全文获取类型
收费全文 | 1842篇 |
免费 | 54篇 |
国内免费 | 14篇 |
专业分类
化学 | 1357篇 |
晶体学 | 45篇 |
力学 | 17篇 |
综合类 | 1篇 |
数学 | 140篇 |
物理学 | 350篇 |
出版年
2021年 | 17篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2017年 | 13篇 |
2016年 | 31篇 |
2015年 | 33篇 |
2014年 | 38篇 |
2013年 | 99篇 |
2012年 | 83篇 |
2011年 | 87篇 |
2010年 | 53篇 |
2009年 | 46篇 |
2008年 | 87篇 |
2007年 | 92篇 |
2006年 | 109篇 |
2005年 | 93篇 |
2004年 | 77篇 |
2003年 | 74篇 |
2002年 | 69篇 |
2001年 | 51篇 |
2000年 | 58篇 |
1999年 | 35篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 23篇 |
1988年 | 33篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1979年 | 35篇 |
1978年 | 19篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 21篇 |
1972年 | 12篇 |
1968年 | 9篇 |
排序方式: 共有1910条查询结果,搜索用时 15 毫秒
91.
pi-Allyl-nickel complexes initiated addition polymerisation of 2-phenyl-1-methylenecyclopropane to give a polymer with three-membered rings; the formed polymer showed a high Tg and negligible thermal decomposition up to 300 degrees C. 相似文献
92.
Sensitive, reactive, and hydrophilic fluorogenic reagents for thiols with the benzofurazan skeleton, 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (AcABD-F) and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (TCAcABD-F) have been developed. These reagents reacted with thiols within 10 min at 60 degrees C. AcABD-F and TCAcABD-F themselves do not fluoresce but are strongly fluorescent after the reaction with thiol compounds. The generated derivatives were highly water-soluble, since they dissociated a proton and ionized in the neutral pH region. The derivatives with four biologically important thiol compounds were separated on a reversed-phase HPLC column and detected fluorometrically at 504 nm with excitation at 388 nm. The detection limit attained for homocysteine with AcABD-F was 25 fmol on column (11 nM) (signal-to-noise ratio = 3), and that for glutathione with TCAcABD-F was 45 fmol on column (20 nM). 相似文献
93.
94.
95.
Y Kawashima T Niwa T Handa H Takeuchi T Iwamoto Y Itoh 《Chemical & pharmaceutical bulletin》1989,37(2):425-429
Prolonged-release spherical micro-matrices of ibuprofen with acrylic polymer (Eudragit RS) were prepared using a novel emulsion-solvent diffusion method. It was found by examining cross sections of the spherical matrix before and after dissolution tests with a scanning electron microscope and a porosimeter that the resultant micro-matrix had a sponge-like internal structure. The spherical matrices were successfully recovered with a relatively high concentration of the drug in ethanol (0.4-0.6 g/ml) and over a wide range of temperatures (5-35 degrees C). The size of the spherical matrix could be easily controlled by varying the agitation speed of the system and the concentration of emulsifier added to the aqueous medium. The drug release rate from the spherical matrix decreased with increasing concentration of polymer formulated due to the reduced diffusion path and increased tortuosity in the matrix. Spherical matrices with ibuprofen:Eudragit RS = 3:1 improved the bioavailability of the drug and prolonged the drug action in beagle dogs. 相似文献
96.
Seiichi Nakamura Jun Inagaki Tomohiro Sugimoto Yasuyuki Ura Shunichi Hashimoto 《Tetrahedron》2002,58(52):10375-10386
An efficient, highly stereoselective synthesis of the C10–C31 (BCDEF ring) portion of pinnatoxin A has been achieved utilizing tandem double hemiketal formation/intramolecular hetero-Michael addition to construct the 6,5,6-dispiroketal (BCD ring) system and subsequent intramolecular ketalization to form the 5,6-bicycloketal (EF ring) system as key steps. 相似文献
97.
Itsuo Mori Yoshikazu Fujita Minako Toyoda Yoko Takeuchi 《Fresenius' Journal of Analytical Chemistry》1992,344(6):292-294
Summary A highly sensitive determination of osmium(VIII) is based on the decolouring reaction with pyrogallolphthalein (gallein) and hydrogen peroxide in the presence of Brij 35. Beer's law was obeyed in the range of 0–0.5 ng of osmium(VIII) per 10 ml and the apparent decomposed absorption coefficient was 2.5×109 l mol–1 cm–1 at 535 nm.Application of xanthene derivatives in analytical chemistry. Part XCIII. Part XCII see ref. [1] 相似文献
98.
Using a technique of laser flash photolysis coupled with vacuum ultraviolet laser-induced fluorescence spectroscopy, the rate coefficients of O(1D) reactions with N2, O2, N2O, and H2O at 295 ± 2 K have been determined to be , kO2=(4.06±0.24)×10-11, kN2O=(1.35±0.08)×10-10 and . The quoted uncertainties include estimated errors and are the 95% confidence level. The kN2 and kN2O values obtained are larger than the current NASA/JPL recommendations by 26% and 16%, respectively, although they are still within the error limits associated with the recommendations. 相似文献
99.
Red–Green–Blue Trichromophoric Nanoparticles with Dual Fluorescence Resonance Energy Transfer: Highly Sensitive Fluorogenic Response Toward Polyanions 下载免费PDF全文
Jinjia Xu Dr. Atsuro Takai Prof. Dr. Masayuki Takeuchi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13014-13018
A red–green–blue (RGB) trichromophoric fluorescent organic nanoparticle exhibiting multi‐colour emission was constructed; the blue‐emitting cationic oligofluorene nanoparticle acted as an energy‐donor scaffold to undergo fluorescence resonance energy transfer (FRET) to a red‐emitting dye embedded in the nanoparticle (interior FRET) and to a green‐emitting dye adsorbed on the surface through electrostatic interactions (exterior FRET). Each FRET event occurs independently and is free from sequential FRET, thus the resultant dual‐FRET system exhibits multi‐colour emission, including white, in aqueous solution and film state. A characteristic white‐emissive nanoparticle showed visible responses upon perturbation of the exterior FRET efficiency by acceptor displacement, leading to highly sensitive responses toward polyanions in a ratiometric manner. Specifically, our system exhibits high sensitivity toward heparin with an extremely low detection limit. 相似文献
100.
trans-Stilbene, 1, 1-diphenylethylene, and α-methylstyrene were allowed to react with dibenzylmagnesium to form their oligomers in hexamethylphosphortriamide (HMPA). One and two molecules of stilbene and 1, 1-diphenylethylene were incorporated into the magnesium carbon bond, and the carbanions obtained in HMPA were stable in analogy with the anionic living polymer having alkali cation as the gegenion in eithers. Intense coloration was observed during the reaction between α-methylstyrene and dibenzylmagnesium as well as in the case of stilbene and 1, 1-diphenylethylene. The low molecular weight products which were formed after a long time in the reaction between α-methylstyrene and dibenzylmagnesium were found to have no magnesium-carbon bond. It was considered that the cleavage of the propagating chain occurred gradually after the rapid propagation had proceeded to consume the monomer. 相似文献