全文获取类型
收费全文 | 406篇 |
免费 | 28篇 |
国内免费 | 18篇 |
专业分类
林业 | 62篇 |
农学 | 31篇 |
基础科学 | 23篇 |
40篇 | |
综合类 | 177篇 |
农作物 | 27篇 |
水产渔业 | 19篇 |
畜牧兽医 | 17篇 |
园艺 | 9篇 |
植物保护 | 47篇 |
出版年
2024年 | 4篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 19篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 25篇 |
2011年 | 17篇 |
2010年 | 23篇 |
2009年 | 28篇 |
2008年 | 27篇 |
2007年 | 15篇 |
2006年 | 13篇 |
2005年 | 25篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 10篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有452条查询结果,搜索用时 812 毫秒
51.
M. Das P. H. Zaidi M. Pal & U. K. Sengupta 《Journal of Agronomy and Crop Science》2002,188(4):219-224
An experiment was undertaken using open‐top chambers to study the effect of CO2 enrichment on crop growth and to assess the variation related to the time of CO2 exposure. In general, enriched CO2 conditions (600 ± 50 p.p.m.) in the chamber positively affected the growth and development of mungbean (Vigna radiata), a short‐duration (60–65 days) summer pulse crop. However, there was significant variability in the effect of the crop stage/time of CO2 exposure. It was observed that high CO2 exposure at an early growth stage [0–20 days after germination (DAG)] had a larger effect than that at a later growth stage (21–40 DAG). The experiment also provided a means of assessing the short‐ and long‐term effects of elevated CO2 on the carbon exchange rate at both stages of exposure. The study revealed that the sensitivity of plants to high CO2 was more pronounced with respect to net photosynthetic rate. The overall photosynthetic activity gave greater growth and development of plants under high CO2. 相似文献
52.
不同激素配比对辣木组培苗生长的影响 总被引:2,自引:0,他引:2
以辣木嫩梢茎段为外植体,在25种不同激素配比的培养基上进行培养,探讨不同激素配比对辣木组培苗生长的影响,并在6种不同生根培养基上进行生根试验。研究结果表明:在MS+6-BA0.02~0.5mg.L-1+NAA0.02mg.L-1+蔗糖3%的培养基上辣木组培苗生长良好,增殖倍数达5.6~8.1。在1/2MS+NAA0.2mg.L-1+蔗糖2%的培养基上生根率最高达79%。用形态学上端朝上与朝下两种方式接种到生根培养基上均能在形态学下端生根。 相似文献
53.
氮肥处理对新稻18号水稻产量及叶片形态特征的影响 总被引:4,自引:0,他引:4
以新稻18号为试验材料,在大田条件下研究了0、232.5 kg/hm2、255.0 kg/hm2、277.5 kg/hm2、300.0kg/hm2、322.5 kg/hm2和345.0 kg/hm2纯氮水平下水稻产量、叶片形态特征的差异及其之间的关系。结果表明,随着施氮量的增加,水稻产量呈先增加后降低的趋势,至255 kg/hm2纯氮水平下水稻产量达最大,此氮肥水平下水稻上三叶的受光姿态较其他处理综合表现较好。从不同氮肥处理对水稻上三叶的形态特征影响来看,倒二叶长受氮肥影响较大,倒一叶长受氮肥影响较小;倒一叶叶宽受氮肥影响较大,倒三叶叶宽受氮肥影响较小,说明氮肥处理对水稻叶片的影响主要表现在倒二叶叶长和倒一叶叶宽两个特性上。以水稻产量为因变量,叶片各形态特征为自变量进行逐步回归分析表明,倒二叶叶长、倒一叶叶宽和叶面指数(LAI)与产量建立的逐步回归方程达到了极显著水平(r=0.996 2**),说明倒二叶叶长、倒一叶叶宽和叶面指数对产量的作用较大。 相似文献
54.
55.
