全文获取类型
收费全文 | 139257篇 |
免费 | 2139篇 |
国内免费 | 842篇 |
专业分类
化学 | 72568篇 |
晶体学 | 2141篇 |
力学 | 5213篇 |
综合类 | 35篇 |
数学 | 12985篇 |
物理学 | 41680篇 |
综合类 | 7616篇 |
出版年
2016年 | 1539篇 |
2015年 | 1247篇 |
2014年 | 1651篇 |
2013年 | 5297篇 |
2012年 | 3962篇 |
2011年 | 5069篇 |
2010年 | 3130篇 |
2009年 | 2890篇 |
2008年 | 4502篇 |
2007年 | 4557篇 |
2006年 | 4602篇 |
2005年 | 4472篇 |
2004年 | 3922篇 |
2003年 | 3539篇 |
2002年 | 3438篇 |
2001年 | 3952篇 |
2000年 | 3062篇 |
1999年 | 2446篇 |
1998年 | 1982篇 |
1997年 | 1983篇 |
1996年 | 1944篇 |
1995年 | 1891篇 |
1994年 | 1636篇 |
1993年 | 1648篇 |
1992年 | 1975篇 |
1991年 | 1931篇 |
1990年 | 1885篇 |
1989年 | 1871篇 |
1988年 | 1885篇 |
1987年 | 1877篇 |
1986年 | 1743篇 |
1985年 | 2344篇 |
1984年 | 2408篇 |
1983年 | 2018篇 |
1982年 | 2307篇 |
1981年 | 2123篇 |
1980年 | 2190篇 |
1979年 | 2226篇 |
1978年 | 2339篇 |
1977年 | 2243篇 |
1976年 | 2246篇 |
1975年 | 2201篇 |
1974年 | 2106篇 |
1973年 | 2259篇 |
1972年 | 1390篇 |
1971年 | 1165篇 |
1970年 | 1206篇 |
1969年 | 1094篇 |
1968年 | 1233篇 |
1967年 | 1302篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Yang T. L. Kao C. L. Kuo C. E. Yeh H. C. Li W. J. Li H. T. Chen C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the... 相似文献
2.
3.
Theoretical and Mathematical Physics - Dynamic systems acting on the plane and possessing the Wada property have been observed. There exist only two topological types, symmetric and antisymmetric,... 相似文献
4.
Hao Lu Xiaodong Wang Hang Wang Andong Zhang Xinming Zheng Na Yu Zheng Tang Xinjun Xu Yahui Liu Ya-Nan Chen Zhishan Bo 《中国科学:化学(英文版)》2022,65(3):594-601
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs. 相似文献
5.
6.
Li Y. Shi W. H. Dong L. M. Xu S. X. Huang H. J. Yin J. R. 《Journal of Applied Spectroscopy》2022,89(3):534-541
Journal of Applied Spectroscopy - Sr3B2O6:Dy3+, Eu3+ single-matrix white-light-emitting materials are prepared using the high-temperature solid-state method. The microstructure, emission spectrum,... 相似文献
7.
Ajit Kumar Singh Seulgi Ji Baghendra Singh Chittaranjan Das Heechae Choi Prashanth W. Menezes Arindam Indra 《Materials Today Chemistry》2022
Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H+ ion transport. 相似文献
8.
Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.
相似文献9.
10.
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