全文获取类型
收费全文 | 61289篇 |
免费 | 3504篇 |
国内免费 | 31篇 |
专业分类
林业 | 3756篇 |
农学 | 1969篇 |
基础科学 | 261篇 |
8170篇 | |
综合类 | 10673篇 |
农作物 | 2404篇 |
水产渔业 | 3144篇 |
畜牧兽医 | 29484篇 |
园艺 | 850篇 |
植物保护 | 4113篇 |
出版年
2021年 | 563篇 |
2020年 | 568篇 |
2019年 | 633篇 |
2018年 | 1243篇 |
2017年 | 1291篇 |
2016年 | 1141篇 |
2015年 | 1003篇 |
2014年 | 1193篇 |
2013年 | 2402篇 |
2012年 | 2348篇 |
2011年 | 2445篇 |
2010年 | 1527篇 |
2009年 | 1516篇 |
2008年 | 2298篇 |
2007年 | 2285篇 |
2006年 | 2026篇 |
2005年 | 1983篇 |
2004年 | 1851篇 |
2003年 | 1793篇 |
2002年 | 1612篇 |
2001年 | 1723篇 |
2000年 | 1639篇 |
1999年 | 1353篇 |
1998年 | 492篇 |
1997年 | 496篇 |
1996年 | 503篇 |
1995年 | 579篇 |
1994年 | 495篇 |
1993年 | 511篇 |
1992年 | 979篇 |
1991年 | 969篇 |
1990年 | 956篇 |
1989年 | 962篇 |
1988年 | 900篇 |
1987年 | 938篇 |
1986年 | 932篇 |
1985年 | 934篇 |
1984年 | 757篇 |
1983年 | 681篇 |
1979年 | 679篇 |
1978年 | 559篇 |
1976年 | 475篇 |
1975年 | 516篇 |
1974年 | 713篇 |
1973年 | 624篇 |
1972年 | 692篇 |
1971年 | 690篇 |
1970年 | 623篇 |
1969年 | 613篇 |
1967年 | 528篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
Tania Khandakar Chris Guppy Sheikh M. F. Rabbi Heiko Daniel 《Soil Use and Management》2021,37(1):120-125
Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil. 相似文献
2.
This paper empirically examines the key factors driving UK direct investment in the Spanish regions over the period 2000–2016 and, consequently, tries to unveil its main motivation. Applying a spatial Durbin panel model to capture spatial linkages, the results point to the existence of complementarity between the FDI received by a region and that of the remaining ones. This outcome, along with a positive and statistically significant spillover effect of market potential, reveals that complex-vertical FDI motivation with agglomeration economies prevails among UK MNEs investing in Spain. Additionally, our findings unveil the role played by some other FDI drivers, such as wages and infrastructure. Furthermore, the paper is unique in decomposing the average direct and spillover effects by region and pairs of regions, so that remarkable differences can be identified. This breakdown has strong significance from a policy perspective since it can guide regional policy makers. In short, our findings point out to the fact that FDI policy should be jointly designed by those regions presenting strong bilateral spillover effects. Thus, greater cooperation among policy makers would be welcome. 相似文献
3.
T. Schöneberg K. Kibler F. E. Wettstein T. D. Bucheli H. R. Forrer T. Musa F. Mascher M. Bertossa B. Keller S. Vogelgsang 《Plant pathology》2019,68(1):173-184
High occurrence of Fusarium poae (FP) and Fusarium langsethiae (FL) and their mycotoxins nivalenol (NIV) and T-2/HT-2 have been observed in Swiss oats. Early prediction of mycotoxin levels is important for farmers and the cereal industry to minimize the risk of contaminated food and feed. Therefore, climate chamber experiments were conducted to investigate the influence of different temperatures (10, 15, 20 °C) and durations (4, 8, 12 h) at 99% relative humidity (RH) on the infection of oats with FP and FL. In addition, to discover the most susceptible period of oats, artificial FL inoculations were conducted at different growth stages. Field experiments were performed to observe the dispersal of these fungal species within the field and to investigate the weather conditions that influence the dispersal. The climate chamber experiments revealed higher contamination with NIV and T-2/HT-2 in the 10 °C treatments and with a prolonged humidity duration of 12 h 99% RH. Inoculations of oat plants at early (DC 61) and mid (DC 65) anthesis, led to higher FL infection and T-2/HT-2 accumulation in the grains compared with treatments at earlier growth stages, which might be due to an increased susceptibility during anthesis. No indication for spore dispersal was observed in the field experiments. The results obtained, together with the cropping factors that influence infection and mycotoxin production, could be used as a first step in developing forecasting models to predict the contamination of oats with the mycotoxins NIV and T-2/HT-2. 相似文献
4.
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
5.
