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71.
72.
Fabiane F. de Almeida Edinaldo N. Santos-Silva Luc Ector Carlos E. Wetzel 《欧洲藻类学杂志》2018,53(2):166-179
A new stalk-forming diatom was observed at high relative abundances on periphytic samples collected in the Rio Negro hydrographic basin (Brazilian Amazon) and is here described using light and scanning electron microscopy. We also present ecological preferences of the new species. Eunotia amazonica sp. nov. co-dominated periphytic samples collected during the rainy seasons of 2013 and 2014 near the city of Manaus (Amazonas, Brazil). The main diagnostic feature of the new species is the stalk-forming growth form (‘Cymbella-like’) illustrated here for the first time in the genus Eunotia Ehrenberg. Previous reports on growth forms in common European databases for this genus included colonial (‘ribbon-like’) but also ‘mobile’, ‘fixed by pads’ or ‘without structures of fixation’. We demonstrated that the three dominant Eunotia species in periphytic samples from the Rio Negro all exhibited distinct ‘growth forms’ or habits: Eunotia amazonica sp. nov. (stalked), Eunotia intricans Metzeltin & Lange-Bertalot (ribbon-like) and Eunotia rabenhorstiana (Grunow) Hustedt (branched-arborescent). The high diversity of species, many of which are unknown to science, as well as the poorly known life-forms and habits of the Eunotiaceae in the region, partially prevent the use of metrics based on life-form to assess ecological changes. Generic assumptions based on robust statistical methods may obscure reality and lead to biased conclusions of diatom community changes in poorly explored regions such as Neotropical freshwater rivers, where the Eunotiaceae are largely dominant, particularly in the Amazon basin. 相似文献
73.
AIM OF THE STUDY: Mechanical lever-out tests were performed in vitro to investigate the initial stability of press fit acetabular cups. METHOD: Five different uncemented, hemispherical press-fit cups were implanted in a standardized manner into Sawbones, Polyurethane foam blocks. Each cup was levered-out by using a 250 mm stainless steel rod, which was connected to the acetabular cup. Loads were then applied to the rod causing the cup to be diplaced. Lever-out forces were recorded by a computer. RESULTS: The results of the lever-out forces ranged between 39,2 and 50,8 Nm. The highest initial stability was achieved by two Titanium cups with a Titanium plasmaspray coating, a flattened pole and a sharp equatorial edge. According to our trials the equatorial rim of the polyurethane cavity is the crucial area for the implant's initial stabilty. There the highest amount of attrition was observed. CONCLUSION: To guarantee a high reproducibilty of the tests it is essential to pay particular attention to the quality of the polyurethane foam blocks, to the exactness of the reaming procedure and to a defined cup insertion. However as our trials were carried out under optimized labaratory conditions one must be careful not to over-interpret its results. Intraoperatively primary stability is also influenced by the quality of the bone. 相似文献
74.
75.
Biochemical and Cytochemical Evidence for the Polar Concentration of Periplasmic Enzymes in a “Minicell” Strain of Escherichia coli 下载免费PDF全文
A number of "surface" enzymes of Escherichia coli (i.e., among those selectively released by osmotic shock) all displayed higher specific activities in extracts of minicells than in extracts of typical rod forms; these enzymes included alkaline phosphatase, cyclic phosphodiesterase, acid hexose monophosphatase, 5'-nucleotidase, and ribonuclease I. In addition, alkaline phosphatase, cyclic phosphodiesterase, and acid hexose monophosphatase were cytochemically localized to regions of minicell periplasm that resembled reactive polar enlargements of the periplasm in rod forms. In contrast, a number of "internal" cytoplasmic enzymes (inorganic pyrophosphatase, beta-galactosidase, glutamine synthetase, polynucleotide phosphorylase, and ribonuclease II) showed elevated or similar specific activities in extracts of rod forms versus extracts of minicells. A specific heat-labile inhibitor for 5'-nucleotidase, known to occur in the cytoplasm, also showed no enrichment in minicells. These findings indicate that the "surface" enzymes are segregated in vivo into the terminal minicell buds, possibly because these enzymes are concentrated in the polar enlargements of the periplasm in typical rod forms. 相似文献
76.
A. Wetzel 《Zoomorphology》1927,9(5):719-737
Ohne Zusammenfassung 相似文献
77.
