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931.
Phillips KS Wilkop T Wu JJ Al-Kaysi RO Cheng Q 《Journal of the American Chemical Society》2006,128(30):9590-9591
A new method to fabricate supported bilayer membrane (SBM) arrays for surface plasmon resonance (SPR) imaging analysis is demonstrated in this work. Thin silicate films are produced on gold SPR substrates using layer-by-layer assembly, followed by calcination. Etching into the glassified substrates using photolithographic techniques generates nanowells of desirable size and depth. Atomic force microscopy and SPR imaging analysis show that the features are well-defined, and the etching process appears to have a surface smoothing effect. After the wells are oxidized with strong acid, vesicles spontaneously fuse onto them to form supported membranes with a high degree of lateral mobility. Fluorescence recovery after photobleaching measurements yielded a diffusion coefficient of 1.1 mum2/s. To demonstrate the feasibility for high-throughput receptor-ligand interaction analysis, binding of cholera toxin (CT) to SBM arrays containing 5 mol % ganglioside GM1 receptor was carried out with SPR imaging. The results showed excellent well-to-well reproducibility (8% RSD at 60 nM CT) and marked detection sensitivity. 相似文献
932.
The Onsager heat of transport Q* has been measured for water vapour at the surface of water, supercooled water, and ice, over the temperature range -8 to +10 degrees C. For liquid water, Q* is constant at -24.7 +/- 3.6 kJ mol(-1) (two standard deviations) over the pressure range 4-9.5 Torr. Provided the ice is suitably aged, the |Q*| values are very similar for water and ice, a result which is consistent with the presence of a liquid-like layer at the surface of ice. The values are slightly larger for ice, in proportion to the ratio of the heat of sublimation of ice to the heat of vaporization of the liquid. Departures from linearity of plots of P against DeltaT are attributed to temperature jumps at the surface of the dry upper plate. Hence jump coefficients and thermal accommodation coefficients have been derived as a function of temperature for collisions of water molecules with type-304 stainless steel. 相似文献
933.
Li C Gawandi V Protos A Phillips RS Amster IJ 《European journal of mass spectrometry (Chichester, England)》2006,12(4):213-221
Chemical tagging of amino acids is an important tool in proteomics analysis, and has been used to introduce isotope labels and mass defect labels into proteolytic peptides by derivatization of cysteine or lysine residues. Here, we present a new reagent with chemical specificity for tryptophan residues. Previously, 2-nitrobenzenesulfenyl chloride has been used as a highly specific reagent for labeling tryptophan residues. We show that this tag undergoes UV dissociation during matrix assisted laser desorption/ionization (MALDI). The multiplicity of photofragments increases the difficulty of characterizing the derivatization products. To overcome this problem, we have synthesized a new reagent, 2-(trifluoromethyl)benzenesulfenyl chloride, which is shown to react quantitatively with tryptophan in peptides and proteins. Most significantly, it exhibits high photostability in MALDI-Fourier transform mass spectrometry analyses. 相似文献
934.
Manning TJ Rhodes E Land M Parkman R Sumner B Lam TT Marshall AG Phillips D 《Natural product research》2006,20(6):611-628
Marine Natural Products (MNPs), such as bryostatin 1, are exposed to a range of physical and chemical conditions through the life cycle of the host organism. These include exposure to sunlight, oxidizing and reducing agents, cation binding, and adsorption to reactive metal oxide surfaces. Using Fourier Transform-Ion Cyclotron Resonance (FT-ICR), Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS), UV/Vis absorbance spectroscopy, and molecular modeling, we studied the impact of UV light, TiO2, I2, and reaction with FeCl3 on the structure of bryostatin 1. Our results demonstrate that natural conditions transform bryostatin to a number of structures, including one with a molar mass of 806 Da, which we have previously identified in the sediment collected from the Gulf of Mexico. To date, at least 20 different structures of bryostatin have been reported in the literature. This work suggests that these variations may be products of the chemical environment in which the bryozoa Bugula neritina resides and are not the result of genetic variations within Bugula. 相似文献
935.
Quality-control materials in the USDA National Food and Nutrient Analysis Program (NFNAP) 总被引:1,自引:0,他引:1
Phillips KM Patterson KY Rasor AS Exler J Haytowitz DB Holden JM Pehrsson PR 《Analytical and bioanalytical chemistry》2006,384(6):1341-1355
The US Department of Agriculture (USDA) Nutrient Data Laboratory (NDL) develops and maintains the USDA National Nutrient Databank
System (NDBS). Data are released from the NDBS for scientific and public use through the USDA National Nutrient Database for
Standard Reference (SR) (). In 1997 the NDL initiated the National Food and Nutrient Analysis Program (NFNAP) to update and expand its food-composition
data. The program included: 1) nationwide probability-based sampling of foods; 2) central processing and archiving of food
samples; 3) analysis of food components at commercial, government, and university laboratories; 4) incorporation of new analytical
data into the NDBS; and 5) dissemination of these data to the scientific community. A key feature and strength of the NFNAP
was a rigorous quality-control program that enabled independent verification of the accuracy and precision of analytical results.
Custom-made food-control composites and/or commercially available certified reference materials were sent to the laboratories,
blinded, with the samples. Data for these materials were essential to ongoing monitoring of analytical work, to identify and
resolve suspected analytical problems, to ensure the accuracy and precision of results for the NFNAP food samples. 相似文献
936.
