全文获取类型
收费全文 | 3173篇 |
免费 | 71篇 |
国内免费 | 6篇 |
专业分类
化学 | 1974篇 |
晶体学 | 65篇 |
力学 | 99篇 |
数学 | 606篇 |
物理学 | 506篇 |
出版年
2023年 | 12篇 |
2022年 | 144篇 |
2021年 | 127篇 |
2020年 | 50篇 |
2019年 | 62篇 |
2018年 | 77篇 |
2017年 | 71篇 |
2016年 | 113篇 |
2015年 | 100篇 |
2014年 | 126篇 |
2013年 | 231篇 |
2012年 | 197篇 |
2011年 | 197篇 |
2010年 | 164篇 |
2009年 | 141篇 |
2008年 | 176篇 |
2007年 | 145篇 |
2006年 | 129篇 |
2005年 | 117篇 |
2004年 | 103篇 |
2003年 | 83篇 |
2002年 | 60篇 |
2001年 | 35篇 |
2000年 | 39篇 |
1999年 | 26篇 |
1998年 | 30篇 |
1997年 | 27篇 |
1996年 | 34篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 37篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 23篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1974年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有3250条查询结果,搜索用时 15 毫秒
51.
Good optical quality U3+-doped PbCl2 single crystals of the composition Pb0.99U0.01Cl2 have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded in a wide spectral range at room and liquid nitrogen temperatures, and are discussed. Strong infrared emission was observed under 514 nm laser pumping to the 5f26d1 bands. The lifetimes of the emitting levels in the visible and near infrared region are given. 相似文献
52.
The paper reports the results of numerical studies on the laser-driven acceleration of super-heavy ions by a multi-PW laser pulse of ultra-relativistic intensity attainable with the Extreme Light Infrastructure lasers currently being built in Europe. Using a multi-dimensional (2D3V) particle-in-cell code, it is shown that multi-GeV super-heavy (thorium) ion beams with an intensity of , fluence and time duration can be produced from a sub-μm thorium target irradiated by a 150-J, 20-fs laser pulse with an intensity of . Such ion beams are impossible to obtain presently with the use of conventional RF-driven accelerators, so they can open the door to new areas of research in both nuclear and high energy-density physics. 相似文献
53.
Jarosław Pykacz 《International Journal of Theoretical Physics》1994,33(7):1403-1416
A new, physically more plausible definition of a fuzzy quantum logic is proposed. It is shown that this definition coincides with the previously studied definition of a fuzzy quantum logic; therefore it defines objects which are traditional quantum logics with ordering sets of states. The new definition is expressed exclusively in terms of fuzzy set operations which are generated by connectives of multiple-valued logic studied by ukasiewicz at the beginning of the 20th century. Therefore, the logic of quantum mechanics is recognized as a version of infinite-valued ukasiewicz logic. 相似文献
54.
Miros?aw Kwiatkowski 《Applied Surface Science》2011,257(21):8912-8922
The aim of this work has been to analyze the problems related to the identification of microporous structure parameters of carbonaceous materials. The new methods for microporous structure parameters identification have been explored with special focus on the influence of the analyzed relative pressure range on the reliability of parameters identification. For that purpose, the adsorption isotherm of nitrogen on active carbon for different ranges of relative pressures p/p0 was analyzed. The conducted research was to provide for an answer to the question of whether the range of the analyzed relative pressures has any effect on the quality of adsorption system parameters identification, as well as what range of the relative pressure permits execution of the reliable identification of microporous structure parameters. 相似文献
55.
This paper presents a system that accurately measures the distance travelled by ultrasound waves through the air. The simple design of the system and its obtained accuracy provide a tool for non-contact distance measurements required in the laser’s optical system that investigates the surface of the eyeball. 相似文献
56.
Bogusław Zegarliński 《Communications in Mathematical Physics》1984,96(2):195-221
The uniqueness and the global Markov property for the regular Gibbs measure corresponding to the interaction $$U_\Lambda (\varphi ): = \lambda \int\limits_\Lambda {d_2 x\int {d\varrho (\alpha ):e^{\alpha \varphi } :_0 (x)} } $$ [forλ>0,d?(α) a probability measure with support in \(( - 2\sqrt {\pi ,} 2\sqrt \pi )\) ] is proved. 相似文献
57.
