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951.
952.
Bindushree Radhakrishnan Goretti Balerdi Eric Cloutet Henri Cramail 《Macromolecular Symposia》2005,229(1):56-65
Summary: The synthesis of polyurethane particles by polyaddition of ethylene glycol (EG) and tolylene-2,4-diisocyanate (TDI) in cyclohexane at 60 °C was investigated in the presence of ω-hydroxy and ω,ω′-dihydroxy polybutadiene, used as reactive steric stabilizers. The effect of the functionality and concentration of the reactive polybutadiene, as well as the monomer addition procedure, onto the polyurethane particle formation was studied. Calibrated PUR particles with an average diameter in the range 1–2 µm could be readily obtained. 相似文献
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Karunakaran Radhakrishnan Henri Cramail Alain Deffieux Philippe Franois Ardchir Momtaz 《Macromolecular rapid communications》2003,24(3):251-254
The effect of various alkylaluminium compounds and their mixtures on ethylene polymerization catalyzed with a tridentate bis(imino)pyridinyliron catalyst is studied. Triethylaluminium and trihexylaluminium are good cocatalysts but yield polyethylenes with broad molar mass distribution (MMD) whereas triisobutylaluminium, a less efficient activator, gives polyethylenes with unimodal and narrow MMD. Specific mixtures of branched and linear alkylaluminium compounds yield highly active catalytic systems and polyethylenes with unimodal and tunable MMD.
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The mechanism of degradation of bioresorbable lactic acid- and glycolic acid-based aliphatic polyesters (PLA/GA) is still far from being totally understood although a majority of authors agree to consider in vivo degradation as essentially hydrolytic. In the past years, we have shown that hydrolysis of large size devices is heterogeneous, i.e. faster inside than at the surface because of reaction-diffusion phenomena involving acid-catalyzed ester cleavage reactions and water-soluble macromolecular fragments. The proposed mechanism is recalled together with some direct or indirect consequences, namely induced crystallization at body temperature, size- and formulation-dependence of the degradation rates. From these features, one can conclude that it is now possible to increase or decrease the degradation rate and to turn on or off heterogeneous degradation by using accelerating or braking factors, however, accurate piloting of the hydrolytic degradation of PLA/GA is still not feasible. 相似文献
959.
Henri E. K. Matimba Steen Ingemann Nico M. M. Nibbering 《Journal of the American Society for Mass Spectrometry》1993,4(1):73-81
The gas-phase reactions of negative ions (O-., NH 2 ? , C2H5NH?, (CH3)2N?, C6H 5 t- , and CH3SCH 2 ? ) with fluorobenzene and 1,4-difluorobenzene have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The O?. ion reacts predominantly by (1) proton abstraction, (2) formal H 2 +. abstraction, and (3) attack on an unsubstituted carbon atom. In addition to these processes, attack on a fluorine bearing carbon atom yielding F? and C6H4FO? ions occurs with 1,4-difluorobenzene. Site-specific deuterium labeling reveals the occurrence of competing 1,2-, 1,3-, and 1,4-H 2 +. abstractions in the reaction of O?. with fluorobenzene. Attack of the O?. ion on the 3- and 4-positions in fluorobenzene with formation of the 3- and 4-fluorophenoxide ions, respectively, is preferred to reaction at the 2-position, as indicated by the relative extent of loss of a hydrogen and a deuterium atom in the reactions with labeled fluorobenzenes. The NH 2 ? , C2H5NH?, (CH3)2N?, C6H 5 ? , and CH3SCH 2 ? anions react with fluoroberuene and 1,4-difluorobenzene only by proton abstraction. The relative importance of H+ and D+ abstraction in the reaction of these anions with labeled fluorobenzenes indicates that the 2-position in fluorobenzene is more acidic than the 3- and 4-positions, suggesting that the literature value of the gas-phase acidity of this compound (ΔH acid o = 1620 ± 8 kJ mol?1) refers to the former site. Based on the occurrence of reversible proton transfer between the CH3O? ion and 1,4-difluorobenzene, the ΔH acid o of this compound is redetermined to be 1592 ± 8 kJ mol?1. 相似文献
960.
Patrick Gurin Nouara Yahi Fodil Azzaz Henri Chahinian Jean-Marc Sabatier Jacques Fantini 《Molecules (Basel, Switzerland)》2022,27(12)
We analyzed the epitope evolution of the spike protein in 1,860,489 SARS-CoV-2 genomes. The structural dynamics of these epitopes was determined by molecular modeling approaches. The D614G mutation, selected in the first months of the pandemic, is still present in currently circulating SARS-CoV-2 strains. This mutation facilitates the conformational change leading to the demasking of the ACE2 binding domain. D614G also abrogated the binding of facilitating antibodies to a linear epitope common to SARS-CoV-1 and SARS-CoV-2. The main neutralizing epitope of the N-terminal domain (NTD) of the spike protein showed extensive structural variability in SARS-CoV-2 variants, especially Delta and Omicron. This epitope is located on the flat surface of the NTD, a large electropositive area which binds to electronegatively charged lipid rafts of host cells. A facilitating epitope located on the lower part of the NTD appeared to be highly conserved among most SARS-CoV-2 variants, which may represent a risk of antibody-dependent enhancement (ADE). Overall, this retrospective analysis revealed an early divergence between conserved (facilitating) and variable (neutralizing) epitopes of the spike protein. These data aid in the designing of new antiviral strategies that could help to control COVID-19 infection by mimicking neutralizing antibodies or by blocking facilitating antibodies. 相似文献