全文获取类型
收费全文 | 148685篇 |
免费 | 1807篇 |
国内免费 | 617篇 |
专业分类
化学 | 84152篇 |
晶体学 | 2222篇 |
力学 | 5565篇 |
综合类 | 6篇 |
数学 | 16222篇 |
物理学 | 42942篇 |
出版年
2016年 | 1675篇 |
2015年 | 1303篇 |
2014年 | 1737篇 |
2013年 | 5976篇 |
2012年 | 4455篇 |
2011年 | 5768篇 |
2010年 | 3446篇 |
2009年 | 3086篇 |
2008年 | 5156篇 |
2007年 | 5271篇 |
2006年 | 5296篇 |
2005年 | 5236篇 |
2004年 | 4566篇 |
2003年 | 4089篇 |
2002年 | 3977篇 |
2001年 | 3917篇 |
2000年 | 2956篇 |
1999年 | 2419篇 |
1998年 | 2143篇 |
1997年 | 2149篇 |
1996年 | 2142篇 |
1995年 | 2031篇 |
1994年 | 1799篇 |
1993年 | 1792篇 |
1992年 | 2003篇 |
1991年 | 1957篇 |
1990年 | 1889篇 |
1989年 | 1903篇 |
1988年 | 1924篇 |
1987年 | 1901篇 |
1986年 | 1809篇 |
1985年 | 2477篇 |
1984年 | 2648篇 |
1983年 | 2177篇 |
1982年 | 2584篇 |
1981年 | 2398篇 |
1980年 | 2389篇 |
1979年 | 2366篇 |
1978年 | 2502篇 |
1977年 | 2385篇 |
1976年 | 2361篇 |
1975年 | 2291篇 |
1974年 | 2136篇 |
1973年 | 2309篇 |
1972年 | 1409篇 |
1971年 | 1082篇 |
1970年 | 997篇 |
1969年 | 991篇 |
1968年 | 1123篇 |
1967年 | 1159篇 |
排序方式: 共有10000条查询结果,搜索用时 3 毫秒
71.
We engage a study of nonmodal linear logic which takes times ⊗ and the linear conditional ⊸ to be the basic connectives instead
of times and linear negation ()⊥ as in Girard's approach. This difference enables us to obtain a very large subsystem of linear logic (called positive linear
logic) without an involutionary negation (if the law of double negation is removed from linear logic in Girard's formulation,
the resulting subsystem is extremely limited). Our approach enables us to obtain several natural models for various subsystems
of linear logic, including a generic model for the so-called minimal linear logic. In particular, it is seen that these models
arise spontaneously in the transition from set theory to multiset theory. We also construct a model of full (nonmodal) linear
logic that is generic relative to any model of positive linear logic. However, the problem of constructing a generic model
for positive linear logic remains open. Bibliography: 2 titles.
Published inZapiski Nauchnykh Seminarov POMI, Vol. 220, 1995, pp. 23–35. Original 相似文献
72.
Summary The paper discusses some developments in the coordinate partitioning method for the dynamic analysis of constrained/closed-loop multibody systems. First, the method is reformulated to a more compact form. Then, a simple and reliable projective criterion for choosing the best coordinates from the redundant ones is proposed, and some advantages are pointed out that may arise in the method by applying inverse kinematics algorithms. Finally, the problem of determination ofphysical reactions of constraints and closing conditions is discussed. A four-bar linkage mechanism serves for an illustration of some aspects of the paper.
On leave from the Department of Mechanics, Technical University of Radom, ul. Malczewskiego 29, 26-600 Radom, Poland 相似文献
Ein Projektionskriterium zur Koordinatenwahl bei Mehrkörpersystemen mit kinematischen Schleifen
Übersicht Bei der Simulation der Bewegunsgleichungen von Mehrkörpersystemen mit kinematischen Schleifen in Minimalform stellt sich die Frage nach der Wahl günstiger verallgemeinerter Koordinaten. Hierfür wird ein Projektionskriterium vorgeschlagen, welches die Trennung der systembeschreibenden redundanten Koordinaten in die verallgemeinerten und davon abhängige Koordinaten gestattet. Durch Anwendung eines Verfahrens zur Rückwärtstransformation der kinematischen Beschreibung lassen sich in diesen explizite Schließbedingungen formulieren, was sich bei der Simulation vorteilhaft auswirkt; diese kann ohne Verletzung der Schließbedingungen erfolgen. Es wird auch gezeigt, wie auch bei Verwendung verallgemeinerter Koordinatenphysikalisch interpretierbare Reaktionen ermittelt werden können. Als Anwendungsbeispiel dient ein ebenes Viergelenk.
On leave from the Department of Mechanics, Technical University of Radom, ul. Malczewskiego 29, 26-600 Radom, Poland 相似文献
73.
X-ray, DSC and optical studies of a new class of substances with aromatic rings in the lateral branches are reported. The thermal behaviour of the substances is discussed. The X-ray measurements lead to a structural model of the SA phases consisting of layer structures with intercalating molecules. 相似文献
74.
75.
Investigations of coated carbon fibres are reported using Raman spectroscopy. Relationships between different process parameters (for example precursor concentration, reactor temperature and various precursors) and the resulting types of carbon fibres are discussed. 相似文献
76.
Classical methods of structural analysis cannot be applied to liquid crystals because higher order reflections disappear during the transition from crystal to liquid crystal due to the reduction in long range orientational and translational correlations. However, in order to relate physical properties to the molecular architecture, it is essential to have information about molecular positions and orientations in the crystalline state as well as in the liquid crystalline state. In this work, the transition from crystalline to liquid crystalline phase is carefully monitored and the relationship between the original lattice and the new molecular positions found using electron diffraction. In addition to this, a new high resolution electron-microscopic technique is described in which the positions of molecules in the crystalline and the quenched discotic phase are directly imaged and the defects observed in the crystalline and LC phase compared and quantitatively analysed. 相似文献
77.
E. Waidmann H. Emons H. W. Dürbeck 《Fresenius' Journal of Analytical Chemistry》1994,350(4-5):293-297
Within the framework of the German Environmental Specimen Bank program, Tl, Cu, Pb, Cd and Zn were determined in homogenized materials from the limnic environment using Isotope Dilution Mass Spectrometry (IDMS) with thermal ionization. The analytical procedures which were developed for the trace metal analysis of bioindicator and sediment samples are described in detail. Results obtained in bream, mussels (Dreissena polymorpha) and sediments of Lake Constance/Estuary of Constance in the sampling years 1981, 1985, 1988, 1990, 1992 and 1993 are discussed and compared with those of bream from the lakeland district of Born-hoeved/Lake Belau and from the River Saar as well as from reference materials. 相似文献
78.
79.
Christopher J. Booth John W. Goodby Judith P. Hardy Olwen C. Lettington Kenneth J. Toyne 《Liquid crystals》1994,16(6):925-940
The synthesis and characterization of seven novel (R)-2-(4-substituted-phenoxy)propanonitriles are described. The propanonitriles were prepared to evaluate their potential use as thermochromics and ferroelectric dopants, as well as to determine their twist sense properties. The materials exhibit smectic and chiral nematic phases of high thermal stability; the mesogenic behaviour of the nitriles is directly related to the type of two-ring core unit employed. The effects of the different molecular geometries and polarizabilities of the liquid crystalline cores on mesophase stability are discussed, particularly in relation to other members of this series. The chiral nematic phase of the propanonitriles is assigned as having a left-handed twist sense from contact preparation studies, and this is in agreement with rules relating absolute configuration and molecular structure to helical twist sense. 相似文献
80.