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61.
Creation of visible artificial optical emissions in the aurora by high-power radio waves 总被引:1,自引:0,他引:1
Generation of artificial light in the sky by means of high-power radio waves interacting with the ionospheric plasma has been envisaged since the early days of radio exploration of the upper atmosphere, with proposed applications ranging from regional night-time street lighting to atmospheric measurements. Weak optical emissions have been produced for decades in such ionospheric 'heating' experiments, where they serve as key indicators of electron acceleration, thermal heating, and other effects of incompletely understood wave-particle interactions in the plasma under conditions difficult to replicate in the laboratory. The extremely low intensities produced previously have, however, required sensitive instrumentation for detection, preventing applications beyond scientific research. Here we report observations of radio-induced optical emissions bright enough to be seen by the naked eye, and produced not in the quiet mid-latitude ionosphere, but in the midst of a pulsating natural aurora. This may open the door to visual applications of ionospheric heating technology or provide a way to probe the dynamics of the natural aurora and magnetosphere. 相似文献
62.
Apolipoprotein-mediated pathways of lipid antigen presentation 总被引:1,自引:0,他引:1
van den Elzen P Garg S León L Brigl M Leadbetter EA Gumperz JE Dascher CC Cheng TY Sacks FM Illarionov PA Besra GS Kent SC Moody DB Brenner MB 《Nature》2005,437(7060):906-910
Peptide antigens are presented to T cells by major histocompatibility complex (MHC) molecules, with endogenous peptides presented by MHC class I and exogenous peptides presented by MHC class II. In contrast to the MHC system, CD1 molecules bind lipid antigens that are presented at the antigen-presenting cell (APC) surface to lipid antigen-reactive T cells. Because CD1 molecules survey endocytic compartments, it is self-evident that they encounter antigens from extracellular sources. However, the mechanisms of exogenous lipid antigen delivery to CD1-antigen-loading compartments are not known. Serum apolipoproteins are mediators of extracellular lipid transport for metabolic needs. Here we define the pathways mediating markedly efficient exogenous lipid antigen delivery by apolipoproteins to achieve T-cell activation. Apolipoprotein E binds lipid antigens and delivers them by receptor-mediated uptake into endosomal compartments containing CD1 in APCs. Apolipoprotein E mediates the presentation of serum-borne lipid antigens and can be secreted by APCs as a mechanism to survey the local environment to capture antigens or to transfer microbial lipids from infected cells to bystander APCs. Thus, the immune system has co-opted a component of lipid metabolism to develop immunological responses to lipid antigens. 相似文献
63.
Porco CC Baker E Barbara J Beurle K Brahic A Burns JA Charnoz S Cooper N Dawson DD Del Genio AD Denk T Dones L Dyudina U Evans MW Fussner S Giese B Grazier K Helfenstein P Ingersoll AP Jacobson RA Johnson TV McEwen A Murray CD Neukum G Owen WM Perry J Roatsch T Spitale J Squyres S Thomas P Tiscareno M Turtle EP Vasavada AR Veverka J Wagner R West R 《Nature》2005,434(7030):159-168
Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titan's nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of these issues. The images reveal intricate surface albedo features that suggest aeolian, tectonic and fluvial processes; they also show a few circular features that could be impact structures. These observations imply that substantial surface modification has occurred over Titan's history. We have not directly detected liquids on the surface to date. Convective clouds are found to be common near the south pole, and the motion of mid-latitude clouds consistently indicates eastward winds, from which we infer that the troposphere is rotating faster than the surface. A detached haze at an altitude of 500 km is 150-200 km higher than that observed by Voyager, and more tenuous haze layers are also resolved. 相似文献
64.
Radisky DC Levy DD Littlepage LE Liu H Nelson CM Fata JE Leake D Godden EL Albertson DG Nieto MA Werb Z Bissell MJ 《Nature》2005,436(7047):123-127
65.
Résumé L'électrophorèse sur papier permet un fractionnement des protéines et des lipides du sang chez les souris. La distribution des diverses fractions est intermédiaire entre celle du rat et celle de l'homme. Il existe des différences entre diverses souches de souris, ainsi qu'entre souris obèses et non obèses. Les méthodes employées ici, quoique faisant ressortir les anomalises accompagnant l'obésité, ne permettent pas de différencier entre les divers types d'obésités. 相似文献
66.
