全文获取类型
收费全文 | 458631篇 |
免费 | 5921篇 |
国内免费 | 1446篇 |
专业分类
化学 | 252772篇 |
晶体学 | 6580篇 |
力学 | 18524篇 |
综合类 | 8篇 |
数学 | 54935篇 |
物理学 | 133179篇 |
出版年
2021年 | 3473篇 |
2020年 | 4007篇 |
2019年 | 4527篇 |
2018年 | 6077篇 |
2017年 | 5790篇 |
2016年 | 8774篇 |
2015年 | 5766篇 |
2014年 | 8365篇 |
2013年 | 21358篇 |
2012年 | 16660篇 |
2011年 | 19799篇 |
2010年 | 13408篇 |
2009年 | 12846篇 |
2008年 | 18043篇 |
2007年 | 18288篇 |
2006年 | 16740篇 |
2005年 | 15515篇 |
2004年 | 13798篇 |
2003年 | 12227篇 |
2002年 | 11897篇 |
2001年 | 12349篇 |
2000年 | 9617篇 |
1999年 | 7329篇 |
1998年 | 6249篇 |
1997年 | 6268篇 |
1996年 | 5979篇 |
1995年 | 5232篇 |
1994年 | 5182篇 |
1993年 | 5283篇 |
1992年 | 5678篇 |
1991年 | 5726篇 |
1990年 | 5446篇 |
1989年 | 5409篇 |
1988年 | 5359篇 |
1987年 | 5184篇 |
1986年 | 4958篇 |
1985年 | 6720篇 |
1984年 | 7007篇 |
1983年 | 5684篇 |
1982年 | 6284篇 |
1981年 | 6064篇 |
1980年 | 5742篇 |
1979年 | 5967篇 |
1978年 | 6261篇 |
1977年 | 6101篇 |
1976年 | 6335篇 |
1975年 | 5784篇 |
1974年 | 5865篇 |
1973年 | 6301篇 |
1972年 | 4022篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
941.
E. Hatta H. Hosoi H. Akiyama T. Ishii K. Mukasa 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):347-349
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface
by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes
itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is
caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure.
The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There
are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions.
Received: 8 July 1997 / Accepted: 4 November 1997 相似文献
942.
A technique for the characterization of an interior crack perpendicular to the surface of the plates is presented. A time-harmonic line load is applied on the upper surface of the plate. The scattered displacement field is calculated by using the strip element method. It is found that there are additional superimposed oscillations in the curve of the absolute values of the displacement in the region between the load and the crack. The mean value of the peaks of the additional oscillations increases with the crack length, and is less dependent on the distance from the load to the crack. The crack position is determined from the displacement distribution curve and the crack length is determined from the mean value of the peaks of the additional oscillations. Approximate polynomial formula of degree four for predicting the length of interior vertical cracks in isotropic homogeneous plates is also proposed. Numerical examples are given to demonstrate the present technique. 相似文献
943.
N. Srinivasan R.C. Johnson N. Kasthurikrishnan P. Wong R.G. Cooks 《Analytica chimica acta》1997,350(3):128-271
An overview of membrane introduction mass spectrometry (MIMS) is presented and comparisons are made with other direct sample introduction techniques. Special attention is given to the unique advantages and the limitations of newer variants on the MIMS technique, including affinity MIMS, reverse-phase and trap MIMS. The salient features of the interfaces used in MIMS are summarized and the various membrane materials commonly used are delineated. The applicability of MIMS is illustrated via discussion of
- 1. (i) bioreactor monitoring (represented by yeast fermentation),
- 2. (ii) environmental monitoring (illustrated by analysis of contaminated ground water samples) and
- 3. (iii) on-line chemical reaction monitoring (exemplified by the photolysis of aryl esters).
944.
The specific heat C
total of crystalline and amorphous Eu2(MoO4)3 is measured in the temperature interval 4.5–30 K. The amorphous state is obtained by applying pressure ∼7 GPa at room temperature.
It is found that the specific heat of the crystal at T⩽7.5 K is described by a cubic function of temperature, while the specific
heat of the amorphous sample has a strongly non-Debye character in the entire experimental temperature interval. The curve
of C
total for amorphous europium molybdate is analyzed in a model of soft atomic potentials, and it is shown that it agrees well with
universal low-temperature anomalies of the specific heat of classical glasses obtained by quenching from the liquid.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 623–627 (25 October 1998) 相似文献
945.
946.
Microencapsulation of DNA Within alginate microspheres and crosslinked chitosan membranes for in vivo application 总被引:4,自引:0,他引:4
T. Alexakis D. K. Boadi D. Quong A. Groboillot I. O’Neill D. Poncelet R. J. Neufeld 《Applied biochemistry and biotechnology》1995,50(1):93-106
Calf thymus DNA was microencapsulated within crosslinked chitosan membranes, or immobilized within chitosan-coated alginate
microspheres. Microcapsules were prepared by interfacial polymerization of chitosan, and alginate microspheres formed by emulsification/
internal gelation. Diameters ranged from 20 to 500 Μm, depending on the formulation conditions. Encapsulated DNA was quantifiedin situ by direct spectrophotometry (260 nm) and ethidium bromide fluorimetry, and compared to DNA measurements on the fractions
following disruption and dissolution of the microspheres. Approximately 84% of the DNA was released upon core dissolution
and membrane disruption, with 12% membrane bound. The yield of encapsulation was 96%. Leakage of DNA from intact microspheres/capsules
was not observed. DNA microcapsules and microspheres were recovered intact from rat feces following gavage and gastrointestinal
transit. Higher recoveries (60%) and reduced shrinkage during transit were obtained with the alginate microspheres. DNA was
recovered and purified from the microcapsules and microspheres by chromatography and differential precipitation with ethanol.
This is the first report of microcapsules or microspheres containing biologically active material (DNA) being passed through
the gastrointestinal tract, with the potential for substantial recovery. 相似文献
947.
We study the conjugate boundary-value problem with boundary conditions whose orders can be as large as the order of the differential equation or larger. We construct the Green's function of the problem over the entire space when the separating surface is a hyperplane, and we describe its properties. Bibliography: 6 titles.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 30, 1989, pp. 20–24. 相似文献
948.
949.
On the basis of the general class of solutions of 6D vacuum Einstein equations and using well-known results of the 6D geometric model of electroweak and gravitational interactions, the variations of fundamental physical constants and their influence on the observed red-shift of galaxies are investigated. By considering the interpretation of extra components of the 6D metric as reproducing the properties of matter in the 4D curved space-time, the effective quantities of matter are obtained. In particular, the states of dust and radiation are shown. The corresponding 5D models were also investigated. 相似文献
950.
We prove that in some reasonable sense, every possible physical law can be reformulated in terms of symmetries. This result explains the well-known success of the group-theoretic approach in physics. 相似文献