels of low-lying configurations are calculated for ions of the KI isoelectronic sequence. The calculations are based on the energy approach to the effective potential method with the most important polarization effects taken into account, including core polarization by the outer electron. The results, some of which are obtained here for the first time for potassium-like ions, can be useful in a number of related fields, such as laser physics, plasmas, and so on.Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–9, November, 1992. 相似文献
992.
993.
Michael S. Roddy 《Order》1994,11(1):1-9
Theretracts (idempotent, isotone self-maps) of an ordered set are naturally ordered as functions. In this note we characterize the possible ways that one retract can cover another one. This gives some insight into the structure of the ordered set of retracts and leads to a natural generalization of the core of an ordered set.Supported by NSERC Operating Grant 41702. 相似文献
994.
Song I. Kassam S.A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(4):1311-1322
Nonparametric detection of a zero-mean random signal in additive noise is considered. The locally optimum detector based on signs and ranks of observations is derived, for good weak-signal detection performance under any specified noise probability density function. This detector is shown to have interesting similarities to the locally optimum detector for random signals. It may also be viewed as a generalization of the locally optimum rank detector for known signals. Examples of the test statistic of the detector are given for some specific noise probability density functions. Asymptotic and finite sample-size performance of the locally optimum rank detector is also considered 相似文献
995.
996.
Let M be a symplectic manifold with a Hamiltonian circle action with isolated fixed points. We prove that σ (M) = b0(M) − b2(M) + b4(M) − b6(M) + … where σ (M) is the signature of M and bi(M) is the ith Betti number of M. 相似文献
997.
P. I. H. Bastiaens S. G. Mayhew E. M. O'Naulláin A. van Hoek A. J. W. G. Visser 《Journal of fluorescence》1991,1(2):95-103
Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems. 相似文献
998.
The diffusion of Ni on a Si (111) surface is investigated by LEED and Auger electron spectroscopy. It is found that, in contrast
to the process on the initially clean Si (111)−7×7 surface, on Si (111) surfaces with submonolayer Co coverages the nature
of the Ni transport mechanism changes at a temperature of about 750 °C, and the Ni surface diffusion coefficients increase
sharply below this temperature.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 611–614 (10 November 1997) 相似文献
999.
The beam divergence in the vertical direction from a graded index separate confinement heterostructure (GRINSCH) multiquantum-well (MQW) laser has been studied. It is demonstrated both theoretically and experimentally that a circular beam MQW laser can be produced by choosing appropriate thicknesses for the GRINSCH layers, while maintaining other desired laser characteristics. The beam divergence is found to be more affected by the index change induced by injected carriers than by strain in the MQW active layer. Theoretical results are in good agreement with the measurements for 1.3-μm InGaAsP strained MQW lasers 相似文献
1000.
A. S. Il'inskii S. V. Trubnikov N. A. Fedoseeva 《Computational Mathematics and Modeling》1994,5(3):195-202
Translated from Matematicheskie Modeli i Optimizatsiya Vychislitel'nykh Algoritmov, pp. 131–143, 1993. 相似文献