Dariusz?BochenekEmail author Przemys?aw?Niemiec Izabela?Szafraniak-Wiza Ma?gorzata?Adamczyk Ryszard?Skulski 《The European Physical Journal B - Condensed Matter and Complex Systems》2015,88(10):277
In the paper the influence of mechanical activation of the powder on the final dielectric properties lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic was examined. The BFN ceramics were obtained by 3-steps route. Firstly, the substrates were pre-homogenized in a planetary ball mill. Than, the powder was activated in vibratory mill (the shaker type SPEX 8000 Mixer Mill) for different duration between 25 h and 100 h. The influence of the milling time on the BFN powder was monitored by X-ray diffraction. The diffraction data confirmed that the milling process of the starting components is accompanied by partial synthesis of the BFN materials. The longer of the high-energy milling duration the powders results in increasing the amount of amorphous/nanocrystalline content. The mechanically activated materials were sintered in order to obtain the ceramic samples. During this temperature treatment the final crystallisation of the powder appeared what was confirmed by XRD studies. The performed dielectric measurements have revealed the reduction of the dielectric loss of the BFN ceramics compared to materials obtained by classic methods. 相似文献
58.
In the paper methods of the terahertz photomixer operational frequency estimation are considered. Three methods are investigated — estimation of the frequency via direct measurements of the laser heterodyne compounds, via calculations from datasheets, and via calculations from raw collected data obtained from the photomixer system. 相似文献
59.
The complexation of L ‐ and D ‐enantiomers of phenylglycine, phenylalanine, and tryptophan with D ‐mannonaphto‐crown‐6‐ether in methanol solution was studied by NMR and isothermal titration calorimetry (ITC) at 298.15 K. The total heat effects attributed to the binding phenomena were measured in the range of 1.8 to 7.7 mJ, and the complexation was found stereo‐specific. The binding topologies were estimated basing on 1H 2D‐ROESY experiments. The analysis of Job plots obtained from 1H NMR‐monitored titrations proved the coexistence of 1:1 and 1:2 (crown ether:amino acids) complexes, which thermodynamic parameters, Ks, ΔG, ΔH°, and TΔS were determined with the aid of ITC. The 1:1 complexes were found enthalpically stabilized, generally by electrostatic interactions between the charged NH group of amino acid and crown ether macrocyclic moiety, while the binding of the second amino acid molecule was driven entropically due to solvatophobic effect. Strong enthalpy–entropy compensation points towards the uniform binding mode of all complexes studied. The mode of complex formation was found solvent dependent. For phenylalanine guest studied in various solvent systems, in contrast to the aqueous media, the noticeable chiral recognition is observed in methanol solution, and the complex stoichiometry (1:2 ether:Phe) differs from the 2:1 one, determined previously for the same host‐guest system in water (J. Thermal. Anal. Cal. 2006; 83: 575–578). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
60.
We discuss the following problems, plaguing the present search for the “final theory”: (1) How to find a mathematical structure rich enough to be suitably approximated by the mathematical structures of general relativity and quantum mechanics? (2) How to reconcile nonlocal phenomena of quantum mechanics with time honored causality and reality postulates? (3) Does the collapse of the wave function contain some hints concerning the future quantum gravity theory? (4) It seems that the final theory cannot avoid the problem of dynamics, and consequently the problem of time. What kind of time, if this theory is supposed to be background free? (5) Will the dynamics of the “final theory” be probabilistic? Quantum probability exhibits some essential differences as compared with classical probability; are they but variations of some more general probabilistic measure theory? (6) Do we need a radically new interpretation of quantum mechanics, or rather an entirely new theory of which the present quantum mechanics is an approximation? (7) If the final theory is to be background free, it should provide a mechanism of space-time generation. Should we try to explain not only the generation of space-time, but also the generation of its material content? (8) As far as the existence of the initial singularity is concerned, one usually expects either “yes” or “not” answers from the final theory. However, if the mathematical structure of the future theory is supposed to be truly more general that the mathematical structures of the present general relativity and quantum mechanics, is a “third answer“ possible? Could this third answer be related to the probabilistic character of the final theory? We discuss these questions in the framework of a working model unifying gravity and quanta. The analysis reveals unexpected aspects of these rather wildly discussed issues. 相似文献