全文获取类型
收费全文 | 936篇 |
免费 | 39篇 |
专业分类
林业 | 40篇 |
农学 | 5篇 |
基础科学 | 1篇 |
150篇 | |
综合类 | 118篇 |
农作物 | 40篇 |
水产渔业 | 41篇 |
畜牧兽医 | 468篇 |
园艺 | 12篇 |
植物保护 | 100篇 |
出版年
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 48篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 27篇 |
2009年 | 14篇 |
2008年 | 42篇 |
2007年 | 36篇 |
2006年 | 35篇 |
2005年 | 42篇 |
2004年 | 33篇 |
2003年 | 39篇 |
2002年 | 32篇 |
2001年 | 21篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1971年 | 13篇 |
1970年 | 8篇 |
1967年 | 5篇 |
排序方式: 共有975条查询结果,搜索用时 15 毫秒
81.
Polar ice-core records suggest that an arctic or boreal source was responsible for more than 30% of the large increase in global atmospheric methane (CH4) concentration during deglacial climate warming; however, specific sources of that CH4 are still debated. Here we present an estimate of past CH4 flux during deglaciation from bubbling from thermokarst (thaw) lakes. Based on high rates of CH4 bubbling from contemporary arctic thermokarst lakes, high CH4 production potentials of organic matter from Pleistocene-aged frozen sediments, and estimates of the changing extent of these deposits as thermokarst lakes developed during deglaciation, we find that CH4 bubbling from newly forming thermokarst lakes comprised 33 to 87% of the high-latitude increase in atmospheric methane concentration and, in turn, contributed to the climate warming at the Pleistocene-Holocene transition. 相似文献
82.
Long-term potentiation (LTP) of synaptic strength, the most established cellular model of information storage in the brain, is expressed by an increase in the number of postsynaptic AMPA receptors. However, the source of AMPA receptors mobilized during LTP is unknown. We report that AMPA receptors are transported from recycling endosomes to the plasma membrane for LTP. Stimuli that triggered LTP promoted not only AMPA receptor insertion but also generalized recycling of cargo and membrane from endocytic compartments. Thus, recycling endosomes supply AMPA receptors for LTP and provide a mechanistic link between synaptic potentiation and membrane remodeling during synapse modification. 相似文献
83.
Collective action processes in complex, multiple-use common-pool resources (CPRs) have only recently become a focus of study. When CPRs evolve into more complex systems, resource use by separate user groups becomes increasingly interdependent. This implies, amongst others, that the institutional framework governing resource use has to be re-negotiated to avoid adverse impacts associated with the increased access of any new stakeholders, such as overexploitation, alienation of traditional users, and inter-user conflicts. The establishment of platforms for resource use negotiation is a way of dealing with complex natural resource management problems. Platforms arise when stakeholders perceive the same resource management problem, realize their interdependence in solving it, and come together to agree on action strategies for solving the problem (Röling, 1994). This article sets the scene for a discussion in this Special Issue about the potential of nested platforms for resource use negotiation in facilitating collective action in the management of complex, multiple-use CPRs. The article has five objectives. First, we define collective action in the context of this paper. Second, we discuss the importance of collective action in multiple-use CPRs. Third, we introduce the concept of platforms to coordinate collective action by multiple users. Fourth, we address some issues that emerge from evidence in the field regarding the role and potential of nested platforms for managing complex CPRs. Finally, we raise five discussion statements. These will form the basis for the collection of articles in this special issue. 相似文献
84.
Defective phagocytosis of isolated rod outer segments by RCS rat retinal pigment epithelium in culture 总被引:5,自引:0,他引:5
Retinal pigment epithelium cultured from normal rats phagocytizes large amounts of rod outer segment fragments isolated from normal rats and from RCS rats with inherited retinal degeneration. Cultured RCS rat pigment epithelium rarely ingests outer segment material, although the cells extend cellular processes around fragments of either type. Both normal and RCS pigment epithelium phagocytize polystyrene spheres. This demonstrates that RCS rat pigment epithelial cells contain a defect in the mechanism for phagocytizing outer segments. 相似文献
85.
L V Knutson C O Berg L J Edwards A D Bratt B A Foote 《Science (New York, N.Y.)》1967,156(774):522-523
Larvae of 13 species of Pherbellia and Colobaea that feed in exposed aquatic snails uitilize a product of the Malpighian tubules before they pupate to form a plate-like structure within the shell or to reinforce the anterior end of the puparium. The substance is partly calcium carbonate, and carbonic anhydrase may be involved in its production. 相似文献
86.
87.
Use of variations in natural nitrogen isotope abundance for environmental studies: a questionable approach 总被引:2,自引:0,他引:2
88.
Edwards CL 《Science (New York, N.Y.)》1910,32(824):502-504
89.
90.
Previous work has identified two families of proteins that transport classical neurotransmitters into synaptic vesicles, but the protein responsible for vesicular transport of the principal excitatory transmitter glutamate has remained unknown. We demonstrate that a protein that is unrelated to any known neurotransmitter transporters and that was previously suggested to mediate the Na(+)-dependent uptake of inorganic phosphate across the plasma membrane transports glutamate into synaptic vesicles. In addition, we show that this vesicular glutamate transporter, VGLUT1, exhibits a conductance for chloride that is blocked by glutamate. 相似文献