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21.
J. Rasmussen O. K. Albrechtsen T. Astrup 《Cellular and molecular life sciences : CMLS》1970,26(8):841-842
Zusammenfassung Nach Abbindung des Rattenuterus wird bei relativ grosser individueller Streubreite ein fibrinolytisch hochaktives Sekret produziert. Die Aktivität wird durch einen in verschiedenen Konzentrationen vorhandenen Plasminogenaktivator, der vermutlich im Oberflächenepithel des Endometriums gebildet wird, verursacht. 相似文献
22.
High-resolution record of Northern Hemisphere climate extending into the last interglacial period 总被引:4,自引:0,他引:4
Andersen KK Azuma N Barnola JM Bigler M Biscaye P Caillon N Chappellaz J Clausen HB Dahl-Jensen D Fischer H Flückiger J Fritzsche D Fujii Y Goto-Azuma K Grønvold K Gundestrup NS Hansson M Huber C Hvidberg CS Johnsen SJ Jonsell U Jouzel J Kipfstuhl S Landais A Leuenberger M Lorrain R Masson-Delmotte V Miller H Motoyama H Narita H Popp T Rasmussen SO Raynaud D Rothlisberger R Ruth U Samyn D Schwander J Shoji H Siggard-Andersen ML Steffensen JP Stocker T Sveinbjörnsdóttir AE Svensson A Takata M 《Nature》2004,431(7005):147-151
Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time. 相似文献
23.
Filamentous microfossils in a 3,235-million-year-old volcanogenic massive sulphide deposit 总被引:7,自引:0,他引:7
Rasmussen B 《Nature》2000,405(6787):676-679
The record of Archaean microfossils is sparse. Of the few bona fide fossil assemblages, most are from shallow-water settings, and they are typically associated with laminated, stromatolitic sedimentary rocks. Microfossils from deep-sea hydrothermal systems have not been reported in Precambrian rocks (> 544 million years old), although thermophilic microbes are ubiquitous in modern sea-floor hydrothermal settings, and apparently have the most ancient lineages. Here, I report the discovery of pyritic filaments, the probable fossil remains of thread-like microorganisms, in a 3,235-million-year-old deep-sea volcanogenic massive sulphide deposit from the Pilbara Craton of Australia. From their mode of occurrence, the micro-organisms were probably thermophilic chemotropic prokaryotes, which inhabited sub-sea-floor hydrothermal environments. They represent the first fossil evidence for microbial life in a Precambrian submarine thermal spring system, and extend the known range of submarine hydrothermal biota by more than 2,700 million years. Such environments may have hosted the first living systems on Earth, consistent with proposals for a thermophilic origin of life. 相似文献
24.
Chemical characterization of element 112 总被引:1,自引:0,他引:1
Eichler R Aksenov NV Belozerov AV Bozhikov GA Chepigin VI Dmitriev SN Dressler R Gäggeler HW Gorshkov VA Haenssler F Itkis MG Laube A Lebedev VY Malyshev ON Oganessian YTs Petrushkin OV Piguet D Rasmussen P Shishkin SV Shutov AV Svirikhin AI Tereshatov EE Vostokin GK Wegrzecki M Yeremin AV 《Nature》2007,447(7140):72-75
The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of (283)112 through the alpha decay of the short-lived (287)114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of (283)112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides. 相似文献
25.
Friesen TL Stukenbrock EH Liu Z Meinhardt S Ling H Faris JD Rasmussen JB Solomon PS McDonald BA Oliver RP 《Nature genetics》2006,38(8):953-956
New diseases of humans, animals and plants emerge regularly. Enhanced virulence on a new host can be facilitated by the acquisition of novel virulence factors. Interspecific gene transfer is known to be a source of such virulence factors in bacterial pathogens (often manifested as pathogenicity islands in the recipient organism) and it has been speculated that interspecific transfer of virulence factors may occur in fungal pathogens. Until now, no direct support has been available for this hypothesis. Here we present evidence that a gene encoding a critical virulence factor was transferred from one species of fungal pathogen to another. This gene transfer probably occurred just before 1941, creating a pathogen population with significantly enhanced virulence and leading to the emergence of a new damaging disease of wheat. 相似文献
26.
Lindblad-Toh K Garber M Zuk O Lin MF Parker BJ Washietl S Kheradpour P Ernst J Jordan G Mauceli E Ward LD Lowe CB Holloway AK Clamp M Gnerre S Alföldi J Beal K Chang J Clawson H Cuff J Di Palma F Fitzgerald S Flicek P Guttman M Hubisz MJ Jaffe DB Jungreis I Kent WJ Kostka D Lara M Martins AL Massingham T Moltke I Raney BJ Rasmussen MD Robinson J Stark A Vilella AJ Wen J Xie X Zody MC;Broad Institute Sequencing Platform Whole Genome Assembly Team Baldwin J Bloom T Chin CW Heiman D Nicol R 《Nature》2011,478(7370):476-482
The comparison of related genomes has emerged as a powerful lens for genome interpretation. Here we report the sequencing and comparative analysis of 29 eutherian genomes. We confirm that at least 5.5% of the human genome has undergone purifying selection, and locate constrained elements covering ~4.2% of the genome. We use evolutionary signatures and comparisons with experimental data sets to suggest candidate functions for ~60% of constrained bases. These elements reveal a small number of new coding exons, candidate stop codon readthrough events and over 10,000 regions of overlapping synonymous constraint within protein-coding exons. We find 220 candidate RNA structural families, and nearly a million elements overlapping potential promoter, enhancer and insulator regions. We report specific amino acid residues that have undergone positive selection, 280,000 non-coding elements exapted from mobile elements and more than 1,000 primate- and human-accelerated elements. Overlap with disease-associated variants indicates that our findings will be relevant for studies of human biology, health and disease. 相似文献
27.
28.
E. C. Frederick M. F. Hamant S. A. Rasmussen A. K. Chan G. E. Goslow Jr 《Cellular and molecular life sciences : CMLS》1978,34(3):372-374
Summary Single motor units in striped skunk medial gastrocnemias were isolated and physiologically characterized. Individual muscle unit fibres tagged by glycogen depletion were analyzed histochemically and found to have histochemical profiles consistently correlated with the physiological findings.This work was supported by the Organized Research Committee, Northern Arizona University. 相似文献
29.
Effect of microtubular antagonists on lymphocyte mitogenesis 总被引:2,自引:0,他引:2
30.
Amole C Ashkezari MD Baquero-Ruiz M Bertsche W Bowe PD Butler E Capra A Cesar CL Charlton M Deller A Donnan PH Eriksson S Fajans J Friesen T Fujiwara MC Gill DR Gutierrez A Hangst JS Hardy WN Hayden ME Humphries AJ Isaac CA Jonsell S Kurchaninov L Little A Madsen N McKenna JT Menary S Napoli SC Nolan P Olchanski K Olin A Pusa P Rasmussen CØ Robicheaux F Sarid E Shields CR Silveira DM Stracka S So C Thompson RI van der Werf DP Wurtele JS 《Nature》2012,483(7390):439-443
The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves. 相似文献