首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   474篇
  免费   13篇
  国内免费   2篇
林业   46篇
农学   3篇
基础科学   1篇
  99篇
综合类   38篇
农作物   22篇
水产渔业   49篇
畜牧兽医   191篇
园艺   15篇
植物保护   25篇
  2023年   5篇
  2022年   1篇
  2021年   12篇
  2020年   16篇
  2019年   14篇
  2018年   10篇
  2017年   7篇
  2016年   11篇
  2015年   17篇
  2014年   22篇
  2013年   25篇
  2012年   34篇
  2011年   43篇
  2010年   25篇
  2009年   19篇
  2008年   46篇
  2007年   31篇
  2006年   33篇
  2005年   25篇
  2004年   28篇
  2003年   14篇
  2002年   12篇
  2001年   8篇
  2000年   2篇
  1996年   2篇
  1995年   5篇
  1994年   1篇
  1993年   1篇
  1990年   2篇
  1989年   1篇
  1987年   1篇
  1986年   3篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1974年   1篇
  1972年   1篇
  1971年   1篇
  1967年   1篇
  1965年   1篇
排序方式: 共有489条查询结果,搜索用时 125 毫秒
81.
The objective of the present study was to determine whether concentrations of different isoflavones (puerarin, genistein, genistin, daidzein, and daidzin) in shoots and roots of five selected soybean genotypes would respond the same or differently to red (650 nm peak transmittance) and far-red (750 nm peak transmittance) light treatments given under controlled environments. Levels of isoflavones (mg g(-1) dry weight biomass) present in seeds, control roots, and shoots and 10 day light-treated seedlings (light, dark, red, and far-red wavelengths) of soybean (Glycine max) were determined by high-performance liquid chromatography analysis in comparison with known isoflavone standards. Seeds of the five soybean genotypes studied consistently stored most of their isoflavones as glucosyl conjugates (e.g., daidzin, genistin, and puerarin). For the five soybean genotypes, isoflavone levels were lower in the seeds as compared with roots plus shoots of control, time zero (first true leaf stage) seedlings. Following 10 days of the respective light treatments, we found that (i) isoflavone levels were enhanced in dark-grown plants over light-grown plants for three of the five genotypes (a new finding) and the reverse occurred for a single genotype (a typical response of legumes) and (ii) generally, far-red end of day (EOD) light treatment enhanced total isoflavone levels in roots plus shoots over red EOD light treatment. Results from the present study show that phytochrome does appear to play a role in regulating isoflavone levels in developing soybean seedlings and that this influence by red/far-red-mediated phytochrome reactions is strongly dependent on the genotypes selected for study.  相似文献   
82.
This study evaluated the effect of dietary supplementation with l-tryptophan (L-TRP), a serotonin precursor, on the aggressiveness of juvenile matrinxã Brycon amazonicus. Fish were kept in individual aquaria for 7 days receiving the diets: D1 (control: 0.47% of TRP), D2 (0.94% of TRP), D3 (1.88% of TRP), and D4 (3.76% of TRP). After this, they were grouped with an intruder fish to establish a resident–intruder relationship during periods of 20 min. Blood cortisol, glucose, chloride, sodium and calcium; hemoglobin, hematocrit, red blood cell count and volume; liver glycogen and lipids were measured. Territoriality had significant effect on the aggressiveness of matrinxã (the residents were more aggressive than intruders, P < 0.001) and tryptophan significantly affected their behavior. Fish fed with the D2 diet presented a longer latency until the first attack (P = 0.0069) and bit the intruder fewer times (P = 0.0136) during the period of observation, compared to the control group. The frequency of bites and chases after the first attack was not affected by the dietary supplementation of TRP. Physiological variables were not significantly affected by the diet, except for a moderate increase in cortisol level in fish fed with D2 diet after the fight, indicating slight activation of the hypothalamus–pituitary–interrenal axis. The results show that juvenile matrinxã have aggressive and territorial behavior and that a diet containing 9.4 g TRP kg?1 alter their aggressiveness, without affecting the stress-related physiological parameters.  相似文献   
83.
84.
Pseudotuberculosis, an infection caused by the ubiquitous enteropathogenic bacterium Yersinia pseudotuberculosis, is a recurrent veterinary problem in livestock and zoo animals. The only vaccine currently available in zoos is Pseudovac (a mixture of killed strains of various serotypes), but its efficacy is not well established. We show here that Pseudovac does not protect guinea pigs against a severe Y. pseudotuberculosis infection. We thus evaluated the possibility of using a live attenuated Y. pseudotuberculosis strain (IP32680) as an oral vaccine against animal pseudotuberculosis. We report that IP32680 is avirulent for guinea pigs and induces a strong IgG response against various serotypes of Y. pseudotuberculosis. One and two oral inoculations of IP32680 provided 50% and 83% protection, respectively against a severe infection with a highly pathogenic strain. The avirulent Y. pseudotuberculosis IP32680 is therefore much more protective than Pseudovac and may represent a valuable oral vaccine against pseudotuberculosis in zoo animals.  相似文献   
85.
