全文获取类型
收费全文 | 1993篇 |
免费 | 60篇 |
国内免费 | 9篇 |
专业分类
化学 | 1455篇 |
晶体学 | 9篇 |
力学 | 45篇 |
数学 | 321篇 |
物理学 | 232篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 26篇 |
2020年 | 28篇 |
2019年 | 40篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 38篇 |
2015年 | 40篇 |
2014年 | 64篇 |
2013年 | 84篇 |
2012年 | 110篇 |
2011年 | 143篇 |
2010年 | 68篇 |
2009年 | 63篇 |
2008年 | 104篇 |
2007年 | 127篇 |
2006年 | 136篇 |
2005年 | 100篇 |
2004年 | 101篇 |
2003年 | 89篇 |
2002年 | 96篇 |
2001年 | 19篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有2062条查询结果,搜索用时 15 毫秒
101.
We report a comparison of theoretical and experimental proton affinities at nitrogen and oxygen sites within a series of small molecules. The calculated proton affinities are determined using the semiempirical methods AM 1, MNDO , and PM 3; the ab initio Hartree–Fock method at the following basis levels: 3-21G //3-21G , 3-21+G //3-21G , 6-31G *//6-31G *, and 6-31+G (d, p)//6-31G *; and Møller–Plesset perturbation calculations: MP 2/6-31G *//6-31G *, MP 3/6-31G *//6-31G *, MP 2/6-31G +(d, p)//6-31G *, MP 3/6-31G +(d, p)//6-31G *, and MP 4(SDTQ )/6-31G +G (d, p)//6-31G *. The semiempirical methods have more nonsystematic scatter from the experimental values, compared to even the minimal 3-21G level ab initio calculations. The thermodynamically corrected 6-31G *//6-31G * proton affinities provide acceptable results compared to experiment, and we see no significant improvement over 6-31G *//6-31G * in the proton affinities with any of the higher-level calculations. © 1992 John Wiley & Sons, Inc. 相似文献
102.
Carl F. Brunius Ulrica Edlund Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3652-3661
This work is devoted to the design of a novel family of hydrosoluble biomaterials: poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐based graft copolymers. A synthesis route has been elaborated in which ω‐functionalized PVP is prepared via chain‐transfer radical polymerization, end‐group modified, and subsequently grafted onto a polyhydroxylated backbone, typically dextran or poly(vinyl alcohol). The resulting graft copolymer biomaterials are designed for use in various biomedical applications, particularly as materials with a stronger potential for plasma expansion than already existing products have. The graft copolymers are potentially degradable because the PVP grafts are connected to the polyol backbone via a hydrolytically labile carbonate or ester linkage. The degradation of the graft copolymers was performed in vitro over a period of 6 weeks. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3652–3661, 2002 相似文献
103.
104.
B. Blanchaert E. Poderós Jorge P. Jankovics E. Adams Ann Van Schepdael 《Chromatographia》2013,76(21-22):1505-1512
The development of a simple reversed phase ion pair liquid chromatographic method for the assay of kanamycin A has been described. Because of the lack of a UV chromophore in the structure of kanamycin A, borate complexation was used to allow direct UV detection at 205 nm. Three columns were evaluated in this study: Zorbax Extend C18 (4.6 mm × 250 mm; 5 μm), XBridge C18 (4.6 mm × 250 mm; 5 μm) and apHera C18 (4.6 mm × 250 mm; 5 μm). The mobile phase was a mixture of 0.1 M disodium tetraborate (pH 9.0) and water (20:80, v/v) supplemented with 0.5 g L?1 sodium octanesulphonate. Final chromatographic conditions were achieved on the XBridge column at 50 °C. The method was validated according to ICH guidelines and applied to a commercially available sample. It is much faster and more specific than the current microbiological assay prescribed in the European Pharmacopoeia. No expensive equipment is necessary to perform this assay making it a viable replacement. 相似文献
105.
106.
Evans Curry Shelby Hildebrand Mark Kunkei Ann Pittman Derald Walling 《International Journal of Mathematical Education in Science & Technology》2013,44(6):997-1001
Completion and performance data from 92 high ability seventh and eighth grade students in an eight‐week summer programme conducted in 1989 and sponsored by the GTE Service Corporation are examined. 相似文献
107.
108.
Knowledge and understanding of the stability profile of a drug is important as it affects its safety and efficacy. In the present work, besifloxacin, a new, fourth‐generation fluoroquinolone antibiotic, was subjected to different forced‐degradation conditions as per International Conference on Harmonization (ICH) guidelines such as hydrolysis (acid, base and neutral), oxidation, thermal and photolysis. The drug degraded under acidic, basic, oxidative and photolytic conditions while it was found to be stable under dry heat and neutral hydrolytic conditions. In total, five degradation products (DPs) were formed under different conditions—DP1 and DP2 (photolysis), DP3 (oxidation), DP4 (acidic), DP3 and DP5 (basic). The chromatographic separation of besifloxacin and its degradation products was achieved on a Sunfire C18 (250 mm × 4.6 mm, 5 μm) column with 0.1% aqueous formic acid–acetonitrile as a mobile phase. The gradient RP‐HPLC method was developed and validated as per ICH guidelines. The degradation products were characterized with the help of LC–ESI–QTOF mass spectrometric studies and the most likely degradation pathway of the drug was proposed. In silico toxicity assessment of the drug and its degradation products was carried out, which indicated that DP3 and DP4 carry a mutagenicity alert. 相似文献
109.
Ann Feng Dr. Wei Cheng Dr. Jennifer Holter Dr. Neil Young Prof. Dr. Richard G. Compton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6981-6986
The charging and controlled oxidative doping of single organometallic ferrocene nanoparticles is reported in aqueous sodium tetrafluoroborate using the nano‐impacts method. It is shown that ferrocene nanoparticles of approximately 105 nm diameter are essentially quantitatively oxidatively doped with the uptake of one tetrafluoroborate anion per ferrocene molecule at suitably high overpotentials. By using lower potentials, it is possible to achieve low doping levels of single nanoparticles in a controlled manner. 相似文献
110.