全文获取类型
收费全文 | 1818篇 |
免费 | 85篇 |
国内免费 | 2篇 |
专业分类
林业 | 65篇 |
农学 | 35篇 |
基础科学 | 27篇 |
213篇 | |
综合类 | 435篇 |
农作物 | 56篇 |
水产渔业 | 70篇 |
畜牧兽医 | 888篇 |
园艺 | 34篇 |
植物保护 | 82篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 16篇 |
2017年 | 28篇 |
2016年 | 36篇 |
2015年 | 27篇 |
2014年 | 41篇 |
2013年 | 58篇 |
2012年 | 95篇 |
2011年 | 115篇 |
2010年 | 39篇 |
2009年 | 37篇 |
2008年 | 118篇 |
2007年 | 112篇 |
2006年 | 140篇 |
2005年 | 132篇 |
2004年 | 120篇 |
2003年 | 120篇 |
2002年 | 126篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 14篇 |
1972年 | 21篇 |
1969年 | 9篇 |
排序方式: 共有1905条查询结果,搜索用时 15 毫秒
91.
Upendra M. Sainju Harry H. Schomberg Bharat P. Singh Wayne F. Whitehead P. Glynn Tillman Sharon L. Lachnicht-Weyers 《Soil & Tillage Research》2007,96(1-2):205-218
Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on soil C fractions at the 0–150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90 Mg C ha−1 greater in rye + blend than in other cover crops in 2001 but was 1.15–2.24 Mg C ha−1 greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50–150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150 mm was greater with rye + blend than with crimson clover and at 0–50 mm was greater in March than in December 2002. The PCM at 0–50 and 0–150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0–50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24 g CO2–C ha−1 d−1 but MBC increased by 90–224 g CO2–C ha−1 d−1 from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1 kg C ha−1 d−1, and PCM decreased by 10 g CO2–C ha−1 d−1 with rye to 79 g CO2–C ha−1 d−1 with blend, but MBC increased by 13 g CO2–C ha−1 d−1 with blend to 120 g CO2–C ha−1 d−1 with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring. 相似文献
92.
High O3 levels during the 1984 growing season in the southern Appalachian Mountains caused extensive damage to a 28 yr old white pine plantation on a 13.4 ha watershed at the Coweeta Hydrologic Laboratory. Ozone stress effects included premature senescence and loss of foliage, stimulation of pine seedling germination, reduced basal area increment, and small but measurable increases in NO3
–-N and K+ concentrations in stream water. There were no observable effects of O3 damage on nutrient concentrations of stemwood and foliage but net nutrient accumulation was reduced due to lower stemwood production. Ozone injury did not predispose trees to root pathogens or bark beetle infestations. 相似文献
93.
Robert M. Bloxam James W. Hornbeck C. Wayne Martin 《Water, air, and soil pollution》1984,23(4):359-374
The effects of storm dynamics on precipitation chemistry were examined using an atmospheric budget for SO4 ? . One hundred storms occurring between 1975 and 1978 at Hubbard Brook Experimental Forest in New Hampshire were used as test data. Concentrations of major ions were usually greater in convective storms than in continuous or layer storms. For example the geometric mean concentrations of SO4 ? in convective and continuous storms were 4.1 and 1.1 mg L?1, respectively. Higher SO4 ? concentrations also occurred when surface wind directions were south or southwest. The summer maximum in convective activity along with the seasonal dependence of surface wind directions and the seasonal atmospheric chemistry cycle can account for the summer maximum in SO4 ? concentrations observed in the northeastern United States. 相似文献
94.
Fabian H. Leendertz Georg Pauli Wayne Boardman Heinz Ellerbrok Sandra Junglen Boesch Christophe 《Biological conservation》2006,131(2):325-337
Until recently, the focus of great ape behavioural and ecological research has been distinct from the focus of scientists working in medical and veterinary sciences. More scientists are calling for a connection between medical and field research due to recent disease outbreaks in great apes, including Ebola, and indications of cross-transmission of Ebola and other viruses between primates and humans. A major limitation to progress is the lack of information on infectious diseases and their transmission in wild primates. Here, we present examples of successful pathogen detection in wild great apes and describe approaches and techniques that can be used in the field, focusing in particular on investigation of deaths and non-invasive sample collection. This interdisciplinary approach is providing new insights to infectious diseases of great apes and is helping to protect the health of great ape populations. This framework can also be applied to other mammals under threat from infectious diseases, including African wild dogs, seals and Tasmanian devils. In addition to providing benefits for great ape conservation, research that integrates infectious disease with primate ecology provides insights to emerging diseases in humans and the role of disease in primate evolution. 相似文献
95.
C. Dale Becker William E. Fallon Dennis W. Crass Al J. Scott 《Water, air, and soil pollution》1983,19(2):171-184
Acute toxicity screening tests were conducted with water soluble fractions (WSFs) of a solvent refined coal (SRC-II) liquid from a pilot plant and three reference organisms: the cladoceran Daphnia magna, the fathead (FH) minnow Pimephales promelas, and larvae of the midge fly Chironomus tentans. Stock WSFs typically contained 900 to 1100 mg l?1 total carbon (TC) and 700 to 800 mg l?1 total dye complexable phenolics, with lower concentrations of aromatic and saturate hydrocarbons and N compounds. Under standard test conditions (temperature 20 °C, pH 7.3 to 8.2 and hardness 65 to 80 mg l?1 CaCO3), mean LC50 values in mg l? TC were 3.3 for daphnia, 11.l for FH minnow, and 13.7 for midge larvae. Acute toxicity was also examined under other water quality conditions (temperature 10 or 25 °C, pH 6.0 or 6.5, and hardness ? 180 to 220 mg 1?1 CaCO3). The coal liquid was less toxic to daphnids at 10 °C than at 20 or 25 °C, but response of other organisms at different temperatures varied. The pH of the liquid had little effect on toxicity values. All organisms were less susceptible in hard water. Chemical compositions of stock WSFs were similar, suggesting that temperature, pH, and hardness had little effect on solubility of major synfucl components. Dilution indexes for stock WSFs were higher than for petroleum oils, and reflect the greater solubility of chemicals from the liquified coal in freshwater. 相似文献
96.
97.
98.
Normile D 《Science (New York, N.Y.)》2003,300(5620):714-715
99.
100.