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排序方式: 共有56条查询结果,搜索用时 15 毫秒
1.
Various components of the Microbial loop such as bacteria, heterotrophic nanoflagellates and autotrophic picoplankton were analyzed, for the first time across the Great Lakes, during a cruise in the summer of 1988. In addition, the size fractionated primary productivity using carbon-14 techniques was also determined. The statistical analysis indicated that bacteria, autotrophic picoplankton and ultraplankton/picoplankton productivity were significantly higher in Lakes Ontario and Erie than Lakes Huron and Michigan. The autotrophic picoplankton and ultraplankton/picoplankton productivity was higher in Lake Erie compared to Lake Ontario.The autotrophic picoplankton showed sensitivity to nutrients and contaminants in various types of environments. A dramatic decrease of autotrophic picoplankton in eutrophic-contaminated areas, such as Ashbridges Bay, Hamilton Harbour and western Lake Erie was observed. Conversely, in Saginaw Bay, another eutrophic environment, the autotrophic picoplankton were significantly higher than in Lake Huron. The sensitivity of autotrophic picoplankton to nutrients/contaminants might have implications to trophic interactions. Our results suggest that structural and functional characteristics of the microbial loop may be operating differently in stressed versus unstressed ecosystems. The possibility of using autotrophic picoplankton as an early warning indicator of environmental perturbation is proposed. 相似文献
2.
Dynamics of autotrophic picoplankton in Lake Constance 总被引:7,自引:0,他引:7
The vertical distribution, biomass concentrations and growthrates of autotrophic picoplankton (APP) were investigated duringthe growing season (March-October) in Lake Constance in differentdepths. Cell numbers determined by epifluorescence microscopyvaried between 1.0 x 103 and 1.6 times; 105 cells ml1depending on season and water depth. Highest concentrationswere recorded above the thermodine in late summer. Numerically,APP consisted almost exclusively of chroococcoid cyanobactena.During lake stratification several peaks of biomass concentrationsoccurred in epilimsietic waters at intervals of 68 weeks.In-situ experiments using a dilution technique and dialysisbags revealed that during summer APP population dynamics wereprimarily driven by combined changes of their growth and grazingrates, whereas temperature was less important. Gross growthrates varied between 0.006 and 0.051 h1, grazing ratesbetween 0.002 and 0.053 h1. On average APP productionwas completely removed by grazing within the microbial community.Ciliates, heterotrophic nanoflagellates and rotifers have beenidentified as the major consumers of APP cells. APP biomassis small compared to larger phytoplankton, ranging from ito5% of total phytoplankton biovolume. Due to its high gross growthrates, which are on the same level as those of free-living pelagicbacteria, APP contributes slightly more to overall primary productionwith maximum percentages of {small tilde}15% in late summer. 相似文献
3.
Seasonal succession of ciliates in lake constance 总被引:3,自引:0,他引:3
We found a recurrent seasonal pattern in abundance and composition of planktonic ciliates in Lake Constance, FRG, over a three-year
period. Abundance peaks occurred in early spring and summer/autumn, while ciliate numbers were low in late spring (clear-water
phase) and winter. Prostomatida and Oligotrichida dominated in early spring. They responded immediately to the phytoplankton
spring bloom, while Haptorida, Peritrichida, and large Scuticociliatida (Histiobalantium) were delayed by 1 to 2 weeks. The spring community broke down at the onset of the clear-water phase.Pelagohalteria viridis containing symbiontic algae appeared shortly after this event. A highly diverse community was recorded in summer/autumn.
Peritrichida, small Oligotrichida, and large Scuticociliatida reached their maxima during this season. Small Scuticociliatida
were rare throughout the year and contributed moderately to total ciliate numbers only during the cold season. The observed
seasonal sequence of pelagic ciliates in Lake Constance is discussed in relation to simultaneously collected data on potential
food organisms and grazers. 相似文献
4.
Temperature dependent growth rates ofPhaeocystis pouchetii (Haptophyceae) were investigated in 5–1 batch cultures. The algae had been isolated from the German Wadden Sea area off Sylt. Microscopic cell counts and fluorescense measurements yielded similar results. The growth ofP. pouchetii reveals a typical optimum curve between 7 °C and 20 °C. Maximal growth rates, 3 divisions per day, were obtained at 15 °C. At 5 °C the algae cultures survived, but multiplication of the cells almost ceased. Results of the culture experiments correspond with observations made onPhaeocystis blooms at the German North Sea coast. 相似文献
5.
Histiobalantium sp. was found regularly in the pelagic zoneof Lake Constance, FRG, over five annual cycles. Maxima of upto 6400 cells l1 were recorded in late summer, with similarnumbers in the 08 and 820 m depth intervals. Onan annual average, the population accounted for 1017%of the total biomass of planktonic ciliates. In the laboratory,Histiobalantium grew well on a diet of the cryptophyte Rhodomonassp. Maximum growth rates obtained in batch cultures were 0.21and 0.33 day11 at 9 and 18°C, respectively. In situexperiments using diffusion chambers yielded positive growthrates in autumn and winter. The highest values recorded at theambient temperatures 5, 14 and 17°C were 0.17, 0.32 and0.40 day1, respectively. Comparing these results withthe different seasonal distributions and higher measured growthrates of other ciliates from Lake Constance, we conclude thatHistiobalantium is a superior competitor at relatively low algalfood concentrations.
2Present address: Fisheries & Oceans Canada, 4160 MarineDrive, West Vancouver, BC, V7V 1N6, Canada 相似文献
6.
