全文获取类型
收费全文 | 15756篇 |
免费 | 2608篇 |
国内免费 | 1859篇 |
专业分类
化学 | 11912篇 |
晶体学 | 190篇 |
力学 | 798篇 |
综合类 | 99篇 |
数学 | 1486篇 |
物理学 | 5738篇 |
出版年
2024年 | 27篇 |
2023年 | 275篇 |
2022年 | 368篇 |
2021年 | 513篇 |
2020年 | 651篇 |
2019年 | 658篇 |
2018年 | 558篇 |
2017年 | 474篇 |
2016年 | 763篇 |
2015年 | 734篇 |
2014年 | 867篇 |
2013年 | 1234篇 |
2012年 | 1408篇 |
2011年 | 1422篇 |
2010年 | 977篇 |
2009年 | 978篇 |
2008年 | 1098篇 |
2007年 | 993篇 |
2006年 | 891篇 |
2005年 | 793篇 |
2004年 | 647篇 |
2003年 | 549篇 |
2002年 | 596篇 |
2001年 | 409篇 |
2000年 | 302篇 |
1999年 | 313篇 |
1998年 | 254篇 |
1997年 | 233篇 |
1996年 | 205篇 |
1995年 | 169篇 |
1994年 | 141篇 |
1993年 | 111篇 |
1992年 | 110篇 |
1991年 | 104篇 |
1990年 | 69篇 |
1989年 | 56篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 5篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
61.
62.
This article studies the inshore-offshore fishery model with impulsive diffusion. The existence and global asymptotic stability of both the trivial periodic solution and the positive periodic solution are obtained. The complexity of this system is also analyzed. Moreover, the optimal harvesting policy are given for the inshore subpopulation, which includes the maximum sustainable yield and the corresponding harvesting effort. 相似文献
63.
Jnos Szanyi Ja Hun Kwak Sarah Burton Jose A. Rodriguez Charles H.F. Peden 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):164-170
Adsorbed ionic NOx species formed upon the interaction of NO2 with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO2 disproportionates on both dehydrated catalyst materials forming NO+ and NO3− species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na+ and Ba2+), respectively. Although the nature of the adsorbed NOx species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO+ and H2O, and NO2 and H2O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO2 on these zeolite catalysts. 相似文献
64.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
65.
66.
67.
Because of package, a single FBG has dual Bragg wavelength. One is sensitive to stress and the other is sensitive to temperature. By using the special mechanism, the wavelengths can be tuned by stress and temperature respectively. 相似文献
68.
69.
With the advances in pulsed laser systems, microscopic imaging techniques such as multiphoton and pump-probe fluorescence microscopy have developed into effective tools for investigating intensity and time-resolved phenomena inside biological systems. However, pulsed lasers used in these techniques usually are commercial systems with repetition frequencies of around 80 MHz. While these systems have proven to be adequate for multiphoton and pump-probe microscopic imaging applications, the temporal separation of the laser pulse train (around 12.5 ns) is long compared to the fluorescence lifetimes of many common fluorescence species. In this work, we present the designs of repetition rate multipliers based on passive optical components that can be used to increase the efficiency in multiphoton and pump-probe fluorescence microscopy. Depending on the lifetime of fluorescence molecules under investigation, the passive repetition rate multiplier can increase the duty cycle of multiphoton or pump-probe microscopy up to fourfold. 相似文献
70.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献