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   135750篇
  免费   7665篇
  国内免费   652篇
林业   6918篇
农学   4923篇
基础科学   1063篇
  17816篇
综合类   22171篇
农作物   5193篇
水产渔业   6740篇
畜牧兽医   68666篇
园艺   2295篇
植物保护   8282篇
  2020年   1133篇
  2019年   1352篇
  2018年   3039篇
  2017年   3328篇
  2016年   2539篇
  2015年   1997篇
  2014年   2236篇
  2013年   4784篇
  2012年   4519篇
  2011年   6011篇
  2010年   4386篇
  2009年   4045篇
  2008年   5317篇
  2007年   5454篇
  2006年   4187篇
  2005年   4036篇
  2004年   3600篇
  2003年   3712篇
  2002年   3421篇
  2001年   4290篇
  2000年   4234篇
  1999年   3305篇
  1998年   1348篇
  1997年   1173篇
  1996年   1123篇
  1995年   1292篇
  1994年   1146篇
  1993年   1142篇
  1992年   2558篇
  1991年   2793篇
  1990年   2785篇
  1989年   2666篇
  1988年   2463篇
  1987年   2500篇
  1986年   2474篇
  1985年   2316篇
  1984年   1950篇
  1983年   1610篇
  1982年   1116篇
  1979年   1713篇
  1978年   1361篇
  1976年   1157篇
  1975年   1174篇
  1974年   1549篇
  1973年   1499篇
  1972年   1480篇
  1971年   1399篇
  1970年   1353篇
  1969年   1255篇
  1967年   1139篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
71.
Various combinations of reoviruses and coccidia were studied to see if interactions would occur. Two reoviruses were used: virus 2035, a moderate to low pathogen, and virus 2177, a nonpathogen. Coccidia used were Eimeria acervulina, E. mitis, and E. maxima at dosages of 10(3) or 10(4) sporulated oocysts/chick and E. brunetti at 10(4) sporulated oocysts/chick. In Hubbard-Hubbard cockerels, a combination of virus 2035 and E. acervulina (10(4) oocysts/chick) or E. maxima (10(3) oocysts/chick) significantly (P less than or equal to 0.05) increased the frequency of stunting (% of chicks with body weight less than 80% of controls) and further depressed weight gain over that seen with either virus or coccidia alone. Conversely, virus 2177 ameliorated the same effects in Shaver-Arbor Acre cockerels given 10(4) oocysts/chick of E. mitis or E. maxima. The interaction could not be attributed to changes in the degree of coccidial infection based on oocyst production. Reovirus did not generally change the effect of coccidia on levels of plasma pigment and plasma protein. In Hubbard-Hubbard cockerels, coccidia-induced effects were not ameliorated by virus 2177, suggesting that breed difference in interaction can be expected.  相似文献   
72.
The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses.  相似文献   
73.
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species.  相似文献   
74.
Softening process and total antioxidant activity were evaluated in kiwifruit differently exposed to light intensity and harvested at two different times (October 10 and November 14). Fruit was stored for 2 months at 0 °C (S1) and then maintained for a week at ambient temperature (S2). The results showed that fruit harvested later presented a faster softening rate during storage than fruit harvested earlier, even if antioxidant activity did not change. Light-exposed fruit showed higher flesh firmness than that of shaded ones. Polygalacturonase activity was higher in kiwifruit maintained for a week at ambient temperature after cool storage and, in particular the highest value was recorded in fruit harvested later. The behaviour of β-galactosidase was different: it did not show changes in fruit harvested later and significantly decreased in light- and shade-exposed fruit harvested earlier.  相似文献   
75.
76.
77.
78.
79.
80.
    
Ohne Zusammenfassung  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