全文获取类型
收费全文 | 10470篇 |
免费 | 523篇 |
国内免费 | 11篇 |
专业分类
林业 | 662篇 |
农学 | 375篇 |
基础科学 | 97篇 |
1762篇 | |
综合类 | 1464篇 |
农作物 | 534篇 |
水产渔业 | 577篇 |
畜牧兽医 | 4296篇 |
园艺 | 340篇 |
植物保护 | 897篇 |
出版年
2023年 | 49篇 |
2022年 | 70篇 |
2021年 | 155篇 |
2020年 | 192篇 |
2019年 | 185篇 |
2018年 | 196篇 |
2017年 | 189篇 |
2016年 | 197篇 |
2015年 | 170篇 |
2014年 | 223篇 |
2013年 | 454篇 |
2012年 | 492篇 |
2011年 | 606篇 |
2010年 | 382篇 |
2009年 | 335篇 |
2008年 | 606篇 |
2007年 | 561篇 |
2006年 | 566篇 |
2005年 | 559篇 |
2004年 | 551篇 |
2003年 | 540篇 |
2002年 | 521篇 |
2001年 | 206篇 |
2000年 | 174篇 |
1999年 | 172篇 |
1998年 | 101篇 |
1997年 | 73篇 |
1996年 | 108篇 |
1995年 | 89篇 |
1994年 | 94篇 |
1993年 | 104篇 |
1992年 | 134篇 |
1991年 | 106篇 |
1990年 | 128篇 |
1989年 | 113篇 |
1988年 | 75篇 |
1987年 | 92篇 |
1986年 | 76篇 |
1985年 | 98篇 |
1984年 | 103篇 |
1983年 | 90篇 |
1982年 | 77篇 |
1981年 | 51篇 |
1980年 | 53篇 |
1979年 | 56篇 |
1978年 | 67篇 |
1977年 | 73篇 |
1976年 | 63篇 |
1975年 | 56篇 |
1974年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Static equilibrium headspace was diluted with a stream of nitrogen to study the stability of the volatile headspace concentration. The headspace dilution profile of 18 volatile compounds above aqueous and ethanolic solutions was measured in real time using atmospheric pressure chemical ionization-mass spectrometry. Under dynamic conditions the volatiles headspace concentration above water solutions decreased readily upon dilution. The presence of ethanol helped to maintain the volatile headspace concentration when the ethanol solution concentration was above 50 mL/L. This effect was such that under dynamic conditions the absolute volatile concentration above an ethanolic solution was higher than that above an aqueous solution, contrary to results observed in equilibrium studies. The ratio of the headspace concentration of volatiles above ethanolic 120 mL/L and water solutions was correlated to their air/water partition coefficient. 相似文献
92.
Benjamin M. Rau Robin Tausch Alicia Reiner Dale W. Johnson Jeanne C. Chambers Robert R. Blank Annmarrie Lucchesi 《Strength and Conditioning Journal》2010,63(2):197-202
Increases in pinyon and juniper woodland cover associated with land-use history are suggested to provide offsets for carbon emissions in arid regions. However, the largest pools of carbon in arid landscapes are typically found in soils, and aboveground biomass cannot be considered long-term storage in fire-prone ecosystems. Also, the objectives of carbon storage may conflict with management for other ecosystem services and fuels reduction. Before appropriate decisions can be made it is necessary to understand the interactions between woodland expansion, management treatments, and carbon retention. We quantified effects of prescribed fire as a fuels reduction and ecosystem maintenance treatment on fuel loads, ecosystem carbon, and nitrogen in a pinyon–juniper woodland in the central Great Basin. We found that plots containing 30% tree cover averaged nearly 40 000 kg · ha?1 in total aboveground biomass, 80 000 kg · ha?1 in ecosystem carbon (C), and 5 000 kg · ha?1 in ecosystem nitrogen (N). Only 25% of ecosystem C and 5% of ecosystem N resided in aboveground biomass pools. Prescribed burning resulted in a 65% reduction in aboveground biomass, a 68% reduction in aboveground C, and a 78% reduction in aboveground N. No statistically significant change in soil or total ecosystem C or N occurred. Prescribed fire was effective at reducing fuels on the landscape and resulted in losses of C and N from aboveground biomass. However, the immediate and long-term effects of burning on soil and total ecosystem C and N is still unclear. 相似文献
93.
