全文获取类型
收费全文 | 140636篇 |
免费 | 7717篇 |
国内免费 | 89篇 |
专业分类
林业 | 5639篇 |
农学 | 4258篇 |
基础科学 | 939篇 |
16253篇 | |
综合类 | 24384篇 |
农作物 | 5319篇 |
水产渔业 | 6712篇 |
畜牧兽医 | 74287篇 |
园艺 | 1596篇 |
植物保护 | 9055篇 |
出版年
2018年 | 1788篇 |
2017年 | 1982篇 |
2016年 | 1848篇 |
2015年 | 1592篇 |
2014年 | 1994篇 |
2013年 | 5234篇 |
2012年 | 3590篇 |
2011年 | 4405篇 |
2010年 | 2854篇 |
2009年 | 2975篇 |
2008年 | 4369篇 |
2007年 | 4114篇 |
2006年 | 3983篇 |
2005年 | 3643篇 |
2004年 | 3509篇 |
2003年 | 3611篇 |
2002年 | 3372篇 |
2001年 | 4350篇 |
2000年 | 4359篇 |
1999年 | 3377篇 |
1998年 | 1355篇 |
1997年 | 1424篇 |
1996年 | 1350篇 |
1995年 | 1667篇 |
1994年 | 1458篇 |
1993年 | 1415篇 |
1992年 | 2985篇 |
1991年 | 3254篇 |
1990年 | 3089篇 |
1989年 | 3113篇 |
1988年 | 2931篇 |
1987年 | 2983篇 |
1986年 | 3109篇 |
1985年 | 2940篇 |
1984年 | 2449篇 |
1983年 | 2106篇 |
1982年 | 1454篇 |
1979年 | 2256篇 |
1978年 | 1822篇 |
1977年 | 1642篇 |
1976年 | 1575篇 |
1975年 | 1640篇 |
1974年 | 2083篇 |
1973年 | 2151篇 |
1972年 | 2045篇 |
1971年 | 1907篇 |
1970年 | 1837篇 |
1969年 | 1702篇 |
1968年 | 1472篇 |
1967年 | 1555篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Six shipments totaling 3452 mummies of the blackmargined aphid,Monellia caryella (Fitch), parasitized withAphelinus perpallidus Gahan, were obtained by air freight during the years 1982-1985 from Texas A&M Research Center, El Paso, Texas. About two-thirds of the mummies did not yield parasites. A colony ofA. perpallidus was established in the laboratory. Under laboratory conditions the percentage of emerged parasites was higher than that in the imported mummies, and the parasite had very limited impact on the aphid population. Field releases of the parasite were made but no establishment ofA. perpallidus was observed through the years. 相似文献
103.
G. Jager H. Velvis 《European journal of plant pathology / European Foundation for Plant Pathology》1988,94(5):225-231
Experiments in the laboratory and on farms with potato tubers in storage are described in which sclerotia ofRhizoctonia solani were inactivated after inoculation of infected tubers with a suspension of conidia and hyphal fragments ofVerticillium biguttatum. Sclerotia on freshly harvested tubers can be killed in a period of six to eight weeks, provided that (1) a direct contact between sclerotia and conidia ofV. biguttatum is obtained, (2) the temperature during the storage period is at least 15 °C, but preferably closer to 20 °C during the first weeks, and (3) the relative humidity of the air between the tubers is at least 99%. Seed tubers are only certified as export quality if the infection withR. solani, visible as sclerotia on the tubers, is assessed as below a specified incidence. To restore the economical value of tubers with many sclerotia, living sclerotia can be inactivated byV. biguttatum. However, also dead sclerotia have to be removed, as dead and living sclerotia cannot be distinguished visually by inspectors. A satisfactory way to remove dead sclerotia from tubers has not yet been found. 相似文献
104.
D D 《Science (New York, N.Y.)》1988,240(4860):1728
105.
Dickson D 《Science (New York, N.Y.)》1988,239(4841):720-721
106.
D. Gerling 《Phytoparasitica》1984,12(2):109-118
Wild and cultivated plants in the vicinity of Kibbutz Nahshon and a few additional locations in Israel were sampled for the presence ofBemisia tabaci Genna-dius (Homoptera: Aleyrodidae). The whiteflies, together with their parasites,Eretmocerus mundus andEncarsia lutea, were found to develop on numerous host species throughout the winter. Especially high levels were reached onLan-tana camara, Abutilon grandifolium andIpomoea batatas. During late winter and spring the population on these hosts declined. From April onwards the populations increased on potatoes and sunflowers. 相似文献
107.
P. H. M. Roseboom D. Peters 《European journal of plant pathology / European Foundation for Plant Pathology》1984,90(4):133-141
Beet yellows virus can be detected in leaf extracts of infected sugarbeet plants by ELISA. The use of discs was studied and proved to be a valuable and qualitatively reliable method. Leaf material could be stored at 4o or 22°C for at least six days without affecting the detection of this virus by ELISA. A dramatic decrease in ELISA values was found when leaf extracts were frozen.In an analysis of the distribution of virus over the plant it was found that young leaves present at the moment of infection and those which had still to develop after infection will contain virus. Symptoms produced by systemic virus invasion occur on the oldest leaves containing virus.Samenvatting Het bietevergelingsvirus kan op betrouwbare wijze met de ELISA methode in geïnfecteerde bieteplanten worden aangetoond. Een aanzienlijke vereenvoudiging van de procedure kan worden bereikt met de zogenaamde disc-method, waarbij intacte ponsstukjes in de putjes van de ELISA-plaat worden geïncubeerd. Hierbij komt voldoende virus uit de ponsstukjes voor ELISA vrij. Bladmateriaal kon op verschillende wijzen bewaard worden zonder dat de mogelijkheid om het virus aan te tonen achteruitging. Met bladextracten die ingevroren waren, werden echter slechte resultaten verkregen.In een analyse naar de verdeling van het virus over het loof bleek het virus voor te komen in de geïnoculeerde bladeren, in die bladeren die op het tijdstip van inoculatie minder dan de helft van hun uiteindelijke lengte bereikt hadden en in de bladeren die nog moesten verschijnen. De symptomen ontwikkelden zich op de oudste systemisch geïnfecteerde bladeren. 相似文献
108.
Gingerich PD 《Science (New York, N.Y.)》1984,226(4677):994-996
109.
Dickson D 《Science (New York, N.Y.)》1984,224(4654):1216-1217
110.