全文获取类型
收费全文 | 18997篇 |
免费 | 1262篇 |
国内免费 | 50篇 |
专业分类
林业 | 1424篇 |
农学 | 787篇 |
基础科学 | 133篇 |
3688篇 | |
综合类 | 966篇 |
农作物 | 823篇 |
水产渔业 | 1544篇 |
畜牧兽医 | 8816篇 |
园艺 | 288篇 |
植物保护 | 1840篇 |
出版年
2023年 | 139篇 |
2022年 | 227篇 |
2021年 | 450篇 |
2020年 | 439篇 |
2019年 | 456篇 |
2018年 | 707篇 |
2017年 | 747篇 |
2016年 | 741篇 |
2015年 | 552篇 |
2014年 | 697篇 |
2013年 | 1060篇 |
2012年 | 1190篇 |
2011年 | 1149篇 |
2010年 | 619篇 |
2009年 | 636篇 |
2008年 | 947篇 |
2007年 | 894篇 |
2006年 | 772篇 |
2005年 | 773篇 |
2004年 | 682篇 |
2003年 | 620篇 |
2002年 | 626篇 |
2001年 | 494篇 |
2000年 | 481篇 |
1999年 | 412篇 |
1998年 | 103篇 |
1997年 | 100篇 |
1996年 | 102篇 |
1995年 | 83篇 |
1992年 | 213篇 |
1991年 | 167篇 |
1990年 | 169篇 |
1989年 | 194篇 |
1988年 | 182篇 |
1987年 | 176篇 |
1986年 | 161篇 |
1985年 | 160篇 |
1984年 | 117篇 |
1983年 | 117篇 |
1982年 | 75篇 |
1981年 | 76篇 |
1980年 | 75篇 |
1979年 | 142篇 |
1978年 | 113篇 |
1977年 | 104篇 |
1976年 | 70篇 |
1974年 | 122篇 |
1973年 | 95篇 |
1972年 | 119篇 |
1971年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
291.
292.
293.
294.
295.
Uemeson José dos Santos Gustavo Pereira Duda Marise Conceição Marques José Romualdo de Sousa Lima Eduardo Soares de Souza 《Arid Land Research and Management》2019,33(3):255-273
Caatinga is a Brazilian dry ecosystem that occupies around 1 million km2 and is one of the largest tropical dry forests of the world. About 46% of the area that was originally covered has been deforested. Land use can cause pronounced reduction in soil carbon stocks that play a major role in the global carbon cycle. The objective of this study was to improve our understanding of the effect of land use on oxidizable carbon fractions, total carbon stocks and humic substances in different layers of soil in a Brazilian semi-arid region. We analyzed soils from tropical dry forest (TDF), forest succession with Anadenanthera falcata (ANA), with Tabebuia alba (TAB), secondary scrubby regeneration (SCR), and non-irrigated maize (MS). Forests showed larger fractions of more labile carbon, except for TDF. The most recalcitrant fraction of carbon stock, humin fraction stock, with the different land use decreased by 38–53% compared to TDF. Oxidizable carbon fractions, carbon stocks, and humic fraction stocks were able to differentiate the successional land uses and agricultural cover from TDF, mainly in the 0–5?cm layer. Our results show that changes in land use, especially with ANA forest succession, showed a larger labile carbon fraction, indicating easy decomposition and loss. Our results provide an alternative tool for the management of deforested areas in tropical dry caatinga ecosystems. This would contribute to the conservation of dry forest systems and could serve as guideline for sustainable management of agriculturally impacted caatinga areas. 相似文献
296.
Journal of Plant Diseases and Protection - Prior to the first occurrence of chestnut blight in 1976, leaf spot caused by Cylindrosporium castaneae was one of the most important diseases of European... 相似文献
297.
Spyra Marcin Kleemann Janina Cetin Nuket Ipek Vázquez Navarrete Cesar Jesús Albert Christian Palacios-Agundez Igone Ametzaga-Arregi Ibone La Rosa Daniele Rozas-Vásquez Daniel Adem Esmail Blal Picchi Paolo Geneletti Davide König Hannes J. Koo HongMi Kopperoinen Leena Fürst Christine 《Landscape Ecology》2019,34(7):1715-1735
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of... 相似文献
298.
Kormann Urs G. Scherber Christoph Tscharntke Teja Batáry Péter Rösch Verena 《Landscape Ecology》2019,34(5):1045-1056
Landscape Ecology - Global change pressures (GCPs) imperil species and associated ecosystem functions, but studies investigating interactions of landscape-scale pressures remain scarce. Loss of... 相似文献
299.
Methyl jasmonate reduces chilling injury and maintains postharvest quality of mango fruit 总被引:5,自引:0,他引:5
González-Aguilar GA Fortiz J Cruz R Baez R Wang CY 《Journal of agricultural and food chemistry》2000,48(2):515-519
Exposure of mango (Mangifera indica cv. Tommy Atkins) fruit to methyl jasmonate (MJ) vapors (10(-)(4) M) for 24 h at 25 degrees C reduced chilling injury during subsequent storage for 21 days at 7 degrees C and after 5 days of shelf life at 20 degrees C. The chilling tolerance induced by MJ was positively correlated with the reduction in the percent ion leakage of mango tissue. The overall quality of MJ-treated fruit was also better than that of control fruit. MJ treatment increased the total soluble solids but did not affect titratable acidity or pH. MJ also did not change the normal climacteric rise in respiration, water loss, and softening rates. The efficacy of MJ to reduce chilling injury and decay of mango could be related to the tolerance induced at low temperature. It was concluded that MJ treatment may prevent chilling injury symptoms of mango without altering the ripening process. 相似文献
300.
de Sio F Laratta B Giovane A Quagliuolo L Castaldo D Servillo L 《Journal of agricultural and food chemistry》2000,48(3):780-784
A new extraction and chromatographic procedure to quantify free and esterified ergosterol in tomato products was devised. The extraction solution was composed of a dichloromethane/methanol mixture in a 2:1 (v/v) ratio. This extraction solvent allowed for higher ergosterol recovery from tomato products (an average of 25% more) compared to hexane, which is frequently employed for ergosterol extraction. Both free and esterified ergosterol were determined by HPLC reverse-phase chromatography employing a Nova-Pak C-18 column (300 x 3.9 mm), filled with 4 mm average particle size and a guard column of the same material. The elution was performed at a flow rate of 1 mL. min(-1) with a linear gradient of solvent A (methanol/water, 80:20, v/v) and solvent B (dichloromethane). The gradient, starting at sample injection, was from 0 to 50% B for 20 min for the free ergosterol analysis and additional 15 min at 50% B to analyze the ergosterol esters. This technique has proven to be more sensitive for ergosterol determination than other reported chromatographic procedures. Moreover, ergosterol esters, extracted from various fungal sources, separated well and were easily quantified. 相似文献