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   528篇
  免费   25篇
林业   76篇
农学   10篇
  51篇
综合类   21篇
农作物   17篇
水产渔业   78篇
畜牧兽医   266篇
园艺   6篇
植物保护   28篇
  2023年   1篇
  2022年   6篇
  2021年   18篇
  2020年   11篇
  2019年   5篇
  2018年   8篇
  2017年   15篇
  2016年   14篇
  2015年   20篇
  2014年   14篇
  2013年   33篇
  2012年   28篇
  2011年   31篇
  2010年   14篇
  2009年   18篇
  2008年   37篇
  2007年   42篇
  2006年   26篇
  2005年   40篇
  2004年   28篇
  2003年   21篇
  2002年   18篇
  2001年   24篇
  2000年   19篇
  1999年   7篇
  1998年   3篇
  1996年   3篇
  1995年   2篇
  1993年   1篇
  1992年   3篇
  1991年   5篇
  1990年   3篇
  1989年   6篇
  1988年   5篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1982年   4篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1975年   1篇
  1974年   3篇
  1973年   1篇
  1968年   1篇
  1963年   1篇
排序方式: 共有553条查询结果,搜索用时 93 毫秒
101.
Because foam cell formation in macrophages is believed to play an essential role in the progression of early atherosclerotic lesions in vivo, prevention of foam cell formation is considered to be one of the major targets for the treatment of atherosclerosis. The present study examined the inhibitory effect of 50 crude plant extracts on foam cell formation. Among those crude extracts, Zizyphi Fructus (ZF) and Zizyphi Semen (ZS) extracts significantly inhibited the foam cell formation induced by acetylated LDL. Furthermore, triterpenoids such as oleanonic acid, pomolic acid, and pomonic acid were the major active compounds, and triterpenoids containing a carboxylic acid at C-28 play an important role in the inhibitory effect on foam cell formation in human macrophages. These data suggest that triterpenoids in Zizyphus jujuba , the plant source of ZF and ZS, may therefore be useful for the prevention of atherosclerosis.  相似文献   
102.
We investigated the role of the cell wall and plasma membrane (PM) of root-tip cells in Al tolerance in Al-tolerant and Al-sensitive cultivars of five plant species (rice, maize, pea, wheat, and sorghum). No correlation was found between the differences in Al tolerance and the cation exchange capacity of cell walls isolated from root-tips (0–1 em). Preliminary exposure to Al for 1 h was sufficient to inhibit subsequent root re-elongation in an Al-free solution, and the inhibitory effect was more pronounced in the Al-sensitive cultivars than in the Al-tolerant ones. Together with the inhibition of root re-elongation, the PM of the root-tip cells of all the Al-sensitive cultivars was more permeabilized than that of the Al-tolerant cultivars, based on the FDA-PI fluorescence staining technique. Exposure for 30 min to Al treatment at 100 µM significantly increased the PM permeability of protoplasts isolated from the root-tips for the Al-sensitive pea cultivar placed in a moderately hypotonic medium. Protoplasts from root-tip portions of all the Al-sensitive cultivars took up more Al than those of the Al-tolerant ones when treated with 100 pM Al under isotonic conditions for 30 min. The co-existence of DNP or hypotonic conditions led to a larger increase of Al uptake by the protoplasts from Al-sensitive maize cultivars. These results suggest that Al ions rapidly alter the PM of the root-tip portion in the Al-sensitive cultivars, irrespective of plant species, resulting in an increase of the PM permeability.  相似文献   
103.
Three types of experiments were designed to evaluate the performance of a bait system intended to control Incisitermes minor (Hagen). In the first type of experiment, Type I, the effectiveness of the bait in a small wood specimen was evaluated. In the second type, Type II, the bait effectiveness was evaluated in a larger wood specimen. Feeding arena lumber with artificial galleries was prepared for the Type III experiment so that the response of the insects to the gel could be observed. In general, the average percentage of termites that died after being exposed to the gel formulation in all three types of experiment was more than 60%, and in the gel control the average percentage of live termites was more than 95% in Types I and III, and more than 75% in Type II. These results suggest that the gel bait system used in this study has the potential to eliminate I. minor colonies. Further investigation will be necessary to increase the reliability of the bait system as a control measure against dry-wood termites.  相似文献   
104.
