全文获取类型
收费全文 | 808篇 |
免费 | 6篇 |
国内免费 | 11篇 |
专业分类
安全科学 | 418篇 |
废物处理 | 5篇 |
环保管理 | 108篇 |
综合类 | 54篇 |
基础理论 | 145篇 |
环境理论 | 1篇 |
污染及防治 | 27篇 |
评价与监测 | 11篇 |
社会与环境 | 13篇 |
灾害及防治 | 43篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 20篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 28篇 |
2013年 | 48篇 |
2012年 | 20篇 |
2011年 | 43篇 |
2010年 | 40篇 |
2009年 | 43篇 |
2008年 | 36篇 |
2007年 | 36篇 |
2006年 | 32篇 |
2005年 | 34篇 |
2004年 | 29篇 |
2003年 | 20篇 |
2002年 | 16篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 15篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
排序方式: 共有825条查询结果,搜索用时 15 毫秒
91.
Crickets can autotomize a limb in order to evade predation; however, this autotomy compromises their escape speed and, therefore,
their ability to avoid subsequent predation events. We recorded two measures of predator-avoidance behaviour in field crickets
(Gryllus bimaculatus) exposed to varying levels of predation threat, with the most extreme level leading to autotomy of a limb. Our first measure
of caution was time to emergence from cover, which was affected by perceived predation treatment, with both autotomized males
and females being significantly more cautious than intact individuals. For males (but not females), the presence of a calling
conspecific encouraged earlier emergence. Our second measure of caution was alteration of male calling behaviour. Autotomized
males remained silent for significantly longer time after disturbance than intact males, but there was no difference in call
rate once they had resumed calling, suggesting that behavioural changes were not merely a result of injury response but a
controlled modification of behaviour as a result of autotomy. These data suggest that autotomy in field crickets results in
altered calling behaviour, which was not significantly altered with different acoustic environments. 相似文献
92.
Statistical inference on patch-specific survival and movement rates from marked animals 总被引:1,自引:0,他引:1
Michael J. Conroy Jon E. Anderson Stephen L. Rathbun David G. Krementz 《Environmental and Ecological Statistics》1996,3(2):99-116
Empirical estimates of patch-specific survival and movement rates are needed to parametrize spatially explicit population
models, and for inference on the effects of habitat quality and fragmentation on populations. Data from radio-marked animals,
in which both the fates and habitat locations of animals are known over time, can be used in conjunction with continuous-time
proportional hazards models to obtain inferences on survival rates. Discrete-time conditional logistic models may provide
inference on both survival and movement rates. We use Monte Carlo simulation to investigate accuracy of estimates of survival
from both approaches, and movement rates from conditional logistic regression, for two habitats. Bias was low (relative bias
< 0.04) and interval coverage accurate (close to the nominal 0.95) for estimates of habitat effect on survival based on proportional
hazards. Bias was high (
relative bias 0.60) and interval coverage poor (
= 0.26 vs. nominal 0.95) for estimates of habitat effect based on conditional logistic regression; bias was especially influenced
by heterogeneity in survival and the shape of the hazard function, whereas both bias and coverage were affected by ‘memory’
effects in movement patterns. Bias estimates of movement rate was low (
relative bias < 0.05), but interval coverage was poor (
= 0.48–0.80), possibly as a result of poor performance of a Taylor series estimate of variance. An example is provided from
a radio-telemetry study of 47 wintering American woodcock (Scolopax minor), illustrating practical difficulties in field studies to parametrize these models. We also discuss extensions of continuous-time
models to explicitly include a movement process, and further examine tradeoffs between continuous and discrete models. 相似文献
93.
