全文获取类型
收费全文 | 21054篇 |
免费 | 187篇 |
国内免费 | 212篇 |
专业分类
安全科学 | 570篇 |
废物处理 | 1026篇 |
环保管理 | 2610篇 |
综合类 | 2740篇 |
基础理论 | 5446篇 |
环境理论 | 4篇 |
污染及防治 | 5757篇 |
评价与监测 | 1697篇 |
社会与环境 | 1480篇 |
灾害及防治 | 123篇 |
出版年
2023年 | 92篇 |
2022年 | 218篇 |
2021年 | 220篇 |
2020年 | 147篇 |
2019年 | 181篇 |
2018年 | 335篇 |
2017年 | 336篇 |
2016年 | 536篇 |
2015年 | 376篇 |
2014年 | 591篇 |
2013年 | 1831篇 |
2012年 | 689篇 |
2011年 | 900篇 |
2010年 | 824篇 |
2009年 | 817篇 |
2008年 | 927篇 |
2007年 | 1013篇 |
2006年 | 911篇 |
2005年 | 732篇 |
2004年 | 743篇 |
2003年 | 740篇 |
2002年 | 692篇 |
2001年 | 924篇 |
2000年 | 641篇 |
1999年 | 402篇 |
1998年 | 280篇 |
1997年 | 254篇 |
1996年 | 304篇 |
1995年 | 278篇 |
1994年 | 258篇 |
1993年 | 240篇 |
1992年 | 248篇 |
1991年 | 214篇 |
1990年 | 219篇 |
1989年 | 225篇 |
1988年 | 199篇 |
1987年 | 167篇 |
1986年 | 134篇 |
1985年 | 148篇 |
1984年 | 187篇 |
1983年 | 166篇 |
1982年 | 206篇 |
1981年 | 152篇 |
1980年 | 123篇 |
1979年 | 157篇 |
1978年 | 122篇 |
1977年 | 110篇 |
1976年 | 103篇 |
1974年 | 95篇 |
1973年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
711.
Most studies of social polygyny in birds have examined male provisioning on the basis of the number of feeding visits. This
may be misleading if males compensate for infrequent visits by bringing larger prey at each visit. We investigated nestling
provisioning in the socially polygynous great reed warbler, Acrocephalus arundinaceus, in south Central Sweden in 1996–1997. We collected data on rate of feeding visits, prey size and the amount of biomass delivered
by males and females. Males had lower rates of feeding visits and provided smaller prey to nestlings in secondary than in
monogamous and primary nests. Secondary females had higher rates of feeding visits and brought larger prey than monogamous
and primary females. These results confirm that secondary females face a potential cost of polygyny through a lower rate of
male feeding, and that this cost was reinforced by the significantly lower male provisioning rate (biomass h–1) at secondary nests. Secondary females compensated for the lack of male assistance by increasing their rate of feeding and
bringing larger prey. As a result, offspring in nests of secondary females received as much food as did those in nests of
primary females. Prey load size increased with the parent’s proportion of feeding visits, suggesting that parents use different
feeding strategies depending on their amount of responsibility for nestling provisioning. We suggest that parents which take
the main responsibility for nestling feeding have to forage further away from the nest, and based on optimal-foraging theory,
they should then on average bring larger prey to their nest.
Received: 4 April 1999 / Received in revised form: 12 October 1999 / Accepted: 23 October 1999 相似文献
712.
Are nest characters of importance when choosing a male in the fifteen-spined stickleback (Spinachia spinachia)? 总被引:4,自引:0,他引:4
S. Östlund-Nilsson 《Behavioral ecology and sociobiology》2000,48(3):229-235
Male fifteen-spined sticklebacks (Spinachia spinachia) build their nests by wrapping epiphytic algae around macroalgae and securing them with secretional threads. In this study,
I show that female fifteen-spined stickleback prefer males which have built their nests above the surrounding vegetation.
High-located nests are safer, because they are less likely to attract egg-predators such as shore crabs (Carcinus maenas). Thus, I found that shore crabs more rapidly find eggs in nests built close to the bottom than in nests well above the it.
Moreover, male-male competition could be an additional explanation as to why males build nests high up. Thus, my field results
suggest that the closer the males were to a neighbour, the higher they built. Larger males were also found to have larger
territories but male size did not correlate with the height of the nest above the surrounding vegetation. Females showed no
preference for nest size, regardless of the presence of egg-predators. However, they tended to choose nests that had no egg-predators
in the vicinity over nests with egg-predators close by. Female choosiness for certain nest characters may provide one explanation
for the evolution of male care in this species.
