全文获取类型
收费全文 | 27897篇 |
免费 | 547篇 |
国内免费 | 124篇 |
专业分类
化学 | 15831篇 |
晶体学 | 166篇 |
力学 | 825篇 |
综合类 | 9篇 |
数学 | 3949篇 |
物理学 | 7788篇 |
出版年
2023年 | 136篇 |
2022年 | 375篇 |
2021年 | 454篇 |
2020年 | 417篇 |
2019年 | 363篇 |
2018年 | 461篇 |
2017年 | 414篇 |
2016年 | 731篇 |
2015年 | 585篇 |
2014年 | 681篇 |
2013年 | 1168篇 |
2012年 | 1435篇 |
2011年 | 1636篇 |
2010年 | 931篇 |
2009年 | 867篇 |
2008年 | 1384篇 |
2007年 | 1382篇 |
2006年 | 1219篇 |
2005年 | 1640篇 |
2004年 | 1645篇 |
2003年 | 1160篇 |
2002年 | 804篇 |
2001年 | 641篇 |
2000年 | 599篇 |
1999年 | 370篇 |
1998年 | 322篇 |
1997年 | 322篇 |
1996年 | 398篇 |
1995年 | 336篇 |
1994年 | 336篇 |
1993年 | 361篇 |
1992年 | 339篇 |
1991年 | 289篇 |
1990年 | 232篇 |
1989年 | 220篇 |
1988年 | 200篇 |
1987年 | 192篇 |
1986年 | 193篇 |
1985年 | 250篇 |
1984年 | 225篇 |
1983年 | 197篇 |
1982年 | 214篇 |
1981年 | 202篇 |
1980年 | 180篇 |
1979年 | 161篇 |
1978年 | 185篇 |
1977年 | 144篇 |
1976年 | 141篇 |
1974年 | 132篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Miloslav Duchoň Anatolij Dvurečenskij Paolo de Lucia 《International Journal of Theoretical Physics》1997,36(9):1941-1958
We present a solution to the moment problem for effect algebras, concerning mean values of all powers of an observable concentrated
on the interval [0, 1] for states from a convex set. We give a solution for particular examples, e.g., for the set of all
effect operators. We examine how this problem is related to a socalled E-property. Finally, we give a solution for observables
studied in the operational approach to physical theories. 相似文献
72.
J.-J. Sauvain L. F. de Alencastro J. Tarradellas R. Camenzind G. Karlaganis C. Vuilleumier 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):555-562
The analysis of PCB in transformer oils has been achieved with three HRGC/ECD based methods, proposed by the International Electrotechnical Commission (IEC/TC 10), by the Comité Européen de Normalisation (CEN/TC 19/WG 22) and by the Deutsches Institut für Normung (DIN 51 527). The same clean-up, described in the CEN/TC 19/WG 22, has been used for all the samples, allowing a comparison of the quantification procedure only. The total chlorine content has also been determined with X-ray fluorescence. These different methods of quantification are compared and their application for legislative purposes is discussed.Dedicated to Professor Dr Dieter Klockow on the occasion of his 60th birthday 相似文献
73.
Patricia Smichowski María Beatriz de la Calle Guntiñas Carmen Cámara 《Fresenius' Journal of Analytical Chemistry》1994,348(5-6):380-384
Summary A method is described for antimony preconcentration based on retention on a column of activated alumina. Recovery is 80% when no pH-control and 4 mol/l HCl as eluent are used. The preconcentration factor is 400. The method was applied to the determination of antimony in spiked tap and sea water. The analytical performance of the method is discussed. 相似文献
74.
75.
76.
Katalytische Epoxidierung und 1,2‐Dihydroxylierung von Olefinen mit Bispidin‐Eisen(II)/H2O2‐Systemen
77.
Rafael Ortega 《Journal of Dynamics and Differential Equations》1992,4(4):651-665
This paper gives sufficient conditions for the existence of periodic solutions of twist type of a time-dependent differential equation of the second order. The concept of periodic solution of twist type is defined in terms of the corresponding Birkhoff normal form and, in particular, implies that the solution is Lyapunov stable. Some applications to nonlocal problems are given. 相似文献
78.
Principles and recent developments in ultrasound contrast agents 总被引:6,自引:1,他引:5
The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications. 相似文献
79.
A general relationship between the volume fraction and the specific interfacial area for averaged dispersed two-phase flows is proposed. This relationship, expressed as a basic set of two scalar evolution equations and two vectorial non-uniformity state equations, is an analytical result obtained by a systematic approach using the derivatives of some generalized functions and a local volume-averaging technique. The proposed set of equations was expressed for measurable macroscopic parameters of the system and has the same generality as the averaged transport equations of two-phase flows. By combination of the basic set of equations, called the averaged topological equations (ATEs), second-order ATEs for the volume fraction were found. The second-order ATEs were expressed both by a Lagrangian formulation and by a Eulerian formulation. The importance and physical meaning of the ATEs developed in this study were clarified within the framework of the theory of kinematic waves. 相似文献
80.
We shall prove here that any binary relation on a base E with cardinality n > 6 is reconstructible from its restrictions of cardinality 2, 3, 4 and (n - 1). This proof needs results of part I of this paper where we characterize any pair of relations R, R' which are 2-, 3- and 4-hypomorphic. As a corollary we obtain that any binary relation is (n - 4)-reconstructible (when n > 9). 相似文献