全文获取类型
收费全文 | 16124篇 |
免费 | 909篇 |
国内免费 | 1280篇 |
专业分类
林业 | 2385篇 |
农学 | 867篇 |
基础科学 | 947篇 |
3470篇 | |
综合类 | 6917篇 |
农作物 | 616篇 |
水产渔业 | 568篇 |
畜牧兽医 | 1171篇 |
园艺 | 384篇 |
植物保护 | 988篇 |
出版年
2024年 | 112篇 |
2023年 | 318篇 |
2022年 | 476篇 |
2021年 | 528篇 |
2020年 | 506篇 |
2019年 | 660篇 |
2018年 | 358篇 |
2017年 | 662篇 |
2016年 | 801篇 |
2015年 | 673篇 |
2014年 | 918篇 |
2013年 | 1051篇 |
2012年 | 1380篇 |
2011年 | 1374篇 |
2010年 | 1122篇 |
2009年 | 1089篇 |
2008年 | 924篇 |
2007年 | 1017篇 |
2006年 | 832篇 |
2005年 | 642篇 |
2004年 | 495篇 |
2003年 | 373篇 |
2002年 | 299篇 |
2001年 | 289篇 |
2000年 | 237篇 |
1999年 | 165篇 |
1998年 | 130篇 |
1997年 | 132篇 |
1996年 | 120篇 |
1995年 | 130篇 |
1994年 | 122篇 |
1993年 | 97篇 |
1992年 | 60篇 |
1991年 | 59篇 |
1990年 | 43篇 |
1989年 | 52篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 1篇 |
1984年 | 8篇 |
1977年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
基于室内土工试验和现场试验成果,对武汉市青山地区的老粘土地基的变形参数进行研究;利用ANSYS有限元软件对老粘土地基进行数值模拟,并与构筑物地基沉降实测值对比,对地基承载性能进行研究。在小于600kPa荷载的作用下,可用Ew作为沉降计算参数;老粘土具有较高的承载能力,由老粘土构成的地基,其承载能力可按《建筑地基基础设计规范》中推荐的公式计算。 相似文献
134.
旅游是伴随着体验经济的出现而不断发展变化的,旅游活动的本质在于追求一种天然的体验活动,旅游活动的内核就是为游客创造一次难忘的经历.而旅游体验与符号及景区开发之间又存在着千丝万缕的关系.为此,本文就旅游体验与符号及景区开发之间的关系进行探讨,通过旅游符号来创造出以旅游体验为导向的景区开发模式,来解决景区开发中所存在的困扰,有效地促进体验经济的发展. 相似文献
135.
旅游是伴随着体验经济的出现而不断发展变化的,旅游活动的本质在于追求一种天然的体验活动,旅游活动的内核就是为游客创造一次难忘的经历。而旅游体验与符号及景区开发之间又存在着千丝万缕的关系。为此,本文就旅游体验与符号及景区开发之间的关系进行探讨,通过旅游符号来创造出以旅游体验为导向的景区开发模式,来解决景区开发中所存在的困扰,有效地促进体验经济的发展。 相似文献
136.
Recent droughts in the humid southeastern United States have focused attention on the need for and use of supplemental irrigation. Total annual rainfall amounts are sufficient for most crops in the region. However, erratic distribution of rainfall and the low water-holding capacities of most soils in the region cause frequent drought stresses in many crops. An on-farm study was conducted in southeastern Alabama to evaluate the effects of farmers' irrigation scheduling decisions on soil moisture variations in peanut fields irrigated with center-pivot irrigation systems. The study showed that the way irrigation was practiced in this high rainfall area often caused soil moisture deficit (SMD) level higher than the desired SMD limit during over 20% of the 140-day growing season. This is partially due to farmers' tendency to delay irrigation in anticipation of rainfall which may or may not occur, as rainfall during the growing season is often erratic and local. In contrast SMD in non-irrigated fields was higher than the SMD limit for half of the growing season.Abbreviations SMD
soil moisture deficit
- ET
evapotranspiration
- Reff
effective rainfall
- WHC
water holding capacity 相似文献
137.
南方易渍农田水稻节水增产灌溉方式试验研究 总被引:1,自引:0,他引:1
吴福增 《中国农村水利水电》1995,(6)
针对我国南方易渍稻田土壤粘重、地下水位高、通透性差等特点,提出不同的灌水方法,并通过对大量的试验结果分析,得出了适宜的灌水方法及地下水埋深。 相似文献
138.
139.
Poor functioning of theirrigation system in Pakistan has been asource of concern for the last few decades,during which time it has been the subject ofconsiderable external assistance andinternal policy reforms. Consequently, thegovernment of Pakistan introducedinstitutional restructuring in irrigationand drainage subsectors to impartnecessary improvements. Under thesereforms, management at secondary canallevel has recently been handed over to theFarmers Organizations (FOs) of selecteddistributaries in pilot areas. This studywas designed to evaluate a farmer-manageddistributary in southern Punjab. Fieldmeasurements revealed that hydraulicaspects of the irrigation service deliveredby the FO management has been significantlyimproved and as a result highlyproportionate and equitable waterdistribution was observed, particularly atthe tail reaches of the distributary. Dueto effective FO management farmers'interventions to increase the outletdischarge by illegal means has been almosteradicated. As a result of theseimprovements imparted by the FO in systemmanagement, the extent of irrigated area hasincreased on average by 6 to 7%, evenunder severe drought-like conditionsprevailing in the country during recentyears. Further cost recoveries haveincreased by an amount of 14% for summerand 23% for winter growing seasons,respectively, from the irrigated area of thedistributary. Thus experience from Hakra4-R distributary has shown that even underundesirable natural circumstancesIrrigation Management Transfer (IMT) wasquite effective in achieving the keytargets of the institutional reformslaunched at pilot scale in the country. 相似文献
140.