全文获取类型
收费全文 | 271828篇 |
免费 | 5260篇 |
国内免费 | 2648篇 |
专业分类
化学 | 150714篇 |
晶体学 | 3178篇 |
力学 | 11853篇 |
综合类 | 150篇 |
数学 | 28501篇 |
物理学 | 85340篇 |
出版年
2020年 | 2265篇 |
2019年 | 2286篇 |
2018年 | 2478篇 |
2017年 | 2290篇 |
2016年 | 4226篇 |
2015年 | 3040篇 |
2014年 | 4370篇 |
2013年 | 11614篇 |
2012年 | 9037篇 |
2011年 | 11256篇 |
2010年 | 7549篇 |
2009年 | 7238篇 |
2008年 | 9962篇 |
2007年 | 10026篇 |
2006年 | 9652篇 |
2005年 | 9075篇 |
2004年 | 7896篇 |
2003年 | 7074篇 |
2002年 | 7033篇 |
2001年 | 7735篇 |
2000年 | 5903篇 |
1999年 | 4792篇 |
1998年 | 4180篇 |
1997年 | 4048篇 |
1996年 | 3828篇 |
1995年 | 3564篇 |
1994年 | 3360篇 |
1993年 | 3124篇 |
1992年 | 3572篇 |
1991年 | 3608篇 |
1990年 | 3333篇 |
1989年 | 3358篇 |
1988年 | 3281篇 |
1987年 | 3173篇 |
1986年 | 3010篇 |
1985年 | 4056篇 |
1984年 | 4283篇 |
1983年 | 3502篇 |
1982年 | 3949篇 |
1981年 | 3674篇 |
1980年 | 3663篇 |
1979年 | 3793篇 |
1978年 | 4044篇 |
1977年 | 3854篇 |
1976年 | 3919篇 |
1975年 | 3771篇 |
1974年 | 3689篇 |
1973年 | 3913篇 |
1972年 | 2460篇 |
1967年 | 2085篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Liu Wenbin Huang Yiwei Huang Guolin Fan Lijiao Xie Yuming Shi Jeffery 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2055-2068
Journal of Radioanalytical and Nuclear Chemistry - Eco-friendly and low-cost composite, amidoxime-functionalized microcrystalline cellulose/mesoporous silica (MCC/MS-AO), were synthesized by... 相似文献
2.
Inas A. Abdallah Sherin F. Hammad Alaa Bedair Mohamed A. Abdelaziz Neil D. Danielson Ahmed H. Elshafeey Fotouh R. Mansour 《Biomedical chromatography : BMC》2022,36(6):e5365
Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid–liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 μl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105 ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma. 相似文献
3.
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
4.
Shilin Jiang Dr. Yalan Liu Dr. Lin Wang Prof. Zhifang Chai Prof. Wei-Qun Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201145
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties. 相似文献
5.
Sakhautdinova G. F. Sakhautdinov I. M. Mustafin A. G. Yunusov M. S. 《Chemistry of Natural Compounds》2022,58(1):185-186
Chemistry of Natural Compounds - 相似文献
6.
Dr. Zaifa Shi Dr. Yihuang Jiang Dr. Jingxiong Yu Prof. Shanjun Chen Prof. Jun Chen Prof. Zichao Tang Prof. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202103546
At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O2 molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O2 is HO2 elimination yielding cyclopentene. The pathways of second and third O2 addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT. 相似文献
7.
Russian Chemical Bulletin - New representatives of (O-Si)-chelate compounds, N-(fluorosilyl)methyl derivatives of N-methylacetamide, N-methylbenzamide, N-phenylacetamide, and N-phenylbenzamide,... 相似文献
8.
9.
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
10.
Alawainati F. A. Manaa H. Henari F. Z. Biyiklioglu Z. Arslan T. Jaafar A. 《Journal of Applied Spectroscopy》2021,88(5):951-957
Journal of Applied Spectroscopy - Detailed measurements of nonlinear optical properties and optical limiting for four phthalocyanine (Pc) derivatives (PcCo, PcCu, PcMn, and PcSi) are reported. The... 相似文献