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   16524篇
  免费   10篇
林业   3624篇
农学   1295篇
基础科学   139篇
  2738篇
综合类   715篇
农作物   2100篇
水产渔业   1779篇
畜牧兽医   1166篇
园艺   1111篇
植物保护   1867篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2019年   2篇
  2018年   2745篇
  2017年   2703篇
  2016年   1186篇
  2015年   65篇
  2014年   22篇
  2013年   16篇
  2012年   796篇
  2011年   2132篇
  2010年   2106篇
  2009年   1262篇
  2008年   1322篇
  2007年   1581篇
  2006年   30篇
  2005年   102篇
  2004年   113篇
  2003年   156篇
  2002年   63篇
  2001年   11篇
  2000年   41篇
  1999年   3篇
  1996年   1篇
  1995年   2篇
  1993年   12篇
  1992年   9篇
  1991年   2篇
  1990年   2篇
  1989年   5篇
  1988年   12篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1978年   2篇
  1977年   4篇
  1974年   1篇
  1973年   1篇
  1972年   2篇
  1971年   1篇
  1969年   1篇
  1968年   5篇
  1967年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The objective of the present study was to describe the prevalence and risk factors associated with cryptosporidiosis in buffalo calves in Middle Egypt. During one year, 458 fecal samples were collected from buffalo calves less than 3 month age in 55 small scale herds and examined for the presence of Cryptosporidium oocysts. Data describing age, gender, season, and herd management practices were gathered to assess potential risk factors. Fecal examination showed that 14.19% of the examined calves were positive for Cryptosporidium spp. Calves at 1-15 days were at the highest risk (P < 0.001), and a significant relationship between season and infection (P < 0.05) was recorded. A significant association between infection and hygiene (P < 0.001), type of floor (P < 0.01) and source of water (P < 0.01) was also recorded. Statistical analysis concerning the clinical signs and fecal characteristics revealed a significant association with fecal consistency (P < 0.001), presence of blood (P < 0.01) and mucous (P < 0.01). Moreover, a significant association was found between infection and the desire for suckling (P < 0.05) and tenesmus (P < 0.05). The results of the present study demonstrated the strong relation between infections by Cryptosporidium spp. and diarrhea in buffalo calves.  相似文献   
72.
73.
Responding to the challenges posed by global warming, peak oil and biofuels will require a paradigm shift in the practice of agriculture and in the role of live stock within the farming system. Farming systems should aim at maximizing plant biomass production from locally available diversified resources, processing of the biomass on farm to provide food, feed and energy and recycling of all waste materials. The approach that is the subject of this paper is that the generation of electricity can be a by-product of food/feed production. The concept is the fractionation of biomass into inedible cell wall material that can be converted to an inflammable gas by gasification, the gas in turn being the source of fuel for internal combustion engines driving electrical generators. The cell contents and related structures such as tree leaves are used as human food or animal feed. As well as providing food and feed the model is highly appropriate for decentralized small scale production of electricity in rural areas. It also offers opportunities for sequestration of carbon in the form of biochar the solid residue remaining after gasification of the biomass.  相似文献   
74.
75.
在食品中加入某些活的微生物早已被证明对人类健康有积极的影响,这一方法已拓展到食品动物生产领域,且已涉及到许多微生物菌种,特别是乳酸菌、芽孢杆菌和酿酒酵母菌。对益生素兴趣的增加基本上是由于微生物耐药性问题的出现,同时自禁止在动物生产中使用抗生素后,益生素被认为是一种可减少病原菌感染并可提高猪、尤其是断奶期间仔猪的健康。然而,仍有必要阐明益生素在猪生产中的作用及潜在作用机制。在评价益生菌功效时,必须考虑所用的特定菌株和治疗猪对应的生长阶段。在实际的养猪生产中,重复益生素的功效还存在问题,因为维持其活性对它们的有益功效极为关键,但利用常规的饲料加工技术难以实现。益生素微生物能够被有效投喂的一种情况是在利用液体发酵饲料的生产系统中。液体饲料可以用活的野生乳酸菌进行发酵,也可将特定分离株作为"启动子"刺激其发酵,后一种方法对发酵的可重复性及其速度有益处。养猪场的微生物应用条件对其发挥正常功效很可能是至关重要的。给利用非理想条件饲养的猪饲喂益生素,所增加的经济效益远大于采用最佳福利条件和管理措施饲养的猪。如果猪出生时使其肠道内建立一个有益的微生物菌群,就有可能会产生较为健康的猪。实现这一效果的最有效方法是给母猪服用益生素,这提供了一个扩大益生菌的手段,使新生仔猪的生活环境中到处都是值得拥有的有益菌株。相比之下,它也许足以在仔猪断奶前后向其提供一个有支持作用和保护作用的肠道菌群,因为就某些肠道菌群的不稳定和损失来说,此时期是一个重要的决定性时刻。  相似文献   
76.
