全文获取类型
收费全文 | 10774篇 |
免费 | 1413篇 |
国内免费 | 893篇 |
专业分类
化学 | 3783篇 |
晶体学 | 120篇 |
力学 | 1769篇 |
综合类 | 165篇 |
数学 | 2830篇 |
物理学 | 4413篇 |
出版年
2023年 | 78篇 |
2022年 | 167篇 |
2021年 | 229篇 |
2020年 | 274篇 |
2019年 | 226篇 |
2018年 | 247篇 |
2017年 | 331篇 |
2016年 | 405篇 |
2015年 | 338篇 |
2014年 | 520篇 |
2013年 | 843篇 |
2012年 | 627篇 |
2011年 | 744篇 |
2010年 | 588篇 |
2009年 | 665篇 |
2008年 | 672篇 |
2007年 | 704篇 |
2006年 | 609篇 |
2005年 | 575篇 |
2004年 | 514篇 |
2003年 | 466篇 |
2002年 | 394篇 |
2001年 | 307篇 |
2000年 | 297篇 |
1999年 | 262篇 |
1998年 | 246篇 |
1997年 | 234篇 |
1996年 | 184篇 |
1995年 | 158篇 |
1994年 | 151篇 |
1993年 | 138篇 |
1992年 | 107篇 |
1991年 | 90篇 |
1990年 | 84篇 |
1989年 | 71篇 |
1988年 | 70篇 |
1987年 | 58篇 |
1986年 | 46篇 |
1985年 | 42篇 |
1984年 | 51篇 |
1983年 | 17篇 |
1982年 | 45篇 |
1981年 | 45篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1974年 | 9篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献
43.
Two groups of 10 speech-language pathology graduate students were each given 7 weeks of singing lessons to determine whether voice lessons could have an effect on their clinical and perceptual skills. Pre-, mid-, and posttests to measure various skills were designed and implemented. With use of paired sample statistical testing, statistically significant results were obtained. In addition, the subjective responses of the students show that the lessons were effective in improving pitch perception, breath control, and legato production or easy onset. This study supports efforts to integrate curricula in vocal performance and speech-language pathology. 相似文献
44.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
45.
Subhashis Ghosal Tapas Samanta 《Annals of the Institute of Statistical Mathematics》1997,49(1):181-197
We study the asymptotic behaviour of the posterior distributions for a one-parameter family of discontinuous densities. It is shown that a suitably centered and normalized posterior converges almost surely to an exponential limit in the total variation norm. Further, asymptotic expansions for the density, distribution function, moments and quantiles of the posterior are also obtained. It is to be noted that, in view of the results of Ghosh et al. (1994, Statistical Decision Theory and Related Topics V, 183-199, Springer, New York) and Ghosal et al. (1995, Ann. Statist., 23, 2145-2152), the nonregular cases considered here are essentially the only ones for which the posterior distributions converge. The results obtained here are also supported by a simulation experiment. 相似文献
46.
47.
This study has investigated the effect of shelf aging, for up to one year in air, on the properties of gamma-irradiated ultra-high molecular weight polyethylene (UHMWPE). A variety of techniques were used to characterize the properties of treated samples. Differential scanning calorimetery (DSC) was used to characterize the morphology. The extent of cross-linking in a polymer network was detected by swelling measurements. The durometer hardness test was used to measure the relative hardness of this material, and changes in density were also measured. Results from all these measurements were combined to explain the changes in the microstructure of the aged, irradiated UHMWPE. This study shows that crystallinity is increased with radiation dose and with aging due to chain scission, which leads to a reduction in the molecular weight of the material. This allows the chains to rearrange to form crystalline regions. Positron annihilation lifetime spectroscopy confirms these conclusions. Fractional free volumes have been deduced from lifetime parameters, which correlate with the data obtained by the other techniques. 相似文献
48.
MAIO Hong GAO Chong-Shou ZHUANG Peng-Fei 《理论物理通讯》2006,46(12)
Bound states, such as qq and q(q), may exist in quark-gluon plasma. As the system is at high density,the volume of the bound states may evoke a reduction in the phase space. We introduce an extended bag model to investigate qualitatively the volume effect on the properties of the system. We find a limit temperature where the bound states start to be completely melted. 相似文献
49.
50.