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81.
It is shown that new parametersX can be defined such that the heat capacity CxT(S/T)x is negative, even when the canonical ensemble [i.e., at fixed T=(U/S)Y and YX] is stable. This implies an extension of the classical theory of polytropes from ideal gases to general fluids. As examples of negative heat capacity systems we treat blackbody radiation and general gas systems with nonsingular T. For the case of a simple ideal gas we even exhibit an apparatus which enforces a constraint X(p, V)=const that makes Cx<0. We then show that it is possible to infer the statistical mechanics of canonicallyunstable systems-for which even the traditional heat capacities are negative-by imposing constraints that stabilize the associated noncanonical ensembles. Two explicit models are discussed. 相似文献
82.
The selectivity of a column system, S, defined by equation 28, includes a variation coefficient (β) of plate number with capacity ratio which has a large influence on the peak capacity, as shown in Fig. 18. Some typical chromatograms are given. In order to predict S for a column system from Kovat's Index, equations 40 and 41 are given to calculate the constant of the carbon number rule for squalane at different temperatures or for different stationary phases. The specific retention value of heptane on squalane at different temperatures can be calculated from equation 42. The nonpolarity index, defined by equation 43, was used to calculate the retention value of heptane on various stationary phases. In liquid chromatography, the order of elution may be reversed by changing the composition of the eluent on the same chemically bonded silica (manufactured in China). The linear relations between the log retention values of different kinds of solutes or of a single solute on the silicas of different surface areas when using the same eluent are given. 相似文献
83.
Predicting the selectivity of imprinted polymers 总被引:2,自引:0,他引:2
Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years.
In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations
were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used
to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally
determined value ofK and separation factors taken from the literature. 相似文献
84.
The purpose of this research was to select an activated carbon and alkaline solution blend that generated the best H2S adsorption on alkaline-activated carbon. RB2 (activated carbon) impregnated with NaOH solution was shown to have the optimum H2S removal efficiency. The optimum NaOH concentration was 50 mg per gram of carbon. H2S adsorption via RB2-NaOH50 was five times that of a corresponding fresh-activated carbon. The adsorption equivalent of H2S is nearly 1 (mol-H2S/mol-AOH), therefore, H2S + AOH AHS + H2O was the major reaction. The H2S adsorption isotherm corresponded to the Freundlich isotherm. 相似文献
85.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
86.
Alain H. Roux Daniel Hétu Gérald Perron Jacques E. Desnoyers 《Journal of solution chemistry》1984,13(1):1-25
Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems. 相似文献
87.
Sergio Cabani Paolo Gianni Vincenzo Mollica Luciano Lepori 《Journal of solution chemistry》1981,10(8):563-595
The thermodynamic properties G
h
o,H
h
o, and C
p,h
oassociated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties C
p
o
,2 and V2
2 of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted. 相似文献
88.
提出了测量气相色谱中吸附等温线的新方法,用不同进样量下测定的容量因子计算平衡时气-固两相组分浓度。利用建立的方法分别测量了正-己烷、正-壬烷和正-十一烷在邻苯二甲酸二辛酯(DOP)、阿皮松-L(Apiezon)和β,β′-氧二丙腈(ODPN)柱上的吸附等温线,讨论了色谱峰形状与吸附等温线的对应关系。研究了气相色谱中进样量对保留值的影响,利用佛伦德利希(Freundlich)吸附等温式导出了描述保留值与进样量关系的数学表达式。理论和实验证明,保留值与进样量具有良好的对数线性关系。 相似文献
89.
90.
Single phase of ammonium tetramolybdate in the micro power form was prepared from polyphase ammonium paramolybdate. Its heat capacity from 14.25℃ to 120.12 ℃ was measured by drop method and the result is
Cp=0.3936+7.4047×10-4T+6.3543×10-3T-2(J•K-1•g-1) 相似文献
Cp=0.3936+7.4047×10-4T+6.3543×10-3T-2(J•K-1•g-1) 相似文献