全文获取类型
收费全文 | 520篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
林业 | 39篇 |
农学 | 43篇 |
基础科学 | 4篇 |
243篇 | |
综合类 | 37篇 |
农作物 | 28篇 |
水产渔业 | 47篇 |
畜牧兽医 | 47篇 |
园艺 | 14篇 |
植物保护 | 40篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 8篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 15篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 14篇 |
2014年 | 25篇 |
2013年 | 52篇 |
2012年 | 14篇 |
2011年 | 18篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 32篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 19篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1971年 | 4篇 |
1970年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有542条查询结果,搜索用时 15 毫秒
11.
Forest soils and carbon sequestration 总被引:36,自引:0,他引:36
Soils in equilibrium with a natural forest ecosystem have high carbon (C) density. The ratio of soil:vegetation C density increases with latitude. Land use change, particularly conversion to agricultural ecosystems, depletes the soil C stock. Thus, degraded agricultural soils have lower soil organic carbon (SOC) stock than their potential capacity. Consequently, afforestation of agricultural soils and management of forest plantations can enhance SOC stock through C sequestration. The rate of SOC sequestration, and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management, and chemical composition of the litter as determined by the dominant tree species. Increasing production of forest biomass per se may not necessarily increase the SOC stocks. Fire, natural or managed, is an important perturbation that can affect soil C stock for a long period after the event. The soil C stock can be greatly enhanced by a careful site preparation, adequate soil drainage, growing species with a high NPP, applying N and micronutrients (Fe) as fertilizers or biosolids, and conserving soil and water resources. Climate change may also stimulate forest growth by enhancing availability of mineral N and through the CO2 fertilization effect, which may partly compensate release of soil C in response to warming. There are significant advances in measurement of soil C stock and fluxes, and scaling of C stock from pedon/plot scale to regional and national scales. Soil C sequestration in boreal and temperate forests may be an important strategy to ameliorate changes in atmospheric chemistry. 相似文献
12.
13.
14.
Tapasya Babu Wooiklee Paye Yumiko Kanke Lawrence Datnoff 《Communications in Soil Science and Plant Analysis》2016,47(12):1578-1597
Calibration of crop responses to applied silicon (Si) serves as a basis for developing Si fertilizer recommendation guidelines. A greenhouse experiment was set up in a randomized complete block design with five replications, two sources of Si (wollastonite and slag) and four Si rates (0, 170, 340 and 680 kg ha?1) to calibrate plant-available Si for growing rice in Louisiana soils. Silicon concentrations were determined in soils using seven different extraction procedures. Based on a quadratic model (p < 0.05), the estimated soil Si critical level using 0.01 M calcium chloride (CaCl2) for Sharkey clay soil was 110 mg kg?1 while for Crowley silt loam and Commerce silt loam, levels were 37 and 43 mg kg?1, respectively. These results suggest that suitability of an extractant that gives the best estimate of plant-available Si could considerably depend on soil type and it is unlikely that there is a universal extractant for all soils. 相似文献
15.
R. Lal 《Geoderma》1976,16(5):419-431
Erosion-induced changes in the physical characteristics of the surface soil under different soil and crop management treatments were monitored over a period of two years. These studies were conducted on field runoff plots established on natural slopes of 1, 5, 10 and 15%. The soil and crop management treatments consisted of bare-fallow, maize-maize (plowed and mulched), maize-maize (plowed), maize-cowpeas (no-till) and cowpeas-maize (plowed).Soil erosion increased the gravel content and decreased the silt and clay contents of the surface horizon. The moisture retention capacity of the surface soil decreased significantly. The infiltration rate decreased from 3.5 cm/min on all plots in February 1972 to 0.2 cm/min under bare-fallow, to 0.6 cm/min under maize-maize (mulch), to 1.5 cm/min under maize-cowpeas (no-till) and to 0.1 cm/min under maize-maize (plowed) in February 1974. Maize yields on the mulch and no-till treatments were maintained while those on plowed plots declined. Artificial soil removal resulted in significant reductions of maize and cowpea yields. 相似文献
16.
