全文获取类型
收费全文 | 6188篇 |
免费 | 469篇 |
国内免费 | 501篇 |
专业分类
林业 | 1251篇 |
农学 | 1257篇 |
基础科学 | 187篇 |
335篇 | |
综合类 | 2239篇 |
农作物 | 528篇 |
水产渔业 | 294篇 |
畜牧兽医 | 619篇 |
园艺 | 202篇 |
植物保护 | 246篇 |
出版年
2024年 | 15篇 |
2023年 | 79篇 |
2022年 | 120篇 |
2021年 | 152篇 |
2020年 | 164篇 |
2019年 | 194篇 |
2018年 | 119篇 |
2017年 | 180篇 |
2016年 | 197篇 |
2015年 | 187篇 |
2014年 | 264篇 |
2013年 | 296篇 |
2012年 | 371篇 |
2011年 | 424篇 |
2010年 | 387篇 |
2009年 | 366篇 |
2008年 | 361篇 |
2007年 | 392篇 |
2006年 | 352篇 |
2005年 | 290篇 |
2004年 | 276篇 |
2003年 | 223篇 |
2002年 | 179篇 |
2001年 | 157篇 |
2000年 | 144篇 |
1999年 | 124篇 |
1998年 | 109篇 |
1997年 | 124篇 |
1996年 | 112篇 |
1995年 | 103篇 |
1994年 | 98篇 |
1993年 | 92篇 |
1992年 | 92篇 |
1991年 | 94篇 |
1990年 | 83篇 |
1989年 | 46篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1955年 | 2篇 |
排序方式: 共有7158条查询结果,搜索用时 125 毫秒
991.
探索家禽良种的社会经济的地位、属性、发展历史和现状。提出21世纪家禽育种、制种的发展方向和方法,建议采用生态优选育种方案与双选育种法及核心群选育法培养优质家禽良种,同时用生物技术进行辅助选择。用科学发展观构建我国家禽育种制种基地。 相似文献
992.
甘肃省农业发展的SWOT分析与战略选择 总被引:2,自引:1,他引:1
本文立足甘肃省实际,采用SWOT分析法,分析了甘肃省农业发展区位、特色农业产业、农业产业化、县域经济整体实力、高科技农业、示范区建设具有的优势;农民收入、劳动力资源、农业信息、农业市场化程度、农业资本盈利性低的劣势;政策、经济、社会文化、自然、交通环境方面的发展机遇;以及经济增长与政策性限制、总体规划、城市发展压力、市场经济发育、管理体制方面面临的困境.应用SWOT矩阵分析,提出甘肃省农业发展的战略选择.从政府领导、科学规划、技术创新、土地使用、运行机制、农产品营销、利益补偿提出了发展对策;提出了区域经济中心、经济转型、绿洲节水、农牧业特色、工农业崛起5种发展模式. 相似文献
993.
分子标记辅助选择下的玉米回交群体农艺性状分析 总被引:2,自引:0,他引:2
以综3为受体亲本、衡白522为供体亲本,通过3代回交,利用SSR标记对BC3F1群体背景进行检测,并进行群体植株重要农艺性状的分析。结果表明,群体背景回复率在94.40%以上,平均回复率为97.75%,最高回复率为100%,远远高于经典遗传学背景回复率。农艺性状分析结果显示,背景回复率并未达到分子标记结果。分子标记辅助选择是提高育种选择效果加速育种进程的有效途径之一,针对数量性状控制的农艺性状的选择还需要进一步研究。 相似文献
994.
新疆小麦黄色素含量基因等位变异的分子检测及其分布 总被引:1,自引:0,他引:1
为了明确新疆小麦材料Psy-A1和Psy-B1位点控制籽粒黄色素含量基因的组成和分布以及与黄色素含量的关系,利用7A和7B染色体上Psy-A1和Psy-B1基因的分子标记YP7A和YP7B,对326份新疆冬、春小麦材料中的等位变异进行检测。结果表明,在Psy-A1位点,含有等位基因Psy-A1a和Psy-A1b的品种(系)分别占83.74%和16.26%,两种基因型黄色素含量平均值的差异达到极显著水平(P<0.01);在Psy-B1位点,含有等位基因Psy-B1a和Psy-B1b的品种(系)分别占83.44%和16.56%,但两种基因型黄色素含量平均值的差异不显著(P>0.05)。不同变异组合类型的分布比例表现不同,Psy-A1a/Psy-B1a所占比例最高,为69.63%;其次是Psy-A1a/Psy-B1b组合类型,为14.11%;Psy-A1b/Psy-B1a组合类型为13.8%;Psy-A1b/Psy-B1b所占比例最低,为2.45%,没有扩增出Psy-B1c和Psy-B1d基因位点。总体来看,新疆小麦高黄色素含量的等位变异类型所占比例较高,冬、春小麦黄色素含量基因型存在一定差异;YP7A可以作为一个稳定、高效的功能标记用于分子标记辅助选择,而YP7B标记则不能独立作为黄色素含量辅助选择的实用性标记。 相似文献
995.
