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141.
Self-organization of 3,5-dihydroxybenzylalcohol (DHBA) based dendrimers of generations 0-3 (G0-G3) on bare and functionalized single crystal silicon (Si/SiO2) surfaces has been examined. The underlying monolayer plays a significant role in the supramolecular assembly leading to ordered structures of DHBA (G0) and generation 1-3 (G1-G3) dendrimers at interfaces. Ordered hyperbranched structures are formed on surfaces containing self-assembled monolayers with complimentary features to the assembling molecules, whereas no such organized assemblies are observed on unfunctionalized surfaces. 相似文献
142.
Hazane F Sauvaigo S Douki T Favier A Beani JC 《Journal of photochemistry and photobiology. B, Biology》2006,82(3):214-223
Ageing process in cells is associated with oxidative stress. Ultraviolet A produces reactive oxygen species responsible for accumulation of DNA and cellular damage. After the evaluation of antioxidant enzyme activities and oxidative stress markers at the basal state, we have studied the responses to UVA stress of coetaneous fibroblasts, isolated from different male donors (2-88 years, n=23) in terms of cytotoxicity, genotoxicity and DNA repair capacities. For this purpose, we have determined level of DNA damage using the comet assay (single strand breaks and alkali-labile sites) and the cell cycle distribution after a 5 J/cm2 irradiation. No differences with age were observed for antioxidant enzyme activities and oxidative stress markers. DNA strand breaks after UVA irradiation (5-20 J/cm2), was found to be age-dependent. DNA repair was slow and also significantly affected by ageing. The cell cycle distribution analysis showed that high repair correlated with high proliferative capacities at basal level. Twenty-four hours after the stress, fraction of young fibroblasts blocked in G1 phase was significantly increased whereas significant modifications concerned the G2-M phase for adult and older fibroblasts. These results indicate an age-dependent decline in the DNA repair capacities correlated with modifications of the cell cycle parameters. 相似文献
143.
Bonnot F Molle T Ménage S Moreau Y Duval S Favaudon V Houée-Levin C Nivière V 《Journal of the American Chemical Society》2012,134(11):5120-5130
Superoxide reductase is a nonheme iron metalloenzyme that detoxifies superoxide anion radicals O(2)(?-) in some microorganisms. Its catalytic mechanism was previously proposed to involve a single ferric iron (hydro)peroxo intermediate, which is protonated to form the reaction product H(2)O(2). Here, we show by pulse radiolysis that the mutation of the well-conserved lysine 48 into isoleucine in the SOR from Desulfoarculus baarsii dramatically affects its reaction with O(2)(?-). Although the first reaction intermediate and its decay are not affected by the mutation, H(2)O(2) is no longer the reaction product. In addition, in contrast to the wild-type SOR, the lysine mutant catalyzes a two-electron oxidation of an olefin into epoxide in the presence of H(2)O(2), suggesting the formation of iron-oxo intermediate species in this mutant. In agreement with the recent X-ray structures of the peroxide intermediates trapped in a SOR crystal, these data support the involvement of lysine 48 in the specific protonation of the proximal oxygen of the peroxide intermediate to generate H(2)O(2), thus avoiding formation of iron-oxo species, as is observed in cytochrome P450. In addition, we proposed that the first reaction intermediate observed by pulse radiolysis is a ferrous-iron superoxo species, in agreement with TD-DFT calculations of the absorption spectrum of this intermediate. A new reaction scheme for the catalytical mechanism of SOR with O(2)(?-) is presented in which ferrous iron-superoxo and ferric hydroperoxide species are reaction intermediates, and the lysine 48 plays a key role in the control of the evolution of iron peroxide intermediate to form H(2)O(2). 相似文献
144.
M N'diaye F Pascaretti-Grizon P Massin MF Baslé D Chappard 《Langmuir : the ACS journal of surfaces and colloids》2012,28(31):11609-11614
PMMA (poly(methyl methacrylate)) is widely used to prepare orthopedic cements. They are in direct contact with cells and body fluids. PMMA, despite its hydrophobic nature, can absorb ~2% w/w water. We have evaluated by vertical interference microscopy if water absorption can produce a significant swelling in different types of PMMA blocks: pure, with a plasticizer, with a cross-linker, and in two types of commercial bone cements. Graphite rods which do not swell in water were used as internal standard. Hardness, indentation modulus, plastic, and elastic works were determined by nanoindentation under a 25mN fixed force. Vertical interference microscopy was used to image the polymer in the dry state and hydrated states (after 24 h in distilled water). On the surface of the polished polymers (before and after hydration), we measured roughness by the fractal dimension, the swelling in the vertical and the lateral directions. For each polymer block, four images were obtained and values were averaged. Comparison and standardization of the images in the dry and hydrated states were done with Matlab software. The average value measured on the graphite rod between the two images (dried and hydrated) was used for standardization of the images which were visualized in 3D. After grinding, a small retraction was noticeable between the surface of the rod and the polymers. A retraction ring was also visible around the graphite rod. After hydration, only the pure PMMA and bone cements had a significant swelling in the vertical direction. The presence of polymer beads in the cements limited the swelling in the lateral direction. Swelling parameters correlated with the nanoindentation data. PMMA can swell by absorbing a small amount of water and this induces a swelling that varies with the polymer composition and particle inclusions. 相似文献
145.
