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741.
Dynamical heterogeneities--strong fluctuations near the glass transition--are believed to be crucial to explain much of the glass transition phenomenology. One hypothesis for their origin is that they emerge from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. To test this hypothesis, we use numerical simulation data to construct coarse grained observables and decompose their fluctuations into two transverse components associated with the postulated soft modes and a longitudinal component unrelated to them. We find that as temperature is lowered and time scales are increased, the time reparametrization fluctuations become increasingly dominant, and that their correlation volumes grow together with those of the dynamical heterogeneities, while the correlation volumes for longitudinal fluctuations remain small. 相似文献
742.
The use of a large apex-angle axicon for common-path interferometric wavefront sensing is proposed. The approach is a variant of point-diffraction interferometry bearing similarities to pyramidal wavefront sensing. A theoretical basis for wavefront sensing with an axicon is developed, and the outcomes of numerical simulations are compared to experimental results obtained with spherical and cylindrical ophthalmic trial lenses. It is confirmed that the axicon can be used for wavefront sensing, although its refraction may ultimately complicate and limit its operational range. 相似文献
743.
Dr. Paulina R. Martínez‐Alanis Brenda N. Sánchez Eguía Prof. Víctor M. Ugalde‐Saldívar Prof. Ignacio Regla Dr. Patricia Demare Dr. Gabriel Aullón Prof. Ivan Castillo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):6067-6079
A series of Cu+ complexes with ligands that feature varying numbers of benzimidazole/thioether donors and methylene or ethylene linkers between the central nitrogen atom and the thioether sulfur atoms have been spectroscopically and electrochemically characterized. Cyclic voltammetry measurements indicated that the highest Cu2+/Cu+ redox potentials correspond to sulfur‐rich coordination environments, with values decreasing as the thioether donors are replaced by nitrogen‐donating benzimidazoles. Both Cu2+ and Cu+ complexes were studied by DFT. Their electronic properties were determined by analyzing their frontier orbitals, relative energies, and the contributions to the orbitals involved in redox processes, which revealed that the HOMOs of the more sulfur‐rich copper complexes, particularly those with methylene linkers (? N? CH2? S? ), show significant aromatic thioether character. Thus, the theoretically predicted initial oxidation at the sulfur atom of the methylene‐bridged ligands agrees with the experimentally determined oxidation waves in the voltammograms of the NS3‐ and N2S2‐type ligands as being ligand‐based, as opposed to the copper‐based processes of the ethylene‐bridged Cu+ complexes. The electrochemical and theoretical results are consistent with our previously reported mechanistic proposal for Cu2+‐promoted oxidative C? S bond cleavage, which in this work resulted in the isolation and complete characterization (including by X‐ray crystallography) of the decomposition products of two ligands employed, further supporting the novel reactivity pathway invoked. The combined results raise the possibility that the reactions of copper–thioether complexes in chemical and biochemical systems occur with redox participation of the sulfur atom. 相似文献
744.
Maria S. Jiménez L. Rodriguez Juan R. Bertolin Maria T. Gomez Juan R. Castillo 《Analytical and bioanalytical chemistry》2013,405(1):359-368
The determination of metal-binding proteins in plankton is important because of their involvement in photosynthesis, which is fundamental to the biogeochemical cycle of the oceans and other ecosystems. We have elaborated a new strategy for screening of Cu and Zn-containing proteins in plankton on the basis of separation of proteins by use of Blue-Native PAGE (BN-PAGE), which entails use of a non-denaturing Tris–tricine system and detection of metals in the proteins by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS). For comparison, denaturing PAGE based on Tris–glycine and Tris–tricine systems and Anodic-Native PAGE have also been investigated. A large number of protein bands with MW between 20 and 75 kDa were obtained by use of Tris–glycine PAGE but detection of metals by LA–ICP–MS was unsuccessful because of loss of metals from the proteins during the separation process. Different protein extraction, purification, and preconcentration methods were evaluated, focussing on both issues—achieving the best extraction and characterization of the proteins while maintaining the integrity of metal–protein binding in the plankton sample. Use of 25 mmol?L?1 Tris–HCl and a protease inhibitor as extraction buffer with subsequent ultrafiltration and acetone precipitation was the most efficient means of sample preparation. Two Cu and Zn proteins were detected, a protein band corresponding to a MW of 60 kDa and another poorly resolved band with a MW between 15 and 35 kDa. 相似文献
745.
Gracia Patricia Blanch Francisco José Morales Fernando de la Peña Moreno María Luisa Ruiz del Castillo 《Journal of separation science》2013,36(2):320-324
A new method based on off‐line coupling of LC with GC in replacement of conventional sample preparation techniques is proposed to analyze acrylamide in coffee brews. The method involves the preseparation of the sample by LC, the collection of the selected fraction, its concentration under nitrogen, and subsequent analysis by GC coupled with MS. The composition of the LC mobile phase and the flow rate were studied to select those conditions that allowed separation of acrylamide without coeluting compounds. Under the conditions selected recoveries close to 100% were achieved while LODs and LOQs equal to 5 and 10 μg/L for acrylamide in brewed coffee were obtained. The method developed enabled the reliable detection of acrylamide in spiked coffee beverage samples without further clean‐up steps or sample manipulation. 相似文献
746.
