全文获取类型
收费全文 | 89811篇 |
免费 | 5534篇 |
国内免费 | 46篇 |
专业分类
林业 | 3760篇 |
农学 | 3469篇 |
基础科学 | 632篇 |
11256篇 | |
综合类 | 13531篇 |
农作物 | 3364篇 |
水产渔业 | 4944篇 |
畜牧兽医 | 47651篇 |
园艺 | 1165篇 |
植物保护 | 5619篇 |
出版年
2020年 | 733篇 |
2019年 | 954篇 |
2018年 | 1584篇 |
2017年 | 1849篇 |
2016年 | 1662篇 |
2015年 | 1407篇 |
2014年 | 1720篇 |
2013年 | 3726篇 |
2012年 | 2932篇 |
2011年 | 3590篇 |
2010年 | 2343篇 |
2009年 | 2332篇 |
2008年 | 3473篇 |
2007年 | 3211篇 |
2006年 | 3144篇 |
2005年 | 2672篇 |
2004年 | 2577篇 |
2003年 | 2592篇 |
2002年 | 2376篇 |
2001年 | 3389篇 |
2000年 | 3305篇 |
1999年 | 2554篇 |
1998年 | 984篇 |
1997年 | 1051篇 |
1996年 | 884篇 |
1995年 | 1022篇 |
1994年 | 895篇 |
1993年 | 896篇 |
1992年 | 1845篇 |
1991年 | 1919篇 |
1990年 | 1856篇 |
1989年 | 1859篇 |
1988年 | 1608篇 |
1987年 | 1595篇 |
1986年 | 1629篇 |
1985年 | 1526篇 |
1984年 | 1225篇 |
1983年 | 1032篇 |
1982年 | 713篇 |
1979年 | 1060篇 |
1978年 | 816篇 |
1975年 | 815篇 |
1974年 | 897篇 |
1973年 | 864篇 |
1972年 | 805篇 |
1971年 | 796篇 |
1970年 | 800篇 |
1969年 | 780篇 |
1968年 | 708篇 |
1967年 | 734篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
C. A. DUIGAN T. E. H. ALLOTT H. BENNION J. LANCASTER D. T. MONTEITH S. T. PATRICK J. RATCLIFFE J. M. SEDA 《水产资源保护:海洋与淡水生态系统》1996,6(1):31-55
1. The environment of the island of Anglesey, North Wales, UK, is described and related to the ecology of the lake systems present. 2. Estimates are given of the number and types of lakes present on the island. Sixteen biological Sites of Special Scientific Interest (SSSIs) have standing water as a recognized habitat feature and their reasons for receiving a conservation designation are discussed. 3. Brief reviews are given of the lacustrine flora, invertebrates, fish and aquatic bird populations of Anglesey and their importance in assessing the conservation value of a site. 4. These reviews are followed by detailed accounts of the current ecology of three of the island's lake systems—Llyn Coron, Llyn Dinam and Llyn Penrhyn—which occur within biological Sites of Special Scientific Interest. Original data are presented on their physical and chemical characteristics, diatom assemblages, macrophyte communities, littoral and open water zooplankton communities and macroinvertebrate assemblages. 5. Artificial enrichment, the introduction of alien species, the legacy of metal mining operations and recreational pressures are identified as the main threats to lake conservation on Anglesey. 6. The Anglesey Wetland Strategy, an informal operational level liaison procedure, is described. Using this mechanism, broad targets and indicative strategies are highlighted by the partner organizations active in wetland conservation on the island, and opportunities for collaboration are developed. 相似文献
963.
S. C. Gupta 《Plant Breeding》1994,112(2):135-140
Screening of a population of Ocimum basilicum var. glabratum Benth., raised from seeds collected from France, West Africa and Kerala (India) was carried out for chemical composition of its essential oils. In all three collections, plants were found to be comprised of 3 chemotypes which were morphologically indistinguishable, but each chemotype was found to be capable of intercrossing freely with the other two. Selfing was carried out during 4 consecutive generations, after which three pure lines were established. Study of the selfed progeny of each collection exhibited an interesting segregation in S2 and S3 generations. Along with segregation in F2 and F3 generations of various hybrids the results can be explained by assuming a gene ‘M’ existing in 3 (or more) allelic forms: The allele M0 for biosynthesis of estragole (methyl chavicol) is dominant to allelcs M1 , for eugenol and M2 for camphor. Also, allele M1 is dominant to allele M2 . The assumption was further confirmed by testcrosses of F1 hybrids of each cross with their recessive parent. 相似文献
964.
965.
966.
Machado Rui Godinho Sérgio Guiomar Nuno Gil Artur Pirnat Janez 《Landscape Ecology》2020,35(6):1291-1308
Landscape Ecology - The Portuguese montado is an agro-silvopastoral system, similar to the Spanish dehesa, known for its cultural, economic and ecological value. Despite its importance, contrasting... 相似文献
967.
968.
S. Papadopoulou M. Kaydan A. Manganaris D. Loukovitis C. Chrysochoidis 《EPPO Bulletin》2020,50(2):299-303
High levels of infestation of a wax soft scale insect (Hemiptera: Coccidae) have been observed on Laurus nobilis L. (Lauraceae) and Diospyros kaki Thunb. (Ebanaceae) in Greece in recent years. Specimens of Ceroplastes were collected from regions of Thessaloniki, Naousa and Kavala (northern Greece) and Attica (southern Greece) in 2012–2017. The specimens were identified based on DNA barcoding and female morphological characteristics as Ceroplastes japonicus Green (Hemiptera: Coccidae). 相似文献
969.
Loren S. Sri-Jayantha Michael T. Doornink Bridget K. Urie 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(1):32
There are limited data on glucocorticoid treatment in dogs. The purpose of this study was to investigate whether dogs of higher body weight experienced more adverse events when receiving glucocorticoid therapy. Data pertaining to glucocorticoid therapy was abstracted from the records of 61 dogs that were prescribed glucocorticoids for treatment of immune-mediated thrombocytopenia or hemolytic anemia from 2014 to 2019. The odds of developing muscle atrophy and polyphagia during therapy were increased by 30% for each 5 kg of additional body weight. Almost half of the dogs (44.3%) fluctuated > 15% from baseline weight during therapy. Dogs whose body condition scored as above ideal were at increased risk (odds ratio = 4.2) for being diagnosed with urinary tract infection. Our findings suggest that standard linear glucocorticoid dosing may place higher body weight dogs at increased risk of developing adverse events. Accelerated glucocorticoid tapering and/or alternative dosing schemes in dogs with higher body weights may be prudent in efforts to improve tolerance and client compliance. 相似文献
970.