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   681篇
  免费   33篇
  国内免费   3篇
林业   61篇
农学   35篇
基础科学   4篇
  122篇
综合类   109篇
农作物   31篇
水产渔业   47篇
畜牧兽医   243篇
园艺   8篇
植物保护   57篇
  2023年   7篇
  2022年   5篇
  2021年   15篇
  2020年   8篇
  2019年   16篇
  2018年   17篇
  2017年   26篇
  2016年   25篇
  2015年   12篇
  2014年   13篇
  2013年   25篇
  2012年   46篇
  2011年   43篇
  2010年   27篇
  2009年   29篇
  2008年   50篇
  2007年   42篇
  2006年   22篇
  2005年   26篇
  2004年   26篇
  2003年   31篇
  2002年   25篇
  2001年   9篇
  2000年   9篇
  1999年   5篇
  1998年   5篇
  1997年   3篇
  1995年   6篇
  1994年   3篇
  1993年   3篇
  1991年   7篇
  1990年   4篇
  1989年   10篇
  1988年   4篇
  1986年   8篇
  1985年   6篇
  1984年   5篇
  1983年   5篇
  1982年   6篇
  1979年   5篇
  1978年   3篇
  1977年   6篇
  1976年   4篇
  1975年   6篇
  1972年   3篇
  1971年   3篇
  1969年   6篇
  1967年   4篇
  1964年   3篇
  1939年   2篇
排序方式: 共有717条查询结果,搜索用时 15 毫秒
71.
72.
A retrospective study was conducted to investigate the cause of rectal prolapse in working donkeys in Ethiopia. Analysis of data on rectal prolapse cases obtained from the Donkey Health and Welfare Project clinic at the School of Veterinary Medicine, Addis Ababa University, from 1995 to 2004 revealed that 83.6% (n = 177) of the cases were associated with Gasterophilus nasalis. The rest 10.7% and 5.7% were associated with work-related (overloading) cause and diarrhoea, respectively. The mean and median numbers of G. nasalis recovered from the rectum of infected donkeys were 66 and 64, respectively, with a range of 2–195. Over 100 G. nasalis larvae were recovered from the rectum of 22% of the donkeys. Circular demarcated ulcer-like and deep circumferential pits or ring-like mucosal lesions were found at the larval attachment sites. G. nasalis infection and the associated rectal prolapse were observed year round. However, the intensity of rectal larval infection and incidence of rectal prolapse were significantly higher during the rainy season (P < 0.01). Age and sex of the donkeys had no significant effect on the intensity of rectal larval infection and incidence of rectal prolapse (P > 0.05).  相似文献   
73.
Liu et al. (Reports, 23 March 2007, p. 1712) reported that the Arabidopsis thaliana gene GCR2 encodes a seven-transmembrane, G protein-coupled receptor for abscisic acid. We argue that GCR2 is not likely to be a transmembrane protein nor a G protein-coupled receptor. Instead, GCR2 is most likely a plant homolog of bacterial lanthionine synthetases.  相似文献   
74.
75.
Complete removal of roots from soil samples is a prerequisite for most of the chemical and biological analyses. A simple electrostatic method of separating roots from sieved, largely mineral soil substrates was optimized and examined by the addition of 14C labeled fine roots to sandy, silt loamy and clay loamy samples. Depending on soil texture, between 40% and 50% of fine roots can be removed from 100 g of sieved soil in less than 10 minutes. The root‐free soil substrate and the extracted roots can be used for analyzes or experiments immediately after the separation. The proportion of the mineral particles remaining in the root fraction depends on duration of separation, distance between the charged plate and the sample, and soil texture. The proportion of separated mineral particles is about 90%—95% (w/w) in sandy and 70%—85% in silt loamy and clay loamy substrates. The electrostatic method of root separation may take place before the analysis of Ct and Nt contents, and is suitable for soil samples preparation for incubation experiments.  相似文献   
76.
Tomàtiga de Ramellet (Ramellet) is a traditional long-storage tomato from the Mediterranean Islands of Mallorca, Menorca, Eivissa (Ibiza), and Formentera (Balearic Islands). To investigate the observed phenotypic and shelf life variability within local varieties, we studied 142 accessions characterized as Ramellet varieties, and 29 accessions representing other local varieties. The 171 accessions constitute a new germplasm collection at the University of Balearic Islands (UIB). The evaluation of the collection demonstrated wide variability in most agronomic, morphological and quality traits of Ramellet accessions and clearly differentiates them from other local varieties with respect to fruit shape, size, fruit composition, and fruit storage. All accessions of Ramellet evaluated have the ripening mutation alcobaça (alc), suggesting an important role for this variant in controlling shelf life. Results of evaluation also showed wide variability between the Ramellet accessions for storage time, suggesting that other traits like fruit size and composition may play a role in fruit conservation. Observed variation within the Ramellet accessions is consistent with a genetically variable population or landrace group. The establishment of this collection will help prevent genetic erosion of this local landrace group and constitute a resource for future investigation and breeding.  相似文献   
77.
The potential utility of micrometer-sized particles as controlled-release devices for the volatilization of insect pheromones for mating disruption applications is evaluated in this study for two pheromone/model compound systems (codlemone/1-dodecanol and disparlure/1,2-epoxyoctadecane). To expedite the measurement of release rates from these particle devices, two techniques based on thermogravimetric analysis (TGA) have been exploited: isothermal TGA (I-TGA) at elevated temperatures (40-80 degrees C) with N(2) convection and volatilization temperature (VT) by dynamic TGA. A correlation between these two methods has been established. Samples that exhibit a higher VT provide a lower release rate from a particle substrate. Using these techniques, it has been demonstrated that chemical interactions between adsorbed liquids and particle surfaces may play a small role in defining release characteristics under conditions of low surface area, whereas parameters associated with total surface area and micropore structure appear to be much more significant in retarding evaporation for uncoated particles containing an adsorbed liquid. Additional regulation of release rates was achieved by coating the particle systems with water-soluble or water-dispersible polymers. By careful selection of particle porosity and coating composition, it is envisioned that the evaporation rate of pheromones can be tailored to specific insect control applications.  相似文献   
78.
79.
Intr0ducti0nNorwayspruce(PiceaabiesKarst)is0l1eoflI1e111ostimportal1tc011iferinFra11ce.lnl99l,tI1etotaIareaofNorwaysprLICewasestimatedt0be723000I11112.ItsvoIUmewasl27Inilli0I1m3.Tl1eanl1uaIvoILl111eiI1crc-mentwas5.74millionm3.ltiswideIyacceptedII1atIargeri11itialspacingssI1ouldbeusednow.l111940's,thedensity0ftl1epIantatiol1rangedfr0m5000to10000stems/hm2.Nowtl1einitiaIdensityvariesbetweenI000to250Ostems/I1m2.TI1eIargestspacit1g111aybe650~800stems/hm2.S0ithasasignifica11cetostLldyt…  相似文献   
80.
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