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311.
Romain Leroy Marie-Noël de Visscher Oudou Halidou Amadou Boureima 《Biodiversity and Conservation》2009,18(10):2663-2677
The giraffe population (Giraffa camelopardalis) in Niger is the last representative of the peralta sub-species which lived throughout West Africa at the beginning of the twentieth century. Protected since the 1970s, giraffes
cohabit with humans in cultivated landscapes. This may not have appeared to pose many problems in the past, but the relationship
between farmers and giraffes has deteriorated with the expansion of cultivated land and that of the giraffe population, with
reported cases of giraffes damaging crops. A survey was conducted in all the affected villages in the Kouré area to establish
the nature, severity and distribution of the damage and to evaluate the local populations’ perception of the problem. Cowpeas
are fed upon in the field at harvest time and in the granaries, as well as ripe mangoes, during the most critical period for
giraffes’ nutrition. The vast majority of farmers interviewed consider giraffes to be rather a problem in spite of tourism
revenues they can obtain from them. This opinion has individually little correlation with damage rate on crops or easy access
to tourism revenues. The damage risk factors are first and foremost considered as uncontrollable by the farmers, even if technical
protection measures could easily be put in place locally. The inter-relationships between the socio-economic context and the
way the problem is perceived are discussed. 相似文献
312.
Characteristics and turnover of exopolymeric substances in a hypersaline microbial mat 总被引:2,自引:0,他引:2
Olivier Braissant Alan W. Decho Kristen M. Przekop Kimberley L. Gallagher Christina Glunk Christophe Dupraz & Pieter T. Visscher 《FEMS microbiology ecology》2009,67(2):293-307
The properties and microbial turnover of exopolymeric substances (EPS) were measured in a hypersaline nonlithifying microbial mat (Eleuthera, Bahamas) to investigate their potential role in calcium carbonate (CaCO3 ) precipitation. Depth profiles of EPS abundance and enzyme activities indicated that c . 80% of the EPS were turned over in the upper 15–20 mm. Oxic and anoxic mat homogenates amended with low-molecular-weight (LMW) organic carbon, sugar monomers, and different types of EPS revealed rapid consumption of all substrates. When comparing the consumption of EPS with that of other substrates, only marginally longer lag times and lower rates were observed. EPS (5–8%) were readily consumed during the conversion of labile to refractory EPS. This coincided with a decrease in glucosidase activity and a decrease in the number of acidic functional groups on the EPS. Approximately half of the calcium bound to the EPS remained after 10 dialyses steps. This tightly bound calcium was readily available to precipitate as CaCO3 . We present a conceptual model in which LMW organic carbon complexed with the tightly bound calcium is released upon enzyme activity. This increases alkalinity and creates binding sites for carbonate and allows CaCO3 to precipitate. Therefore, this model explains interactions between EPS and CaCO3 precipitation, and underscores the critical role of aerobic and anaerobic microorganisms in early diagenesis and lithification processes. 相似文献
313.
The rate of synonymous substitution in enterobacterial genes is inversely related to codon usage bias 总被引:31,自引:14,他引:31
Genes sequences from Escherichia coli, Salmonella typhimurium, and other
members of the Enterobacteriaceae show a negative correlation between the
degree of synonymous-codon usage bias and the rate of nucleotide
substitution at synonymous sites. In particular, very highly expressed
genes have very biased codon usage and accumulate synonymous substitutions
very slowly. In contrast, there is little correlation between the degree of
codon bias and the rate of protein evolution. It is concluded that both the
rate of synonymous substitution and the degree of codon usage bias largely
reflect the intensity of selection at the translational level. Because of
the high variability among genes in rates of synonymous substitution,
separate molecular clocks of synonymous substitution might be required for
different genes.
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In laboratory experiments, isolated eastern tent caterpillars, Malacosoma americanum (Fabricius) (Lepidoptera: Lasiocampidae), grew more slowly than their grouped siblings even though factors previously reported to give grouped caterpillars an advantage were eliminated from our experimental design. Analysis of time-lapse videorecordings of daily foraging bouts showed that, despite their slower growth, isolated individuals fed significantly more often than their grouped siblings. This finding is consistent with previous observations showing that the rate at which tent caterpillars assimilate food is largely independent of foraging frequency and suggests that increased metabolic costs associated with superfluous activity may cause isolated caterpillars to grow slower. More rapid growth of grouped caterpillars also appears attributable to the significantly longer periods of time solitary caterpillars spent inactive during episodes of molting. Our study shows that the distinctive temporal pattern of foraging characteristic of intact colonies of eastern tent caterpillars is a emergent property of the group. 相似文献
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