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排序方式: 共有616条查询结果,搜索用时 15 毫秒
611.
1. Micro-crustacea of the genus Daphnia and Eudiaptomus have evolved different physiological mechanisms for coping with life in a rapidly changing environment. In this paper, we analyse some of the physical and biological factors influencing the winter abundance of the two species in a small lake (Esthwaite Water in Cumbria).
2. The results demonstrate that much of the year-to-year variation in their relative abundance can be related to long-term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.
3. Year-to-year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring 'cohort'. The most important factor influencing the overwintering performance of the two species was the water temperature.
4. Winter air temperatures over much of Europe are influenced by the atmospheric pressure variation known as the North Atlantic Oscillation (NAO). Winter water temperatures in Esthwaite Water were strongly correlated with this empirical index and there was a significant positive correlation between the NAO and the number of overwintering Eudiaptomus. 相似文献
2. The results demonstrate that much of the year-to-year variation in their relative abundance can be related to long-term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.
3. Year-to-year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring 'cohort'. The most important factor influencing the overwintering performance of the two species was the water temperature.
4. Winter air temperatures over much of Europe are influenced by the atmospheric pressure variation known as the North Atlantic Oscillation (NAO). Winter water temperatures in Esthwaite Water were strongly correlated with this empirical index and there was a significant positive correlation between the NAO and the number of overwintering Eudiaptomus. 相似文献
612.
In the mountain range of South Norway, transparent and melanic members of the Daphnia longispina complex occur. Melanic populations inhabit clearwater lakes and ponds, while transparent populations are found in ponds with slightly humic water. Mixed populations have not been detected. The distribution patterns of the two morphs are related to ambient levels of short-wave radiation, and the light absorptive properties of the inhabited waters. The pigment present is probably melanin, which is deposited in the dorsally directed parts of the carapace, head shield and antennae. Allozyme studies indicate that these distinct morphs are only remotely related, the alpine transparent group being closer to lowland, likewise transparent, populations. A melanic population found at Svalbard is closely related to the melanic mainland populations. Clonal diversity in ponds and shallow lakes is very low, in contrast to populations of deeper lakes.Deceased. 相似文献
613.
Rüdiger J. Paul Michael Colmorgen Stefan Hüller Florian Tyroller Dietmar Zinkler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):399-408
During hypoxia, oxyregulating water-breathers usually control O2 uptake by changing ventilatory convection. Using optical techniques we studied ventilation, circulation and respiratory control
in small animals, a millimetre in size, which were more or less pronounced oxyregulators (Daphnia magna, Folsomia candida). In Daphnia we found no adaptive changes in the ventilatory water flow rate during hypoxia. Frequency and amplitude of the movements
of the thoracic limbs remained constant during this environmental condition. During anoxia there was a reduction in both.
In contrast to ventilatory convection, the circulatory blood flow rate adapted to hypoxia. At low oxygen partial pressures,
the heart frequency strongly increased (compensatory tachycardia) in Daphnia, whereas the stroke volume remained constant. Accordingly, there was an increase in cardiac output during hypoxia. Folsomia also showed a marked increase of heart frequency during severe hypoxia. The adaptive changes in blood flow rate should help
to maintain sufficient partial pressure differences between medium, blood and tissues and should help to avoid anoxic zones
in the animal. During anoxia, the heart continued to beat in Daphnia (at a rate more or less similar to normoxia, but with a reduced stroke volume) for periods of many hours. The heart frequency
showed typical courses during anoxia and subsequent normoxia, which are probably related to energy metabolism.
Accepted: 28 February 1997 相似文献
614.
Demographic costs of Chaoborus-induced defences in Daphnia pulex: a sensitivity analysis 总被引:2,自引:0,他引:2
Summary We examined the demographic costs of Chaoborus-induced defensive spine structures in Daphnia pulex. Our aim was to assess the role of resource limitation and the interaction effects of limiting food level and antipredator structures on fitness of D. pulex and to pinpoint those life stages that are most sensitive to changes in the defence regime. Chaoborus-induced and typical morphotypes of D. pulex were reared at high and low food concentrations. Instar-based matrix population models were used to quantify the effects of predator-induction, food and their interaction on fitness of D. pulex. Predator-induction caused a statistically significant reduction in fitness at low food levels, but not at high food levels. Sensitivity analyses revealed that the fitness effects were primarily due to changes in the growth rate in instars 1–5, and secondarily to small reductions in the fertility of instars 5–10. The interaction between Chaoborus exposure and low food concentration was negative, and mediated through growth and fertility components. Both these components were reduced more in the Chaoborus-exposed, low food treatment than would be expected in the absence of interaction. 相似文献
615.
Nra P. Znkai 《International Review of Hydrobiology》1983,68(2):227-237
Filtering rates of three species of Daphnia were studied in situ by the 14C technique during the summer in a lake with a water temperature of 20-25°C (Lake Balaton, Hungary). The renewal time of gut contents proved to be 3-5 min in each of the three species whether fed on natural or artificial food. From May to September, filtering rates of D. cucullata, D. hyalina and D. galeata averaged 7.8, 10.3 and 9.2 ml ind.−1 day−1, respectively. Identically long individuals of all three species had almost the same filtering rates in spring, whereas in summer animals of identical weights had similar filtering rates regardless of species because of the length variability of the helmets. The grazing rate of adult filter-feeding crustaceans is suggested to be approximately 7 % per day. 相似文献
616.
Ekkehard Vareschi Rainer Reuter Dietmar Brandorff Manfred Jannsen Edmund Knig Dirk L. Wübben 《International Review of Hydrobiology》1999,84(5):411-417
Vertical migration is a key subject in understanding zooplankton ecology and its influence on aquatic ecosystems. This paper introduces a device for automatically recording vertical plankton migrations to study proximate factors regulating the stimulus, timing and amplitude of these movements under controlled laboratory conditions. The instrument records the light scattered by organisms at their respective depths and processes the signals in real time to a graphic representation of the organisms vertical distribution. Organisms of different taxa from a size of <40 μ, to > 10 000 μm were used for these experiments. Daphnia migrations in response to UV light are used to demonstrate the basic functions of the instrument. 相似文献