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   1916篇
  免费   96篇
林业   223篇
农学   103篇
基础科学   15篇
  432篇
综合类   74篇
农作物   354篇
水产渔业   284篇
畜牧兽医   370篇
园艺   29篇
植物保护   128篇
  2023年   15篇
  2022年   51篇
  2021年   82篇
  2020年   96篇
  2019年   91篇
  2018年   122篇
  2017年   132篇
  2016年   119篇
  2015年   65篇
  2014年   107篇
  2013年   208篇
  2012年   136篇
  2011年   135篇
  2010年   113篇
  2009年   75篇
  2008年   110篇
  2007年   74篇
  2006年   52篇
  2005年   29篇
  2004年   28篇
  2003年   26篇
  2002年   21篇
  2001年   16篇
  2000年   17篇
  1999年   2篇
  1998年   6篇
  1997年   3篇
  1996年   10篇
  1995年   2篇
  1994年   6篇
  1993年   4篇
  1992年   5篇
  1991年   6篇
  1990年   5篇
  1989年   5篇
  1988年   2篇
  1986年   3篇
  1985年   2篇
  1984年   3篇
  1983年   7篇
  1981年   3篇
  1979年   4篇
  1978年   3篇
  1976年   1篇
  1975年   3篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1939年   1篇
排序方式: 共有2012条查询结果,搜索用时 15 毫秒
71.
This paper explores the influence over time of past policies on people’s attitudes towards the use of forestland in Bangladesh. The discourses of the attitudes of people were captured from the observed social tradition towards forest resources. Forests were reserved systematically and solely through the Forest Department. The conservation processes were not participatory, and rights and tenure were strictly controlled. People were socially excluded and alienated from the forest, and the socio-political factors stimulated negative attitudes among people. Forests were considered to be government property, and therefore managing forests was the responsibility of the government. People only used forest resources to meet their own requirements, either with formal permission or illegally. This situation continued even after the independence of Bangladesh in 1971. As a result, the forests of Bangladesh have been degraded heavily in recent decades.  相似文献   
72.
对孟加拉国4个苗圃(IFES、IFESCU、BFRI和ANC)内水黄皮叶斑病症状和严重性进行了调查,结果表明:IFESCU苗圃内叶斑病侵染率及致病指标最高、BFRI次之、ANC最低.与叶斑病相关联的组织从发病植株分离出来,被分离的真菌形成致病性.结果证实胶孢炭疽菌即为致病菌.观察了杧果炭疽病菌丝体生长抑制性并对杀菌剂(Bavistin, Cupravite and Dithane M-45) 有效性和浓度(0.05, 0.10, 0.50, 1.00, 1.50 和 2.00%)进行了鉴定.0.05% Bavistin和Cupravite潜伏8天后,菌丝体生长分别处于最低和最高水平.结果表明:Bavistin杀菌效果最好、Diathane M-45次之,Cupravite对菌丝体生长的抑制作用最低.图1表4参27.  相似文献   
73.
Cultural studies have shown that unautoclaved Armillatox, a proprietary fungicide, when incorporated in an agar medium killed inocula of A. mellea mycelia at 550 ppm concentration and rhizomorphs at 50 000 ppm. Evidence on detoxification of Armillatox in agar culture and its probable role on new rhizomorph production is reported. Although Armillatox at 10000 ppm appeared to cause profuse production of new rhizomorphs in liquid culture, the difference in the dry weight between the treated and the control Samples has been found to be statistically insignificant.  相似文献   
74.
A survey on the symptom and severity of the leaf spot disease of Pongamia pinnata L. was conducted in the nurseries of the Institute of Forestry and Environmental Sciences, University of Chittagong (IFESCU), Bangladesh Forest Research Institute (BFRI) and Aronnak Nursery in Chittagong. The highest infection percentage and disease index were found in IFESCU nursery, followed by BFRI and the lowest was recorded in Aronnak nursery. The associated organism of leaf spot disease of P. pinnata was isolated from the diseased plant parts and the pathogenicity was established with the isolated fungus. Colletorichum gloeosprioides Penz was proved to be pathogenic. The inhibition of mycelial growth of C. gloeosporioides was observed and identified as suitable fungicides (Bavistin, Cupravite and Dithane M-45) and doses (0.05, 0.10, 0.50, 1.00, 1.50 and 2.00). The lowest and highest mycelial growth were respectively found on Bavistin and on Cupravite at the concentration of 0.05 after 8th day of incubation. It indicates that out of the three tested fungicides, Bavistin showed most effective, followed by Diathane M-45, and Cupravite was ineffective for its very little inhibition on mycelial growth.  相似文献   
75.
The crude extract of Mikania cordata (1 and 3 g/kg, p.o.) and deoxymikanolide (1) (10 mg/kg, p.o.) significantly inhibited acetic acid-induced writhing in mice. Three other sesquiterpene dilactones isolated from the same plant, namely mikanolide, dihydromikanolide and scandenolide, did not show significant analgesic activity.  相似文献   
76.
Journal of Pest Science - Conflicting views regarding synthetic pesticides include the successful use as pest management tools for agriculture and forestry on one hand and the threats to components...  相似文献   
77.
78.
European Journal of Forest Research - Many studies have been conducted on the effects of changes in plant diversity and species composition on ecosystem functioning and plant productivity due to...  相似文献   
79.

