全文获取类型
收费全文 | 1343篇 |
免费 | 63篇 |
国内免费 | 3篇 |
专业分类
化学 | 1138篇 |
晶体学 | 10篇 |
力学 | 18篇 |
数学 | 109篇 |
物理学 | 134篇 |
出版年
2023年 | 24篇 |
2022年 | 25篇 |
2021年 | 36篇 |
2020年 | 41篇 |
2019年 | 33篇 |
2018年 | 18篇 |
2017年 | 15篇 |
2016年 | 43篇 |
2015年 | 42篇 |
2014年 | 44篇 |
2013年 | 61篇 |
2012年 | 105篇 |
2011年 | 128篇 |
2010年 | 65篇 |
2009年 | 53篇 |
2008年 | 101篇 |
2007年 | 95篇 |
2006年 | 83篇 |
2005年 | 91篇 |
2004年 | 76篇 |
2003年 | 71篇 |
2002年 | 48篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1965年 | 1篇 |
1881年 | 1篇 |
1876年 | 1篇 |
排序方式: 共有1409条查询结果,搜索用时 13 毫秒
101.
Gaoussou Timit Anne‐Claire Mitaine‐Offer Tomofumi Miyamoto Chiaki Tanaka Thomas Paululat Clment Delaude Marie‐Aleth Lacaille‐Dubois 《Helvetica chimica acta》2010,93(11):2237-2244
The five new presenegenin glycosides 1 – 5 were isolated from Securidaca welwitschii, together with one known sucrose diester. Compounds 1 – 4 were obtained as pairs of inseparable (E)/(Z)‐isomers of a 3,4‐dimethoxycinnamoyl derivative, i.e., 1 / 2 and 3 / 4 . Their structures were elucidated mainly by 2D‐NMR techniques and mass spectrometry as 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐{O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[β‐D ‐glucopyranosyl‐(1→3)]‐4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]‐β‐D ‐fucopyranosyl} ester ( 1 ) and its (Z)‐isomer 2 , 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐{O‐β‐D ‐galactopyranosyl‐(1→4)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐3‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[β‐D ‐glucopyranosyl‐(1→3)]‐4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]‐β‐D ‐fucopyranosyl} ester ( 3 ) and its (Z)‐isomer 4 , and 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐[O‐β‐D ‐galactopyranosyl‐(1→3)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐fucopyranosyl] ester ( 5 ) (presenegenin=(2β,3β,4α)‐2,3,27‐trihydroxyolean‐12‐ene‐23,28‐dioic acid). 相似文献
102.
Vincent Larraillet Aleksey Vorobyev Claire Brunet Jér?me Lemoine Yury O. Tsybin Rodolphe Antoine Philippe Dugourd 《Journal of the American Society for Mass Spectrometry》2010,21(4):670-680
We compare product-ion mass spectra produced by electron detachment dissociation (EDD) and electron photodetachment dissociation
(EPD) of multi-deprotonated peptides on a Fourier transform and a linear ion trap mass spectrometer, respectively. Both methods,
EDD and EPD, involve the electron emission-induced formation of a radical oxidized species from a multi-deprotonated precursor
peptide. Product-ion mass spectra display mainly fragment ions resulting from backbone cleavages of Cα-C bond ruptures yielding a and x ions. Fragment ions originating from N-Cα backbone bond cleavages are also observed, in particular by EPD. Although EDD and EPD methods involve the generation of a
charge-reduced radical anion intermediate by electron emission, the product ion abundance distributions are drastically different.
Both processes seem to be triggered by the location and the recombination of radicals (both neutral and cation radicals).
Therefore, EPD product ions are predominantly formed near tryptophan and histidine residues, whereas in EDD the negative charge
solvation sites on the backbone seem to be the most favorable for the nearby bond dissociation. 相似文献
103.
