全文获取类型
收费全文 | 3481篇 |
免费 | 245篇 |
国内免费 | 1篇 |
专业分类
化学 | 2324篇 |
晶体学 | 18篇 |
力学 | 136篇 |
数学 | 548篇 |
物理学 | 481篇 |
无线电 | 220篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 26篇 |
2020年 | 37篇 |
2019年 | 44篇 |
2018年 | 66篇 |
2017年 | 48篇 |
2016年 | 136篇 |
2015年 | 102篇 |
2014年 | 116篇 |
2013年 | 237篇 |
2012年 | 254篇 |
2011年 | 278篇 |
2010年 | 142篇 |
2009年 | 162篇 |
2008年 | 222篇 |
2007年 | 228篇 |
2006年 | 216篇 |
2005年 | 222篇 |
2004年 | 184篇 |
2003年 | 172篇 |
2002年 | 127篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 36篇 |
1998年 | 17篇 |
1997年 | 22篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 13篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1985年 | 25篇 |
1984年 | 28篇 |
1983年 | 12篇 |
1982年 | 28篇 |
1981年 | 13篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 20篇 |
1974年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有3727条查询结果,搜索用时 390 毫秒
131.
Julien Parinet Jean Serodes François Proulx 《International journal of environmental analytical chemistry》2013,93(6):505-515
This paper describes a method of determining the following compounds in water characterised by complex matrices (raw waters and drinking waters): geosmin, 2-methylisoborneol (2-MIB), 2-isobutyl-3-methoxypyrazine (IBM), 2-isopropyl-3-methoxypyrazine (IPM) and 2,4,6-trichloroanisole (TCA). The method is carried out using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) and ion trap mass spectrometry (ITMS). Several parameters of extraction and desorption were optimised through the use of a Combi PAL autosampler to automate various tasks (temperature extraction, extraction time, stir speed). Quantities of NaCl and the liquid volume/total volume ratio were also optimised. Double fragmentation (tandem MS/MS) was optimised on the target compounds. The method resulted in good linearity obtained for concentrations of 1 to 100?ng?L?1 and provided detection limits of approximately below 1?ng?L?1. Good precision (1–8%) was obtained. This method was successfully applied to the analysis of earthy and musty odours in municipal raw source waters with high concentrations of natural organic matter and in the corresponding treated waters. This is the first time MS/MS has been used to analyse odorous compounds in waters destined for human consumption. In addition, the method as developed is simple to use and lends itself to easy interpretation of chromatograms. 相似文献
132.
Jean M. J. Tronchet Fabienne De Villedon De Naide Alessandra Ricca Istvan Komaromi Françise Barbalat-Rey Michel Geoffroy 《Journal of carbohydrate chemistry》2013,32(4-5):537-556
Abstract A series of 3-(N-arylmethyl-N-hydroxyamino)-l,2-O-cyclopentylidene-3-deoxy-5-O-toluoyl-α-D-riboses has been prepared. The blocking groups used were chosen to allow an easy nucleosidation of these compounds to spin labelled analogs of natural nucleosides. The conformational behavior of the N-arylmethyl-N-hydroxyamino group has been studied using 3/CH NMR coupling data and molecular mechanics computations. Upon spontaneous oxidation, these hydroxylamines led to the corresponding aminoxyl free radicals which were submitted to EPR spectroscopy and quantum mechanical computations at a semiempirical level (PM3). 相似文献
133.
Jean M. J. Tronchet Françoise Barbalat-Rey Jeannine F. Tronchet Faranak Raehidzadeh 《Journal of carbohydrate chemistry》2013,32(2):193-204
Replacement of the alkyl group of l-aryl-3-alkyltriazenes with a sugar moiety did not significantly modify their tautomeric behaviour. The same replacement done on 1-aryl-3-alkyl-3-methyl-triazenes did not affect to any large extent their rotameric properties. In contrast, the most prominent biological properties, anticancer activity and toxicity, of 1-aryl-3-methyltria-zenes disappeared on replacement of the methyl group with a sugar moiety. Unexpectedly, the N-acetyltriazene 15 was highly cyto-toxic. 相似文献
134.
