全文获取类型
收费全文 | 626篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
化学 | 496篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 75篇 |
物理学 | 61篇 |
出版年
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 6篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 19篇 |
2014年 | 16篇 |
2013年 | 35篇 |
2012年 | 28篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 47篇 |
2007年 | 39篇 |
2006年 | 35篇 |
2005年 | 18篇 |
2004年 | 26篇 |
2003年 | 23篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 12篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1967年 | 3篇 |
1943年 | 2篇 |
排序方式: 共有658条查询结果,搜索用时 15 毫秒
91.
Dr. Marion Daniel-Bertrand Sébastien Garcia-Argote Dr. Alberto Palazzolo Dr. Irene Mustieles Marin Dr. Pier-Francesco Fazzini Dr. Simon Tricard Dr. Bruno Chaudret Dr. Volker Derdau Dr. Sophie Feuillastre Dr. Grégory Pieters 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21300-21306
Radiolabelling is fundamental in drug discovery and development as it is mandatory for preclinical ADME studies and late-stage human clinical trials. Herein, a general, effective, and easy to implement method for the multiple site incorporation of deuterium and tritium atoms using the commercially available and air-stable iridium precatalyst [Ir(COD)(OMe)]2 is described. A large scope of pharmaceutically relevant substructures can be labelled using this method including pyridine, pyrazine, indole, carbazole, aniline, oxa-/thia-zoles, thiophene, but also electron-rich phenyl groups. The high functional group tolerance of the reaction is highlighted by the labelling of a wide range of complex pharmaceuticals, containing notably halogen or sulfur atoms and nitrile groups. The multiple site hydrogen isotope incorporation has been explained by the in situ formation of complementary catalytically active species: monometallic iridium complexes and iridium nanoparticles. 相似文献
92.
93.
Based on the principle of supercritical chromatography, a fractionation process for fatty acid methyl esters (FAMEs) under supercritical conditions was studied with the aim of obtaining in extracts highly enriched eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish cannery waste. Yields of the fractionation process were enhanced by using adjuvant material and modifying CO(2) volumetric density and temperature. The combination of adjuvant properties with optimized pressure and temperature conditions permitted efficient fractionations of FAMEs, according to chain length and degree of unsaturation, in high purity (up to 95% of FAME) and good yields (45% of EPA and DHA starting potential). This work shows how green technologies, such as supercritical processes, can constitute a good alternative to the use of organic solvents in classical methods for valorisation of complex food industry waste. 相似文献
94.
Gröger T Welthagen W Mitschke S Schäffer M Zimmermann R 《Journal of separation science》2008,31(19):3366-3374
In tobacco research, the comparison of different tobacco blends as well as the puff-dependent behaviour of cigarettes is a matter of particular interest. For the investigation of smoke characteristics, GC x GC offers different ways for data analysis, namely, compound target analysis, automated peak-based compound classification and comprehensive pixel-based data analysis. This study will show the application as well as the pros and cons of these types of data analysis for very complex matrices like cigarette particulate matter. In addition, new aspects about the recently discovered puff-dependent behaviour of compounds in cigarette smoke will be presented. Automated peak-based compound classification including mass spectrometric pattern recognition is used for the classification of tobacco particulate matter samples and the puff-dependent investigation of different compound classes. This compound group specific analysis is further reinforced by applying an even more comprehensive pixel-based analysis. This kind of analysis is used to generate fingerprints of different types of cigarettes. The combination of fast feature reduction methods like analysis of variance (ANOVA) and t-test with multivariate feature transformation methods like partial least squares discriminate analysis (PLSDA) for feature selection provides a powerful tool for a detailed inspection of different types of cigarettes. 相似文献
95.
96.
Heckenroth M Kluser E Neels A Albrecht M 《Dalton transactions (Cambridge, England : 2003)》2008,(44):6242-6249
Palladation of C2-protected diimidazolium salts with Pd(OAc)2 afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF4, AgOAc) and Br?nsted acids (H2SO4, H3PO4, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis base. The abnormal carbene bonding mode induces new reaction patterns such as the formation of a Pd-Ag adduct. Based on metallation studies including the palladation of a dissymmetric diimidazolium salt, a rationale for the selective activation of the C4-H bond in the diimidazolium precursor salts is proposed. 相似文献
97.
A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalized building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards beta-hydroxy-alpha-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into trans beta-hydroxy-alpha-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO2 insertion and cyclisation sequence gave the cis beta-hydroxy-alpha-methylene lactone counterparts along with an interesting cis-trans equilibration of the pi-allyl intermediates. 相似文献
98.
[2,3]-Wittig rearrangements of (E)-3-aza-allylic alcohol derivatives can provide access to syn or anti optically enriched 1,2-aminoalcohols by using a chirality transfer or a chiral auxiliary. 相似文献
99.
Bottier C Géan J Desbat B Renault A Marion D Vié V 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10901-10909
Puroindolines (PINs), basic and cysteine-rich proteins of wheat endosperm, are composed of two proteins, puroindoline-a (PIN-a) and puroindoline-b (PIN-b). Using a monolayer assay at the air/liquid interface, both PIN-a and PIN-b were studied in pure components and mixed with wheat galactolipids, 1,2-di-O-acyl-3-O-(beta-d-galactopyranosyl)- sn-glycerol (MGDG) and 2-di-O-acyl-3-O-(beta-d-galactopyranosyl-1,6-beta-d-galactopyranosyl)-sn-glycerol (DGDG). Following the adsorption of PINs at the air/liquid interface thanks to surface pressure increases, we concluded that PIN-a displays a more amphipathic character than PIN-b. Compression isotherms combined with ellipsometric measurements showed that the area per molecule is smaller and the protein film is more condensed for PIN-a than for PIN-b. According to the polarization modulation-infrared reflection-absorption spectroscopy data, both proteins display a highly alpha-helical structure and the alpha-helices are oriented rather parallel to the interface. By measuring the overpressure due to PIN adsorption into MGDG and DGDG monolayers, we observed that PIN-a interacts more strongly into lipid films than PIN-b. The observation by atomic force microscopy of mixed protein/lipid films showed that the nature of the lipid plays a significant role in the organization of PINs, particularly for PIN-a. The presence of galactolipids at the interface stabilizes the alpha-helical structure of PINs, but significant changes were observed concerning the orientation of the alpha-helices. They adopt a perfect parallel orientation to the interface in the MGDG monolayer, whereas the bundle of alpha-helices orients normal to the interface in the DGDG film. 相似文献
100.
Coupling of liquid chromatography at critical conditions (LCCC) with on-line mass spectrometry (MS) detection was implemented via an electrospray ionization (ESI) interface, using a mobile phase containing the cationizing agent. Critical conditions established for poly(ethylene oxide) were used to characterize a poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) in both MS and MS/MS modes. As co-oligomer molecules were successfully separated according to the PS block size, structural information could be reached from simplified MS spectra. The microstructure of this copolymer, synthesized by nitroxide-mediated polymerization, could further be unambiguously characterized in LCCC/ESI-MS/MS experiments since the PS block size could be reached by both the co-oligomer chromatographic behavior and its MS/MS pattern. 相似文献