全文获取类型
收费全文 | 38773篇 |
免费 | 2257篇 |
国内免费 | 286篇 |
专业分类
林业 | 1658篇 |
农学 | 1437篇 |
基础科学 | 324篇 |
5650篇 | |
综合类 | 5694篇 |
农作物 | 1517篇 |
水产渔业 | 1844篇 |
畜牧兽医 | 20016篇 |
园艺 | 460篇 |
植物保护 | 2716篇 |
出版年
2021年 | 370篇 |
2020年 | 430篇 |
2019年 | 475篇 |
2018年 | 795篇 |
2017年 | 836篇 |
2016年 | 761篇 |
2015年 | 637篇 |
2014年 | 795篇 |
2013年 | 1915篇 |
2012年 | 1336篇 |
2011年 | 1571篇 |
2010年 | 1071篇 |
2009年 | 1116篇 |
2008年 | 1509篇 |
2007年 | 1356篇 |
2006年 | 1286篇 |
2005年 | 1113篇 |
2004年 | 1061篇 |
2003年 | 1045篇 |
2002年 | 926篇 |
2001年 | 1263篇 |
2000年 | 1245篇 |
1999年 | 941篇 |
1998年 | 397篇 |
1997年 | 421篇 |
1996年 | 342篇 |
1995年 | 393篇 |
1994年 | 342篇 |
1992年 | 658篇 |
1991年 | 787篇 |
1990年 | 686篇 |
1989年 | 722篇 |
1988年 | 664篇 |
1987年 | 627篇 |
1986年 | 675篇 |
1985年 | 598篇 |
1984年 | 463篇 |
1983年 | 412篇 |
1979年 | 554篇 |
1978年 | 431篇 |
1977年 | 358篇 |
1976年 | 366篇 |
1975年 | 398篇 |
1974年 | 461篇 |
1973年 | 475篇 |
1972年 | 448篇 |
1970年 | 369篇 |
1969年 | 401篇 |
1968年 | 358篇 |
1967年 | 362篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Myers N 《Science (New York, N.Y.)》1995,269(5222):358-360
Among the environmental problems ahead, the most important ones could be those that are still unknown to us. This conceptual article explores this prospect on the grounds that it is important not only to supply answers to recognized questions but to raise appropriate new questions. 相似文献
82.
Wade N 《Science (New York, N.Y.)》1979,206(4421):912-913
83.
84.
Intranuclear cisternal and vesicular structures, bound by a single membrane, were observed for the first time in some glandular "bird's eye" cells of canine circummanal gland carcinomas. The role of these intranuclear structures is not clear. It is suggested that they may be involved in cellular adaptation to an environment of nutrient deficiency, as a result of cell overcrowding. 相似文献
85.
86.
Two strains of bovine Theileria from northern Nigeria were shown to be identical to Theileria mutans in the indirect immunofluorescent antibody test. One of the strains was transmitted by the tick Amblyomma variegatum; large macroschizonts, typical for T mutans, could be demonstrated in infected cattle. It is concluded from these experiments and from the literature that there is reliable evidence so far for the occurrence in Nigeria of only two bovine Tehileria species, T mutans and T velifera. 相似文献
87.
Summary On two occasions an anaplasm was isolated from sheep on the Dutch island of Ameland. The organism proved to be highly pathogenic for splenectomised sheep; a non-splenectomised animal recovered spontaneously after the packed cell volume had decreased by 40%. Treatment with oxytetracycline was effective. Its pathogenicity for goats appeared to be low, and the organism was apparently not infective to splenectomised cattle. This anaplasm differs from Anaplasma ovis in that less than 30% of the organisms are marginally situated in the red cell, as against over 70% in A. ovis; cross-immunity with A. ovis was incomplete and the latter appeared to be far more pathogenic to goats than the Dutch anaplasm, for which the name Anaplasma mesaeterum sp.n. is proposed. Its ultrastructure is similar to that of A. marginale and A. ovis. The vector is either Ixodes ricinus or Haemaphysalis punctata. Its practical importance remains to be ascertained. 相似文献
88.
Wade N 《Science (New York, N.Y.)》1979,206(4420):800-801
89.
90.