全文获取类型
收费全文 | 143篇 |
免费 | 25篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 5篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有168条查询结果,搜索用时 31 毫秒
21.
New perspectives on nitrogen-fixing microorganisms in tropical and subtropical oceans 总被引:7,自引:0,他引:7
New molecular and microscopic evidence indicates that the open ocean harbors a diverse range of novel free-living and symbiotic nitrogen-fixing microorganisms. Although the extent to which these microorganisms fix nitrogen is currently unclear, ongoing research indicates that they might make a substantial contribution to the open ocean nitrogen budget. 相似文献
22.
Zbigniew S. Kolber Sasha Tozzi Jonathan P. Zehr David M. Karl 《Journal of phycology》2012,48(3):595-606
This study describes the relationships between dinitrogen (N2) fixation, dihydrogen (H2) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H2 produced:N2 fixed (H2:N2) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 μmol photons · m?2 · s?1, the rate of N2 fixation, as measured by acetylene reduction, saturated at light intensities of 200 μmol photons · m?2 · s?1. In contrast, net H2 production continued to increase with light levels up to 1,000 μmol photons · m?2 · s?1. The H2:N2 ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐p‐benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N2 fixation and net H2 production, while the H2:N2 ratio increased with increasing level of PQ pool reduction. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N2 fixation and H2 cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H2:N2 ratio and modulate net H2 production. 相似文献
23.
Fingerprinting Diazotroph Communities in the Chesapeake Bay by Using a DNA Macroarray 总被引:12,自引:4,他引:8 下载免费PDF全文
Bethany D. Jenkins Grieg F. Steward Steven M. Short Bess B. Ward Jonathan P. Zehr 《Applied microbiology》2004,70(3):1767-1776
Investigations of the distribution and diversity of nitrogen-fixing microorganisms in natural environments have often relied on PCR amplification and sequence analysis of a portion of one of the key enzymes in nitrogen fixation, dinitrogenase reductase, encoded by nifH. Recent work has suggested that DNA macroarrays provide semiquantitative fingerprints of diversity within mixtures of nifH amplicons (G. F. Steward, B. D. Jenkins, B. B. Ward, and J. P. Zehr, Appl. Environ. Microbiol. 70:1455-1465, 2004). Here we report the application of macroarrays for a study in the Chesapeake Bay. Samples from different locations in the bay yielded distinct fingerprints. Analysis of replicates and samples from different locations by cluster analysis showed that replicates clustered together, whereas different samples formed distinct clusters. There was a correspondence between the hybridization pattern observed and that predicted from the distribution of sequence types in a corresponding clone library. Some discrepancies between the methods were observed which are likely a result of the high nifH sequence diversity in the Chesapeake Bay and the limited number of sequences represented on this version of the array. Analyses of sequences in the clone library indicate that the Chesapeake Bay harbors unique, phylogenetically diverse diazotrophs. The macroarray hybridization patterns suggest that there are spatially variable communities of diazotrophs, which have been confirmed by quantitative PCR methods (S. M. Short, B. D. Jenkins, and J. P. Zehr, Appl. Environ. Microbiol., in press). The results show that DNA macroarrays have great potential for mapping the spatial and temporal variability of functional gene diversity in the environment. 相似文献
24.
25.
A rapid method for preparing and directly sequencing plasmid and phagemid miniprep DNA is described. This protocol is a novel combination of two fairly standard procedures, resulting in quick and easy generation of sequence data. The lack of extensive manipulations in the purification process allows the production of DNA sequence data in a single day. 相似文献
26.
Julie C Robidart Christina M Preston Ryan W Paerl Kendra A Turk Annika C Mosier Christopher A Francis Christopher A Scholin Jonathan P Zehr 《The ISME journal》2012,6(3):513-523
Monterey Bay, CA is an Eastern boundary upwelling system that is nitrogen limited much of the year. In order to resolve population dynamics of microorganisms important for nutrient cycling in this region, we deployed the Environmental Sample Processor with quantitative PCR assays targeting both ribosomal RNA genes and functional genes for subclades of cyanobacteria (Synechococcus) and ammonia-oxidizing Archaea (Thaumarchaeota) populations. Results showed a strong correlation between Thaumarchaea abundances and nitrate during the spring upwelling but not the fall sampling period. In relatively stratified fall waters, the Thaumarchaeota community reached higher numbers than in the spring, and an unexpected positive correlation with chlorophyll concentration was observed. Further, we detected drops in Synechococcus abundance that occurred on short (that is, daily) time scales. Upwelling intensity and blooms of eukaryotic phytoplankton strongly influenced Synechococcus distributions in the spring and fall, revealing what appear to be the environmental limitations of Synechococcus populations in this region. Each of these findings has implications for Monterey Bay biogeochemistry. High-resolution sampling provides a better-resolved framework within which to observe changes in the plankton community. We conclude that controls on these ecosystems change on smaller scales than are routinely assessed, and that more predictable trends will be uncovered if they are evaluated within seasonal (monthly), rather than on annual or interannual scales. 相似文献
27.
James A. Burns Jonathan P. Zehr Joseph P. Montoya Adam B. Kustka Douglas G. Capone 《Journal of phycology》2006,42(4):900-904
Despite nearly two decades of intensive research, many questions regarding the physiology and ecology of the marine, non‐heterocystous cyanobacterium, Trichodesmium, remain unresolved. We note here the effect of EDTA (ethylenediaminetetraacetate) on N2 fixation by Trichodesmium, and the use of EDTA as a means of extending the viability of natural Trichodesmium spp. populations. We examined nitrogenase activity (NA) as a function of EDTA concentration, time of collection, light level, and iron addition. Samples collected early in the day and treated with EDTA maintain a steady rate of activity for hours longer than controls. Furthermore, samples preincubated through the night with EDTA were active the next morning, compared with controls that were inactive. The discovery that (10–50 μM) low concentrations of EDTA prolong the duration of NA of Trichodesmium during experimental manipulations without affecting the rate of acetylene reduction allows for longer term manipulative experiments to be conducted. 相似文献
28.
29.
30.