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941.
942.
Ambiphilic reduction of cyclohexanones with methylaluminum bis(2, 6-di-tert-butyl-4-methylphenoxide) and tert-butylmagnesium chloride provides the corresponding equatorial alcohols with high stereoselectivity. 相似文献
943.
The recently proposed method of momentum electron density for interatomic interactions is applied to the two states of the H
2
+
system. The processes of the attractive 2P
u
and repulsive 3d
g
interactions are analysed based on the behaviour of the momentum density and Compton profile. The results are compared with the previous ones for the 1
S
g
and 2p
u
states. The guiding principle of contraction and expansion for the energy-density relation in momentum space is shown to be common to both the and states. 相似文献
944.
A novel CsF-catalyzed three-component coupling reaction of a silylphosphine, activated alkenes and aldehydes is described. Multi-functional phosphines were obtained by forming both carbon-phosphorus and carbon-carbon bonds in good yields under mild conditions. 相似文献
945.
Minoru Sasaki 《Tetrahedron letters》2004,45(9):1911-1913
Regio- and stereospecific alkyl and alkynyl substitution reactions of epoxy selenides with organoaluminum reagents have been developed, which proceed via episelenonium ion intermediates to give the C2 alkyl substitution products with double inversion of the configuration and the C1 alkynyl substitution products with migration of the arylseleno group in high yields, respectively. 相似文献
946.
A basic host polymer exhibiting pH-regulatable saccharide recognition has been investigated. Poly(m-ethynylpyridine) bearing dialkylamino groups forms helical complexes with saccharides to show induced circular dichroism (ICD). When trifluoroacetic acid was titrated on these complexes, the ICD was gradually enhanced until the amount of the acid reached ca. 0.5 molar equivalence versus the pyridine rings in the polymer, and further addition of the acid suppressed the ICD. The proper addition of the acid also increased the binding constants between the polymer and saccharides. These findings would be due to stabilization of the helical structure consisting of cisoid conformations for each of the adjacent pyridine pairs, which were caused by half-protonation of the pyridine rings. Computational analyses indicated that the pyridinium-pyridine dimeric structure prefers its cisoid conformation to its transoid one. 相似文献
947.
The acyclic asymmetric induction is described which involves heteroconjugate addition of MeLi to α-hydroxy hetero-olefins and concomitant intramolecular silicon-migration to produce α,α-sulfonyl-dianion of the adduct being of utility for the second CC bond formation in one pot. It also contains the first chemical proof of the regiochemical assignment to the hetero-olefins. 相似文献
948.
Ooi T Kameda M Taniguchi M Maruoka K 《Journal of the American Chemical Society》2004,126(31):9685-9694
A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention of an unfavorable yet inevitable retro aldol process involving the chiral catalyst. On the basis of this information, a reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-beta-hydroxy-alpha-amino esters almost exclusively in an essentially optically pure form. 相似文献
949.
Bunichiro Yamada Takashi Kontani Minoru Yoshioka Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2381-2393
The absolute rate constants for propagation (kp) and for termination (kt) of ethyl α-fluoroacrylate (EFA) were determined by means of the rotating sector method; kp = 1120 and kt = 4.8 × 108 L/mol.s at 30°C. The monomer reactivity ratios for the copolymerizations with various monomers were obtained. By combining the kp values for EFA from the present study and those for common monomers with the monomer reactivity ratios, the absolute values of the rate constants for cross-propagations were also evaluated. Reactivities of EFA and poly(EFA) radical, being compared with those of methyl acrylate and its polymer radical, were found to be little affected by the α-fluoro substitution. Poly(EFA) prepared with the radical initiator was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Although the glass transition temperature obtained by DSC for poly(EFA) resembled that of poly(ethyl α-chloroacrylate), its TGA thermogram showed fast chain de polymerization to EFA that was distinct from complicated degradation of poly(ethyl α-chloroacrylate). 相似文献
950.
Masami Inoue Reiko Abe Hideo Tamamura Minoru Ohta Keiko Asami Hisayuki Kitani Hideko Kamei Yumiko Nakamura Tokuhiro Watanabe Akihiro Ohta 《Journal of heterocyclic chemistry》1985,22(5):1291-1296
In order to examine the α-substitution of side chains, various derivatives of 2,5-diisopropyl- and 2,5-disec-butylpyrazine 1-oxides were subjected to the reaction with phosphoryl chloride and acetic anhydride. Chlorination and acetoxylation were recognized to take place on the pyrazine ring in almost all cases. 相似文献