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61.
Min Hsien Liu 《中国化学会会志》2007,54(1):141-148
Density functional theory (DFT) calculations are made and least squares calibration performed for various halohydrocabons, which were 27 straight‐chain alkyl halides, 20 branch‐chain alkyl halides and 19 aromatic halides, to determine their enthalpies of formation (ΔHf). The mean absolute error (M. |A.E.|) in ΔHf across 66 molecular computations was only 7.8 kJ/mol (1.9 kcal/mol). Grouping the molecules by their structural characteristics improved M. |A.E.| of ΔHf by 0.2–2.2 kJ/mol over that obtained using corresponding modified data for the same 66 unclassified molecules. 相似文献
62.
A. K. Galwey 《Journal of Thermal Analysis and Calorimetry》2005,82(2):423-437
Summary A representational model, proposed to account for the physical changes that accompany the melting of alkali halides, was described
in Part 1 [1]. The liquid is portrayed as undergoing continual dynamic structural reorganization of its constituent ions between
individual small domains, zones of various regular, crystal-type arrays. These alternative arrangements are stabilized by
the enthalpy of melting, which, in liquids, relaxes the restriction for solids that only the single, most stable, crystal
structure can be present. The dynamic character of the melt accounts for its fluid character and the loss of long-range order
[1, 2]. This model is extended here to consider the phase diagrams of binary, common ion, alkali halide mixtures comprehensively
reviewed in [3]. Factors determining whether each of these yields a eutectic, or a solid solution, on cooling are discussed
and several trends in the 70-phase diagrams are identified. Eutectic formation, involving maintenance of the liquid state
below the melting points of the pure components, is ascribed to the participation, in an extended dynamic equilibrium, of
additional domains having the regular structures characteristic of double salts. The known crystalline double binary halides
[3], Li/Cs or Rb/F, Cl, Br or I, melt at temperatures well below those of the simpler pure component salts. It is concluded
that the set/liq model for melting, proposed in [1, 2], accounts for some important properties of the phase diagrams presented
in [3]. 相似文献
63.
Macrocycle opening in derivatives of benzocrown ethers under the action of amines is affected by the nature of the heteroatoms in the macrocycle, the nature of the functional group in the benzene ring of the crown ether, and the length, branching, and number of hydrocarbon radicals at the amine nitrogen atom. A distinguishing feature of this reaction is the template effect of MeNH3
+, Me2NH2
+, Na+, and K+ ions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 687–692, March, 1996.For Part I see Ref. 1. 相似文献
64.
关于Liesegang环形成机理的研究 总被引:1,自引:0,他引:1
本文研究了Liesegang环的形成,受到两扩散电解质溶液的浓度比、离子浓度积及光照等条件影响。侧重对成环的微观汇聚过程进行了探讨。 相似文献
65.
An improved synthesis of the anti-cancer agent DMU-212 (trans-3,4,5,4′-tetramethoxystilbene) is described. The methodology involves the use of a Pd-oxazoline catalyst as a mediator of a regio-selective (Heck) C-C bond formation reaction. A simple isolation step is then used to obtain the title material. The compound has been further characterised in the solid-state by X-ray diffraction methods. 相似文献
66.
We have investigated the effect of salt concentration and temperature on the average aggregation number and micro-polarity of the interior of micelles of sodium dodecyl sulfate (SDS). sodium tetradecyl sulfate (STDS) and lithium dodecyl sulfate (LiDS). The transient fluorescence decay of micelle-solubilized pyrene has been measured and analyzed. An exponent weighted average aggregation number <n>e was obtained by this technique. For SDS and STDS in NaCl solution, <n>e increases as the temperature is lowered or salt concentration is increased <n>e increased from ~ 50 to ~ 250 over [NaCl] = 0 to 0.8 M. Due to the strong counterion binding of lithium in the micellar solution, the LiDS micelle is much, smaller and does not increase appreciabily even at [LiCl] =0.8 M. From the fluorescence spectrum fine structure of pyrene and the fluorescence decay of the monomer and excimer, we can understand the local polarity and the water penetration to the interior of the micelle upon addition of salts and with changing temperature. The interior of the micelle becomes more nonpolar as the salt concentration is increased and the temperature is lowered. A complete kinetic analysis of the time–dependence of the fluorescence is given. The kinetic analysis is in agreement with the results reached by fluorescence spectral analysis. 相似文献
67.
Samarium diiodide is an efficient precatalyst for the Friedel-Crafts reaction involving various aromatic substrates and chelating electrophiles. Alkyl 3,3,3-trifluoropyruvates are transformed into α-hydroxyesters in good yields with total regioselectivity. In reactions involving an ethyl glyoxylate or a glyoxylic imine, α-hydroxyesters or α-aminoesters are obtained with variable amounts of products resulting from a double Friedel-Crafts reaction. 相似文献
68.
Akira Ando 《Journal of fluorine chemistry》2005,126(5):765-770
Treatment of 2-chloro-3,3-difluoroprop-2-en-1-ol derivatives (2) with methanesulfonyl chloride in the presence of a base did not give the expected esters but 2-chloro-1,1-difluoroprop-2-enyl methanesulfonates (4) through a novel [3,3] sigmatropic rearrangement. Reaction of 4 with diethylzinc in the presence of tetrakis(triphenylphosphine) palladium gave 1-alkyl- or 1-aryl-2-chloro-3-fluoropenta-1,3-dienes in moderate to good yields through a CC bond formation followed by dehydrofluorination. 相似文献
69.
On the Thermodynamics of Vaporization and the Enthalpies of Formation of CaSe, SrSe and BaSe The congruent vaporization of the solid compounds CaSe, SrSe and BaSe of stoichiometric composition was studied over the temperature ranges 1832?2138 K, 1862?2122 K and 1860?2158 K, respectively, by the Knudsen effusion weight-loss method. Using enthalpy and entropy data from the literature for gaseous M, MSe, Se2 and Se (M = Ca, Sr, Ba) and estimated data for the standard entropies and enthalpy functions of solid MSe, it can be shown that within the given temperature ranges CaSe and SrSe vaporize predominatly to the atomic species, while in case of BaSe the mode of vaporization to the atoms and to the molecular species BaSe are of about equal importance. The Se2-content of the gas phase is very small in all cases. The following second and third law enthalpies and entropies (indices II and III respectively) were derived for the vaporization to the gaseous elements: see “Inhaltsübersicht”. The following standard enthalpies of formation of MSe(s) were derived from the third law enthalpies (in kJ · mol?1): CaSe: ?445 ± 44; SrSe: ?451 ± 42; BaSe: ?467 ± 44. 相似文献
70.
用晶内形成法制备了Ni_xB/沸石催化剂,用饱和氢化学吸附法结合TEM方法考察了负载金属的分散性,并研究了其己环烷脱氢反应性。结果表明,Ni_xB/沸石样品上负载金属的分散性高,金属粒径分布也相对集中;金属负载量、载体结构和性质以及Ni_xB的制备条件对负载金属的分散性有明显影响。Ni_xB/沸石样品呈现较好的环己烷脱氢反应性。 相似文献