全文获取类型
收费全文 | 325篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 150篇 |
晶体学 | 1篇 |
力学 | 17篇 |
数学 | 36篇 |
物理学 | 123篇 |
出版年
2016年 | 3篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 16篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1966年 | 2篇 |
1920年 | 2篇 |
1910年 | 5篇 |
1909年 | 8篇 |
1908年 | 2篇 |
1907年 | 4篇 |
1906年 | 4篇 |
1905年 | 2篇 |
1904年 | 9篇 |
1900年 | 2篇 |
1892年 | 2篇 |
1888年 | 5篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
1.
Thorsten Hamann Erin Osborne Heather L. Youngs Julie Misson Laurent Nussaume Chris Somerville 《Cellulose (London, England)》2004,11(3-4):279-286
We have used Affymetrix gene chips to measure the expression of 10 CESA and 29 CSL genes of Arabidopsis in different developmental stages or organs. These measurements reveal that many of the genes exhibit different levels of expression in the various organs. While several CESA genes are highly expressed in all the tissues examined, very few CSL genes approach such high levels of expression. This suggests that the CSL genes either encode enzymes for the synthesis of minor components of cell walls or are expressed only in specific cell types. The expression data also highlights the potential importance of the CESA genes for primary and secondary cell wall formation during different developmental stages and in the different organs examined. 相似文献
2.
Given one or more vibrational modes of a membrane, the free vibration equation can be applied to infer the mass surface density. This paper considers determining the surface density of an inhomogeneous membrane from digitized holographic projections (interferograms) of the modeshapes. Spatially discrete numerical models of the membrane surface are presented, which can be used to solve both forward and inverse vibration problems. The accuracy of the discrete models is examined for exactly solvable free vibration problems involving inhomogeneous membranes. For the solution of the inverse problem, error estimates are given for the mass surface density deduced from modeshape interferograms. The practicability of the method is investigated using simulated experimental data for membranes with composite and continuously inhomogeneous density profiles. Strategies are discussed for reducing errors in the reconstructed densities. 相似文献
3.
Jo E Sanna MG Gonzalez-Cabrera PJ Thangada S Tigyi G Osborne DA Hla T Parrill AL Rosen H 《Chemistry & biology》2005,12(6):703-715
The essential role of the sphingosine 1-phosphate (S1P) receptor S1P(1) in regulating lymphocyte trafficking was demonstrated with the S1P(1)-selective nanomolar agonist, SEW2871. Despite its lack of charged headgroup, the tetraaromatic compound SEW2871 binds and activates S1P(1) through a combination of hydrophobic and ion-dipole interactions. Both S1P and SEW2871 activated ERK, Akt, and Rac signaling pathways and induced S1P(1) internalization and recycling, unlike FTY720-phosphate, which induces receptor degradation. Agonism with receptor recycling is sufficient for alteration of lymphocyte trafficking by S1P and SEW2871. S1P(1) modeling and mutagenesis studies revealed that residues binding the S1P headgroup are required for kinase activation by both S1P and SEW2871. Therefore, SEW2871 recapitulates the action of S1P in all the signaling pathways examined and overlaps in interactions with key headgroup binding receptor residues, presumably replacing salt-bridge interactions with ion-dipole interactions. 相似文献
4.
Adams MR Aïd S Anthony PL Averill DA Baker MD Baller BR Banerjee A Bhatti AA Bratzler U Braun HM Breidung H Busza W Carroll TJ Clark HL Conrad JM Davisson R Derado I Dhawan SK Dietrich FS Dougherty W Dreyer T Eckardt V Ecker U Erdmann M Faller F Fang GY Figiel J Finlay RW Gebauer HJ Geesaman DF Griffioen KA Guo RS Haas J Halliwell C Hantke D Hicks KH Hughes VW Jackson HE Jancso G Jansen DM Jin Z Kaufman S Kennedy RD Kinney ER Kirk T Kobrak HG Kotwal AV Kunori S Lancaster S Lord JJ Lubatti HJ 《Physical review letters》1995,74(9):1525-1529
5.
