全文获取类型
收费全文 | 2521篇 |
免费 | 202篇 |
国内免费 | 363篇 |
专业分类
化学 | 1689篇 |
晶体学 | 12篇 |
力学 | 230篇 |
综合类 | 64篇 |
数学 | 492篇 |
物理学 | 599篇 |
出版年
2023年 | 34篇 |
2022年 | 56篇 |
2021年 | 112篇 |
2020年 | 76篇 |
2019年 | 46篇 |
2018年 | 49篇 |
2017年 | 63篇 |
2016年 | 91篇 |
2015年 | 86篇 |
2014年 | 101篇 |
2013年 | 152篇 |
2012年 | 112篇 |
2011年 | 158篇 |
2010年 | 116篇 |
2009年 | 162篇 |
2008年 | 154篇 |
2007年 | 163篇 |
2006年 | 173篇 |
2005年 | 141篇 |
2004年 | 115篇 |
2003年 | 121篇 |
2002年 | 96篇 |
2001年 | 86篇 |
2000年 | 63篇 |
1999年 | 71篇 |
1998年 | 77篇 |
1997年 | 66篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 36篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 13篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有3086条查询结果,搜索用时 546 毫秒
71.
化学教学内容情感性艺术处理的策略 总被引:1,自引:0,他引:1
化学教学内容是教学系统的基本要素之一。对教学内容作情感性艺术处理,显示了教师高超的化学教学艺术。其艺术策略分为:一是巧妙组织教学内容来调节学生的学习心向,包括心理匹配策略、超出预期策略;二是有效地利用教学内容中的情感资源来陶冶学生的情操,包括展示情感策略、发掘情感策略、诱发情感策略、赋予情感策略。 相似文献
72.
构建了一个由制造商、回收商和零售商组成的闭环供应链模型,运用Stackelberg博弈对产能约束下制造商的合作策略进行了研究。研究发现:制造商始终有与回收商或零售商合作的经济动机,且当产能较小时,更倾向于与零售商合作;反之,则更倾向与回收商进行合作。此外,相对于无合作模式,不同合作策略对于回收率、供应链整体利润、新产品与再制品总体环境影响程度以及消费者剩余的影响会随着制造商产能大小的变化发生改变,而不同合作策略对于总体环境影响程度的影响与制造商的再制造水平也存在关联。 相似文献
73.
A. Zielenkiewicz K. Busserolles G. Roux-Desgranges A. H. Roux J-P. E. Grolier W. Zielenkiewicz 《Journal of solution chemistry》1995,24(7):623-632
Densities and specific heat capacities of ternary aqueous systems containing dipeptides (glycyl-glycine or L--alanyl-L--alanine) and nucleic acid bases (cytosine or thymine) or their alkyl derivatives (1,3-diethylthymine or caffeine) were determined at 25°C by flow calorimetry and flow densimetry. The partial molar volumes and heat capacities of transfer at infinite dilution of the different nucleic acid bases from water to water+dipeptide solutions were obtained therefrom. Except for the case of the transfer of cytosine to aqueous glycyl-glycine solutions where a small positive dependence of the transfer quantities was observed with the dipeptide concentration, the values of the heat capacities of transfer were in general low, positive or negative, depending on the compensation of hydrophobic-hydrophilic interactions between the dipeptide and the base. The volumes of transfer of most of the bases are very small, within the limit of the experimental error. 相似文献
74.
Andrea Posilicano 《Potential Analysis》1996,5(3):241-271
We prove a convergence theorem for sequences of Diffusion Processes corresponding to Dirichlet Forms of the kind
.We obtain convergence in total variation norm of the corresponding probability measures on the path space C(+;d) under hypotheses which, for example, are satisfied in the case of H
loc
1
(
d
)-convergence of the 's, but we can allow more singular situations as regards the approximating sequences. We use then these results to give a criterion of convergence for generalized Schrödinger operators in which the potential function should not necessarily exists as a measurable function. We obtain convergence not only in strong resolvent sense, but we also obtain convergence in the uniform operator topology up to sets of arbitrarily small Lebesgue measure. Applications to the problem of the approximation of ordinary Schrödinger operators by generalized ones corresponding to zero-range interactions are given. 相似文献
75.
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
76.
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
77.
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
78.
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
79.
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
80.
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