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61.
62.
A velocity dipole in the distribution of radio galaxies 总被引:1,自引:0,他引:1
The motion of our Galaxy through the Universe is reflected in a systematic shift in the temperature of the cosmic microwave background-because of the Doppler effect, the temperature of the background is about 0.1 per cent higher in the direction of motion, with a correspondingly lower temperature in the opposite direction. This effect is known as dipole anisotropy. If our standard cosmological model is correct, a related dipole effect should also be present as an enhancement in the surface density of distant galaxies in the direction of motion. The main obstacle to finding this signal is the uneven distribution of galaxies in the local supercluster, which drowns out the small cosmological signal. Here we report a detection of the expected cosmological dipole anisotropy in the distribution of galaxies. We use a survey of radio galaxies that are mainly located at cosmological distances, so the contamination from nearby clusters is small. When local radio galaxies are removed from the sample, the resulting dipole is in the same direction as the temperature anisotropy of the microwave background, and close to the expected amplitude. The result therefore confirms the standard cosmological interpretation of the microwave background. 相似文献
63.
High resolution X-ray analysis of the hormone-binding protein prealbumin has shown that it has a structural complementarity to double-helical DNA. The proposed binding site is composed of two symmetry-related beta-sheets containing a pair of helically disposed arms, which can interact with the bases in the wide groove of DNA. A palindromic target sequence is indicated by the symmetry of the protein. The two identical thyroid hormone binding sites on prealbumin are located in a channel that runs completely through the molecule. These two structural features suggest prealbumin as a model for the thyroid hormone nuclear receptor, providing a number of detailed predictions of its properties. 相似文献
64.
65.
Evidence from the Pacific troposphere for large global sources of oxygenated organic compounds 总被引:1,自引:0,他引:1
The presence of oxygenated organic compounds in the troposphere strongly influences key atmospheric processes. Such oxygenated species are, for example, carriers of reactive nitrogen and are easily photolysed, producing free radicals-and so influence the oxidizing capacity and the ozone-forming potential of the atmosphere-and may also contribute significantly to the organic component of aerosols. But knowledge of the distribution and sources of oxygenated organic compounds, especially in the Southern Hemisphere, is limited. Here we characterize the tropospheric composition of oxygenated organic species, using data from a recent airborne survey conducted over the tropical Pacific Ocean (30 degrees N to 30 degrees S). Measurements of a dozen oxygenated chemicals (carbonyls, alcohols, organic nitrates, organic pernitrates and peroxides), along with several C2-C8 hydrocarbons, reveal that abundances of oxygenated species are extremely high, and collectively, oxygenated species are nearly five times more abundant than non-methane hydrocarbons in the Southern Hemisphere. Current atmospheric models are unable to correctly simulate these findings, suggesting that large, diffuse, and hitherto-unknown sources of oxygenated organic compounds must therefore exist. Although the origin of these sources is still unclear, we suggest that oxygenated species could be formed via the oxidation of hydrocarbons in the atmosphere, the photochemical degradation of organic matter in the oceans, and direct emissions from terrestrial vegetation. 相似文献
66.
RNA-guided genetic silencing systems in bacteria and archaea 总被引:12,自引:0,他引:12
Clustered regularly interspaced short palindromic repeat (CRISPR) are essential components of nucleic-acid-based adaptive immune systems that are widespread in bacteria and archaea. Similar to RNA interference (RNAi) pathways in eukaryotes, CRISPR-mediated immune systems rely on small RNAs for sequence-specific detection and silencing of foreign nucleic acids, including viruses and plasmids. However, the mechanism of RNA-based bacterial immunity is distinct from RNAi. Understanding how small RNAs are used to find and destroy foreign nucleic acids will provide new insights into the diverse mechanisms of RNA-controlled genetic silencing systems. 相似文献
67.
John G. Blake 《西北部美国博物学家》2011,41(2)
An investigation of the avifauna of Mt. Dellenbaugh, Arizona, and nearby areas on the Shivwits Plateau was conducted during fall 1974 and during spring and summer 1975. A total of 92 species of birds was recorded, of which 56 were considered resident. Species composition is discussed in relation to habitat. 相似文献
68.
E. Blake Hart 《西北部美国博物学家》2011,42(4)
Recent distribution maps show raccoon as occupying only the extreme eastern - northeastern portion of Wyoming. However, there is substantial evidence that raccoon are common throughout Wyoming and currently inhabit all the major and many of the minor drainages throughout Wyoming. 相似文献
69.
Ballif BC Hornor SA Jenkins E Madan-Khetarpal S Surti U Jackson KE Asamoah A Brock PL Gowans GC Conway RL Graham JM Medne L Zackai EH Shaikh TH Geoghegan J Selzer RR Eis PS Bejjani BA Shaffer LG 《Nature genetics》2007,39(9):1071-1073
We have identified a recurrent de novo pericentromeric deletion in 16p11.2-p12.2 in four individuals with developmental disabilities by microarray-based comparative genomic hybridization analysis. The identification of common clinical features in these four individuals along with the characterization of complex segmental duplications flanking the deletion regions suggests that nonallelic homologous recombination mediated these rearrangements and that deletions in 16p11.2-p12.2 constitute a previously undescribed syndrome. 相似文献
70.
Cooper GM Coe BP Girirajan S Rosenfeld JA Vu TH Baker C Williams C Stalker H Hamid R Hannig V Abdel-Hamid H Bader P McCracken E Niyazov D Leppig K Thiese H Hummel M Alexander N Gorski J Kussmann J Shashi V Johnson K Rehder C Ballif BC Shaffer LG Eichler EE 《Nature genetics》2011,43(9):838-846
To understand the genetic heterogeneity underlying developmental delay, we compared copy number variants (CNVs) in 15,767 children with intellectual disability and various congenital defects (cases) to CNVs in 8,329 unaffected adult controls. We estimate that ~14.2% of disease in these children is caused by CNVs >400 kb. We observed a greater enrichment of CNVs in individuals with craniofacial anomalies and cardiovascular defects compared to those with epilepsy or autism. We identified 59 pathogenic CNVs, including 14 new or previously weakly supported candidates, refined the critical interval for several genomic disorders, such as the 17q21.31 microdeletion syndrome, and identified 940 candidate dosage-sensitive genes. We also developed methods to opportunistically discover small, disruptive CNVs within the large and growing diagnostic array datasets. This evolving CNV morbidity map, combined with exome and genome sequencing, will be critical for deciphering the genetic basis of developmental delay, intellectual disability and autism spectrum disorders. 相似文献