全文获取类型
收费全文 | 5194篇 |
免费 | 155篇 |
国内免费 | 23篇 |
专业分类
化学 | 3422篇 |
晶体学 | 21篇 |
力学 | 139篇 |
数学 | 681篇 |
物理学 | 1109篇 |
出版年
2023年 | 31篇 |
2022年 | 38篇 |
2021年 | 124篇 |
2020年 | 74篇 |
2019年 | 97篇 |
2018年 | 66篇 |
2017年 | 78篇 |
2016年 | 204篇 |
2015年 | 125篇 |
2014年 | 174篇 |
2013年 | 280篇 |
2012年 | 319篇 |
2011年 | 380篇 |
2010年 | 226篇 |
2009年 | 228篇 |
2008年 | 318篇 |
2007年 | 326篇 |
2006年 | 273篇 |
2005年 | 290篇 |
2004年 | 247篇 |
2003年 | 213篇 |
2002年 | 178篇 |
2001年 | 67篇 |
2000年 | 78篇 |
1999年 | 56篇 |
1998年 | 47篇 |
1997年 | 50篇 |
1996年 | 74篇 |
1995年 | 54篇 |
1994年 | 60篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 37篇 |
1990年 | 37篇 |
1989年 | 39篇 |
1988年 | 24篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 28篇 |
1984年 | 45篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 33篇 |
1980年 | 30篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 15篇 |
1975年 | 20篇 |
1974年 | 11篇 |
1973年 | 16篇 |
排序方式: 共有5372条查询结果,搜索用时 26 毫秒
51.
52.
We investigate decay properties of correlation functions in a class of chaotic billiards. First we consider the statistics of Poincaré recurrences (induced by a partition of the billiard): the results are in agreement with theoretical bounds by Bunimovich, Sinai, and Bleher, and are consistent with a purely exponential decay of correlations out of marginality. We then turn to the analysis of the velocity-velocity correlation function: except for intermittent situations, the decay is purely exponential, and the decay rates scale in a simple way with the (uniform) curvature of the dispersing arcs. A power-law decay is instead observed when the system is equivalent to an infinite-horizon Lorentz gas. Comments are given on the behaviour of other types of correlation functions, whose decay, during the observed time scale, appears slower than exponential. 相似文献
53.
Roberto H. Schonmann 《Communications in Mathematical Physics》1989,124(1):1-7
Consider the + phase of the two dimensional nearest neighbor ferromagnetic Ising model at a temperature belowT
c
. Let + be the restriction of this measure to a coordinate axis. We prove that there is no one dimensional translation invariant summable interaction for which + is a Gibbs measure. This is proven by showing that if such an interaction existed, + would have large deviation properties different from those it actually has. Percolation methods are used in the proof.Work supported by the U.S. Army Research Office through the Mathematical Sciences Institute at Cornell and by a NSF grant to Cornell. This work was finished while the author was visiting Rutgers University, being supported by the NSF grant 86-12369 相似文献
54.
55.
Gutiérrez de Dios FJ Gómez R Feliu JM 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7439-7448
Rhodium adlayers on Pt(100) substrates have been prepared by electrodeposition from dilute Rh(III) acidic solutions. The initially disordered layer is electrochemically annealed by applying a polarization program consisting of high-sweep-rate multicycle sequences between 0.05 and 0.78 V(RHE) in 0.1 M H(2)SO(4). In this way, a pseudomorphic Rh monolayer can be prepared on Pt(100) substrates. The degree of order of the electrochemically annealed layer has been evidenced not only through voltammetric experiments but also by means of scanning tunneling microscopy with atomic resolution for iodine-protected adlayers, which show a c(2 x 2) structure. The electrochemically induced ordering of the Rh adlayer appears to be a consequence of the repeated cycles of adsorption/desorption of H and, especially, oxygenated species. Voltammetry in sulfuric acid solutions permits examination of the energetics of H/anions and OH/O adsorption as a function of the Rh coverage. The first monolayer adsorbs both hydrogen and oxygenated species more strongly than the second one. This can be explained through an electronic effect caused by the underlying Pt(100) substrate. 相似文献
56.
Substrate relaxation is shown to play an important role in the 1 : 2 regular chemisorption of hydrogen atoms above alternate carbon atoms in a graphite monolayer. Binding energy, population analysis and electron density maps show that the direct HC bond is strengthened on relaxation. 相似文献
57.
Carlo Mazzocchia Akim Kaddouri Giovanni Modica Roberto Nannicini Guido Audisio Costantino Barbieri Fabio Bertini 《Journal of Analytical and Applied Pyrolysis》2003,70(2):263-276
Pyrolysis of hardware components wastes consisting mainly in computers and television components was performed under nitrogen. The degradation products were separated in three fractions, solid, liquid and gaseous. Analyses of the three phases were carried out using gas chromatography (GC), mass spectrometry (MS), thermal analysis and infrared spectroscopy. The energetic content of the gas phase and the economic value of the liquid phase were also determined. The gas fraction produced was rich in light hydrocarbons and hydrogen. Consequently, its calorific value was high and widely sufficient to make the pyrolysis process self-sustained. The main products of the liquid phase were phenol and isopropylphenol (ca. 50–80 wt.%). The presence of Br-based compounds, deriving from the flame retardant employed in hardware components, were also detected. A controlled combustion of the solid phase permitted to obtain the glass fibres unaltered, which can be recycled. 相似文献
58.
A rapid access to carbocyclic nucleosides containing a fused isoxazoline ring is proposed starting from cyclopentadiene. The route involves an hetero Diels-Alder cycloaddition reaction of nitrosocarbonylbenzene followed by a 1,3-dipolar cycloaddition of nitrile oxides, cleavage of the N-O tether and elaboration of the heterocyclic aminols into nucleosides via linear construction of purine and pyrimidine heterocycles. 相似文献
59.
Jesús Valdés-Martínez Ruben A. Toscano Roberto Salcedo Raymundo Cea-Olivares Adrian Meléndez 《Monatshefte für Chemie / Chemical Monthly》1990,121(8-9):641-647
Summary The crystal and molecular structure of salicylaldehyde semicarbazone was obtained by single crystal X-ray diffraction. The O atom of the semicarbazone fragment isanti to the N atom of the hydrazinic group. The distribution of bond lengths in the semicarbazone fragment indicates delocalization of the -electrons. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds.
Semicarbazone und Thiosemicarbazone, 12. Mitt.: Die Kristallstruktur des Salicylaldehyd-Semicarbazons
Zusammenfassung Die Kristallstruktur und die molekulare Struktur des Salicylaldehyd-Semicarbazons wurde über Einkristall-Röntgenstreuung ermittelt. Das O-Atom des Semicarbazonteils stehtanti zum N-Atom der Hydrazin-Gruppierung. Die Bindungslängen in der Semicarbazoneinheit zeigen eine Delokalisierung der -Elektronen an. Die Geometrie der Verbindung wird durch stabilisierende intra- und intermolekulare Wasserstoffbrückenbindungen bestimmt.相似文献
60.
Nelson Durán Klaus Zinner Roberto Casadei de Baptista Carmen C. C. Vidigal Giuseppe Cilento 《Photochemistry and photobiology》1976,24(4):383-388
Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献