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71.
Rainer P. H. Garten 《中国化学会会志》1994,41(3):259-274
Selected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace- and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis. A review on the state-of-the-art of wet-chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high-resolution local microanalysis in non-conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic products and devices. 相似文献
72.
Sergei N. Yurchenko Jürgen Breidung Walter Thiel 《Theoretical chemistry accounts》2005,114(4-5):333-340
We report a theoretical study of the ground electronic state of BiH3. The potential energy surface (PES) is obtained from coupled cluster CCSD(T) calculations with a large basis set (289 contracted
Gaussian functions). The previously available quartic force field (P4) is extended by adding the dominant quintic and sextic
stretching terms to yield improved potential functions in symmetry coordinates (P6) and Morse-type coordinates (M4). Second-order
rovibrational perturbation calculations on the P4-PES and full variational calculations on the P6-PES and M4-PES yield almost
identical vibrational term values which is rationalized by considering the local mode behavior of BiH3 and the Morse-type character of the M4-PES. The remaining deviations between the computed and observed vibrational term values
must thus be caused by imperfections in the CCSD(T) surface. A refinement of this ab initio surface by a restrained fit to
experimental data allows an essentially perfect reproduction of the observed vibrational term values. Variational calculations
on this refined surface provide predictions for several overtone and combination bands that have not yet been observed.
Dedicated to Hermann Stoll on the occasion of his 60th birthday 相似文献
73.
The stability of poly(N-methylaniline) (PNMA) as electrode material has been studied in aqueous solutions of sulfuric acid with the use of electrochemical
and in situ Raman spectroscopic techniques. It has been shown that the electrochemical decomposition of electrodeposited PNMA
films follows a first-order reaction kinetics. The decomposition rate constants vary between 1.2 × 10−5 and 2.0 × 10−3 s−1 for electrode potential varying between 0.2 and 1.0 V vs Ag/AgCl, respectively. In situ Raman spectroscopy has been applied
in obtaining kinetic data at selected electrode potentials, and good correlation of these data with the corresponding data
obtained by cyclic voltammetry has been found. As compared to polyaniline, the decomposition of PNMA proceeds at nearly the
same rate at electrode potentials not exceeding 0.5 V. The decomposition of PNMA proceeds faster within the potential limits
of 0.5 to 0.8 V and slower at electrode potentials exceeding 0.8 V as compared to polyaniline.
This article is dedicated to Professor Algirdas Vaškelis (Institute of Chemistry, Vilnius, Lithuania) on the occasion of his
70th birthday and in honour of his contributions to electrochemistry and physical chemistry. 相似文献
74.
Anatoliy Nechepurenko 《Journal of solid state chemistry》2004,177(2):616-618
The investigation of sintering conditions for magnesiothermic amorphous boron (MgmBn) powder is presented. The results of chemical and X-ray analyses of magnesiothermic boron (MgmBn) indicate that it consists of amorphous boron MgB12 and a lesser amount of β-rhombohedral boron. The MgmBn-sintering process is determined by the conditions of amorphous boron transformation into β-boron (crystallization), such as the process of decomposition of MgB12 followed by formation of the “new” centers of active elementary boron. As a result of the experimental investigations of this process the following three stages—thermal decompositions, crystallization and MgmBn sintering—were combined into one sintering process with the sintered bodies as a result of it. 相似文献
75.
Leo P. Kadanoff Anthony Houghton Mehmet C. Yalabik 《Journal of statistical physics》1976,14(2):171-203
Approximate recursion relations which give upper and lower bounds on the free energy are described. Optimal calculations of the free energy can then be obtained by treating parameters within the renormalization equations variationally. As an example, a particularly simple lower bound approximation which preserves the symmetry of the Hamiltonian (the one-hypercube approximation) is described. The approximation is applied to both the Ising model and the Wilson-Fisher model. At the fixed point a parameter is set variationally and critical indices are calculated. For the Ising model the agreement with the exact results atd = 2 is surprisingly good, 0.1%, and is good atd=3 and evend=4. For the Wilson-Fisher model the recursion relation is reduced to a one-dimensional integral equation which can be solved numerically givingv=0.652 atd=3, or by expansion in agreement with the results of Wilson and Fisher to leading order in . The method is also used to calculate thermodynamic functions for thed = 2 Ising model; excellent agreement with the Onsager solution is found.Supported in part by the National Science Foundation under Grants Nos. MPS73-04886A01 and GH-41512 and by the Brown University Materials Research Laboratory supported by the National Science Foundation. M.C.Y. was supported by a grant from the Scientific and Technical Research Council of Turkey. 相似文献
76.
对河北省的经济结构进行了简单概括,指出发展软件产业带动经济发展的必要性,结合高校的工作经历从多个方面论述了软件产业化过程中需要解决的问题,并对全省软件产业化提出了自己的观点。 相似文献
77.
考虑临界的具阻尼的Gross-Pitaevskii(GP)方程iψt=-Δψ+|x|2ψ+g|ψ|4/Dψ+iaψ,
t≥0, x∈RD, g<0, a<0,这里D是空间维数.这个方程很好地描述了吸引的玻色-爱因斯坦凝聚(BEC).通过偏微分方程的严格理论和变分方法,获得了整体解的一个充分条件,而这个条件利用了非线性数量场方程-Δu+(2)/(b)u-|u|4/Du=0的唯一正解. 相似文献
78.
79.
IntroductionUsingtheMethodofMoments(MoM)t1)forthescatteringbyelectricallylargebodiesresultsinlargematriceswhichdictateexcessivecomputerstorageandexecutiontime.TheSpatialDecompositionTechnique(SDT)[2jwasproposedtocircumventhighdemandonthecomputerresourcesandalsoreducenumericaldiffculties.ltdividesthescattererintoanarbitrarynumberofNdistinctspatialsubzones'Atthevirtualinterfaceseparatingthetwosubzones,thetangentialvirtualcurrentspnonesideoftheinterfacemustbeequal,butoppositetothetangentialvi… 相似文献
80.
候仁恩 《上饶师范学院学报》1996,(3)
本文主要是在Banach空间中建立了集值测度的勒贝格分解定理,把文[2]在有限维向量空间中集值测度的勒贝格分解定理,推广到了无穷维空间. 相似文献