全文获取类型
收费全文 | 756821篇 |
免费 | 6454篇 |
国内免费 | 2048篇 |
专业分类
化学 | 396163篇 |
晶体学 | 11147篇 |
力学 | 36148篇 |
综合类 | 26篇 |
数学 | 94157篇 |
物理学 | 227682篇 |
出版年
2020年 | 6717篇 |
2019年 | 7516篇 |
2018年 | 9889篇 |
2017年 | 10034篇 |
2016年 | 14348篇 |
2015年 | 8229篇 |
2014年 | 13312篇 |
2013年 | 32725篇 |
2012年 | 24521篇 |
2011年 | 29710篇 |
2010年 | 21738篇 |
2009年 | 21526篇 |
2008年 | 27809篇 |
2007年 | 27759篇 |
2006年 | 25582篇 |
2005年 | 23049篇 |
2004年 | 21359篇 |
2003年 | 19099篇 |
2002年 | 18961篇 |
2001年 | 20794篇 |
2000年 | 16178篇 |
1999年 | 12597篇 |
1998年 | 10702篇 |
1997年 | 10592篇 |
1996年 | 10018篇 |
1995年 | 9148篇 |
1994年 | 9043篇 |
1993年 | 8720篇 |
1992年 | 9571篇 |
1991年 | 9937篇 |
1990年 | 9551篇 |
1989年 | 9486篇 |
1988年 | 9271篇 |
1987年 | 9090篇 |
1986年 | 8627篇 |
1985年 | 11155篇 |
1984年 | 11603篇 |
1983年 | 9755篇 |
1982年 | 10237篇 |
1981年 | 9615篇 |
1980年 | 9254篇 |
1979年 | 9899篇 |
1978年 | 10470篇 |
1977年 | 10195篇 |
1976年 | 10134篇 |
1975年 | 9674篇 |
1974年 | 9579篇 |
1973年 | 9797篇 |
1972年 | 7028篇 |
1971年 | 6127篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
62.
In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed. 相似文献
63.
Dean A. Carlson 《Journal of Mathematical Analysis and Applications》2002,276(2):561-588
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate feedback Nash equilibria for a class of n-person differential games. Both the finite-horizon and infinite-horizon cases are considered. Examples are given to illustrate the presented results. 相似文献
64.
A numerical procedure, with an exact strain-displacement relationship of twisted and curved cylindrical panels having variable thickness derived by considering the Green strain tensor on general shell theory, is presented using the principle of virtual work and the Rayleigh-Ritz method with algebraic polynomials as in-plane and transverse displacement functions. The accuracy and applicability of the procedure are verified by comparing the present results with previous experimental and theoretical results for several panels. The effects of variation ratio of thickness in chordwise and lengthwise directions, twist, and curvature both in two directions aforementioned on vibrations of cylindrical panels are studied in detail, and typical vibration mode shapes are plotted to demonstrate the effects. 相似文献
65.
The Wheeler–DeWitt equation of arbitrary Hartle–Hawking factor ordering for several minisuperspace universe models, such as the pure gravity Friedmann–Robertson–Walker and Taub ones, is mapped onto the dynamics of corresponding classical oscillators. The latter ones are studied by the classical Ermakov invariant method, which is a natural approach in this context. For the more realistic case of a minimally coupled massive scalar field, one can study, within the same type of approach, the corresponding squeezing features as a possible means of describing cosmological evolution. Finally, we comment on the analogy with the accelerator physics. 相似文献
66.
A.-S. F. Obada M. Darwish H. H. Salah 《International Journal of Theoretical Physics》2002,41(9):1755-1768
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined. 相似文献
67.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991. 相似文献
68.
K. A. Bronnikov 《Annalen der Physik》1991,503(8):527-534
A multidimensional generalization of the Reissner-Nordström solution of general relativity is obtained for the case of n Ricci-flat internal spaces. A two-parameter family of black-hole solutions for an arbitrary dimensionality D is selected. Nontrivial black holes with D > 4 are shown to exist only with a nonzero electric charge. Observational consequences are discussed, in particular, a violation of Coulomb's law. 相似文献
69.
A. L. Apanasenko A. V. Kuznichenko Yu. B. Govyadovskii V. G. Yakunin 《Journal of Applied Spectroscopy》1991,54(3):271-276
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991. 相似文献
70.
A. S. Merkur'ev 《Journal of Mathematical Sciences》1991,57(6):3489-3497
This article considers the splitting properties of finite-dimensional division rings over universal splitting fields of quadratic forms. An example of a field with u-invariant equal to 6 is constructed, which contradicts Kaplansky's conjecture concerning u-invariants.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im, V. A. Steklova Akademii Nauk SSSR, Vol. 175, pp. 75–89, 1989. 相似文献