园丰脐橙系湖南省园艺研究所1993年从资兴市坪石乡华盛顿脐橙园中选出的具有自主知识产权的优良变异株系,经过10多年的观察鉴定,其主要经济性状稳定。多点试验结果表明:该品种适应性强,树势生长强壮,树姿较开张,结果早,花量中等,自然坐果率高,以树冠内堂和下部结果为主,无明显大小年结果现象,丰产稳产;果实近圆形,平均单果重264 g,果型指数:1.03,果形较整齐,l2月上中旬成熟。果实含可溶性固形物12.1%,总糖9.87 g/100mL,总酸0.85 g/100mL,维生素C为59.74mg/100mL,固酸比14.24,可食率71.20%。果皮橙红或深橙红,果肉脆嫩化渣,酸甜可口,品质上乘。高接树1 a可恢复树冠,第2年开花结果,第3、4年平均产量可达25~30 kg/株。 相似文献
56.
《Scandinavian Journal of Forest Research》2012,27(1-4):270-274
Site index was calculated for 66 experimental plantations in western Canada and northern Sweden, containing a wide range of Pinus contorta provenances drawn from seed lots belonging to the IUFRO international provenance testing program. Growth data from recommended provenances were used to calculate the site index. Site index was defined as predicted average height of the 100 largest trees by diameter ha‐1 at age 50. Latitude and altitude explained 56% of site index variation by fitting the function: Site Index (m) = 99.8 ‐ 1.226 ? Latitude (°N) ‐ 0.01205 ? Altitude (m). The site index pattern indicated that forest productivity of the sites investigated decreased approximately by 0.8 m3 ha‐1 yr‐1 per one‐degree latitude northwards and per 100 m increase in altitude. 相似文献
57.
《Scandinavian Journal of Forest Research》2012,27(1-4):376-381
The role of the resin‐top disease caused by Peridermium pini in volume and value losses to Scots pine (Pinus sylvestris L.) was surveyed in two heavily infected stands in northern Finland. Of the Scots pines, 26% were infected by the disease. Peridermium pini caused 2% volume losses to saw timber trees and 3% volume losses to pulpwood trees in the stem‐lesion class and 10% and 14% in the dead‐top class, respectively. The disease caused saw timber volume losses to saw timber trees of 34% and 22% in the stem‐lesion and dead‐top class, respectively. However, saw timber volume losses increased the pulpwood volume in both disease classes. The disease reduced the marketing value of saw timber trees and pulpwood trees by 18% and 3% in the stem‐lesion class and by 15% and 14% in the dead‐top class. 相似文献
58.
59.
Bente Flatland Kathleen P. Freeman Linda M. Vap Kendal E. Harr 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2013,42(4):405-423
Point‐of‐care testing (POCT) refers to any laboratory testing performed outside the conventional reference laboratory and implies close proximity to patients. Instrumental POCT systems consist of small, handheld or benchtop analyzers. These have potential utility in many veterinary settings, including private clinics, academic veterinary medical centers, the community (eg, remote area veterinary medical teams), and for research applications in academia, government, and industry. Concern about the quality of veterinary in‐clinic testing has been expressed in published veterinary literature; however, little guidance focusing on POCT is available. Recognizing this void, the ASVCP formed a subcommittee in 2009 charged with developing quality assurance (QA) guidelines for veterinary POCT. Guidelines were developed through literature review and a consensus process. Major recommendations include (1) taking a formalized approach to POCT within the facility, (2) use of written policies, standard operating procedures, forms, and logs, (3) operator training, including periodic assessment of skills, (4) assessment of instrument analytical performance and use of both statistical quality control and external quality assessment programs, (5) use of properly established or validated reference intervals, (6) and ensuring accurate patient results reporting. Where possible, given instrument analytical performance, use of a validated 13s control rule for interpretation of control data is recommended. These guidelines are aimed at veterinarians and veterinary technicians seeking to improve management of POCT in their clinical or research setting, and address QA of small chemistry and hematology instruments. These guidelines are not intended to be all‐inclusive; rather, they provide a minimum standard for maintenance of POCT instruments in the veterinary setting. 相似文献
60.
刘晓敏 《北京农业职业学院学报》2019,33(4):91-95
高端贯通培养项目是北京市职业教育改革的一个重大项目。为了使项目有效实施和稳步推进,该项目结合不同的教学内容,从高端贯通培养项目学生的学习现状和教学问题出发,针对性提出了适应高端贯通项目学生基础文化课的三种理科教学模式:五环探索教学模式、师生双主体互动教学模式和学生为中心的分享学习教学模式,并详细阐述这三种教学模式的设计与实施方法,以期有效提高高端贯通培养项目的理科课堂教学效率,丰富和发展理科教学理论与实践。 相似文献