全文获取类型
收费全文 | 18919篇 |
免费 | 125篇 |
国内免费 | 8篇 |
专业分类
林业 | 3762篇 |
农学 | 1329篇 |
基础科学 | 156篇 |
3088篇 | |
综合类 | 1254篇 |
农作物 | 2228篇 |
水产渔业 | 1996篇 |
畜牧兽医 | 2064篇 |
园艺 | 1147篇 |
植物保护 | 2028篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 44篇 |
2020年 | 54篇 |
2019年 | 48篇 |
2018年 | 2790篇 |
2017年 | 2744篇 |
2016年 | 1230篇 |
2015年 | 103篇 |
2014年 | 75篇 |
2013年 | 124篇 |
2012年 | 914篇 |
2011年 | 2247篇 |
2010年 | 2169篇 |
2009年 | 1327篇 |
2008年 | 1434篇 |
2007年 | 1709篇 |
2006年 | 156篇 |
2005年 | 263篇 |
2004年 | 249篇 |
2003年 | 303篇 |
2002年 | 236篇 |
2001年 | 42篇 |
2000年 | 74篇 |
1999年 | 29篇 |
1998年 | 30篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 35篇 |
1992年 | 34篇 |
1991年 | 19篇 |
1990年 | 33篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1977年 | 12篇 |
1975年 | 18篇 |
1974年 | 19篇 |
1973年 | 16篇 |
1968年 | 12篇 |
1967年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
Huimin Yang Murray Unkovich Ann McNeill Xianzhi Wang 《Biology and Fertility of Soils》2011,47(4):377-385
Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil
mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in
an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18
permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3− by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year.
We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher
than that of non-N2 fixing species examined. 相似文献
52.
53.
54.
Umma Tamima 《林业研究》2016,27(4):853-861
The objective was to evaluate the performance of the co-management of Nishorgo Support Project at Chunati Wildlife Sanctuary in Bangladesh. I adopted the Focus Groups Discussion method for opinion survey and applied the SWOTAHP technique for data analysis. Local people did not participate in the decision-making process of forest management and they perceived co-management as a threat to their livelihoods. Moreover, mistrust and misunderstanding among different stakeholders, political and ethical conflicts, lack of property rights of tribal communities, and lack of accountability and transparency were identified as the drawbacks of co-management. 相似文献
55.
56.
57.
58.
David B. Bunnell Justin G. Mychek‐Londer Charles P. Madenjian 《Ecology of Freshwater Fish》2014,23(4):604-614
Using a 37‐year recruitment time series, we uncovered a field pattern revealing a strong, inverse relationship between bloater Coregonus hoyi recruitment success and slimy sculpin Cottus cognatus biomass in Lake Michigan (United States), one of the largest freshwater lakes of the world. Given that slimy sculpins (and deepwater sculpin Myoxocephalus thompsonii) are known egg predators that spatiotemporally overlap with incubating bloater eggs, we used recently published data on sculpin diets and daily ration to model annual bloater egg consumption by sculpins for the 1973–2010 year‐classes. Although several strong year‐classes were produced in the late 1980s when the proportion of eggs consumed by slimy sculpins was extremely low (i.e., <0.001) and several weak year‐classes were produced when the proportion of bloater eggs consumed was at its highest (i.e., >0.10–1.0), egg predation failed to explain why recruitment was weak for the 1995–2005 year‐classes when the proportion consumed was also low (i.e., <0.02). We concluded that egg predation by slimy and deepwater sculpins could have limited bloater recruitment in some years, but that some undetermined factor was more important in many other years. Given that slimy sculpin densities are influenced by piscivorous lake trout Salvelinus namaycush, the restoration of which in Lake Michigan has lagged behind those in lakes Superior and Huron, our study highlights the importance of an ecosystem perspective when considering population dynamics of fishes. 相似文献
59.
We incorporated explanatory factors including stream habitat type and fish density into individual‐based models with dynamic connections among adjacent habitat units to infer dispersal behaviour of juvenile steelhead Oncorhynchus mykiss in a Great Lakes watershed. We used mark–recapture data and an inverse modelling approach to estimate daily probability of steelhead moving out of a habitat unit, P(move), according to four competing models. The models used included (i) a null model where all fish had equal movement probability; (ii) a habitat‐dependent model where P(move) depended on the habitat type; (iii) a density‐dependent model of P(move); and (iv) a model where P(move) depended on both density and habitat type. The habitat‐dependent model provided the most parsimonious fit to the observed data according to Akaike's information criteria (AICc). In the null model, P(move) averaged 0.70, whereas P(move) averaged 0.75 in pools, 0.68 in riffles and 0.73 in runs in the habitat‐dependent model. 相似文献
60.