全文获取类型
收费全文 | 3632篇 |
免费 | 209篇 |
国内免费 | 311篇 |
专业分类
林业 | 241篇 |
农学 | 238篇 |
基础科学 | 240篇 |
960篇 | |
综合类 | 1502篇 |
农作物 | 137篇 |
水产渔业 | 196篇 |
畜牧兽医 | 350篇 |
园艺 | 79篇 |
植物保护 | 209篇 |
出版年
2024年 | 44篇 |
2023年 | 130篇 |
2022年 | 136篇 |
2021年 | 189篇 |
2020年 | 185篇 |
2019年 | 162篇 |
2018年 | 129篇 |
2017年 | 171篇 |
2016年 | 218篇 |
2015年 | 171篇 |
2014年 | 213篇 |
2013年 | 304篇 |
2012年 | 331篇 |
2011年 | 249篇 |
2010年 | 212篇 |
2009年 | 185篇 |
2008年 | 152篇 |
2007年 | 190篇 |
2006年 | 159篇 |
2005年 | 117篇 |
2004年 | 104篇 |
2003年 | 53篇 |
2002年 | 45篇 |
2001年 | 52篇 |
2000年 | 30篇 |
1999年 | 45篇 |
1998年 | 22篇 |
1997年 | 13篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
排序方式: 共有4152条查询结果,搜索用时 15 毫秒
21.
Ethan T. Noel 《Human Dimensions of Wildlife》2017,22(4):347-361
Anthropogenic food conditioning of bears has resulted in recent increases in human–bear conflicts (HBCs) in Florida. Garbage is the leading cause of food conditioning of bears. Despite increased HBCs and related human safety concerns, municipal governments in Florida have generally not taken independent steps to prevent HBCs through altered garbage management. Rather, governments have relied on the Florida Fish and Wildlife Conservation Commission to manage garbage-related HBCs. We used semi-structured interviews to identify obstacles to securing garbage from bears at the municipal level. Respondents included local government administrations and waste service providers. Political and economic costs of implementing bear-resistant garbage management practices were the major obstacles to securing garbage. Respondents argued that households will not pay for, or support, the implementation of bear-resistant trash cans. Recent adoption by four counties of ordinances requiring residents to secure their garbage from bears suggests that objections to adopting bear-resistant garbage management were overstated. 相似文献
22.
Post-recovery wolf management remains controversial. In Michigan, dialogue centers on hunting wolves but controversy may be more nuanced than simple pro- or anti-hunting positions. Social identity may cause stakeholders to organize in groups and identity differences may be driving controversy. To explore stakeholder disagreement over wolf management, we conducted semi-structured key informant interviews (n = 21) about identity and stewardship in August–September 2012. Four overarching identity themes emerged regarding: (a) management objectives, (b) focal levels, (c) control methods, and (d) justifications for methods. Themes indicated two main researcher-defined identity groups. Interviewees from both groups identified six common stewardship themes: (a) bequest values, (b) ecosystem health, (c) education, (d) existence values, (e) pride in natural resources, and (f) sustainability. Findings suggest stakeholders may be conflicting over opposing identities vis-à-vis organization affiliation, which may be related to what management strategies individuals oppose. Establishing common stewardship objectives through established participation methods may help alleviate controversy. 相似文献
23.
24.
P. Colangeli S. Iannetti L. Ruocco L. Forlizzi D. Cioci P. Calistri 《Zoonoses and public health》2013,60(2):182-188
In the framework of the international obligations subscribed by the Italian government, the Italian Ministry of Health should provide the European Union (EU) (European Commission, European Food Safety Authority – EFSA) with a set of data and information related to the report and the spread of zoonoses and to the activities put in place for monitoring and control of zoonoses. In 2008, the Italian Ministry of Health commissioned the Istituto G. Caporale (ICT) to implement an information system able to provide information and data on the monitoring and control of zoonoses in the national territory, in accordance with the national and community legislation. The system is part of the e‐Government process that involves all public administrations of the EU and refers to the use of information and communication technologies for the digital processing of documents in order to obtain simplification and interoperability of administrative procedures through the Internet, as defined in the strategic lines published by the National Centre for Information Systems in Public Administration (DigitPA) in 2009–2011. 相似文献
25.
26.
P. Spolti R. M. Valdebenito‐Sanhueza F. F. Laranjeira E. M. Del Ponte 《Plant pathology》2012,61(2):271-280
The incidence of sooty blotch/flyspeck (SBFS) and bitter and bull’s eye rots were assessed in a Fuji apple orchard during two seasons. Using a regular sampling design, 252 trees were selected and 20 fruits per tree were sampled at harvest and scored for disease incidence. For bitter and bull’s eye rots, additional assessments were made on all symptomless fruit after a 30‐day period of storage. Randomness in the spatial pattern was assessed using beta‐binomial analysis of incidence data for three sampling scales (one, three or six adjacent trees as sampling units) and using Spatial Analysis by Distance Indices (sadie ) for disease counts for the 3‐tree sampling scale. sadie was also used for testing spatial associations between a pair of diseases, between years for the same disease or between rotted and latently infected fruit. Using a toroidal‐shifts procedure, 360 maps of disease counts were created based on the observed data, which were further analysed using sadie . Most datasets showed an aggregated spatial pattern, which was more consistent for the two fruit rots than SBFS, which showed distinct patterns depending on the year or method of analysis. The two fruit rots were spatially associated in most situations but SBFS and bull’s eye rot were dissociated in one season. Results from virtual orchards showed that the patterns observed in the original maps may accurately represent those in similar apple‐growing areas. Hypotheses regarding aspects of ecology and epidemiology of pathogens studied and potential efficacy of control measures in the region are discussed. 相似文献
27.
