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991.
The presence of an orthopyridyl substituent instead of a p-Tolyl on a chiral sulfoxide group increased drastically the asymmetric induction observed during the addition of arylmethylsulfoxide on carbonyl compounds. 相似文献
992.
Pierre Longevialle Guy Bouchoux And Yannik Hoppilliard 《Journal of mass spectrometry : JMS》1989,24(10):919-925
The neutral fragment produced in the main decomposition process of 3-amido steroids after electron impact is shown, by thermochemical arguments, to have the amide structure rather than enolamide as would be expected from a simple McLafferty rearrangement. It is proposed that the enolamide to amide tautomerization takes place during the decomposition process involving ion-neutral complexes, and is responsible for the lack of regioselectivity in the origin of the hydrogen transferred. An energy barrier of unknown origin is shown to exist in the formation of the accompanying [amide + H]+ ion. 相似文献
993.
A quantum mechanical perturbed stationary state study of the collinear collision of two identical diatomic molecules within the normal mode decomposition technique is presented. Various collision systems are investigated and are classified in three different groups according to their dynamical behaviour. 相似文献
994.
V. G. Zaetz M. Aderholz V. V. Ammosov A. E. Asratyan T. Coghen O. Erriquez V. A. Gapienko G. S. Gapienko J. Guy G. T. Jones V. S. Kaftanov U. F. Katz V. A. Korotkov S. P. Krutchinin M. A. Kubantsev P. Marage D. R. O. Morrison N. Schmitz K. E. Varvell W. Venus W. Wittek 《Zeitschrift fur Physik C Particles and Fields》1995,66(4):583-590
Most of the measured events on hydrogen, deuterium and neon targets from BEBC at CERN and the 15-foot Bubble Chamber at Fermilab are combined to measure spin-density matrix elements for 0 production in the current-fragmentation region in neutrino and antineutrino charged-current interactions. The spin-alignment parameter is found to be 0.08±0.11 for neutrino and 0.41±0.11 for antineutrino interactions. The parity-odd density matrix element Im(10+–10) is consistent with zero in both reactions. In the combined neutrino and antineutrino data an indication of parity violation is observed: Im 1–1=0.38±0.16 atx
B
>0.2,Q
2>8 GeV2 andz>0.6. 相似文献
995.
Dieter Seebach Jean-Marc Lapierre Guy Greiveldinger Konstantinos Skobridis 《Helvetica chimica acta》1994,77(7):1673-1688
Chiral triols 1 – 3 (‘tris(hydroxymethyl)methane’ derivatives), prepared from (R)-3-hydroxybutanoic acid and aldehydes, are used as center pieces of dendrimers. The triols may be employed as such or after attachment of spacers containing alkyl or aryl moieties (see 5 and 7 ). The branches combined with the original or elongated triols are those first reported by Fréchet ( 9 – 12 , benzyl ethers of 3,5-dihydroxybenzyl alcohol and bromide). In this way, 1st-, 2nd-, and 3rd-generation chiral dendrimers without ( 13 – 15 ), or with aliphatic ( 16 – 18 ) or aromatic ( 19 – 21 ) spacers are prepared. The molecular weights range from 447 to 2716 Dalton. Two of the chiral triols, i.e., 2 and 3 , are used as center pieces for chiral dendrimers containing 6 NH2, or 6 and 12 NO2 groups on the periphery ( 22 – 27 ), with 3,5-dinitrobenzoyl chloride as the branching unit. All compounds thus synthesized are of course monodisperse and are fully characterized. In some cases, the optical activity of the dendrimers indicates that conformationally chiral substructures might be present. The NH2- and NO2-substituted compounds avidly clathrate smaller molecules; they are sorbents exchanging host molecules through the gas phase. 相似文献
996.
Trapmann S Schimmel H Kramer GN Van den Eede G Pauwels J 《Journal of AOAC International》2002,85(3):775-779
Certified reference materials (CRMs) are an essenIial tool in the quality assurance of analytical measurements. They are produced, certified, and used in accordance with relevant ISO (International Organization for Standardization) and BCR (Community Bureau of Reference) guidelines. The Institute for Reference Materials and Measurements (IRMM; Geel, Belgium) has produced the first powdery genetically modified organism (GMO) CRMs in cooperation with the Institute for Health and Consumer Protection (Ispra, Italy). Until now, different weight percentages in the range of 0-5% for 4 GMOs in Europe were produced and certified: Bt (Bacillus thuringiensis)-11 and Bt-176 maize, Roundup Ready soybean, and MON810 maize. Bt-11 and Bt-176 maize and Roundup Ready soybean were produced by IRMM on behalf of Fluka Chemie AG (Buchs, Switzerland). Characterization of used base material is the first step in production and is especially important for GMO CRMs. The production of powdery GMO CRMs and methods used for production control are described. Thorough control of homogeneity and stability are essential for certification of reference materials and ensure validity of the certificate for each bottle of a batch throughout a defined shelf-life. Because production of reference materials and their maintenance are very labor- and cost-intensive tasks, the usefulness of new types of GMO CRMs must be estimated carefully. 相似文献
997.
