全文获取类型
收费全文 | 21654篇 |
免费 | 3538篇 |
国内免费 | 2434篇 |
专业分类
化学 | 11347篇 |
晶体学 | 227篇 |
力学 | 867篇 |
综合类 | 130篇 |
数学 | 1622篇 |
物理学 | 5812篇 |
无线电 | 7621篇 |
出版年
2024年 | 112篇 |
2023年 | 569篇 |
2022年 | 755篇 |
2021年 | 835篇 |
2020年 | 834篇 |
2019年 | 840篇 |
2018年 | 684篇 |
2017年 | 718篇 |
2016年 | 887篇 |
2015年 | 1067篇 |
2014年 | 1269篇 |
2013年 | 1663篇 |
2012年 | 1914篇 |
2011年 | 2005篇 |
2010年 | 1425篇 |
2009年 | 1443篇 |
2008年 | 1454篇 |
2007年 | 1437篇 |
2006年 | 1183篇 |
2005年 | 972篇 |
2004年 | 767篇 |
2003年 | 618篇 |
2002年 | 563篇 |
2001年 | 515篇 |
2000年 | 457篇 |
1999年 | 369篇 |
1998年 | 297篇 |
1997年 | 257篇 |
1996年 | 266篇 |
1995年 | 208篇 |
1994年 | 233篇 |
1993年 | 177篇 |
1992年 | 153篇 |
1991年 | 133篇 |
1990年 | 111篇 |
1989年 | 89篇 |
1988年 | 56篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 43篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was... 相似文献
2.
3.
三维异质异构集成技术是实现电子信息系统向着微型化、高效能、高整合、低功耗及低成本方向发展的最重要方法,也是决定信息化平台中微电子和微纳系统领域未来发展的一项核心高技术。文章详细介绍了毫米波频段三维异质异构集成技术的优势、近年来的发展趋势以及面临的挑战。利用硅基MEMS 光敏复合薄膜多层布线工艺可实现异质芯片的低损耗互连,同时三维集成高性能封装滤波器、高辐射效率封装天线等无源元件,还能很好地处理布线间的电磁兼容和芯片间的屏蔽问题。最后介绍了一款新型毫米波三维异质异构集成雷达及其在远距离生命体征探测方面的应用。 相似文献
4.
5.
Donglei Wei Huili Li Chuanqing Yang Jianmin Fu Hou Chen Liangjiu Bai Wenxiang Wang Huawei Yang Lixia Yang Ying Liang 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1588-1594
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst. 相似文献
6.
Liang Zhao 《Journal of Differential Equations》2019,266(9):5615-5624
In this paper, let be n-dimensional noncompact metric measure space which satisfies Poincaré inequality with some Ricci curvature condition. We obtain a Liouville theorem for positive weak solutions to weighted p-Lichnerowicz equation where are real constants. 相似文献
7.
8.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling. 相似文献
9.
Simultaneous determination of cinnamaldehyde and its metabolite in rat tissues by gas chromatography–mass spectrometry
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hang Zhao Qian Yang Yanhua Xie Jiyuan Sun Honghai Tu Wei Cao Siwang Wang 《Biomedical chromatography : BMC》2015,29(2):182-187
Cinnamaldehyde (CA), an active ingredient isolated from the traditional Chinese medicine Cortex Cinnamomi, has a wide range of bioactivities. To clarify the distribution characteristics of CA, a selective and sensitive method utilizing gas chromatography–mass spetrometry was initially developed for simultaneously determining the concentration of CA and its metabolite cinnamyl alcohol in rat tissues. Selected ion masses of m/z 131, 105 and 92 were chosen, and separation of the analytes was performed on a DB‐5 ms (30 m × 0.25 mm, 0.25 µm, thickness) capillary column by gas chromatography–mass spectrometry. The calibration curves demonstrated good linearity and reproducibility over the range of 20–2000 and 20–4000 ng/mL for various tissue samples. Recoveries ranged from 86.8 to 107.5%, while intra‐ and interday relative standard deviations were all <11.3%. The analysis method was successfully applied in tissue distribution studies for CA and cinnamyl alcohol. As CA and cinnamyl alcohol may inter‐convert to one another, simultaneous determination of both analytes provides a comparative and accurate data for tissue study. The concentrations of CA and cinnamyl alcohol remaining in spleen were the highest among the main organs, including heart, liver, spleen, lung, kidney and brain. In addition, there was no long‐term accumulation of CA in rat tissues. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献