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321.
Kessler A Coleman CM Charoenying P O'Shea DF 《The Journal of organic chemistry》2004,69(23):7836-7846
An effective synthesis of the functionalized indole ring system has been developed from substituted o-aminostyrene starting material. Our methodology involves a novel cascade reaction sequence of alkyllithium addition to the styrene double bond and subsequent trapping of the intermediate organolithium with a suitable electrophile, followed by an in situ ring closure and dehydration to generate the indole ring. This new reaction sequence allows for the introduction of molecular diversity at all positions on the indole scaffold. The procedure was shown to be successful with a range of both C and N substituents on the o-aminostyrenes. The reaction sequence was tolerant to the reactivity range of alkyllithiums such as tert-, sec-, and n-butyllithium. The electrophiles used were DMF, which generated indole products with C-2 unsubstituted, and nitriles, which incorporated the nitrile substituent at C-2. The o-aminostyrene starting materials were generated by a Pd-catalyzed cross-coupling reaction of a vinyl boronic acid equivalent with the readily available substituted o-bromoanilines. 相似文献
322.
Summary The kinetics and mechanisms of the oxidation of Nb(CN)
inf8
sup5–
by the oxyanions S2O
inf8
sup2–
, BrO
inf3
sup–
, and IO
inf4
sup–
have been investigated in alkaline aqueous media (pH 12). The second-order rate constant for the electron transfer reaction between Nb(CN)
inf8
sup5–
and S2O
inf8
sup2–
at 25.0 °C, I = 0.36m (K+), is 11.1± 0.3 m
–1
s
–1 with H
= 30 ± 2kJmol–1 and S
= - 125 + 7JK–1 mol–1. The rate constant for the oxidation of Nb(CN)
inf8
sup5–
by BrO
inf3
sup–
at 25.0 °C, I = 0.20m (Na+), is 2.39 ± 0.08m
–1
s
–1 with H = 28 ± 2kJmol–1 and S
= -139 ± 7JK–1mol–1. The oxidation of Nb(CN)
inf8
sup5–
by IO
inf4
sup–
proceeds by two parallel pathways involving the monomeric IO
inf4
sup–
ion and the hydrated dimer H2I2O
inf10
sup4–
. The second-order rate constant for the oxidation of Nb(CN)
inf8
sup5–
by monomeric IO
inf4
sup–
at 5.0 °C, I = 0.050m (Na+), is (3.3 ± 0.6) × 103
m
–1
s
–1 with H
= 75 ± 6 kJ mol–1 and S
= 94 ± 15 J K–1 mol–1, while the rate constant for the oxidation by H2I2O
inf10
sup4–
is (1.8 ± 0.1) × 103
m
–1
s
–1 with H
= 97 ± 5 kJ mol–1 and S
= 166 ± 16 J K–1 mol–1 under the same reaction conditions. The rate constants for each of the oxidants employed display specific cation catalysis with the order of increasing rate constants: Li+ < Na+ < NH
inf4
sup+
< K+ < Rb+ < Cs+, in the same direction as the electronic polarizability of the cations. The results are discussed in terms of the outer-sphere electron-transfer processes and compared with the corresponding data and mechanisms reported for other metal-cyano reductants. 相似文献
323.
[reaction: see text] A stepwise route to unsymmetrical tetraarylazadipyrromethenes by a condensation of 2,4-diaryl-5-nitroso-pyrroles with 2,4-diarylpyrroles is described. This modular building-block approach allows for the introduction of up to four different aryl substituents on the azadipyrromethene and is tolerant of a varied substituent set. An efficient synthesis of the 2,4-diarylpyrroles building blocks from 1,3-diaryl-4-nitro-butan-1-ones by nitro hydrolysis to a keto-aldehyde and subsequent ammonia condensation reaction has been achieved. The facile conversion of 2,4-diarylpyrroles into their alpha-nitroso analogues by their reaction with sodium nitrite generated the second building block required for the synthesis. 相似文献
324.
Jerome A. Imonigie Donal H. Macartney 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(2):195-203
The effects of -, -, dm-(heptakis(2,6-di-O-methyl)--) and -cyclodextrins (CD) on the kinetics of the electron-transfer reaction of the ferrocenemonocarboxylate anion (FCA–) with bis(pyridine-2,6-dicarboxylato)cobaltate(III) have been investigated in aqueous solution (0.20 M Na2HPO4, pH 9.2) at 25.0°C. Substantial decreases in the rate constants for the electron-transfer reactions were observed upon cyclodextrin inclusion of the reductant, due to an increase in the FCA0/– reduction potential and to the insulation of the reductant from oxidant. The inclusion stability constants for {FCA·CD}– were evaluated from the1H NMR and kinetic data, and the order of the stability constants was found to be -CDdm-CD-CD>-CD. 相似文献
325.
John F. Gallagher Clare M. Coleman Donal F. O'Shea 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):o139-o141
The orange title compound, C19H17N3O4S, can be synthesized either via microwave‐mediated combinatorial chemistry strategies or conventional synthetic procedures. The phenyl and meta‐nitrophenyl C6 rings are essentially coplanar with the central imidazolyl ring, with interplanar angles of 0.87 (5) and 0.97 (4)°, respectively, resulting in optimum conjugation (SCH2 moiety included); λmax = 281 nm in CH3CN. The principal intermolecular interactions are Nimid—H?Onitro and Nimid—H?O=C [N?O = 3.058 (2) and 3.432 (3) Å, and N—H?O = 128 and 153°, respectively]. The closest H?S distance is an intramolecular C—H?S contact, with H?S = 2.54 Å and C—H?S = 136°. 相似文献
326.
Abstract In this paper we investigate two new types of generalized equilibrium problems. The theory is self contained and relies only
on Brouwer’s fixed point theorem.
Keywords G-convex space, Fixed point, Weakly G–KKM-mapping, Generalized equilibrium problem, Weakly equilibrium problem
Mathematics Subject Classification (2000) 54H25, 54C60, 91B50 相似文献
327.
Second order problems with functional conditions including Sturm–Liouville and multipoint conditions
In this paper we study the solvability of equations of the form ‐(d/dt)φ (t, u, u (t), u ′(t)) = f (t, u, u (t), u ′(t)) for a.e. t ∈ I = [a, b ], together with functional‐boundary conditions which cover, amongst others, Sturm–Liouville and multipoint boundary data as particular cases. Our approach uses upper and lower solutions together with growth restrictions of Nagumo's type. An example is presented to show the applicability of the obtained results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
328.
The paper presents existence results for positive solutions of the differential equations x ″ + μh (x) = 0 and x ″ + μf (t, x) = 0 satisfying the Dirichlet boundary conditions. Here μ is a positive parameter and h and f are singular functions of non‐positone type. Examples are given to illustrate the main results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
329.
Ravi P. Agarwal Kanishka Perera Donal O'Regan 《Proceedings of the American Mathematical Society》2008,136(1):279-286
We obtain positive solutions in the sense of distributions of singular boundary value problems using perturbation and variational methods.
330.
In this paper, we employ a well‐known fixed point theorem for cones to study the existence of positive periodic solutions to the n ‐dimensional system x ″ + A (t)x = H (t)G (x). Moreover, the eigenvalue intervals for x ″ + A (t)x = λH (t)G (x) are easily characterized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献