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31.
Jean-Michel Widmaier 《Macromolecular Symposia》1995,93(1):179-186
As a rule, interpenetrating polymer networks (IPNs) are multiphase systems, and the degree of microphase separation is determined by the competition between the chemical kinetics of reaction and the physical kinetics of phase separation. For semi-IPNs of crosslinked polyurethane and linear polystyrene obtained by a one-step process, the development of the morphology has been followed by light transmission measurements and by optical microscopy, and finally examined by scanning electron microscopy. When phase separation takes place after gelation, the rather short elastic chains of polyurethane limit the growth of the styrenic phase at a submicroscopic level and the materials thus formed are transparent. On the contrary, when the reaction medium can phase-separate before gelation of polyurethane, the final morphology results from a superposition of two levels of phase separation: i) a fine dispersion of the components and ii) a gross phase separation of polystyrene noduli surrounded by a polyurethane-rich shell. 相似文献
32.
Gaulier C Hospital A Legeret B Delmas AF Aucagne V Cisnetti F Gautier A 《Chemical communications (Cambridge, England)》2012,48(33):4005-4007
A reducing agent-free version of CuAAC able to operate under open air conditions is reported. A readily-synthesizable, hydrophilic and highly stable Cu(I)-NHC allows the clean ligations of unprotected peptides comprising sensitive side chains, at millimolar concentrations. 相似文献
33.
Dolain C Jiang H Léger JM Guionneau P Huc I 《Journal of the American Chemical Society》2005,127(37):12943-12951
Chiral groups attached to the end of quinoline-derived oligoamide foldamers give rise to chiral helical induction in solution. Using various chiral groups, diastereomeric excesses ranging from 9% to 83% could be measured by NMR and circular dichroism. Despite these relatively weak values and the fact that diastereomeric helices coexist and interconvert in solution, the right-handed or left-handed helical sense favored by the terminal chiral group could be determined unambiguously using X-ray crystallography. Assignment of chiral induction was performed in an original way using the strong tendency of racemates to cocrystallize, and taking advantage of slow helix inversion rates, which allowed one to establish that the stereomers observed in the crystals do correspond to the major stereomers in solution. The sense of chiral helical induction was rationalized on the basis of sterics. Upon assigning an Rs or Ss chirality to the stereogenic center using a nomenclature where the four substituents are ranked according to decreasing sizes, it is observed that Rs chirality always favors left-handed helicity and Ss chirality favors right-handed helicity (P). X-ray structures shed some light on the role of sterics in the mechanism of chiral induction. The preferred conformation at the stereocenter is apparently one where the bulkiest group should preferentially point away from the helix, the second largest group should be aligned with the helix backbone, and the smallest should point to the helix. 相似文献
34.
Available data from various sources seem to indicate an important role of solvation in the cleavage rates of intermediate pi ion radicals, in the passage from concerted to stepwise electron-transfer/bond breaking reaction pathways and even in the very existence of pi ion radicals. After preliminary computations treating the solvent as dielectric continuum, these expectations are examined with the help of a simple model system involving the anion radical of ONCH(2)Cl and two molecules of water, which allows the application of advanced computational techniques and a treatment of these solvent effects that emphasizes the role of solvent molecules that sit close to the charge centers of the molecule. A pi ion radical minimum indeed appears upon introduction of the two water molecules, and cleavage is accompanied by their displacement toward the leaving anion, thus offering a qualitative mimicry of the experimental observations. 相似文献
35.
Sawicki M Siaugue JM Jacopin C Moulin C Bailly T Burgada R Meunier S Baret P Pierre JL Taran F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3689-3697
New tripodal gem-(bis-phosphonates) uranophiles were discovered by a screening method that allowed for the selection of ligands with strong uranyl-binding properties in a convenient microtiter-plate format. The method is based on competitive uranium binding by using Sulfochlorophenol S as chromogenic chelate. This dye compound was found to present high uranyl complexation properties and allowed to highlight ligands presenting association constants for UO(2+)(2) up to 10(18) at pH 7.4 and 10(20) at pH 9. A collection of 40 known ligands including polycarboxylate, hydroxamate, catecholate, hydroxypyridonate and hydroxyquinoline derivatives was tested. Also screened was a combinatorial library prepared from seven amine scaffolds and eight acrylates bearing diverse chelating moieties. Among these 96 tested candidates, a tripod derivative bearing gem-bis-phosphonates moieties was found to present the highest complexation properties over a wide range of pH and was further studied. 相似文献
36.
