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   25篇
林业   30篇
农学   47篇
基础科学   6篇
  124篇
综合类   36篇
农作物   25篇
水产渔业   21篇
畜牧兽医   146篇
园艺   13篇
植物保护   51篇
  2022年   7篇
  2021年   4篇
  2020年   15篇
  2019年   7篇
  2018年   25篇
  2017年   20篇
  2016年   24篇
  2015年   4篇
  2014年   17篇
  2013年   44篇
  2012年   19篇
  2011年   25篇
  2010年   19篇
  2009年   13篇
  2008年   16篇
  2007年   26篇
  2006年   24篇
  2005年   9篇
  2004年   14篇
  2003年   6篇
  2002年   6篇
  2001年   10篇
  2000年   7篇
  1999年   10篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   5篇
  1994年   5篇
  1993年   4篇
  1992年   7篇
  1991年   3篇
  1990年   9篇
  1989年   9篇
  1988年   8篇
  1987年   6篇
  1986年   6篇
  1985年   6篇
  1983年   5篇
  1982年   2篇
  1981年   6篇
  1979年   4篇
  1977年   2篇
  1976年   2篇
  1973年   3篇
  1971年   4篇
  1970年   3篇
  1969年   3篇
  1968年   2篇
  1967年   3篇
排序方式: 共有499条查询结果,搜索用时 15 毫秒
1.
Grain yield and yield components (grains per ear, grain weight, 1000-grain weight, ear weight, ear seed ratio and dry matter partitioning between ear and seed) were examined in a wheat genotype (PBW-343) with well-filled grains and a Triticale genotype (DT-46) with poorly filled grains (showing grain shrivelling) grown in pots. Six days after anthesis (DAA), benzyladenine (BA) @2 µg ear−1 and abscisic acid (ABA) @4 µg ear−1 were injected at the base of the mother shoot ear in both species. It was observed that, in both wheat and Triticale , BA increased the grain weight, grain number and partitioning of dry matter between ear and seed, whereas ABA decreased the grain weight, grain number and dry matter partitioning between ear and seed. However, these decreases were slower in Triticale than in wheat. BA treatment increased the grain dry matter accumulation, which in turn resulted in better filling of grains and increased the grain weight in both wheat and Triticale . The average grain weight of Triticale was lower than that of wheat. Thus, it appears that variation in grain weight between wheat and Triticale might be due to different availabilities of growth-promoting phytohormones such as cytokinins and assimilates.  相似文献   
2.
Canine influenza virus is an emerging, highly contagious, respiratory pathogen that has not previously been radiographically described. In this retrospective case series study, we describe the thoracic radiographic appearance of confirmed canine influenza virus in six dogs. Radiographic findings varied, but included abnormal unstructured interstitial (one) and unstructured interstitial and alveolar (five) pulmonary patterns, which were distributed cranioventral (four), diffuse (one), and caudodorsal (one). The right middle (five), left cranial (five), and right cranial (four) lung lobes were most commonly affected. Additionally, mild pleural effusion was present in one dog. Intrathoracic lymphadenopathy and cranial mediastinal widening/fluid accumulation were not detected in any dog. Canine influenza virus should be considered as a differential diagnosis for canine patients with respiratory signs and a cranioventral unstructured interstitial to alveolar pulmonary pattern.  相似文献   
3.
4.
Transplanting of rice seedling in puddled soil is one of the most widely used cultivation practices. The present research is aimed at determining what specific implements are needed to obtain optimal puddle bed for transplantating. Puddling experiments were carried out by the use of pair of bullocks with traditional country plough (T1), pair of bullocks with lug wheel puddler (T2), power tiller with rotary puddler (T3), tractor with cage wheel and 9-tine cultivator (T4) and tractor with cage wheel and rotavator (T5). One summer ploughing was done at friable moisture condition (18.6% db) and then tilled soil was flooded to saturation (24 h) for preparation of puddled bed. Weeding efficiency, puddling depth, percentage increase in bulk density, puddling index, percolation rate and grain yield of paddy were studied for the above treatments. Puddling performance by different implements in comparison to the traditional animal drawn country plough (T1) shows that there is a definite reduction in time requirement for field preparation. Increase in weeding efficiency, bulk density, grain yield and puddling index were also observed. The highest values of weeding efficiency and puddling index were found 98.6% and 79.3, respectively, for rotavator (T5). The total time requirement for preparation of puddle field for treatment T4 (tractor with cultivator) was found to be the lowest (9.4 h ha−1) with 67% weeding efficiency and 62.7 puddling index as compared to all other alternatives tested. Energy requirement for preparation of puddle field was found highest (2390 MJ ha−1) for rotavator (T5) followed by T3, T4, T1, and T2 treatments.  相似文献   
5.
