全文获取类型
收费全文 | 593篇 |
免费 | 10篇 |
国内免费 | 6篇 |
专业分类
化学 | 321篇 |
晶体学 | 4篇 |
力学 | 10篇 |
数学 | 104篇 |
物理学 | 170篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 20篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 19篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 33篇 |
2012年 | 27篇 |
2011年 | 28篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 35篇 |
2006年 | 23篇 |
2005年 | 24篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1973年 | 2篇 |
1968年 | 2篇 |
1930年 | 2篇 |
排序方式: 共有609条查询结果,搜索用时 15 毫秒
1.
P. Di Martino P. Conflant M. Drache J. -P. Huvenne A. -M. Guyot-Hermann 《Journal of Thermal Analysis and Calorimetry》1997,48(3):447-458
The polymorphic forms II and III of paracetamol were obtained by melting the marketed form I. Under the melting and cooling conditions used, it was possible to obtain forms I, II and III. The recrystallization conditions and the physical properties of forms II and III were investigated by means of various techniques: thermomicroscopy, DSC analysis, infrared microspectrometry and X-ray powder diffraction at room temperature and as a function of temperature. Form III was found to be very unstable. However, its formation seems to be an important intermediate step in the preparation of form II. 相似文献
2.
A. Ouardaoui D. M. Martino C. A. Steren H. van Willigen 《Applied magnetic resonance》1997,13(3-4):275-284
The mechanism of 4-chlorophenol (4CP) photolysis was investigated with the aid of Fourier Transform Electron Paramagnetic Resonance (FT-EPR) and pulsed-laser photolysis combined with High Performance Liquid Chromatography (HPLC) detection-of stable (diamagnetic) products. With FT-EPR transient free radicals produced by pulsed-laser excitation of solutions of 4CP in alcohols could be identified. Time profiles of the FT-EPR spectra provided information on reaction kinetics and Chemically Induced Dynamic, Electron Polarization (CIDEP) effects. It was found that 4CP photolysis in alcohols leads to the simultaneous formation of the phenoxyl radical and radicals produced by hydrogen abstraction from the solvent. CIDEP patterns establish that these radicals are formed in a reaction sequence involving a triplet state precursor and radical pair intermediate. Results of earlier transient optical absorption measurements indicate that the triplet precursor must be the carbene 4-oxocyclohexa-2,5-dienylidene. This assignment is supported by the finding that photolysis of quinone diazide in a hydrogen-donating solvent gives the same free radical products as those obtained from 4CP. The formation of the phenoxyl radical intermediate accounts for the finding that photolysis of deoxygenated solutions of 4CP in alcohols gives phenol as stable diamagnetic product. By contrast, photolysis of aerated and deoxygenated aqueous solutions of 4CP produces benzoquinone and hydroquinone as primary products, respectively. 相似文献
3.
FexNi100−x nanometric films were deposited on SiO2/Si substrates at room temperature using the pulsed laser deposition technique. The targets were Fe-Ni amorphous magnetic foils with composition Fe50Ni50, Fe35Ni65 and Fe22Ni78. Morphological and structural properties of the deposited films were investigated using scanning electron microscopy, Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and X-ray reflectivity. Electrical and magnetic characteristics of the films were investigated by using the four-point probe and the magneto-optic Kerr effect techniques, respectively. The film properties are strictly dependent on the Fe-Ni compositional ratio. 相似文献
4.
5.
A stereocontrolled cyclisation of suitably substituted indole derivatives can be explained by the revised Pictet-Spengler reaction mechanism. 相似文献
6.
7.
D. Mauri D. Scholl H. C. Siegmann E. Kay 《Applied Physics A: Materials Science & Processing》1989,49(5):439-447
The spin polarizationP of the low energy cascade electrons excited with a primary unpolarized electron beam is measured with ultrathin films of permalloy (Ni80Fe20) as a function of film thickness, external magnetic field, and temperatureT. Surface adsorbates of small concentrations of less than 10% of a monolayer can change the Curie point and the saturation value ofP
0(T0) by as much as 30%. The Ta-substrate induces a magnetically dead region in permalloy. Conventional spin wave theory cannot account for the observed smallT-dependence of the magnetizationM. Films on a nonmagnetic substrate are compared to similar films coupled to bulk permalloy over an interface of Ta. TheT-dependence ofM with the coupled films can be explained by spin wave theory. At lowT, the films coupled to the bulk exhibit a faster decrease ofM than the uncoupled films. We propose that this thermal stabilization of the magnetization in very thin ferromagnetic films is due to quenching of the long wavelength spin modes. 相似文献
8.
A ligand known to form a fluorescent complex with aluminum ion was immobilized on silica gel. The immobilization sequence was verified by cross-polarization magicangle spinning n.m.r. spectroscopy and diffuse reflectance u.v. spectroscopy. The solid-state fluorescence of the immobilized ligand complexed with aluminum ion was similar to the fluorescence of a solvated complex of a model ligand. The potential to eliminate possible interfering species by isolating the complex from solution was demonstrated. 相似文献
9.
Purification of NAD glycohydrolase from Neurospora crassa conidia by a polyclonal immunoadsorbent. 总被引:1,自引:0,他引:1
M Pace D Agnellini G Lippoli P G Pietta P L Mauri S Cinquanta 《Journal of chromatography. A》1991,539(2):517-523
NAD glycohydrolase from Neurospora crassa conidia was purified by affinity chromatography on a column of polyclonal antibodies bound to an agarose matrix. The procedure was easy, non-denaturating and suitable for repetitive use of the gel. The enzyme obtained appeared homogeneous by sodiumdodecyl sulphate-polyacrylamide gel electrophoresis. 相似文献
10.
Synthesis of 1-(4-substituted)benzyl-6-hydroxyisoquinolines with potential activity on NA+,K+-atpase
Alberto Cerri Paola Mauri Marina Mauro Piero Melloni 《Journal of heterocyclic chemistry》1993,30(6):1581-1591
The synthesis of 1-(4-substituted)benzyl-6-hydroxyisoquinolines, to be evaluated in the displacement of the specific 3H-ouabain binding to Na+,K+-ATPase, is described. The key step involved a cyclization to the isoquinoline ring under Pictet-Gams conditions which was best performed with the 6-hydroxy group protected as the benzyl ether. When an unsaturated ester group was present in position 4 of the 1-benzyl group, this was best introduced before the cyclization step, since the IIeck reaction on 1-(4-bromobenzyl)-6-hydroxyisoquinoline ( 8 ) with acrylic acid derivatives was not successful in all cases. 相似文献