全文获取类型
收费全文 | 160329篇 |
免费 | 22319篇 |
国内免费 | 28215篇 |
专业分类
林业 | 11391篇 |
农学 | 9702篇 |
基础科学 | 8738篇 |
46247篇 | |
综合类 | 43071篇 |
农作物 | 9515篇 |
水产渔业 | 10366篇 |
畜牧兽医 | 56080篇 |
园艺 | 3555篇 |
植物保护 | 12198篇 |
出版年
2023年 | 1161篇 |
2022年 | 1538篇 |
2021年 | 1656篇 |
2020年 | 3371篇 |
2019年 | 7001篇 |
2018年 | 7468篇 |
2017年 | 8379篇 |
2016年 | 9071篇 |
2015年 | 8754篇 |
2014年 | 8135篇 |
2013年 | 10865篇 |
2012年 | 9368篇 |
2011年 | 8880篇 |
2010年 | 6833篇 |
2009年 | 6319篇 |
2008年 | 6426篇 |
2007年 | 6300篇 |
2006年 | 5762篇 |
2005年 | 5159篇 |
2004年 | 5212篇 |
2003年 | 4840篇 |
2002年 | 4390篇 |
2001年 | 4457篇 |
2000年 | 4205篇 |
1999年 | 3620篇 |
1998年 | 2292篇 |
1997年 | 2202篇 |
1996年 | 1983篇 |
1995年 | 2182篇 |
1994年 | 2094篇 |
1993年 | 1806篇 |
1992年 | 2738篇 |
1991年 | 2622篇 |
1990年 | 2576篇 |
1989年 | 2412篇 |
1988年 | 2213篇 |
1987年 | 1986篇 |
1986年 | 2059篇 |
1985年 | 1807篇 |
1984年 | 1590篇 |
1983年 | 1464篇 |
1979年 | 1543篇 |
1978年 | 1171篇 |
1976年 | 1133篇 |
1975年 | 1195篇 |
1974年 | 1284篇 |
1973年 | 1303篇 |
1972年 | 1248篇 |
1971年 | 1118篇 |
1969年 | 1167篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
995.
996.
997.
Shell aragonite from 96 specimens of the freshwater gastropod Limnaea stagnalis grown in laboratory tanks at different temperatures in water with variable strontium/calcium ratios have been analyzed for its strontium content in order to evaluate the mechanisms of strontium uptake in molluskan aragonite. Within the limits defined by natural freshwater environments, the strontium/calcium ratio in the aragonite was found to be linearly related to the strontium/calcium ratio in the water. A distribution coefficient k(A)(Sr) = 0.237 +/- 0.029, unaffected by variations in temperature and growth rate, has been found. This finding substantiates the existence of a strontium-discriminating effect in aragonite precipitated by mollusks as compared to the case for nonbiogenic aragonite which contains about five times as much strontium when precipitated under the same conditions. 相似文献
998.
Two marine sediment cores from a basin on the southeastern Labrador Shelf penetrate a mud sequence extending back to 21,000 carbon-14 years before the present (B.P.). The benthic foraminifera are dominated by subartic nearshore species indicative of ice-free summer waters. The pollen record indicates the presence of a sedge-shrub tundra in eastern Labrador as early as 21,000 years B.P. Both sources of evidence suggest less extensive continental ice than has previously been reported for this subarctic region. 相似文献
999.
The percentage of lymphoid cells from the bursa of Fabricius, thymus, spleen, peripheral blood, and cecal tonsils reactin with chicken antisera to turkey bursa and thymus were evaluated, using 1-day-old to 5-week-old turkeys. For this, rabbit anti-chicken globulin fluorescein isothiocyanate conjugate was used. The percentage of lymphoid cells showing immunoglobulin surface determinants from these organs also was examined, using a direct immunofluorescence test with a rabbit anti-turkey globulin fluorescein isothiocyanate conjugate. This study suggests that the bursa-specific antigen and immunoglobulin surface determinants could be used as markers for bursa-derived cells in the turkey. It also was found that thymus-specific antigen could be used as a marker for thymus-derived cells. 相似文献
1000.