Louis A. Florence Edward C. Kinzel Robert L. Olmon James C. Ginn Markus B. Raschke Glenn D. Boreman 《Infrared Physics & Technology》2012,55(6):449-453
Tapered slot antennas (TSAs) consist of a planar non-resonant structure which couples incident radiation to a propagating waveguide mode. They are commonly used at microwave and radio frequencies because they are fundamentally broadband and have small profiles. Because of their planar layout and broadband response they have recently been scaled to infrared frequencies where they have advantages for sensing and energy harvesting. We use scattering-type scanning near-field optical microscopy (s-SNOM) to study the mode transformation of two types of TSA operating in the thermal infrared (λ0 = 10.6 μm) with respect to electric field amplitude and phase. The results agree well with simulation showing both the phase reversal across the tapered slot and the traveling of wave fronts along the tapered slot, yet they also reveal high sensitivity of device performance to inhomogeneities in the geometry or illumination. This study will aid future design and analysis of practical non-resonant antennas operating at optical and infrared frequencies. 相似文献
146.
An efficient synthesis of original bis-β-cyclodextrin-[2]cryptorotaxanes in moderate to high yields is described. A synthetic approach based on the template-directed self-assembly threading process in aqueous medium gives a structure stabilized exclusively through non-covalent interactions. This procedure reveals a simple and efficient way to prepare highly organized supramolecular receptors from carefully designed subunits. 相似文献
147.
Q Yang V Guillerm F Ragon AD Wiersum PL Llewellyn C Zhong T Devic C Serre G Maurin 《Chemical communications (Cambridge, England)》2012,48(79):9831-9833
A series of porous Zr oxoclusters-based MOFs was computationally explored for their gas storage/capture performances. The highly porous UiO-67(Zr) and UiO-68(Zr) solids show exceptionally high CH(4) and CO(2) adsorption capacities under operating conditions that make these thermal, water and mechanical resistant materials very promising for physisorption-based processes. 相似文献
148.
J Alliot E Gravel F Pillon DA Buisson M Nicolas E Doris 《Chemical communications (Cambridge, England)》2012,48(65):8111-8113
A novel approach for the asymmetric synthesis of the active (1S,2R)-enantiomer of the antidepressant milnacipran is reported. The two stereogenic centers borne by the cyclopropane ring were sequentially installed starting from phenylacetic acid. 相似文献
149.
Issa M. El Nahhal Shehata M. Zourab Fawzi S. Kodeh Florence Babonneau Wafaa Hegazy 《Journal of Sol-Gel Science and Technology》2012,62(2):117-125
Cresol Red (CR) pH indicator was encapsulated into silica network using the sol–gel process. Transparent monolithic disks
of entrapped CR were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox
LA,GLA) alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12–14) and TX-100 surfactants. UV/VIS spectra showed that the
encapsulated CR retains its structure in terms of its response to pH. At the neutral conditions it is found that the HY surfactant
is considered as proton donor as favor the cationic form of the indicator, while CTAB surfactant favor the neutral, however
GLA surfactant, the anionic form of CR is more favored because GLA has a zwitterionic head. The surfactant GLA with TEOS has
shifted the equilibrium to the ionized form of CR due to the electrostatic interaction between the surfactant and the CR anion.
Therefore their pH range is dependent on the nature of a surfactant used. It is found that the HY surfactant is more efficient
as far as loading of CR is concern and it widened the working pH range. 相似文献
150.
Uptake for lead, copper, cadmium, nickel and manganese from aqueous solution using the Moringa oleifera seeds biomass (MOSB) and amine-based ligand (ABL) was investigated. Experiments on two synthetic multi-solute systems revealed that MOSB performed well in the biosorption and followed the decreasing orders Pb(II) > Cu(II) > Cd(II) > Ni(II) > Mn(II) and Zn(II) > Cu(II) > Ni(II). The general trend of the heavy metal ions uptake by the amine-based ligand followed decreased in the order Mn > Cd > Cu > Ni > Pb, which is the reverse trend for what was observed for MOSB. Comparing the single- and multi-metal solutions, there was no clear effect in the biosorption capacity of MOSB suggesting the presence of sufficient active binding sites for all metal ions studied. The MOSB performance is also not affected by pH in the range 3.5–8. 相似文献