Castillo John J. Rindzevicius Tomas Wu Kaiyu Schmidt Michael S. Janik Katarzyna A. Boisen Anja Svendsen Winnie Rozlosnik Noemi Castillo-León Jaime 《Journal of nanoparticle research》2014,16(7):1-8
Traditionally, organosilica nanoparticles have been prepared inside micelles with an external silica shell for mechanical support. Here, we compare these hybrid core–shell particles with organosilica particles that are robust enough to be produced both inside micelles and alone in a sol–gel process. These particles form from octadecyltrimethoxy silane as silica source either in microemulsions, resulting in water-dispersible particles with a hydrophobic core, or precipitate from an aqueous mixture to form particles with both hydrophobic core and surface. We examine size and morphology of the particles by dynamic light scattering and transmission electron microscopy and show that the particles consist of Si–O–Si networks pervaded by alkyl chains using nuclear magnetic resonance, infrared spectroscopy, and thermogravimetric analysis. 相似文献
747.
A molecular crystal of silver cyclic amide Ag2(C4H4NO2)2(H2O) is studied using first-principles density functional theory calculations within the generalized gradient approximation (GGA). A number of different exchange-correlation functionals are considered for a possible treatment of the system. It is found that the Perdew-Burke-Ernzerhof (PBE) GGA exchange-correlation functionals are adequate for the Ag2(C4H4NO2)2(H2O) crystal. The results obtained show the possibility to reproduce rather well the geometry of at least some molecular crystals by means of the periodic solid-state calculations if the computational parameters are chosen adequately. The present work also reports the analysis of the chemical bonding in the material and gives the total and partial density of states. Our solid-state computations point out the possible magnetic properties of the molecular crystal under study. 相似文献
748.
Beobide G Wang WG Castillo O Luque A Román P Tagliabue G Galli S Navarro JA 《Inorganic chemistry》2008,47(12):5267-5277
A series of manganese(II) coordination polymers containing the bridging ligand pyrimidine-4,6-dicarboxylate (pmdc) have been prepared. The stoichiometries and structural features of these materials, which range from the one-dimensional (1D) chains in ([Mn(mu-pmdc)(H2O)3].2H2O)n (1) and ([Mn2(mu-pmdc)2(H2O)5].2H2O)n (2) to the two-dimensional layers in ([Mn(mu3-pmdc)(H2O)].H2O)n (3) or the three-dimensional porous network in ([Mn(pmdc)].2H2O)n (4), are extremely dependent on the synthetic conditions (i.e., temperature and solvent). In spite of the structural diversity of these systems, crystallographic studies revealed that the pmdc ligand typically displays a tetradentate mu-(kappaO,kappaN:kappaO',kappaN') coordination mode with the carboxylate groups almost coplanar with the pyrimidine ring [as in compounds 1 and 2 and compound 5 described below)]. In compound 3, the pmdc moiety adopts a pentadentate mu3-(kappaO,kappaN:kappaO',kappaN':kappaO) coordination mode. The thermal, magnetic, and adsorption properties of these systems were also studied. The results showed that these compounds behave as antiferromagnets as a consequence of efficient magnetic exchange through the pmdc bridges. Compound 4 possesses permanent porosity, as proved by gas sorption data (N2 at 77 K and CO2 at 293 K). Finally, the heteronuclear iron(II)/manganese(II) compound ([FeMn(mu-pmdc)2(H2O)5].2H2O)n (5), which is isomorphous to 2, was also prepared and fully characterized. 相似文献
749.
Ramos S Campos-Terán J Mas-Oliva J Nylander T Castillo R 《Langmuir : the ACS journal of surfaces and colloids》2008,24(16):8568-8575
To provide better understanding of how a protein secondary structure affects protein-protein and protein-surface interactions, forces between amphiphilic alpha-helical proteins (human apolipoprotein AII) adsorbed on a hydrophilic surface (mica) were measured using an interferometric surface force apparatus (SFA). Forces between surfaces with adsorbed layers of this protein are mainly composed of electrostatic double layer forces at large surface distances and of steric repulsive forces at small distances. We suggest that the amphiphilicity of the alpha-helix structure facilitates the formation of protein multilayers next to the mica surfaces. We found that protein-surface interaction is stronger than protein-protein interaction, probably due to the high negative charge density of the mica surface and the high positive charge of the protein at our experimental conditions. Ellipsometry was used to follow the adsorption kinetics of this protein on hydrophilic silica, and we observed that the adsorption rate is not only controlled by diffusion, but rather by the protein-surface interaction. Our results for dimeric apolipoprotein AII are similar to those we have reported for the monomeric apolipoprotein CI, which has a similar secondary structure but a different peptide sequence and net charge. Therefore, the observed force curves seem to be a consequence of the particular features of the amphiphilic alpha-helices. 相似文献
750.
A fully automated method for the determination of medium volatility compounds in aromatic samples was developed. Specifically, the determination of methyl jasmonate in jasmine fragrances was performed by using the through oven transfer adsorption-desorption (TOTAD) interface for the on-line coupling between RPLC-GC. A study of the most relevant variables involved in the performance of the TOTAD interface for medium volatility compounds was carried out by testing different values of helium flow (100, 300, 400, and 500 mL/min), transfer speed (0.1, 0.3, 0.5, and 2.0 mL/min), and methanol/water percentages (86:14, 85:15, 83:17, 80:20, and 70:30). The method developed provided satisfactory repeatability (RSD for retention times of 0.15% and for peak areas of 9.4%) and recovery (71%) as well as excellent LOD (0.01 mg/L) for methyl jasmonate in commercial jasmine essence under the experimental conditions selected as optimum. Additional advantages of the automated RPLC-TOTAD-GC method proposed in the present work are its rapidness, reliability, and the possibility of directly introducing the sample with no further pretreatment. 相似文献