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991.
992.
993.
Spin states in amorphous Fe100–x Zrx (7x12) are investigated using hyperfine field distributions (HFDs) as derived from57Fe transmission Mössbauer experiments. The existence of low-, medium- and high-spin states is demonstrated by three-dimensional projections of HFDs. Temperature dependences of the corresponding average values revealed anomalous behaviour in the vicinity ofT fc. An increase in the hyperfine magnetic fields observed towards low temperatures is discussed in terms of a ferromagnet-to-spin-glass transition. Utilizing also theT c values, which were obtained from a thermal scanning Mössbauer technique, we propose a diagram of spin states in amorphous Fe-Zr.  相似文献   
994.
Five tridecapeptide lactones, named theonellapeptolides Ia (1), Ib (2), Ic (3), Id (4), and Ie (5), were isolated from the Okinawan marine sponge Theonella swinhoei. Following the structure elucidation of theonellapeptolide Id (4), the structures of theonellapeptolides Ia (1), Ib (2), Ic (3), and Ie (5) were determined on the basis of chemical and physicochemical evidence including high performance liquid chromatography and circular dichroism combined analysis of the amino acid compositions. Theonellapeptolides Ib (2), Ic (3), Id (4), and Ie (5) exhibit moderate cytotoxic activity towards for L1210 in vitro (IC50 1.6, 1.3, 2.4, and 1.4 micrograms/ml, respectively), and theonellapeptolide Ie (5) exhibits ion-transport activities for Na+ and K+ ions.  相似文献   
995.
This study clearly demonstrates that clathrated water molecules can contribute to both chemical stabilization and destabilization of clathrates. The solid-state stabilities for two isomorphic clathrates of cephalosporin, cefazolin sodium and FK041, were investigated in terms of the effects of water content. The isomorphic ranges of water content were estimated to be 3.5-5 mol/mol for alpha-form cefazolin sodium and 2-4 mol/mol for FK041 hydrate. Upon the isomorphic dehydration, alpha-form cefazolin sodium was destabilized as the water content decreased below 4.25 mol/mol owing to the disruption of hydrogen bonding network in lattice channels. In this case, the hydration of clathrated water up to 4.25 mol/mol contributed to the physical and chemical stability of the crystals. On the contrary, the isomorphic hydration in FK041 hydrate contributed to the chemical destabilization owing to the high water activity. The difference in water activity between alpha-form cefazolin sodium and FK041 hydrate could be attributed to the size of water channels.  相似文献   
996.
Optically pure forms (>/=98% ee) of N-(o-tert-butylphenyl)-5-(methoxymethyl)-2-pyrrolidinone having atropisomerism and N-(o-tert-butyldiphenylsiloxyphenyl)-5-(methoxymethyl)-2-pyrrolidinon e having an atropisomerism-like structure were prepared from ortho-substituted aniline derivatives and (S)-5-(methoxymethyl)butyrolactone in a stereoselective manner. The reactions of Li-enolates from these lactams with various electrophiles and subsequent dearylation of the products gave 3, 5-cis-disubstituted-2-pyrrolidinone derivatives.  相似文献   
997.
Application of the fluoren-9-ylmethoxycarbonyl (Fmoc)-based solid-phase segment condensation approach to the preparation of sulfated peptides was investigated through the synthesis of human big gastrin-II, a 34-residue sulfated tyrosine [Tyr(SO3H)]-containing peptide. Highly acid-sensitive 2-chlorotrityl resin (Clt resin) was exclusively employed as an anchor-resin for the preparation of the three peptide segments having the C-terminal Pro residue as well as of the Tyr(SO3H)-containing resin-bound segment. By using the PyBOP-mediated coupling protocol [PyBOP=benzotriazolyloxytris(pyrrolidino)phosphonium hexafluorophosphatel, we successively condensed each segment and constructed the 34-residue peptide-resin without any difficulty. The final acid treatment of the fully protected peptide-resin at low temperature (90% aqueous TFA, 0 degree C for 8 h), which can detach a Tyr(SO3H)-containing peptide from the resin and remove the protecting groups concurrently with minimum deterioration of the sulfate, afforded a crude sulfated peptide. After one-step HPLC purification, a highly homogeneous human big gastrin-II was easily obtained in 14% yield from the protected peptide-resin. The sulfate form of the C-terminal glycine-extended gastrin (G34-Gly sulfate), a posttranslational processing intermediate of gastrin-II, was also successfully prepared with the segment condensation approach (11% yield). These results demonstrated the usefulness of the segment condensation protocol for preparing large Tyr(SO3H)-containing peptides.  相似文献   
998.
We show how high-resolution magic angle-spinning NMR spectroscopy can be used to characterize 13C-labeled saccharides that have been prepared using solid-phase synthesis techniques while they are still bound to a solid-support resin. With the use of 13C-labeled glucose as the starting material, we have successfully synthesized mono-, di- and trisaccharides with uniform 13C labeling of the saccharide rings. Using these materials, we have been able to assign the 13C and 1H spectra and to characterize various impurities on the resin beads.  相似文献   
999.
By the reaction of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr3, GaBr3 or FeCl3 in CH3CN/CS2 charge transfer (CT) salts of 1 with counteranions of FeBr4, GaBr4 or FeCl4 (12·FeBr4, 12·GaBr4 and 12·FeCl4) as plate crystals were obtained. Their crystal structures are apparently similar to each other, in which 1 molecules are dimerized in the parallel direction of their molecular long axes, and the dimers are stacked with changing the direction of the molecular long axes alternately to form a one- dimensional column. The counteranions intervene between the 1-stacked columns and are aligned in a zigzag manner. The room-temperature electrical conductivities of 12·FeBr4 and 12·GaBr4 are fairly high (10-15 S cm−1), but a small value (0.8 S cm−1) is obtained for 12·FeCl4. For all CT salts, temperature dependences of electrical conductivity are semiconducting in spite of very small activation energies (30-90 meV). Based on the comparison between their electrical conducting and magnetic properties, it is suggested that the d spins of FeBr4 or FeCl4 ions exert almost no influence on the π conducting electrons in the 1-stacked column.  相似文献   
1000.
A stable radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) has long been used as a convenient method for the antioxidant assay of biological materials such as cysteine, glutathione, ascorbic acid, tocopherol and polyhydroxy aromatic compounds (hydroquinone, pyrogallol, etc.). In this study, non-reductive scavenging of DPPH was investigated by electron spin resonance (ESR) analyses for the purpose of developing a useful method for quantitative determination of peroxyradical. Since DPPH was degraded in the presence of peroxyradical derived from UV-irradiated benzoylperoxide and the peroxyradical-induced degradation of DPPH was inhibited by the addition of a spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), it is concluded that DPPH is non-reductively scavenged by peroxyradical. Therefore, it is suggested that DPPH could be a useful agent for the quantitative measurement of peroxyradical.  相似文献   
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