Received: 29 December / 1999 Revised: 18 April 2000 / Accepted: 28 May 2000 相似文献
713.
Comparative Analysis of Management Regimes and Medicinal Plant Trade Monitoring Mechanisms for American Ginseng and Goldenseal 总被引:7,自引:0,他引:7
Christopher S. Robbins 《Conservation biology》2000,14(5):1422-1434
Abstract: Two popular and profitable native North American medicinal plants, American ginseng ( Panax quinquefolius ) and goldenseal ( Hydrastis canadensis ), both of which are listed in Appendix 2 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), are monitored under disparate domestic strategies that are designed to satisfy CITES requirements. The P. quinquefolius program has benefited the species by encouraging U.S. states to enact laws to protect wild populations and regulate collection, and by establishing a transparent system under which harvest, commerce, and export can be monitored, evaluated, and controlled routinely. But certain programmatic constraints, such as insufficient funding and gaps in biological monitoring, undermine its effectiveness as a management strategy for the species. The joint industry and government H. canadensis initiative is intended to give commercial traders more responsibility in monitoring plant trade and the federal government access to information that may otherwise be difficult to obtain without the help of traders. I examined the structure, successes, and deficiencies of the P. quinquefolius program, promising features of the evolving H. canadensis program, Turkey's management of geophytes, and other sources of information from federal agencies that might contribute to more effective management of medicinal plants in the United States. Although the main goal of domestic monitoring programs for P. quinquefolius and H. canadensis is to implement their CITES listings, it is conceivable that similar programs could be established for non–CITES medicinal plants, thereby minimizing or replacing the need for CITES protection. 相似文献
714.
Training Captive-Bred or Translocated Animals to Avoid Predators 总被引:11,自引:0,他引:11
Andrea S. Griffin †§ Daniel T. Blumstein †‡ and Christopher S. Evans 《Conservation biology》2000,14(5):1317-1326
Abstract: Animal reintroductions and translocations are potentially important interventions to save species from extinction, but most are unsuccessful. Mortality due to predation is a principal cause of failure. Animals that have been isolated from predators, either throughout their lifetime or over evolutionary time, may no longer express appropriate antipredator behavior. For this reason, conservation biologists are beginning to include antipredator training in pre-release preparation procedures. We describe the evolutionary and ontogenetic circumstances under which antipredator behavior may degenerate or be lost, and we use principles from learning theory to predict which elements can be enhanced or recovered by training. The empirical literature demonstrates that training can improve antipredator skills, but the effectiveness of such interventions is influenced by a number of constraints. We predict that it will be easier to teach animals to cope with predators if they have experienced ontogenetic isolation than if they have undergone evolutionary isolation. Similarly, animals should learn more easily if they have been evolutionarily isolated from some rather than all predators. Training to a novel predator may be more successful if a species has effective responses to similar predators. In contrast, it may be difficult to teach proper avoidance behavior, or to introduce specialized predator-specific responses, if appropriate motor patterns are not already present. We conclude that pre-release training has the potential to enhance the expression of preexisting antipredator behavior. Potential training techniques involve classical conditioning procedures in which animals learn that model predators are predictors of aversive events. However, wildlife managers should be aware that problems, such as the emergence of inappropriate responses, may arise during such training. 相似文献
715.
716.
Heavy Extinctions of Forest Avifauna in Singapore: Lessons for Biodiversity Conservation in Southeast Asia 总被引:6,自引:0,他引:6
Abstract: The consequences of rapid rainforest clearance on native avifauna are poorly understood. In Southeast Asia, Singapore, a newly developing country, has had 95% of its native lowland rainforest cleared. Most of the rainforest was lost in the mid- to late-nineteenth century. We compared avifauna checklists from 1923, 1949, and 1998 to determine the extent of extinctions between 1923 and 1998 in Singapore. Of 203 diurnal bird species, 65 were extirpated in Singapore in the past 75 years. Four of these species were nonforest- dependent species, whereas 61 (94%) were forest bird species dependent on the primary or old secondary forest to survive. Twenty-six forest bird species became extinct between 1923 and 1949, whereas 35 forest species disappeared after 1949. We compared the body lengths, feeding guilds, and vertical feeding zones between extinct and extant forest bird species to determine whether extinction patterns were dependent on these characteristics. Larger forest bird species went extinct between 1923 and 1949. Body sizes, however, did not affect the loss of forest bird species between 1949 and 1998. We observed high losses of insectivorous birds; the insectivore-carnivore and insectivore-granivore guilds lost> 80% of the species present in 1923. The highest losses were among birds that fed in the canopy. None of the forest bird species are currently common (>100 individuals/species) within Singapore. Our study shows that more than half the forest avifauna became locally extinct after extensive deforestation. Based on this fact, the countries within Southeast Asia should reconsider their heavy deforestation practices. 相似文献
717.
