全文获取类型
收费全文 | 653篇 |
免费 | 81篇 |
国内免费 | 18篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 22篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 26篇 |
2005年 | 34篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1931年 | 4篇 |
排序方式: 共有752条查询结果,搜索用时 15 毫秒
91.
A. Fransson M. Chierici H. Hop H. S. Findlay S. Kristiansen A. Wold 《Polar Biology》2016,39(10):1841-1857
Late winter-to-summer changes (April to July) in ocean acidification state, calcium carbonate (CaCO3) saturation for aragonite (Ω a) and calcite (Ω c) and biogeochemical properties were investigated in 2013 and 2014 in Kongsfjorden, Svalbard. We investigated physical (salinity, temperature) and chemical (carbonate system, nutrient) properties in the water column from the glacier front in the fjord to the west Spitsbergen shelf. The average range of Ω a in the upper 50 m in the fjord in winter was 1.59–1.74 and in summer 1.65–2.66. The lowest Ω a (1.5) was close to the reported critical threshold for aragonite-forming organisms such as the pteropod Limacina helicina. In summer 2013, Ω a, pHT and salinity were generally lower than in 2014 as a result of a larger influence of high-CO2 water from the coastal current and less Atlantic water. The inner fjord was influenced by glacial water in summer which decreased Ω a by 0.7. Biological CO2 consumption based on a winter-to summer decrease in nitrate was larger in 2014 than in 2013, suggesting more primary production in 2014. The influence of freshwater decreased Ω a by the same amount as the biological effect increased Ω a. The seasonal increase in temperature only played a minor role on the increase of Ω a. The biological effect showed more inter-annual variability than the effect of freshwater. Based on this study, we suggest that changes in the inflow of different water masses and freshwater directly influence ocean acidification state, but also indirectly affect the biological drivers of carbonate chemistry in the fjord. 相似文献
92.
Duarte AM Wolfs CJ van Nuland NA Harrison MA Findlay JB van Mierlo CP Hemminga MA 《Biochimica et biophysica acta》2007,1768(2):218-227
Vacuolar (H+)-ATPase (V-ATPase) is a proton pump present in several compartments of eukaryotic cells to regulate physiological processes. From biochemical studies it is known that the interaction between arginine 735 present in the seventh transmembrane (TM7) segment from subunit a and specific glutamic acid residues in the subunit c assembly plays an essential role in proton translocation. To provide more detailed structural information about this protein domain, a peptide resembling TM7 (denoted peptide MTM7) from Saccharomyces cerevisiae (yeast) V-ATPase was synthesized and dissolved in two membrane-mimicking solvents: DMSO and SDS. For the first time the secondary structure of the putative TM7 segment from subunit a is obtained by the combined use of CD and NMR spectroscopy. SDS micelles reveal an alpha-helical conformation for peptide MTM7 and in DMSO three alpha-helical regions are identified by 2D 1H-NMR. Based on these conformational findings a new structural model is proposed for the putative TM7 in its natural environment. It is composed of 32 amino acid residues that span the membrane in an alpha-helical conformation. It starts at the cytoplasmic side at residue T719 and ends at the luminal side at residue W751. Both the luminal and cytoplasmatic regions of TM7 are stabilized by the neighboring hydrophobic transmembrane segments of subunit a and the subunit c assembly from V-ATPase. 相似文献
93.
D. L. Findlay R. E. Hecky S. E. M. Kasian M. P. Stainton L. L. Hendzel E. U. Schindler 《Freshwater Biology》1999,41(1):131-145
1. The effects of nitric acidification on phytoplankton were studied in a small, eperimentally manipulated, oligotrophic lake (L302N) in the Eperimental Lakes Area of Canada. The focus was altered after 9 years of acidification to investigate the possibility of using nutrient additions to stimulate recovery, followed by a controlled incremental recovery, in which the pH was increased to a predetermined target level. 2. Five years of additions of HNO3 to L302N reduced its pH from 6.5 to 6.1. Nitrate concentration increased because the algal community was severely P deficient. The phytoplankton community structure and productivity were not significantly affected by these additions. 3. The phytoplankton community was significantly affected when pH was subsequently decreased over three successive years from 6.1 to 5.1 by the addition of HCl. Dominance shifted from chrysophytes to a co-dominance of chlorophytes and dinoflagellates, which altered the size structure of the community. Species diversity significantly decreased, although phytoplankton productivity remained unchanged. 4. At pH 5.1 nitrate and sulphate additions were made, creating conditions like those in lakes in eastern North America, which receive high loadings of nitrogen from the atmosphere. The phytoplankton assemblage shifted to dominance by small coccoidal chlorophytes. However, biomass and productivity were unaffected. 5. Finally, phosphate, as phosphoric acid, was added, along with nitrate and sulphate, to the epilimnion, which stimulated internal alkalinity generation and productivity. It is concluded that CO2 concentrations and the form of N (nitrate vs. ammonia) affect algal composition but that P determines algal biomass and productivity. Chlorophytes were found to be good competitors for P when N and CO2 were high; it is epected that cyanobacteria would be more competitive for P in low CO2 systems. Conversely, dinoflagellates are most competitive in systems with low pH and high P, such as that which occurred in L302N. Although the P additions reduced N concentrations and created alkalinity, this is not a recommended remedial procedure in acidified lakes because it enhanced dinoflagellate abundance, which has been associated with fish kills. 6. When all additions ceased, the pH of L302N recovered from 5.1 to 5.8, chrysophytes and chlorophytes became more abundant and dinoflagellates decreased in abundance. Phytoplankton biomass decreased and species diversity increased. Phytoplankton productivity remained unchanged 相似文献
94.
