全文获取类型
收费全文 | 1939篇 |
免费 | 71篇 |
国内免费 | 8篇 |
专业分类
化学 | 1394篇 |
晶体学 | 19篇 |
力学 | 75篇 |
数学 | 294篇 |
物理学 | 236篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 42篇 |
2020年 | 55篇 |
2019年 | 43篇 |
2018年 | 31篇 |
2017年 | 25篇 |
2016年 | 55篇 |
2015年 | 49篇 |
2014年 | 68篇 |
2013年 | 118篇 |
2012年 | 127篇 |
2011年 | 169篇 |
2010年 | 74篇 |
2009年 | 77篇 |
2008年 | 134篇 |
2007年 | 130篇 |
2006年 | 107篇 |
2005年 | 110篇 |
2004年 | 93篇 |
2003年 | 96篇 |
2002年 | 103篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1895年 | 1篇 |
1887年 | 2篇 |
排序方式: 共有2018条查询结果,搜索用时 16 毫秒
81.
Nada Marquise Philip J. Harford Floris Chevallier Thierry Roisnel Vincent Dorcet Anne-Laure Gagez Sophie Sablé Laurent Picot Valérie Thiéry Andrew E.H. Wheatley Philippe C. Gros Florence Mongin 《Tetrahedron》2013
The efficiency of the deprotocupration–aroylation of 2-chloropyridine using lithiocuprates prepared from CuX (X=Cl, Br) and LiTMP (TMP=2,2,6,6-tetramethylpiperidido, 2 equiv) was investigated. CuCl was identified as a more suitable copper source than CuBr for this purpose. Different diaryl ketones bearing a halogen at the 2 position of one of the aryl groups were synthesized in this way from azines and thiophenes. These were then involved in palladium-catalyzed ring closure: substrates underwent expected CH-activation-type arylation to afford fluorenone-type compounds, and were also subjected to cyclization reactions leading to xanthones, notably in the presence of oxygen-containing substituents or reagents. 相似文献
82.
Arbia Khemiri Bertrand Naudin Xavier Franck Philippe Chan Tchi Song Thierry Jouenne Pascal Cosette 《Analytical and bioanalytical chemistry》2013,405(30):9835-9842
In prokaryote organisms, N-glycosylation of proteins is often correlated to cell–cell recognition and extracellular events. Those glycoproteins are potential targets for infection control. To date, many surface-glycosylated proteins from bacterial pathogens have been described. However, N-linked Pseudomonas surface-associated glycoproteins remain underexplored. We report a combined enrichment and labeling strategy to identify major glycoproteins on the outside of microorganisms. More precisely, bacteria were exposed to a mix of biotinylated lectins able to bind with glycoproteins. The latter were then recovered by avidin beads, digested with trypsin, and submitted to mass spectrometry. The targeted mixture of glycoproteins was additionally deglycosylated in the presence of H2 18O to incorporate 18O during PNGase F treatment and were also analyzed using mass spectrometry. This approach allowed us to identify a few tens of potential N-glycoproteins, among which flagellin FliC was the most abundant. To detect the possible sites of FliC modifications, a de novo sequencing step was also performed to discriminate between spontaneous deamidation and N-glycan loss. This approach led to the proposal of three potential N-glycosylated sites on the primary sequence of FliC: N26, N69, and N439, with two of these three asparagines belonging to an N-X-(S/T) consensus sequence. These observations suggest that flagellin FliC is a heterogeneous protein mixture containing both O- and N-glycoforms. Figure
Analytical scenario developed for bacterial glycoprotein enrichment. This strategy includes three main steps: (1) exposure of Pseudomonas aeruginosa cells to a mixture of biotinylated lectins [wheat germ agglutinin (WGA) and concanavalin A (ConA)]; (2) enrichment of N-glycoproteins by elution with avidin beads; and (3) mass spectrometry (MS) identification and characterization of intact and deglycosylated peptides before and after H2 18O PNGase F enzymatic treatment, respectively 相似文献
83.
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
84.
Dr. Chih‐Kai Liang Dr. Galina V. Dubacheva Dr. Thierry Buffeteau Dr. Dominique Cavagnat Dr. Philippe Hapiot Dr. Bruno Fabre Prof. James H. R. Tucker Dr. Dario M. Bassani 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(38):12748-12758
The synthesis of an anthracene‐bearing photoactive barbituric acid receptor and its subsequent grafting onto azide‐terminated alkanethiol/Au self‐assembled monolayers by using an CuI‐catalyzed azide–alkyne reaction is reported. Monolayer characterization using contact‐angle measurements, electrochemistry, and spectroscopic ellipsometry indicate that the monolayer conversion is fast and complete. Irradiation of the receptor leads to photodimerization of the anthracenes, which induces the open‐to‐closed gating of the receptor by blocking access to the binding site. The process is thermally reversible, and polarization‐modulated IR reflection–absorption spectroscopy indicates that photochemical closure and thermal opening of the surface‐bound receptors occur in 70 and 100 % conversion, respectively. Affinity of the open and closed surface‐bound receptor was characterized by using force spectroscopy with a barbituric‐acid‐modified atomic force microscope tip. 相似文献
85.
