全文获取类型
收费全文 | 307476篇 |
免费 | 2922篇 |
国内免费 | 1010篇 |
专业分类
化学 | 160771篇 |
晶体学 | 5030篇 |
力学 | 13554篇 |
综合类 | 10篇 |
数学 | 33494篇 |
物理学 | 98549篇 |
出版年
2020年 | 2370篇 |
2019年 | 2539篇 |
2018年 | 3234篇 |
2017年 | 3086篇 |
2016年 | 4865篇 |
2015年 | 3164篇 |
2014年 | 4737篇 |
2013年 | 13165篇 |
2012年 | 10032篇 |
2011年 | 12307篇 |
2010年 | 8278篇 |
2009年 | 7992篇 |
2008年 | 11113篇 |
2007年 | 11257篇 |
2006年 | 10947篇 |
2005年 | 10031篇 |
2004年 | 9190篇 |
2003年 | 8192篇 |
2002年 | 7974篇 |
2001年 | 9075篇 |
2000年 | 7036篇 |
1999年 | 5518篇 |
1998年 | 4543篇 |
1997年 | 4548篇 |
1996年 | 4271篇 |
1995年 | 4074篇 |
1994年 | 3720篇 |
1993年 | 3631篇 |
1992年 | 4117篇 |
1991年 | 4058篇 |
1990年 | 3967篇 |
1989年 | 3773篇 |
1988年 | 3828篇 |
1987年 | 3821篇 |
1986年 | 3575篇 |
1985年 | 4754篇 |
1984年 | 5052篇 |
1983年 | 4208篇 |
1982年 | 4597篇 |
1981年 | 4420篇 |
1980年 | 4324篇 |
1979年 | 4425篇 |
1978年 | 4603篇 |
1977年 | 4550篇 |
1976年 | 4635篇 |
1975年 | 4363篇 |
1974年 | 4227篇 |
1973年 | 4510篇 |
1972年 | 2861篇 |
1971年 | 2201篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
The authors study a one-dimensional model for optical tunnellingwith a refractive index in the shape of a square well. The relevanceof the model and its limiting cases are discussed. The mainresult is the leading behaviour of the exponentially small imaginarypart of the eigenvalue which determines the radiation loss.The leading behaviour of the imaginary part is calculated usingBerry's formula which controls the asymptotic expansion of theAiry function Bi(z) to better-than-exponential accuracy. 相似文献
82.
Ingrid Lukkari Jaromir Ruzicka Gary D. Christian 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):813-818
Summary Automated methods for the determination of ammonium and ammonia are reviewed, and techniques based on gas diffusion using a semi-permeable membrane were selected for the determination of both total ammonium-nitrogen and free ammonia in fermentation samples. A simple and robust instrument based on sequential injection analysis (SIA) consisting of a piston pump and two selector valves was used. Two different methods of ammonia detection, the Berthelot method and detection using pH-indicators, have been evaluated and compared. The indicator method showed higher reproducibility and the range of determination could easily be adjusted to match the concentrations of the samples. The range of determination could be adjusted from 0.05 mmol/l to 350 mmol/l, depending on choice of acceptor solution. This method has been evaluated with fermentation medium samples and tested on-line in a yeast fermentation process.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
83.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
84.
85.
The Mathematical Intelligencer encourages comments about the material in this issue. Letters to the editor should be sent
to either of the editors-in-chief, Chandler Davis or Marjorie Senechal. 相似文献
86.
87.
A modernized conception of hierarchical structure of reality is proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–6, December, 1980. 相似文献
88.
The classical (first integral) methods of studying restrictions on the possible motion of gravitationally interacting bodies are reviewed. The simple and flexible inequality method is extended to a similar approach to the relationship between possible forbidden motion and (asymptotic) symmetries in the relativistic few-body problem. This extended method is used to reproduce the standard results of bounded motion for a test particle in a Schwarzschild geometry. The existence of bounded motion is shown for the general relativistic few-body problem and the difficulties in determining such bounded motion is analysed. The use of this approach to obtaining a relativistic alternative to the classical Roche lobe analysis in contact binaries is discussed. 相似文献
89.
J. W. Barrett 《International Journal of Theoretical Physics》1991,30(9):1171-1215
This article is about a different representation of the geometry of the gravitational field, one in which the paths of test bodies play a crucial role. The primary concept is the geometry of the motion of a test body, and the relation between different such possible motions. Space-time as a Lorentzian manifold is regarded as a secondary construct, and it is shown how to construct it from the primary data. Some technical problems remain. Yang-Mills fields are defined by their holonomy in an analogous construction. I detail the development of this idea in the literature, and give a new version of the construction of a bundle and connection from holonomy data. The field equations of general relativity are discussed briefly in this context. 相似文献
90.
We consider three one-dimensional quantum, charged and spinless particles interacting through delta potentials. We derive
sufficient conditions which guarantee the existence of at least one bound state. 相似文献