全文获取类型
收费全文 | 252850篇 |
免费 | 14958篇 |
国内免费 | 690篇 |
专业分类
林业 | 23560篇 |
农学 | 14035篇 |
基础科学 | 2985篇 |
42626篇 | |
综合类 | 25836篇 |
农作物 | 17233篇 |
水产渔业 | 16800篇 |
畜牧兽医 | 95514篇 |
园艺 | 6367篇 |
植物保护 | 23542篇 |
出版年
2021年 | 2505篇 |
2020年 | 2915篇 |
2019年 | 3690篇 |
2018年 | 3951篇 |
2017年 | 4258篇 |
2016年 | 4755篇 |
2015年 | 4331篇 |
2014年 | 5717篇 |
2013年 | 16294篇 |
2012年 | 6068篇 |
2011年 | 7935篇 |
2010年 | 7284篇 |
2009年 | 7835篇 |
2008年 | 7347篇 |
2007年 | 6497篇 |
2006年 | 7125篇 |
2005年 | 6294篇 |
2004年 | 6193篇 |
2003年 | 5939篇 |
2002年 | 5370篇 |
2001年 | 5623篇 |
2000年 | 5328篇 |
1999年 | 5116篇 |
1998年 | 4117篇 |
1997年 | 4190篇 |
1996年 | 3875篇 |
1995年 | 4465篇 |
1994年 | 3838篇 |
1993年 | 3548篇 |
1992年 | 4110篇 |
1991年 | 4304篇 |
1990年 | 4089篇 |
1989年 | 4065篇 |
1988年 | 3637篇 |
1987年 | 3673篇 |
1986年 | 3545篇 |
1985年 | 3885篇 |
1984年 | 3613篇 |
1983年 | 3455篇 |
1982年 | 2864篇 |
1981年 | 2767篇 |
1980年 | 2742篇 |
1979年 | 3222篇 |
1978年 | 2858篇 |
1977年 | 2679篇 |
1976年 | 2492篇 |
1974年 | 2657篇 |
1973年 | 2639篇 |
1972年 | 2425篇 |
1971年 | 2384篇 |
排序方式: 共有10000条查询结果,搜索用时 539 毫秒
911.
M. Bhalov 《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
912.
913.
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
914.
915.
916.
917.
Field experiments were conducted to characterize the demography of Abutilon theophrasti and Setaria faberi in a conventionally managed 2‐year (maize/soya bean) rotation, and in 3‐year (maize/soya bean/triticale + red clover) and 4‐year (maize/soya bean/triticale + lucerne/lucerne) rotations managed with 72% and 79% lower herbicide inputs respectively. Rates of weed seedling recruitment, seedling survival and adult plant fecundity were determined for populations in each phase of each rotation and used to calculate annual rates of weed population change, Δ. In both years of the study, Δ for A. theophrasti populations declined or remained stable in all three rotation systems. Despite greater rates of seedling survival and fecundity in maize and soya bean in the 3‐ and 4‐year rotations, increases in Δ for A. theophrasti populations were prevented in these systems because of low fecundity in triticale and low seedling survival and fecundity in lucerne. For Setaria faberi populations, Δ remained stable in the 2‐year rotation, increased in the 3‐year rotation in both years, and increased in the 4‐year rotation in 1 year. The results of this study indicate that when herbicide use is reduced, rotations that include triticale and lucerne can facilitate the suppression of A. theophrasti. Rotations that include lucerne can contribute to restraining S. faberi population growth, given adequate levels of seedling mortality in this crop. 相似文献
918.
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
919.
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
920.