Prof. Dr. Karen Hemelsoet Qingyun Qian Thierry De Meyer Kristof De Wispelaere Dr. Bart De Sterck Prof. Dr. Bert M. Weckhuysen Prof. Dr. Michel Waroquier Prof. Dr. Veronique Van Speybroeck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16595-16606
The optical absorption properties of (poly)aromatic hydrocarbons occluded in a nanoporous environment were investigated by theoretical and experimental methods. The carbonaceous species are an essential part of a working catalyst for the methanol‐to‐olefins (MTO) process. In situ UV/Vis microscopy measurements on methanol conversion over the acidic solid catalysts H‐SAPO‐34 and H‐SSZ‐13 revealed the growth of various broad absorption bands around 400, 480, and 580 nm. The cationic nature of the involved species was determined by interaction of ammonia with the methanol‐treated samples. To determine which organic species contribute to the various bands, a systematic series of aromatics was analyzed by means of time‐dependent density functional theory (TDDFT) calculations. Static gas‐phase simulations revealed the influence of structurally different hydrocarbons on the absorption spectra, whereas the influence of the zeolitic framework was examined by using supramolecular models within a quantum mechanics/molecular mechanics framework. To fully understand the origin of the main absorption peaks, a molecular dynamics (MD) study on the organic species trapped in the inorganic host was essential. During such simulation the flexibility is fully taken into account and the effect on the UV/Vis spectra is determined by performing TDDFT calculations on various snapshots of the MD run. This procedure allows an energy absorption scale to be provided and the various absorption bands determined from in situ UV/Vis spectra to be assigned to structurally different species. 相似文献
86.
87.
Le Fur E Demers E Maris T Wuest JD 《Chemical communications (Cambridge, England)》2003,(24):2966-2967
Single crystals built from porous molecular networks can react with agents that penetrate the crystals, cleave fragments from the network, and thereby increase the volume available for guests, all without loss of crystallinity. 相似文献
88.
Maria D. Manrique-Juarez Dr. Fabrice Mathieu Dr. Victoria Shalabaeva Dr. Jean Cacheux Sylvain Rat Dr. Liviu Nicu Dr. Thierry Leïchlé Dr. Lionel Salmon Dr. Gábor Molnár Dr. Azzedine Bousseksou 《Angewandte Chemie (International ed. in English)》2017,56(28):8074-8078
We report on a bistable MEMS device actuated by spin-crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140 nm thick film of the [Fe(HB(tz)3)2] (tz=1,2,4-triazol-1-yl) molecular spin-crossover complex. Switching from the low-spin to the high-spin state of the ferrous ions at 338 K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66 Hz in the resonance frequency in the high-spin state as well as by the drop in the quality factor around the spin transition. 相似文献
89.
Thierry K. Slot N. Raveendran Shiju Gadi Rothenberg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17433-17436
We present a new device for quantifying gases or gas mixtures based on the simple principle of bubble counting. With this device, we can follow reaction kinetics down to volume step sizes of 8–12 μL. This enables the accurate determination of both time and size of these gas quanta, giving a very detailed kinetic analysis. We demonstrate this method and device using ammonia borane hydrolysis as a model reaction, obtaining Arrhenius plots with over 300 data points from a single experiment. Our device not only saves time and avoids frustration, but also offers more insight into reaction kinetics and mechanistic studies. Moreover, its simplicity and low cost open opportunities for many lab applications. 相似文献
90.
Thierry Sifferlen Magnus Rueping Karl Gademann Bernhard Jaun Dieter Seebach 《Helvetica chimica acta》1999,82(12):2067-2093
To test the effect of NH−C=S groups (Scheme 1) on the stability of β-peptide secondary structures, we have synthesized three β-thiohexapeptide analogues of H-(β-HVal-β-HAla-β-HLeu)2-OH ( 1 ) with one, two, and three C=S groups in the N-terminal positions (cf. 2 – 4 and model in Fig. 1). The first C=S group was introduced selectively by treatment with Lawesson reagent of Boc-β-dipeptide esters ( 6 and 8 ). A series of fragment-coupling steps (with reagents as for the corresponding sulfur-free building blocks) and another thionation reaction led to the title compounds with a C=S group in residues 1, 1, and 3, as well as 1, 2, and 3 of the β-hexapeptide (Schemes 2 and 3). The sulfur derivatives, especially those with three C=S groups, were much more soluble in organic media than the sulfur-free analogues (>1000-fold in CHCl3; Table 1). The UV and CD spectra (in CHCl3, MeOH, and H2O) of the new compounds were recorded and compared with those of the parent β-hexapeptide 1 (Figs. 2 – 4); they indicate the presence of more than one secondary structure under the various conditions. Most striking is a pronounced exciton splitting (Δλ ca. 20 nm, amplitude up to +121000) of the ππ*C=S band near 270 nm with the β-trithiohexapeptide (with and without terminal protecting groups), and strong, so-called `primary solvent effects', in the CD spectra. The CD spectrum of the β-dithiohexapeptide 3 undergoes drastic changes upon irradiation with 266-nm laser light of a MeOH solution (Fig. 5). The NMR structure in CD3OH of the unprotected β-trithiohexapeptide 4 was determined to be an (M)-314-helix (Fig. 7), very similar to that of the non-thionated analogue (cf. 1 ). NMR and mass spectra of the β-hexapeptides with C=S and with C=O groups are compared (Figs. 6 and 8). 相似文献