Rapid changes in biodiversity are occurring globally, yet the ecological impacts of diversity loss are poorly understood. Here we use data from marine invertebrate communities to parameterize models that predict how extinctions will affect sediment bioturbation, a process vital to the persistence of aquatic communities. We show that species extinction is generally expected to reduce bioturbation, but the magnitude of reduction depends on how the functional traits of individual species covary with their risk of extinction. As a result, the particular cause of extinction and the order in which species are lost ultimately govern the ecosystem-level consequences of biodiversity loss.  相似文献   
6.
With continuous outbreaks of stripe rust (Puccinia striiformis f. sp. tritici) epidemics and rapid breakdown of deployed resistance in bread wheat (Triticum aestivum L.) cultivars in North West Plains Zone (NWPZ) in India warrant knowledge and deployment of new and durable sources of resistance to stripe rust. Bread wheat cultivar PBW 343, until recently the most widely cultivated wheat variety in India, is now highly susceptible to stripe rust (score 9 on a 1–9 scale), whereas PBW 621 (score 5.05–5.65) and HD 2967 (score 5.40–6.20) show low levels of resistance. We conducted an experiment, spanning three crop seasons (2013–2014 to 2015–2016), in which parental lines, F1 and F2 populations, F3 and F4 families from two bread wheat crosses, PBW 621/PBW 343 and HD 2967/PBW 343 were generated and evaluated for stripe rust resistance against a virulent pathotype. While the F1 revealed partial dominance, the segregation pattern for stripe rust resistance in F2 and F3 showed transgressive segregation for resistance in both crosses. Chi-square analysis indicated that resistant segregants possessed two genes, one contributed by PBW 621 or HD 2967 (depending on the cross) and the other, unexpectedly but obviously, came from the most susceptible cultivar, PBW 343. Possible genetic mechanisms for this residual resistance and implications for breeding programs are discussed.  相似文献   
7.
The disposition kinetics and dosage regimen of enrofloxacin were investigated in breeding buffalo bulls following a single intramuscular administration of 5 mg/kg. The absorption half-life, half-life of the terminal phase, apparent volume of distribution and total body clearance were 0.262±0.099 h, 1.97±0.23 h, 0.61±0.13 L/kg and 210.2±18.6 ml/(kg.h), respectively. Therapeutic plasma levels (1 g/ml) were maintained for up to 6 h. A satisfactory intramuscular dosage regimen for enrofloxacin in buffalo bulls would be 8.5 mg/kg followed by 8.0 mg/kg at 8 h intervals.  相似文献   
8.
9.
10.
Aeciospores in Uromyces fabae were found to be repeating spores and play an important role in pea rust outbreaks in the North Eastern Plain Zone (NEPZ) of India. Experiments conducted on pea rust from 2001 to 2004 revealed the dominance of aeciospores at all growth stages of pea in this region. Urediospore production was erratic and was only observed in a few samples of stems and tendrils (5–10%). Inoculation of pea plants either by aeciospores or urediospores resulted in the production of aeciospores. Production of aeciospores was observed at a temperature range of 10–25 °C, with a maximum at 25 ± 2 °C. Among the different growth stages of pea, the pod formation stage was highly susceptible and produced the maximum number (744) of aecidia/leaf at 20–25 °C. Significant effects of growth stages and temperature were also noticed for pustule number. Urediospore production mainly coincided with the senescence of the pea plants. Maximum germination (2%) of aeciospores was observed at 25 °C, whereas maximum urediospore germination (3.5%) was at 15 °C. Temperatures > 15 °C decreased urediospore germination. A relative humidity (RH) of 100% was favourable for aeciospore germination while 98% RH favoured urediospore germination. Typical histo-pathological behaviour of the aeciospores was observed.  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