全文获取类型
收费全文 | 25818篇 |
免费 | 4722篇 |
国内免费 | 3681篇 |
专业分类
化学 | 19239篇 |
晶体学 | 409篇 |
力学 | 1486篇 |
综合类 | 245篇 |
数学 | 2442篇 |
物理学 | 10400篇 |
出版年
2024年 | 74篇 |
2023年 | 456篇 |
2022年 | 881篇 |
2021年 | 942篇 |
2020年 | 1082篇 |
2019年 | 1058篇 |
2018年 | 959篇 |
2017年 | 878篇 |
2016年 | 1312篇 |
2015年 | 1304篇 |
2014年 | 1542篇 |
2013年 | 2056篇 |
2012年 | 2457篇 |
2011年 | 2467篇 |
2010年 | 1728篇 |
2009年 | 1739篇 |
2008年 | 1831篇 |
2007年 | 1667篇 |
2006年 | 1550篇 |
2005年 | 1369篇 |
2004年 | 1047篇 |
2003年 | 821篇 |
2002年 | 886篇 |
2001年 | 669篇 |
2000年 | 511篇 |
1999年 | 478篇 |
1998年 | 404篇 |
1997年 | 336篇 |
1996年 | 288篇 |
1995年 | 242篇 |
1994年 | 204篇 |
1993年 | 167篇 |
1992年 | 163篇 |
1991年 | 150篇 |
1990年 | 101篇 |
1989年 | 72篇 |
1988年 | 51篇 |
1987年 | 36篇 |
1986年 | 42篇 |
1985年 | 46篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1971年 | 6篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
83.
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
84.
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
85.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
86.
87.
88.
时间分辨红外发射光谱法对自由基反应的研究 总被引:2,自引:0,他引:2
在过去的 15年中 ,傅立叶变换红外发射光谱法广泛应用于研究气相自由基反应 .Sloan首先研究了O(1D)的反应 ,随后Leone和Hancock研究了O(3 P)的反应 .此后 ,孔繁敖和朱起鹤等研究了小自由基 ,包括CH、CH2 、CH3 、C2 H3 、C2 H5、C2 H、C3 H3 和C3 H5与O2 、NO、N2 O、NO2 等分子的反应。在红外光谱中观察到各个反应的初生产物和初步反应通道 ,和从头算的理论研究结合起来 ,这些反应的机理已基本弄清 . 相似文献
89.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献
90.
Hyun Chul Choi Min Kyu Lee Hyun Joon Shin Seung Bin Kim 《Journal of Electron Spectroscopy and Related Phenomena》2003,130(1-3):85-96
To investigate the formation of a solid electrolyte interface (SEI) on the Li1+xV3O8 electrode surface in the thermodynamic stability range of the organic electrolyte, we applied scanning photoelectron microscopy (SPEM) to a pristine electrode and to an electrode after ten cycles. The F K-edge absorption spectrum of the cycled electrode showed that LiF forms on the electrode surface during the lithium insertion–extraction process in the Li1+xV3O8/Li cell. The photoelectron spectrum for the cycled electrode showed intense spectral features corresponding to Li 1s, F 2s, F 2p, and P 2p electron signals, whereas these spectral features were of negligible intensity for the pristine electrode. The above results give strong support for the formation of an SEI that consists of LiF and compounds containing phosphorus during operation of the battery. The SPEM images also revealed that the fluorine distribution on the surface of the cycled electrode was inhomogeneous. 相似文献