全文获取类型
收费全文 | 20300篇 |
免费 | 3898篇 |
国内免费 | 5475篇 |
专业分类
化学 | 16680篇 |
晶体学 | 538篇 |
力学 | 1129篇 |
综合类 | 462篇 |
数学 | 2635篇 |
物理学 | 8229篇 |
出版年
2024年 | 23篇 |
2023年 | 272篇 |
2022年 | 550篇 |
2021年 | 626篇 |
2020年 | 771篇 |
2019年 | 803篇 |
2018年 | 715篇 |
2017年 | 878篇 |
2016年 | 912篇 |
2015年 | 1096篇 |
2014年 | 1310篇 |
2013年 | 1665篇 |
2012年 | 1752篇 |
2011年 | 1873篇 |
2010年 | 1608篇 |
2009年 | 1677篇 |
2008年 | 1736篇 |
2007年 | 1605篇 |
2006年 | 1434篇 |
2005年 | 1257篇 |
2004年 | 1040篇 |
2003年 | 805篇 |
2002年 | 936篇 |
2001年 | 868篇 |
2000年 | 731篇 |
1999年 | 538篇 |
1998年 | 336篇 |
1997年 | 250篇 |
1996年 | 238篇 |
1995年 | 184篇 |
1994年 | 186篇 |
1993年 | 129篇 |
1992年 | 122篇 |
1991年 | 107篇 |
1990年 | 94篇 |
1989年 | 90篇 |
1988年 | 70篇 |
1987年 | 74篇 |
1986年 | 54篇 |
1985年 | 55篇 |
1984年 | 45篇 |
1983年 | 42篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
101.
102.
Xin Dong Juan Yang Xiao-Ting Zheng Yan Chen Li-Hong Ye Bin Wang Hui Zheng Jun Cao Qiu-Yan Wang Yu-Han Hu 《Electrophoresis》2020,41(1-2):123-130
A novel micro matrix solid phase dispersion method was successfully used for the extraction of quaternary alkaloids in Phellodendri chinensis cortex. The elution of target compounds was accomplished with sodium hexanesulfonate as the eluent solvent. A neutral ion pair was formed between ion-pairing reagent and positively charged alkaloids in this process, which was beneficial for selectively extraction of polar alkaloids. Several parameters were optimized and the optimal conditions were listed as follows: silica gel as the sorbent, silica to sample mass ratio of 1:1, the grinding time of 1 min. The exhaustive elution of targets was achieved by 200 µL methanol/water (9:1) containing 150 mM sodium hexane sulfonate at pH 4.5. The method validation covered linearity, recovery, precision of intraday and interday, limits of detection, limits of quantitation, and repeatability. This established method was rapid, simple, environmentally friendly, and highly sensitive. 相似文献
103.
Hui Xie Prof. Dr. Jijun Jiang Prof. Dr. Jun Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7365-7368
A rhodium(III)-catalyzed C−H/N−H bond functionalization of benzimidates with α-chloroaldehydes to afford isoquinolin-3-ol derivatives is reported. No external oxidants are needed in this process, and interestingly, evolution of hydrogen gas is observed. 相似文献
104.
105.
106.
107.
108.
Nonlinear Dynamics - This paper introduces a multigroup COVID-19 model with immunity, in which the total population of each group is partitioned into five compartments, that is, susceptible,... 相似文献
109.
Natural products with a variety of pharmacological effects are important sources for commercial drugs, and it is very crucial to develop effective techniques to selectively extract and isolate bioactive natural components from the plants against the background of sustainable development. Ionic liquids (ILs) are a kind of designable material with unique physicochemical properties, including good thermal stability, negligible vapor pressure, good solvation ability, etc. ILs have already been used in pharmaceuticals for extraction, purification, drug delivery, etc. It has been reported that multi-interactions, like hydrogen bonding, hydrophobic interactions, play important roles in the extraction of bioactive components from the plants. In this review, recent progress in the understanding of scientific essence of hydrogen bonding, the special interaction, in ILs was summarized. The extraction of various natural products, one important area in pharmaceutical, by conventional and functional ILs as well as the specific roles of multi-interactions in this process were also reviewed. Moreover, problems existing in bioactive compound extraction by ILs and the future developing trends of this area are given, which might be helpful for scientists, especially beginners, in this field. 相似文献
110.
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