Volker Leen Dr. Wenwu Qin Prof. Dr. Wensheng Yang Jie Cui Chan Xu Xiaoliang Tang Dr. Weisheng Liu Prof. Dr. Koen Robeyns Dr. Luc Van Meervelt Prof. David Beljonne Prof. Dr. Roberto Lazzaroni Prof. Dr. Claire Tonnelé Noël Boens Prof. Wim Dehaen Prof. 《化学:亚洲杂志》2010,5(9):2016-2026
Starting from the conformationally unconstrained compound 3,5‐di‐(2‐bromophenoxy)‐4,4‐difluoro‐8‐(4‐methylphenyl)‐4‐bora‐3a,4a‐diaza‐s‐indacene ( 1 ), two BODIPY dyes ( 2 and 3 ) with increasingly rigid conformations were synthesized in outstanding total yields through palladium catalyzed intramolecular benzofuran formation. Restricted bond rotation of the phenoxy fragments leads to dyes 2 and 3 , which absorb and fluoresce more intensely at longer wavelengths relative to the unconstrained dye 1 . Reduction of the conformational flexibility in 2 and 3 leads to significantly higher fluorescence quantum yields compared to those of 1 . X‐ray diffraction analysis shows the progressively more extended planarity of the chromophore in line with the increasing conformational restriction in the series 1 → 2 → 3 , which explains the larger red shifts of the absorption and emission spectra. These conclusions are confirmed by quantum chemical calculations of the lowest electronic excitations in 1 , 1a , 2 , 2a , 3 and dyes of related chemical structures. The effect of the molecular structure on the visible absorption and fluorescence emission properties of 1 , 1a , 2 , 2a , 3 has been examined as a function of solvent by means of the new, generalized treatment of the solvent effect (J. Phys. Chem. B 2009 , 113, 5951–5960). Solvent polarizability is the primary factor responsible for the small solvent‐dependent shifts of the visible absorption and fluorescence emission bands of these dyes. 相似文献
104.
We report a new type of black silicon: flexible black silicon. A silicon-on-insulator (SOI) wafer is irradiated by automatically scanning a femtosecond laser and then split by etching out the SOI silica middle layer. Large-area, uniform micro spikes on the surface of a very thin flexible silicon layer are obtained. The black silicon shows good flexibility and optical properties. The absorption spectrum of the flexible black silicon is as high as 97% in the visible and insensitive to the change of the incident angle of the light, which makes it a potential good candidate as an absorber for the solar-thermo generator. 相似文献
105.
A specific scheme is used for fiber delivery of ultrashort pulses using conventional elements. Starting from a standard femtosecond Ti:Al(2)O(3) oscillator (150 fs @ 830 nm), perfectly compressed ultrashort pulses with a duration of 45 fs are produced at the output of a standard two meter long single-mode fiber. The setup allows compensating independently and simultaneously second and third orders of chromatic dispersion as well as management of self-phase modulation in the fiber. It includes an optimized dispersion compensation line made of the assembly of diffraction gratings and prisms. The unsurpassed performances of the device are experimentally and numerically highlighted. Fiber delivery of sub-30 fs multinanojoule pulses is discussed. 相似文献
106.
Claire DelabardeChristopher J.G. Plummer Pierre-Etienne BourbanJan-Anders E. Månson 《Polymer Degradation and Stability》2011,96(4):595-607
Dry, compression molded films of medical grade poly-l-lactide (PLLA) showed a marked reduction in tensile strength and strain after accelerated ageing in aqueous NaOH at 50 °C, accompanied by mass loss, surface erosion, increased hydrophilicity and, in the case of the initially amorphous films, cold crystallization owing to the plasticizing effect of the ageing medium. Addition of well dispersed nanosized hydroxyapatite (nHA) particles resulted in increases in the rate of mass loss during ageing, identified with accelerated degradation at the matrix/particle interfaces. However, the associated decreases in tensile strength and strain to fail with ageing time were far less marked in the presence of the nHA than in the unmodified films. This implied that nHA acts as an effective toughener of the bulk material, consistent with TEM observations of the deformed films, which indicated failure of the particle-matrix interfaces to promote plastic deformation of the PLLA. 相似文献
107.
108.
1,3,5-Triazepan-2,6-diones are a class of conformationally restricted heterocycles derived from dipeptides. With the aim to develop a general and practical method useful for library production, three polymer-assisted syntheses, all based on a catch and release approach, have been evaluated and compared. The method involving a Hofmann rearrangement of N-Boc dipeptide carboxamides and subsequent trapping of the isocyanate on polymer-supported N-hydroxysuccinimide (PS-HOSu) was found to be the most reliable and versatile, allowing rapid access to the 1,3,5-triazepan-2,6-dione skeleton. 相似文献
109.
110.