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111.
L.M. León M.C. Gonzalez J.R. Quintana F. Zamora Armando Martinez G.M. Guzman 《European Polymer Journal》1982,18(3):229-231
The Ptitsyn-Eizner λ flexibility parameter for poly(N-vinylcarbozole) solutions under theta conditions has been found to be 6.31, demonstrating the rigidity imparted to the polymer chain by the carbazole group. A study has been made of the variation of this parameter with solvent and temperature. A study has been made of the variation of λ in a conformational transition of poly(methyl methacrylate). 相似文献
112.
The synthesis of the new esterglycidyl compounds produced by condensation of bis-carboxyimides with a large excess of epichlorohydrin were reported. To define the optimal conditions of condensation the process with monofunctional compounds were studied at first. For all synthesis, yield and epoxide and chlorine contents were found. The structure of glycidyl esters was determined by elementary analysis, IR and 1H and 13C NMR spectra. The physical properties were also defined. 相似文献
113.
Chinchilla D Zavaleta J Martinez K Gomez FA 《Analytical and bioanalytical chemistry》2005,383(4):625-631
Multiple-injection affinity capillary electrophoresis (MIACE) is used to determine binding constants (K
b) between receptors and ligands using as model systems vancomycin and teicoplanin from Streptomyces orientalis and Actinoplanes teichomyceticus, respectively, and their binding to D-Ala-D-Ala peptides and carbonic anhydrase B (CAB. EC 4.2.1.1) and the binding of the latter to arylsulfonamides. A sample plug
containing a non-interacting standard is first injected followed by multiple plugs of sample containing the receptor and then
a final injection of sample containing a second standard. Between each injection of sample, a small plug of buffer is injected
which contains an increasing concentration of ligand to effect separation between the multiple injections of sample. Electrophoresis
is then carried out in an increasing concentration of ligand in the running buffer. Continued electrophoresis results in a
shift in the migration time of the receptor in the sample plugs upon binding to their respective ligand. Analysis of the change
in the relative migration time ratio (RMTR) or electrophoretic mobility (μ) of the resultant receptor–ligand complex relative to the non-interacting standards, as a function of the concentration of
ligand yields a value for K
b. The MIACE technique is a modification in the ACE method that allows for the estimation of binding affinities between biological
interactions on a timescale faster than that found for standard ACE. In addition sample volume requirements for the technique
are reduced compared to traditional ACE assays. These findings demonstrate the advantage of using MIACE to estimate binding
parameters between receptors and ligands. 相似文献
114.
Simplified procedures for the analysis of polycyclic aromatic hydrocarbons in water, sediments and mussels 总被引:9,自引:0,他引:9
We describe in this paper simple and robust analytical protocols to determine the 16 polycyclic aromatic hydrocarbons (PAHs) of the US Environmental Protection Agency priority list in water, sediment and mussels. For water samples, eight different solid-phase extraction (SPE) sorbents have been compared and among them, C18 provided highest recoveries and limits of detection of 0.3-15 ng/L. For lyophilized sediments, Soxhlet and ultrasonic extraction were compared, and the last one permitted to recover all analytes with highest repetitivity and was validated by analysing a certified reference material. Finally, the analysis of mussels was undertaken using Soxhlet, ultrasonic and pressurized liquid extraction (PLE) and the performance of several clean-up steps are compared. Whereas for the former two, incomplete recovery or losses of some analytes were evidenced, PLE permitted a more efficient extraction and although alkaline digestion was necessary to remove coextracted compounds, the method gave acceptable recoveries and limits of detection of 0.5-7.7 microg/kg dry mass, as for sediments. In all cases, analysis was performed by gas chromatography coupled to mass spectrometry and internal standard quantification was performed using five deuterated PAHs. Each method performance is discussed for the three matrices analysed and the paper reports advantages and disadvantages of each for their routine application in monitoring programs. 相似文献
115.
Tenorio FJ Murray I Martinez A Klabunde KJ Ortiz JV 《The Journal of chemical physics》2004,120(17):7955-7962
Two stable products of reactions of water molecules with the Al3O3- cluster, Al3O4H2- and Al3O5H4-, are studied with electronic structure calculations. There are several minima with similar energies for both anions and the corresponding molecules. Dissociative absorption of a water molecule to produce an anionic cluster with hydroxide ions is thermodynamically favored over the formation of Al3O3-(H2O)n complexes. Vertical electron detachment energies of Al3O4H2- and Al3O5H4- calculated with ab initio electron propagator methods provide a quantitative interpretation of recent anion photoelectron spectra. Contrasts and similarities in these spectra may be explained in terms of the Dyson orbitals associated with each transition energy. 相似文献
116.