Guy PaillotinNicholas E. Geacintov†Jacques Breton 《Photochemistry and photobiology》1983,37(4):475-478
The spatial non-uniformity of a light beam must be taken into account in interpreting phenomena which depend on the light intensity in a non-linear manner. Omission of this effect may lead to incorrect values of parameters obtained from a fitting of theoretical curves, which describe the dependence of a given phenomenon on light intensity, to the experimental data. The effect of spatial non-uniformity of excitation light beams is illustrated utilizing non-linear intensity-dependent fluorescence phenomena in photosvnthetic svstems and a Gaussian light beam profile. 相似文献
998.
Willemsen P Scippo ML Kausel G Figueroa J Maghuin-Rogister G Martial JA Muller M 《Analytical and bioanalytical chemistry》2004,378(3):655-663
We have studied stable transformed human mammary cell lines with highly inducible steroid receptor-mediated luciferase reporter gene expression. Cells responding specifically to glucocorticoids, progestagens, androgens, or estrogens are described and characterized. The use of this high-throughput, cell-based assay for analysis of steroid (ant)agonists is reported. Systematic characterization of endocrine-disrupting activity on human receptors and in a human-cell system is interpreted for a selection of xenobiotics. We show that the phytoestrogens apigenin and genistin have progestagenic and androgenic activity, respectively. Finally, application of cell-based assays to the analysis of environmental samples is discussed. 相似文献
999.
A re-investigation of resveratrol synthesis by Perkins reaction. Application to the synthesis of aryl cinnamic acids 总被引:1,自引:0,他引:1
A re-investigation of resveratrol synthesis by Perkins reaction allowed to improve this method and to determine the configuration of the intermediates. The results were applied to the synthesis of several aryl cinnamic acids for biological evaluation. 相似文献
1000.
Alcock NW Clarkson G Glover PB Lawrance GA Moore P Napitupulu M 《Dalton transactions (Cambridge, England : 2003)》2005,(3):518-527
The potentially pentadentate ligand 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine (H2L1), readily prepared from reaction of a diester of pyridine-2,6-dicarboxylic acid (H2dipic) and 2-aminomethylpyridine (ampy), shows limited tendency to form 1:1 M:L complexes with labile metal ions, although [CuL1] and [NiL1] were observed as minor species, the latter characterized by a crystal structure analysis. A mononuclear complex formed with inert Co(III) was characterized by a crystal structure as the neutral 1:2 complex [Co(L1)(HL1)] with two ligands acting as tridentate ligands, one coordinated by the central pyridine and its two flanking deprotonated amido groups, and the other by the central pyridine, one amido and one terminal pyridine group, with the remaining poorly coordinating protonated amide remaining unbound along with other terminal pyridine groups. Fe(III) is known to form a symmetrical 1:2 complex, but that complex is anionic due to binding of all four deprotonated amido groups; the unsymmetrical neutral Co(III) complex converts into a symmetrical anionic species only on heating for hours in aqueous base in the presence of activated carbon. The most remarkable tendency of H2L1, however, is towards the formation of robust double helical complexes: a dinuclear Cu(II) complex [Cu2L1(2)] forms, as well as a trinuclear Ni(II) complex [Ni(3)(L1)2(OAc)2(MeOH)2]. Moreover, in the presence of added H2dipic, the tetranuclear complex [Cu4(L1)2(dipic)2(OH2)2] is obtained. All helical complexes have been characterized by X-ray crystal structure analyses, and all crystals feature a racemic mixture of left- and right-handed double helices stabilized by inter-ligand pi-stacking (inter-ring distances of 3.2-3.8 A) of ligands which each span several metal ions. Using the chelating ligand pentane-2,4-dione (acac), each of the two pairs of adjacent monodentate ligands in [Ni3(L1)2(OAc)2(OH2)2] have been shown to be available for substitution without destroying the helical structure, to form [Ni3(L1)2(acac)2], also characterized by a crystal structure. 相似文献