全文获取类型
收费全文 | 269254篇 |
免费 | 16039篇 |
国内免费 | 4848篇 |
专业分类
林业 | 27883篇 |
农学 | 19861篇 |
基础科学 | 6167篇 |
47511篇 | |
综合类 | 30550篇 |
农作物 | 19086篇 |
水产渔业 | 17586篇 |
畜牧兽医 | 88227篇 |
园艺 | 7489篇 |
植物保护 | 25781篇 |
出版年
2021年 | 3934篇 |
2020年 | 4158篇 |
2019年 | 4888篇 |
2018年 | 4697篇 |
2017年 | 5383篇 |
2016年 | 5790篇 |
2015年 | 5877篇 |
2014年 | 7083篇 |
2013年 | 18062篇 |
2012年 | 7841篇 |
2011年 | 9679篇 |
2010年 | 9300篇 |
2009年 | 9976篇 |
2008年 | 8849篇 |
2007年 | 7988篇 |
2006年 | 8510篇 |
2005年 | 7787篇 |
2004年 | 6506篇 |
2003年 | 6156篇 |
2002年 | 5402篇 |
2001年 | 5763篇 |
2000年 | 5543篇 |
1999年 | 5856篇 |
1998年 | 5061篇 |
1997年 | 4970篇 |
1996年 | 4692篇 |
1995年 | 5149篇 |
1994年 | 4451篇 |
1993年 | 4147篇 |
1992年 | 4207篇 |
1991年 | 4302篇 |
1990年 | 3901篇 |
1989年 | 3801篇 |
1988年 | 3339篇 |
1987年 | 3363篇 |
1986年 | 3187篇 |
1985年 | 3514篇 |
1984年 | 3354篇 |
1983年 | 3175篇 |
1982年 | 2725篇 |
1981年 | 2699篇 |
1980年 | 2629篇 |
1979年 | 2802篇 |
1978年 | 2620篇 |
1977年 | 2433篇 |
1976年 | 2292篇 |
1975年 | 2105篇 |
1974年 | 2262篇 |
1973年 | 2154篇 |
1971年 | 1962篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
91.
针对不同设备设计不同喷液量,飞行参数验证防治效果,从而验证无人机在稻田全程应用的可能性,旨在探索2种小型多旋翼植保无人机低空喷洒在整个水稻生长时期病虫草害防治过程中的防效。结果表明:当喷洒水田封闭式除草剂的喷洒量为10650、15000 mL/hm2,其对杂草的株防效与鲜重防效与人工电动喷雾相近。在病虫害的防治试验中,使用推荐用量且喷洒量为10650、15000 mL/hm2时,以及使用70%推荐用量(减量30%)且喷洒量为15000 mL/hm2时,防治效果均与人工电动喷雾器无显著差异。通过验证,选择合适的药剂,配合科学的喷洒参数,可在保证药效的前提下减少农药使用量。多旋翼植保无人机在水稻田有进行大面积全程飞防植保应用有广阔的前景。 相似文献
92.
93.
94.
95.
Alexander Jarryd Ehlers Smith David A. Ehlers Smith Yvette C. Downs Colleen T. 《Landscape Ecology》2019,34(3):537-549
Landscape Ecology - The effects of changing land use, and especially urbanisation, on species and functional diversity are of global concern. Eco-estates are a form of urban housing development... 相似文献
96.
Fang Chen Hao Zhang Na Zhao Xuehai Yang Encun Du Shaowen Huang Wanzheng Guo Wei Zhang Jintao Wei 《Animal Science Journal》2021,92(1):e13619
Heat stress in poultry is deleterious to productive performance. Chlorogenic acid (CGA) exerts antibacterial, anti-inflammatory, and antioxidant properties. This study was conducted to evaluate the effects of dietary supplemental CGA on the intestinal health and cecal microbiota composition of young hens challenged with acute heat stress. 100-day-old Hy-line brown pullets were randomly divided into four groups. The control group (C) and heat stress group (HS) received a basal diet. HS + CGA300 group and HS + CGA600 group received a basal diet supplemented with 300- and 600-mg/kg CGA, respectively, for 2 weeks before heat stress exposure. Pullets of HS, HS + CGA300, and HS + CGA600 group were exposed to 38°C for 4 h while the control group was maintained at 25°C. In this study, dietary CGA supplementation had effect on mitigate the decreased T-AOC and T-SOD activities and the increasing of IL-1β and TNFα induced by acute heat stress. Dietary supplementation with 600 mg/kg CGA had better effect on increasing the relative abundance of beneficial bacterial genera, such as Rikenellaceae RC9_gut_group, Ruminococcaceae UCG-005, and Christensenellaceae R-7_group, and deceasing bacteria genera involved in inflammation, such as Sutterella species. Therefore, CGA can ameliorate acute heat stress damage through suppressing inflammation and improved antioxidant capacity and cecal microbiota composition. 相似文献
97.
Vimal Nair Min Cheol Kim James A. Golen Arnold L. Rheingold Gabriel A. Castro Paul R. Jensen William Fenical 《Marine drugs》2020,18(11)
A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway. 相似文献
98.
Spyra Marcin Kleemann Janina Cetin Nuket Ipek Vázquez Navarrete Cesar Jesús Albert Christian Palacios-Agundez Igone Ametzaga-Arregi Ibone La Rosa Daniele Rozas-Vásquez Daniel Adem Esmail Blal Picchi Paolo Geneletti Davide König Hannes J. Koo HongMi Kopperoinen Leena Fürst Christine 《Landscape Ecology》2019,34(7):1715-1735
Landscape Ecology - Several case studies investigated the role of ecosystem services in participatory planning processes. However, no systematic study exists that cuts across a large number of... 相似文献
99.
100.