全文获取类型
收费全文 | 2741篇 |
免费 | 176篇 |
国内免费 | 217篇 |
专业分类
林业 | 493篇 |
农学 | 231篇 |
基础科学 | 99篇 |
250篇 | |
综合类 | 942篇 |
农作物 | 177篇 |
水产渔业 | 77篇 |
畜牧兽医 | 404篇 |
园艺 | 100篇 |
植物保护 | 361篇 |
出版年
2024年 | 20篇 |
2023年 | 63篇 |
2022年 | 100篇 |
2021年 | 102篇 |
2020年 | 99篇 |
2019年 | 108篇 |
2018年 | 68篇 |
2017年 | 120篇 |
2016年 | 124篇 |
2015年 | 98篇 |
2014年 | 177篇 |
2013年 | 186篇 |
2012年 | 216篇 |
2011年 | 223篇 |
2010年 | 157篇 |
2009年 | 145篇 |
2008年 | 158篇 |
2007年 | 132篇 |
2006年 | 124篇 |
2005年 | 93篇 |
2004年 | 79篇 |
2003年 | 55篇 |
2002年 | 52篇 |
2001年 | 48篇 |
2000年 | 52篇 |
1999年 | 47篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 26篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有3134条查询结果,搜索用时 15 毫秒
1.
腐蚀管道剩余寿命的性能衰减模型研究 总被引:4,自引:0,他引:4
管道在长期的运行过程中,由于介质和土壤的腐蚀性,管材的微塑性变形、结构转变和渗氢等。不仅会使管道出现各种腐蚀损伤,而且还存在着老化效应和氢化作用,导致管材的脆变并改变材料的塑性,使机械性质参数发生衰退,从管材性能衰减和腐蚀损伤角度研究了管道的剩余寿命,提出了根据结构承载能力的极限值确定塑性变形时工作寿命的方法,为了确定剩余使用寿命,对剪切损伤率和屈服性能比等概念进行定义,在掌握管材金属剪切损害率和屈服性能比的时间特性基础上,建立了剩余寿命计算模型。并给出了算例。 相似文献
2.
3.
蝇害已经成为危害规模化畜禽养殖的重要问题。文章回顾了防治蝇害的三代杀虫剂的发展过程和存在的问题 ;展望了作为新一代环境友好防治蝇害药物的昆虫生长调节剂的开发前景。 相似文献
4.
The occurrence of hide damage light flecks and spots was determined on tanned hides from 28 herds during a period of 8 to 12 months. Light flecks and spots are described as small areas of grain loss up to 3 mm in diameter that are seen on dyed crust cattle leather. Damage was found on 75.8% of all hides. The neck and shoulders were the anatomical region with the highest prevalence of damage. Sixty-eight per cent of all hides had light flecks and spots in this region. The forelimbs and dewlap were the anatomical region with the second highest occurrence with a prevalence of 39.1%. This distribution corresponded to the known distribution of lice in cattle. No significant differences were observed in age, sex, prevalence of lice in the herd assessed in March or infestations with different lice species. The frequency of light flecks and spots varied significantly during the year. The frequency was highest in the late winter and early spring, decreased significantly during the summer and was lowest in the autumn. This variation supported the importance of lice in the development of light flecks and spots and suggested a relatively long healing period for the damages induced by lice. 相似文献
5.
巫溪红池坝改良草地鼠类调查报告 总被引:1,自引:0,他引:1
对重庆巫溪红池坝改良草地中鼠形动物的种类进行抽样调查、室内饲养、解剖鼠胃和洞道研究,结果显示,该改良草地中有鼠形动物2目3科4种,其对草地危害方式和为害程度均不一样。提出了改良草地中鼠害的防治措施。 相似文献
6.
The influence of an eradication programme for lice on the prevalence of light flecks and spots on cattle hides was studied in 33 dairy cattle herds during a period of two and a half years. Lice were eradicated from the main group of herds after 9 to 12 months and the quality of the hides before and after treatment was compared. Hides from slaughtered animals were collected during the study period, tanned and examined with special emphasis on the occurrence of the grain damage light flecks and spots. The prevalence of hides without light flecks and spots increased from 24.2% before treatment to 61.6% after treatment. The prevalence of hides free from the damage increased significantly in all examined anatomical regions. The improvement in hide quality was most marked in the shoulders and neck region which corresponded to the major predilection site of cattle lice. The prevalence of hides with light flecks and spots started to decrease in the first period (2-40 days) after eradication. The changes after treatment suggested that most healing process took place over a period of about 4 months. The eradication programme eliminated the seasonal variation in the prevalence of light flecks and spots which was present before treatment. 相似文献
7.
8.
9.
夏大豆成熟期害鼠防治指标的研究潘学锋(安徽省霍邱县植保站237400)刘同群(霍邱县城西湖乡农技站)摘要本文通过大田调查夏大豆田的害鼠发生种类及其密度与产量损失的关系,结果表明,沿淮地区夏大豆田的害鼠种类为黑线姬鼠、黑线仓鼠、褐家鼠、小家鼠等,其中以... 相似文献
10.
Fractional excretion of electrolytes in volume‐responsive and intrinsic acute kidney injury in dogs: Diagnostic and prognostic implications 下载免费PDF全文