全文获取类型
收费全文 | 11991篇 |
免费 | 811篇 |
国内免费 | 1045篇 |
专业分类
林业 | 1462篇 |
农学 | 1059篇 |
基础科学 | 777篇 |
1725篇 | |
综合类 | 5946篇 |
农作物 | 617篇 |
水产渔业 | 442篇 |
畜牧兽医 | 952篇 |
园艺 | 283篇 |
植物保护 | 584篇 |
出版年
2024年 | 74篇 |
2023年 | 242篇 |
2022年 | 475篇 |
2021年 | 515篇 |
2020年 | 438篇 |
2019年 | 533篇 |
2018年 | 308篇 |
2017年 | 545篇 |
2016年 | 663篇 |
2015年 | 616篇 |
2014年 | 771篇 |
2013年 | 804篇 |
2012年 | 1064篇 |
2011年 | 1028篇 |
2010年 | 823篇 |
2009年 | 755篇 |
2008年 | 627篇 |
2007年 | 748篇 |
2006年 | 537篇 |
2005年 | 429篇 |
2004年 | 321篇 |
2003年 | 256篇 |
2002年 | 186篇 |
2001年 | 185篇 |
2000年 | 108篇 |
1999年 | 141篇 |
1998年 | 104篇 |
1997年 | 92篇 |
1996年 | 81篇 |
1995年 | 72篇 |
1994年 | 63篇 |
1993年 | 55篇 |
1992年 | 45篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1962年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
992.
本文以不同水平人工草地绵羊放牧系统的监测分析资料为基础,针对原系统中存在的问题,提出了系统优化方案。 相似文献
993.
应用特尔菲法,从人工造林、更新的核查实绩和难易程度两方面建立起了人工造林、更新实绩综合评价指标体系,并通过建立评价模型,对人工造林,更新全过程全方位实行定量评价。经实践检验,评价模型应用效果良好,具有推广价值。 相似文献
994.
陈定福 《西南大学学报(自然科学版)》1988,(3)
长吻鮠(Leiocassis longirostris Giinther)、大鳍鳠(Hemiba-grus macropterus Bleeker)、南方大口鲶(Silurus soldatorvi meridionalisChen).鲶鱼(Silurus asotus Linnaeus)的血清蛋白,经盘状电泳分离,从负极到正极可分为脂蛋白、球蛋白、运铁蛋白、清蛋白和前清蛋白5个组分。电泳图谱具种间差异,亲缘关系越远差异越大。同种鱼雌、雄间的电泳图谱基本相似,但不完全相同,鲶鱼具有雌性特异蛋白。 相似文献
995.
996.
A.D.?IwaroEmail author J.-M.?Thévenin D.R.?Butler A.B.?Eskes 《European journal of plant pathology / European Foundation for Plant Pathology》2005,113(2):173-182
The detached pod test by spray method (DPT-SM) was developed to facilitate the screening of cacao genotypes for resistance
to Phytophthora pod rot (PPR) caused by Phytophthora palmivora. The test has been adopted in many cacao research institutes, and it is imperative that its validity be assessed. In this
study, 40 genotypes from various cacao groups were selected and screened for resistance to PPR by DPT-SM and field observations.
Significant variation was observed in the reactions of the selected accessions based on the disease rating scale for DPT-SM
and the percentage pod rot from field observations. A correlation coefficient of 0.68 (P<0.001) was observed between the results of year-1 and year-2 field observations. However, relatively lower correlation values
were obtained between year-3 and year-1 (r=0.32; P=0.041) and year-3 and year-2 (r=0.35; P=0.025) field observations. A higher level of susceptibility was observed in the third year of field observations (63%) than
in the first (15%) and second (25%) years. This suggests that the predisposing factors for PPR were unstable between the years
of field observations. Data obtained from the Trinidad and Tobago Meteorological Services showed that the rainfall in November
of the third year was higher than the amounts of rainfall in November of the first 2 years of field observations. This month
marks the beginning of the main pod harvest season (November–February) and the high rainfall in November of the third year,
and the presence of large number of mature pods may account in part for the increase in PPR in the third year of field observations
than in the first 2 years. This shows that absolute reliance could not be placed on a single year of field observations in
determining clonal resistance to PPR. A correlation coefficient of 0.59 (P<0.001) was obtained between the result of year-2 field observations and DPT-SM. Relatively lower correlation values were
observed between DPT-SM and year-1 (r=0.55; P<0.001) and year-3 (r=0.44; P=0.005) field observations. The result of DPT-SM, however, shows a higher correlation (r=0.66; P<0.001) with the average of years 1–3 field observations. This suggests that a stronger association may exist between the
result of DPT-SM and the cumulative data on field observations for a period longer than 3 years. The correlation (r=0.66; P<0.001) observed in this study confirms the usefulness of DPT-SM as an effective method of assessing clonal resistance to
PPR and predicting field reaction in the long term. Since field observations are labour intensive and expensive to conduct
on a yearly basis, the DPT-SM offers a cheaper and effective means of assessing clonal resistance to PPR. Being a non-destructive
inoculation method, the DPT-SM provides a suitable option for cacao collections in genebanks to be assessed. It is also a
cost-effective method for use in cacao breeding programmes. Based on its reliability, the DPT-SM has been adopted in the CFC/ICCO/IPGRI
cocoa project ‘Cocoa Germplasm Utilization and Conservation: A Global Approach’ for the assessment of cacao resistance to
PPR in several cocoa producing countries. 相似文献
997.
温度、光照和发芽床对假俭草种子萌发的影响 总被引:3,自引:0,他引:3
实验室内进行了假俭草种子净度检验样品最低限量和发芽检验方法的研究,探讨了光照(以黑暗为对照)、温度(分别包括20℃恒温,15/25℃、20/30℃、20/35℃和25/35℃变温)和发芽床(分设纸上TP和砂中S)等因素对种子发芽的影响。结果表明:假俭草种子净度检验样品最低限量是3g,送验样最低量以及计数其它植物种子检验样品最低量均为30g;最佳萌发条件为20/30℃或20/35℃变温(16小时低温,8小时高温),高温时段设光照,和纸上(TP)发芽;发芽的初次和未次计数时间分别以第10天和第21天为宜;种子的幼苗发育可划分为单子叶植物子叶留土类型。 相似文献
998.
本文描述了安远县林业土壤的分布规律及乌石嶂山的土壤类型和理化性质的垂直变化情况,重点分析了全县主要林业土壤类型的理化性状和林业生产情况,并对主要林业生产单位的土壤物理性质和肥力状况作了综合评价。 相似文献
999.
本文通过对18个杨树品种无性系在9个试验点的G×E互作分析,用8个参数评价生产力,遗传稳定性和生长适应性,并经综合评定,从村冠积比(材积/冠积)方面将18个品系划分为不同类型,为各试验区评选出了适合栽培的优良品系。 相似文献
1000.
本从我国住宅产业发展现状入手,针对我国住宅现代化生产相关问题进行分析和研究,提出住宅产业现代化是解决信房矛盾的前提,模数协调是住宅现代化生产的技术基础,认证制度是住宅现代化生产的有力保证,住宅性能评价体系是住宅现代化生产的重要内容,对当前形势下我国住宅产业的发展方向具有一定的指导意义。 相似文献