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   1946篇
  免费   69篇
  国内免费   79篇
林业   202篇
农学   250篇
基础科学   59篇
  429篇
综合类   276篇
农作物   112篇
水产渔业   75篇
畜牧兽医   521篇
园艺   49篇
植物保护   121篇
  2022年   41篇
  2021年   45篇
  2020年   35篇
  2019年   23篇
  2018年   32篇
  2017年   45篇
  2016年   40篇
  2015年   39篇
  2014年   32篇
  2013年   125篇
  2012年   87篇
  2011年   85篇
  2010年   82篇
  2009年   68篇
  2008年   90篇
  2007年   77篇
  2006年   91篇
  2005年   89篇
  2004年   37篇
  2003年   44篇
  2002年   55篇
  2001年   48篇
  2000年   42篇
  1999年   57篇
  1998年   34篇
  1997年   46篇
  1996年   34篇
  1995年   23篇
  1994年   20篇
  1993年   17篇
  1992年   20篇
  1991年   21篇
  1990年   26篇
  1989年   22篇
  1988年   20篇
  1987年   20篇
  1985年   20篇
  1983年   18篇
  1981年   18篇
  1980年   12篇
  1979年   31篇
  1978年   14篇
  1977年   18篇
  1976年   15篇
  1971年   28篇
  1970年   18篇
  1969年   15篇
  1968年   12篇
  1967年   23篇
  1966年   25篇
排序方式: 共有2094条查询结果,搜索用时 0 毫秒
91.
Ficus species are multipurpose trees well known by rural populations in Sahelian and Sudanian zones of Africa. Their uses are well documented but their amenability for vegetative propagation has not been extensively studied. This paper compares the rooting ability of stem and aerial root cuttings from thirteen Ficus species found in West Africa. It highlights the differences between species belonging to the sub-genera Sycomorus and Urostigma. The former show no capacity to propagate from cuttings whereas the latter, with epiphytic development, can be propagated by cuttings, although this capacity varies among species. Thus, F. thonningii, F. leprieurii and F. ovata are easily propagated, while F. platyphylla and F. elasticoides are propagated with difficulty. The rooting capacity also varies depending on the cutting material used. It decreases in the following order: long leafless hardwood cuttings (pole) > nodal cuttings > apical cuttings. Rooting potential increases when the cuttings are harvested towards the end of the dry season(March to May). Aerial root can be used for cuttings in all species of the sub-genus Urostigma. The capacity of root cuttings to regenerate is greatest when cuttings are collected at the beginning of the dry season (November). In this case, wound-induced adventitious roots arise at the basal end of the cutting while de novo buds are developed from the cambium at the distal end. The subsequent morphological development is identical to that of a stem cutting. These results clarify and allow the optimal use of the knowledge and methods developed by the indigenous people of the Sahel and could assist and promote fig tree (Ficus sp.) domestication in the dry tropics.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   
92.
Four male buffaloes of 3 to 312 years were subjected to heavy loads during hot dry conditions for 3 h continuously. Rectal temperature, respiration rate and heart rate increased significantly. The blood pH, PO2, increased significantly and PCO2 declined. During work, buffaloes were not able to eliminate heat produced and exhibited such distress symptoms as profuse salivation, frothing, lack of leg co-ordination, excitement and tongue protrusion. The muzzle secretion of buffaloes increased greatly. Even 3 h after discontinuation of work, the physiological reactions had not fully disappeared.  相似文献   
93.
Patchouli oil is one of the most important essential oils used in modern perfumery and cosmetic industries. There is hardly any preparation of oriental nature where patchouli oil is not used. It is used mainly because of fixative property as it gives tenacity to other perfumes. Field experiments were conducted at Bangalore, India, to study the influence of sources and doses of N and K on herbage, oil yield, nutrient uptake, nitrogen utilization efficiency and oil content of patchouli [Pogostemon cablin (Blanco) Benth.]. The results revealed that application of 200 kg N/ha and 41.5 kg K/ha produced significant higher patchouli herbage and oil yields compared with controls. Similarly, N and K uptake were also higher at 200 kg N and 41.5 kg K/(ha year) compared with controls. DCD-coated urea produced higher herbage, oil yield and N uptake and utilization efficiency compared with prilled urea. There was no effect of sources of K on the yield of patchouli. The oil content was not influenced by N, K doses or sources applied. N and K depletion were noticed in the soil.  相似文献   
94.
95.
The clinical signs and gross lesions caused by Eimeria uzura (10(5) oocysts) in Japanese quail (Coturnix coturnix japonica) exhibited little or no influence in the face of intercurrent dietary aflatoxicosis (1 p.p.m. of aflatoxin B1 from Day 0 to 55). Similarly, no significant differences in the mucosal morphology of the intestine were evident histologically between the two groups of Japanese quail. The nervous signs of ataxia, leg weakness, incoordination of movement, torticollis and terminal opisthotonos were toxin-induced manifestations. In the aflatoxic quail, hypoplastic changes and selective depletion of lymphocytes were more prominent in the bursa of fabricius. Increased relative mean weights of liver, kidney, spleen, crop, proventriculus and gizzard were observed in birds due to aflatoxin sensitivity. The combination of E. uzura infection and aflatoxicosis in Japanese quail may cause significant weight loss, and increased oocyst production and reproductive potential.  相似文献   
96.
97.
The crude leaf extracts of Croton cajucara Benth. were studied for their antinociceptive property in chemical and thermal models of nociception in mice. All the tested extracts (hexanic, chloroformic and methanolic), at oral doses of 100 and 200 mg/kg demonstrated significant inhibition of acetic acid-induced writhing and the second phase response of formalin, but did not manifest a significant effect in hot-plate test.  相似文献   
98.
Laboratory experiments were conducted to test the effect of various concentrations of Trifluralin on certain fungi. The ectotrophic mycorrhizal fungi tested were: Amanita citrina Schaefer, Tricholoma pessundatum (Fr.) Quel., and Tricholoma saponaceum (Fr.) Qtiel. All exhibited sensitivity to Trifluralin concentrations. The consequence of such fungitoxicity was discussed.  相似文献   
99.
Pot experiments were performed to investigate the effects of Tritluralin on the mycorrhizal symbiosis of conifer seedlings. Infected forcst soils and potting mixturcs were mixed, pottcd and treated with Trifluralin at levels of 0.2 and 0.4ml/m2 Seeds of Pinus sylvestris L. and Picea abies (L.) Karst. were sown in the pots. The concentrations tested, though recommended by the manufacturer produced phytotoxicity. The seedling growth in general and that of the rootsystem and laceral roots in particular, were severely inhibited. Mycorrhizal development in the seedlings was consequently adversely affected.  相似文献   
100.
The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study.Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea.The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (>4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed.  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