David Goulson Jemma L. Cruise Kate R. Sparrow Adele J. Harris Kirsty J. Park Matthew C. Tinsley Andre S. Gilburn 《Behavioral ecology and sociobiology》2007,61(10):1523-1529
Flowers exhibit great intra-specific variation in the rewards they offer. At any one time, a significant proportion of flowers
often contain little or no reward. Hence, foraging profitably for floral rewards is problematic and any ability to discriminate
between flowers and avoid those that are less rewarding will confer great advantages. In this study, we examine discrimination
by foraging bees among flowers of nasturtium, Tropaeolum majus. Bee visitors included carpenter bees, Xylocopa violacea, which were primary nectar robbers; honeybees, Apis mellifera, which either acted as secondary nectar robbers or gathered pollen legitimately and bumblebees, Bombus hortorum, which were the only bees able to gather nectar legitimately. Many flowers were damaged by phytophagous insects. Nectar volume
was markedly lower in flowers with damaged petals (which were also likely to be older) and in flowers that had nectar-robbing
holes. We test whether bees exhibit selectivity with regards to the individual flowers, which they approach and enter, and
whether this selectivity enhances foraging efficiency. The flowers approached (within 2 cm) by A. mellifera and B. hortorum were non-random when compared to the floral population; both species selectively approached un-blemished flowers. They both
approached more yellow flowers than would be expected by chance, presumably a reflection of innate colour preferences, for
nectar standing crop did not vary according to flower colour. Bees were also more likely to accept (land on) un-blemished
flowers. A. mellifera gathering nectar exhibited selectivity with regards to the presence of robbing holes, being more likely to land on robbed
flowers (they are not able to feed on un-robbed flowers). That they frequently approached un-robbed flowers suggests that
they are not able to detect robbing holes at long-range, so that foraging efficiency may be limited by visual acuity. Nevertheless,
by using a combination of long-range and short-range selectivity, nectar-gathering A. mellifera and B. hortorum greatly increased the average reward from the flowers on which they landed (by 68% and 48%, respectively) compared to the
average standing crop in the flower population. Overall, our results demonstrate that bees use obvious floral cues (colour
and petal blemishes) at long-range, but can switch to using more subtle cues (robbing holes) at close range. They also make
many mistakes and some cues used do not correlate with floral rewards. 相似文献
94.
In crested penguins (Eudyptes spp.), second-laid eggs typically hatch before first eggs. Amongst a variety of factors that have been considered as mechanisms underlying this reversal, has been the idea that crested penguins can adjust the degree of hatching asynchrony by manipulating egg positions (i.e. placing the smaller first egg in the supposedly thermally disadvantaged anterior position) during incubation (termed Preferential Incubation Hypothesis). We tested this in the Snares crested penguin (Eudyptes robustus) and the closely related, but synchronously-hatching, yellow-eyed penguin (Megadyptes antipodes). Snares crested penguins were more likely to place their first eggs, which are smaller than second eggs, in the anterior incubation position than were yellow-eyed penguins, which have a clutch of two similar-sized eggs. But when yellow-eyed penguins, a non-brood reducing species, were provided with an artificial size-dimorphic clutch, they also placed smaller eggs more frequently in the anterior position, suggesting that a general preference exists among penguins to place smaller eggs in the anterior position. Egg temperatures of small first eggs of Snares crested penguins were higher in the anterior than in the posterior position. Large first eggs in lesser size-dimorphic clutches experienced high temperature differences in relation to position, while small first eggs in greater size-dimorphic clutches were incubated at similar temperatures. In yellow-eyed penguins, large eggs within clutches generally had higher egg temperatures than small eggs. Incubation periods of second eggs declined with increasing egg size. Egg-size variation, rather than egg positioning behaviour, influenced hatching patterns in Snares crested penguins. In lesser size-dimorphic clutches, second eggs were more likely to hatch first while in greater size-dimorphic clutches, small first eggs were more likely to hatch at the same time or before the second eggs. This was similar in yellow-eyed penguins, where second eggs hatched earlier in clutches with large first eggs. Our data contradicts the Preferential Incubation Hypothesis and we conclude that this hypothesis is unlikely to explain the reversed hatching asynchrony in crested penguins.Communicated by C. Brown 相似文献
95.
顾志龙 《中国安全科学学报》1998,8(1):73-77
论述了将小型链条炉排工业锅炉的炉拱设计成在运行中可以全量调节的结构,以适应燃用多种煤种的需要,并减少与固定拱操作有关的意外伤亡事故。这项技术有创新性,适用性和推广价值 相似文献
96.
煤矿自燃火灾治理关键技术的研究与应用 总被引:10,自引:2,他引:8
介绍了使用同位素测氡法探测煤矿自燃火源位置的原理及应用效果。实践证明,该方法是解决煤矿自燃火灾治理难题的关键技术,由于投资少,精度高,软件处理直观可靠,它有重要推广价值 相似文献
97.
在对8# 雷管装药进行简化处理的基础上,其空中爆炸一定范围内的压力场分布可通过理论计算求得。近场参数可用自相似方法求解,而非近场参数又可用MacCorm ack 两步格式对偏微分方程进行数值求解。将获得的压力场与实测结果进行比较,两者基本一致 相似文献
98.
99.
100.