Zusammenfassung Die Hemmung der Phenylpyruvat- undp-Hydroxyphenylpyruvat-Oxydasen durch Chelat-Wirkstoffe wurde offenbar durch die Bildung eines Enzym-Wirkstoff-Komplexes verursacht, der bei Behandlung mit Kationen oder mit Sephadex trennbar ist. Die Reinigung des Enzyms führt zur Kupferanreicherung des Präparates, welches eine scheinbar funktionelle Einheit mit dem Enzym bildet.
This work was supported in part by Research Grant No. MH-02278 from the National Institute of Mental Health, U.S.P.H.S.
We wish to thank Dr.W. A. Bulen for helpful discussions about the mechanism of inhibition, and Dr.M. D. Armstrong for his encouragement during this project. 相似文献
This work was supported in part by Research Grant No. MH-02278 from the National Institute of Mental Health, U.S.P.H.S.
We wish to thank Dr.W. A. Bulen for helpful discussions about the mechanism of inhibition, and Dr.M. D. Armstrong for his encouragement during this project. 相似文献
67.
Resumen Se medió glutation reducido (GSH) en glóbulos rojos de 427 ovejas pertenecientes a 6 razas diferentes. 25% de las ovejas de raza «Finnish Landrace» dieron un contenido de GSH de un tercio del valor obtenido en el resto. Datos familiares indican que esta deficiencia es heredada como un factor autosómico recesivo. En las ovejas que tienen esta deficiencia, la concentracion media de potasio en glóbulos rojos fué significativamente menor que la observada en las ovejas con niveles normales de GSH. 相似文献
68.
Linda H. Crabbe A. E. S. Gussin Elizabeth A. Tyrrell 《Cellular and molecular life sciences : CMLS》1969,25(8):793-793
Zusammenfassung Es wird gezeigt, dassBacillus cereus die Disaccharid Trehalose fermentieren kann. Die für diese Fermentwirkung benötigte Trehalase wurde durch das Substrat ermöglicht, während Puromycin den Vorgang verhinderte. Dies beweist die Notwendigkeit einer neuen Proteinsynthese.
Publication No. 1 from the Department of the Biological Sciences of Smith College.
This work was supported in part by National Science Foundation Grants to A.E.S.G. and by an Alfred P. Sloan Foundation Summer Participant Grant to L.H.C. We thank MissJudith G.Arnold for technical assistance. 相似文献
Publication No. 1 from the Department of the Biological Sciences of Smith College.
This work was supported in part by National Science Foundation Grants to A.E.S.G. and by an Alfred P. Sloan Foundation Summer Participant Grant to L.H.C. We thank MissJudith G.Arnold for technical assistance. 相似文献
69.
70.
Vernal pools are seasonal pools occurring in Mediterranean-type climates within which grow concentric zones of vegetation. We studied two vernal pools that lie within an Artemisia tridentata/Festuca idahoensis shrub-steppe landscape in the Channeled Scabland of eastern Washington to determine the relationship between vegetation zonation and soil characteristics. Abundant plant species in the pools include Elymus cinereus, Poa scabrella, Lomatium grayi, Allium geyeri, Eleocharis palustris, Epilobium minutum, Myosurus aristatis, Deschampsia danthonioides, and Psilocarphus oregonus . We surveyed topography, measured plant species frequency and cover to describe the vegetation zones, and used Sorenson's index of percent to similarity to verify our designation of plant zones as communities. In one pool we described soil profiles and sampled soils throughout the growing season according to plant communities. We analyzed soils for pH; electrical conductivity; sodium, calcium, and magnesium ions; sodium absorption ratio; particle size; organic carbon; and water matric potential. ANOVA tests of soil characteristics and topography among plant communities showed that only differences in topography are statistically significant. There are, however, trends in particle size, some soil chemical parameters, and soil moisture potential among plant communities along the topographic gradient. Electrical conductivity decreased with increasing dryness of the soil through spring and summer. Seasonal changes in soil moisture potential showed that shallower soils in the centers of pools were wetter during the wet season and drier during the dry season than are deeper soils. These changes in moisture may be the most important influence on vegetation distribution within the vernal pools. 相似文献