全文获取类型
收费全文 | 504198篇 |
免费 | 7429篇 |
国内免费 | 2207篇 |
专业分类
化学 | 237987篇 |
晶体学 | 6019篇 |
力学 | 18597篇 |
综合类 | 59篇 |
数学 | 49927篇 |
物理学 | 129966篇 |
无线电 | 71279篇 |
出版年
2020年 | 3524篇 |
2019年 | 3535篇 |
2018年 | 3810篇 |
2017年 | 3715篇 |
2016年 | 6782篇 |
2015年 | 5152篇 |
2014年 | 7369篇 |
2013年 | 20635篇 |
2012年 | 15848篇 |
2011年 | 19548篇 |
2010年 | 13043篇 |
2009年 | 13860篇 |
2008年 | 19523篇 |
2007年 | 20300篇 |
2006年 | 19487篇 |
2005年 | 18113篇 |
2004年 | 16388篇 |
2003年 | 14654篇 |
2002年 | 14475篇 |
2001年 | 15797篇 |
2000年 | 12678篇 |
1999年 | 10345篇 |
1998年 | 8984篇 |
1997年 | 8724篇 |
1996年 | 8478篇 |
1995年 | 7964篇 |
1994年 | 7575篇 |
1993年 | 7290篇 |
1992年 | 7868篇 |
1991年 | 7786篇 |
1990年 | 7250篇 |
1989年 | 6876篇 |
1988年 | 7007篇 |
1987年 | 5841篇 |
1986年 | 5686篇 |
1985年 | 7670篇 |
1984年 | 7790篇 |
1983年 | 6492篇 |
1982年 | 6891篇 |
1981年 | 6821篇 |
1980年 | 6531篇 |
1979年 | 6712篇 |
1978年 | 6788篇 |
1977年 | 6701篇 |
1976年 | 6632篇 |
1975年 | 6447篇 |
1974年 | 6371篇 |
1973年 | 6499篇 |
1972年 | 3978篇 |
1971年 | 3222篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
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
2.
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
3.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state.... 相似文献
4.
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
5.
Dr. Kyung-Seok Kang Dr. Krishnan A. Iyer Prof. Dr. Jeffrey Pyun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200115
In this concept review, the fundamental and polymerization chemistry of inverse vulcanization for the preparation of statistical and segmented sulfur copolymers, which have been actively developed and advanced in various applications over the past decade is discussed. This concept review delves into a discussion of step-growth polymerization constructs to describe the inverse vulcanization process and discuss prepolymer approaches for the synthesis of segmented sulfur polyurethanes. Furthermore, this concept review discusses the advantages of inverse vulcanization in conjunction with dynamic covalent polymerization and post-polymerization modifications to prepare segmented block copolymers with enhanced thermomechanical and flame retardant properties of these materials. 相似文献
6.
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
7.
Shannon Lee Scott L. Carnahan Georgiy Akopov Philip Yox Lin-Lin Wang Aaron J. Rossini Kui Wu Kirill Kovnir 《Advanced functional materials》2021,31(16):2010293
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials. 相似文献
8.
Kravchenko V. F. Konovalov Ya. Yu. 《Journal of Communications Technology and Electronics》2022,67(8):952-964
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically... 相似文献
9.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
10.
Experimental Mechanics - Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients... 相似文献