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881.
The highly solvatochromic dye Nile red is used in conjunction with synchronous scan fluorescence spectroscopy to elucidate
changes in the internal environment of cytochrome c, upon incorporation into differently modified sol–gel derived media. Nile red was first studied in a variety of solvents
in order to quantify changes in polarity. Matrix modifications involved the addition of several silanes, intended to interact
with any unreacted hydroxyl entities left from the matrix forming reaction, while polymers were used to help reduce shrinkage
and modify the internal pore environment. Slight unfolding of the protein was observed on incorporation into the sol–gel derived
media. During the aging process further changes were monitored by using difference synchronous scan fluorescence spectra and
complementary measurements of catalytic activity, expressed as the initial velocity. Combining Nile red synchronous scan fluorescence
with cytochrome c activity data lead to a method to elucidate effects linked to protein conformation and those related to the sol–gel derived
host.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
882.
M. Haridas S. Srivastava J. K. Basu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):93-100
Optical properties of polymer capped gold nanoparticles of various sizes (diameter 3–6 nm) have been studied. We present a
new scheme to extract size dependent variation of total dielectric function of gold nanoparticles from measured UV-Vis absorption
data. The new scheme can also be used, in principle, for other related systems as well. We show how quantum effect, surface
atomic co-ordination and polymer-nanoparticle interface morphology leads to a systematic variation in interband part of the
dielectric function of gold nanoparticles, obtained from the analysis using our new scheme. Careful analysis enables identification
of the possible changes to the electronic band structure in such nanoparticles. 相似文献
883.
D. Shanmukaraj G.X. Wang R. Murugan H.K. Liu 《Journal of Physics and Chemistry of Solids》2008,69(1):243-248
The role of inorganic ceramic fillers namely nanosized Al2O3 (15-25 nm) and TiO2 (10-14 nm) and ferroelectric filler SrBi4Ti4O15 (SBT CIT) (0.5 μm) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO8:LiClO4+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.72×10−5 S cm−1 at 21 °C for 2 wt% of SrBi4Ti4O15 (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi4Ti4O15 (SBT CIT) as fillers. 相似文献
884.
N. Kirova 《Journal of Physics and Chemistry of Solids》2008,69(9):2248-2251
We consider properties of junctions for the field effect transistors (FET) geometry where molecular crystals or conducting polymers are used as semiconducting layers. In the molecular crystal Coulomb interaction of free electrons with surface polar phonons of the dielectric layer can lead to self-trapping of carriers and to the formation of a strongly coupled long-range surface polaron. The effect is further enhanced in presence of the bias electric field and strongly depends on the gate dielectric used.In conducting polymers instead of the usual band bending near the contact interface, new allowed electronic bands appear inside the band gap. As a result the bias electric field and the injected charge penetrate into the polymer via creation of the soliton lattice whose period changes with the distance from the contact surface. The current through the contact is performed via moving solitons. 相似文献
885.
Henry Bukola Ezekiel 《Journal of Physics and Chemistry of Solids》2008,69(11):2932-2935
The use of laser ablation as a method through which the simultaneous patterning and activation of carbon fibre electrodes can be achieved has been investigated. Laser-induced exfoliation of the carbon fibre substrates was observed leading to creation of edge plane sites that enhance electrode performance. The laser-mediated surface modification is compared to that attainable using conventional surface anodisation using electrochemical means. 相似文献
886.
N. Mine 《Applied Surface Science》2008,255(4):973-976
In this work, we investigated the bombardment of polymer surfaces (PC, PMMA) with very low energy (250 eV) Cs+ ions.In the positive mode, we observed many cations combining a molecular fragment of the polymer (M) with two Cs atoms, similar to the well-known MCs2+ clusters commonly observed in inorganic depth profiling with Cs. For example, Cs2COOH+ or Cs2C6H5O+ were measured on PC and Cs2CH3O+ or Cs2C4H5O2+ were measured on PMMA. In fact, most of the polymer characteristic fragments measured in negative spectra also appear in the positive spectra, combined with two Cs atoms. It is remarkable that stable negative ions tend to combine not with one Cs, but with two Cs atoms to create the MCs2+ cluster.This effect is, to some extent, similar to the well-known cationisation of polymers (with Ag or Au) although here few clusters with only one Cs atom are detected (MCs+ clusters), like in classical cationisation. The most abundant clusters are the MCs2+ clusters, but heavier clusters (MCs3+, MCs4+ and above) are also measured with high yields in the spectrum.Surprisingly, some of those MCs2+ clusters were still detected even after a very long sputtering fluence (above 1017 ions/cm2), proving that some molecular depth profiling is also possible in this “Cs2-cationisation” mode. In other words, this work could open the way to an extension of the MCsn+ cluster analysis, commonly used in inorganic depth profiling, to the in-depth molecular analysis of organic layers. 相似文献
887.
