全文获取类型
收费全文 | 37260篇 |
免费 | 781篇 |
国内免费 | 167篇 |
专业分类
化学 | 20797篇 |
晶体学 | 226篇 |
力学 | 1197篇 |
综合类 | 9篇 |
数学 | 5306篇 |
物理学 | 10673篇 |
出版年
2022年 | 177篇 |
2021年 | 477篇 |
2020年 | 497篇 |
2019年 | 415篇 |
2018年 | 511篇 |
2017年 | 440篇 |
2016年 | 794篇 |
2015年 | 697篇 |
2014年 | 823篇 |
2013年 | 1439篇 |
2012年 | 1754篇 |
2011年 | 2056篇 |
2010年 | 1155篇 |
2009年 | 1071篇 |
2008年 | 1743篇 |
2007年 | 1766篇 |
2006年 | 1671篇 |
2005年 | 2113篇 |
2004年 | 2020篇 |
2003年 | 1469篇 |
2002年 | 1067篇 |
2001年 | 952篇 |
2000年 | 887篇 |
1999年 | 528篇 |
1998年 | 458篇 |
1997年 | 455篇 |
1996年 | 572篇 |
1995年 | 510篇 |
1994年 | 486篇 |
1993年 | 551篇 |
1992年 | 514篇 |
1991年 | 443篇 |
1990年 | 357篇 |
1989年 | 356篇 |
1988年 | 344篇 |
1987年 | 337篇 |
1986年 | 291篇 |
1985年 | 390篇 |
1984年 | 367篇 |
1983年 | 303篇 |
1982年 | 332篇 |
1981年 | 316篇 |
1980年 | 295篇 |
1979年 | 282篇 |
1978年 | 306篇 |
1977年 | 235篇 |
1976年 | 251篇 |
1975年 | 201篇 |
1974年 | 231篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Riaan Schmuhl Sankhanilay Roy Chowdhury Johan E. ten Elshof Albert van den Berg Dave H.A. Blank 《Journal of Sol-Gel Science and Technology》2004,31(1-3):249-252
Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated. 相似文献
82.
We give a criterion to decide if a given w-homogeneous derivation on A?k[X1,X2,X3] is locally nilpotent. We deduce an algorithm which decides if a k-subalgebra of A, which is finitely generated by w-homogeneous elements, is the kernel of some locally nilpotent derivation. 相似文献
83.
We discuss the approximation of performance measures in multi-class M/M/k queues with preemptive priorities for large problem instances (many classes and servers) using class aggregation and server reduction. We compared our approximations to exact and simulation results and found that our approach yields small-to-moderate approximation errors. 相似文献
84.
85.
It is a well-known feature of odd space-time dimensions d that there exist two inequivalent fundamental representations A and B of the Dirac gamma matrices. Moreover, the parity transformation swaps the fermion fields living in A and B. As a consequence, a parity-invariant Lagrangian can only be constructed by incorporating both the representations. Based upon these ideas and contrary to long-held belief, we show that in addition to a discrete exchange symmetry for the massless case, we can also define chiral symmetry provided the Lagrangian contains fields corresponding to both the inequivalent representations. We also study the transformation properties of the corresponding chiral currents under parity and charge-conjugation operations. We work explicitly in 2 + 1 dimensions and later show how some of these ideas generalize to an arbitrary number of odd dimensions. 相似文献
86.
87.
A.M. van der Kraan 《Hyperfine Interactions》1998,111(1-4):23-34
In modern society the application of catalysts, and hence, research in the field of catalysis, is becoming more and more important. In the strongly increasing chemical industry most reaction processes are performed with the aid of catalysts. Knowledge about the structure of the active sites present at the surface of catalysts will facilitate the design of new catalysts with better performances. Such knowledge can be obtained by Mössbauer spectroscopy, which is an excellent in-situ characterization technique due to the high penetrating power of the γ-radiation used and the sensitivity of the spectral parameters for the chemical state and local environment of the Mössbauer atoms. 相似文献
88.
An analytic and numerical study of the behavior of the linear nonhomogeneous wave equation of the form ε2utt = Δu + tf with high wave speed (ε 1) is carried out. This study was initially motivated by meteorological observations which have indicated the presence of large spatial scale gravity waves in the neighborhood of a number of summer and winter storms, mainly from visible images of ripples in clouds in satellite photos. There is a question as to whether the presence of these waves is caused by the nearby storms. Since the linear wave equation is an approximation to the full system describing pressure waves in the atmosphere, yet is considerably more tractable, we have chosen to analyze the behavior of the linear nonhomogeneous wave equation with high wave speed. The analysis is shown to be valid in one, two, and three space dimensions. Partly because of the high wave speed, the solution is known to consist of behavior which changes on two different time scales, one rapid and one slow. Additionally, because of the presence of the nonhomogeneous forcing term tf, we show that there is a component of the solution which will vary only on a very large spatial scale. Since even the linearized wave equation can give rise to persistent large spatial scale waves under the right conditions, the implication is that certain storms could be responsible for the generation of large-scale waves. Numerical simulations in one and two dimensions confirm analytic results. 相似文献
89.
Th. Gerrits H. A. M. van den Berg J. Hohlfeld O. Gielkens L. Br Th. Rasing 《Journal of magnetism and magnetic materials》2002,240(1-3):283-286
We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses. 相似文献
90.
S. Moss de Oliveira P. M. C. de Oliveira F. C. de Sá Barreto 《Journal of statistical physics》1995,78(5-6):1619-1627
Using the finite-size scaling renormalization group, we obtain the two-dimensional flow diagram of the Blume-Capel model forS=1 andS=3/2. In the first case our results are similar to those of mean-field theory, which predicts the existence of first- and second-order transitions with a tricritical point. In the second case, however, our results are different. While we obtain in theS=1 case a phase diagram presenting a multicritical point, the mean-field approach predicts only a second-order transition and a critical endpoint. 相似文献