全文获取类型
收费全文 | 214篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 151篇 |
力学 | 3篇 |
数学 | 23篇 |
物理学 | 45篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 19篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1942年 | 1篇 |
1938年 | 1篇 |
1933年 | 1篇 |
1929年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
61.
Albuquerque IF Bondar NF Carrigan R Chen D Cooper PS Dai Lisheng Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Li Chengze Li Yunshan Luksys M Mahon JR McCliment E Morelos A Newsom C Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng Zheng Shuchen Zhong Yuanyuan 《Physical review D: Particles and fields》1994,50(1):R18-R20
62.
Paul D. Robinson Kevin R. Smith Lori A. Vermeulen 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):o632-o634
The structure of the title compound, C14H16N2O6S2·2C6H6O2, consists of 2,2′‐(4,4′‐bipyridinium‐1,1′‐diyl)di(ethanesulfonate) molecules (with crystallographically imposed twofold symmetry) that are hydrogen bonded to each other, as well as to hydroquinone molecules, in a complex three‐dimensional motif. The orange color of the crystals is indicative of the donor–acceptor interaction between the electron‐rich hydroquinone π‐donor and the electron‐deficient bipyridinium π‐acceptor. The dihedral angle between the bipyridyl planes is 38.31 (11)°. The distance from the centroid of one of the hydroquinone molecules to the center of the bipyridinium group is 3.653 (3) Å, which is within the range typically observed for molecular complexes exhibiting charge‐transfer characteristics. 相似文献
63.
The oxidation of [RuIII(hedta)(H2O)]=(1) to its RuIV monomeric complex at a glassy carbon electrode is abserved to promote oxidation of alcohols bearing an a-hydrogen (i-PrOH benzyl alcohol,sec-phenethyl alcohol). Tertiary substitution blocks the oxidation (t-BuOH). The oxidation of the alcohols is detected by an enhancement in the current of the RuIV/III waves at potentials above 0.96V, caused by scavenging (reduction) of RuIV by the alcohols. Binuclear complexes which possess RuIV bridged by oxo to either a second RuIV or to RuIII in species of composition [LRuORuL]n−, L=hedta3−, fail to oxidize the alcohols. The terminal oxo moiety attached to RuIV is postulated to facilitate the oxidation of primary and secondary alcohols in a manner analogous to Meyer's [RuO(trpy)(bpy)]2+ catalyst. The dissociation of the (III,IV) binuclear complex into its monomers provides a pathway which increases catalytic
activity at the expense of the inactive (III, IV) binuclear complex's concentration.
TMC 2531 相似文献
64.
Lee K. Robertst Donathan G. Beasley Douglas B. Learn Lori D. Giddens John Beard Joseph W. StanfieW 《Photochemistry and photobiology》1996,63(6):874-884
Acute exposure to UV radiation causes immunosuppression of contact hypersensitivity (CH) responses. Past studies conducted with unfiltered sunlamps emitting nonsolar spectrum UV power (wavelengths below 295 nm) or using excessive UV doses have suggested sunscreens may not prevent UV-induced immunosuppression in mice. This study was thus designed to evaluate critically the effects of different UV energy spectra on the immune protection capacity of sunscreen lotions. Minimum immune suppression doses (MISD), i.e. the lowest UV dose to cause~50% suppression of the CH response to dinitrofluorobenzene in C3H mice, were established for three artificial UV sources. The MISD for each UV source was 0.25 kJ/m2 for unfiltered FS20 sunlamps (FS), 0.90 kJ/m2 for Kodacel-filtered FS20 sunlamps (KFS), which do not emit UV power at wavelengths <290 nm, and 1.35 kJ/m2 for a 1000 W filtered xenon arc lamp solar simulator. Using MISD as baseline, sunscreens with labeled sun protection factors (SPF) of 4, 8, 15 and 30 were tested with each UV source to establish their relative immune protection factors. The immune protection factor of each sunscreen exceeded its labeled SPF in tests conducted with the solar simulator, which has a UV power spectrum (295–400 nm) similar to that of sunlight. Conversely, sunscreen immune protection factors were significantly less than the labeled SPF in tests conducted with FS and KFS. Comparison of the immunosuppression effectiveness spectra showed that relatively small amounts of nonsolar spectrum UV energy, i.e. UVC (200–290 nm) and/or shorter wavelength UVB (between 290 and 295 nm), produced by FS and KFS contributes significantly to the induction of immunosuppression. For example, 36.3% and 3.5% of the total immunosuppressive UV energy from FS and KFS, respectively, lies below 295 nm. Sunscreen absorption spectra showed that transmission of immunosuppressive UV energy below 295 nm for FS was at least eight-fold higher than that for KFS. Compared to the solar simulator UV spectrum the transmission of nonsolar immunosuppressive UV energy through sunscreens was >15-fold higher for FS and ≥1.5-fold higher for KFS. These data demonstrate that relevant evaluations of sunscreen immune protection can only be obtained when tests are conducted with UV sources that produce UV power spectra similar to that of sunlight and UV doses are employed that are based on established MISD. 相似文献
65.