Jean M. J. Tronchet Nicoletta Bizzozero Françoise Barbalat-Rey Michel Geoffroy 《Journal of carbohydrate chemistry》2013,32(1):155-160
Abstract Deoxy hydroxyamino sugars represent a potentially useful series of sugar analogs owing mainly to the fact that they oxidize spontaneously to nitroxide free radicals to give spin-labeled sugar derivatives whose structure is very close to that of the parent sugar.3 We describe herin two synthetic pathways towards these compounds, reduction of sugar oximes and conjugate addition to enolones derivatives, both in the pyranose series. 相似文献
135.
Chadi Khoury François Le Goffic Marie‐Noëlle Rager 《Journal of carbohydrate chemistry》2013,32(7):395-409
The synthesis of 2‐acetamido‐2‐deoxy‐6‐O‐octanoyl‐D‐glucono‐1,5‐lactone 9 and 2‐acetamido‐2‐deoxy‐6‐O‐octanoyl‐α‐D‐glucopyranose 7 from 2‐acetamido‐2‐deoxy‐α‐D‐glucopyranose is reported. For both targets, the key intermediate was allyl 2‐acetamido‐3,4‐di‐O‐benzyl‐2‐deoxy‐6‐O‐octanoyl‐α‐D‐glucopyranoside 5. Surface tension measurements (critical micellar concentration of 22.3 mM and 5 mM for 9 and 7, respectively) showed up the surface activity of both compounds, while enzyme inhibition assays indicated that 9 could inhibit bovine β‐N‐acetylglucosaminidase (Ki=6.5 µM) but not Serratia marcescens chitobiase nor hen egg‐white lysozyme. Moreover, 7 was shown to induce chitinase production of S. marcescens and to be readily metabolized by these bacteria. 相似文献
136.
137.
Dr. Stéphane Le Gac Dr. Btissam Najjari Dr. Vincent Dorcet Dr. Thierry Roisnel Dr. Luca Fusaro Prof. Dr. Michel Luhmer Dr. Eric Furet Dr. Jean‐François Halet Dr. Bernard Boitrel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):11021-11038
Overhanging carboxylic acid porphyrins have revealed promising ditopic ligands offering a new entry in the field of supramolecular coordination chemistry of porphyrinoids. Notably, the adjunction of a so‐called hanging‐atop (HAT) PbII cation to regular PbII porphyrin complexes allowed a stereoselective incorporation of the N‐core bound cation, and an allosterically controlled Newton’s cradle‐like motion of the two PbII ions also emerged from such bimetallic complexes. In this contribution, we have extended this work to other ligands and metal ions, aiming at understanding the parameters that control the HAT PbII coordination. The nature of the N‐core bound metal ion (ZnII, CdII), the influence of the deprotonation state of the overhanging COOH group and the presence of a neutral ligand on the opposite side (exogenous or intramolecular), have been examined through 1H NMR spectroscopic experiments with the help of radiocrystallographic structures and DFT calculations. Single and bis‐strap ligands have been considered. They all incorporate a COOH group hung over the N‐core on one side. For the bis‐strap ligands, either an ester or an amide group has been introduced on the other side. In the presence of a base, the mononuclear ZnII or CdII complexes incorporate the carbonyl of the overhanging carboxylate as apical ligand, decreasing its availability for the binding of a HAT PbII. An allosteric effector (e.g., 4‐dimethylaminopyridine (DMAP), in the case of a single‐strap ligand) or an intramolecular ligand (e.g., an amide group), strong enough to compete with the carbonyl of the hung COO?, is required to switch the N‐core bound cation to the opposite side with concomitant release of the COO?, thereby allowing HAT PbII complexation. In the absence of a base, ZnII or CdII binds preferentially the carbonyl of the intramolecular ester or amide groups in apical position rather than that of the COOH. This better preorganization, with the overhanging COOH fully available, is responsible for a stronger binding of the HAT PbII. Thus, either allosteric or acid–base control is achieved through stereoselective metalation of ZnII or CdII. In the latter case, according to the deprotonation state of the COOH group, the best electron‐donating ligand is located on one or the other side of the porphyrin (COO?>CONHR>COOR>COOH): the lower affinity of COOH for ZnII and CdII, the higher for a HAT PbII. These insights provide new opportunities for the elaboration of innovative bimetallic molecular switches. 相似文献
138.