宁夏西海固地区农业生态环境面源污染调查研究 总被引:1,自引:0,他引:1
农业生态环境面源污染控制与保护已成为区域农业和社会协调发展的重大问题。通过调查分析,西海固地区的农业面源污染源主要有化肥、农药、地膜、土壤侵蚀、牲畜禽粪便污染、有污染的灌溉水源与农村生活污水和农村固体废弃物等,并对西海固地区农业面源污染现状及其成因进行了分析。基于农业生态环境面源污染具有污染发生的广泛性、复杂性和治理难度大等特点,提出了防治农业面源污染与保护农业生态环境的对策及建议。 相似文献
28.
以马铃薯早熟品种大西洋、中熟品种克新1号、晚熟品种青薯168脱毒基础苗为试验材料,研究品种、培养基质和接种量对马铃薯脱毒基础苗苗鲜重、根鲜重、苗干重、根干重、叶片数、株高、茎粗、根长和根条数等性状指标的影响,培养14 d时,测定各性状指标。结果表明:三个品种的主要农艺性状均在液体培养基上表现为最佳,其平均单株鲜重、干重、株高、茎粗、节长和根条数分别为:159.4 mg、9.1 mg、7.3 cm、1.16 mm、1.4 cm、5.6条。在液体培养基上,降低了马铃薯工厂化生产成本,同时还可缩短马铃薯脱毒基础苗培养时间7~9 d。接种量对马铃薯单株根鲜重、苗干重、叶片数、株高、茎粗、根长有显著性影响(P<0.05);不同成熟期品种苗鲜重、根鲜重、根干重、叶片数、株高、茎粗、根长和根条数受品种影响显著(P<0.05);不同成熟期品种、不同接种密度处理对马铃薯单株根鲜重、苗干重、根干重、叶片数、株高、茎粗、根长影响有显著性交互作用(P<0.05);早熟品种大西洋,接种密度为0.67株/cm2时,中熟品种克新1号和晚熟品种青薯168接种密度为0.80株/cm2时,综合农艺性状表现最好。 相似文献
29.
耕作方式及秸秆还田对土壤性质、微生物碳源代谢及小麦产量的影响 总被引:1,自引:0,他引:1
以小麦品种济麦22为试验材料,采用裂区试验设计,耕作方式为主区,分别设常规翻耕(C)、深松(S)、旋耕(R)处理,副区为秸秆还田量,分别设秸秆全还田(P)和秸秆不还田(A)处理,采用Biolog Eco技术测定土壤微生物碳源代谢功能,并分析土壤基本理化性质和作物产量。结果显示:深松与秸秆还田均有利于土壤含水量和有机碳含量的提高,0~15 cm土层分别提高了9.78%和24.00%,15~30 cm土层分别提高了7.08%和15.81%;深松提高了15~30 cm土层的pH值6.67%,秸秆还田提高了0~15 cm土层的pH值4.32%。深松和秸秆还田均有利于代谢多样性(丰富度指数、香浓多样性指数)、碳源代谢强度的提高,0~15 cm土层分别提高了26.84%、3.84%和38.02%,15~30 cm土层分别提高了11.87%、 3.63%和14.74%。主成分分析表明常规翻耕秸秆不还田和旋耕耕作秸秆不还田碳源代谢功能相近,15~30 cm层次内常规翻耕秸秆全还田碳源代谢功能和深松耕作秸秆全还田处理相近。深松和秸秆还田平均提高了小麦产量5.82%,微生物碳源代谢功能与小麦产量具有极显著的相关性。 相似文献
30.
和田河流域沙和基岩的角闪石成分及石英~(18)O值 总被引:1,自引:0,他引:1
本文运用电子探针和氧同位素测试等手段,分析了和田河流域沙物质及某些有关基岩所含角闪石的种类、普通角闪石的化学成分和石英的δ~(18)O值。沙物质和岩浆岩(钾长花岗岩)在所含角闪石种类以及普通角闪石化学成分上的差异性明显大于相似性,说明后者为前者提供的角闪石有限。另外,沙丘沙含有多种变质成因的角闪石。产生这种现象的合理解释是:变质岩风化产物是沙的重要物源。沙物质中石英δ~(18)O值介于变质石英氧同位素成分范围,并且粒度愈细的石英,δ~(18)O值愈高。根据基岩中云母片岩所含石英颗粒最细、δ~(18)O值最高的特点判断,细沙物质在风扬过程中混入了较多的高δ~(18)O值细粒变质石英。 相似文献