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61.
Atsuko Ito Keiko Iwai Chiyuki Oyama Setsu Morimoto Hiroaki Kato 《Hyperfine Interactions》1992,71(1-4):1371-1374
Magnetization and Mössbauer measurements have been made on a diluted antiferromagnets FexMg1?xTiO3 with x=0.2, 0.3 and 0.7. It has been demonstrated that this system exhibits a spin glass or a reentrant spin glass like behavior in the samples with x around the percolation concenrration xc≈0.25. It has been shown that various sizes of magnetic clusters are formed well above the transition temperatures determined by the magnetization measurements in the samples with x near xc. The behavior of Fe0.2Mg0.8TiO3 is discussed as a typical cluster glass. 相似文献
62.
63.
Three isolectins were isolated from seeds of Erythrina variegata (Linn.) var. Orientalis by ion-exchange chromatography, followed by affinity chromatography on lactose-Sepharose 4B and acid-treated Sepharose 4B columns. The purified isolectins (EVLI, EVLII and EVLIII) are all specific for galactopyranosides and N-acetylgalactosamine, and their affinities for simple sugars are EVLIII greater than EVLII greater than EVLI. EVLI and EVLIII are homodimers made up of an A-subunit of molecular mass 36,000 and a B-subunit of molecular mass 33,000, whereas EVLII is a heterodimer composed of the A- and B-subunits. Upon treatment with trifluoromethansulphonic acid, the molecular masses of both subunits decreased to 31,000. Rechromatography of EVLII on the acid-treated Sepharose 4B column again produced the homodimeric lectins (EVLI and EVLIII). It is suggested that the constituent subunits of Erythrina variegata isolectins are eschangeable with each other in vitro. 相似文献
64.
Yamasaki Y Sagayama H Goto T Matsuura M Hirota K Arima T Tokura Y 《Physical review letters》2007,98(14):147204
Magnetic ferroelectrics or multiferroics, which are currently extensively explored, may provide a good arena to realize a novel magnetoelectric function. Here we demonstrate the genuine electric control of the spiral magnetic structure in one such magnetic ferroelectric, TbMnO3. A spin-polarized neutron scattering experiment clearly shows that the spin helicity, clockwise or counterclockwise, is controlled by the direction of spontaneous polarization and hence by the polarity of the small electric field applied on cooling. 相似文献
65.
Prof. Hiroshi Watanabe Ming-Long Yao Atsuko Yamagishi Kunihiro Osaki Toshiyuki Shitata Hirokazu Niwa Yotaro Morishima 《Rheologica Acta》1996,35(5):433-445
Linear and nonlinear viscoelastic properties were examined for a 50 wt% suspension of spherical silica particles (with radius of 40 nm) in a viscous medium, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture. The effective volume fraction of the particles evaluated from zero-shear viscosities of the suspension and medium was 0.53. At a quiescent state the particles had a liquid-like, isotropic spatial distribution in the medium. Dynamic moduli G* obtained for small oscillatory strain (in the linear viscoelastic regime) exhibited a relaxation process that reflected the equilibrium Brownian motion of those particles. In the stress relaxation experiments, the linear relaxation modulus G(t) was obtained for small step strain (0.2) while the nonlinear relaxation modulus G(t, ) characterizing strong stress damping behavior was obtained for large (>0.2). G(t, ) obeyed the time-strain separability at long time scales, and the damping function h() (–G(t, )/G(t)) was determined. Steady flow measurements revealed shear-thinning of the steady state viscosity () for small shear rates (< –1; = linear viscoelastic relaxation time) and shear-thickening for larger (>–1). Corresponding changes were observed also for the viscosity growth and decay functions on start up and cessation of flow, + (t, ) and – (t, ). In the shear-thinning regime, the and dependence of +(t,) and –(t,) as well as the dependence of () were well described by a BKZ-type constitutive equation using the G(t) and h() data. On the other hand, this equation completely failed in describing the behavior in the shear-thickening regime. These applicabilities of the BKZ equation were utilized to discuss the shearthinning and shear-thickening mechanisms in relation to shear effects on the structure (spatial distribution) and motion of the suspended particles.Dedicated to the memory of Prof. Dale S. Parson 相似文献
66.
