全文获取类型
收费全文 | 2819篇 |
免费 | 145篇 |
国内免费 | 6篇 |
专业分类
化学 | 1937篇 |
晶体学 | 20篇 |
力学 | 65篇 |
数学 | 393篇 |
物理学 | 555篇 |
出版年
2023年 | 20篇 |
2022年 | 18篇 |
2021年 | 35篇 |
2020年 | 45篇 |
2019年 | 47篇 |
2018年 | 48篇 |
2017年 | 58篇 |
2016年 | 115篇 |
2015年 | 75篇 |
2014年 | 124篇 |
2013年 | 211篇 |
2012年 | 217篇 |
2011年 | 232篇 |
2010年 | 137篇 |
2009年 | 132篇 |
2008年 | 160篇 |
2007年 | 135篇 |
2006年 | 104篇 |
2005年 | 147篇 |
2004年 | 99篇 |
2003年 | 107篇 |
2002年 | 84篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 26篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 27篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 13篇 |
排序方式: 共有2970条查询结果,搜索用时 468 毫秒
51.
L. Barral J. Cano A. J. López J. López P. Nogueira C. Ramírez 《Journal of Thermal Analysis and Calorimetry》1996,47(3):791-797
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol–1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetan peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.This work was supported by the Xunta de Galicia through grant XUGA-17201A92. 相似文献
52.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
53.
Graciela Díaz de Delgado Ramírez V. Belkis Miguel Delgado José Rosquete P. Carmelo 《Journal of chemical crystallography》1995,25(7):371-374
The title compound, formula C15H20O2, is orthorhombic, P212121 witha=8.747(2),b=12.025(3),c=12.554(3)Å,Z=4, andD
m
=1.32(2)g/ml. The structural analysis shows that the compound corresponds to eudesma-4(15),7(11)-dien-8,12-olide, a sesquiterpene lactone previously isolated fromAster umbellatus but whose crystal structure was unknown. 相似文献
54.
Federico Sánchez-Bringas Ana Irene Ramírez-Galarza 《Annals of Global Analysis and Geometry》1995,13(2):129-140
LetM be a compact orientable surface,I:M R4 an immersion of classC
r
and
a normal unitary smooth vector field. We prove that in the space of pairs (I,
) the family of pairs all whose umbilical points are Darbouxian is generic. 相似文献
55.
56.
57.
58.
59.
60.
[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin. 相似文献