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21.
Anionic surfactants are preconcentrated from 5-ml samples by extraction as the ion-pair with ethyl violet into toluene. The absorbance of aliquots of the toluene phase is measured at 610 nm in a flow-injection system. A phase converter is located prior to the injection valve to convert a water stream to, pumped with ordinary pump tubing, to a toluene stream. The working range was 0.01–1.0 mg l?1 and the reproductibility (r.s.d, n = 10) was 2% for 0.4 mg l?1 sodium dodecyl sulphate. The non-aqueous flow-injection system serves to miniaturize the extraction from separatory funnel (200 ml) to test tube (10 ml) scale without loss of precision or validity. 相似文献
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24.
We previously theorized that, since the stereoselectivity of anomeric radical reactions is significantly influenced by the kinetic anomeric effect, which can be controlled by restricting the conformation of the radical intermediate, the proper conformational restriction of the pyranose ring of the substrates would therefore make highly alpha- and beta-stereoselective anomeric radical reactions possible. This theory was based on our previous results of the anomeric radical reactions with d-xylose derivatives as the substrates. We herein report the anomeric radical deuteration reactions with the conformationally restricted 1-phenylseleno-d-glucose derivatives, 2g and 3g, restricted in a (4)C(1)-conformation by an O-cyclic diketal moiety, and 4g, 5g, 6g, 7g, and 8g, restricted in a (1)C(4)-conformation by bulky O-silyl protecting groups. The radical deuterations with Bu(3)SnD, using the (4)C(1)-restricted substrates 2g and 3g, afforded the corresponding alpha-products (alpha/beta = 98:2) highly stereoselectively, whereas the (1)C(4)-restricted substrate 6g, having a trigonal (sp(2)) carbon substituent, i.e., -CHO, at the 5-position, selectively gave the beta-products (alpha/beta = 0:100). Thus, the stereoselectivity was significantly increased by the conformational restriction and was completely inverted by changing the substrate conformation from the (4)C(1)-form to the (1)C(4)-form. On the other hand, the deuterations with the (1)C(4)-restricted substrates 4g and 5g showed that the 1,5-steric effect due to the tetrahedral carbon substituent (-CH(2)OTIPS or -CH(2)OH) at the 5-axial position dominantly prevented the hydride transfer from the beta-face competing with the kinetic anomeric effect. This study suggests that, depending on the restricted conformation of the substrates to the (4)C(1)- or the (1)C(4)-form, the alpha- or beta-products would be obtained highly stereoselectively via anomeric radical reactions of hexopyranoses. 相似文献
25.
Yoshio Tanaka Morishige Atsukawa Yukio Shimura Akira Okada Hideki Sakuraba Tokuji Sakata 《Journal of polymer science. Part A, Polymer chemistry》1975,13(5):1017-1028
A soluble and self-crosslinkable linear copolymer with pendant epoxy and pyridyl groups was obtained from glycidyl methacrylate (M1) and 2-vinylpyridine (M2) or 2-vinyl-5-ethylpyridine (M2) by the action of azobisisobutyronitrile. The monomer reactivity ratios were determined in tetrahydrofuran at 60°C: r1 = 0.510, r2 = 0.620 with 2-vinylpyridine and r1 = 0.57, r2 = 0.62 with 2-vinyl-5-ethylpyridine. These were consistent with the calculated values with the reported Q and e values for these monomers. The intrinsic viscosities of the copolymers with 2-vinylpyridine and with 2-vinyl-5-ethylpyridine were found to be 0.17–0.19 and 0.26–0.38, respectively, in tetrahydrofuran at 30°C; they were independent of the copolymer composition. The copolymers were amorphous, had no clear melting points, and became insoluble crosslinked polymers under heating without further addition of any curing agents. 相似文献
26.
Yukio Shimura Wen-Shi Lin 《Journal of polymer science. Part A, Polymer chemistry》1970,8(8):2171-2180
α,ω-Dihydroxyl polystyrene was synthesized by the addition of styrene oxide to polystyryl dianion initiated with sodium naphthalene. Diglyme was found to be an unsuitable solvent for the preparation of low molecular weight compounds. Block copolymerization of the α,ω-dihydroxyl polystyrenes (M?n = 2250, 3140, and 6200) with poly(ethylene glycols) (M?n = 404, 1960, and 5650) was pursued by introducing urethane linkages with 4,4′-diphenylmethane diisocyanate. The mechanical, thermal, and viscoelastic properties, solution viscosity, molecular weight distribution, and moisture absorption of the block copolymers obtained were examined. Incorporation of styrene blocks was found to disturb the crystallization and fusion of poly(ethylene glycol) blocks. Films cast from benzene solution were soft and elastic and absorbed up to 5.8% moisture. 相似文献
27.
The most effective optical isomer (1-) of permethric acid (, R = H), a potent intermediate in the production of synthetic pyrethroid, was enantioselectively prepared. 相似文献
28.
The magnetic susceptibility of UO2ThO2 solid solutions has been measured from room temperature to 2.0 K. The magnetic moment and the Weiss constant have been determined in the temperature range in which the Curie-Weiss law holds. For the solid solutions showing antiferromagnetic transition, the Néel temperature has been also determined. These values decrease monotonically with increasing ThO2 concentration. The results were analyzed using the molecular field theory which includes the interaction between next-nearest neighbor spins. The interactions between nearest neighbor spins, J1, and those between next-nearest neighbor spins, J2, both decrease with increasing ThO2 concentration. The change of J1 with composition is larger than that of J2. The effect of magnetic dilution with ThO2 is considered to be stronger on the interaction between nearest neighbor uranium ions. 相似文献
29.
We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO3 with CH2I2 in 25–100 Torr of N2 diluent at 298 K. The rate constant of reaction of NO3 + CH2I2 is determined to be (4.0 ± 1.2) × 10−13 cm3 molecule−1 s−1 in 100 Torr of N2 diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH2I2 with NO3 has the potential importance at nighttime in the atmosphere. 相似文献
30.
Contribution of individual zinc ligands to metal binding and peptide folding of zinc finger peptides
Little is known about the contribution of individual zinc-ligating amino acid residues for coupling between zinc binding and protein folding in zinc finger domains. To understand such roles of each zinc ligand, four zinc finger mutant peptides corresponding to the second zinc finger domain of Sp1 were synthesized. In the mutant peptides, glycine was substituted for one of four zinc ligands. Their metal binding and folding properties were spectroscopically characterized and compared to those of the native zinc finger peptide. In particular, the electronic charge-transfer and d-d bands of the Co(II)-substituted peptide complexes were used to examine the metal coordination number and geometry. Fluorescence emission studies revealed that the mutant peptides are capable of binding zinc despite removing one ligand. Circular dichroism results clearly showed the induction of an alpha-helix by zinc binding. In addition, the structures of certain mutant zinc finger peptides were simulated by molecular dynamics calculation. The information indicates that His23 and the hydrophobic core formed between the alpha-helix and the beta-sheet play an essential role in alpha-helix induction. This report demonstrates that each ligand does not contribute equally to alpha-helix formation and coordination geometry in the zinc finger peptide. 相似文献