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721.
The first hominin of Europe 总被引:3,自引:0,他引:3
Carbonell E Bermúdez de Castro JM Parés JM Pérez-González A Cuenca-Bescós G Ollé A Mosquera M Huguet R van der Made J Rosas A Sala R Vallverdú J García N Granger DE Martinón-Torres M Rodríguez XP Stock GM Vergès JM Allué E Burjachs F Cáceres I Canals A Benito A Díez C Lozano M Mateos A Navazo M Rodríguez J Rosell J Arsuaga JL 《Nature》2008,452(7186):465-469
The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins. 相似文献
722.
723.
Fruchter AS Levan AJ Strolger L Vreeswijk PM Thorsett SE Bersier D Burud I Castro Cerón JM Castro-Tirado AJ Conselice C Dahlen T Ferguson HC Fynbo JP Garnavich PM Gibbons RA Gorosabel J Gull TR Hjorth J Holland ST Kouveliotou C Levay Z Livio M Metzger MR Nugent PE Petro L Pian E Rhoads JE Riess AG Sahu KC Smette A Tanvir NR Wijers RA Woosley SE 《Nature》2006,441(7092):463-468
When massive stars exhaust their fuel, they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. On occasion, this stellar collapse also powers an even more brilliant relativistic explosion known as a long-duration gamma-ray burst. One would then expect that these long gamma-ray bursts and core-collapse supernovae should be found in similar galactic environments. Here we show that this expectation is wrong. We find that the gamma-ray bursts are far more concentrated in the very brightest regions of their host galaxies than are the core-collapse supernovae. Furthermore, the host galaxies of the long gamma-ray bursts are significantly fainter and more irregular than the hosts of the core-collapse supernovae. Together these results suggest that long-duration gamma-ray bursts are associated with the most extremely massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long gamma-ray bursts are relatively rare in galaxies such as our own Milky Way. 相似文献
724.
Hinke CB Böhmer M Boutachkov P Faestermann T Geissel H Gerl J Gernhäuser R Górska M Gottardo A Grawe H Grębosz JL Krücken R Kurz N Liu Z Maier L Nowacki F Pietri S Podolyák Z Sieja K Steiger K Straub K Weick H Wollersheim HJ Woods PJ Al-Dahan N Alkhomashi N Ataç A Blazhev A Braun NF Čeliković IT Davinson T Dillmann I Domingo-Pardo C Doornenbal PC de France G Farrelly GF Farinon F Goel N Habermann TC Hoischen R Janik R Karny M Kaşkaş A Kojouharov IM Kröll T Litvinov Y Myalski S Nebel F 《Nature》2012,486(7403):341-345
The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During β(+)-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of (100)Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the β-decay of (100)Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear β-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, (100)In, are well reproduced by modern, large-scale shell model calculations. 相似文献
725.
Pyruvate carboxylation was stimulated by 2 gastric secretagogues, histamine and dibutyryl cyclic AMP, and by butyrate. Thiocyanate, an inhibitor of acid secretion, produced a slight decrease. Avidin significantly reduced acid secretion and this effect was overcome by biotin and oxalacetate. The results suggest that carboxylation of pyruvate is one of the reactions controlling oxidative metabolism and acid secretion in toad gastric mucosa. 相似文献
726.
Rats given a daily dose of propranolol 45 mg/kg b.wt retain water and sodium for 4 days, escaping during the 5th and 6th days in which their excretions are larger than basal values. Afterwards, in the period studied, they make a new retention and clearing is less accentuated. No relationship could be found between these retentions and plasma renin activity or renal renin content. 相似文献
727.
Lesions affecting the ventrolateral area of the nucleus reticularis pontis oralis produced, in chronic implanted cats, a significant decrease of paradoxical sleep. 相似文献
728.
Proteolytic activity was detected outside dialysis bag filled with Bromelia hemisphaerica fruit juice. The dialysable protease was concentrated and purified from small molecular weight contaminants on Sephadex G-10 columns. Acrylamide gel electrophoresis of the dialysable protease, in the presence of SDS and 2-mercaptoethanol, demonstrated a single protein band of about 8000 daltons mol. wt. The same single band with identical mobility was shown with Hemisphaericin, the enzyme retained inside the dialysis bag. The small protease, named Hemisphaericin-D was antigenic in rabbits and the antibodies cross-reacted fully with Hemisphaericin. Hemisphaericin-D appears not to be a degradation product of Hemisphaericin. 相似文献
729.
Highly purified E. coli tRNA1Val and tRNA1Ala have been isolated, based on the properties of heteroaminoacylated tRNAs and their behaviour on BD-cellulose chromatography. 相似文献
730.
Cyclic AMP was determined during the development of the diptera Ceratitis capitata. The concentration of the nucleotide reaches a peak at apolysis with a sharp decline in the pharate adult stage. A gradual increase takes place through the longevity of adult stage reaching a maximum plateau at the end of life. 相似文献