全文获取类型
收费全文 | 93880篇 |
免费 | 26241篇 |
国内免费 | 19821篇 |
专业分类
化学 | 61120篇 |
晶体学 | 1326篇 |
力学 | 6238篇 |
综合类 | 282篇 |
数学 | 11994篇 |
物理学 | 58982篇 |
出版年
2024年 | 451篇 |
2023年 | 961篇 |
2022年 | 1164篇 |
2021年 | 1181篇 |
2020年 | 1527篇 |
2019年 | 2094篇 |
2018年 | 1998篇 |
2017年 | 2647篇 |
2016年 | 2995篇 |
2015年 | 3279篇 |
2014年 | 3279篇 |
2013年 | 5400篇 |
2012年 | 5965篇 |
2011年 | 7512篇 |
2010年 | 10434篇 |
2009年 | 10694篇 |
2008年 | 4685篇 |
2007年 | 4058篇 |
2006年 | 3720篇 |
2005年 | 3807篇 |
2004年 | 4581篇 |
2003年 | 3731篇 |
2002年 | 3646篇 |
2001年 | 3772篇 |
2000年 | 2770篇 |
1999年 | 2912篇 |
1998年 | 2404篇 |
1997年 | 2171篇 |
1996年 | 2499篇 |
1995年 | 2874篇 |
1994年 | 2936篇 |
1993年 | 2985篇 |
1992年 | 2511篇 |
1991年 | 2157篇 |
1990年 | 1827篇 |
1989年 | 1903篇 |
1988年 | 1867篇 |
1987年 | 1160篇 |
1986年 | 1220篇 |
1985年 | 885篇 |
1984年 | 991篇 |
1982年 | 897篇 |
1981年 | 745篇 |
1980年 | 786篇 |
1979年 | 538篇 |
1978年 | 552篇 |
1977年 | 643篇 |
1976年 | 1054篇 |
1973年 | 444篇 |
1972年 | 536篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
11.
Hui Li Jian Liu Juan Zhao Huiting He Dr. Dabo Jiang Prof. Steven Robert Kirk Prof. Qiong Xu Dr. Xianxiang Liu Prof. Dulin Yin 《ChemistryOpen》2021,10(4):477-485
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss. 相似文献
12.
13.
14.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone... 相似文献
15.
Ionics - This study aims to explore the potential merits of palladium oxide sensing electrode. PdO is applied on a solid-state potentiometric sensor on an yttria-stabilized zirconia (YSZ)... 相似文献
16.
17.
18.
Numerical Algorithms - A singularly perturbed Volterra integro-differential equation with an integrable singularity in the integral term is considered. The upwind difference method is used to... 相似文献
19.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight 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)
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
20.
András Gy. Németh Renáta Szabó Dr. Attila Domján Prof. György M. Keserű Dr. Péter Ábrányi-Balogh 《ChemistryOpen》2021,10(1):16-27
The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol. 相似文献