全文获取类型
| 收费全文 | 188183篇 |
| 免费 | 10593篇 |
| 国内免费 | 106篇 |
专业分类
| 林业 | 7695篇 |
| 农学 | 6013篇 |
| 基础科学 | 1321篇 |
| 22525篇 | |
| 综合类 | 33005篇 |
| 农作物 | 6925篇 |
| 水产渔业 | 9531篇 |
| 畜牧兽医 | 96302篇 |
| 园艺 | 2365篇 |
| 植物保护 | 13200篇 |
出版年
| 2018年 | 2450篇 |
| 2017年 | 2652篇 |
| 2016年 | 2502篇 |
| 2015年 | 2191篇 |
| 2014年 | 2706篇 |
| 2013年 | 7005篇 |
| 2012年 | 5002篇 |
| 2011年 | 6193篇 |
| 2010年 | 4018篇 |
| 2009年 | 4092篇 |
| 2008年 | 6217篇 |
| 2007年 | 5849篇 |
| 2006年 | 5703篇 |
| 2005年 | 5283篇 |
| 2004年 | 5255篇 |
| 2003年 | 5242篇 |
| 2002年 | 5075篇 |
| 2001年 | 5969篇 |
| 2000年 | 5774篇 |
| 1999年 | 4734篇 |
| 1998年 | 2015篇 |
| 1997年 | 1980篇 |
| 1996年 | 1888篇 |
| 1995年 | 2234篇 |
| 1994年 | 2099篇 |
| 1993年 | 2016篇 |
| 1992年 | 3979篇 |
| 1991年 | 4156篇 |
| 1990年 | 4260篇 |
| 1989年 | 4142篇 |
| 1988年 | 3845篇 |
| 1987年 | 3861篇 |
| 1986年 | 3983篇 |
| 1985年 | 3822篇 |
| 1984年 | 3253篇 |
| 1983年 | 2895篇 |
| 1982年 | 1970篇 |
| 1981年 | 1847篇 |
| 1980年 | 1821篇 |
| 1979年 | 2943篇 |
| 1978年 | 2437篇 |
| 1977年 | 2104篇 |
| 1976年 | 1919篇 |
| 1975年 | 2024篇 |
| 1974年 | 2565篇 |
| 1973年 | 2621篇 |
| 1972年 | 2565篇 |
| 1971年 | 2339篇 |
| 1970年 | 2208篇 |
| 1969年 | 2096篇 |
排序方式： 共有10000条查询结果，搜索用时 17 毫秒
101.
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints. 相似文献
102.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves. 相似文献
103.
104.
105.
106.
Wodsedalek JE 《Science (New York, N.Y.)》1917,46(1189):366-367
107.
108.
109.
110.