全文获取类型
收费全文 | 5136篇 |
免费 | 145篇 |
国内免费 | 22篇 |
专业分类
化学 | 3373篇 |
晶体学 | 27篇 |
力学 | 156篇 |
数学 | 677篇 |
物理学 | 1070篇 |
出版年
2023年 | 30篇 |
2022年 | 82篇 |
2021年 | 124篇 |
2020年 | 77篇 |
2019年 | 92篇 |
2018年 | 62篇 |
2017年 | 73篇 |
2016年 | 199篇 |
2015年 | 112篇 |
2014年 | 162篇 |
2013年 | 277篇 |
2012年 | 311篇 |
2011年 | 368篇 |
2010年 | 220篇 |
2009年 | 231篇 |
2008年 | 322篇 |
2007年 | 329篇 |
2006年 | 269篇 |
2005年 | 285篇 |
2004年 | 240篇 |
2003年 | 205篇 |
2002年 | 173篇 |
2001年 | 67篇 |
2000年 | 67篇 |
1999年 | 60篇 |
1998年 | 51篇 |
1997年 | 48篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 60篇 |
1993年 | 39篇 |
1992年 | 28篇 |
1991年 | 35篇 |
1990年 | 33篇 |
1989年 | 38篇 |
1988年 | 32篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 44篇 |
1983年 | 20篇 |
1982年 | 30篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 12篇 |
1975年 | 18篇 |
1974年 | 9篇 |
1970年 | 8篇 |
排序方式: 共有5303条查询结果,搜索用时 15 毫秒
51.
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
52.
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
53.
54.
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
55.
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
56.
Cinquina AL Roberti P Giannetti L Longo F Draisci R Fagiolo A Brizioli NR 《Journal of chromatography. A》2003,987(1-2):221-226
A high-performance liquid chromatography-diode array detection method (HPLC-DAD) combined with liquid chromatography-mass spectrometry was developed for the determination of enrofloxacin and its metabolite ciprofloxacin in goat milk. The HPLC-DAD method validation was compliant with the "DG SANCO 1805/2000" European regulation. The residues were extracted from milk with phosphate buffer, purified on a C18 Speedisk cartridge SPE (Baker) and then analysed using HPLC-DAD set at 277 nm. The decision limit (CCa) calculated by spiking samples at 100 microg/kg with both analytes, taking into account the maximum residue limit (MRL) of 100 microg/kg established by the European Union for the sum of enrofloxacin and its metabolite ciprofloxacin in milk, was 105.3 microg/kg for enrofloxacin and 105.5 microg/kg for ciprofloxacin. The detection capability (CCbeta) was 110.7 and 110.9 microg/kg for enrofloxacin and ciprofloxacin, respectively. The mean recoveries of the method, calculated by spiking samples at 50, 100 and 150 microg/kg were 84% for enrofloxacin and 88% for ciprofloxacin. The limit of quantification was 20 microg/kg for both analytes. The HPLC-DAD validated method was successfully applied for the first time in goats milk, and proved to be suitable for the sensitive and accurate quantification and confirmation analysis of enrofloxacin and ciprofloxacin for regulatory purposes. 相似文献
57.
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
58.
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
59.
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
60.
D. S. Gouveia R. Rosenhaim M. A. M. A. de Maurera S. J. G. Lima C. A. Paskocimas E. Longo A. G. Souza I. M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2004,75(2):453-460
With the aim of obtaining materials with applications in pigments, CoxZn7-xSb2O12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic
cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for
the synthesis of a zinc antimoniate spinel, CoxZn7-xSb2O12 (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated
a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two
different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added
to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol
was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two
alcohols - both presented the spinel phase (Co, Zn)2.33Sb0.67O4. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb2O6.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献