全文获取类型
收费全文 | 1918篇 |
免费 | 101篇 |
国内免费 | 197篇 |
出版年
2023年 | 27篇 |
2022年 | 27篇 |
2021年 | 23篇 |
2020年 | 51篇 |
2019年 | 55篇 |
2018年 | 58篇 |
2017年 | 55篇 |
2016年 | 83篇 |
2015年 | 65篇 |
2014年 | 70篇 |
2013年 | 122篇 |
2012年 | 62篇 |
2011年 | 67篇 |
2010年 | 66篇 |
2009年 | 87篇 |
2008年 | 97篇 |
2007年 | 112篇 |
2006年 | 79篇 |
2005年 | 86篇 |
2004年 | 70篇 |
2003年 | 60篇 |
2002年 | 59篇 |
2001年 | 45篇 |
2000年 | 38篇 |
1999年 | 32篇 |
1998年 | 52篇 |
1997年 | 30篇 |
1996年 | 42篇 |
1995年 | 47篇 |
1994年 | 40篇 |
1993年 | 33篇 |
1992年 | 49篇 |
1991年 | 26篇 |
1990年 | 42篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有2216条查询结果,搜索用时 15 毫秒
51.
Post-exercise metabolic rate in Atlantic cod and its dependence upon the method of exhaustion 总被引:1,自引:0,他引:1
This study tests whether or not post-exercise oxygen consumption rates ( M o2 ) in fish are dependent upon how exhaustion is induced. A group of eight Atlantic cod ( Gadus morhua ) were each exercised using (1) a critical swimming speed ( U crit ) protocol, (2) an exercise protocol designed to measure anaerobic capacity of fish ( U burst ), and (3) a protocol in which the fish were chased to exhaustion manually. M o2 was measured for a 2-h period following exhaustion induced by all three exercise regimes ( U crit , U burst and chase). Post-exercise M o2 following exhaustion from the U burst and chase protocols were significantly higher than post-exercise M o2 following the U crit protocol. Each fish during the U crit protocol exhibited maximal M o2 during exercise rather than during recovery, yet 75% of the fish during U brust recovery and 100% during chase recovery exhibited M o2 higher than that measured during U crit exercise. These results, as well as the large interindividual variations in M o2 among the eight fish, show that post-exhaustion M o2 is specific to the exercise regime employed, thus, investigators must exercise caution when combining results from different exercise protocols and/or individuals. 相似文献
52.
M. P. Francescato T. Talon P. E. di Prampero 《European journal of applied physiology and occupational physiology》1995,71(4):355-361
Energy costs and energy sources in karate (wado style) were studied in eight male practitioners (age 23.8 years, mass. 72.3 kg, maximal oxygen consumption (VO2max) 36.8 ml · min–1 · kg–1) performing six katas (formal, organized movement sequences) of increasing duration (from approximately. 10 s to approximately 80 s). Oxygen consumption (VO2) was determined during pre-exercise rest, the exercise period and the first 270 s of recovery in five consecutive expired gas collections. A blood sample for lactate (la–) analysis was taken 5 min after the end of exercise. The overall amount of O2 consumed during the exercise and in the following recovery increased linearly with the duration of exercise (t) from approximately 1.51 (for t equal to 10.5 s (SD 1.6)) to approximately 5.81, for t equal to 81.5 s (SD 1.0). The energy release from la– production (VO21a
–) calculated assuming that an increase of 1 mmol · l–1 la– corresponded to a VO2 of 3 mlO2 · kg–1 was negligible for t equal to or less than 20 s and increased to 17.3 ml · kg–1 (la– = 5.8 mmol · l–1 above resting values) for t equal approximately to 80 s. The overall energy requirement (VO2eq) as given by the sum of VO2 and VO2la
– was described by VO2eq = 0.87 + 0.071 · t (n = 64; r
2 = 0.91), where VO2eq is in litres and t in seconds. This equation shows that the metabolic power (VO2eq · t
–1) for this karate style is very high: from approximately 9.51 · min–1 for t equal to 10 s to approximately 4.91 · min–1 for t equal to 80 s, i.e. from 3.5 to 1.8 times the subjects' VO2max. The fraction of VO2eq derived from the amount of O2 consumed during the exercise increased from 11% for t equal to 10 s to 41 % for t equal to 80 s whereas VO21a
– was negligible far t equal to or less than 20 s and increased to 13 % o for t equal to 80 s. The remaining fraction (from 90% for t equal to 10 s to 46% for t equal to 80 s), corresponding to the amount of O2 consumed in the recovery after exercise, is derived from anaerobic alactic sources, i.e. from net splitting of high energy phosphates during the exercise. 相似文献
53.