Zinc is an essential cofactor for type I isopentenyl diphosphate:dimethylallyl diphosphate isomerase
Isopentenyl diphosphate (IPP) isomerase catalyzes the interconversion of IPP and dimethylallyl diphosphate (DMAPP). This is an essential reaction in the mevalonate pathway for biosynthesis of isoprenoid compounds. A crystal structure of Escherichia coli type I IPP isomerase shows a his3glu2 octahedral metal binding site (Durbecq, V. et al. EMBO, 2001, 20, 1530-1537). A metal ion analysis of recombinant E. coli type I IPP isomerase purified from metal-free buffer or buffer containing 10 muM ZnCl2 and 10 muM MnCl2 indicated that the protein contained one atom of Zn2+ per molecule. The metal content and the activity of the enzyme did not change when dialyzed for 6 h against metal-free buffer but rapidly decreased upon dialysis against buffer containing o-phenanthroline. Structural and catalytic roles for Zn2+ are discussed. 相似文献
66.
William N. Setzer Show-Yee Liou Gregory E. Easterling Robbie C. Simmons Lori M. Gullion Edward J. Meehan Gregory J. Grant Gary M. Gray 《Heteroatom Chemistry》1998,9(2):123-128
The functionalized mesocyclic trithioethers, 1,4,7-trithiacyclodecane-9,9-dimethanol (10S3-diMeOH), 9 -methyl-1, 4, 7 - trithiacyclodecane - 9 -carboxylic acid (Me-10S3-acid), 1,4,7-trithiacycloundecane-9,10-diol (dihydroxy-11S3), 1,5,9-trithiacyclododecane-3,3-dimethanol (12S3-diMeOH), 3-methyl-1,5,9-trithiacyclododecane-3-carboxylic acid (Me-12S3-acid), and 1 , 5 , 9 - trit hiacyclo tride cane -11 , 12 - diol ( dihydroxy - 13S3), have been synthesized using the cesium dithiolate technique. The single-crystal X-ray structure has been determined for 3-methyl-1,5,9-trithiacyclododecane-3-carboxylic acid. The compound crystallizes in the monoclinic space group P21/n, with a = 9.513(2) Å, b = 5.706(1) Å, c = 25.70(1) Å, β = 96.50(1)°, Z = 4, and R = 0.075. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:123–128, 1998 相似文献
67.
68.
Kalovidouris SA Gama CI Lee LW Hsieh-Wilson LC 《Journal of the American Chemical Society》2005,127(5):1340-1341
We report a fucose alpha(1-2) galactose-mediated pathway for the modulation of neuronal growth and morphology. Our studies provide strong evidence for the presence of Fucalpha(1-2)Gal glycoproteins and lectin receptors in hippocampal neurons. Additionally, we show that manipulation of Fucalpha(1-2)Gal-associated proteins using small-molecule and lectin probes induces dramatic changes in neuronal morphology. These findings may provide a novel pathway to stimulate neuronal growth and regeneration. 相似文献
69.
Michael De Rosa Nicola Stepani Todd Cole Jaclyn Fried Lisa Huang-Pang Lori Peacock Michael Pro 《Tetrahedron letters》2005,46(34):5715-5717
The 2-nitrobenzenesulfonamide cleavage using a solid-phase thiophenolate reagent gives simple 2-(alkylamino)-pyrroles without the presence of the competing nucleophilic substitution product. 相似文献
70.
Sang M. Lee Lori Sharp Franz A. James Wynne 《The Journal of the Operational Research Society》1979,30(10):885-896
One of the most difficult tasks of state highway patrol administrators is allocation of manpower; i.e. determining the most effective level of operational manpower for patrol tasks. Typically, administrators resolve the allocation problem by relying on prior statistical data and by employing subjective analysis. In general, only limited systematic analyses have been applied to the problem. This paper presents an integer goal programming model for allocating highway patrolmen to road segments within a patrol region. The model is demonstrated via a case example of the Nebraska State Patrol. The results of the model are valuable to the patrol administrator for considering departmental goals and priority structure, in addition to available historical data, in the assignment of state patrol manpower. 相似文献