全文获取类型
收费全文 | 18057篇 |
免费 | 1054篇 |
国内免费 | 680篇 |
专业分类
林业 | 4169篇 |
农学 | 596篇 |
基础科学 | 1303篇 |
2335篇 | |
综合类 | 6782篇 |
农作物 | 683篇 |
水产渔业 | 1053篇 |
畜牧兽医 | 1266篇 |
园艺 | 317篇 |
植物保护 | 1287篇 |
出版年
2024年 | 97篇 |
2023年 | 305篇 |
2022年 | 342篇 |
2021年 | 501篇 |
2020年 | 570篇 |
2019年 | 654篇 |
2018年 | 430篇 |
2017年 | 521篇 |
2016年 | 667篇 |
2015年 | 563篇 |
2014年 | 978篇 |
2013年 | 1153篇 |
2012年 | 1492篇 |
2011年 | 1480篇 |
2010年 | 1123篇 |
2009年 | 1196篇 |
2008年 | 1086篇 |
2007年 | 1116篇 |
2006年 | 918篇 |
2005年 | 893篇 |
2004年 | 702篇 |
2003年 | 596篇 |
2002年 | 434篇 |
2001年 | 411篇 |
2000年 | 338篇 |
1999年 | 232篇 |
1998年 | 176篇 |
1997年 | 165篇 |
1996年 | 135篇 |
1995年 | 107篇 |
1994年 | 78篇 |
1993年 | 63篇 |
1992年 | 67篇 |
1991年 | 66篇 |
1990年 | 37篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
81.
Georgia M. E. Gray 《Human Dimensions of Wildlife》2017,22(3):282-290
Common strategies to protect swimmers from unprovoked shark bite incidents on coastal beaches are controversial. We surveyed beach users on two Sydney beaches to gauge their knowledge and attitudes to current and topical shark bite mitigation strategies. Most interviewees (>55%) were aware that shark nets were deployed on each beach, and gave relatively strong (>60%) support for their use. In contrast, beach users were overwhelming against (>80%) the general culling of sharks, and also opposed (>70%) the strategy of catching and killing sharks following a shark bite incident. There was little difference between genders in their attitudes to each strategy, but the oldest age category (51+) surveyed was generally most supportive of the lethal strategies. The results demonstrated the dichotomies in public attitudes to the different mitigation strategies, particularly passive versus active culling, and highlighted the need for greater public education for the development of socially acceptable solutions to shark hazards. 相似文献
82.
Contextual influences on animal decision‐making: Significance for behavior‐based wildlife conservation and management 下载免费PDF全文
Survival and successful reproduction require animals to make critical decisions amidst a naturally dynamic environmental and social background (i.e. “context”). However, human activities have pervasively, and rapidly, extended contextual variation into evolutionarily novel territory, potentially rendering evolved animal decision‐making mechanisms and strategies maladaptive. We suggest that explicitly focusing on animal decision‐making (ADM), by integrating and applying findings from studies of sensory ecology, cognitive psychology, behavioral economics and eco‐evolutionary strategies, may enhance our understanding of, and our ability to predict how, human‐driven changes in the environment and population demography will influence animal populations. Fundamentally, the decisions animals make involve evolved mechanisms, and behaviors emerge from the combined action of sensory integration, cognitive mechanisms and strategic rules of thumb, and any of these processes may have a disproportionate influence on behavior. Although there is extensive literature exploring ADM, it generally reflects a canalized, discipline‐specific approach that lacks a unified conceptual framework. As a result, there has been limited application of ADM theory and research findings into predictive models that can enhance management outcomes, even though it is likely that the relative resilience of species to rapid environmental change is fundamentally a result of how ADM is linked to contextual variation. Here, we focus on how context influences ADM, and highlight ideas and results that may be most applicable to conservation biology. 相似文献
83.