Abstract: We examined cougar ( Puma concolor ) dispersal, emigration, and immigration in the San Andres Mountains, New Mexico, from 1985 to 1995 to quantify the effects of dispersal on the local population and surrounding subpopulations. We captured, tagged, and radio-collared animals to detect the arrival of new immigrants and dispersal characteristics of progeny. We found that cougars in southern New Mexico exhibited a metapopulation structure in which cougar subpopulations were separated by expanses of noncougar habitat and linked by dispersers. Of 43 progeny (n = 20 males , 23 females ) studied after independence, only 13 females exhibited philopatric behavior. Males dispersed significantly farther than females, were more likely to traverse large expanses of noncougar habitat, and were probably most responsible for nuclear gene flow between habitat patches. We estimated that an average of 8.5 progeny (i.e., cougars born in the study area) successfully emigrated from and 4.3 cougars successfully immigrated to the San Andres Mountains each year. Concurrently, an average of 4.1 progeny were recruited into the San Andres cougar population. Protected cougar subpopulations can contribute to metapopulation persistence by supplying immigrants to surrounding subpopulations that are affected by fragmentation or offtake by humans. Cougar population dynamics and dispersal behavior dictate that cougar management and conservation should be considered on a regional scale. 相似文献
718.
Factors Affecting Population Assessments of Desert Tortoises 总被引:1,自引:0,他引:1
Jerome E. Freilich ‡ Kenneth P. Burnham † Christopher M. Collins and C. Ann Garry 《Conservation biology》2000,14(5):1479-1489
Abstract: Desert tortoises have been a subject of controversy since their listing as threatened in 1990. With a wide geographic range and more living individuals than any other listed land animal, biologists have needed to detect population trends against a "noisy" background of strong annual changes. We obtained annual population estimates of desert tortoises over 6 consecutive years at a 2.59-km2 plot in Joshua Tree National Park, California. Our estimates, based on weekly spring surveys, varied substantially, particularly between wet and dry years. Concurrently, we followed 10 radiotagged animals for 3 years to corroborate the surveys. Population density was determined separately for each year and for all years combined. Our best population estimate was an average of 67 adult tortoises, three times more than the density reported in a 1978 survey of the same site. Annual mortality was low ( <10%), and the animals showed extreme site fidelity. Apparent changes in population size were most strongly related to the animals' varying susceptibility to capture. In dry years, home ranges decreased, captures decreased, and effort required to find each tortoise nearly doubled. Our data confirm that tortoises are likely to be undercounted during dry years and call into question earlier studies conducted during droughts. 相似文献
719.
B. Miller # R. Reading J. Hoogland † T. Clark ‡ G. Ceballos § R. List S. Forrest †† L. Hanebury ‡‡ P. Manzano § J. Pacheco § and D. Uresk§§ 《Conservation biology》2000,14(1):318-321
720.
Uncertainty plays a major role in Integrated Coastal Zone Management (ICZM). A large part of this uncertainty is connected
to our lack of knowledge of the integrated functioning of the coastal system and to the increasing need to act in a pro-active
way. Increasingly, coastal managers are forced to take decisions based on information which is surrounded by uncertainties.
Different types of uncertainty can be identified and the role of uncertainty in decision making, scientific uncertainty and
model uncertainty in ICZM is discussed. The issue of spatial variability, which is believed to be extremely important in ICZM
and represents a primary source of complexity and uncertainty, is also briefly introduced. Some principles for complex model
building are described as an approach to handle, in a balanced way, the available data, information, knowledge and experience.
The practical method of sensitivity analysis is then introduced as a method for a posterior evaluation of uncertainty in simulation
models. We conclude by emphasising the need for the definition of an analysis plan in order to handle model uncertainty in
a balanced way during the decision making process. 相似文献