全文获取类型
收费全文 | 2748篇 |
免费 | 50篇 |
国内免费 | 39篇 |
专业分类
化学 | 1740篇 |
晶体学 | 15篇 |
力学 | 74篇 |
数学 | 338篇 |
物理学 | 670篇 |
出版年
2021年 | 26篇 |
2020年 | 23篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2016年 | 34篇 |
2015年 | 30篇 |
2014年 | 40篇 |
2013年 | 106篇 |
2012年 | 100篇 |
2011年 | 130篇 |
2010年 | 80篇 |
2009年 | 55篇 |
2008年 | 120篇 |
2007年 | 148篇 |
2006年 | 123篇 |
2005年 | 111篇 |
2004年 | 111篇 |
2003年 | 103篇 |
2002年 | 105篇 |
2001年 | 79篇 |
2000年 | 73篇 |
1999年 | 57篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 50篇 |
1995年 | 38篇 |
1994年 | 48篇 |
1993年 | 46篇 |
1992年 | 47篇 |
1991年 | 29篇 |
1990年 | 42篇 |
1989年 | 41篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 50篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 41篇 |
1979年 | 35篇 |
1978年 | 46篇 |
1977年 | 37篇 |
1976年 | 33篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 39篇 |
1972年 | 15篇 |
1971年 | 15篇 |
排序方式: 共有2837条查询结果,搜索用时 15 毫秒
11.
12.
Gerald W. Evans Robert Fairbairn 《The Journal of the Operational Research Society》1989,40(11):971-981
A 0-1 integer linear programme for the selection and scheduling of US National Aeronautics and Space Administration (NASA) missions over a long planning horizon is presented. This model was formulated to allow a higher-level user-interaction with an advanced missions database currently being developed. The model implicitly considers the multi-objective nature of the problem, which results from the desire to maximize benefits in several categories as well as from the desire to minimize cost. In addition, the model allows the planner much flexibility in the selection process. This is accomplished by allowing the planner the ability to specify long- or short-term budget constraints, precursor/follow-on mission requirements, or any number of other idiosyncratic constraints which might be of importance in the decision process. Small example problems are solved in order to illustrate the approach, and areas for further research are discussed. 相似文献
13.
The Dirac equation is solved for two novel terms which describe the interaction energy between the half-integral spin of a
fermion and the classical, circularly polarized, electromagnetic field. A simple experiment is suggested to test the new terms
and the existence of radiation-induced fermion resonance. 相似文献
14.
In many metrics of physical interest, the gravitational field can be represented as an optical medium with an effective index of refraction. We show that, in such a metric, the orbits of both massive and massless particles are governed by a variational principle which involves the index of refraction and which assumes the form of Fermat's principle or of Maupertuis's principle. From this variational principle we derive exact equations of motion of Newtonian form which govern both massless and massive particles. These equations of motion are applied to some problems of physical interest. 相似文献
15.
16.
17.
Kurt V. Schenker Wolfgang Von Philipsborn C. Anderson Evans Werner Skuballa Georg-Alexander Hoyer 《Helvetica chimica acta》1986,69(7):1718-1727
The configurations of the 5,6-double bond in the carbacyclins iloprost ( 3 ; (E)) and isoiloprost ( 4 ; (Z)) are based on a complete assignment of the 13C and 1H resonances determined by 1D and 2D 13C-NMR and 1H-NMR methods. 相似文献
18.
M. Jonathan Fray Paul Allen Paul R. Bradley Clare E. Challenger Michael Closier Tim J. Evans Mark L. Lewis John P. Mathias Carly L. Nichols Yvonne M. Po-Ba Hayley Snow Mark H. Stefaniak Hannah V. Vuong 《Tetrahedron》2006,62(29):6869-6875
The synthesis of ten substituted aminomethylene tetrahydro-isoquinolines is described, proceeding in eight steps from 5-hydroxyisoquinoline via reductive amination of N-Boc tetrahydro-isoquinoline 5-carboxaldehyde. Likewise, reductive amination was used to prepare four substituted dihydro-isoindoles from the corresponding aldehyde. The dihydro-isoindole ring system was conveniently accessed via a 2+2+2 cycloaddition reaction. 相似文献
19.
The effect of intramolecular dipole-dipole interaction on polarisation at frequencies from 0 – 1012 Hz in dipolar media is investigated using a numerical solution of the Sturm-Liouville eigenvalue problem to which the governing Smoluchowski equation reduces. The results of Budó for the long-wavelength limit are extended to all frequencies up to the far infrared, where the predominant inertial effects are treated using a preliminary first-order correction. The numerical method of Pryce may be used to investigate much more realistic interaction potentials than the simple harmonic and cosine form considered by Budó. These simple forms are, however, sufficient to indicate that the integrated absorption intensity per molecule in the far infrared is very sensitive to dipole-dipole interaction and relative hydrodynamic drag on both interacting groups. Applications of the theory to the disordered solid and nematic phases are considered. 相似文献
20.
Summary Inverse gas chromatography is shown to be suitable for the study of the oxidation of vegetable oils. With air as carrier gas
characteristic plots of retention index versus time are obtained for hydroxylic test solutes that are consistent with the
oxidation behaviour of vegetable oils. Shifts of retention are found to be accompanied by changes of column efficiency due
to the oxidative crosslinking of polyunsaturated vegetable oils. The technique also leads to useful information concerning
the oxidation of antioxidant inhibited systems.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献