A. Di Francesco I. Cameldi F. Neri L. Barbanti A. Folchi A. Spadoni E. Baraldi 《Plant pathology》2019,68(8):1525-1532
Bull’s eye rot is a typical quiescent postharvest apple disease in major fruit-growing areas. The susceptibility of different apple cultivars to Neofabraea spp. (N. vagabunda and N. malicorticis) was assessed, with Granny Smith showing the most resistance and Cripps Pink the most susceptibility. To assess the factors involved in conidial germination, Neofabraea spp. were grown on crude protein extracts (CPEs) collected from apple fruits at different storage periods. Fungal germ tube growth rate and pathogenic enzyme (cellulase and xylanase) activity were assessed. Results showed that CPEs collected after 2 and 4 months of storage progressively stimulated conidial germination and germ tube elongation, while a lesser effect was observed from CPEs after 1 month of storage. Xylanase proved to be the main degrading enzyme secreted by all the isolates, while cellulase was produced only by N. vagabunda isolates. Overall, the isolate ID02 was the most virulent, based on more rapid germ tube elongation and greater activity of the lytic enzymes. 相似文献
6.
A. Pérez-Sierra P. Romón-Ochoa C. Gorton A. Lewis H. Rees S. Van Der Linde J. Webber 《Plant pathology》2019,68(4):727-737
Chestnut blight, caused by Cryphonectria parasitica, was identified in Devon, UK, in December 2016. Intensive surveys detected the disease at further sites in Devon (seven), Berkshire (one), Dorset (one), Derbyshire (four) and a cluster of eight sites in southeast London. Over 570 survey samples were tested, and 227 were positive for C. parasitica by isolation and real-time PCR. A total of 227 isolates were tested for mating type, and 197 screened for vegetative compatibility group (VCG) and compared with VCGs known from mainland Europe. The same isolates were also screened for the presence of Cryphonectria hypovirus 1 (CHV-1). Eleven VCGs were identified within the UK population. Five corresponded to already known European VCGs but six were unique. The European VCGs mainly came from the Devon, Dorset, Berkshire and Derbyshire disease outbreaks, whilst unique VCGs were almost exclusively from the southeast London cluster. Both mating types were detected, but only one mating type was present at each site, with the exception of a single Devon site. Perithecia of C. parasitica were never observed at any site. CHV-1 was found in seven isolates from three different locations and was always subtype-I, which has limited hypovirulence. Therefore, although CHV-1 is associated with C. parasitica at some outbreaks, it probably has limited impact on virulence. The diversity of VCGs and their distribution at outbreak sites, together with findings of CHV-1, suggests C. parasitica has been introduced to the UK multiple times over at least two decades through international plant trade. 相似文献
7.
In May 2017 and 2018, Planococcus vovae (Nasonov) (Hemiptera: Pseudococcidae) was collected in Hammam Sousse (Tunisia) on the ornamental plant Cupressus macrocarpa (Cupressaceae). The infestation was observed on needles which showed symptoms of desiccation and chlorosis. This is the first record of P. vovae in Tunisia and in North Africa. 相似文献
8.
Peterman William E. Winiarski Kristopher J. Moore Chloe E. Carvalho Carolina da Silva Gilbert Anthony L. Spear Stephen F. 《Landscape Ecology》2019,34(9):2197-2208
Landscape Ecology - Landscape resistance surfaces are often used to address questions related to movement, dispersal, or population connectivity. However, modeling landscape resistance is... 相似文献
9.
Jeannette S. Bayuelo-Jiménez Takashi Muraoka Eulogio de la Cruz-Torres Esperanza Quintero-Ponce Lydia C. Paredes-Gutiérrez Mohammad Zaman 《Soil Use and Management》2020,36(2):240-249
Land-use change from forest to agriculture in the volcanic ash-derived soils of Mexico has increased over recent decades. It is likely that land uses and management practices, particularly fertilizer use have affected phosphorus (P) distribution and availability. The objective of this study was to evaluate the effects of land-use types (native forest and maize mono-cropping), and the related P addition, on the forms and distribution of soil P and their isotopic exchangeability. An Andisol, sampled from a cropping site, along with the contiguous area under native forest was treated with 32P-labelled potassium phosphate (KH232PO4). The soil samples were extracted after incubation times of 7, 21, 35 and 49 days. Phosphorus content and 32P recovery in fractions sequentially extracted were assessed for each incubation time. Total soil P was dominated by inorganic fractions (79 to 86%) in both land-use types. Resin-Pi, bicarbonate extractable inorganic P (Bic-Pi) and sodium hydroxide extractable inorganic P (NaOH0.1-Pi) were all raised with P addition. However, the proportion of organic P fraction was reduced under cropped soil. The recovery of 32P in soils with P addition indicates that resin-Pi, Bic-Pi and NaOH0.1-Pi comprised nearly all the exchangeable P. In native soils with no P addition, more than 19% of the 32P was recovered in Bic-Po and NaOH0.1-Po forms. This finding indicates that organic P cycling is crucial when soil Pi reserves are presented in an inadequate amount. Ecologically based management has to be designed for replenishment and succeeding maintenance of soil organic P compounds to increase sustainable agricultural production. 相似文献
10.
Morantes César Fernández Yarza Florencia Montes María L. Mercader Roberto C. Curutchet Gustavo Torres Sánchez Rosa M. 《Water, air, and soil pollution》2020,231(1):1-13
Water, Air, & Soil Pollution - The treatment efficiency of Chlorella sorokiniana and Scenedesmus species, immobilized in sodium alginate, was evaluated for removing nitrate from groundwater.... 相似文献