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301.
302.
Akhtar W Filidou V Sekiguchi T Kawakami E Itahashi T Vlasenko L Morton JJ Itoh KM 《Physical review letters》2012,108(9):097601
Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the m(s)=±1 sublevels differs significantly from that of the m(s)=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor (29)Si nuclear spin. We measure the coherence time of the (29)Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance. 相似文献
303.
Permanent binary phase masks with planar surfaces and high tolerance to laser radiation are recorded in the volume of photo-thermo-refractive glass using the contact copying technique and binary amplitude master masks. Conversion of a Gaussian beam to higher order modes is shown. 相似文献
304.
The measurement of the two-mode squeezed vacuum generated in an optical parametric amplifier (OPA) was performed with photon number resolving multipixel photon counters (MPPCs). Implementation of the MPPCs allows for the observation of noise reduction in a broad dynamic range of the OPA gain, which is inaccessible with standard single photon avalanche photodetectors. 相似文献
305.
Zhou Guannan Simerly Thomas Golovko Leonid Tychinin Igor Trachevsky Vladimir Gomza Yury Vasiliev Aleksey 《Journal of Sol-Gel Science and Technology》2012,62(3):470-482
The objective of this work was to synthesize functionalized mesoporous silsesquioxanes with high concentrations of amine groups.
During typical sol–gel syntheses, these materials are obtained by co-condensation of organic precursors with suitable linkers,
such as tetraethoxysilane, necessary to prevent the mesoporous structure from collapsing. Thus, concentrations of amine groups
in organosilicas usually do not exceed 2.7–3.4 mmol g−1. The use of bridged bis-trimethoxysilanes, however, allowed formation of mesoporous materials with no linker. Polycondensation of bis-trimethoxysilanes containing amine groups was conducted in acidic, neutral and basic media, resulting in high yields of solid
bridged silsesquioxanes. Gelation occurred quickly if no acid or base was added to the reaction mixture. The hybrid organic/inorganic
nature of obtained materials was confirmed by FT-IR and MAS CP NMR spectroscopy. Elemental analysis showed that amino group
concentration in the products was 3.3–4.1 mmol g−1. Measurement of particle size distribution confirmed that choice of reaction media significantly affects particle sizes and
agglomeration degrees, with the largest agglomerates (up to 50 μm) formed in basic media. A morphology study, using small-angle
X-Ray scattering, displayed two-level fractal structures composed of aggregated 6.5–10.5 nm particles. Reactions in the presence
of a surfactant resulted in formation of mesoporous structures. Furthermore, the obtained bridged silsesquioxanes were thermally
stable down to 260 °C, but could reversibly absorb water and CO2 at temperatures below 120 °C. Thus, condensation of the bridged precursor without a linker resulted in formation of a highly
functionalized mesoporous material. 相似文献
306.
Miller EM Sheps L Lu YJ Case AS McCoy AB Lineberger WC 《The Journal of chemical physics》2012,136(4):044313
Negative-ion photoelectron spectroscopy of ICN(-) (X??(2)Σ(+)) reveals transitions to the ground electronic state (X??(1)Σ(+)) of ICN as well as the first five excited states ((3)Π(2), (3)Π(1), Π(0(-) ) (3), Π(0(+) ) (3), and (1)Π(1)) that make up the ICN A continuum. By starting from the equilibrium geometry of the anion, photoelectron spectroscopy characterizes the electronic structure of ICN at an elongated I-C bond length of 2.65 A?. Because of this bond elongation, the lowest three excited states of ICN ((3)Π(2), (3)Π(1), and Π(0(-) ) (3)) are resolved for the first time in the photoelectron spectrum. In addition, the spectrum has a structured peak that arises from the frequently studied conical intersection between the Π(0(+) ) (3) and (1)Π(1) states. The assignment of the spectrum is aided by MR-SO-CISD calculations of the potential energy surfaces for the anion and neutral ICN electronic states, along with calculations of the vibrational levels supported by these states. Through thermochemical cycles involving spectrally narrow transitions to the excited states of ICN, we determine the electron affinity, EA(ICN), to be 1.34(5) (+0.04∕-0.02) eV and the anion dissociation energy, D(0)(X??(2)Σ(+) I-CN(-)), to be 0.83 (+0.04/-0.02) eV. 相似文献
307.
Anil Khanal Yan Pan Leonid S. Brown Lars Konermann 《Journal of mass spectrometry : JMS》2012,47(12):1620-1626
Kinetic folding experiments by pulsed hydrogen/deuterium exchange (HDX) mass spectrometry (MS) are a well‐established tool for water‐soluble proteins. To the best of our knowledge, the current study is the first that applies this approach to an integral membrane protein. The native state of bacteriorhodopsin (BR) comprises seven transmembrane helices and a covalently bound retinal cofactor. BR exposure to sodium dodecyl sulfate (SDS) induces partial unfolding and retinal loss. We employ a custom‐built three‐stage mixing device for pulsed‐HDX/MS investigations of BR refolding. The reaction is triggered by mixing SDS‐denatured protein with bicelles. After a variable folding time (10 ms to 24 h), the protein is exposed to excess D2O buffer under rapid exchange conditions. The HDX pulse is terminated by acid quenching after 24 ms. Subsequent off‐line analysis is performed by size exclusion chromatography and electrospray MS. These measurements yield the number of protected backbone N–H sites as a function of folding time, reflecting the recovery of secondary structure. Our results indicate that much of the BR secondary structure is formed quite late during the reaction, on a time scale of 10 s and beyond. It is hoped that in the future it will be possible to extend the pulsed‐HDX/MS approach employed here to membrane proteins other than BR. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
308.
EM Chainikova RL Safiullin LV Spirikhin MF Abdullin 《The journal of physical chemistry. A》2012,116(31):8142-8147
The electronic spectra were measured and the unimolecular decay kinetics of the isomeric forms (cis and trans) of 4-methoxyphenylnitroso oxide in acetonitrile, benzene, and hexane was studied using flash photolysis. The cis form absorbed in a shorter wavelength region and was more labile than the trans form. The difference between the reactivity of the two species increased on going from hexane to acetonitrile. The temperature dependences of reaction rate constants were studied for both isomeric forms. The analysis of products of flash photolysis of 4-methoxyphenyl azide in the presence of oxygen allowed for understanding the mechanism of thermal decay of nitroso oxides. It was shown that the trans nitroso oxide is converted into cis nitroso oxide. The latter undergoes an unusual ring cleavage reaction to form 4-methoxy-6-oxohexa-2,4-dienenitrile N-oxide derivative. We conclude that the nitro- and nitrosobenzenes, which are the main products of the steady-state photolysis of aromatic azides in the presence of oxygen, are formed by the photochemical transformation of the nitroso oxides. 相似文献
309.
We consider the second-order linear differential equation y" + A(t)y = 0 on the semiaxis with complex-valued potential function. Sufficient conditions for the potential function assuring that
all solutions of the equation converge to zero at infinity are obtained. It is shown that the conditions imposed on the potential
function are close to the necessary ones. One of the results seems to be new even in the case of real-valued function A(·). 相似文献
310.