全文获取类型
收费全文 | 54905篇 |
免费 | 2854篇 |
国内免费 | 288篇 |
专业分类
林业 | 3628篇 |
农学 | 2430篇 |
基础科学 | 489篇 |
9847篇 | |
综合类 | 6608篇 |
农作物 | 2531篇 |
水产渔业 | 3098篇 |
畜牧兽医 | 23862篇 |
园艺 | 1243篇 |
植物保护 | 4311篇 |
出版年
2021年 | 577篇 |
2020年 | 625篇 |
2019年 | 605篇 |
2018年 | 2234篇 |
2017年 | 2356篇 |
2016年 | 1625篇 |
2015年 | 994篇 |
2014年 | 1164篇 |
2013年 | 2398篇 |
2012年 | 2322篇 |
2011年 | 3079篇 |
2010年 | 2493篇 |
2009年 | 2293篇 |
2008年 | 2677篇 |
2007年 | 2822篇 |
2006年 | 1663篇 |
2005年 | 1558篇 |
2004年 | 1426篇 |
2003年 | 1409篇 |
2002年 | 1209篇 |
2001年 | 1427篇 |
2000年 | 1431篇 |
1999年 | 1088篇 |
1998年 | 417篇 |
1997年 | 452篇 |
1996年 | 369篇 |
1995年 | 407篇 |
1992年 | 743篇 |
1991年 | 819篇 |
1990年 | 726篇 |
1989年 | 785篇 |
1988年 | 718篇 |
1987年 | 663篇 |
1986年 | 709篇 |
1985年 | 638篇 |
1984年 | 497篇 |
1983年 | 446篇 |
1979年 | 584篇 |
1978年 | 461篇 |
1977年 | 401篇 |
1976年 | 373篇 |
1975年 | 403篇 |
1974年 | 485篇 |
1973年 | 518篇 |
1972年 | 478篇 |
1971年 | 361篇 |
1970年 | 370篇 |
1969年 | 414篇 |
1968年 | 382篇 |
1967年 | 371篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Wilson JA Heath AC Stringfellow L Haack NA Clark AG 《New Zealand veterinary journal》1996,44(5):185-187
Four groups of five Romney lambs were treated by plunge dipping with one of four registered organophosphorus flystrike preventatives. Untreated lambs acted as controls. The sheep were challenged at weekly intervals with larval implants of organophosphate-susceptible and -resistant strains of Lucilia cuprina. All four treatments provided 19-21 weeks protection against susceptible larvae but chlorfenvinphos provided the longest protection (16-17 weeks), followed by propetamphos (15-16 weeks), dichlofenthion (10-13 weeks) and diazinon (9-13 weeks), against the resistant strain. 相似文献
62.
63.
W. J. Blok G. J. Bollen 《European journal of plant pathology / European Foundation for Plant Pathology》1993,99(3):29-40
Replant disease is a common phenomenon in asparagus growing in the Netherlands. It is distinct from the decline phenomenon reported from many other asparagus producing area’s. The involvement of autotoxins from root residues of former asparagus crops was evaluated. Residues of aspar agus roots decompose extremely slowly. At two locations, each with fields where asparagus production was terminated 1 and 10 years before, biomass of root residues was 4180 and 11060 kg dw ha?1 after 1 year and 420 and 1140 kg dw ha?1 after 10 years.Although 10-year-old residues were for the greater part decomposed, crude aqueous extracts inhibited root growth of asparagus seedlings significantly and even more of garden cress. In root observation boxes with field soil mixed with non-sterilized or sterilized asparagus root fragments, growth of secondary roots was inhibited. Non-sterilized strawberry roots did not inhibit root growth, suggesting that effects of organic matter were not involved. In a pot experiment, sterilized asparagus root fragments inhibited root growth when added at a rate of 20 g1?1, but not a 2 g1?1 Addition of non-sterilized root fragments strongly inhibited root growth at both levels. This was probably due to simultaneous infection byFusarium oxysporum present in these residues. When an asparagus field is replanted, the amount of root residues left behind in soil after termination of the crop in the previous season is about 2 g dw 1?1, that corresponds to approx. 11000 kg dw ha?1. This level is too low for considering direct growth inhibition by autotoxins as a major factor. Their possible indirect effects are briefly discussed. 相似文献
64.
65.
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
66.
Wade N 《Science (New York, N.Y.)》1979,206(4421):912-913
67.
68.
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
69.
70.
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