The current study was conducted to evaluate the effects of increasing carbon to nitrogen (C/N) ratios on water quality, growth performance, and body composition of Litopenaeus vannamei juveniles. Shrimp with initial average weight of 2.50?±?0.3 g were cultivated for 35 days in 300-L tanks (160 L of water volume) with a density of 1 g per liter. The experiment was performed in five treatments with three replicates. One control group and four biofloc treatments with different C/N ratio were considered: C/N of 10 (CN10), 14 (CN14), 18 (CN18), and 22 (CN22). Shrimp were fed three times a day, and molasses just was added as a carbon sources to the biofloc treatments after each feeding. According to the results, the lowest amount of dissolved oxygen (5.33 mg L?1) and pH (7.83) was observed in CN22 treatment, which showed a significant difference with other treatments (P?<?0.05). The highest level of total ammonia nitrogen (1.05 mg L?1) and nitrite (mg L?1) were recorded in control group, while the highest total density of heterotrophic bacteria was obtained in CN22 treatment. Growth performance parameters were at the highest level in the CN14 treatment, so the highest amount of final weight (6.88 g), biomass, and survival rate (94.79%) were observed in this treatment. The biochemical composition (protein, lipid, and ash) of the shrimp body and produced biofloc were affected by different C/N ratios, so these parameters were increased by rising of C/N ratio. In general, this study showed that the growth performance and body composition of Pacific white shrimp juveniles and water quality were suitable for rearing in biofloc system with C/N ratio of 14 than other treatments.

  相似文献   
80.

Aquaculture is a major supplier of animal protein for Bangladesh’s population, and the Mymensingh division is a major contributor to finfish aquaculture, producing 43% of the total pond pangasius and 9% of the total amount of tilapia (figures from 2018). We conducted a finfish farmer survey covering Netrokona, Jamalpur and Mymensingh districts to understand current finfish farming practices and identify factors that drive farmers in their species choice between pangasius or tilapia cultivation. We found that most finfish farmers in Mymensingh are experienced practitioners and practise polyculture with a range of stocking densities for each species. Using an economic model of polyculture practice, we have shown that over a production cycle, pangasius gain body mass at a rate nearly 4 times greater than that for tilapia, resulting in substantially larger revenues and providing a strong incentive for their culture. High levels of tilapia aquaculture likely persist due to their short production cycle and an associated decreased economic risk due to crop loss from disease, both factors providing a strong incentive for their culture. Our findings also indicate production yield differences through different species selection in polyculture systems. For example, co-culturing pangasius, tilapia and carp together was less productive than co-culture of pangasius with tilapia. Furthermore, higher yields of tilapia were obtained when co-cultured with carp compared with pangasius, the reasons for which are not known and warrant further investigation. Our study uses information provided by finfish farmers to produce a useful guide on fish species choices to maximise production yields, and therefore food production, from their ponds.

  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