全文获取类型
收费全文 | 40240篇 |
免费 | 6532篇 |
国内免费 | 4604篇 |
专业分类
化学 | 28328篇 |
晶体学 | 434篇 |
力学 | 2390篇 |
综合类 | 302篇 |
数学 | 4965篇 |
物理学 | 14957篇 |
出版年
2024年 | 36篇 |
2023年 | 799篇 |
2022年 | 830篇 |
2021年 | 1301篇 |
2020年 | 1634篇 |
2019年 | 1530篇 |
2018年 | 1336篇 |
2017年 | 1296篇 |
2016年 | 1908篇 |
2015年 | 1843篇 |
2014年 | 2137篇 |
2013年 | 2935篇 |
2012年 | 3437篇 |
2011年 | 3636篇 |
2010年 | 2446篇 |
2009年 | 2309篇 |
2008年 | 2650篇 |
2007年 | 2406篇 |
2006年 | 2153篇 |
2005年 | 1827篇 |
2004年 | 1449篇 |
2003年 | 1243篇 |
2002年 | 1290篇 |
2001年 | 988篇 |
2000年 | 884篇 |
1999年 | 899篇 |
1998年 | 757篇 |
1997年 | 716篇 |
1996年 | 755篇 |
1995年 | 647篇 |
1994年 | 596篇 |
1993年 | 426篇 |
1992年 | 409篇 |
1991年 | 382篇 |
1990年 | 277篇 |
1989年 | 219篇 |
1988年 | 167篇 |
1987年 | 151篇 |
1986年 | 165篇 |
1985年 | 130篇 |
1984年 | 89篇 |
1983年 | 75篇 |
1982年 | 52篇 |
1981年 | 39篇 |
1980年 | 35篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
In order to improve the signal-to-noise ratio and mitigate the damage of noise to the communication quality,an effective interference suppression algorithm,which is based on the improved density-based spatial clustering of applications with noise algorithms,is proposed for visible light communication systems using the complementary metal–oxide–semiconductor image sensor as the receiver.Experimental results show that the algorithm can learn the region where the payload data is located,filter out the noise data,and greatly decrease the interference.The effect of the algorithm is also studied through bit error ratio performance. 相似文献
42.
43.
44.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
45.
46.
Two new homosecoiridoids, named loniaceticiridoside (1) and lonimalondialiridoside (2), were isolated from an aqueous extract of the flower buds of Lonicera japonica. Their structures including the absolute configuration were determined by extensive spectroscopic studies, especially by 2D NMR and CD data analysis. A proposed biosynthetic pathway and preliminary investigations of the biological activity of compounds 1 and 2 are also discussed. 相似文献
47.
48.
A rapid method had been used for comparative study on Artemisia halodendron Turcz. and its two related plants by gas phase-mass spectrometry (GC-MS). The comparison of the volatile oils obtained in three plants by GC-MS were similar in 20 compositions. However, n-Hexadecanoic acid (10.40%), Biphenyl (7.867%) and 9,12-Octadecadienoic acid (7.25%) were the predominant in the volatile oils of A. halodendron Turcz., whereas these constituents did not exist in the other two plants. And the study investigated the effect of three plants against CCl4-induced hepatotoxicity in mice. 70% ethanol extracts of A. halodendron Turcz. showed weaker protective effect than the other two plants. It suggested that they provide a basis for the identification of the A. halodendron Turcz. from the other two plants and the ethanol extract from three plants exerted a protecting effect against hepatotoxicity. 相似文献
49.
50.
It is believed that there are more fundamental gauge symmetries beyond those described by the Standard Model of particle physics. The scales of these new gauge symmetries are usually too high to be reachable by particle colliders. Considering that the phase transition (PT) relating to the spontaneous breaking of new gauge symmetries to the electroweak symmetry might be strongly first order, we propose considering the stochastic gravitational waves (GW) arising from this phase transition as an indirect way of detecting these new fundamental gauge symmetries. As an illustration, we explore the possibility of detecting the stochastic GW generated from the PT of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
in the space-based interferometer detectors. Our study demonstrates that the GW energy spectrum is reachable by the LISA, Tianqin, Taiji, BBO, and DECIGO experiments only for the case where the spontaneous breaking of \begin{document}$ {\bf{B}}-{\bf{L}}$\end{document} ![]()
![]()
is triggered by at least two electroweak singlet scalars. 相似文献