全文获取类型
收费全文 | 769篇 |
免费 | 36篇 |
专业分类
林业 | 67篇 |
农学 | 27篇 |
基础科学 | 3篇 |
95篇 | |
综合类 | 77篇 |
农作物 | 12篇 |
水产渔业 | 28篇 |
畜牧兽医 | 442篇 |
园艺 | 4篇 |
植物保护 | 50篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 37篇 |
2012年 | 37篇 |
2011年 | 31篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 30篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 12篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1996年 | 8篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 10篇 |
1970年 | 8篇 |
1968年 | 4篇 |
1966年 | 11篇 |
1938年 | 6篇 |
排序方式: 共有805条查询结果,搜索用时 15 毫秒
51.
Linda Dykes Leo Hoffmann Jr.Ostilio Portillo-Rodriguez William L. RooneyLloyd W. Rooney 《Journal of Cereal Science》2014
The reported high phenolic levels in sorghum have led an interest from sorghum breeding programs in developing and identifying germplasms with high phenolic levels, which require screening a large number of samples to find those with the highest levels. Since wet chemistry screening methods are slow, expensive, and destructive, the use of NIR calibration curves could be an alternative. The objectives of this project were to determine the variation range in total phenols, condensed tannins, and 3-deoxyanthocyanidin levels in a diverse set of sorghum genotypes and to assess the predictive value of NIR curves to estimate these compounds in sorghum. A calibration curve to estimate each compound was developed and validated with an independent validation set. Calibration curve correlations for total phenols, condensed tannins, and 3-deoxyanthocyanidins were r = 0.98, 0.97, and 0.99, respectively. Correlations between NIR-predicted values and reference values in the validation set were significant for total phenols (r = 0.93), condensed tannins (r = 0.81) and 3-deoxyanthocyanidin (r = 0.82). These indicated that sufficient variation for these compounds existed within sorghum and that NIR calibration curves could be used to rapidly and non-destructively predict total phenols, condensed tannins, and 3-deoxyanthocyanidins concentrations in whole grain sorghum. 相似文献
52.
53.
In 3 experiments young broiler chickens were supplied on various feeding levels in the growth range between 200 and 2500 g live weight (2.8 and 2.0 in experiment 1, 2.8, 2.3 and 1.8 in experiments 2 and 4, maintenance = feeding level 1.0). In experiments 1 and 2 short-time measurings (30 min) of heat production by means of gas exchange were made at 500, 1000, 1500 and 2000 g live weight in the post-absorptive state and on the maintenance level of feeding. In experiment 1 the heat production of the restrictively fed chickens was in 3 out of the 4 stages of development studied significantly lower by 10-14% than that of the intensively fed ones. In experiment 2 such an effect could not be observed. Fed on the level of energy maintenance, broilers weighing approximately 2000 g (experiment 3) did not show a significant influence of the sex on heat production as a result of 30-minute gas exchange measurings in the post-absorptive state. In experiment 4 24-hour measurings of the energy metabolism were carried out in the growth development in periods of feeding on the maintenance level by means of indirect calorimetry. In the live weight range between 0.9 and 1.3 kg there was only a low, non-significant decrease of the energy maintenance requirement of 4-6% of the highly restrictively fed chickens in comparison to the intensively fed ones. After continued feed restriction (live weight range 1.7-2.2 kg) an energy maintenance requirement reduced by 17% was measured. In an analogously arranged experiment with 24-hour energy metabolism measurings (experiment 5) male Wistar rats in the growth range between 70 and 280 g were supplied on the feeding levels 1.8 and 1.4 resp. In all three periods studied on the feeding level maintenance--beginning at 140-150 g live weight--the highly restrictively fed animals showed a slightly reduced energy maintenance requirement by 8%, 3% (non-significant) and 6% in comparison with the intensively fed animals. 相似文献
54.
55.
56.
N2O Emissions from True Meadows Dependent on Location and N Fertilization Agricultural production is thought to be a main anthropogenic emitter of nitrous oxide (N2O), which contributes to global warming and the destruction of the ozone layer. There is still considerable uncertainty about the amount of N2O emission, and the site‐specific parameters that affect N2O emission. From October 1995 until March 1998 experiments were conducted at established field plots (true meadows) at three different sites, i.e. low mountain range (Eifel), lowland (Niederrhein), and moist meadows (Münsterland). Plots were fertilized with calcium ammonium nitrate (CAN) at nitrogen equivalents ranging from 0 to 360 kg N ha–1. N2O fluxes were measured throughout the whole year using the closed‐chamber method. In addition, data on temperature, water‐filled pore space and precipitation were collected. N2O emission rates (mg N2O‐N ha–1 h–1) were highest either after fertilizer application or in winter during frost, depending on the experimental site and N dosage. The annual amount of N losses due to N2O emission was dependent on the experimental site and the type and dosage of fertilizer. Disregarding the 360 kg N ha–1 level of the CAN treatments, the N losses in this experiment were less than 1.5 kg N2O‐N ha–1 yr–1. At low fertilizer dosage there was no reliable correlation between the amount of N that was applied and the amount of N2O that was emitted. However, with high fertilizer levels the N2O emissions increased gradually. Finally, N2O emissions were more influenced by the amount of CAN than by the site. 相似文献
57.
