全文获取类型
收费全文 | 334篇 |
免费 | 31篇 |
专业分类
林业 | 9篇 |
农学 | 63篇 |
基础科学 | 2篇 |
51篇 | |
综合类 | 54篇 |
农作物 | 30篇 |
水产渔业 | 32篇 |
畜牧兽医 | 95篇 |
园艺 | 7篇 |
植物保护 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 16篇 |
2012年 | 17篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 23篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 3篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1958年 | 3篇 |
排序方式: 共有365条查询结果,搜索用时 296 毫秒
91.
M. Riccardi C. Pulvento A. Lavini R. d'Andria S.‐E. Jacobsen 《Journal of Agronomy and Crop Science》2014,200(4):246-260
Drought and salinity are the most important abiotic stresses that affect plant's growth and productivity. The aim of the present work was to evaluate the effect of salt and water deficit on water relations, growth parameters and capacity to accumulate inorganic solutes in quinoa plants. An irrigation experiment was carried out in 2009 and 2010 in the Volturno river plain. Three treatments irrigated with fresh water (Q100, Q50 and Q25) and three irrigated with saline water (Q100S, Q50S and Q25S) were tested. For saline irrigation, water with an electrical conductivity of 22 dS m?1 was used. Actual evapotranspiration (ETa), water productivity (WP), biomass allocation, relative growth rate (RGR), net assimilation rate (NAR), specific leaf area, leaf area ratio and ions accumulation of quinoa plants were evaluated. WP and plant growth were not influenced by saline irrigation, as quinoa plants incorporated salt ions in the tissues (stems, roots, leaves) preserving seed quality. Treatment with a reduction in the irrigation water to 25 % of full irrigated treatment (Q25) caused an increase in WP and a reduced dry matter accumulation in the leaves. Quinoa plants (Q25) were initially negatively affected by severe drought with RGR and NAR reduction, and then, they adapted to it. Quinoa could be considered a drought tolerant crop that adapt photosynthetic rate to compensate for a reduced growth. 相似文献
92.
基于改进Bayes抠图算法的麦穗小穗自动计数方法 总被引:1,自引:1,他引:0
小麦产量评估需人工获取田间单位面积的麦穗数和麦穗小穗数,往往耗时耗力。为了实现高效、自动地麦穗小穗计数,提出一种基于改进Bayes抠图算法的麦穗小穗自动计数方法。该方法首先利用改进Bayes抠图算法对获取地自然生长条件下的麦穗图像进行抠图,将麦穗从自然背景中分割出来。然后对该图像进行平滑滤波和二值化,运用迭代极限腐蚀运算对二值化图像进行腐蚀处理,去除麦穗图像中的麦芒,分离出麦穗上每个单独的麦穗小穗。再运用面积滤波滤除掉面积过小的区域,对剩余区域的黑洞进行填充,由此每个单独的麦穗小穗形成一个单独的连通区域,最后对连通区域进行标记和计数,完成麦穗小穗的自动计数。使用4个小麦品种的麦穗图像对麦穗上的小穗进行计数验证,结果表明,该方法在识别4个品种田间麦穗单幅图像中小穗数量的平均计数精度达到94.53%,平均相对误差为5.47%,对比已有麦穗小穗自动计数方法,计数精度显著提高,这对于小麦在线产量预估具有重要意义。 相似文献
93.
Methods to remove dioxins and polychlorinated biphenyls (PCBs) from fishmeal were investigated and compared. The tested methods include (i) lowering the fat content and simultaneously the level of toxic contaminants using either organic solvents or (ii) lowering the fat content using protease and (iii) removal of dioxins and PCBs using either oil extraction or (iv) breakdown of dioxin and PCBs using oxidoreductase. The results showed that the organic solvents tested (ethanol, isopropanol, and isohexane) were efficiently lowering the oil content of the fishmeal by 80%. However, the treated fishmeal has a low fat content and may contain traces of solvent. The protease alcalase was not as efficient as the solvent extraction and only removed approximately 30% of the oil but presented the advantage of being a mild process. Other proteases, alone or in combination with other enzymes, might give better yield if the reaction conditions are optimized. In contrast, extraction of dioxin and PCBs using olive oil or fish oil was very effective and resulted in 60-75% extraction of dioxin and PCBs, respectively, after a single extraction step. No preference for the oil type was observed. This method is very simple and quick and does not require an important investment for the fishmeal producer. It is expected that with optimization this method could be implemented at an industrial scale without too many difficulties. In contrast, the oxidoreductases tested did not result in a major degradation of dioxins and PCBs with only 10-15% degradation achieved. However, with the recent advancement in biotechnology, it is possible that future research will result in the development of enzymes that effectively degrade recalcitrant contaminants. 相似文献
94.
95.
We know little about the ability of protozoa to colonize soils, including their successional patterns. To elucidate this issue, we investigated in which order different protozoan morpho-types colonize sterile soil. We used sterilized soils with different carbon content, and exposed them to the atmosphere for a period of 14 months. Bacteria and flagellates occurred in high numbers after 25 days. Ciliates reached high abundance levels after 137 days, followed by amoebae after 245 days. Numbers of distinguishable protozoan morpho-types increased until 245 days after exposure and declined thereafter. DGGE bands showed a remarkable shift in bacterial diversity with time and a significant increase of detectable gene-types until day 137. 相似文献
96.
