全文获取类型
收费全文 | 578篇 |
免费 | 49篇 |
国内免费 | 49篇 |
专业分类
林业 | 78篇 |
农学 | 43篇 |
基础科学 | 17篇 |
131篇 | |
综合类 | 300篇 |
农作物 | 17篇 |
水产渔业 | 7篇 |
畜牧兽医 | 40篇 |
园艺 | 3篇 |
植物保护 | 40篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 30篇 |
2021年 | 45篇 |
2020年 | 33篇 |
2019年 | 30篇 |
2018年 | 31篇 |
2017年 | 43篇 |
2016年 | 48篇 |
2015年 | 39篇 |
2014年 | 54篇 |
2013年 | 53篇 |
2012年 | 37篇 |
2011年 | 37篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 16篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 13篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有676条查询结果,搜索用时 125 毫秒
1.
覆盖免耕在休闲期的节水和生育期的调温效应 总被引:10,自引:2,他引:8
对免耕覆盖、秸秆还田和常规耕作在休闲期的节水效果研究表明:在夏季休闲期,免耕覆盖比常规耕作多贮水30.62mm,比秸秆还田多23.91mm;在冬季储水灌溉期间,可将储水定额从2100m3/hm2减少到600和975m3/hm2。对春小麦生育期土壤表层,5、10、15、20和25cm处温度变化观测发现:免耕覆盖土壤温度在气温较低的8:00可以提高土壤表层温度,在气温较高的14:00可以减缓土壤温度的升高,而在19:00气温降低时可以减缓土壤温度的降低,使土壤温度一直保持在一个稳定的状态,这有利于调节农田小气候,创造作物良好的生长环境。 相似文献
2.
2011年10月-2014年10月连续3年在河北省任县安排了定位试验,通过饲用黑麦不同播期与棉花构建几种棉草复种茬口搭配方式,从产量、经济效益、水分利用效率和养分利用效率以及对土壤肥力影响等方面综合分析棉花饲用黑麦复种的可行性及复种方式。结果表明,棉花可与饲用黑麦复种,为降低饲用黑麦对棉花的影响,饲用黑麦可适当推迟到10月20日播种,次年4月底收获,效益可提高5470.1元·hm-2。棉花饲用黑麦复种与棉花单作相比,平均水分利用率提高16.49%;水分经济利用效率提高56.54%;并且土壤有机质平均增长幅度提高5.71%,土壤含盐量平均降低幅度达到23.72%,土壤改良效果明显;是适用于该区域的高效复种模式。 相似文献
3.
农民工返乡创业能够有效培育农村经济发展的内生力量,对促进乡村振兴战略具有重要现实意义。在当前信息时代背景下,社会资本因互联网的嵌入已分化为现实社会资本和虚拟社会资本,这对农民工返乡创业意愿的影响效应可能不同。基于互联网嵌入视角,利用西安市406个农民工的微观调查数据,运用结构方程模型,分析现实社会资本和虚拟社会资本对农民工返乡创业意愿的影响效应。结果表明,农民工返乡创业意愿较为强烈;现实社会资本对农民工返乡创业意愿具有直接正向影响;虚拟社会资本对农民工返乡创业意愿具有直接负向影响、间接正向影响;虚拟社会资本可以转化为现实社会资本;虚拟社会资本正在逐步取代部分现实社会资本成为提升农民工返乡创业意愿的重要推力;互联网嵌入对于现实社会资本具有直接负向影响,对虚拟社会资本具有直接正向影响,对农民工返乡创业意愿没有直接影响。据此,提出加快农村地区经济组织发展,增加现实社会资本的累积;建立并完善信息服务平台,加强互联网信息审核机制的政策建议。 相似文献
4.
通过对山东省潍坊市、安徽省安庆市的228户农户进行实地问卷调查,研究并分析了农户对农房抵押贷款的参与意愿及相关原因。研究结果表明:农户对于农房抵押贷款具有一定参与意愿,不同地区农户参与意愿有着较为明显的差异,被调查农户中潍坊市农户参与意愿高于安庆市农户;对农房生活保障功能的依赖是阻碍农户参与的主要原因;金融机构的正规性、自身的偿还能力以及政策细节与稳定性是农户在选择参与农房抵押贷款时所关注的主要方面;在政策期望方面,简化抵押贷款的手续步骤、加大政策宣传、降低贷款利息等得到较高关注。 相似文献
5.
6.
