全文获取类型
收费全文 | 344379篇 |
免费 | 19152篇 |
国内免费 | 8388篇 |
专业分类
林业 | 32629篇 |
农学 | 25642篇 |
基础科学 | 9669篇 |
55306篇 | |
综合类 | 51568篇 |
农作物 | 20611篇 |
水产渔业 | 19689篇 |
畜牧兽医 | 119807篇 |
园艺 | 8317篇 |
植物保护 | 28681篇 |
出版年
2021年 | 5004篇 |
2020年 | 5266篇 |
2019年 | 5929篇 |
2018年 | 5585篇 |
2017年 | 6578篇 |
2016年 | 7074篇 |
2015年 | 7350篇 |
2014年 | 8548篇 |
2013年 | 19855篇 |
2012年 | 10770篇 |
2011年 | 13202篇 |
2010年 | 11893篇 |
2009年 | 12190篇 |
2008年 | 11984篇 |
2007年 | 11168篇 |
2006年 | 11548篇 |
2005年 | 10313篇 |
2004年 | 8338篇 |
2003年 | 7975篇 |
2002年 | 6984篇 |
2001年 | 7894篇 |
2000年 | 7873篇 |
1999年 | 7660篇 |
1998年 | 6025篇 |
1997年 | 5762篇 |
1996年 | 5331篇 |
1995年 | 5859篇 |
1994年 | 5097篇 |
1993年 | 4763篇 |
1992年 | 5735篇 |
1991年 | 5853篇 |
1990年 | 5435篇 |
1989年 | 5390篇 |
1988年 | 4767篇 |
1987年 | 4574篇 |
1986年 | 4414篇 |
1985年 | 4630篇 |
1984年 | 4189篇 |
1983年 | 3951篇 |
1982年 | 3136篇 |
1981年 | 2998篇 |
1980年 | 2966篇 |
1979年 | 3734篇 |
1978年 | 3248篇 |
1977年 | 3017篇 |
1976年 | 2831篇 |
1974年 | 3157篇 |
1973年 | 3118篇 |
1972年 | 2876篇 |
1971年 | 2806篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
J D Brogdon A H Brightman L C Helper S A Mclaughlin A L Johnson 《Journal of the American Veterinary Medical Association》1989,194(8):1079-1081
A mandibular parosteal osteosarcoma was diagnosed in a 7-year-old Collie with prolapse of the third eyelid. Diagnosis was made by histologic evaluation of a mass removed by surgical excision. The dog was euthanatized because of local recurrence of the tumor, with metastasis to the lungs. Parosteal osteosarcomas are rarely reported in dogs and usually involve long bones in human beings. 相似文献
992.
993.
G. C. W. England W. Edward Allen D. J. Porter 《The Journal of small animal practice》1989,30(8):441-443
A two-year-old dog was presented with no scrotal testes. There was no history of castration but at laparotomy no testes were found. To confirm that the dog was truly anorchid a human chorionic gonadotrophin stimulation test was performed. This was then validated in normal entire and castrated dogs. 相似文献
994.
帽儿山地区21年生长白落叶松种源试验 总被引:3,自引:1,他引:2
对在黑龙江省的东北林业大学帽儿山实验林场21年生长白落叶松种源试验林进行方差分析。结果表明,种源间差异显著;生长性状,抗性与各种源间的经度,纬度,海拔高度及气候因子相关分析结果表明,海拔垂直梯度渐变为主,纬向渐变为辅的连续变异是长白落叶松生长性状的基本变异模式,降水量和日照时数是影响长白落叶松生长的主要气候因子,用长白落叶松各种源的相关性状作聚类分析并参照地理气象因子在,遗传距离0.370的水平上将长白落叶松分布范围区10个参试种源划为6个种源区:Ⅰ小北湖种源区。Ⅱ白刀山种源区,Ⅲ完达山种源区,Ⅳ白河种源区,Ⅴ大石头种源区,Ⅵ桓仁种源区;用Duncan法对种源间进行多重比较,并用综合指数法进行选择,表明小北湖种源是长白落叶松优良基因资源中心,是该试验点最佳种源,大海林种源也是可选择种源;从长白落叶松的低等效纬度地区向高等效纬度地区调种,可望获得较大的遗传增益。 相似文献
995.
盐分对碱茅种子发芽影响的机制 总被引:15,自引:0,他引:15
耐碱茅种子在盐(NaCl与Na2SO4)及干旱(PEG-6000模拟)胁迫下发芽及其机制的比较研究表明,种子发芽率随溶液渗透势的降低而下降,在等渗条件下三种溶液中的发芽率次序为Na2SO4>NaCl>PEG。NaCl与Na2SO4主要通过影响种子吸水量及对膜的毒性影响发芽,根据相关及通径分析结果,其机制为:(1)溶液渗透势及Na+浓度决定的种子吸水对发芽的直接正效应(通径系数0.73);(2)溶液Na+浓度引起的膜毒性对发芽的直接负效应(-0.51);(3)种子从溶液中吸收Na使种子吸水增加对发芽的间接正效应(0.30)及使膜毒性增大对发芽的间接负效应(-0.24)。 相似文献
996.
Bull sperm pellets experimentally infected with various concentrations of Mycoplasma (M.) bovis, M. bovigenitalium, and M. californicum were stored several months at -196 degrees C and were subsequently tested for mycoplasmas, using different methods and culturing media. M. bovis was reliably identified by laboratory diagnosis up to a concentration of 10(2) cfu/pellet. M. bovigenitalium and M. californicum were found to make higher demands on the quality of culturing substrates. Recommended are 1-h broth incubation and 5-d broth breeding. 相似文献
997.
In this study, the effects of nitrogen (N) rate (60, 120, 180 and 240 kg N ha?1 applied in three equal dressings at seeding and after the first and second cuttings) and stubble height (7, 14 and 21 cm) on the dry matter (DM) yield, crude protein (CP) content, and CP yield of a sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf., cv. Pioneer 988] in the three‐cut system was investigated. The N rate had no significant effect in the first and third cuttings, but in the second cutting DM yields increased significantly with increase in N rate. The highest yield of 9.1 t ha?1 was obtained with 80 kg N ha?1 for the average of 2 years at the second cutting, but no significant difference was found among the 40, 60 and 80 kg N ha?1 rates. CP content and yield were not significantly affected by N rate at the first and third cuttings, but CP content and yield were significantly affected by application of N at the second cutting. Stubble height had a significant effect on CP content at the third cutting. However, it had no significant effect on CP content at the first and second cuttings. Stubble height had a significant effect on the CP yield at the first cutting, but no significant effect on CP yield at the second and third cuttings. 相似文献
998.
999.
本文针对郑州渔区现阶段鱼病现状及存在的主要问题,分析了多种鱼病的成因和防治措施,讨论了水质及营养对鱼病的影响,提出了健康养殖方向。 相似文献
1000.