Socioeconomic impact of widespread adoption of precision farming and controlled traffic systems in Denmark 总被引:1,自引:0,他引:1
Hans Grinsted Jensen Lars-Bo Jacobsen S?ren Marcus Pedersen Elena Tavella 《Precision Agriculture》2012,13(6):661-677
In this study we assess the economic profitability of implementing various precision farming (PF) technologies and controlled traffic farming (CTF) on 4 main crops in Denmark. The study provides insight into technological requirements, and identifies related costs and benefits to farmers and the Danish society as a whole. At the farm level, the findings from the study indicate that an implementation of CTF systems may have a significant impact on fuel savings due to a reduced overlap with auto guidance systems and easier movement with tractors and tools in the field. The PF site-specific weed management approach may facilitate large savings in the use of herbicides. At the national level, the results clearly show that the benefits to the Danish economy of adopting this new technology is positive with increased income to farmers and a reduction in fuel consumption and pesticides/herbicides use. The obtained results reflect the long term economic effect of implementing new production methods in Denmark where soil fertility increases over time due to reduced traffic increasing yields. Over all, the Danish GDP is estimated to increase by 34?million?? due to the implementation of PF and CTF on larger farms in Denmark. The results also clearly show that adoption of PF and CTF farming systems will benefit the environment. The agricultural sectors input of environmental harmful inputs are reduced in all scenarios presented in this paper. The adoption of PF and CTF systems should thus be of interest to politicians since it clearly facilitates aims of environmental policies currently under implementation by the Danish government. 相似文献
97.
Henrik Baktoft Kim Aarestrup Søren Berg Mikkel Boel Lene Jacobsen Niels Jepsen Anders Koed Jon C. Svendsen Christian Skov 《Ecology of Freshwater Fish》2012,21(3):386-394
Abstract – Temperate lakes can be ice covered for several months each year, yet little is known about the behaviour and activity of the fish during the cold season. As northern pike represents the top of the food web in many northern temperate lakes and may structure the ecosystem both directly and indirectly, a detailed understanding of the behaviour of this species during winter is important. We continuously monitored the activity of adult northern pike (Esox lucius) in a small temperate lake from late summer to winter for two consecutive years using an automatic acoustic positional telemetry system. Four subsample periods representing different temperature regimes from each year were chosen for further investigation. The results revealed that pike activity was similar between seasons. In all periods, a distinct diel pattern, showing increased activity during day as compared to night, was evident. Our findings indicate that the fish component of temperate lentic ecosystems can be more active during the cold season than previously assumed. This may have implications for the structuring effect of pike on the lower trophic levels. 相似文献
98.
Jacobsen S Niewold TA Kornalijnslijper E Toussaint MJ Gruys E 《Veterinary immunology and immunopathology》2005,104(1-2):21-31
The aim of the present study was to characterise the serum amyloid A (SAA) response to intramammary inoculation of Escherichia coli and to examine the distribution of hepatically and extrahepatically produced SAA isoforms in plasma and milk from cows with mastitis. Milk and plasma SAA concentrations were determined before and after experimental induction of E. coli mastitis in six dairy cows. The milk SAA response was characterised by low or undetectable levels before inoculation, very rapid and large increases in concentration after inoculation, and rapid decline towards baseline levels after resolution of disease. In plasma from cows with experimentally induced E. coli mastitis, four hepatically derived SAA isoforms with apparent isoelectric point (pI) values of 5.8, 6.2, 6.8 and 7.4 were demonstrated by denaturing isoelectric focusing. In milk three highly alkaline isoforms with apparent pI values above 9.3 appeared 12 h post-inoculation. These isoforms were not present in any of the plasma samples, and it therefore seems likely that they were locally produced, tissue-specific isoforms. At 24-36 h post-inoculation one or more acidic isoforms corresponding to those found in plasma appeared in the milk samples. The isoforms demonstrated in plasma from cows with E. coli mastitis were also present in serum obtained from three cows with clinical Streptococcus uberis mastitis. In conclusion, experimentally induced E. coli mastitis is accompanied by a prominent SAA response. The results of the present study indicate that SAA accumulation in mastitic milk is the result of both local synthesis of SAA and of hepatically derived SAA gaining access to the milk due to increased permeability of the blood-milk barrier. 相似文献
99.
Previous studies have noted that susceptibility to systemic lipopolysaccharide (LPS) exposure seems to differ between individual cows. However, to date inter-individual variation in the response to intravenous injection of LPS has been reported only as an empirical finding, and its existence or extent has never been backed up by statistical analyses. The aim of the present study was therefore to investigate the dose-dependency of clinical, haematological and blood biochemical responses to intravenous LPS injection in dairy cattle and to determine the extent to which these responses differed between individual cows. Eight dairy cows each received three intravenous injections of Escherichia coli LPS (10, 100, and 1000 ng/kg, consecutively) at three-week intervals. All three LPS doses induced clinical, haematological, and blood biochemical responses lasting up to several days. The strength of all of the responses increased significantly with an increasing LPS dose. A statistically significant inter-individual variation was demonstrated for all clinical, haematological, and blood biochemical responses except for serum calcium concentrations. More than half of the statistical variation in white blood cell and thrombocyte counts could be attributed to the individual. The results of this study show that despite the existence of a dose-response relationship between LPS and ensuing clinical, haematological, and blood biochemical responses, the majority of responses to LPS differ significantly in strength and duration from cow to cow. 相似文献
100.
Jacobsen H Holm P Schmidt M Avery B Greve T Callesen H 《Acta veterinaria Scandinavica》2003,44(1-2):87-95
The general objective of this study was to perform follow-up studies including selected peri- and postnatal characteristics on calves born after transfer of in vitro produced (IVP) embryos vitrified by the 'Open Pulled Straw' (OPS) method. An overall pregnancy rate of 16% after transfer of the OPS-vitrified IVP embryos was achieved and resulted in birth of 9 calves, with 11 AI calves serving as controls. There were no immediate or long-term effects on these calves with respect to birth weight, gestation length, perinatal mortality, growth rate, disease susceptibility and reproductive performance. 相似文献