全文获取类型
收费全文 | 489058篇 |
免费 | 27359篇 |
国内免费 | 18125篇 |
专业分类
化学 | 272321篇 |
晶体学 | 7507篇 |
力学 | 23347篇 |
综合类 | 33篇 |
数学 | 55089篇 |
物理学 | 176245篇 |
出版年
2019年 | 4573篇 |
2018年 | 5482篇 |
2017年 | 6094篇 |
2016年 | 8453篇 |
2015年 | 6381篇 |
2014年 | 8412篇 |
2013年 | 21165篇 |
2012年 | 16335篇 |
2011年 | 20551篇 |
2010年 | 18410篇 |
2009年 | 18339篇 |
2008年 | 17260篇 |
2007年 | 17082篇 |
2006年 | 16005篇 |
2005年 | 15049篇 |
2004年 | 14864篇 |
2003年 | 13108篇 |
2002年 | 12800篇 |
2001年 | 14742篇 |
2000年 | 11245篇 |
1999年 | 9443篇 |
1998年 | 7977篇 |
1997年 | 7818篇 |
1996年 | 7824篇 |
1995年 | 7672篇 |
1994年 | 7794篇 |
1993年 | 7548篇 |
1992年 | 7976篇 |
1991年 | 7532篇 |
1990年 | 7162篇 |
1989年 | 7113篇 |
1988年 | 7184篇 |
1987年 | 6505篇 |
1986年 | 6187篇 |
1985年 | 7687篇 |
1984年 | 7998篇 |
1983年 | 6375篇 |
1982年 | 7026篇 |
1981年 | 6812篇 |
1980年 | 6700篇 |
1979年 | 6674篇 |
1978年 | 7129篇 |
1977年 | 6971篇 |
1976年 | 7240篇 |
1975年 | 6241篇 |
1974年 | 6297篇 |
1973年 | 6585篇 |
1972年 | 4734篇 |
1968年 | 4021篇 |
1967年 | 4103篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using... 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.
Chuprin A. S. Belova S. A. Bugaenko M. G. Vologzhanina A. V. Loktev A. S. Voloshin Ya. Z. Buznik V. M. Dedov A. G. 《Kinetics and Catalysis》2022,63(1):108-116
Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the... 相似文献
5.
Automotive proton exchange membrane fuel cell stacks need to meet manufacturer specified rated beginning-of-life (BOL) performance before being assembled into vehicles and shipped off to customers. The process of “breaking-in” of a freshly assembled stack is often referred to as “conditioning.” It has become an intensely researched area especially in automotive companies, where imminent commercialization of fuel cell electric vehicles (FCEVs) demands a short, energy- and cost-efficient, and practical conditioning protocol. Significant advances in reducing the conditioning time from 1 to 2 days to as low as 4h or less, in some cases without the use of additional inert gases such as nitrogen, and with minimal use of hydrogen, and specialized test stations will be discussed. 相似文献
6.
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
7.
Chemistry of Natural Compounds - O- and N-propylamino-derivatives of betulin and betulonic acid oxime and methyl ester were synthesized. Their antitumor activity against a panel of 60 human cancer... 相似文献
8.
Romanenko G. V. Fokin S. V. Bogomyakov A. S. Zueva E. M. Ovcharenko V. I. 《Journal of Structural Chemistry》2022,63(3):441-450
Journal of Structural Chemistry - The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is... 相似文献
9.
Hassan E. A. M. Elabid A. E. A. Bashier E. O. Elagib T. H. H. 《Mechanics of Composite Materials》2022,58(2):261-270
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial... 相似文献
10.
Chetan Bhadaliya Bala Krishna Panigrahy Dipanjan Goswami Sovan Maiti Sanjay Jagannath Gurule Arshad H. Khuroo 《Biomedical chromatography : BMC》2022,36(4):e5337
A selective, highly sensitive, precise, and novel bioanalytical method has been developed and validated to quantify sinococuline, an active constituent present in the phytopharmaceutical drug product containing Cocculus hirsutus plant extract, in vivo. Chromatographic separation was achieved on a Luna Omega Polar-C18 bonded analytical column maintained at 45°C. The isocratic mobile phase consisted of methanol and ammonium formate buffer (60:40, v/v) at acidic pH with a low flow rate of 0.250 mL/min. Detection was performed on an API 4000 mass spectrometer using electrospray ionization in positive polarity and multiple reaction monitoring mode to achieve a lower limit of quantification of 1.50 ng/mL. Excellent accuracy and precision were obtained after extracting the analyte from plasma samples using a chemical analogue as an internal standard in the absence of an isotope-labeled compound. The extraction efficacy was evidenced from recovery study, and the analyte was found to be stable in plasma. Validation study demonstrated linearity with coefficient of correlation, r ≥ 0.99, and minimal matrix effect. This bioanalytical method was successfully applied to evaluate pharmacokinetic parameters of sinococuline from a phase I clinical trial of an aqueous extract of C. hirsutus in healthy human volunteers. 相似文献