Attachment of an amino acid to a solid support by its side chain is sometimes necessary to take advantage of an alpha-carboxylic group available for diverse modifications, including the incorporation of a fluorophore for the preparation of fluorogenic substrates. In contrast to most other amino acids, anchoring the guanidinium group of an arginine to a resin requires the use of a supplementary linker. To avoid the usually multistep synthesis of such a linker as well as its difficult attachment to the guanidine group, we developed a simple method where the guanidine group is built on a Rink amide resin. Our strategy followed the steps of guanidine formation: (i) addition of an isothiocyanate derivative of ornithine to the amino group of a solid support, yielding Nomega-linked thiocitrulline; (ii) S-methylation of thiourea; (iii) guanidinylation using ammonium acetate. Cleavage of the resin generated the arginine-containing compound, the amine group of the resin becoming part of the guanidine. We have demonstrated the usefulness of this method by the synthesis of a series of fluorogenic substrates for trypsin-like serine proteases, which were obtained in high yield and purity. Then, our strategy also allowed generation from the same precursor differentially substituted arginine derivatives, including Nomega-methyl- and Nomega-ethylarginines. The ability to prepare such analogues together with the intermediates thiocitrulline and S-methylisothiocitrulline from a unique precursor while the alpha-amine and carboxylic groups remain available for modification also makes this method a powerful tool for combinatorial solid-phase synthesis of NO synthase inhibitors. 相似文献
117.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献
118.
Koji Yagi Veronica Garcia Ma. E. Rivas Javier Salas Andres Camargo Takeo Tabata 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):179-184
Some crown ethers were found to show significant antifungal activity against some wood-decay fungi, phytopathogenic fungi and eumycetes,Trichophytons for dermatomycosis. Their toxicity was evaluated by the paper disc method as well as by determining the values of ED50, i.e., the concentration which inhibits the mycelium growth by 50%. The fungi examined areTyromyces palustris, Picnoporous coccineus, Coriolous versicolor, Pyricularia filamentosa, Fusarium sp., Trichophyton rubrum, Trichophyton sp., etc. Among the 26 crown ethers tested, 3,5-di-t-butyl-benzo-15-crown-5 showed relatively high activity, the highest ED50 value of which being 8 M or 3 ppm. Other alkylbenzocrown ethers, dicyclohexyl crown ethers and Kryptofix 22DD also showed considerable activity. On the other hand, unsubstituted crown ethers, benzocrown ethers with a polar substituent, Kryptofix 222B and Kryptofix 221 were inactive. 相似文献
119.
H. -J. Sue E. I. Garcia Meitin D. M. Pickelman C. J. Bott 《Colloid and polymer science》1996,274(4):342-349
The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT
g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed. 相似文献
120.
F. Bosch Reig V. Peris Martinez F. Bosch Mossi J. V. Gimeno Adelantado 《Fresenius' Journal of Analytical Chemistry》1992,342(4-5):295-298
Summary An algorithm for quantifying interelemental effects in X-ray fluorescence techniques is developed. By applying an addition process, the ratio between the mass absorption coefficients of the analyte and the unknown sample (
i
*
/
s
*
) is calculated to correct the fluorescence intensity of the element to be determined and linearize the I-c calibration plot. This coefficient can be calculated graphically and numerically. The method is applied to the determination of tin in lead alloys with good results over wide concentration ranges.Notation used Q
Constant of proportionality in Eq. (4)
X-ray fluorescence intensity of the I
i
o
standard
- I
i
s
unknown sample
- I
i
ns
dilute unknown sample
- I
i
ms
unknown sample after addition of i analyte
Corrected fluorescence intensity of the I
i
cs
unknown sample
- I
i
msc
unknown sample after addition of i analyte
Relationship of fluorescence intensity between Ri
sample and standard
- R
i
dilute sample and standard
Factor of fm
addition
- fx
addition equivalent to the mass fraction of the i analyte in the unknown sample
Mass absorption coefficient of
i
*
analyte
-
s
*
unknown sample
-
ms
*
unknown sample after addition
Mass fraction of c
i
s
analyte
- c
i
ms
unknown sample after addition 相似文献