全文获取类型
| 收费全文 | 277994篇 |
| 免费 | 16040篇 |
| 国内免费 | 666篇 |
专业分类
| 林业 | 23806篇 |
| 农学 | 14060篇 |
| 基础科学 | 2966篇 |
| 43956篇 | |
| 综合类 | 33555篇 |
| 农作物 | 17159篇 |
| 水产渔业 | 17057篇 |
| 畜牧兽医 | 111546篇 |
| 园艺 | 6362篇 |
| 植物保护 | 24233篇 |
出版年
| 2020年 | 2895篇 |
| 2019年 | 3675篇 |
| 2018年 | 4035篇 |
| 2017年 | 4451篇 |
| 2016年 | 4848篇 |
| 2015年 | 4347篇 |
| 2014年 | 5699篇 |
| 2013年 | 16327篇 |
| 2012年 | 6522篇 |
| 2011年 | 8465篇 |
| 2010年 | 7406篇 |
| 2009年 | 7987篇 |
| 2008年 | 7873篇 |
| 2007年 | 6966篇 |
| 2006年 | 7550篇 |
| 2005年 | 6911篇 |
| 2004年 | 6723篇 |
| 2003年 | 6604篇 |
| 2002年 | 5926篇 |
| 2001年 | 6445篇 |
| 2000年 | 6111篇 |
| 1999年 | 5634篇 |
| 1998年 | 4180篇 |
| 1997年 | 4256篇 |
| 1996年 | 3971篇 |
| 1995年 | 4572篇 |
| 1994年 | 3999篇 |
| 1993年 | 3706篇 |
| 1992年 | 4825篇 |
| 1991年 | 5027篇 |
| 1990年 | 4819篇 |
| 1989年 | 4860篇 |
| 1988年 | 4352篇 |
| 1987年 | 4361篇 |
| 1986年 | 4331篇 |
| 1985年 | 4622篇 |
| 1984年 | 4180篇 |
| 1983年 | 3858篇 |
| 1982年 | 3141篇 |
| 1981年 | 2997篇 |
| 1980年 | 2938篇 |
| 1979年 | 3791篇 |
| 1978年 | 3285篇 |
| 1977年 | 3067篇 |
| 1976年 | 2882篇 |
| 1975年 | 2848篇 |
| 1974年 | 3206篇 |
| 1973年 | 3152篇 |
| 1972年 | 2998篇 |
| 1971年 | 2912篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
991.
Howard A. Clonts Curtis M. Jolly Syed Abdulkadir L. Alsagoff 《Journal of the World Aquaculture Society》1989,20(4):268-276
The merits of integrated aquaculture farming (IAF) as a strategy for bolstering income for the rural poor have been recognized, but the economic efficiency and sustainability are yet to be determined. The effects of one species on another and the economic benefits, net of government support, have not been critically evaluated. The concept of a foodniche for alternative species in an aquatic environment has not been properly tested in an economic setting. Thus, this report reflects the results of applying the technique of mixed integer linear programming to determine the optimum combination of species within the context of a foodniche. The objective also included maximizing revenues, with minimal external input requirements, for a representative small Malaysian wet-rice farm. It was found that the foodniche concept permitted flexibility in stocking rates, and that farmers could actually stock species at the exact rate that was optimal for profit, instead of standard fixed rates. Also, government subsidies for pond construction were essential for IAF success. The net revenues from IAF were low without interest-free loans for pond construction. 相似文献
992.
M. B&#x;halov 《EPPO Bulletin》2004,34(3):365-367
Erwinia amylovora has been spreading in the Czech Republic since 1986 regardless of emergency phytosanitary measures which have been taken. Its spread follows the predominant wind direction (west to east). The infested area now covers two thirds of the area of the country. Wild Crataegus spp. are the most important and widespread host plants. E. amylovora is still regulated as a quarantine pest, and areas free from fireblight are subject to special phytosanitary measures. 相似文献
993.
994.
Long‐term experiments are a classical case of repeated measurements. Traits are measured on the same experimental unit over many years so that correlations arise between the observations made on the same plot in consecutive years. This paper describes the analysis of a three‐crop‐rotation long‐term experiment. We analysed the yields of the crops and the organic carbon content in the topsoil over 30 consecutive years. Several variance–covariance approaches are discussed and the trait‐specific best fit is interpreted. Mixed models are used to describe the structure of the experiment. Both yields and soil organic carbon show a more or less pronounced variance heterogeneity. Especially for yields, the heterogeneity of cycles and years is dominant. The consideration of correlations results in a better model fit in all cases. 相似文献
995.
996.
997.
A. Wjtowicz 《EPPO Bulletin》2003,33(3):515-516
A computer system Agrogis has been developed to record information on pest infestation of plants in different regions of Poland. Data can be entered manually or from disks, and can be displayed in the form of charts and maps. Agrogis will be made available on the Internet. 相似文献
998.
糖类寄生螨快速分离检验方法 总被引：1，自引：0，他引：1
本文对糖类寄生螨的快速分离检验方法进行了改进。将糖类溶解后，经过500目/英寸标准检验筛进行过筛分离。此方法对各种可溶性糖类中的寄生螨类能取得100％的快速分离检验结果。 相似文献
999.
1000.
浙江淳安新安江开发公司封山育林效益研究 总被引：2，自引：0，他引：2
浙江省淳安县新安江开发公司所属16个国营林场22475.53hm~3荒山迹地,封山育林30年,现有天然次生林总蓄积量135万m~3,年总生长率8.07％,活立木直接经济价值2.25亿元。到1987年止公司已获中间利用净收入2135万元。近20年累计天然次生林比无林地多涵蓄水10亿m~3,每年进入水库的泥沙量减少80％,对调节水库水源、延长发电年限、纯洁水质都起到良好作用。公司长期实施的5项管护技术,把封山育林提高到科学经营水平,在千岛湖区成功地建立了森林生态屏障。 相似文献