全文获取类型
收费全文 | 152952篇 |
免费 | 2685篇 |
国内免费 | 613篇 |
专业分类
化学 | 87921篇 |
晶体学 | 2274篇 |
力学 | 5913篇 |
综合类 | 6篇 |
数学 | 14772篇 |
物理学 | 45364篇 |
出版年
2021年 | 1041篇 |
2020年 | 1145篇 |
2019年 | 1115篇 |
2016年 | 2086篇 |
2015年 | 1696篇 |
2014年 | 2225篇 |
2013年 | 6361篇 |
2012年 | 5497篇 |
2011年 | 6678篇 |
2010年 | 4066篇 |
2009年 | 3723篇 |
2008年 | 5815篇 |
2007年 | 5746篇 |
2006年 | 5681篇 |
2005年 | 5487篇 |
2004年 | 4785篇 |
2003年 | 4140篇 |
2002年 | 4054篇 |
2001年 | 4132篇 |
2000年 | 3186篇 |
1999年 | 2519篇 |
1998年 | 2120篇 |
1997年 | 2156篇 |
1996年 | 2139篇 |
1995年 | 2021篇 |
1994年 | 1817篇 |
1993年 | 1812篇 |
1992年 | 2027篇 |
1991年 | 1933篇 |
1990年 | 1834篇 |
1989年 | 1816篇 |
1988年 | 1814篇 |
1987年 | 1784篇 |
1986年 | 1677篇 |
1985年 | 2297篇 |
1984年 | 2369篇 |
1983年 | 1990篇 |
1982年 | 2331篇 |
1981年 | 2116篇 |
1980年 | 2148篇 |
1979年 | 2127篇 |
1978年 | 2263篇 |
1977年 | 2178篇 |
1976年 | 2202篇 |
1975年 | 2153篇 |
1974年 | 1971篇 |
1973年 | 2172篇 |
1972年 | 1319篇 |
1968年 | 1060篇 |
1967年 | 1114篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
871.
Unsteady mass transfer in a steady flow field of a laminar forced flow against a rotating disk is analyzed by using a very effective solution method. Rigorous numerical solutions have been obtained for steady and unsteady mass transfer for any relative flow strength of external flow and rotation-induced flow for 0.1 ≤Sc ≤ 10000. Simple but very accurate correlation equations of Sherwood number for both the steady and unsteady mass transfer are proposed. 相似文献
872.
Summary We review the phase behaviour of mixtures of colloids and non-adsorbing polymers. The exclusion of polymer molecules from
overlapping ?depletion zones? between two neighbouring colloidal particles results in an unbalanced osmotic pressure pushing
the particles together. This depletion potential is separately tunable in range and depth. Theory predicts that the resulting
phase behaviour is sensitive to ξ=r
g/R, the ratio of the radius of gyration of a polymer molecule, to the radius of the colloid. At large ξ, a stable colloidalliquid phase becomes possible. This has been confirmed by recent experiments. The formation of non-equilibrium ?transient gel? states
when the size ratio is small (≈0.08) is also introduced briefly.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
873.
W. Ochs 《Zeitschrift fur Physik C Particles and Fields》1991,50(2):339-344
We propose a method to perform the intermittency analysis of multi hadron production in up to three momentum space dimensions. The analysis of realistic (approximately) selfsimilar cascade models shows that the strongest rise of multiplicity moments with decreasing phase space intervals and the closest approach to a power law occurs in three dimensions. Moments of higher orderF (q) are related to the second momentF (2) by a power law in good approximation. These powers are found independent of the dimensions in the models and in available data; furthermore, they are only weakly dependent on the reaction type. The relevance to the quark gluon plasma search is discussed. 相似文献
874.
Ultrasonic analysis of edible fats and oils 总被引:7,自引:0,他引:7
Low intensity ultrasound is a powerful analytical technique for investigating the physico-chemical properties of many biological and non-biological materials. In this article its application for the characterization of edible fats and oils is assessed. Ultrasound can be used to determine the dynamic rheology and composition of oils, the oil content and droplet size of emulsions and the solid fat content of partially crystalline emulsions. It is capable of rapid and precise measurements, is non-destructive and non-invasive, can be used on-line or off-line and is relatively inexpensive. Ultrasonic techniques will therefore prove a useful addition to the existing analytical techniques used to characterize fats and oils. 相似文献
875.
W. J. Ricker 《Rendiconti del Circolo Matematico di Palermo》1997,46(2):197-212
We make a detailed study of the compactness properties of the integration map associated with the classical Volterra (vector valued) measure inX=L p([0, 1]), forp in [1, ∞], and inX=C([0, 1]), whereX is equipped with its relevant weak or weak-star topology. The spaceX (a Frechet space) of all complex valued sequences, equipped with the pointwise convergence topology, is also considered. 相似文献
876.
Properties of matrix-assisted laser desorption. Measurements with a time-to-digital converter. 总被引:2,自引:0,他引:2
Some properties of matrix-assisted laser desorption have been studied using single-ion-counting methods and a time-to-digital converter. The methods allow examination of the process for irradiances near the reported threshold for observation with a transient recorder. All measurements were made using bovine insulin as a test compound. We present direct evidence that an irradiance threshold near 10(6) W cm-2 exists for ion production, and that the process is a collective effect, either involving a large number of molecular ions (approximately 10(4) in a successful event or none at all. Above the threshold, the yield is found to scale with a high power (4th to 6th) of the irradiance. Measurements of initial velocity distributions indicate an axial velocity spread corresponding to approximately 50 eV and a radial velocity spread corresponding to approximately 2.4 eV. Thus the ejection or extraction mechanism appears to be strongly asymmetric. 相似文献
877.
H. S. Dollar N. I. M. Gould W. H. A. Schilders A. J. Wathen 《Computational Optimization and Applications》2007,36(2-3):249-270
The problem of finding good preconditioners for the numerical solution of a certain important class of indefinite linear systems is considered. These systems are of a 2 by 2 block (KKT) structure in which the (2,2) block (denoted by -C) is assumed to be nonzero. In Constraint preconditioning for indefinite linear systems, SIAM J. Matrix Anal. Appl. 21 (2000), Keller, Gould and Wathen introduced the idea of using constraint preconditioners that have a specific 2 by 2 block structure for the case of C being zero. We shall give results concerning the spectrum and form of the eigenvectors when a preconditioner of the form considered by Keller, Gould and Wathen is used but the system we wish to solve may have C ≠0. In particular, the results presented here indicate clustering of eigenvalues and, hence, faster convergence of Krylov subspace iterative methods when the entries of C are small; such a situations arise naturally in interior point methods for optimization and we present results for such problems which validate our conclusions. 相似文献
878.
879.
880.