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   24319篇
  免费   1931篇
  国内免费   62篇
林业   1971篇
农学   1228篇
基础科学   188篇
  5054篇
综合类   1767篇
农作物   1093篇
水产渔业   2029篇
畜牧兽医   10137篇
园艺   527篇
植物保护   2318篇
  2023年   221篇
  2022年   285篇
  2021年   503篇
  2020年   537篇
  2019年   615篇
  2018年   1059篇
  2017年   995篇
  2016年   975篇
  2015年   774篇
  2014年   908篇
  2013年   1411篇
  2012年   1613篇
  2011年   1652篇
  2010年   969篇
  2009年   903篇
  2008年   1365篇
  2007年   1311篇
  2006年   1095篇
  2005年   1126篇
  2004年   1007篇
  2003年   904篇
  2002年   817篇
  2001年   675篇
  2000年   658篇
  1999年   521篇
  1998年   176篇
  1997年   165篇
  1996年   141篇
  1995年   161篇
  1994年   103篇
  1993年   96篇
  1992年   202篇
  1991年   167篇
  1990年   177篇
  1989年   156篇
  1988年   150篇
  1987年   131篇
  1986年   117篇
  1985年   122篇
  1984年   91篇
  1983年   99篇
  1982年   57篇
  1980年   49篇
  1979年   84篇
  1978年   50篇
  1974年   53篇
  1973年   51篇
  1972年   50篇
  1971年   49篇
  1970年   56篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
This system uses the shelter of the harbour entrance and coastal polluted zones for aquaculture purposes. Water from the open sea is supplied by forced circulation to the rearing area, which is separated from harbour water by a plastic sheet. Rafts, enclosures or cages can be used for intensive rearing of mollusks or fish.  相似文献   
993.
The role of dermonecrotic toxin (DNT) of Bordetella bronchiseptica and Pasteurella multocida, purified by repeated chromatography in Sephacryl S-200 gel, in the pathogenesis of atrophic rhinitis (AR) of swine was studied bacteriologically, clinically and pathologically. Two-week-old specific pathogen-free (SPF) piglets were parenterally treated with 30 micrograms of DNT 3 times at 2-day interval and 7-week-old piglets were treated with 15 micrograms of DNT twice a week for 5 weeks. In 2- to 3-week-old piglets, both B. bronchiseptica DNT and P. multocida DNT produced nasal turbinate lesions with similar severity, characterized by damage of the cilia, epithelial metaplasia, intensive proliferation of osteoblasts, regressive changes, and diffuse osteocytic osteolysis. In 7- to 12-week-old piglets, treatment with B. bronchiseptica DNT failed to produce progressive changes in the nasal turbinates. Histopathological examination revealed osteogenic processes and osteoid synthesis besides the proliferation of osteoblasts and mild osteocytic osteolysis. Moreover, severe gross pathological lesions developed in the stomach, liver, kidneys, and lymphoid organs. The piglets' appetite and body weight gain gradually decreased during the DNT treatment and in the last week when the toxic signs appeared. Treatment of 7- to 12-week-old piglets with P. multocida DNT resulted in progressive AR. Histopathologically, diffuse osteocytic osteolysis was observed in the nasal turbinates. Neither clinical signs nor pathological lesions of the visceral organs developed in these piglets. The authors emphasize that the DNT of B. bronchiseptica basically differs from that of P. multocida in biological properties, though there are certain similarities between the DNTs.  相似文献   
994.
995.
The isolation of N-methyl-4-hydroxy-3-(2',3'-epoxyisobutyl)-2-quinolone (1), a new natural compound, and candicine (2) from Galipea officinalis trunk bark is reported. This is the first report of candicine in the genus Galipea.  相似文献   
996.
The biochemical and serological characteristics of 486 P. haemolytica and 31 P. trehalosi strains (517 in total) isolated from different lesions of cattle, sheep, goats, pigs and poultry were examined. A total of 476 P. haemolytica strains (97.9%) showed the characteristics typical of the former biotype A of P. haemolytica, while 10 isolates (2.1%), all from poultry, could not be biotyped. A total of 481 strains (93.0%) could be assigned to one of the 17 serotypes of P. haemolytica-P. trehalosi and 36 strains (7.0%) could not. The majority (83.6%) of the cattle isolates were serotypes A1 and A2. Among strains isolated from sheep all serotypes of P. haemolytica could be identified with the exception of A14, but serotypes A1, A2, A6, A8 and A5 were the most frequent. The overwhelming majority (94%) of the caprine isolates were A2, other serotypes occurred only sporadically. The pig isolates, which could be isolated only very rarely, represented different serotypes, while none of the 10 strains isolated from poultry could be biotyped or serotyped.  相似文献   
997.
998.
999.
This study aimed to assess the combined effects of density of adults of Branchiura sowerbyi and the source of organic matter on the production of eggs and young species. The experimental units used were 250‐mL beakers with 100 mL of fine sand (0.074–0.210 mm) and 150 mL of chlorine‐free water with constant aeration at the temperature 25 C. The experiment was conducted based on a two‐factor model with six treatments and three repetitions, applied in a completely random design. The densities 5 individuals/38.5cm2 (D5; 1298/m2) and 8 individuals/38.5cm2 (D8; 2078/m2) were assessed with commercial fish feed (FF), commercial poultry feed (PF), and turkey manure (TM) as sources of organic matter. A total of 1223 cocoons and 2138 eggs were produced, with average hatching of 40.0 ± 15.1%. The highest number of cocoons and eggs was found with the use of PF, D8 having produced the highest number of cocoons and eggs. The hatching rate was not influenced by the source of organic matter or density and no influence was registered from the density of adults on the survival. The PF provided the highest growth of adults, and generally the use of TM provided the worst performance.  相似文献   
1000.
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