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51.
An effective synthetic approach to the preparation of a new crown-ether vinylogs involving the Horner–Emmons olefination of carbonyl precursors with the use of C2- and C5-phosphonates was proposed. The effects of the conjugation chain length and the nature of the terminal polar functions in the phosphonate reagent on the yield and process stereoselectivity were discussed.  相似文献   
52.
A theoretical study of geminal and vicinal 77Se‐1 H coupling constants in the benchmark dimethyl and diethyl selenides has been performed at the SOPPA level followed by the NJC analysis within the NBO approach to reveal their stereochemical behavior in respect with the three main structural factors, namely, (i) the dihedral angle dependences, (ii) the bond angle dependences and (iii) the lone pair effects. It has been demonstrated that both geminal and vicinal couplings provide a unique stereospecificity in respect with the orientational lone pair effect together with the geometry of a coupling pathway, which is of prime importance for the stereochemical studies of organoselenium compounds. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
53.
Stereochemical structure of nine Z‐2‐(vinylsulfanyl)ethenylselanyl organyl sulfides has been investigated by means of experimental measurements and second‐order polarization propagator approach calculations of their 1H–1H, 13C–1H, and 77Se–1H spin–spin coupling constants together with a theoretical conformational analysis performed at the MP2/6‐311G** level. All nine compounds were shown to adopt the preferable skewed s‐cis conformation of their terminal vinylsulfanyl group, whereas the favorable rotational conformations with respect to the internal rotations around the C–S and C–Se bonds of the internal ethenyl group are both skewed s‐trans. Stereochemical trends of 77Se–1H spin–spin coupling constants originating in the geometry of their coupling pathways and the selenium lone pair effect were rationalized in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
54.
The calculations of geminal and vicinal 29Si–1H spin–spin coupling constants across double bond in 15 alkenylmethylsilanes and alkenylchlorosilanes were carried out at the second‐order polarization propagator approach level in a good agreement with experiment. Two structural trends, namely, (i) the geometry of the coupling pathway and (ii) the effect of the electrowithdrawing substituent, have been interpreted in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Thus, the marked difference between cisoidal and transoidal 29Si–1H spin–spin coupling constants across double bond was accounted for the delocalization contributions including bonding and antibonding Si–C and C–H orbitals, whereas the chlorine effect was explained in terms of the steric contributions including bonding Si–Cl orbitals. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
55.
56.
This article considers the possibility of applying the positron annihilation spectroscopy method for investigating the pore space of rocks from oil-gas and methane-coal deposits. The diagnostics of the structure was performed using the method of spectrometry of angular correlation of annihilation rays (ACAR). Using the samples of porous silicon, the authors have shown the applicability of the ACAR method for determination of the average dimensions of spherical and cylindrical nanosized objects and their concentration   相似文献   
57.
Four‐component relativistic calculations of 77Se–13C spin–spin coupling constants have been performed in the series of selenium heterocycles and their parent open‐chain selenides. It has been found that relativistic effects play an essential role in the selenium–carbon coupling mechanism and could result in a contribution of as much as 15–25% of the total values of the one‐bond selenium–carbon spin‐spin coupling constants. In the overall contribution of the relativistic effects to the total values of 1J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin‐orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second‐order polarization propagator approach (CC2) with the four‐component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of 1J(Se,C). Solvent effects in the values of 1J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2–78.4) are next to negligible decreasing negative 1J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of 77Se–13C spin‐spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1–0.2‐Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
58.
The extremely high theoretical energy density of the lithium-oxygen couple makes it very attractive for next-generation battery development. However, there are a number of challenging technical hurdles that must be addressed for Li-Air batteries to become a commercial reality. In this article, we demonstrate how the invention of water-stable, solid electrolyte-protected lithium electrodes solves many of these issues and paves the way for the development of aqueous and nonaqueous Li-Air batteries with unprecedented energy densities. We also show data for fully packaged Li-Air cells that achieve more than 800 Wh/kg.  相似文献   
59.
We present the molecular dynamics study of benzene molecules confined into the single wall carbon nanotube. The local structure and orientational ordering of benzene molecules are investigated. It is found that the molecules mostly group in the middle distance from the axis of the tube to the wall. The molecules located in the vicinity of the wall demonstrate some deviation from planar shape. There is a tilted orientational ordering of the molecules which depends on the location of the molecule. It is shown that the diffusion coefficient of the benzene molecules is very small at the conditions we report here. © 2015 Wiley Periodicals, Inc.  相似文献   
60.
Novel electrochemical DNA‐sensor based on glassy carbon electrode (GCE) modified with Ag nanoparticles, Neutral red covalently attached to its surface and native DNA adsorbed on modifier coating was developed for the estimation of DNA damage on example of model system based on Fenton reagent. As was shown, the oxidation process resulted in synchronous increase of electron transfer resistance and capacitance measured by electrochemical impedance spectroscopy (EIS). The contribution of each sensor component on the signal was specified and sensitivity estimated against similar surface coatings. The shift of EIS parameters was found to be higher than that of similar biosensors reported. The DNA sensor was tested on the estimation of antioxidant capacity of green tea infusions again the results of coulometric titration with electrogenerated bromine.  相似文献   
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