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991.
Composite diffusion coeffcients have been measured for the various species labeled with35S which are present in a number of aqueous solutions due to the introduction of the labeled material as35SO
4
2–
. The solutions were of two components consisting of water and either sodium sulfate. The diffusion coeffcient measured for sodium chloride solutions is similar to literature data for the corresponding diffusion in sodium sulfate solutions. The results for sulfuric acid and ammonium hydrogen sulfate have been interpreted using literature data for the relative concentrations of the hydrogen sulfate and sulfate ions to obtain estimates for the diffusion coefficents of those ions. The results for perchloric acid, regarded as representing the diffusion coefficient of the hydrogen sulfate ion, have a much different concentration dependence to that observed for the estimates for that ion in sulfuric acid and ammonuim hydrogen sulfate. The difference is attributed to the effect of the perchlorate ion on the water structure. 相似文献
992.
Solubilization of phospholipid bilayers by C14-alkyl betaine/anionic mixed surfactant systems 总被引:1,自引:0,他引:1
The mechanisms governing the solubilizing interactions between zwitterionic/anionic mixed surfactant systems at different molar fractions of the zwitterionic surfactant (X
zwitter) and unilamellar liposomes were investigated. Solubilization was detected as a decrease in static lightscattering of liposome suspensions. Three parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant system a) saturated the liposomesRe
sat; b) resulted in 50% solubilization of liposomesRe
50%, and c) led to a complete solubilization of these structuresRe
sol. These parameters corresponded to theRe at which light scattering stars to decrease, reaches 50% of the original value and shows no further decrease. From these parameters the surfactant partition coefficients for these three steps (K
sat,K
50% andK
sol) were also determined. The mixed systems were formed byN-tetradecyl-N, N-dimethylbetaine (C14-Bet) and sodium dodecyl sulphate (SDS) in PIPES buffer at pH 7.20. Liposomes were formed by egg phosphatidylcholine and phosphatidic acid (9:1 molar ratio). When the range ofX
zwitter was about 0.4–0.6Re andK parameters showed a maximum, whereas the critical micelle concentration (CMC) of these systems exhibited a minimum. Given that the ability of the surfactant systems to solubilize liposomes is inversely related toRe
sol, this capacity appeared to be directly correlated with the CMC of the systems. The progressive rise ofK during the process indicates that an increasing surfactant partition equilibrium governs the interaction process from the saturation until the solubilization of vesicles, the free surfactant concentration remaining almost constant with similar values to the CMC for each mixed system studied. 相似文献
993.
A novel determination method of electroinactive molecules by means of electrochemical technique is presented. A new self-assembled monolayer containing cyclodextrin (CD) is prepared with mono(6-o-p-tolylsulfonyl)-β-cyclodextrin. Although this derivatization process leads to a β-CD coverage of 10% of a full monolayer, this layer shows an effective host-guest response to ferrocene. The interfacial ferrocene complexation gives a response similar to that expected for a Langmuir adsorption isotherm yielding a stability constant of 4.2 ×104 mol-1· L and a maximum ferrocene coverage of 8.6×10-12 mol/cm2. The redox peak currents of the surface-confined ferrocene decrease upon addition of competing β-CD guest species to the solution, such as m-toluic acid (mTA) and sodium dodecyl sulfonate (SDS). This principle has been used for the determination of the electroinactive molecules, mTA and SDS in the concentration ranges of 0.8-2.7 μmol/L and 5-100 nmol/L, respectively. 相似文献
994.
Single crystals of a new form of sodium octoborate, β-Na2B8O13, were obtained fortuitously from a complex Na2O-B2O3-P2O5 mixture, and studied. The compound is monoclinic, space group P21/c; the unit cell parameters are a=11.731(4) Å, b=7.880(3) Å, c=10.410(4) Å, β=99.883(3)°; Z=4. The crystal structure was solved from 1653 reflections until R1=0.0444; it consists of two infinite, independent, and interleaved boron-oxygen networks containing a complex borate anion (B8O13)2− formed by six BO3 triangles (Δ) and two BO4 tetrahedra (T), which can be viewed as a B5O10 group linked to a B3O7 group; this leads to a Fundamental Building Block (FBB) with the shorthand notation: 8: ∞3 [(5:4Δ+T)+(3:2Δ+T)]. This FBB is identical to that described in other octoborates such as α-Na2B8O13 and Ag2B8O13. However, some subtle differences exist in the interlinking of the octoborate anions found in these three compounds, which explains their different structure and unit cell parameters. 相似文献
995.
The interactions between sodium dodecyl sulphate (SDS) and three autoassociative polymers (hydrophobically end-capped poly(ethylene oxide) urethanes) are studied by conductimetry, fluorescence, and viscometry. By the first two techniques the interactions are found to increase with the hydrophobicity of the polymer and to be stronger than those observed for a polyethylene oxide (PEO) of the same order of molecular weight. The results seem to be consistent with a model where SDS micelles are formed around hydrophobic chain ends in a first stage, and along the main chain in a second stage. For the more hydrophobic sample already self-aggregated in water and of relatively large reduced viscosity, the addition of SDS induces a loss in viscosity contrary to the less hydrophobic ones and PEO. Such effect may be attributed to the destruction of the chain end association by the formation of SDS micelles around one end in the first stage of the interaction. 相似文献
996.
An improved laser fluorimeter and its application for the determination of ultratrace concentrations of uranium are described. The system developed uses a collecting lens-filter system, by which the density of laser radiation on the sample is increased greatly and the interfering stray light can be reduced to a great degree. In addition, both laser and lamp sources are joined together in the instrument. A strong green phosphor from uranium-doped sodium metaphosphate (NaPO3: U) has been found suitable and has been used for the determination of ultratraces of uranium. A detection limit (3) of 0.36 pg of uranium (in 30 mg NaH2PO4 per pellet) was obtained. In the case of peak-to-background intensity ratios relative standard deviations (RSD) are 6.4% and the linear dynamic range extends from 1 pg to 103 ng of uranium. 相似文献
997.
998.
999.
J. L. Oscarson S. E. Gillespie J. J. Christensen R. M. Izatt P. R. Brown 《Journal of solution chemistry》1988,17(9):865-885
The aqueous reactions, {ie865-1}were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, H and S values were determined from the fits of the calculated and experimental heats while Cp values were calculated from the variation of H values with temperature. The log K and H values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the Cp values for these reactions are approximately zero.Deceased 5 September 1987 相似文献
1000.
Brandon EF van Ooijen RD Sparidans RW Lázaro LL Heck AJ Beijnen JH Schellens JH 《Journal of mass spectrometry : JMS》2005,40(6):821-831
The cyclic depsipeptide aplidine is a new anti-cancer drug of marine origin. Four metabolites of this compound were found after incubation with pooled human microsomes using gradient high-performance liquid chromatography with ultraviolet detection. After chromatographic isolation, the metabolites have been identified using nano-electrospray triple quadrupole mass spectrometry. A highly specific sodium-ion interaction with the cyclic structure opens the depsipeptide ring, and cleavage of the amino acid residues gives sequence information when activated by collision-induced dissociation in the second quadrupole. The aplidine molecule could undergo the following metabolic reactions: hydroxylation at the isopropyl group (metabolites apli-h 1 and apli-h 2); C-dealkylation at the N(Me)-leucine group (metabolite apli-da); hydroxylation at the isopropyl group and C-dealkylation at the N(Me)-leucine group (metabolite apli-da/h), and C-demethylation at the threonine group (metabolite apli-dm). The identification of these metabolites formed in vitro may greatly aid the elucidation of the metabolic pathways of aplidine in humans. 相似文献