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251.
The use of a Co(porphyrin)-amide ligand, , in the palladium(II)-catalyzed 1,4-diacetoxylation of conjugated dienes under O2 results in aerobic oxidation. The catalyst was highly active under O2, and the 1,4-diacetoxylation reaction could also be performed under air. 相似文献
252.
Baraldi A Giacomello D Rumiz L Moretuzzo M Lizzit S Buatier de Mongeot F Paolucci G Comelli G Rosei R Nieuwenhuys BE Valbusa U Kiskinova MP 《Journal of the American Chemical Society》2005,127(15):5671-5674
The changes in the surface composition of a Pt(50)Rh(50)(100) alloy due to an ongoing 2H(2) + O(2)-->2H(2)O chemical reaction have been studied in situ. Exploiting the high-energy resolution and surface sensitivity of synchrotron radiation core-level spectroscopy it was possible to monitor the population of the two transitions metals atoms at the gas-surface interface. Sequences of fast high-resolution core-level spectra of the Rh3d(5/2), Pt4f(7/2), and O1s core levels showed a continuous exchange of atoms between the first and subsurface layers. An unexpected Pt surface enrichement was found under slightly oxidizing conditions, opposite to what found in a highly oxidizing atmosphere. 相似文献
253.
Florio S Perna FM Luisi R Barluenga J Fañanás FJ Rodríguez F 《The Journal of organic chemistry》2004,69(26):9204-9207
The diastereoselective synthesis of pentacarbonyl-3-oxa-2-bicyclo[3.1.0]hexylidene- and pentacarbonyl(cyclopropylmethoxymethylene)tungsten compounds 4 and 9 by the reaction of lithiated oxazolinyloxiranes 2 and 8 and Fischer carbene tungsten complexes 3 is described. A mechanism for the formation of 4 and 9 is reported as well as their oxidation to cyclopropane-gamma-lactone 13 and -carboxylate 14. 相似文献
254.
[reaction: see text]. Stereospecific beta-lithiation of beta-aryl-substituted oxazolinyloxiranes is described. The trapping reaction of such reactive intermediates with carbonyl compounds gave alpha,beta-epoxy-gamma-butyrolactones after deblocking of the oxazoline moiety. This methodology has been also extended to the synthesis of optically active alpha,beta-epoxy-gamma-butyrolactones. 相似文献
255.
5-(3-Buten-l-ynyl)-2,2'-bithienyl (1a), a natural product first isolated from Tagetes roots which shows nematicidal and photo-induced fungicidal activity, and 2-phenyl-5-(3-buten-l-ynyl) thiophen (1b) have been synthesized using two different methods. The first one (Method A) involves the palladium-catalyzed cross-coupling of vinyl bromide with the Grignard reagents derived from 5-ethynyl-2,2'-bithienyl (6a) and 2-ethynyl-5-phenylthiophen (6b). The second method (Method B) utilizes the coupling reaction of vinyl bromide with 6a and 6b, respectively, in the presence of a catalytic amount of (PPh3)4Pd and CuI. Such reaction, which was carried out under phase-transfer conditions employing BnEt3N+Cl- as phase transfer agent and 2.5NaqNaOH as base, has been also employed to prepare a large number of heterocyclic acetylene derivatives including some naturally-occurring compounds. The experimetal conditions of Method B allow also the direct production of heterocyclic acetylene derivatives (1) starting from 1-alkynyltrimethylsilanes (5) and organic halides (2). 相似文献
256.
