全文获取类型
收费全文 | 94550篇 |
免费 | 4212篇 |
国内免费 | 4668篇 |
专业分类
化学 | 20639篇 |
晶体学 | 391篇 |
力学 | 3753篇 |
综合类 | 502篇 |
数学 | 10466篇 |
物理学 | 19418篇 |
综合类 | 48261篇 |
出版年
2024年 | 192篇 |
2023年 | 721篇 |
2022年 | 1427篇 |
2021年 | 1571篇 |
2020年 | 1591篇 |
2019年 | 1566篇 |
2018年 | 1404篇 |
2017年 | 1647篇 |
2016年 | 1865篇 |
2015年 | 2126篇 |
2014年 | 4053篇 |
2013年 | 4806篇 |
2012年 | 4801篇 |
2011年 | 5267篇 |
2010年 | 4168篇 |
2009年 | 5495篇 |
2008年 | 5720篇 |
2007年 | 6824篇 |
2006年 | 6037篇 |
2005年 | 5026篇 |
2004年 | 4378篇 |
2003年 | 4419篇 |
2002年 | 4603篇 |
2001年 | 3582篇 |
2000年 | 3137篇 |
1999年 | 2551篇 |
1998年 | 2220篇 |
1997年 | 1536篇 |
1996年 | 1436篇 |
1995年 | 1262篇 |
1994年 | 1212篇 |
1993年 | 936篇 |
1992年 | 980篇 |
1991年 | 740篇 |
1990年 | 655篇 |
1989年 | 564篇 |
1988年 | 459篇 |
1987年 | 387篇 |
1986年 | 300篇 |
1985年 | 244篇 |
1984年 | 233篇 |
1983年 | 140篇 |
1982年 | 189篇 |
1981年 | 181篇 |
1980年 | 121篇 |
1979年 | 149篇 |
1978年 | 126篇 |
1977年 | 119篇 |
1976年 | 75篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
Speed of sound and densities of the ternary mixture 2-propanol + diethyl ether + n-hexane and also the binary mixtures 2-propanol
+ diethyl ether and 2-propanol + n-hexane have been measured at the entire composition range at 298.15 K. The excess isentropic
compressibilities and the excess speed of the sound have been calculated from experimental densities and speed of sound. These
excess properties of the binary mixtures were fitted to Redlich-Kister equation, while the Cibulka’s equation was used to
fit the values related to the values to the ternary system. These excess properties have been used to discuss the presence
of significant interactions between the component molecules in the binary mixtures and also the ternary mixtures.
Speed of sound of the binary mixtures and the ternary mixture have been compared with calculated values from free length theory
(FLT), collision factor theory (CFT), Nomoto’s relation (NR), Van Deal’s ideal mixing relation (IMR) and Junjie’s relation
(JR). The results are used to compare the relative merits of these theories and relations in terms of the root mean square
deviation relative (RMSDr). 相似文献
952.
In this paper, we applied multifractal modeling techniques to analyze the traffic data collected from the Beijing Yuquanying. The results indicated that multifractal characteristics obviously exist in the traffic system; the degree of fractality of these traffic data tends to increase as the traffic system becomes congested; the Hölder exponent that measures the local rate of fractality may be used as indicators to predict the presence of the traffic congestion. 相似文献
953.
We characterize δ-I-sets, discuss the relation between δ-sets, δ-I-sets and I
δ-sets and generalize some of the results. 相似文献
954.
Frank Natterer Olga Klyubina 《计算数学(英文版)》2007,25(3):368-373
We study the initial value problem of the Helmholtz equation with spatially variable wave number. We show that it can be stabilized by suppressing the evanescent waves. The stabilized Helmholtz equation can be solved numerically by a marching scheme combined with FFT. The resulting algorithm has complexity n^2 log n on a n x n grid. We demonstrate the efficacy of the method by numerical examples with caustics. For the Maxwell equation the same treatment is possible after reducing it to a second order system. We show how the method can be used for inverse problems arising in acoustic tomography and microwave imaging. 相似文献
955.
利用变温X射线衍射技术,在预烧过程中分析了Nd掺杂Bi4Ti3O12后生成Bi3.15Nd0.85Ti3O12(BNT)相的形成过程以及微结构的变化.实验观察到以30℃/min的升温速率,BNT相在700℃时开始形成,其衍射峰强度随温度的继续升高而增强,衍射峰半高宽随烧结时间延长而减小.X射线衍射分析结果表明,在900℃恒温条件下,烧结约2h,可形成单一的BNT相. 相似文献
956.
半正二阶三点边值问题的解和正解 总被引:8,自引:0,他引:8
考察了非线性二阶三点边值问题的n个解和正解的存在性,其中允许非线性项有一个负的下界并且n是一个任意的自然数.主要结论表明该问题可以具有n个解或者正解,只要非线性项在某些有界集上的“高度”是适当的. 相似文献
957.
P. Kh. Atanasova T. L. Bojadjiev S. N. Dimova 《Computational Mathematics and Mathematical Physics》2006,46(4):666-679
Partial critical dependences of the form current-magnetic field in a two-layered symmetric Josephson junction are modeled. A numerical experiment shows that, for the zero interaction coefficient between the layers of the junction, jumps of the critical currents corresponding to different distributions of the magnetic fluxes in the layers may appear on the critical curves. This fact allows a mathematical interpretation of the results of some recent experimental results for two-layered junctions as a consequence of discontinuities of partial critical curves. 相似文献
958.
Parasteh Pirasteh Ali Soltani Lazhar Haji Nicolas Errien 《Applied Surface Science》2006,253(4):1999-2002
In order to understand the optical loss mechanisms in porous silicon based waveguides, structural and optical studies have been performed. Scanning and transmission electron microscopic observations of porous silicon layers are obtained before and after an oxidation process at high temperature in wet O2. Pore size and shape of heavily p-type doped Si wafers are estimated and correlated to the optical properties of the material before and after oxidation. The refractive index was measured and compared to that determined by the Bruggeman model. 相似文献
959.
Standardization and certification in the area of environmentally degradable plastics 总被引:1,自引:0,他引:1
Andrej Krzan Sarunya Hemjinda Stanislav Miertus Emo Chiellini 《Polymer Degradation and Stability》2006,91(12):2819-2833
Environmentally degradable polymers and plastics (EDPs) are a group of polymeric materials experiencing a rapid growth in number as well as in their applications and quantities used. The assessment of their key characteristic - degradability, including eventually biodegradability as the ultimate stage, is scientifically and technically a challenging issue and has led to differing interpretations in the past. In order to standardize techniques and criteria a number of standards were established by different standardization bodies which are also used as a basis for certification schemes. An up-to-date inventory of the rapidly growing standardization body is presented with basic interpretation to help guide the non-expert. A basic introduction to EDPs and polymer degradation is added for clarity. 相似文献
960.
A Series of Exact Solutions of (2+1)-Dimensional CDGKS Equation 总被引:1,自引:0,他引:1
YANG Zong-Hang 《理论物理通讯》2006,46(11)
An algebraic method with symbolic computation is devised to uniformly construct a series of exact solutions of the (2 1)-dimensional Caudrey-Dodd-Gibbon-Kotera-Sawda equation. The solutions obtained in this paper include solitary wave solutions, rational solutions, triangular periodic solutions, Jacobi and Weierstrass doubly periodic solutions. Among them, the Jacobi periodic solutions exactly degenerate to the solutions at a certain limit condition. Compared with most existing tanh method, the method used here can give new and more general solutions. More importantly, this method provides a guideline to classify the various types of the solution according to some parameters. 相似文献