全文获取类型
收费全文 | 152篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
丛书文集 | 1篇 |
理论与方法论 | 5篇 |
现状及发展 | 35篇 |
研究方法 | 27篇 |
综合类 | 85篇 |
自然研究 | 3篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 8篇 |
2011年 | 16篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1946年 | 5篇 |
1945年 | 1篇 |
排序方式: 共有156条查询结果,搜索用时 15 毫秒
101.
Jean Brachet 《Cellular and molecular life sciences : CMLS》1946,2(2):41-48
Summary A survey of the biochemistry of regenerating animals has been made: after a critical discussion ofChild's metabolic gradients theory, the relative importance of respiration rate, carbohydrates, proteins and nucleic acids metabolism are stressed. The similarities between biochemical processes in the embryo and the regenerating organism are pointed out.
Une grande partie de cet article est la reproduction d'un chapitre de notre livre « Embryologie chimique » (Masson, Paris, etDesoer, Liége); nous tenons à remercier les éditeurs de l'ouvrage qui ont bien voulu marquer leur accord. On y trouvera une bibliographie étendue sur les modifications chimiques dont l'organisme en régénération est le siège. 相似文献
Une grande partie de cet article est la reproduction d'un chapitre de notre livre « Embryologie chimique » (Masson, Paris, etDesoer, Liége); nous tenons à remercier les éditeurs de l'ouvrage qui ont bien voulu marquer leur accord. On y trouvera une bibliographie étendue sur les modifications chimiques dont l'organisme en régénération est le siège. 相似文献
102.
103.
104.
Barbara Jean Tracy C. R. Tracy D. S. Dobkin 《Cellular and molecular life sciences : CMLS》1979,35(6):751-752
Summary
Hagenius brevistylus lost mass by evaporation in a moderately desiccating environment at the rate of 20.4 mg h–1, and died of desiccation in less than 1 day at a body mass of 79.8% of their normally hydrated mass. It was estimated thatHagenius minimally would have to consume the equivalent of 60% of its body mass each day to meet its daily water requirements. This amount of food is equivalent to that necessary to power flight of a dragonfly for 4.6h.This research was financed in part by a grant from the American Philosophical Society to C.R.T., and was conducted at the University of Michigan Biological Station, Douglas Lake (USA). 相似文献
105.
Seismic waves increase permeability 总被引:10,自引:0,他引:10
Earthquakes have been observed to affect hydrological systems in a variety of ways--water well levels can change dramatically, streams can become fuller and spring discharges can increase at the time of earthquakes. Distant earthquakes may even increase the permeability in faults. Most of these hydrological observations can be explained by some form of permeability increase. Here we use the response of water well levels to solid Earth tides to measure permeability over a 20-year period. At the time of each of seven earthquakes in Southern California, we observe transient changes of up to 24 degrees in the phase of the water level response to the dilatational volumetric strain of the semidiurnal tidal components of wells at the Pi?on Flat Observatory in Southern California. After the earthquakes, the phase gradually returns to the background value at a rate of less than 0.1 degrees per day. We use a model of axisymmetric flow driven by an imposed head oscillation through a single, laterally extensive, confined, homogeneous and isotropic aquifer to relate the phase response to aquifer properties. We interpret the changes in phase response as due to changes in permeability. At the time of the earthquakes, the permeability at the site increases by a factor as high as three. The permeability increase depends roughly linearly on the amplitude of seismic-wave peak ground velocity in the range of 0.21-2.1 cm s(-1). Such permeability increases are of interest to hydrologists and oil reservoir engineers as they affect fluid flow and might determine long-term evolution of hydrological and oil-bearing systems. They may also be interesting to seismologists, as the resulting pore pressure changes can affect earthquakes by changing normal stresses on faults. 相似文献
106.
Novel microbial communities of the Haakon Mosby mud volcano and their role as a methane sink 总被引:5,自引:0,他引:5
Niemann H Lösekann T de Beer D Elvert M Nadalig T Knittel K Amann R Sauter EJ Schlüter M Klages M Foucher JP Boetius A 《Nature》2006,443(7113):854-858
Mud volcanism is an important natural source of the greenhouse gas methane to the hydrosphere and atmosphere. Recent investigations show that the number of active submarine mud volcanoes might be much higher than anticipated (for example, see refs 3-5), and that gas emitted from deep-sea seeps might reach the upper mixed ocean. Unfortunately, global methane emission from active submarine mud volcanoes cannot be quantified because their number and gas release are unknown. It is also unclear how efficiently methane-oxidizing microorganisms remove methane. Here we investigate the methane-emitting Haakon Mosby Mud Volcano (HMMV, Barents Sea, 72 degrees N, 14 degrees 44' E; 1,250 m water depth) to provide quantitative estimates of the in situ composition, distribution and activity of methanotrophs in relation to gas emission. The HMMV hosts three key communities: aerobic methanotrophic bacteria (Methylococcales), anaerobic methanotrophic archaea (ANME-2) thriving below siboglinid tubeworms, and a previously undescribed clade of archaea (ANME-3) associated with bacterial mats. We found that the upward flow of sulphate- and oxygen-free mud volcano fluids restricts the availability of these electron acceptors for methane oxidation, and hence the habitat range of methanotrophs. This mechanism limits the capacity of the microbial methane filter at active marine mud volcanoes to <40% of the total flux. 相似文献
107.
