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841.
Shibata T Buurma NJ Brazier JA Thompson P Haq I Williams DM 《Chemical communications (Cambridge, England)》2006,(33):3516-3518
Incorporation of a bicyclic cytosine analogue, 3-beta-D-(2'-deoxyribofuranosyl)-7,8-dihydropyrido[2,3-d]pyrimidine, into synthetic DNA duplexes results in a greatly enhanced thermal stability (3-4 degrees C per modification) compared to the corresponding unmodified duplex. 相似文献
842.
A multivariate distribution is said to have multiplicative correlation if the correlation matrix R = (r
ij
) is written as r
ij
= δ
i
δ
j
or r
ij
= −δ
i
δ
j
(i ≠ j) for a parameter vector
. We first determine feasible values for
and show that variables with such a correlation matrix can always be decomposed into a common “signal” variable plus individual
“noise” variables. It is also shown that a special case of this correlation matrix implies a sum constraint among variables
and vice versa. Such properties illustrate why many multivariate distributions have such a correlation structure. Furthermore,
several invariance properties lead to simple relations among several multivariate distributions. 相似文献
843.
Para- and meta-isomers of center-to-edge phosphorus(V) porphyrin heterodimers (p- and m-Pm-PCl2) composed of a phosphorus(V) tetraphenylporphyrin (P) and a phosphorus(V) tetrakis(4-methoxyphenyl)porphyrin (Pm) were synthesized to investigate the geometry and solvent-polarity dependences of the relaxation dynamics of the lowest singlet excited state (S1) of the porphyrin dimer. The geometrical difference between m- and p-Pm-PCl2 in solution was confirmed by 1H NMR on the basis of the porphyrin ring current model. By the photoexcitation of the dimers, only the fluorescence from 1Pm*-P was observed in both dimers because of the efficient singlet energy transfer from the higher energy 1P* to the lower energy 1Pm*. However, the 1Pm*-P fluorescence had features that differ from the typical fluorescence from monomeric 1Pm*, especially for the solvent-polarity dependence of the quantum yields. Furthermore, all the fluorescence decay curves of 1Pm*-P were double-exponential. The special fluorescence features of 1Pm*-P are due to the equilibrium between 1Pm*-P and the charge-transfer (CT) excited state of the dimer ((Pm-P)CT). By the excited-state equilibrium, 1Pm*-P is efficiently quenched through (Pm-P)CT in highly polar solvents. The contribution of (Pm-P)CT to the decay process of 1Pm*-P is more remarkable in m-Pm-PCl2 than in p-Pm-PCl2, depending on the interaction between the two porphyrin -systems in the heterodimer. 相似文献
844.
[reaction: see text] Rh-dppf was found to be an efficient catalyst for the cross-coupling between primary alkyl halides bearing beta-hydrogens and arylzinc compounds possessing carbonyl groups such as ester, amide, or ketone at the ortho position. Various functional groups such as ester, nitrile, or acyloxylate moieties on the halides were tolerated under the catalysis conditions. Arylzinc compounds free of ortho-carbonyl groups reacted well with ethyl 3-iodopropanoate, suggesting that the essential intramolecular interaction between carbonyl groups and Rh promotes the reductive elimination. 相似文献
845.
Enantioselective cycloaddition using chiral transition metal catalysts is an atom-economical and efficient synthetic tool for the construction of chiral carbo- and heterocyclic skeletons. This short account discloses our recent results of inter- and intramolecular enantioselective [2 + 2 + 2] cycloadditions of alkyne and/or alkene moiety(ies). Chiral iridium complexes catalyzed the alkyne trimerization for the generation of axial chirality(ies), and chiral rhodium ones catalyzed alkyne-alkyne-alkene cyclization for the generation of a quaternary carbon including spirocyclic system. 相似文献
846.
847.
848.
Importance of a Fluorine Substituent for the Preparation of meta‐ and para‐Pentafluoro‐λ6‐sulfanyl‐Substituted Pyridines 下载免费PDF全文
Dr. Mikhail Kosobokov Benqiang Cui Dr. Andrii Balia Kohei Matsuzaki Etsuko Tokunaga Norimichi Saito Prof. Dr. Norio Shibata 《Angewandte Chemie (International ed. in English)》2016,55(36):10781-10785
Although there are ways to synthesize ortho‐pentafluoro‐λ6‐sulfanyl (SF5) pyridines, meta‐ and para‐SF5‐substituted pyridines are rare. We disclose herein a general route for their synthesis. The fundamental synthetic approach is the same as reported methods for ortho‐SF5‐substituted pyridines and SF5‐substituted arenes, that is, oxidative chlorotetrafluorination of the corresponding disulfides to give pyridylsulfur chlorotetrafluorides (SF4Cl‐pyridines), followed by chloride/fluoride exchange with fluorides. However, the trick in this case is the presence on the pyridine ring of at least one fluorine atom, which is essential for the successful transformation of the disulfides into m‐and p‐SF5‐pyridines. After enabling the synthesis of an SF5‐substituted pyridine, ortho‐F groups can be efficiently substituted by C, N, S, and O nucleophiles through an SNAr pathway. This methodology provides access to a variety of previously unavailable SF5‐substituted pyridine building blocks. 相似文献
849.
Masaya Itakura Kai Ota Shohei Shibata Takayuki Inoue Yusuke Ide Masahiro Sadakane Tsuneji Sano 《Journal of Crystal Growth》2011,314(1):274-278
In this study, hydrothermal conversions of ?BEA and FAU type zeolites using various structure-directing agents were carried out. Highly crystalline and pure RUT type zeolites were obtained from both zeolites in the presence of tetramethylammonium hydroxide. There were no major differences between the characteristics of the RUT type zeolites obtained from the two starting zeolites. However, the Si/Al ratio and the crystallization rate of the RUT type zeolites were strongly dependent on both the framework structure and the Si/Al ratio of the starting zeolite. That is, the crystallization rate of the RUT type zeolite from the *BEA type zeolite did not depend on the Si/Al ratio of the starting *BEA type zeolite, whereas the crystallization rate of the RUT type zeolite from the FAU type zeolite was dependent on the Si/Al ratio of the starting FAU type zeolite. This suggests that the chemical structure and the concentration of locally ordered aluminosilicate species produced by the decomposition/dissolution of the starting zeolite can be altered by changing the framework structure of the zeolite. 相似文献
850.
Yoshihiro Shibata 《Mathematical Methods in the Applied Sciences》1995,18(11):871-895
We prove a global in time existence theorem of classical solutions of the initial boundary value problem for a non-linear thermoviscoelastic equation in a bounded domain for very smooth initial data, external forces and heat supply which are very close to a specific constant equilibrium state. Our proof is a combination of a local in time existence theorem and some a priori estimates of local in time solutions. Such a priori estimates are proved basically for suitable linear problems by using some multiplicative techniques. An exponential stability of the constant equilibrium state also follows from our proof of the existence and regularity theorems. 相似文献