A comparative study of pre- and post-dispersal damage to the acrons of two oaks,Quercus serrata Thunb. andQ. mongolica Fischer, was done over 3 years in a species-rich deciduous forest in central Japan. The numbers of acorns bored into by moth larvae and byKobuzo rectirostris (Roelofs) was low and relatively uniform each year for both oak species, but the numbers bored into byCurculio spp. varied from year to year. The proportions of acorns attacked were independent of the density of acorns produced for both oak species. The proportions of the dispersed acorns of both oak species on the forest floor that disappeared between autumn and spring were less than 27%, and were lower for species in the stand that belong to family Fagaceae. However, by the next summer, most dispersed sound acorns had been infested by moths that specialized on post-dispersal acorns.  相似文献   
105.
Yellow mosaic disease, caused by wheat yellow mosaic virus (WYMV), is one of the most serious diseases of winter wheat in Japan and China. A single major QTL for WYMV resistance in the Japanese wheat variety 'Yumechikara', designated Q.Ymym, has been mapped on a 43.6 cM linkage block between the two markers Xcfd233 and Xgwm349 on chromosome 2D. We were able to obtain two recombinants within the block, which facilitated reducing the size of the linkage block. The pseudomolecule sequence of 'Chinese Spring' (CS) indicated that the original Q.Ymym region of 43.6 cM corresponded to 68.5 Mb and the narrowed Q.Ymym region represents a size of 27.3 Mb. The sequence features of the Q.Ymym region were unique in comparison with CS sequences, which may have led to the low recombination rate within the block. The Q.Ymym haplotype block was detected in other WYMV-resistant varieties but not in the susceptible varieties used in this study. The unique sequence structure of the Q.Ymym region allowed the development of co-dominant markers for use in marker-assisted selection.  相似文献   
106.
107.
108.
109.
Extraskeletal osteosarcoma is extremely rare in mice. This case report demonstrates a spontaneous murine extraskeletal osteosarcoma that exhibited various histological growth patterns in an ICR mouse. At necropsy, the tumor mass was located in the abdominal wall and was 45 × 30 × 25 mm in size. Histopathologically, the tumor showed the following four growth patterns: a solid pattern of polygonal cells embedded in an osteoid eosinophilic matrix with calcification, an irregular sheet pattern of short spindle cells accompanying some eosinophilic multinucleated cells, a fascicular pattern of spindle cells and a cystic pattern lined by short spindle cells. Immunohistochemically, most of the tumor cells were positive for vimentin, proliferating cell nuclear antigen and osterix. The multinucleated cells mentioned above were desmin positive and were regarded as regenerative striated muscles but not tumor cells. Since no clear continuity with normal bone tissues was observed, the tumor was diagnosed as an “extraskeletal osteosarcoma.”  相似文献   
110.
Volatile organic compounds (VOCs) in milk were investigated as quantitative markers of herbage intake (HI) at pasture. Eight Holstein cows were fed indoors with concentrate and conserved forages (grass silage, corn silage and hay) (NG), then were divided into three treatments according to the duration of access to pasture: 4 h (G4), 8 h (G8), and 20 h (G20) per day. The HIs were 4.3, 8.6, and 13.0 kg dry matter/day for the G4, G8 and G20 treatments, respectively. Milk from cows was sampled and analyzed VOCs by the steam distillation‐extraction method and gas chromatography‐mass spectrometry (GC‐MS). From the intensity of the GC peak area, the levels of 1‐phytene (3,7,11,15‐tetramethyl‐1‐hexadecene) and 2‐phytene (3,7,11,15‐tetramethyl‐2‐hexadecene) were lowest in NG treatment and markedly increased with grazing time at pasture. With simple regression analysis on the HI to each diterpenoid, a strong correlation was found between the intensity of 1‐phytene in the milk and the HI (r = 0.807, P < 0.001). 1‐phytene content in milk could be useful as a quantitative marker of the HI of grazing cows.  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