Biotinylated epidermal growth factor: a useful tool for the histochemical analysis of specific binding sites 总被引:1,自引:0,他引:1
Summary Epidermal growth factor (EGF) was labelled with biotin via modification of either the amino or carboxyl groups, using suitable reagents, namely biotinyl-N-hydroxysuccinimide ester or biotinamidocaproyl hydrazide. To assure that the specific binding capacity of EGF is retained despite its chemical modification, displacement of the EGF by biotinylated derivatives in a routine binding assay was performed. The inhibitory potency compared to unmodified EGF was only slightly reduced. This result is the prerequisite for testing the usefulness of biotinylated EGF in histochemistry. The biotinylated probes were applied to sections of human tumour tissue and of monkey organs (liver, kidney, uterus of Cynomolgus and Rhesus monkey) to localize the specific binding sites for EGF. Formalin-fixed, paraffin-embedded tissue sections were deparaffinized and incubated with the probes at a concentration of 10 g ml–1 at room temperature for 60 min. Specific binding of the EGF was visualized by the avidin-biotin techniques (ABC). A positive reaction in conjunction with appropriate controls by competitive inhibition was seen for all monkey tissue sections and for the following number of cancer cases: breast carcinoma: 7/10; mesothelioma: 2/4; lung carcinoma: 1/3; colon carcinoma: 1/3.The staining properties were similar for both types of probes that differed in the functional group that is involved in modification by biotion attachment. However, the batches with modification of the amino groups stained more intensely and more distinctly than the carboxyl modified EGF. Overall, the data indicate that the ligand properties of the EGF are not impaired by biotinylation of the two types of functional groups. Thus, biotinylated EGF is a useful tool for histochemical detection and identification of EGF specific binding sites in mammalian tissue. 相似文献
7.
Thomas Weisse Michael Moser Ulrike Scheffel Peter Stadler Thomas Berendonk Guntram Weithoff Helmut Berger 《European journal of protistology》2013,49(2):255-271
We investigated the morphology, phylogeny of the 18S rDNA, and pH response of Oxytricha acidotolerans sp. nov. and Urosomoida sp. (Ciliophora, Hypotricha) isolated from two chemically similar acid mining lakes (pH ~ 2.6) located at Langau, Austria, and in Lusatia, Germany. Oxytricha acidotolerans sp. nov. from Langau has 18 frontal-ventral-transverse cirri but a very indistinct kinety 3 fragmentation so that the assignment to Oxytricha is uncertain. The somewhat smaller species from Lusatia has a highly variable cirral pattern and the dorsal kineties arranged in the Urosomoida pattern and is, therefore, preliminary designated as Urosomoida sp. The pH response was measured as ciliate growth rates in laboratory experiments at pH ranging from 2.5 to 7.0. Our hypothesis was that the shape of the pH reaction norm would not differ between these closely related (3% difference in their SSU rDNA) species. Results revealed a broad pH niche for O. acidotolerans, with growth rates peaking at moderately acidic conditions (pH 5.2). Cyst formation was positively and linearly related to pH. Urosomoida sp. was more sensitive to pH and did not survive at circumneutral pH. Accordingly, we reject our hypothesis that similar habitats would harbour ciliate species with virtually identical pH reaction norm. 相似文献
8.
Marco Senteler Bernhard Weisse Dominique A. Rothenfluh 《Computer methods in biomechanics and biomedical engineering》2016,19(5):538-548
OpenSim offers a valuable approach to investigating otherwise difficult to assess yet important biomechanical parameters such as joint reaction forces. Although the range of available models in the public repository is continually increasing, there currently exists no OpenSim model for the computation of intervertebral joint reactions during flexion and lifting tasks. The current work combines and improves elements of existing models to develop an enhanced model of the upper body and lumbar spine. Models of the upper body with extremities, neck and head were combined with an improved version of a lumbar spine from the model repository. Translational motion was enabled for each lumbar vertebrae with six controllable degrees of freedom. Motion segment stiffness was implemented at lumbar levels and mass properties were assigned throughout the model. Moreover, body coordinate frames of the spine were modified to allow straightforward variation of sagittal alignment and to simplify interpretation of results. Evaluation of model predictions for level L1–L2, L3–L4 and L4–L5 in various postures of forward flexion and moderate lifting (8 kg) revealed an agreement within 10% to experimental studies and model-based computational analyses. However, in an extended posture or during lifting of heavier loads (20 kg), computed joint reactions differed substantially from reported in vivo measures using instrumented implants. We conclude that agreement between the model and available experimental data was good in view of limitations of both the model and the validation datasets. The presented model is useful in that it permits computation of realistic lumbar spine joint reaction forces during flexion and moderate lifting tasks. The model and corresponding documentation are now available in the online OpenSim repository. 相似文献
9.
Thomas Weisse 《International Review of Hydrobiology》1991,76(3):327-337
The relative contribution to the pelagic carbon flux of bacteria, autotrophic picoplankton (APP), and heterotrophic nano- and microplankton is highest in pristine oligotrophic waters. Increased nutrient loading stimulates picoplankton production but reduces the importance of the microbial food web. Not all microorganisms are affected in the same way by eutrophication and contaminant enrichment. In contrast to bacteria and heterotrophic nanoflagellates, the APP was found to be highly sensitive to heavy metal contamination. The changing significance of the microbial loop has far-reaching consequences for the entire ecosystem including alterations occurring in the benthos. The structure and functioning of the microbial food web is similar in marine, brackish, and freshwater ecosystems. 相似文献
10.
Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m?2 · s?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m?2 · s?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m?2 · s?1 and 200 μmol photon · m?2 · s?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m?2 · s?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues. 相似文献