Influence of Three Contrasting Detrital Carbon Sources on Planktonic Bacterial Metabolism in a Mesotrophic Lake 总被引:3,自引:0,他引:3
Abstract
Lakes receive organic carbon from a diversity of sources which vary in their contribution to planktonic microbial food webs.
We conducted a mesocosm study to test the effects of three different detrital carbon sources (algae, aquatic macrophytes,
terrestrial leaves) on several measures of microbial metabolism in a small meso-eutrophic lake (DOC ≈ 5 mg/L). Small DOC additions
(ΔC < 1 mg/L) affected bacterial numbers, growth, and pathways of carbon acquisition. Macrophyte and leaf detritus significantly
increased TDP and color, but bacterial densities initially (+12 h) were unaffected. After 168 h, densities in systems amended
with terrestrial detritus were 60% less than in controls, while production rates in mesocosms with macrophyte detritus were
4-fold greater. Detritus treatments resulted in greater per-cell production rates either through stable cell numbers and greater
growth rates (macrophyte-C) or lower densities with stable production rates (terrestrial-C). After only 12 h, rates of leucine
aminopeptidase (LAPase) activity were 2.5× greater in macrophyte-C systems than in controls, but LAPase and β-N-acetylglucosamindase activities in systems amended with terrestrial-C were only 50% of rates in controls. After 168 h, β-xylosidase
rates were significantly greater in communities with terrestrial and phytoplankton detritus. Microbial utilization of >20%
of 102 carbon sources tested were affected by at least one detritus addition. Macrophyte-C had positive (6% of substrates)
and negative (14%) effects on substrate use; terrestrial detritus had mainly positive effects. An ordination based on carbon-use
profiles (+12 h) revealed a cluster of macrophyte-amended communities with greater use of psicose, lactulose, and succinamic
acid; controls and algal-detritus systems were more effective in metabolizing two common sugars and cellobiose. After 168
h, communities receiving terrestrial detritus were most tightly clustered, exhibiting greater use of raffinose, pyroglutamic
acid, and sebacic acid. Results suggest that pelagic bacterial communities respond to changes in organic carbon source rapidly
and by different routes, including shifts in per-cell production rates and variations in degradation of a variety of compounds
comprising the DOC pool.
Received: 5 June 1998; Accepted: 24 August 1998 相似文献
95.
The DIF1 gene of Arabidopsis is required for meiotic chromosome segregation and belongs to the REC8/RAD21 cohesin gene family 总被引:5,自引:0,他引:5
Anuj M. Bhatt Clare Lister Tania Page Paul Fransz Kim Findlay Gareth H. Jones Hugh G. Dickinson Caroline Dean 《The Plant journal : for cell and molecular biology》1999,19(4):463-472
Cohesins are a group of conserved proteins responsible for cohesion between replicated sister chromatids during mitosis and meiosis and which are implicated in double-strand break repair and meiotic recombination. We describe here the identification and characterisation of an Arabidopsis gene - DETERMINATE, INFERTILE1 (DIF1), which is a homolog of the Schizosaccharomyces pombe REC8/RAD21 cohesin genes, and is essential for meiotic chromosome segregation. Five independent alleles of the DIF1 gene were isolated by transposon mutagenesis, and the mutants show complete male and female sterility. Pollen mother cells (PMCs) of dif1 mutants show multiple meiotic defects which are represented by univalent chromosomes and chromosome fragmentation at metaphase I, and acentric fragments and chromatin bridges in meiosis I and II. Consequently, chromosome segregation is strongly affected, resulting in meiotic products of uneven size, shape and of variable ploidy. The similarities in phenotype, and the sequence homology between DIF1 and the REC8/RAD21 cohesins suggests that cohesin function is largely conserved between eukaryotes and highlights the essential role cohesins play in plant meiosis. 相似文献
96.
97.
