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151.
Takeda Y Okumura S Minakata S 《Angewandte Chemie (International ed. in English)》2012,51(31):7804-7808
It's all the hype: An oxidative dimerization reaction of aromatic amines utilizing tert-butyl hypoiodite (tBuOI) under mild reaction conditions leads to aromatic azo compounds. The method allows access to unsymmetric aromatic azo compounds, which are difficult to prepare by conventional synthetic methods, in a selective manner. 相似文献
152.
153.
The three-component direct Mannich reaction between aldehydes, p-toluenesulfonamide, and enolizable ketones was achieved for the first time with organic bases as the catalysts. The corresponding N-tosylated β-aminoketones were obtained in high yields and good to excellent diastereoselectivities using TMG as the catalyst. Through reduction of the ketone group, the reaction product may be converted into β-aminol with excellent diastereoselectivity. 相似文献
154.
《Journal of Coordination Chemistry》2012,65(1-2):95-106
Abstract A cobalt(III) complex containing (R)-2-methylaziridine (R-meaz), [Co(R-meaz)(NH3)5]3+, was prepared and the two diastereomers arising from the presence of the chiral nitrogen atom (N(R) and N(S)) were separated by column chromatography. Molecular mechanics calculations estimated the N(R)-isomer to be more stable. This result was supported by the x-ray structure determination of the more abundant (ca. 94%) isomer, N(R)-[Co(R-meaz)(NH3)5]Br3H2O. Crystal data: monoclinic, P21, a = 7.357(1), b = 9.780(1), c = 10.426(1) Å, μ = 93.58(1)°, V= 748.7(3) Å3, Z= 2. Kinetic studies of isomerization (epimerization) between the two isomers revealed that inversion at the nitrogen center was very slow (5 × 10?2 M?1 S?1at 25 °C). The small rate constant seems to be related to the strained three-membered structure of the meaz ligand. The reaction of Na3[Co(N02)6] and R-meaz yielded a complex containing two dimerized R-meaz chelates, trans-[Co(NO2)2(di-R-meaz)2] (di-R-meaz =RR)-α,2-dimethyl-l-aziridineethanamine). The crystal strucrure of trans-[Co(NO2)2 (di-R-meaz)2]C1O4H2O was established by x-ray crystallography. Crystal data: orthorhombic, P212121, a = 11.784(6), b = 21.023(9), c = 8.608(7) Å, V = 2133(2) Å3, Z = 4. 相似文献
155.
Chelation-controlled addition of organocuprates to N-carbamoyl aminoaldehydes, prepared from functionalized amino acids, generated predominately the threo-β-amino alcohol derivatives through chelation with the carbamoyl moiety. The carbamate group is a stronger chelating group than other potentially good chelators, for example ethers, esters, thioethers, and gives good diastereoselectivity with cuprates. Thus addition of lithium divinylcuprate to the aldehyde generated from the serine derivative 25 in the presence of extra copper for chelation afforded the threo compound 26 in 83% yield. Cross-metathesis and cleavage of the protecting groups furnished l-threo sphingosine 21. In addition the lyso-sphingolipid protein kinase C inhibitor, safingol, 22, was prepared from commercially available O-benzyl N-BOC serine 28 in six steps and 56% overall yield by this method. 相似文献
156.
We have postulated a novel pathway that could assist in the nucleation of soot particles through covalent dimerization and oligomerizations of a variety of PAHs. DFT calculations were performed with the objective of obtaining the relative thermal stabilities and formation probabilities of oligomeric species that exploit the facile dimerization that is known to occur in linear oligoacenes. We propose that the presence of small stretches of linear oligoacence (tetracene or longer) in extended PAH, either embedded or tethered, would be adequate for enabling the formation of such dimeric and oligomeric adducts; these could then serve as nuclei for the growth of soot particles. Our studies also reveal the importance of π‐stacking interactions between extended aromatic frameworks in governing the relative stabilities of the oligomeric species that are formed. © 2012 Wiley Periodicals, Inc. 相似文献
157.
Viktor Háda Antal Tungler László Szepesy 《Reaction Kinetics and Catalysis Letters》2001,73(1):109-115
High diastereoselectivities were obtained in the heterogeneous catalytic hydrogenation of chiral pyrrole and pyridine derivatives with complete conversion, in non-acidic medium. The products of the hydrogenations, secondary and tertiary amines act as catalyst modifiers, increasing the d.e. values in the last period of the reactions. 相似文献
158.
E. I. Klimova M. Martinez Garcia T. Klimova L. Ruiz Ramirez J. M. Mendez Stivalet N. N. Meleshonkova 《Russian Chemical Bulletin》2000,49(3):514-519
3,5-Bis(ferrocenylmethylene)-1-methyl-4-methylenepiperidine, a diferrocenyltriene with a fixeds-cisoid conformation of the exocyclic double bonds, was synthesized. On heating, this compound cyclodimerizes according to
the [4+2]-cycloaddition scheme; it forms Diels-Alder adducts with azodicarboxylic and maleic acidN-phenylimides. The compound easily cyclodimerizes in the presence of acids by a proton cyclodimerization mechanism to give
a spiro cyclodimer. The triene also adds a 3,5-bis(ferrocenylmethylene)-1,4-dimethyl-1-azonia-4-cyclohexyl salt to the terminal
methylene group yielding linear and cyclic addition products.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 511–516, March, 2000. 相似文献
159.
Ion Grosu Loïc Toupet Gerard Plé Sorin Mager Eugen Mesaros Andreea Varga Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2000,131(3):277-286
Summary. The synthesis and stereochemistry of new dibrominated spiro-1,3-dioxane derivatives are reported. Investigations by means
of NMR methods and single crystal X-ray diffraction for two compounds revealed the high regio- and diastereoselectivity of
the bromination reaction of some new spiro-1,3-dioxanes and the asymmetric induction of the chiral carbon atom located in
the spiro skeleton.
Received July 13, 1999. Accepted October 21, 1999 相似文献
160.
The influences of Dzyaloshinskii Moriya (DM) interaction and Kaplan-Shekhtman-Entinwohlman-Aharony (KSEA) interaction on the dimerization of a spin-Peierls system are investigated theoretically by using the Lanczos numerical method. The ground state of the spin-Peierls system is still dimerized phase when both of the DM and the KSEA interactions have the same value with Heisenberg interaction. It is found that the KSEA interaction and uniform DM interaction are always against systemic dimerization, but the staggered DM interaction acts in favour of dimerization. Furthermore, the influences of the DM and the KSEA interactions are also studied in terms of the ground state index rate and the energy gap index rate of the dimerized Heisenberg system. The results show that the DM interaction makes the index rates larger, while the KSEA interaction makes them smaller. 相似文献