Aamir Lal Eui-Joon Kil Vo T. B. Thuy Chairina Fadhila Phuong T. Ho Hee-Seong Byun Hang T. Dao Ji-Kwang Kim Sukchan Lee 《Plant pathology》2020,69(6):1026-1033
Milk vetch dwarf virus (MDV) is an important member of the genus Nanovirus and is transmitted by the aphid Aphis craccivora. MDV has multiple single-stranded DNA genome components, each approximately 1 kb, and two or three alpha-satellite molecules. It mainly infects plants of the legume family Fabaceae. Recently, papaya (Carica papaya) collected in Yesan, South Korea, displaying symptoms of leaf yellowing and dwarfism, was identified as a new host for MDV. To examine the geographical distribution of MDV, papaya samples with symptoms were harvested in South Korea, Vietnam, and Taiwan in August 2018, along with tomato and pepper samples grown in adjacent fields in Vietnam. The results revealed the presence of MDV not only in papaya but also in pepper and tomato. This MDV infection in members of the Solanaceae family was confirmed by Southern blot hybridization performed using a PCR product of segment S as a probe. Based on sequence analysis of three MDV components (M, S, and C3), we verified the presence of three different isolates of MDV in these three countries and homology between sequences of isolates from papaya and from members of the Solanaceae from Vietnam. Taken together, our results clearly demonstrate MDV infection in Vietnam and Taiwan for the first time and confirm that MDV can infect economically important pepper and tomato. 相似文献
17.
18.
Chemical composition of the kernels and seedcoats of 8 cucurbit species, viz watermelon, muskmelon, cucumber, pumpkin, spongegourd, bottlegourd, bittergourd and snakegourd have been studied. The proportion of kernels in these seeds ranged from 48.0 to 75.5%. Oil content in kernels varied from 41.0 to 56.5%, protein 28.07 to 34.34%, crude fibre 1.25 to 2.60% and mineral matter 3.01 to 5.01%. Kernels were quite rich in calcium, iron and phosphorus. The cucurbit species compared well with some of the conventional kernels such as cashewnut and almond in their chemical make-up. Although quite low in fat and protein, the seedcoats of these cucurbit species were quite rich in crude fibre and mineral matter and could be of use as animal feed. 相似文献
19.
G. Girmay B. R. Singh H. Mitiku T. Borresen R. Lal 《Land Degradation \u0026amp; Development》2008,19(4):351-367
The effect of soil management and land use change are of interest to the sustainable land management for improving the environment and advancing food security in developing countries. Both anthropogenic changes and natural processes affect agriculture primarily by altering soil quality. This paper reviews and synthesizes the available literatures related to the influence of soil management and land use changes on soil carbon (C) stock in Ethiopia. The review shows that topsoil C stock declines approximately 0–63%, 0–23%, and 17–83% upon land use conversion from forest to crop land, to open grazing, and to plantation, respectively. An increase of 1–3% in soil C stock was observed within 10 years of converting open grazed land to protected enclosures. However, there was a little change in soil C stock below 20 cm depth. There is a large potential of increasing SOC pool with adoption of land restorative measures. Total potential of soil C sequestration with the adoption of restoration measures ranges 0·066–2·2 Tg C y−1 on rain‐fed cropland and 4·2–10·5 Tg C y−1 on rangeland. Given large area and diverse ecological conditions in Ethiopia, research data available in published literature are rather scanty. Therefore, researchable priorities identified in this review are important. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
Gayacharan Tripathi Kuldeep Aski Muraleedhar S. Singh Neeta Kumar Ashok Lal Hanuman 《Genetic Resources and Crop Evolution》2022,69(3):1229-1245
Genetic Resources and Crop Evolution - Blackgram [Vigna mungo (L.) Hepper] is a protein rich pulse crop of Indian origin. The crop is cultivated in diverse range of agro-ecological regions,... 相似文献