The objective of this study was to evaluate and compare physical parameters in groups of sheep with different phenotypic characteristics in the Centre-west region of Brazil. Five groups of sheep, with nine animals per group, were selected, three groups of Santa Inês animals with different coat colours (white, brown and black), one group with crossbred animals (Santa Inês × Bergamasca) and one group with animals of the Bergamasca breed. The following traits were evaluated: coat thickness, number and length of hair, pigmentation level in the coat and the skin as well as the percentage area of sweats glands in the skin tissue, carried out by histological analysis. The number of hairs and the area of sweats glands were not significantly different between the evaluated groups. The Bergamasca breed showed low pigmentation of the skin and long hairs. The levels of pigmentation of the hair and of the skin were highly correlated. Between the Santa Inês groups, the group with white hair showed the better parameters for heat adaptation, while the brown hair group showed the lower heat adaptation when compared with another hair breed groups.  相似文献   
77.
The aim of this study was to determine the fattening performance and the slaughter and carcass characteristics of Akkeçi (Saanen × Kilis (B1) crossbred) male kids raised in individual crates (IC) or in group pen housing (GP). In both GP and IC groups, total 13 heads of male kids, whose initial body weights were 21.43 ± 1.03 kg and 20.61 ± 0.98 kg, respectively, evaluated for their fattening performances. After 56 days of the fattening period, the final body weights and average daily weight gains of the GP and IC kids were recorded as 30.84 ± 0.82 kg and 25.84 ± 0.76 kg; 182.42 ± 14.77 g and 92.09 ± 13.76 g, respectively (P < 0.001). Adrenal gland weights of the GP and IC groups were similar as 1.66 ± 0.25 g and 1.77 ± 0.22 g, respectively. Although, the carcass conformation of kids was similar between groups, there were significant differences between GP and IC groups for some slaughter and carcass characteristics. In general, although housing kids reared in individual crates provides opportunity to individually feed and monitor a kid, the results obtained from the individual crates in the present study were not satisfactorily from the ethological and production points of view.  相似文献   
78.
An ultrastructural study was performed on chloride cells of euryhaline R.r.Caspicus of south of Caspian Sea. The chloride cells are distributed in the interlamellar region of filaments. They are oval to elongated form with an apical positioned nucleus, expanded tubular system and heteromorphic mitochondria. These cells are surrounded by pavement cell and accessory cell. A small and depressed surface formed by pavement cells is in contact with the aquatic milieu. There is also channel system in accessory cells. One of the typical features was the important changes in microtubules and mitochondria of chloride cells in some fishes. Swelling and rupture of cristae and degeneration of microtubules were from these changes.  相似文献   
79.
80.
The present study was conducted to evaluate two Indian native chicken breeds, namely, Aseel and Kadaknath for fertility, hatchability, genetic parameters of juvenile growth traits, and semen quality traits at the onset of sexual maturity. The fertility was similar in Aseel (86.96%) and Kadaknath (85.15%); however, a relatively higher hatchability was observed in Kadaknath (77.94%) than Aseel (70.74%). Heritability estimates of body weights at 4 weeks of age were almost similar in Aseel (0.37) and Kadaknath (0.39), while the estimate of body weight at 6 weeks of age was higher in Aseel (0.42) than Kadaknath (0.31). The heritability estimate of shank length at 6 weeks of age was lower in Aseel (0.16) compared to Kadaknath (0.35). The age at first egg in the flock was comparable in Aseel (148 days) and Kadaknath (150 days). Aseel breed with significantly (P ≤ 0.001) higher body weight, absolute and relative testes weights had significantly higher semen volume (P ≤ 0.05) and sperm motility (P ≤ 0.01) but had lower seminal plasma cholesterol level (P ≤ 0.05) as compared to Kadaknath. It can be concluded that there is a scope for genetic improvement of these two native breeds for juvenile growth traits since heritability estimates of these traits were relatively high.  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