Dennis M. Allen William S. Johnson Virginia Ogburn-Matthews 《Environmental Biology of Fishes》1995,42(1):37-50
Synopsis In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result. 相似文献
54.
InAnurogryllus muticus females, mating stimulates burrow construction, burrow provisioning, feeding, egg production, and egg-laying. Since mating often occurs before the ovaries are fully developed, the time span between mating and oviposition is used for increased food intake and the accumulation of nutrient reserves in the fatbody. Oviposition triggers maternal care of eggs and emerging hatchlings, and blocks egg consumption. Hatchling behavior is investigated. When hatchlings eat eggs, they prefer newly laid over older, embryonic eggs. 相似文献
55.
鳜鱼的耗氧率及其池塘养殖 总被引:18,自引:1,他引:17
本文较详细地报道了鳜鱼的耗氧率和窒息点,并对鳜鱼和作其饲料的鱼同池饲养的可能性进行了探讨。结果表明,鳜鱼耗氧量和体重正相关(r=0.99),耗氧率与体重反相关(r=-0.97);在水温20℃,鱼种耗氧率约为0.14mg/g.h.,成鱼约为0.12mg/g.h.;耗氧量和耗氧率均与水温正相关(r=0.90,r=0.94),水温13—30℃时,体重230±11.7g的鳜鱼。耗氧量为14.31—42.13mg/尾。h.,耗氧率为0.059—0.175mg/g.h.;鳜鱼耗氧率昼夜变化与家鱼相反,黄昏至凌晨是高峰期,为0.12—0.15mg/g.h.(T=20℃),白天是低谷期,为0.07—0.10mg/g.h;;鳜鱼的窒息点与家鱼类较接近,变化范围为0.45—0.76mg/L;鳜鱼和作其饲料的鱼在同一池塘中饲养,既可持续不断地提供鳜鱼充足的适口饵料,又简单易行,成本低,效益高,有较大的价值。 相似文献
56.
The biology of the veliid bug M. d. atrolineata, its predatory behavior, and the effects of plural hunting were studied to evaluate its role as a predator of the brown planthopper Nilaparvata lugens in the Philippines. The probability of planthoppers falling onto the water surface and provision of habitat continuity was measured by a sticky trap placed at the base of rice hills in a greenhouse and in paddy fields. The developmental period of immature stages combined was 21 days. If given prey, females laid 25 eggs on the average during an adult life span of 18 days. Starved adults could survive for only 3–5 days. The functional response to prey density was sigmoid, and the maximum number of prey killed was 7 per day. Prey feeding was completed in 12–36 min. The percentage of successful prey attacks averaged 5–8%, decreasing with higher (and larger) developmental. stages of prey, but adult prey were found the soonest. Plural hunting increased the probability of capturing prey by as much as 2.5 times that by individual hunting. Late-instar nymphs, which may be more active, fell from rice hills in a greenhouse more than early-instar nymphs, and the number falling increased with density. In the field the percentage of planthoppers falling to the water in 1 day varied considerably, from 1% for nymphs in one field to 67% for adults in another field. On the basis of work described above and given the high density of veliid predators in flooded paddy fields of tropical Asia, M. d. atrolineata is considered one of the most important natural enemies of the brown planthopper. 相似文献
57.