996.
ZHAN Xiao-deng ZHOU Hai-peng CHAI Rong-yao ZHUANG Jie-yun CHENG Shi-hua CAO Li-yong Chinese National Center for Rice Improvement State 《水稻科学》2012,19(1):29-35
Genetic improvement is one of the most effective strategies to prevent rice from blast and bacterial blight(BB) diseases,the two most prevalent diseases jeopardizing rice production.Rice hybrids with dural resistance to blast and BB are needed for sustainable production of food.An incomplete diallele design resulted in 25 crosses between five blast and five BB resistant germplasm accessions.Only one pair of parents,DH146 × TM487,showed polymorphism for all the markers to identify one blast resistance gene Pi25 and three BB resistance genes,Xa21,xa13 and xa5,thus it was used in the marker-assisted selection(MAS).F2 individuals of DH146 × TM487 were genotyped using flanking markers of RM3330 and sequence tagged site(STS) marker SA7 for Pi25.The resistant F2 plants with Pi25 were used for pyramiding BB resistance genes Xa21,xa13 and xa5 identified by the markers pTA248,RM264 and RM153,respectively in subsequent generations.Finally,after selection for agronomic traits and restoration ability among 12 pyramided lines,we acquired an elite restorer line,R8012 including all four target genes(Pi25+Xa21+xa13+xa5).Hybrid Zhong 9A/R8012 derived from the selected line showed stronger resistance to blast and BB,and higher grain yield than the commercial checks uniformally in experimental plots,2007 state-wide yield trial and 2008 nation-wide yield trial.This study provides a paradigmatic example to show that MAS is a practically feasible tool in effectively pyramiding multiple resistance genes.The resultant restoring line and its hybrid would play an important role in securing rice production in China. 相似文献
997.
998.
999.
Jonathan C. P. Reum Timothy E. Essington Correigh M. Greene Casimir A. Rice Patrick Polte Kurt L. Fresh 《Fisheries Oceanography》2013,22(4):324-336
Variation in growth and body size during critical life history stages can have important implications for life history schedules and survivorship. For Pacific herring (Clupea pallasii), there is still debate as to whether juvenile body size is governed by density‐dependent or ‐independent processes and few have evaluated whether the relative importance of either process shifts over the course of early ontogeny. We used a unique data set consisting of seasonal measurements of abundance, body size, and spatial distribution within a semi‐enclosed basin of Puget Sound (Washington State, U.S.A.) to measure the relative importance of temperature and cohort abundance on body size at distinct time periods, and evaluated whether density‐dependent habitat shifts might be responsible for density‐dependent growth. Over the 9 years of sampling (2001–2010) midsummer body size was positively related to temperatures experienced during the egg/yolk sac and larval stages and unrelated to cohort abundance. However, fall body size was negatively correlated with abundance and uncorrelated with both midsummer body size and temperature, indicating a shift from density‐independent to density‐dependent control over the course of the growing season. Thus, density‐dependent effects may supplant density‐independent effects exhibited early in herring life history. Our data on spatial distributions of herring and their zooplankton prey indicate that density‐dependent reductions in growth may be explained by density‐dependent habitat shifts that lead to reduce overlap of herring with zooplankton. Evidence of density‐dependent growth in marine fish populations is often attributed to exploitative competition, but our results suggest that these patterns may partly be mediated by density‐dependent distribution expansions in to prey‐poor habitat. 相似文献
1000.
The behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean was investigated using archival tag data for 28 fish [49–72 cm fork length (FL) at release, 3–503 days] released in Japanese waters around the Nansei Islands (24–29°N, 122–132°E) and east of central Honshu (Offshore central Honshu, 32–36°N, 142–148°E). Vertical behavior was classified into three types based on past studies: ‘characteristic’ (non‐associative), ‘associative’ (associated with floating objects) and ‘other’ (behavior not fitting into these two categories). The proportion of fish showing associative behavior decreased and that of characteristic behavior increased as fish grew, and this shift was pronounced at 60–70 cm FL. The fish usually stayed above the 20°C isotherm during the daytime and nighttime when showing associative behavior and below the 20°C isotherm during daytime for characteristic behavior. A higher proportion of characteristic behavior was seen between December and April around the Nansei Islands, and between September and December for offshore central Honshu. Seasonal changes in vertical position were also observed in conjunction with changes in water temperature. In this study, ‘other’ behavior was further classified into five types, of which ‘afternoon dive’ behavior, characterized by deep dives between around noon and evening, was the most frequent. The present study indicated that in the northwestern Pacific Ocean, the vertical behavior of bigeye tuna changes with size, as well as between seasons and regions. 相似文献