Diehl R Halloin H Kretschmer K Lichti GG Schönfelder V Strong AW von Kienlin A Wang W Jean P Knödlseder J Roques JP Weidenspointner G Schanne S Hartmann DH Winkler C Wunderer C 《Nature》2006,439(7072):45-47
Gamma-rays from radioactive 26Al (half-life approximately 7.2 x 10(5) years) provide a 'snapshot' view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along its plane. This led to the conclusion that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/- 0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9 (+/- 1.1) events per century. 相似文献
108.
Moreira MC Klur S Watanabe M Németh AH Le Ber I Moniz JC Tranchant C Aubourg P Tazir M Schöls L Pandolfo M Schulz JB Pouget J Calvas P Shizuka-Ikeda M Shoji M Tanaka M Izatt L Shaw CE M'Zahem A Dunne E Bomont P Benhassine T Bouslam N Stevanin G Brice A Guimarães J Mendonça P Barbot C Coutinho P Sequeiros J Dürr A Warter JM Koenig M 《Nature genetics》2004,36(3):225-227
Ataxia-ocular apraxia 2 (AOA2) was recently identified as a new autosomal recessive ataxia. We have now identified causative mutations in 15 families, which allows us to clinically define this entity by onset between 10 and 22 years, cerebellar atrophy, axonal sensorimotor neuropathy, oculomotor apraxia and elevated alpha-fetoprotein (AFP). Ten of the fifteen mutations cause premature termination of a large DEAxQ-box helicase, the human ortholog of yeast Sen1p, involved in RNA maturation and termination. 相似文献
109.
Nusbaum C Zody MC Borowsky ML Kamal M Kodira CD Taylor TD Whittaker CA Chang JL Cuomo CA Dewar K FitzGerald MG Yang X Abouelleil A Allen NR Anderson S Bloom T Bugalter B Butler J Cook A DeCaprio D Engels R Garber M Gnirke A Hafez N Hall JL Norman CH Itoh T Jaffe DB Kuroki Y Lehoczky J Lui A Macdonald P Mauceli E Mikkelsen TS Naylor JW Nicol R Nguyen C Noguchi H O'Leary SB O'Neill K Piqani B Smith CL Talamas JA Topham K Totoki Y Toyoda A Wain HM Young SK Zeng Q Zimmer AR Fujiyama A Hattori M 《Nature》2005,437(7058):551-555
Chromosome 18 appears to have the lowest gene density of any human chromosome and is one of only three chromosomes for which trisomic individuals survive to term. There are also a number of genetic disorders stemming from chromosome 18 trisomy and aneuploidy. Here we report the finished sequence and gene annotation of human chromosome 18, which will allow a better understanding of the normal and disease biology of this chromosome. Despite the low density of protein-coding genes on chromosome 18, we find that the proportion of non-protein-coding sequences evolutionarily conserved among mammals is close to the genome-wide average. Extending this analysis to the entire human genome, we find that the density of conserved non-protein-coding sequences is largely uncorrelated with gene density. This has important implications for the nature and roles of non-protein-coding sequence elements. 相似文献
110.
Riassunto Nel ratto intossicato con estratto diAmanita phalloide le prime alterazioni strutturali dell'epatocita si realizzano a livello del nucleo e del nucleolo con formazioni di «nucleolar caps». Da queste stesse strutture iniziano i fenomeni di regressione delle alterazioni. Le manifestazioni sia del danno che della sua regressione a livello citoplasmatico risultano essere successive a quelle nucleari. Il comportamento del DNA e di alcuni enzimi del tessuto epatico è risultato nel complesso coerente con le alterazioni morfologiche. In rapporto con la dose usata queste alterazioni risultano reversibili poichè nelle cellule colpite entro 12 h cominciano i fenomeni di ristrutturazione. 相似文献