D. L. Lawson R. W. Merritt M. M. Martin J. S. Martin J. J. Kukor 《Entomologia Experimentalis et Applicata》1984,35(2):105-114
The larvae of Alsophila pometaria (Harr.), feeding on the young foliage of oak, has a higher relative growth rate (RGR) and relative nitrogen accumulation rate (RNAR) than the larvae of Anisota senatoria (J. E. Smith), feeding on the mature foliage of oak. Although the young oak foliage is more efficiently digested by A. pometaria (higher AD's), it is not more efficiently assimilated and used for growth (no difference in ECI's). Thus, the higher growth rate of A. pometaria is due entirely to a higher consumption rate (RCR and RNCR). Young foliage is significantly higher in nitrogen and water than mature foliage, but phenol and tannin levels are comparable in young and old foliage. A. pometaria consumes the foliage of different oak species at the same rate, independent of nitrogen content, while A. senatoria increases its consumption rate in response to decreased nitrogen levels. As a result, the growth rate of A. pometaria is directly related to leaf nitrogen content, while the growth rate of A. senatoria is independent of leaf nitrogen. The two species of insects have digestive systems that are very similar biochemically, and that are well-designed for effective protein digestion. Tannins and phenols do not influence the nutrional indices of either species. We suggest that the major benefit of spring feeding is the availability of succulent, high-nitrogen foliage, and not the avoidance of high-tannin foliage. The spring feeder appears to have a feeding strategy that favors rapid growth at the expense of efficiency, while the late summer feeder has a strategy that favors efficiency over rate.
Résumé Alimentées sur feuillage jeune de chêne, les chenilles d'Alsophila pometaria avaient un taux relatif de croissance (RGR) et un taux relatif d'accumulation d'azote (RNAR) plus élevés que les chenilles d'Anisota senatoria alimentées sur feuillage mûr de chêne. Bien que le jeune feuillage soit plus efficacement digéré par A. pometaria (AD plus élevé), il n'est pas assimilé et utilisé pour la croissance avec de meilleurs rendements (les ECI ne sont pas différents). Ainsi le taux de croissance plus élevé d'A. pometaria est dû entièrement à un taux de consommation plus important (RCR et RNCR). Le feuillage jeune est significativement plus riche en azote et en eau que le feuillage mûr, mais les niveaux de phénol et de tanins sont les mêmes. A pometaria consomme les feuilles de différentes espèces de chênes au même taux, indépendamment de la teneur en azote, tandis que A. senatoria accroît sa consommation en réponse à une diminution de la teneur en azote. Il en résulte que le taux de croissance d'A. pometaria dépend directement de la teneur en azote des feuilles, tandis que celui d'A. senatoria en est indépendant. Les systèmes digestifs des deux insectes sont biochimiquement semblables et sont efficaces pour la digestion des protéines. Les tanins et les phénols n'influent pas sur les indices nutritionnels de ces deux espèces. Nous estimons que le principal intérêt de l'alimentation printanière est la disponibilité en feuillage succulent, riche en azote, et non l'absence de feuilles à haute teneur en tanin. L'alimentation printanière semble correspondre à une strategie alimentaire qui favorise la croissance aux dépens de l'efficacité tandis que l'alimentation en fin d'été est une stratégie qui favorise l'efficacité sur la rapidité.相似文献
58.
59.
60.
The influence of zooplankton food resources on the morphology of the estuarine clupeid Gilchristella aestuarius (Gilchrist, 1914) 总被引:1,自引:0,他引:1
Stephen J. M. Blaber Digby P. Cyrus Alan K. Whitfield 《Environmental Biology of Fishes》1981,6(3-4):351-355
Synopsis The body shape of the estuarine clupeidGilchristella aestuarius from the St. Lucia system is different from that of the same species in other estuaries. The morphology ofG. aestuarius is discussed in relation to long term food availability in the St. Lucia system. 相似文献