Clinical and patho-morphological investigation of spontaneously occurring Seriodontal isease in dogs
Diagnostic evaluation of, and treatment planning for, different periodontal diseases of dogs are a common problem in veterinary dentistry. Therefore the aim of the present study was to propose a classification for inflammatory periodontal disease. One hundred and twenty-three male and female poodles (from two to over 12 years) were used for the clinical investigations; 120 periodontitis teeth were analysed for pathomorphological signs of inflammation. The recorded data made it possible to differentiate five forms of gingivitis (gingivitis simplex, hyperplastica, ulcerosa, granulomatosa and desquamativa) and three forms of periodontitis (juvenile, rapidly progressive adult and chronic adult periodontitis). The pathomorphological investigations allowed a differentiation between acute progressive inflammation, chronic nonprogressive inflammation, chronic proliferative inflammation and chronic resorptive inflammation. It is concluded that standardised diagnoses as well as the pathomorphological background may be helpful tools for providing effective treatment strategies. 相似文献
58.
The energy requirement of pregnant and lactating sows is derived on the basis of extensive experimental studies of the energy metabolism (indirect calorimetry, slaughtering) according to the factorial method. For the first reproduction cycle (RC) 0.41 MJ metabolizable energy (ME) or 0.29 MJ net energy fat, pig (NEFpig) resp. were necessary for energy maintenance requirement for pregnant and lactating sows and, depending on age, 0.44 MJ ME or 0.31 MJNEFpig in the second or third RC and 0.47 MJ ME/kg LW0.75.d or 0.33 MJ NEFpig/kg LW0.75.d in the 4th-8th RC. A linear increase of up to 6% of the energy requirement caused by pregnancy between the 85th and 115th day of pregnancy is taken into consideration. Energy requirement per 1 MJ retention both in pregnancy and lactation is 1.45 MJ ME or 1.03 MJ NEFpig, per 1 MJ milk yield it is 1.33 MJ ME or 0.91 MJ NEFpig. 1 MJ body energy for milk yield corresponds to 1.20 MJ ME or 0.82 MJ NEFpig. Equations describing energy retention in the products of conception, uterus and udder are established as well as equations characterizing the connections between live weight gain or loss and energy content of the gain or loss. 相似文献
59.
Solute Accumulation as a Cause for Quality Losses in Sugar Beet Submitted to Continuous and Temporary Drought Stress 总被引:1,自引:0,他引:1
Adaptation to low water availability in sugar beet includes the accumulation of solutes relevant for the technical quality of the beet. Two sugar beet genotypes were grown in pot experiments under drought stress of different severity to study effects on taproot composition and concentration of solutes relevant for technical quality, reversibility of drought effects after re‐watering and genotypic differences in drought response. Differences in stress sensitivity between the genotypes were not observed as reductions in taproot and leaf dry weight and white sugar yield were the same. Increasing dry matter concentration with decreasing water supply could, in part, be attributed to an increase in the concentration of cell wall components. The major solutes in the taproot were sucrose, potassium, amino N (the sum of amino acids) and betaine. Sucrose concentration decreased considerably under drought, indicating limited availability of assimilates. In contrast, all further solutes increased in concentration with increasing severity of stress. However, the response of individual solutes varied largely. Changes in amino N and nitrate were most pronounced and probably reflect accumulation of non‐utilized metabolites under limited growth. The drought‐induced accumulation of taproot solutes implicates a considerable decrease in the technical quality of the beet. It was only in part reversible by re‐watering. Genotypic variability for solute accumulation under water deficiency was observed but was not linked to drought tolerance. 相似文献
60.
Nitrogen mineralization in loamy arable soils after increasing the ploughing depth and ploughing grasslands 总被引:2,自引:0,他引:2
Abstract. Increasing the ploughing depth and ploughing in grassland has been common in Germany during the past 20 years. Incubation studies were conducted with topsoils from luvisols and gleysols at different times after change of management in order to assess its influence on nitrogen mineralization and its kinetic parameters.
The results show that deep ploughing slows the mineralization of nitrogen. The difference between earlier (1967–72) and more recently (1980–82) deepened topsoil has become smaller after a further three years of cultivation, however. The preceding crops (wheat or sugar beet), the amount of N fertilizer as well as clay and nitrogen contents cause a variation in N mineralization. The results indicate a continuing approach of an'equilibrium'organic matter and nitrogen content. The enrichment capacity of intensively managed soils may be replenished within 10 years.
Gleysols formerly under grass mineralize more nitrogen than'traditionally'ploughed soils, even 27 years after the ploughing-in. While nitrogen from easily decomposable materials decreases within the first 10 years, the resistant fraction is a long-lasting determinant for N mineralization. Both processes need to be considered when applying fertilizer to minimize nitrate leaching. 相似文献
The results show that deep ploughing slows the mineralization of nitrogen. The difference between earlier (1967–72) and more recently (1980–82) deepened topsoil has become smaller after a further three years of cultivation, however. The preceding crops (wheat or sugar beet), the amount of N fertilizer as well as clay and nitrogen contents cause a variation in N mineralization. The results indicate a continuing approach of an'equilibrium'organic matter and nitrogen content. The enrichment capacity of intensively managed soils may be replenished within 10 years.
Gleysols formerly under grass mineralize more nitrogen than'traditionally'ploughed soils, even 27 years after the ploughing-in. While nitrogen from easily decomposable materials decreases within the first 10 years, the resistant fraction is a long-lasting determinant for N mineralization. Both processes need to be considered when applying fertilizer to minimize nitrate leaching. 相似文献