全文获取类型
收费全文 | 399208篇 |
免费 | 26251篇 |
国内免费 | 17727篇 |
专业分类
化学 | 217202篇 |
晶体学 | 5881篇 |
力学 | 21105篇 |
综合类 | 37篇 |
数学 | 45927篇 |
物理学 | 153034篇 |
出版年
2021年 | 3391篇 |
2020年 | 3848篇 |
2019年 | 4932篇 |
2018年 | 6209篇 |
2017年 | 6815篇 |
2016年 | 9031篇 |
2015年 | 6027篇 |
2014年 | 8504篇 |
2013年 | 18238篇 |
2012年 | 15199篇 |
2011年 | 18899篇 |
2010年 | 17582篇 |
2009年 | 17933篇 |
2008年 | 15797篇 |
2007年 | 15277篇 |
2006年 | 13910篇 |
2005年 | 13066篇 |
2004年 | 13108篇 |
2003年 | 11343篇 |
2002年 | 11230篇 |
2001年 | 12045篇 |
2000年 | 9151篇 |
1999年 | 7729篇 |
1998年 | 6613篇 |
1997年 | 6435篇 |
1996年 | 6375篇 |
1995年 | 6284篇 |
1994年 | 6461篇 |
1993年 | 6348篇 |
1992年 | 6429篇 |
1991年 | 6290篇 |
1990年 | 5713篇 |
1989年 | 5844篇 |
1988年 | 5697篇 |
1987年 | 5031篇 |
1986年 | 4809篇 |
1985年 | 5699篇 |
1984年 | 5966篇 |
1983年 | 4638篇 |
1982年 | 5151篇 |
1981年 | 4893篇 |
1980年 | 4611篇 |
1979年 | 4855篇 |
1978年 | 5053篇 |
1977年 | 5125篇 |
1976年 | 5434篇 |
1975年 | 4571篇 |
1974年 | 4561篇 |
1973年 | 4806篇 |
1972年 | 3623篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
941.
942.
微模塑法制备PMMA/SiO2二氧化硅杂化材料微结构 总被引:1,自引:0,他引:1
以摩尔比为 1∶1的甲基丙烯酸甲酯 (MMA)、甲基丙烯酸 (3 三乙氧基硅烷基 )丙酯 (ESMA)单体、0 .2 %(单体总量的质量分数 )的偶氮二异丁腈AIBN引发剂和四氢呋喃 (THF)溶剂 ,及 2 0 % (总质量分数 )的正硅酸乙酯TEOS合成出PMMA/SiO2 有机 无机杂化的杂化溶胶 .将溶胶在洗净的普通光学玻璃基片表面甩膜 .利用软刻蚀中的微模塑法 ,把有机硅弹性印章复制有精细图纹一面轻放在杂化溶胶膜上进行微模塑 ,外加 1N压力于12 0℃下处理 2h使溶胶凝胶化 .印章剥离后在基片表面就形成了PMMA/SiO2 有机 无机杂化材料的微图纹结构 .从微图纹的光学显微镜照片可以看出微模塑方法制备杂化材料复制的图纹精细度高 ,操作简单易行 ,是一类比较理想的微细图纹结构加工的方法 . 相似文献
943.
Let Cld
AW
(X) be the hyperspace of nonempty closed subsets of a normed linear space X with the Attouch–Wets topology. It is shown that the space Cld
AW
(X) and its various subspaces are AR's. Moreover, if X is an infinite-dimensional Banach space with weight w(X) then Cld
AW
(X) is homeomorphic to a Hilbert space with weight 2
w(X). 相似文献
944.
The authors study the bifurcation problems of rough heteroclinic loop connecting three saddle points for the case β1 > 1, β2 > 1, β3 < 1 and β1β2β3 < 1. The existence, number, coexistence and incoexistence of 2-point-loop, 1-homoclinic orbit and 1-periodic orbit are studied. Meanwhile, the bifurcation surfaces and existence regions are given. 相似文献
945.
Geerk J. Linker G. Meyer O. Politis C. Ratzel F. Smithey R. Strehlau B. Xiong G. C. 《Zeitschrift für Physik B Condensed Matter》1987,67(4):507-511
Thin superconducting films of La1.8Sr0.2CuO4 have been prepared by magnetron sputter deposition and subsequent temperature treatment. The composition of the films has been determined by Rutherford backscattering and the structure by thin film X-ray diffraction. The onset of superconductivity was about 32 K and the midpoint near 28 K. Defect production in the films by He ion bombardment revealed a drasticT
c
reduction with a sensitivity similar to that observed in the Chevrel phases. Oxygen implantation and subsequent annealing led to an enhancement of theT
c
onset. 相似文献
946.
947.
For three‐dimensional flows with one inhomogeneous spatial coordinate and two periodic directions, the Karhunen–Loeve procedure is typically formulated as a spatial eigenvalue problem. This is normally referred to as the direct method (DM). Here we derive an equivalent formulation in which the eigenvalue problem is formulated in the temporal coordinate. It is shown that this so‐called method of snapshots (MOS) has some numerical advantages when compared to the DM. In particular, the MOS can be formulated purely as a matrix composed of scalars, thus avoiding the need to construct a matrix of matrices as in the DM. In addition, the MOS avoids the need for so‐called weight functions, which emerge in the DM as a result of the non‐uniform grid typically employed in the inhomogeneous direction. The avoidance of such weight functions, which may exhibit singular behaviour, guarantees satisfaction of the boundary conditions. The MOS is applied to data sets recently obtained from the direct simulation of turbulence in a channel in which viscoelasticity is imparted to the fluid using a Giesekus model. The analysis reveals a steep drop in the dimensionality of the turbulence as viscoelasticity is increased. This is consistent with the results that have been obtained with other viscoelastic models, thus revealing an essential generic feature of polymer‐induced drag reduced turbulent flows. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
948.
We consider a splitting finite-difference scheme for an initial-boundary value problem for a two-dimensional nonlinear evolutionary
equation. The problem is split into nonlinear and linear parts. The linear part is also split into locally one-dimensional
equations. We prove the convergence and stability of the scheme in L
2 and C norms.
Printed in Lietuvos Matematikos Rinkinys, Vol. 45, No. 3, pp. 413–434, July–September, 2005. 相似文献
949.
950.