全文获取类型
收费全文 | 7918篇 |
免费 | 937篇 |
国内免费 | 469篇 |
专业分类
化学 | 1048篇 |
晶体学 | 14篇 |
力学 | 1175篇 |
综合类 | 169篇 |
数学 | 3790篇 |
物理学 | 3128篇 |
出版年
2024年 | 20篇 |
2023年 | 61篇 |
2022年 | 126篇 |
2021年 | 165篇 |
2020年 | 200篇 |
2019年 | 199篇 |
2018年 | 169篇 |
2017年 | 219篇 |
2016年 | 221篇 |
2015年 | 179篇 |
2014年 | 300篇 |
2013年 | 567篇 |
2012年 | 354篇 |
2011年 | 376篇 |
2010年 | 328篇 |
2009年 | 410篇 |
2008年 | 481篇 |
2007年 | 478篇 |
2006年 | 478篇 |
2005年 | 386篇 |
2004年 | 375篇 |
2003年 | 363篇 |
2002年 | 359篇 |
2001年 | 309篇 |
2000年 | 313篇 |
1999年 | 240篇 |
1998年 | 235篇 |
1997年 | 175篇 |
1996年 | 161篇 |
1995年 | 113篇 |
1994年 | 123篇 |
1993年 | 85篇 |
1992年 | 92篇 |
1991年 | 96篇 |
1990年 | 80篇 |
1989年 | 62篇 |
1988年 | 63篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 44篇 |
1984年 | 58篇 |
1983年 | 27篇 |
1982年 | 25篇 |
1981年 | 31篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有9324条查询结果,搜索用时 0 毫秒
81.
Wansoo T Rhee 《Operations Research Letters》1985,4(3):121-123
Consider independent identically distributed random variables (Xi) valued in [0,1]. Let B(n) be the optimal (minimum) number of unit size bins needed to pack n items of size X1, X2,…,Xn. We prove that there exists a numerical constant C such that for t > 0, The constant C does not depend on the distribution of X. 相似文献
82.
Monot Frédéric Benoit Yves Ballerini Daniel Vandecasteele Jean-Paul 《Applied biochemistry and biotechnology》1990,(1):375-386
Utilization of lipases for synthesis of esters of hydrophilic polyols has been investigated. The choice of a suitable solvent
is crucial in this type of reaction. An interesting case is fatty acid esters from neopentylpolyols, such as trimethylolpropane,
which are of great interest as high temperature lubricants. Enzymatic synthesis of trimethylolpropane tricaprylate was studied
as an alternative to chemical manufacturing. Triester production occurred only if the water produced by esterification was
continuously removed from the medium. In these condition, kinetics of appearance and transformation of mono-, di- and triesters
were determined in order to define optimal conditions. 相似文献
83.
84.
Summary {\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}}
\viewkind4\uc1\pard\f0\fs20 New explanations are given for two types of irregular thermogravimetric (TG) data. A TG relationship between mass and temperature is derived on the basis of migration behavior of bubbles generated in bulk of sample system, and superposed on that derived on the basis of kinetics of the 4\super th\nosupersub order event, which is superposed on the experimental TG data obtained from three reference papers. This suggests that these TG data are reflecting migration of bubbles. A dependence of TG behavior on heating rate, which is contrary to usual that, is shown and is explained in terms of event-rate determination by boiling.
\par } 相似文献
85.
The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained. 相似文献
86.
A theory is developed for the potential distribution around a charged spherical colloidal particle carrying ionized groups on the particle surface in a medium containing its counterions (i.e., counterions produced from dissociation of the particle surface groups) and a small amount of added salts on the basis of the theory of Imai and Oosawa. Numerical solutions to the Poisson–Boltzmann equation for the potential distribution are obtained for the case of dilute (but not infinitely dilute) particle suspensions of volume fraction 1 for
a1 (where is the Debye–Hückel parameter and a is the particle radius). Here we have taken into account the effects of (i) counterions from the particle surface groups, and (ii) the finite particle volume fraction. These effects, which are usually neglected in the conventional Poisson–Boltzmann equation, are found to be important. It is found that, as in the case of completely salt-free media, there is a certain critical value of the particle charge (which is the same as that for the completely salt-free case). When the particle charge is lower than the critical value, the potential is given by a Coulomb potential. If the particle charge is higher than the critical value, then counterions are accumulated in the vicinity of the particle surface (counterion condensation) and the potential becomes less dependent on the particle charge. The above behaviors can be observed even for the case where the electrolyte concentration is higher than the concentration of counterions from the particle surface groups, if the conditions
1 and a1are both satisfied. 相似文献
87.
合成了6种氨基酸水杨醛席夫碱(Sal-AA):Sal-Gly(甘氨酸)、Sal-Phe(苯丙氨酸)、Sal-Arg(精氨酸)、Sal-Tyr(酪氨酸)、Sal-Met(甲硫氨酸)、Sal-Glu(谷氨酸)及其金属铜配合物。并分别在2种不同介质(三氯甲烷和甲醇)中,与四苯基卟啉TPP进行反应,研究了其紫外可见光谱性质,讨论了卟啉作为人工信号转导体系的传递介质,与氨基酸水杨醛席夫碱铜配合物的反应中,实现信号分子铜离子进一步传递的可能性以及溶剂对该信号传递的影响。结果表明,在三氯甲烷为溶剂时,除了Sal-Met的铜配合物之外,其余均能被TPP夺取而形成Metal TPP。而在以甲醇为溶剂时,只有Sal-Gly的铜配合物能被TPP所夺取。 相似文献
88.
The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”. 相似文献
89.
In this article, the results of calculations of scattering spectra of low-absorptive spherical particles are presented. It was obtained using different approximate and numerical methods. The comparative evaluations of application of single scattering approximation, the average field approximation and of the methods of computer modeling on the basis of Monte-Carlo method on various scattering multiplicity were performed. The comparison demonstrates the good agreement of calculated results with experimental scattering spectra of eye lens. By using the obtained spectral data the colour coordinates are calculated. The regularities of changes in colour characteristics in dependence of disperse system parameters are analyzed. 相似文献
90.