Di Berardo C Capstick DS Bibb MJ Findlay KC Buttner MJ Elliot MA 《Journal of bacteriology》2008,190(17):5879-5889
The chaplins are a family of eight secreted proteins that are critical for raising aerial hyphae in Streptomyces coelicolor. These eight chaplins can be separated into two main groups: the long chaplins (ChpA to -C) and the short chaplins (ChpD to -H). The short chaplins can be further subdivided on the basis of their abilities to form intramolecular disulfide bonds: ChpD, -F, -G, and -H contain two Cys residues, while ChpE has none. A "minimal chaplin strain" containing only chpC, chpE, and chpH was constructed and was found to raise a substantial aerial mycelium. This strain was used to examine the roles of specific chaplins. Within this strain, the Cys-containing ChpH was identified as the major polymerization unit contributing to aerial hypha formation and assembly of an intricate rodlet ultrastructure on the aerial surfaces, and the two Cys residues were determined to be critical for its function. ChpC augmented aerial hypha formation and rodlet assembly, likely by anchoring the short chaplins to the cell surface, while ChpE was essential for the viability of wild-type S. coelicolor. Interestingly, the lethal effects of a chpE null mutation could be suppressed by the loss of the other chaplins, the inactivation of the twin arginine translocation (Tat) secretion pathway, or the loss of the rodlins. 相似文献
98.
A. V. Tsyganova V. E. Tsyganov K. C. Findlay A. Y. Borisov I. A. Tikhonovich N. J. Brewin 《Cell and Tissue Biology》2009,3(1):93-102
The interface between the host cell and the microsymbiont is an important zone for development and differentiation during
consecutive stages of Rhizobium-legume symbiosis. Legume root nodule extensins, otherwise known as arabinogalactan protein-extensins
(AGPEs) are abundant components of infection thread matrix. We have characterized the origin and distribution of these glycoproteins
at the symbiotic interface of root nodules of symbiotically defective mutants of pea (Pisum sativum L.) by using immunogold localization with MAC265 an anti-AGPE monoclonal antibody. For mutants with defective growth of infection
threads, the AGPE epitope was abundant in the extracellular matrix surrounding infected host cells in the central infected
tissue of the nodule, as well as in the lumen of Rhizobiuminduced infection threads. This seems to indicate a mistargeting
of AGPE as a consequence of abnormal growth of the infection threads. Furthermore, mutants in the gene sym33 showed reduced labeling with MAC265 and, in some infection threads and droplets, the label was completely absent, a phenomenon
that is not observed in wild-type nodules. This suggests an alteration in the composition of the infection thread matrix for
sym33 mutants, which may be correlated to the absence of endocytosis of rhizobia into the host cytoplasm. 相似文献
99.
Cherdsak Liewlaksaneeyanawin Jun Zhuang Michelle Tang Nima Farzaneh Gillian Lueng Claire Cullis Susan Findlay Carol E. Ritland Jörg Bohlmann Kermit Ritland 《Tree Genetics & Genomes》2009,5(1):247-255
Conserved ortholog set (COS) markers are evolutionary conserved, single-copy genes, identified from large databases of express
sequence tags (ESTs). They are of particular use for constructing syntenic genetic maps among species. In this study, we identified
a set of 1,813 putative single-copy COS markers between spruce and loblolly pine, then designed primers for 931 of these markers
and tested these primers with DNA from spruce, pine, and Douglas fir. Of these 931 primers, 56% (524) amplified a product
in both spruce and pine, and 71% (373) of these were single-banded; 224 amplicons were single-banded in all three species.
Even though these COS markers were selected from large EST databases, a substantial proportion (20–30%) of amplicons displayed
multiple bands or smears, suggesting significant paralogy. Sequencing of three single-banded amplicons showed high nucleotide
similarities among 29 conifer species, suggesting orthology of single-banded amplicons. Screening for COS marker polymorphism
in two pedigrees of white spruce and two pedigrees of loblolly pine revealed an average informativeness of 36% for spruce
and 24% for pine (e.g., at least one parent was heterozygous for a single-nucleotide polymorphism within the entire amplified
product). This corresponds to an average nucleotide heterozygosity of 0.05% and 0.03%, respectively, which is considerably
lower than that found in other studies of spruce and pine. Thus, the advantages of COS markers for constructing syntenic maps
are offset by their lower polymorphism.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
100.
Peter J. Davies Ian A. Wright Sophia J. Findlay Olof J. Jonasson Shelley Burgin 《Aquatic Ecology》2010,44(4):685-700
Internationally, waterways within urban areas are subject to broad-scale environmental impairment from urban land uses. In
this study, we used in-stream macroinvertebrates as surrogates to measure the aquatic health of urban streams in the established
suburbs of northern Sydney, in temperate south eastern Australia. We compared these with samples collected from streams flowing
in adjacent naturally vegetated catchments. Macroinvertebrates were collected over a 30-month period from riffle, edge and
pool rock habitats and were identified to the family level. Macroinvertebrate assemblages were assessed against the influence
of imperviousness and other catchment and water quality variables. The study revealed that urban streams were significantly
impaired compared with those that flowed through naturally vegetated non-urban catchments. Urban streams had consistently
lower family richness, and sensitive guilds were rare or missing. We found that variation in community assemblages among the
in-stream habitats (pool edges, riffles and pool rocks) were more pronounced within streams in naturally vegetated catchments
than in urban waterways. 相似文献