Abstract
Decomposition of standing litter of the emergent macrophyte Erianthus giganteus (plumegrass) was quantified in a small freshwater wetland in Alabama, USA. Living green shoots of E. giganteus were tagged and periodically retrieved for determination of leaf and culm mass loss, litter-associated fungal biomass (ergosterol),
and nitrogen and phosphorus concentrations. Laboratory studies were also conducted to examine the effects of plant litter
moisture content and temperature on rates of CO2 evolution from plant litter. Culm and leaf material lost 25 and 32% AFDM, respectively, during plant senescence and early
litter decay. Fungal biomass, as determined by ergosterol concentrations, increased significantly in both leaf and culm litter
during decomposition, with maximum biomass accounting for 3.7 and 6.7% of the total detrital weight in culm and leaf litter,
respectively. Spatial differences in fungal biomass were observed along the culm axis, with upper regions of the culm accumulating
significantly greater amounts of fungal mass than basal regions (p < 0.01, ANOVA). Rates of CO2 evolution from both leaf and culm litter increased rapidly after wetting (0 to 76 μg CO2−C g−1 AFDM h−1 within 5 min). In addition, rates of CO2 evolution from water saturated culms increased exponentially as the temperature was increased from 10 to 30°C. These results
provide evidence that considerable microbial colonization and mineralization of standing emergent macrophyte litter can occur
before collapse of senescent shoot material to the water and sediment surface.
Received: 5 December 1998; Accepted: 31 March 1999 相似文献
78.
A study of bacterial surface oligosaccharides were investigated among
different strains of Neisseria gonorrhoeae to correlate structural features
essential for binding to the MAb 2C7. This epitope is widely expressed and
conserved in gonococcal isolates, characteristics essential to an effective
candidate vaccine antigen. Sample lipooligosaccharides (LOS), was prepared
by a modification of the hot phenol-water method from which de-O-acetylated
LOS and oligosaccharide (OS) components were analyzed by ES-MS-CID-MS and
ES-MSnin a triple quadrupole and an ion trap mass spectrometer,
respectively. Previously documented natural heterogeneity was apparent from
both LOS and OS preparations which was admixed with fragments induced by
hydrazine and mild acid treatment. Natural heterogeneity was limited to
phosphorylation and antenni extensions to the alpha-chain. Mild acid
hydrolysis to release OS also hydrolyzed the beta(1-->6) glycosidic
linkage of lipid A. OS structures were determined by collisional and
resonance excitation combined with MS and multistep MSn which provided
sequence information from both neutral loss, and nonreducing terminal
fragments. A comparison of OS structures, with earlier knowledge of MAb
binding, enzyme treatment, and partial acid hydrolysis indicates a generic
overlapping domain for 2C7 binding. Reoccurring structural features include
a Hepalpha(1-->3)Hepbeta(1-->5)KDO trisaccharide core branched on the
nonreducing terminus (Hep-2) with an alpha(1-->2) linked GlcNAc
(gamma-chain), and an alpha-linked lactose (beta-chain) residue. From the
central heptose (Hep-1), a beta(1-->4) linked lactose (alpha-chain),
moiety is required although extensions to this residue appear unnecessary.
相似文献
79.
80.
Patrick Martin Enrique Martinez-Ansemil Adrian Pinder Tarmo Timm Mark J. Wetzel 《Hydrobiologia》2008,606(1):117-127
One of the predicted consequences of climate change is an increase in the occurrence of extreme rainfall and a subsequent
increase in frequency of high flow events in rivers. High flow events have the potential to impact estuarine communities like
mussel assemblages due to decreased salinity and/or the transport of sediments, organic matter and nutrients from the terrestrial
environment to the estuary. The impact of two high flow events was investigated using mussels located within the Conwy estuary,
North Wales, using the ‘Beyond BACI’ approach. Three study sites were chosen, the potentially impacted site (Conwy) and two
control sites located outside the estuary. Sampling took place over 18 months with samples being collected before and after
each event. On each sampling occasion, the following data were collected: the total haemocyte count (THC) and condition index
(CI) of the mussels and the diversity (Hloge) of their associated macrofauna. A significant effect of the first event (22nd October 2004) was found on the CI of the Conwy
mussels, whereas a significant effect of the second event (10th October 2005) was found on mussel THC. No effect of either
event was found on the diversity of the associated fauna. The results of this study suggest that any increase in the number
or intensity of heavy precipitation or high flow events have potential implications for the health and resilience of estuarine
mussel populations.
Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan
Challenges to Marine Ecosystems 相似文献