Van den Hout K. D. Bakker D. J. Berdowski J. J. M. Van Jaarsveld J. A. Reinds G. J. Bril J. Breeuwsma A. Groenenberg J. E. De Vries W. Van Pagee J. A. Villars M. Sliggers C. J. 《Water, air, and soil pollution》1999,109(1-4):357-396
In the pilot study ESQUAD the impact of atmospheric deposition of three heavy metals (cadmium, copper and lead) and two persistent organic pollutants (benzo(a)-pyrene and lindane) on the quality of European soils and seawater has been calculated. Calculations have been made of atmospheric transport and deposition using a detailed emissions database for Europe. This enabled deposition maps to be produced to a resolution of approximately 50 km. The distribution of pollutant concentrations in forest soils was calculated for each grid cell using a database of soil property parameters in Europe. For the North Sea, a model was used to map long-term concentrations in water and sediment, which are due to atmospheric deposition and other, non-atmospheric sources. The model calculations allowed detailed comparisons of deposition fluxes and concentrations of the substances studied with critical loads and environmental quality threshold values, including critical loads. Although significant uncertainties were identified, the study gives insight in how threshold exceedance rates in Europe relate to pollutant type, threshold type, environmental compartment and chemophysical phase (adsorbed, dissolved). For all pollutants and for all compartments exceedances were calculated for at least some of the quality thresholds that were chosen. 相似文献
94.
A method to estimate the magnitude of discontinuities or similarities in parent materials having equivalent mineralogical composition is proposed. It is based on a particle size distribution index which compares for two samples the weight percentages of all fractions taken between selected size limits.The indexes form a matrix and are used to construct a dendrogram which illustrates the clustering into groups. The calculations are carried out by computer using a Fortran programme.The technique was applied to a set of soil samples of Mollisols in the humid undulating pampa in Argentina and good agreement with field observations was obtained. 相似文献
95.
A neutral and an acidic soil were treated with different doses (0–3,000 mg Cu kg–1 soil as CuSO4) of copper. The percentages of inhibition of nitrification in both soils varied from 5 to 97%, but for the N mineralization
these percentages varied from 8 to 65%. The toxic effect of Cu for basal nitrification and N mineralization was assessed as
critical. Nitrification was more sensitive than ammonification to copper toxicity. It appears that an ecological dose of inhibition
for nitrification and N mineralization higher than 10% is suitable as an indicator for Cu contamination. Soil resiliency assessed
by N mineralization in the lime treatments varied from 11 to 154% in the sandy soil and from 70 to 168% in the sandy loam
soil. A combined application of lime and compost significantly increased soil resiliency. The percentage increase varied from
904 to 1,390% in the sandy soil and from 767 to 2,230% in the sandy loam soil. It appears that compost was a powerful agent
for recovering the soil fertility of Cu-contaminated soils as assessed by N transformation. The acidic sandy soil showed a
lower capacity for recovery after Cu toxicity stress.
Received: 27 February 1999 相似文献
96.
Spake Rebecca Soga Masashi Kawamura Kazuhiro Cooke Robert S. Yamaura Yuichi Eigenbrod Felix 《Landscape Ecology》2020,35(5):1055-1071
Landscape Ecology - Functional responses to landscape heterogeneity are context-dependent, hampering the transferability of landscape-scale conservation initiatives. Japan provides a unique... 相似文献
97.
D.J. Alderman P. Van Banning A. Perez-Colomer 《Aquaculture (Amsterdam, Netherlands)》1977,10(4):335-340
Regularly occurring mortalities of the flat oyster, Ostrea edulis L., on two sites, one in Galicia, Spain, and one in Yugoslavia, are reported. The oysters involved showed an apparent neoplastic condition of the haemocytes. No pathogen has been detected and the possible involvement of adverse water quality is suggested. 相似文献
98.
99.
Moerkens Rob Berckmoes Els Van Damme Veerle Wittemans Lieve Tirry Luc Casteels Hans De Clercq Patrick De Vis Raf 《植物病害和植物保护杂志》2017,124(3):295-303
Journal of Plant Diseases and Protection - Macrolophus pygmaeus Rambur (Hemiptera: Miridae) is a key biological control agent in greenhouse tomato crops. In the present study, we describe the... 相似文献
100.
Effect of an intensive mechanical removal effort on a population of non‐native rainbow trout Oncorhynchus mykiss in a South African headwater stream 下载免费PDF全文
Jeremy Shelton Olaf Weyl Johannes Van Der Walt Sean Marr Dean Impson Kristine Maciejewski Donovan Tye Helen Dallas Karen Esler 《水产资源保护:海洋与淡水生态系统》2017,27(5):1051-1055