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121.
Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation. 相似文献
122.
123.
基团的电子效应与单取代苯对位1H、13C的化学位移*韩长日冯娇杨钟照平(海南师范学院化学系海口571158)关键词1H的化学位移13C的化学位移基团电负性共轭效应引言在1H、13C核磁共振谱中,化学位移值的大小主要取决于屏蔽作用的大小,而屏蔽作用的大... 相似文献
124.
V. Degiorgio M. Corti R. Piazza L. Cantú A. R. Rennie 《Colloid and polymer science》1991,269(5):501-505
The structure of aqueous solutions of two polyoxyethylene non-ionic amphiphiles, C10E5 and C8E4, is studied by small-angle neutron-scattering along isothermal paths crossing the isotropic single-phase region from 0% to 100% amphiphile volume fractions. The scattered intensityI(k) shows a peak at a valuek
m
, which grows monotonically as the amphiphile volume fraction increases. The interpretation of the scattering data lead to the following conclusion: as increases the micellar structure becomes less and less sharp, but some orientational correlations between neighboring amphiphile molecules are preserved even in the pure amphiphile phase. 相似文献
125.
David W. Schwenke 《Theoretical chemistry accounts》1988,74(5):381-402
A new method for the direct calculation of resonance parameters is presented. It is based upon searching for poles of the scattering matrix at complex energies. This search is expedited by the use of analytic derivatives of the scattering matrix with respect to the total energy. This procedure is applied initially to a single channel problem, but is generalizable to more complicated systems. Using the most accurate available potential energy data, we calculate resonance parameters for all of the physically important quasibound states of the ground electronic state of the hydrogen molecule. Corrections to the Born-Oppenheimer potential are included and assessed. The new method has no difficulty locating resonances with widths greater than about 1×10–7 cm–1. It is easier to find narrow resonances by monitoring the dependence of the imaginary part of the reactance matrix on the real part of a complex energy than to monitor the dependence of the eigenphase sum on energy at real energies. 相似文献
126.
四苯硼钠-甲苯胺蓝缔合物纳米微粒体系减色效应研究 总被引:2,自引:2,他引:2
在PH4.0醋酸-醋酸钠介质中,甲苯胺蓝在600nm处有一个吸收峰,随着四苯硼钠浓度的增大甲苯胺蓝在600nm处吸收峰降低,颜色减弱,这是由于甲苯胺蓝-四苯硼钠缔合物分子间存在较强的疏水作用及分子间作用力,聚集形成纳米微粒所致,甲苯胺蓝-四苯硼钠纳米微粒体系亦在600mm处有1个吸收峰,在400mm、470mm和580mm处产生3共振散射峰,其中400mm和580mm为甲苯胺蓝-四苯硼钠复合纳米微粒产生的特征共振散射峰,这也表明有纳米微粒存在,丙酮浓度的影响实验结果等表明,纳米微粒的形成是产生其减色效应的原因。 相似文献
127.
Melvyn P. Melrose 《Theoretical chemistry accounts》1997,95(3-4):67-79
Algebraic expressions for the vertical Delocalisation Energy (DE) of benzene are derived from non-empirical MO theory. For
comparison with early work in the π-electron approximation, and ultimately with Hückel theory, the results are formulated
in terms of a core resonance integral,β, and π-electronic repulsion integrals. All integral values are inferred from the results ofab initio SCF calculations. Two expressions are derived, which refer to two ways of forming the localised π MOs: one where three pairs
of adjacent atomic orbitals are selected from a set of six orthogonalised orbitals; and another where a non-orthogonal set
of atomic orbitals is used. The first expression is formally similar to an expression originally derived by Pople from a different
point of view and with many approximations. This expression gives too large a magnitude for DE when used with anab initio value ofβ. The second expression gives a result much closer to an empirical value of DE and shows that the main reason for DE being
about 50% of 2β rather than 2β is the stabilising effect of overlap in the localised structure, and that the less important factor is the inclusion of electronic
repulsion. 相似文献
128.
In weakly acidic buffer medium, the interaction of amikacin with calf thymus DNA, yeast RNA and denatured DNA has been investigated by using resonance Rayleigh scattering (RRS) technique. The result shows that calf thymus DNA is capable of enhancing the RRS intensity of the amikacin, while yeast RNA and denatured DNA have very little enhancement effect. Based on the characteristics, a sensitive assay for detecting double-stranded DNA in the presence of denatured DNA and yeast RNA has been developed. The enhancement of the RRS signal is directly proportional to the concentration of double-stranded DNA in the range 0.02-12.0 μg ml−1 for calf thymus DNA and its detection limit (3σ) is 2.5 ng ml−1. The method shows a wide linear range and high sensitivity, and almost no interference can be observed from RNA, denatured DNA, amino acid and most of the metal ions. The trace amounts of nucleic acid in synthetic samples and practical samples are determined with satisfactory results. Therefore, the proposed method is promising for as an effect means for recognition in vivo and determination in situ of double-stranded DNA. 相似文献
129.
130.
Chemical reactions occurring at the mineral–water interface are controlled by an interfacial layer, nanometers thick, whose properties may deviate from those of the respective bulk mineral and water phases. The molecular-scale structure of this interfacial layer, however, is poorly constrained, and correlations between macroscopic phenomena and molecular-scale processes remain speculative. The application of high-resolution X-ray scattering techniques has begun to provide substantial new insights into the molecular-scale structure of the mineral–water interface. In this review, we describe the characteristics of synchrotron-based X-ray scattering techniques that make them uniquely powerful probes of mineral–water interfacial structures and discuss the new insights that have been derived from their application. In particular, we focus on efforts to understand the structure and distribution of interfacial water as well as their dependence on substrate properties for major mineral classes including oxides, carbonates, sulfates, phosphates, silicates, halides and chromates. We compare these X-ray scattering results with those from other structural and spectroscopic techniques and integrate these to provide a conceptual framework upon which to base an understanding of the systematic variation of mineral–water interfacial structures. 相似文献