Lazarus EA Navratil GA Greenfield CM Strait EJ Austin ME Burrell KH Casper TA Baker DR DeBoo JC Doyle EJ Durst R Ferron JR Forest CB Gohil P Groebner RJ Heidbrink WW Hong R Houlberg WA Howald AW Hsieh C Hyatt AW Jackson GL Kim J Lao LL Lasnier CJ Leonard AW Lohr J La Haye RJ Maingi R Miller RL Murakami M Osborne TH Perkins LJ Petty CC Rettig CL Rhodes TL Rice BW Sabbagh SA Schissel DP Scoville JT Snider RT Staebler GM Stallard BW Stambaugh RD St John HE Stockdale RE Taylor PL Thomas DM 《Physical review letters》1996,77(13):2714-2717
6.
7.
Bulloch EM Jones MA Parker EJ Osborne AP Stephens E Davies GM Coggins JR Abell C 《Journal of the American Chemical Society》2004,126(32):9912-9913
(6S)-6-Fluoroshikimate has antimicrobial activity. The molecular basis of this effect had not been identified, but there was speculation that (6S)-6-fluoroshikimate is first converted in vivo into 2-fluorochorismate, which then could inhibit 4-amino-4-deoxychorismate synthase (ADCS). 2-Fluorochorismate was prepared from E-fluorophosphoenolpyruvate and erythose-4-phosphate by the sequential reactions of DAHP synthase, dehydroquinate synthase, dehydroquinase, shikimate dehydrogenase, EPSP synthase, and chorismate synthase. Inhibition studies on ADCS showed that it was inhibited rapidly and irreversibly by 2-fluorochorismate. Electrospray mass spectrometry of the inactivated enzyme showed an additional mass of 198 +/- 10 Da. A novel peptide of 1087.6 Da was identified in the HPLC trace for the tryptic digest of 2-fluorochorismate-inactivated ADCS. Sequencing of this peptide by MS/MS showed that the peptide corresponded to residues 272-279 with a modification of 206.1 Da on Lys-274. This observation is particularly exciting in the context of a recent proposal for the catalytic mechanism of ADCS. 相似文献
8.
McCaffery AJ Osborne MA Marsh RJ Lawrance WD Waclawik ER 《The Journal of chemical physics》2004,121(1):169-180
Vibrational relaxation of the 6(1) level of S(1)((1)B(2u)) benzene is analyzed using the angular momentum model of inelastic processes. Momentum-(rotational) angular momentum diagrams illustrate energetic and angular momentum constraints on the disposal of released energy and the effect of collision partner on resultant benzene rotational excitation. A kinematic "equivalent rotor" model is introduced that allows quantitative prediction of rotational distributions from inelastic collisions in polyatomic molecules. The method was tested by predicting K-state distributions in glyoxal-Ne as well as J-state distributions in rotationally inelastic acetylene-He collisions before being used to predict J and K distributions from vibrational relaxation of 6(1) benzene by H(2), D(2), and CH(4). Diagrammatic methods and calculations illustrate changes resulting from simultaneous collision partner excitation, a particularly effective mechanism in p-H(2) where some 70% of the available 6(1)-->0(0) energy may be disposed into 0-->2 rotation. These results support the explanation for branching ratios in 6(1)-->0(0) relaxation given by Waclawik and Lawrance and the absence of this pathway for monatomic partners. Collision-induced vibrational relaxation in molecules represents competition between the magnitude of the energy gap of a potential transition and the ability of the colliding species to generate the angular momentum (rotational and orbital) needed for the transition to proceed. Transition probability falls rapidly as DeltaJ increases and for a given molecule-collision partner pair will provide a limit to the gap that may be bridged. Energy constraints increase as collision partner mass increases, an effect that is amplified when J(i)>0. Large energy gaps are most effectively bridged using light collision partners. For efficient vibrational relaxation in polyatomics an additional requirement is that the molecular motion of the mode must be capable of generating molecular rotation on contact with the collision partner in order to meet the angular momentum requirements. We postulate that this may account for some of the striking propensities that characterize polyatomic energy transfer. 相似文献
9.