Clarke TM Gordon KC Kwok WM Phillips DL Officer DL 《The journal of physical chemistry. A》2006,110(24):7696-7702
The steady-state and transient emission properties of unsubstituted terthiophene and a series of 3'-[E-2-(4-R-phenyl)ethenyl]-2,2':5',2' '-terthiophenes (where R = H, MeO, NH(2), CN, NMe(2), NO(2)) have been examined. The R = NO(2) compound is nonemissive at room temperature in all solvents but cyclohexane. All of the other compounds show measurable steady-state emission in a variety of solvents. The behavior of these spectra may be split into two groups. The first group, those substituted compounds with R = CN, NH(2) and NMe(2), show solvatochromic behavior, where their Lippert-Mataga plots suggest changes in dipole upon photoexcitation ranging from 12.5 to 16.0 D. For the second group, where R = H and MeO (and unsubstituted terthiophene as well), the Lippert-Mataga plots indicate dipole moment changes ranging from 0 to 7.9 D. The difference in behavior between the two groups of emissive compounds can be attributed to a charge-transfer character of the emitting state in the first group. This conclusion is supported by density functional theory calculations, which show that the frontier MOs in the group one compounds are spatially separated whereas those of group two have frontier MOs that are delocalized over both the styryl and terthiophene moieties. Picosecond time-resolved fluorescence spectroscopy reveals that unsubstituted terthiophene has the shortest emission lifetime of 140 ps in acetonitrile. For the styryl substituted terthiophenes, the lifetimes are much longer and range from 320 to 670 ps for R = CN and NMe(2) respectively, a result that can be explained in terms of a smaller rate of intersystem crossing in these compounds. 相似文献
937.
John G. Bruno Maria P. Carrillo Taylor Phillips Carrie J. Andrews 《Journal of fluorescence》2010,20(6):1211-1223
A novel high-throughput screening method is described in which a family of DNA aptamers selected against E. coli outer membrane proteins (OMPs) is subjected to PCR in the presence of fluorophore-dUTP conjugates using Deep Vent® exo- polymerase. The fluorophore-doped aptamers and their complementary strands are then heated to render them single-stranded and screened in filter well microtiter plates for fluorescence resonance energy transfer (FRET) assay potential. Using this system, a superior competitive FRET-aptamer designated EcO 4R was identified and the location of its putative binding pocket was determined by individually testing FRET potential in each of the secondary loop structures. By labeling the binding pocket with Alexa Fluor (AF) 647 and binding the aptamer to heavily Black Hole Quencher-3 (BHQ-3)-labeled E. coli bacteria, detection of as few as 30 live unlabeled E. coli per ml was achieved in a competitive displacement FRET assay format. The far red fluorescence emission enables detection in largely blue-green autofluorescent matrices. In addition, the competitive transfer of AF 647-EcO-4R aptamer to unlabeled E. coli cells after a 15 min equilibration period was verified by fluorescence microscopy. The present study also demonstrated that high aptamer affinity is not well correlated with competitive FRET potential. 相似文献
938.
Motivated by recent experiments on bilayer polyhedra composed of amphiphilic molecules, we study the elastic bending energies of bilayer vesicles forming polyhedral shapes. Allowing for segregation of excess amphiphiles along the ridges of polyhedra, we find that bilayer polyhedra can indeed have lower bending energies than spherical bilayer vesicles. However, our analysis also implies that, contrary to what has been suggested on the basis of experiments, the snub dodecahedron, rather than the icosahedron, generally represents the energetically favorable shape of bilayer polyhedra. 相似文献
939.
We have calculated the minimum energies for each of three positionings of the adatom unit cells for Ru(0001)–(3 × 3)–4Kr (high Kr coverage) and for Ru(0001)–(5 × 5)–Kr (low Kr coverage). The differences between the results for the low and high-coverage cases may clarify puzzles posed by the experimental results of Narloch and Menzel. The low-coverage solution converges to a structure having Kr in the top site at a height of 3.09 Å above the substrate with the adsorption energy 185 meV. In the high-coverage case, adatom unit cells with a corner Kr at top, fcc hollow, and hcp hollow locations are found to have nearly the same adsorption energy of 175 meV. The height of the corner atom above the substrate is found to be 3.35, 3.54, and 3.50 Å for the top, fcc hollow and hcp hollow sites, respectively. These results are explained by demonstrating that there is an enhancement of the substrate electronic density of states at krypton orbital energies in the low-coverage case. 相似文献
940.
P. Sajkiewicz P. J. Phillips 《Journal of polymer science. Part A, Polymer chemistry》1995,33(5):853-862
Extraction and swelling experiments were carried out in order to measure the crosslinkability by dicumyl peroxide (DCP) of new homogeneous linear low-density polyethylenes (LLDPEs) with different molecular weight, branch content, and length of branches. Considering that the tertiary radicals are most probable macroradicals, our results indicate that tertiary carbons in LLDPEs could be either sites for scission reaction of effective coupling, depending upon degree of branching and to a lesser extent on degree of crosslinking. In the range of branching between 16 and n CH3/1000 C (n ? 31 for low DCP concentration and decreases with DCP content approaching the value of 23 for the range above ca. 6 DCP moles per number average PE mole), the tertiary carbons seem to be rather the sites for effective coupling. In this range of branching an increase of crosslinkability with branch concentration and molecular weight of PE is due to the increase of crosslinking efficiency, but the scission probability is very low. At branch content exceeding the value of n CH3/1000 C, the dominant reaction on tertiary carbons is scission, leading to a small decrease of crosslinkability with increasing branch content. The possible mechanisms favoring tertiary carbons for either coupling or scission are discussed. © 1995 John Wiley & Sons, Inc. 相似文献