Arnaud Delcorte 《Applied Surface Science》2008,255(4):954-958
This contribution reviews the state-of-the-art in the domains of molecular imaging and depth profiling, the two methodological platforms required for 3D molecular imaging by secondary ion mass spectrometric (SIMS). Using molecular dynamics calculations, it also describes some of the mechanisms that make cluster projectiles such as C60 so different for organic sample analysis. The discussion addresses issues that deserve proper attention on the way to 3D molecular imaging in SIMS, such as ultimate lateral resolution, limited molecular yields, chemical effects and damage, and highlights solutions currently in embryo in the many research teams concerned by 3D molecular imaging. 相似文献
888.
We present experimental observations at comparatively low supercooling of morphology transitions from dendritic to faceted
structures in polymer crystals growing in thin films of a poly-2-vinylpyridineblock-polyethyleneoxid copolymer. Our results
are compared with theoretical concepts describing morphological instabilities of single crystals. Although these concepts
originally were not developed for polymers, they allow to describe and interpret our experimental results quite well. In particular,
the measured temperature dependence of the width W and frequency of dendritic side branches and the radius of curvature ρ
of the growth tips of the crystals follow these concepts. We present preliminary evidence for the influence of polymer attachment
kinetics and reorganisation processes behind the growth front. Polymer thin films provide valuable model systems for studying
general concepts of crystallisation and allow to distinguish at which point the connectivity of the crystallising units within
chain-like molecules starts to play a measurable role. 相似文献
889.
I. Y. Erukhimovich A. Johner J. F. Joanny 《The European physical journal. E, Soft matter》2008,27(4):435-445
We present a new ab initio approach to describe the statistical behavior of long ideal polymer chains near a plane hard wall. Forbidding the solid half-space
to the polymer explicitly (by the use of Mayer functions) without any other requirement, we derive and solve an exact integral
equation for the partition function G
D(r,r′, N) of the ideal chain consisting of N bonds with the ends fixed at the points r and r′ . The expression for G(r,r′, s) is found to be the sum of the commonly accepted Dirichlet result G
D(r,r′, N) = G
0(r,r′, N) - G
0(r,r”, N) , where r” is the mirror image of r′ , and a correction. Even though the correction is small for long chains, it provides a non-zero value of the monomer density
at the very wall for finite chains, which is consistent with the pressure balance through the depletion layer (so-called wall
or contact theorem). A significant correction to the density profile (of magnitude 1/is obtained away from the wall within one coil radius. Implications of the presented approach for other polymer-colloid problems
are discussed. 相似文献
890.
The pure diolefinic ligand 1,4‐bis(pyridin‐4‐yl)‐1,3‐butadiene (bpbde) is photostable in the crystalline state. With the assistance of coordination‐driven metal‐organic assemblies, the photoreactivity of this diolefinic ligand can be significantly enhanced. A hydrothermal reaction of bpbde with Cd(NO3)2?4 H2O and the auxiliary ligand adipic acid resulted in the formation of a two‐dimensional photoreactive coordination polymer (CP), [Cd(adipate)(bpbde)]n ( 1 ). When the aliphatic carboxylic acid was replaced by pimelic acid, another photoreactive CP [Cd(pimelate)(bpbde)]n ( 2 ) with a three‐dimensional framework was obtained. With irradiation of 365 nm UV light, the bpbde ligands in crystalline 1 and 2 underwent a regioselective photochemical [2+2] cycloaddition reaction and converted to 3,4,7,8‐tetra(pyridin‐4‐yl)tricyclo[4.2.0.02,5]octane (tptco) and 1,3‐bis(pyridin‐4‐yl)‐2,4‐bis(2‐(pyridin‐4‐yl)vinyl)cyclobutane (bpbpvcb), respectively. The results provide an interesting insight into the rational design of highly regio‐ or stereoselective photocatalytic reactions for the formation of special organic molecules. 相似文献