Celestino Angeli Mariachiara Pastore Renzo Cimiraglia 《Theoretical chemistry accounts》2007,117(5-6):743-754
The n-electron valence state perturbation theory (NEVPT) is a form of multireference perturbation theory which is based on a zero
order reference wavefunction of CAS-CI type (complete active space configuration interaction) and which is characterized by
the utilization of correction functions (zero order wavefunctions external to the CAS) of multireference nature, obtained
through the diagonalization of a suitable two-electron model Hamiltonian (Dyall’s Hamiltonian) in some well defined determinant
spaces. A review of the NEVPT approach is presented, starting from the original second order state-specific formulation, going
through the quasidegenerate multi-state extension and arriving at the recent implementations of the third order in the energy
and of the internally contracted configuration interaction. The chief properties of NEVPT—size consistence and absence of
intruder states—are analyzed. Finally, an application concerning the calculation of the vertical spectrum of the biologically
important free base porphin molecule, is presented. 相似文献
257.
Lithiated N-sulfonyloxazolinylaziridines 6a and 7a, generated by deprotonation of the corresponding aziridines 6 and 7 with sec-BuLi/TMEDA at −98°C in THF, were found to be chemically and configurationally stable to be stereospecifically captured by electrophiles, while warming up to rt resulted in the formation of oxazolinylazirine 15. In contrast, lithiation of N-phenyloxazolinylaziridines 8 and 9 led to oxazolinylenamine 18. Tricyclic aziridines 10 and 11 resulted from an intramolecular addition of the aziridinyllithium 6a to the phenyl ring of the benzenesulfonyl group. 相似文献
258.
Béni Z Ros R Tassan A Scopelliti R Roulet R 《Dalton transactions (Cambridge, England : 2003)》2005,(2):315-325
The reaction of [Pt3(mu-CO)3(PCy3)3](1) with one mole-equivalent of iodo-acetonitrile was quantitative at -70 degrees C giving the oxidative addition product [Pt3(mu-CO)3(PCy3)3(I)(CH2CN)](2). Fragmentation of was observed in solution giving [Pt2I(CH2CN)(CO)2(PCy3)2](3) which is the major product at room temperature if the starting cluster/reactant ratio is equal to or less than 1 to 1.5. Dimer 3 decomposes slowly in solution giving [Pt2I2(CO)2(PCy3)2](4a) and succinonitrile. Monomer [PtI(CH2CN)(CO)(PCy3)] was the final product of the reaction when using excess of iodo-acetonitrile. The reactions of with one mole-equivalent of halogens X2 gave the new 44-electron clusters [Pt3X(micro-CO)2(micro-X)(PCy3)3](X = I2(7a) or Br2(7b)) by oxidative addition followed by substitution of CO by X-. Fragmentation of and took place in solution when using one and a half mole-equivalents of X2 giving dimers 4a and [Pt2Br2(CO)2(PCy3)2](4b) as well as [Pt2X2(mu-X)2(CO)2(PCy3)2]. Monomers cis-[PtX2(CO)(PCy3)] were the final products of the reaction of with excess of halogens. Insertion of SnCl2 was observed into the Pt-Pt bond but not into the Pt-X bond, when equimolar amounts of SnCl2 x 2H2O were added to a solution of 4a or its chloro-analogue giving [Pt2X2(micro-SnCl2)(CO)2(PCy3)2]. The Pt(I) dimers have unusually small J(Pt-Pt) values as observed by 195Pt NMR and calculated by DFT. These values showed periodic changes comparing 4a and its analogues with other halides and mixed halide dimers. 相似文献
259.
The ortho lithiation-trapping sequence of phenylaziridines is described. This methodology, which counts on the ability of the aziridino group to act as a directed metalation group (DMG), provides an easy access to functionalized arylaziridines as well as to phthalans and phthalides. The importance of the aziridine N-substituent in this DoM reaction is stressed as well. [reaction: see text] 相似文献
260.
The lowest excited states of the diimide molecule have been calculated by three different SCF-type methods, the performances of which are analyzed in regard to the prediction of geometries and energies. The calculations have been performed with two basis sets (STO-3G and 4-31G) both supplemented with more diffuse functions on the N atoms. Lowest energy pathways for thetrans-cis interconversion in the various states are presented for the three calculation methods and for the two basis sets. 相似文献