86.
Virus-induced gene silencing (VIGS) is an alternative reverse genetics tool for silencing of genes in some plants, which are difficult to transform. The pea early-browning virus (PEBV) has been developed as a VIGS vector and used in pea for functional analysis of several genes. However, the available PEBV-VIGS protocols are inadequate for studying genes involved in the symbiosis with arbuscular mycorrhizal fungi (AMF).  相似文献   
87.

Background  

Gene silencing vectors based on Barley stripe mosaic virus (BSMV) are used extensively in cereals to study gene function, but nearly all studies have been limited to genes expressed in leaves of barley and wheat. However since many important aspects of plant biology are based on root-expressed genes we wanted to explore the potential of BSMV for silencing genes in root tissues. Furthermore, the newly completed genome sequence of the emerging cereal model species Brachypodium distachyon as well as the increasing amount of EST sequence information available for oat (Avena species) have created a need for tools to study gene function in these species.  相似文献   
88.
89.
Zinc (Zn) is a plant nutrient; however, at elevated levels it rapidly becomes phytotoxic. In order to obtain insight into the physiological background of its toxicity, the impact of elevated Zn2+ concentrations (1 to 10 μM) in the root environment on physiological functioning of Chinese cabbage was studied. Exposure of Chinese cabbage (Brassica pekinensis) to elevated Zn2+ concentrations (≥ 5 μM) in the root environment resulted in leaf chlorosis and decreased biomass production. The Zn concentrations of the root and shoot increased with the Zn2+ concentration up to 68‐fold and 14‐fold, respectively, at 10 μM compared to the control. The concentrations of the other mineral nutrients of the shoot were hardly affected by elevated Zn2+ exposure, although in the root both the Cu and Fe concentrations were increased at ≥ 5 µM, whereas the Mn concentration was decreased and the Ca concentration strongly decreased at 10 µM Zn2+. The uptake and metabolism of sulfur and nitrogen were differentially affected at ≥ 5 µM Zn2+. Zn2+ exposure resulted in an increase of sulfate uptake and the activity of the sulfate transporters in the root, and in enhanced total sulfur concentration of the shoot, which could be ascribed partially to an accumulation of sulfate. Moreover, Zn2+ exposure resulted in an up to 6.5‐fold increase in water‐soluble non‐protein thiol (and cysteine) concentration of the root. However, nitrate uptake by the root and the nitrate and total nitrogen concentrations of the shoot were decreased upon Zn2+ exposure, demonstrating the absence of a mutual regulation of the uptake and metabolism of sulfur and nitrogen at toxic Zn levels. Evidently, elevated Zn2+ concentrations in the root environment did not only disturb the uptake, distribution and assimilation of sulfate, it also affected the uptake and metabolism of nitrate in Chinese cabbage.  相似文献   
90.
The objective of this study was to determine the effect of using a gonadotrophin releasing factor (GnRF) vaccine on growth performance of male pigs. Vaccinated pigs were compared with surgically castrated pigs and entire males under conventionally managed farm conditions. Male pigs were randomly assigned to three treatment groups: pigs surgically castrated during the first week of life (group "C", n=274), pigs immunised twice during the fattening period with a GnRF vaccine, the first when 13-14 weeks of age and the second when 20-21 weeks of age (group "V" n=280) and entire males (group "E", n=56). Average daily weight gain (ADG) was measured during the study. Additionally, feed conversion ratio (FCR) as defined by feed intake/weight gain and feed consumption was assessed during the fattening period. No difference in the ADG during the fattening period could be determined between "C" and "V". From the start of the study until slaughter at study day 160/173 the ADG in group "E" was lower (625 g/day; P) than in group "C" (681 g/day; P < 0.001) and group "V" (675 g/day; P < 0.01). The FCR during the fattening period until study day 160, three days before the first batch of pigs were slaughtered at 24-25 weeks of age, was higher in group"C" (2.72 kg feed intake/kg weight gain) compared with group "V" (2.44 kg feed intake/kg weight gain; P < 0.001) and group "E" (2.44 kg feed intake/kg weight gain; P <0.01). Pigs in group "V" performed similarly to those in group "E" until the second vaccination (day 135) after which time they showed a substantial increase in feed intake and ADG, while retaining an FCR advantage over group C.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号