全文获取类型
收费全文 | 81782篇 |
免费 | 7100篇 |
国内免费 | 5094篇 |
专业分类
化学 | 24667篇 |
晶体学 | 1810篇 |
力学 | 3968篇 |
综合类 | 398篇 |
数学 | 18873篇 |
物理学 | 44260篇 |
出版年
2023年 | 198篇 |
2022年 | 462篇 |
2021年 | 464篇 |
2020年 | 755篇 |
2019年 | 1021篇 |
2018年 | 974篇 |
2017年 | 725篇 |
2016年 | 595篇 |
2015年 | 514篇 |
2014年 | 1208篇 |
2013年 | 1789篇 |
2012年 | 1312篇 |
2011年 | 1849篇 |
2010年 | 2399篇 |
2009年 | 6924篇 |
2008年 | 7984篇 |
2007年 | 6428篇 |
2006年 | 5862篇 |
2005年 | 4032篇 |
2004年 | 3835篇 |
2003年 | 4041篇 |
2002年 | 5268篇 |
2001年 | 3790篇 |
2000年 | 3533篇 |
1999年 | 3366篇 |
1998年 | 2789篇 |
1997年 | 1946篇 |
1996年 | 1756篇 |
1995年 | 2217篇 |
1994年 | 2147篇 |
1993年 | 1608篇 |
1992年 | 1109篇 |
1991年 | 835篇 |
1990年 | 688篇 |
1989年 | 604篇 |
1988年 | 570篇 |
1987年 | 410篇 |
1985年 | 949篇 |
1984年 | 624篇 |
1983年 | 489篇 |
1982年 | 643篇 |
1981年 | 794篇 |
1980年 | 720篇 |
1979年 | 563篇 |
1978年 | 582篇 |
1977年 | 539篇 |
1976年 | 541篇 |
1975年 | 319篇 |
1974年 | 356篇 |
1973年 | 462篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
HIRONOBU Ishihara 《Geometriae Dedicata》1997,67(3):309-336
Several classification results for ample vector bundles of rank 2 on Hirzebruch surfaces, and on Del Pezzo surfaces, are obtained. In particular, we classify rank 2 ample vector bundles with c2 less than seven on Hirzebruch surfaces, and with c2 less than four on Del Pezzo surfaces. 相似文献
33.
矩阵方程A^TXB=C的正定和半正定解 总被引:5,自引:1,他引:4
何楚宁 《高校应用数学学报(A辑)》1997,(4):475-480
给出了矩阵方程A^TXB=C在正定和半正定矩阵类中有解的充要条件及解的一般表达式。 相似文献
34.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
35.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
36.
本文研究作为双层桥模型的梁方程耦合系统,利用Leray-Schauder不动点定理,得到了一个关于这种系统的解的存在性定理,它类似于McKenna和Walter文2中关于吊桥方程的一个定理。 相似文献
37.
38.
39.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
40.
Surface texturing has been recognized as an effective means to improve the tribological performances of sliding surfaces. Usually, generation additional hydrodynamic pressure to increase the load carrying capacity is regarded as the most significant effect of surface texture. In the case of silicon carbide sliding against identical material in water, the experimental results indicate that surface texture is also helpful to improve the running-in progress to smooth the contact surfaces, showing another reason to result in low friction. Based on the consideration of enhancing the generation of hydrodynamic pressure and improving running-in progress, a surface texture pattern, which was combined with large (circle, 350 μm in diameter) and small (rectangular, 40 μm in length) dimples, was designed to maximize the texture effect on the load carrying capacity of SiC surfaces sliding in water. The friction coefficient of such textured surface was evaluated and compared with that of untextured and those only with large or small dimples only. The friction reduction mechanisms of the patterns with different dimples in size are discussed. 相似文献