139.
Michael Biacchi Ricky Bhajun Nassur Saïd Alain Beck Yannis Nicolas François Emmanuelle Leize‐Wagner 《Electrophoresis》2014,35(20):2986-2995
mAbs are highly complex proteins that present a wide range of microheterogeneity that requires multiple analytical methods for full structure assessment and quality control. As a consequence, the characterization of mAbs on different levels is particularly product‐ and time‐consuming. CE‐MS couplings, especially to MALDI, appear really attractive methods for the characterization of biological samples. In this work, we report the last instrumental development and performance of the first totally automated off‐line CE‐UV/MALDI‐MS/MS. This interface is based on the removal of the original UV cell of the CE apparatus, modification of the spotting device geometry, and creation of an integrated delivery matrix system. The performance of the method was evaluated with separation of five intact proteins and a tryptic digest mixture of nine proteins. Intact protein application shows the acquisition of electropherograms with high resolution and high repeatability. In the peptide mapping approach, a total number of 154 unique identified peptides were characterized using MS/MS spectra corresponding to average sequence coverage of 64.1%. Comparison with NanoLC/MALDI‐MS/MS showed complementarity at the peptide level with an increase of 42% when using CE/MALDI‐MS coupling. Finally, this work represents the first analysis of intact mAb charge variants by CZE using an MS detection. Moreover, using a peptide mapping approach CE‐UV/MALDI‐MS/MS fragmentation allowed 100% sequence coverage of the light chain and 92% of the heavy chain, and the separation of four major glycosylated peptides and their structural characterization. 相似文献
140.
Dewang Ma Nicolas Martin Christophe Tribet Françoise M. Winnik 《Analytical and bioanalytical chemistry》2014,406(29):7539-7547
Complexes formed between poly(acrylates) and polyclonal immunoglobulin G (IgG) in its native conformation and after heat stress were characterized using asymmetric flow field-flow fractionation (AF4) coupled with on-line UV-Vis spectroscopy and multi-angle light-scattering detection (MALS). Mixtures of IgG and poly(acrylates) of increasing structural complexity, sodium poly(acrylate) (PAA), a sodium poly(acrylate) bearing at random 3 mol % n-octadecyl groups, and a random copolymer of sodium acrylate (35 mol %), N-n-octylacrylamide (25 mol %) and N-isopropylacrylamide (40 mol %), were fractionated in a sodium phosphate buffer (0.02 M, pH 6.8) in the presence, or not, of 0.1 M NaCl. The AF4 protocol developed allowed the fractionation of solutions containing free poly(acrylates), native IgG monomer and dimer, poly(acrylates)/IgG complexes made up of one IgG molecule and a few polymer chains, and/or larger poly(acrylates)/IgG aggregates. The molar mass and recovery of the soluble analytes were obtained for mixed solutions of poly(acrylates) and native IgG and for the same solutions incubated at 65 °C for 10 min. From the combined AF4 results, we concluded that in solutions of low ionic strength, the presence of PAA increased the recovery ratio of IgG after thermal stress because of the formation of electrostatically-driven PAA/IgG complexes, but PAA had no protective effect in the presence of 0.1 M NaCl. Poly(acrylates) bearing hydrophobic groups significantly increased IgG recovery after stress, independently of NaCl concentration, because of the synergistic effect of hydrophobic and electrostatic interactions. The AF4 results corroborate conclusions drawn from a previous study combining four analytical techniques. This study demonstrates that AF4 is an efficient tool for the analysis of protein formulations subjected to stress, an important achievement given the anticipated important role of proteins in near-future human therapies. ? 相似文献