蔬菜种植农户对无公害农药的认知和购买意愿——基于河北省120家菜农的调查分析 总被引:1,自引:0,他引:1
为了考察我国农户对无公害农药的接受程度,从源头上保障农产品质量,笔者以河北省为例,通过问卷调查和访谈具体考察了蔬菜种植农户对无公害农药的认知程度和购买意愿.研究表明,户主年龄、文化程度、居住地到中心城市的距离是影响农户对无公害农药认知的重要因素;而无公害农药的价格、土地的获得成本、种植面积和市场检测机制直接决定着农户对无公害农药的购买意愿. 相似文献
7.
湖州市是一座江南古城,有着浓厚的文化底蕴.湖州太湖旅游度假区位于湖州市境内,其区域内河道网络纵横交错,产生了众多的桥梁和滨水地带.为进一步提升湖州滨湖度假区环境品质,增加度假休闲氛围,打造国内一流休闲旅游度假区,现对滨湖休闲景现带的景观设计理念进行研究探讨. 相似文献
8.
《Communications in Soil Science and Plant Analysis》2012,43(17):2109-2121
Organic inputs are believed to be able to increase soil phosphorus (P) availability. Natural fallow and pig slurry amendments are the two important organic inputs for agricultural soils. The purposes of the study are to investigate P accumulation and to compare the differences of P fractionation patterns as affected by natural fallow and pig slurry drip irrigation in a coastal saline soil. The study showed that P accumulation occurred mainly in upper soil profiles and that natural fallow or pig slurry drip irrigation alone would not significantly influence total P distribution in soil profiles. However, soil P fractionation demonstrated that, from bottom to top, bioavailable P content and percentage increased whereas residual P percentage declined. The percentage of extractable inorganic P was almost twice as much as that of extractable organic P. In comparison with natural fallow conditions, under pig slurry drip-irrigation conditions, the transformation efficiency of superphosphate fertilizer HCl Pi into residual P was lower whereas the transformation efficiency of superphosphate fertilizer HCl Pi into bioavailable P was higher. The higher bioavailable P percentage and lower average Corg/P ratio in a long-term pig slurry drip-irrigation plot than those in other plots indicated that long-term pig slurry drip-irrigation was more efficient in improving soil P availability than natural fallow and short-term pig slurry drip irrigation. 相似文献
9.
Increasing fiscal constraints on the government, a lackadaisical performance by public sector animal health and breeding services and pressure from donor partners have prompted the governments of various developing countries to rethink the role of the public sector in the provision of veterinary services. Various countries have started to implement, or have already implemented, privatization of some veterinary services. The results are mixed. It is established that private provision alone is not optimal, and a blend of private and public sector veterinary services is required to utilize the virtues of both.The privatization process has also begun in India. Certain state governments in India are pursuing a cost recovery approach and are encouraging private practitioners to cope with the financial constraints and to deliver broad and effective animal health and breeding services. This paper considers the global aspects of the privatization of veterinary services as well as the scenario in India, so as to gain an insight into the very complex and debatable issue of privatization of veterinary services. 相似文献
10.
《Scandinavian Journal of Forest Research》2012,27(1-4):266-280
The concepts of Multiple‐use forestry and preservation of “virgin”; coniferous forests are elements of an ongoing debate in Norway, regarding aesthetical and biological consequences of current forest management practices. A study, based on the Contingent Valuation Method (CVM), was performed during the fall of 1990. Data were collected through in‐person interviews of 1204 persons above 15 years of age. The main objectives of the study were to analyze: 1) Attitudes toward the present state of Norwegian forests, 2) Attitudes toward and maximum willingness to pay for changes in current forest management, 3) Preferences and maximum willingness to pay for preservation of “virgin”; coniferous forests, and 4) Attitudes toward society's right to impose restrictions on forest management on private forest land. Based on responses to statements related to the forest area people usually visit, the study showed a low degree of conflict regarding the present state of Norwegian forests. A ranking of possible results of two alternative forest management strategies, i.e. 1) a more cautious forest management or 2) preservation of “virgin”; coniferous forests, gave the highest average scores to “Preservation of endangered plants and animals”; and “Preservation of “virgin”; forests for our descendants”;, both related to the second management strategy. The maximum willingness to pay for a more cautious forest management was 277 Norwegian kroner (NOK) per household and year, with a median value of NOK 50. 47% of the sample preferred the preservation alternative A specified by the governmental committee, Barskogutvalget, while 18% preferred alternative B and 9% preferred alternative C, corresponding to the governmental decision. 15% preferred a 0‐alternative, i.e. no further preservation of “virgin”; coniferous forests. Two possible sources of bias, related to the CVM, were tested. 相似文献