Gomila A Le Poul N Cosquer N Kerbaol JM Noël JM Reddy MT Jabin I Reinaud O Conan F Le Mest Y 《Dalton transactions (Cambridge, England : 2003)》2010,39(48):11516-11518
We report the self-induced "electroclick" immobilization of the [Cu(II)(6-ethynyl-TMPA)(H(2)O)](2+) complex, by its simple electro-reduction, onto a mixed azidoundodecane-/decane-thiol modified gold electrode. The redox response of the grafted [Cu(II/I)(TMPA)] at the modified electrode is fully reversible indicating no Cu coordination change and a fast electron transfer. 相似文献
37.
Sylvain Dulaurent Christian Moesch Pierre Marquet Jean-Michel Gaulier Gérard Lachâtre 《Analytical and bioanalytical chemistry》2010,396(6):2235-2249
In clinical or forensic toxicology, general unknown screening procedures are used to identify as many xenobiotics as possible, belonging to numerous chemical classes. We present here a general unknown screening procedure based on liquid chromatography coupled with use of a single linear ion trap mass spectrometer, and focus on the identification of pesticides and/or metabolites in whole blood. After solid-phase extraction (SPE), the compounds of interest were separated using a reversed-phase column and identified by the mass spectrometer operated first in the full-scan mass spectrometry (MS) mode, in the positive and negative polarities, followed by MS2 and MS3 scanning of ions selected in data-dependent acquisition. The total scan time was 2.45 s. Two mass spectral libraries (MS2 and MS3), each of 450 spectra, were created for the 320 pesticides and metabolites detected after injection of pure solutions. Robustness of the spectra and matrix effects were studied and were satisfactory for the present application. Detection limits for the 320 compounds were studied by extracting 1 mL spiked blood at concentrations between 10 μg/L and 10 mg/L. If necessary, it was possible to decrease the detection limits of some compounds by 10–100-fold by scanning MS2 in only one polarity, owing to a shorter total scan time. However, at the same time, the detection specificity decreased as no confirmation could be recorded in the following MS3 scan and no information could be registered in the other polarity. So, in these rare cases, confirmation by another method was required. 相似文献
38.
Magali Bonne Stéphane Pronier Fabien Can Xavier Courtois Sabine Valange Jean-Michel Tatibouët Sébastien Royer Patrice Marécot Daniel Duprez 《Solid State Sciences》2010,12(6):1002-1012
Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO2/SiO2 nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400 °C), nanocomposites having titania nanodomains (~2–3 nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55 wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800 °C does not allow to detect the anatase to rutile transition. Even at 800 °C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ~10 nm, a size close to that of the silica host support porosity (8.4 nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO2/SiO2 solids are promising in term of thermal stability. 相似文献
39.
Toubas D Essendoubi M Adt I Pinon JM Manfait M Sockalingum GD 《Analytical and bioanalytical chemistry》2007,387(5):1729-1737
The incidence of fungal infections, in particular candidiasis and aspergillosis, has considerably increased during the last
three decades. This is mainly due to advances in medical treatments and technologies. In high risk patients (e.g. in haematology
or intensive care), the prognosis of invasive candidiasis is relatively poor. Therefore, a rapid and correct identification
of the infectious agent is important for an efficient and prompt therapy. Most clinical laboratories rely on conventional
identification methods that are based on morphological, physiological and nutritional characteristics. However, these have
their limitations because they are time-consuming and not always very accurate. Moreover, molecular methods may be required
to determine the genetic relationship between the infectious strains, for instance in Candida outbreaks. In addition, the latter methods require time, expensive consumables and highly trained staff to be performed adequately.
In this study, we have applied the FTIR spectroscopic approach to different situations encountered in routine mycological
diagnosis. We show the potentials of this phenotypic approach, used in parallel with routine identification methods, for the
differentiation of 3 frequently encountered Candida species (C. albicans, C. glabrata and C. krusei) by using both suspensions and microcolonies. This approach, developed for an early discrimination, may help in the initial
choice of antifungal treatment. Furthermore, we demonstrate the feasibility of the method for intraspecies comparison (typing)
of 3 Candida species (C. albicans, C. glabrata and C. parapsilosis), particularly when an outbreak is suspected. 相似文献
40.
Shunichi Fukuzumi Ikuo Nakanishi Jean-Michel Barbe Roger Guilard Eric Van Caemelbecke Ning Guo Karl M. Kadish 《Angewandte Chemie (International ed. in English)》1999,38(7):964-966
Slow electron transfer to manganese(iii) porphyrins results when the macrocycle deviates from planarity. This was demonstrated by measuring the kinetics of homogeneous electron transfer from a series of semiquinone radical anions to synthetic manganese porphyrins (shown schematically; R1=H, Cl, F; R2=H, F). Three of the four porphyrins studied have nonplanar macrocycles. These results could have implications for the role of manganese in biological electron transfer processes. 相似文献