全文获取类型
收费全文 | 220674篇 |
免费 | 30316篇 |
国内免费 | 15427篇 |
专业分类
化学 | 151687篇 |
晶体学 | 2604篇 |
力学 | 12190篇 |
综合类 | 930篇 |
数学 | 24688篇 |
物理学 | 74318篇 |
出版年
2023年 | 2688篇 |
2022年 | 5041篇 |
2021年 | 5515篇 |
2020年 | 6921篇 |
2019年 | 7906篇 |
2018年 | 6823篇 |
2017年 | 6354篇 |
2016年 | 10807篇 |
2015年 | 9722篇 |
2014年 | 11716篇 |
2013年 | 15217篇 |
2012年 | 15907篇 |
2011年 | 15825篇 |
2010年 | 12463篇 |
2009年 | 12290篇 |
2008年 | 12401篇 |
2007年 | 10988篇 |
2006年 | 9995篇 |
2005年 | 8695篇 |
2004年 | 7321篇 |
2003年 | 6229篇 |
2002年 | 6876篇 |
2001年 | 5678篇 |
2000年 | 4947篇 |
1999年 | 3874篇 |
1998年 | 3236篇 |
1997年 | 2995篇 |
1996年 | 2940篇 |
1995年 | 2452篇 |
1994年 | 2369篇 |
1993年 | 2155篇 |
1992年 | 1990篇 |
1991年 | 1962篇 |
1990年 | 1792篇 |
1989年 | 1572篇 |
1988年 | 1309篇 |
1987年 | 1247篇 |
1986年 | 1216篇 |
1985年 | 1209篇 |
1984年 | 1087篇 |
1983年 | 946篇 |
1982年 | 899篇 |
1981年 | 766篇 |
1979年 | 827篇 |
1978年 | 817篇 |
1977年 | 812篇 |
1976年 | 928篇 |
1975年 | 818篇 |
1974年 | 847篇 |
1973年 | 851篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
S. Yu. Davydov 《Technical Physics》2002,47(1):92-96
A relationship is analyzed between the ionization energy of atoms I and the work function φ of a metal composed of these atoms. The transition energy ∑=I?φ is assumed to be the sum of kinetic K and coulombic C contributions. Contribution K is calculated in the framework of a model of uniform gas of quasi-free electrons, and C is determined from experimental values of Σ. Calculations performed for a wide range of metals have shown that the dimensionless coefficients determining the Coulombic contribution C differ insignificantly between various groups of metals. The relationships obtained have been used for determining the work function of binary alloys. 相似文献
992.
Sanzhizhapov D. B. Tonevitskii Yu. V. Mognonov D. M. Doroshenko Yu. E. 《Russian Journal of Applied Chemistry》2003,76(4):619-622
New polyimidates were prepared from bisphenols and mono- and dicarboxylic acid imidoyl chlorides. The structures of the polymers were determined, and their physicochemical, chemical, and thermal properties were studied. The possibility of preparing film and compression materials with good mechanical characteristics from these polymers was examined. 相似文献
993.
Hongyi Yu 《应用数学学报(英文版)》1991,7(3):284-288
In this paper, we study the PBVP for integro-differential equations of Volterra type in Banach spaces. By developing monotone iterative technique for the PBVP, we get some results concerning the existence of extremal solutions, which are the limits of monotone sequences.The project supported by the Natural Science Foundation of Shandong Province. 相似文献
994.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
995.
A combined programming and iteration algorithm for finite element analysis of three-dimensional contact problems 总被引:3,自引:0,他引:3
Comparing with two-dimensional contact problems, three-dimensional frictional contact problems are more difficult to deal
with, because of the unknown slip direction of the tangential force and enormous computing time. In order to overcome these
difficulties, a combined PQP (Parametric Quadratic Programming) and iteration method is derived in this paper. The iteration
algorithm, which alleviates the difficulty of unknown slip direction, is used along with the PQP method to cut down computing
costs. Numerical example is given to demonstrate the validity of the present algorithm.
The project supported by the Machinary and Electronics Ministry of China 相似文献
996.
After having introduced by ion implantation 57Fe to a local concentration of 7 at% into Co6Ag94, we observed it by conversion electron Mössbauer spectroscopy in the as-prepared state and after isochronal annealing. A superferromagnetic state is inferred, which is correlated with the ordering of the magnetic moments on the Fe clusters through chain-like or dendritic Co/Fe linear structures. The magnetic moment disordering temperature lies above 473 K. 相似文献
997.
998.
In this article, a kind of auxiliary design BSA* for constructing BSAs is introduced and studied. Two powerful recursive constructions on BSAs from 3‐IGDDs and BSA*s are exploited. Finally, the necessary and sufficient conditions for the existence of a BSA(v, 3, λ; α) with α = 2, 3 are established. © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 61–76, 2007 相似文献
999.
1000.
L. G. Smirnova Yu. B. Grunin S. V. Krasil'nikova M. A. Zaverkina D. R. Bakieva E. V. Smirnov 《Colloid Journal》2003,65(6):778-781
The pulsed NMR, isopiestic and pycnometric methods are applied to investigate the physicochemical properties of softwood [GOST (State Standard) 9571-89] and hardwood [GOST 28172-89] celluloses, as well as flax cellulose [GOST 10330-76, 9394-76], both in the initial state and subjected to chemical treatment. Possible changes occurring in the supramolecular structure of a polymer are analyzed. The structural and sorption characteristics of the investigated samples are calculated. Their water absorption capacities are determined. 相似文献