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971.
[reaction: see text]. Glycoproteins are particularly suited to protein semisynthesis since homogeneous samples for biological analyses are not readily available using traditional recombinant techniques. Here we apply glycosyl iodoacetamides, normally used for the modification of bacterially derived proteins, to solid-phase glycopeptide synthesis. This provides access to glycopeptide alpha-thioesters, which may lend themselves to the semisynthesis of homogeneous N-linked glycoprotein mimics and novel glycopeptide libraries. 相似文献
972.
Maria Gdaniec Tomasz Bytner Monika Szyrszyng Tadeusz Połonski 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(3):243-247
The crystalline inclusion compounds of cholic acid (CA) and deoxycholic acid (DCA) with several nitrosobenzenes were prepared. The IR spectra and crystal structures of these compounds confirmed inclusion of the monomeric form of the C-nitroso compounds. The DCA compounds have 2 : 1 host:guest stoichiometry and P21 symmetry. Guest molecules are enclosed in channels and disordered. In the CA-nitrobenzene inclusion compound (1·CA) the host:guest stoichiometry is 1 : 1. The host molecules form typical CA bilayer aggregates and guest molecules are accommodated in helicoidal channels. The guest nitroso group is not coplanar with the phenyl ring; the torsion angle on the C–N bond is 8.6(8)°. The solid-state circular dichroism spectrum of 1·CA shows the negative Cotton effect at 780 nm corresponding to the n–* electronic transition that can be associated with the P helicity of the guest molecule. The extremely weak magnitude of the Cotton effects exhibited by the DCA complexes points to a nearly planar arrangement of the NO group and the phenyl ring in the guest molecules. 相似文献
973.
Differences between the rates of oxidation of substrates by horseradish peroxidase in buffer, aqueous micellar solution of
Brij 35 and in reverse micelles formed of Brij 30 in several hydrocarbons are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
974.
In vivo study of triazine herbicides in plants by SPME 总被引:1,自引:0,他引:1
The use of SPME for in vivo monitoring of herbicide levels in plant tissues is evaluated. Fibers are exposed to the plant tissue with the aid of buffer located at the fiber/tissue interface region. Following this extraction period the extracted amount is estimated by solvent desorption and LC-MS-MS. 相似文献
975.
976.
Gruszecki WI Gagoś M Hereć M 《Journal of photochemistry and photobiology. B, Biology》2003,69(1):49-57
Fluorescence emission from amphotericin B dissolved in 2-propanol-water was recorded in the spectral region 500-650 nm. The fluorescence excitation spectrum corresponds to the absorption spectrum of the monomeric drug. The large energy shift between the excitation and emission bands indicates that emission takes place from an energy level different than that responsible for absorption. These levels were attributed to the 2(1)A(g) and 1(1)B(u) states, respectively. Excitation of the same sample with short wavelength radiation (below 350 nm) yields light emission between 400 and 550 nm. The fluorescence excitation spectrum corresponding to this emission band displays distinct maxima at 350, 334 and 318 nm. This band was analyzed in terms of the exciton splitting theory and assigned to amphotericin B in a dimeric form, in which chromophores are spaced by 4.9 A. The binding energy of the dimers, determined to be 4.9 kJ/mol, indicates that the structures are stabilized by van der Waals interactions. The same type of molecular structures was also detected in the lipid membranes formed with dipalmitoylphosphatidylcholine. Linear dichroism of amphotericin B embedded in lipid multibilayers indicates that molecules are distributed between two fractions: parallel (38%) and perpendicular (62%) with respect to the membrane. The biological importance of such membrane organization is discussed. 相似文献
977.
Gas-liquid chromatography was applied to investigate the mechanism of alpha-cyclodextrin (alpha-CD) complexation processes with some chiral monoterpenoids differing from each other in chemical properties and structure. They were chosen from hydrocarbons, alcohols, aldehydes and ketones of acyclic, monocyclic and bicyclic structure. The relationships between the retention factor, k, of a guest solute (G) and alpha-CD concentration were studied. The obtained data enabled the stoichiometry, the stability of individual complexes and the separation factor of enantiomers to be determined. It was found that almost all the investigated monoterpenoids, apart from the acyclic ones, form inclusion complexes with alpha-CD. Straight-line relations (r vs. [alpha-CD]) were observed for monocyclic alcohols and pulegone, without any trace of enantioselectivity. This behaviour indicates that the 1:1 stoichiometry of the G-CD complexes does not lead to chiral recognition. Parabolic relations arising from 1:2 stoichiometry were found for limonene, alpha-phellandrene, some monocycylic ketones and all the investigated bicyclic terpenoids. It appeared that only the second step of complexation displayed marked enantioselectivity. However, a loss of efficiency resulting from slower equilibration is then noticeable. Attempts are made to rationalize the chromatographic results with respect to the structure of the investigated compounds. 相似文献
978.
The complex of Fe(II) ions of general formula [Fe L 2](BF4)2 with triphenylamine-hydrazone ligand L has been synthesized and characterized. Oxidative electropolymerization of the complex proceeded smoothly on the working electrode producing a homogenous thin film of metallopolymer. The film thickness and morphology of the layer was investigated by microscopy techniques such as scanning electron microscopy and atomic force microscopy, and the composition of the film was confirmed by X-ray photoelectron spectroscopy analysis. It was found that fifty successive oxidation/reduction cycles resulted in a 120 nm thick film on the electrode surface. The metallopolymer was also characterized using cyclic voltammetry and spectroelectrochemical methods. The film was found to change its color from yellow to green-blue, exhibit high change in transmittance of 60 % at 770 nm, and possess good electrochemical stability during 375 cycles of switching of the potential between −0.1 V and +1.5 V, owing to the presence of metal ions that link two ligand molecules resulting in formation of highly cross-linked film. The switching times (coloration and bleaching) were calculated to be 34.2 s and 7.3 s, respectively. Coloration efficiency of the formed film of polymeric complex was found to be 144 cm2 C−1. 相似文献
979.
980.
Monika Bosacka Anna Błońska-Tabero Elżbieta Filipek Jana Luxova Petra Šulcová 《Journal of Thermal Analysis and Calorimetry》2017,130(1):95-101
A new dichromium(III) cobalt(II) diphosphate(V) of the formula CoCr2(P2O7)2 was detected in the Co3Cr4(PO4)6–Cr(PO3)3 system. The new compound was obtained as a result of high-temperature solid-state reactions between CoCO3, Cr2O3 and (NH4)2HPO4 as well as between Cr(PO3)3 and Co3Cr4(PO4)6. CoCr2(P2O7)2 was characterized using XRD, DTA and IR methods. Results demonstrated that CoCr2(P2O7)2 crystallizes in the triclinic system and its unit cell parameters were calculated. Its infrared spectrum was presented. CoCr2(P2O7)2 melts incongruently at 1270±10 °C with a formation of solid α-CrPO4. The compound Co3Cr4(PO4)6, component of the system under study, was obtained for the first time as a pure phase. Its thermal stability was also investigated. Co3Cr4(PO4)6 is stable in air up to 1410 ± 20 °C. 相似文献