Yasuda M Nakajima H Takeda R Yoshioka S Yamasaki S Chiba K Baba A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3856-3867
Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC6H4)3CH, L?B(OC6H4)3SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (Cipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of Cipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC6H3F)3CH and the ortho‐phenyl‐substituted compound B(OC6H3Ph)3CH were less than that of the unsubstituted borate B(OC6H4)3CH. The ligand‐exchange rate of B(OC6H4)3SiMe was much faster than that of B(OC6H4)3CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)3 or by the strong Lewis acid BF3?OEt2. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity. 相似文献
67.
Kikura-Hanajiri R Kawamura M Miyajima A Sunouchi M Goda Y 《Analytical and bioanalytical chemistry》2011,400(1):165-174
In order to develop an analytical method for the discrimination of dextromethorphan (an antitussive medicine) from its enantiomer,
levomethorphan (a narcotic) in biological samples, chiral analyses of these drugs and their O-demethyl and/or N-demethyl metabolites in rat plasma, urine, and hair were carried out using LC-MS/MS. After the i.p. administration of dextromethorphan
or levomethorphan to pigmented hairy male DA rats (5 mg/kg/day, 10 days), the parent compounds and their three metabolites
in plasma, urine and hair were determined using LC-MS/MS. Complete chiral separation was achieved in 12 min on a Chiral CD-Ph
column in 0.1% formic acid–acetonitrile by a linear gradient program. Most of the metabolites were detected as being the corresponding
O-demethyl and N, O-didemethyl metabolites in the rat plasma and urine after the hydrolysis of O-glucuronides, although obvious differences in the amounts of these metabolites were found between the dextro and levo forms.
No racemation was observed through O- and/or N-demethylation. In the rat hair samples collected 4 weeks after the first administration, those differences were more clearly
detected and the concentrations of the parent compounds, their O-demethyl, N-demethyl, and N, O-didemethyl metabolites were 63.4, 2.7, 25.1, and 0.7 ng/mg for the dextro forms and 24.5, 24.6, 2.6, and 0.5 ng/mg for the
levo forms, respectively. In order to fully investigate the differences of their metabolic properties between dextromethorphan
and levomethorphan, DA rat and human liver microsomes were studied. The results suggested that there might be an enantioselective
metabolism of levomethorphan, especially with regard to the O-demethylation, not only in DA rat but human liver microsomes as well. The proposed chiral analyses might be applied to human
samples and could be useful for discriminating dextromethorphan use from levomethorphan use in the field of forensic toxicology,
although further studies should be carried out using authentic human samples. 相似文献
68.
Itoh A Saitoh T Tani K Uchigaki M Sugimoto Y Yamada J Nakajima H Ohshiro H Sun S Tanahashi T 《Chemical & pharmaceutical bulletin》2011,59(8):947-951
From the embryos of the seeds of Nelumbo nucifera, three bisbenzylisoquinoline alkaloids, nelumboferine and nelumborines A and B, were isolated along with four known compounds, neferine, liensinine, isoliensinine and anisic acid. The structures of the new alkaloids were determined mainly by spectroscopic methods. 相似文献
69.
Akiko Watanabe Naotoshi Kiyota Tetsuo Yamasaki Kazuhiro Tanda Tatsunori Miyagoe Masanori Sakamoto Masami Otsuka 《Journal of heterocyclic chemistry》2011,48(5):1132-1139
Four isomers of the monomer of peptide nucleic acid (PNA) were derived from (2S,4R)‐4‐hydroxyproline; they had different stereochemistries at the C2 and C4 positions in the pyrrolidine ring. These different backbone conformations corresponding to four different stereochemistries were realized through a combination of inversions at the C2 and the C4 positions in pyrrolidine ring. The obtained backbone frameworks were reacted with N‐benzoyl thymine to give the corresponding PNA monomers. Spectroscopic comparison of the resultant monomers confirmed their stereochemistries. J. Heterocyclic Chem., (2011). 相似文献
70.
The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO. 相似文献