Summary Existing tests for differentiating carbonate and hydrogen carbonate are shown to be unreliable. New tests have been developed which enable carbonate and hydrogen carbonate to be differentiated readily; cyanate and other anions may also be tested for in the mixture. The recommended tests are applicable in the presence of other anions.Preliminary water extraction is done to remove hydrogen carbonates and soluble carbonates and cyanates. The insoluble portion is then treated with hydrochloric acid; the evolution of carbon dioxide confirms insoluble carbonates or cyanates. The latter are confirmed by making the solution alkaline and testing for ammonia. Insoluble carbonate is tested for by extracting another portion of the sample with water and treating the residue with acetic acid. Cyanates do not react under these conditions.The original water extract is divided into three parts: one portion is treated with hydrochloric acid; the evolution of carbon dioxide indicates that any of the three ions may be present. A further portion is treated with phenolphthalein. The red colour indicates soluble carbonate. Barium chloride is added until the colour is discharged; slow evolution of carbon dioxide in the cold or on gently warming indicates the presence of hydrogen carbonate. The third portion is made alkaline and boiled to expel any ammonia present from ammonium salts. The solution is then acidified, made alkaline again and then tested for ammonia. A positive test indicates that soluble cyanates are present.
Part XIX: Mikrochim. Acta [Wien]1964, 179. 相似文献
Zusammenfassung Bekannte Reaktionen zur Unterscheidung von Carbonat und Hydrogencarbonat erwiesen sich als ungeeignet. Daher wurden neue Tests ausgearbeitet; Cyanat und andere Anionen können dabei gleichfalls nachgewiesen werden.Zunächst wird zur Entfernung von Hydrogencarbonat, löslichen Carbonaten und Cyanaten mit Wasser extrahiert. Der unlösliche Anteil wird mit Salzsäure behandelt; die Freisetzung von Kohlendioxid zeigt unlösliche Carbonate oder Cyanate an. Letztere werden nachgewiesen, indem man alkalisiert und auf Ammoniak prüft. Unlösliche Carbonate sind durch Extraktion einer weiteren Probe mit Wasser und Ansäuern des Rückstandes mit Essigsäure nachweisbar. Cyanate reagieren unter diesen Bedingungen nicht.Der wäßrige Extrakt wird in drei Teile geteilt. Ein Teil wird mit Salzsäure behandelt; Kohlendioxidentwicklung zeigt die Gegenwart einer der drei Ionenarten an. Ein weiterer Teil gibt mit Phenolphthalein Rotfärbung, wenn lösliche Carbonate vorliegen. Man setzt Bariumchlorid bis zur Entfärbung zu: langsame Kohlendioxidentwicklung in der Kälte oder bei leichtem Erwärmen zeigt Hydrogencarbonat an. Der dritte Teil wird alkalisiert und durch Kochen vollständig von Ammoniak aus Ammoniumsalzen befreit. Dann säuert man an, alkalisiert wieder und prüft auf Ammoniak. Ein positives Ergebnis zeigt das Vorhandensein löslicher Cyanate an.
Résumé On montre que les procédés de recherche qui existent actuellement pour différencier le carbonate de l'hydrogéno-carbonate ne sont pas exacts. On a mis au point de nouvelles réactions permettant de distinguer rapidement un carbonate d'un hydrogéno-carbonate; on peut aussi rechercher les cyanates et d'autres anions dans le mélange. Les procédés de recherche que l'on recommande peuvent s'appliquer en présence d'autres anions.On effectue l'extraction préliminaire par l'eau pour séparer les hydrogénocarbonates, les carbonates solubles et les cyanates. La partie insoluble est alors traitée par l'acide chlorhydrique; le dégagement de gaz carbonique indique la présence de carbonates ou de cyanates insolubles. On confirme l'existence de ces derniers en rendant la solution basique et en faisant l'essai á l'ammoniac. On caractérise les carbonates insolubles en extrayant par l'eau une autre portion de l'échantillon et en traitant le résidu par l'acide acétique. Les cyanates ne réagissent pas dans ces conditions.L'extrait par l'eau initial est divisé en trois parties: l'une est traitée par l'acide chlorhydrique; le dégagement de gaz carbonique indique que l'un des trois ions peut être présent. Une autre est traitée par la phénolphtaléine. L'apparition d'une coloration rouge indique un carbonate soluble. On ajoute du chlorure de baryum jusqu'á disparition de la coloration; un faible dégagement de gaz carbonique á froid ou sous chauffage doux montre la présence d'un hydrogéno-carbonate. La troisiéme partie est rendu alcaline et soumise á l'ébullition pour éliminer l'ammoniac des sels d'ammonium. On acidifie alors la solution, on la rend de nouveau alcaline et on fait ensuite l'essai á l'ammoniac. Une réaction positive indique la présence de cyanates solubles.
Part XIX: Mikrochim. Acta [Wien]1964, 179. 相似文献