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341.
342.
D. J. Carlsson L. H. Gan D. M. Wiles 《Journal of polymer science. Part A, Polymer chemistry》1978,16(9):2353-2363
The photolysis reactions of a series of isomeric fully aromatic polyamides (aramids) have been investigated in the absence of oxygen by ultraviolet and luminescence spectroscopy. Several of the aramids were found to undergo photo-Fries rearrangements to give 2-aminobenzophenone backbone units when irradiated either as films, fibers, or dissolved in liquids. Quantum yields for this rearrangement were low, < 1 × 10?6 mole/einstein, and increased with decreasing aramid glass transition temperature and increasing backbone mobility. The formation of gel, carbon monoxide, and a strong ESR signal were consistent with a free-radical mechanism for the rearrangement. 相似文献
343.
Carlsson AH Malmberg JN Anderson D Lisak M Ostrovskaya EA Alexander TJ Kivshar YS 《Optics letters》2000,25(9):660-662
We study, numerically and analytically, linear and nonlinear waveguides induced by optical vortex solitons in a Kerr medium. Both fundamental and first-order guided modes are analyzed, as well as cases of effective defocusing and focusing nonlinearity. 相似文献
344.
Carlsson F Elofsson U Arnebrant T Malmsten M 《Journal of colloid and interface science》2001,233(2):320-328
The interaction between the local anaesthetic agents prilocaine and lidocaine, on one hand, and poly(N-isopropyl acrylamide) (pNIPAM), on the other, is investigated through studies of the polymer phase behavior and through surface tension and adsorption measurements. In particular, the cloud points (CP) for pNIPAM in the presence of lidocaine and prilocaine under different conditions were compared to the effects of electrolytes and alcohols. It was found that the electrolytes affect the CP of pNIPAM in a lyotropic manner, whereas alcohols depress the CP of pNIPAM in an alkyl chain length dependent way; i.e., the longer the chain, the larger the decrease in CP. Lidocaine and prilocaine affect the CP of pNIPAM in a pH-dependent manner. Below the pK(a) of lidocaine and prilocaine, these cosolutes do not substantially affect the CP in the concentration range investigated, but rather behave analogous to simpler electrolytes. Above the pK(a), on the other hand, they strongly depress the CP already at low concentrations. In parallel, at low pH, the surface tension reduction due to lidocaine or prilocaine is marginal, whereas at high pH the surface tension is reduced considerably. Thus, the poor solubility of prilocaine and lidocaine at high pH causes these to become more surface active and simultaneously interact in a more pronounced way with pNIPAM. Furthermore, it was found from ellipsometry that an adsorbed pNIPAM layer contracts when lidocaine is added, presumably due to a lidocaine-pNIPAM interaction similar to that causing pNIPAM to phase separate. Analogous to this, it was demonstrated that an adsorbed pNIPAM layer shrinks and swells reversibly when the temperature is cycled above and beneath the CP. Copyright 2001 Academic Press. 相似文献
345.
Helder S. Domingos Paul D. Bristowe Johan Carlsson Bo Hellsing 《Interface Science》2001,9(3-4):231-235
Ab initio density functional plane-wave pseudopotential calculations were performed for a = 7 ( = 21.79°) [0001] twist boundary in ZnO with and without the presence of Sb impurities. The segregation energies revealed a significant driving force for segregation and it was shown that the formation of an Sb monolayer was favoured. Decreased coordination in the boundary core suggested a trend towards the formation of an intergranular phase. The impurity states caused by the monolayer were located within the band gap and higher in energy relative to the state produced by a single impurity. Charge transfer to the Sb monolayer was observed indicating a possible enhancement of the grain boundary potential barrier. 相似文献
346.
N. Carlsson S. Anand S. -B. Carlsson B. Gustafson P. Omling P. Ramvall L. Samuelson W. Seifert Q. Wang 《Journal of Crystal Growth》1997,170(1-4):127-131
The influence of the layer structure on the electrical properties in (i) modulation doped InP/GaInAs quantum well samples, and, (ii) GaAs/GaInP resonant tunneling diodes has been investigated. The results reveal the importance of the different scattering processes. In particular, the influence of interface roughness scattering has been evaluated for both types of structures. 相似文献
347.
Azuma M Carlsson S Rodgers J Tucker MG Tsujimoto M Ishiwata S Isoda S Shimakawa Y Takano M Attfield JP 《Journal of the American Chemical Society》2007,129(46):14433-14436
The valence state change of BiNiO3 perovskite under pressure has been investigated by a powder neutron diffraction study and electronic-state calculations. At ambient pressure, BiNiO3 has the unusual charge distribution Bi(3+)(0.5)Bi(5+)(0.5)Ni(2+)O3 with ordering of Bi(3+) and Bi(5+)charges on the A sites of a highly distorted perovskite structure. High-pressure neutron diffraction measurements and bond valence sum calculations show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high-pressure phase is metallic Bi(3+)Ni(3+)O3. This unprecedented charge transfer between A and B site cations coupled to electronic instabilities at both sites leads to a variety of ground states, and it is predicted that a Ni-charge disproportionated state should also be observable. 相似文献
348.
This paper deals with numerical behavior of a recently presented column generation approach for optimization of so called step-and-shoot radiotherapy treatment plans. The approach and variants of it have been reported to be efficient in practice, finding near-optimal solutions by generating only a low number of columns. The impact of different restrictions on the columns in a column generation method is studied, and numerical results are given for quadratic programs corresponding to three patient cases. In particular, it is noted that with a bound on the two-norm of the columns, the method is equivalent to the conjugate-gradient method. Further, the above-mentioned column generation approach for radiotherapy is obtained by employing a restriction based on the infinity-norm and non-negativity. The column generation method has weak convergence properties if restricted to generating feasible step-and-shoot plans, with a “tailing-off” effect for the objective values. However, the numerical results demonstrate that, like the conjugate-gradient method, a rapid decrease of the objective value is obtained in the first few iterations. For the three patient cases, the restriction on the columns to generate feasible step-and-shoot plans has small effect on the numerical efficiency. 相似文献
349.
Porous hydrogels such as agarose are commonly used to analyze DNA and water-soluble proteins by electrophoresis. More recently lyotropic liquid crystals, such as the diamond cubic phase formed by the lipid monoolein and water, has become a new type of well-defined porous structure of interest for both hydrophilic and amphiphilic analytes. Here we compare these two types of matrixes by investigating the nature of retardation they confer to an oligonucleotide that migrates in their respective aqueous phases. The retardation for a 25-mer oligonucleotide was found to be about 35-fold stronger in the cubic phase than in an agarose hydrogel modified to have the same average pore size. According to modelling, the strong retardation is primarily due to the fact that hydrodynamic interaction with the continuous monoolein membrane is a stronger source of friction than the steric interactions (collisions) with discrete gel fibres. A secondary effect is that the regular liquid crystal has a narrower pore-size distribution than the random network of the agarose gel. In agreement with experiments, these two effects together predict that the retardation in the cubic phase is a 30-fold stronger than in an agarose gel with the same average pore radius. 相似文献
350.
Carlsson AE 《Physical review letters》2004,92(23):238102
The average branching number and cluster size in branched actin solutions with filament capping are evaluated using analytic theory and simulation methods. The average number of daughter branches per filament in steady state is much less than unity, regardless of the concentration of branching stimulant. Much more highly branched structures are obtained in the initial stages of polymerization. 相似文献