Ruscena WIEDERHOLT Anne M. TRAINOR Nicole MICHEL Patrick D. SHIREY Ronald R. SWAISGOOD Doug TALLAMY Susan C. COOK‐PATTON 《Integrative zoology》2015,10(5):436-452
In its 40‐year history, the science of conservation has faced unprecedented challenges in terms of environmental damage and rapid global change, and environmental problems are only increasing as greater demands are placed on limited natural resources. Conservation science has been adapting to keep pace with these changes. Here, we highlight contemporary and emerging trends and innovations in conservation science that we believe represent the most effective responses to biodiversity threats. We focus on specific areas where conservation science has had to adjust its approach to address emerging threats to biodiversity, including habitat destruction and degradation, climate change, declining populations and invasive species. We also document changes in attitudes, norms and practices among conservation scientists. A key component to success is engaging and maintaining public support for conservation, which can be facilitated through the use of technology. These recent trends in conservation and management are innovative and will assist in optimizing conservation strategies, increasing our leverage with the general public and tackling our current environmental challenges. 相似文献
84.
85.
Previous experiments have shown that mixed or conjoint grazing, when two or more animal species are grazed together, can lead to improved performance of one or more of the species and a higher total output per unit area. Sequential grazing systems, when different animal species graze an area in succession, also have the potential to improve productivity. This experiment directly compared these two approaches for integrating the grazing of cattle and sheep when pastured on improved permanent pasture. Four treatments were compared: 1) sheep only from May to October (S/S); 2) cattle only from May to July followed by sheep only from August to October (C/S); 3) cattle and sheep from May to July, sheep only for the rest of the growing season (C + S/S); and 4) cattle and sheep from May to October (C + S/C + S). Each treatment was replicated three times. From May until weaning at the end of July the plots were grazed by steers and ewes and lambs, and from weaning until October by steers and lambs. Sward heights were maintained at 6 cm using a “put and take” stocking system. Animal performance and sward composition data were collected during three growing seasons, 2001–2003. During the pre-weaning period lambs grazing plots which were grazed only by sheep had significantly poorer growth rates than those grazing plots where there was mixed grazing. Lambs grazing the sheep only plots also had lower liveweight gain during the post-weaning period, with the highest growth rates being recorded on the C + S/C + S treatment. Carrying capacity and total liveweight gain per unit area post-weaning were also consistently higher for the C + S/C + S treatment, while carrying capacity pre-weaning was highest for the C/S treatment. Measurements of clover content in the grazed horizon and botanical separation of material from quadrat cuts indicated that even under relatively controlled conditions choice of grazing system can influence sward composition. However, there was no clear link between any single sward change and the growth of the animals, indicating that the improved performance of cattle and sheep under mixed grazing is the result of a combination of factors, rather than a response to a particular sward parameter. 相似文献
86.
将“精益管理思维”应用于高校图书馆管理,试图从新视角为解决诸如图书馆利用率不高、图书经费不足及树立图书馆形象等实际问题,从而顺应社会及时代的发展趋势。 相似文献
87.
农户作为农业经营主体的主要组成部分,只有对其进行正确的分析和评价,把握其特点,才能为甘肃省各级政府农业发展、区域经济发展以及农业经营主体发展政策的制定提供参考。本研究从甘肃省农业经营主体这一视角介绍了农户经营主体的历史变迁,探讨了农户经营主体演变的特点,对农户经营主体变迁中存在的问题进行了较为详细地分析,并给出了相应建议。 相似文献
88.
Severe equine asthma (SEA) syndrome is a chronic recurrent respiratory disease, common among adult horses. The disease occurs in genetically susceptible individuals after their exposure to organic dust. Thus, environmental management has proved essential in controlling airway challenge and disease exacerbation. This is a demanding process that can only be achieved through the horse owners’ cooperation. One year after initial diagnosis of SEA in a group of 39 horses, owner compliance to an environmental management protocol was evaluated. The overall compliance to the protocol was poor and the horses’ clinical health and need for pharmacological management was related to the successful implementation of the environmental recommendations provided on disease diagnosis. 相似文献
89.
肉用仔鸡从出生到8周龄出栏这一阶段的饲养管理,是肉鸡养殖业生产的重要环节之一,其目的是要求生长速度快,肉质细嫩、味美,耗料少,成活率高,经济收益大。为此,我们要在其不同日龄阶段应当采取不同的饲养管理措施,搞好肉用仔鸡的饲养。 相似文献
90.