全文获取类型
收费全文 | 228941篇 |
免费 | 13126篇 |
国内免费 | 22895篇 |
专业分类
林业 | 19085篇 |
农学 | 20002篇 |
基础科学 | 14115篇 |
28379篇 | |
综合类 | 98534篇 |
农作物 | 14508篇 |
水产渔业 | 8419篇 |
畜牧兽医 | 34316篇 |
园艺 | 15046篇 |
植物保护 | 12558篇 |
出版年
2024年 | 1143篇 |
2023年 | 3876篇 |
2022年 | 9183篇 |
2021年 | 9970篇 |
2020年 | 8957篇 |
2019年 | 9056篇 |
2018年 | 6577篇 |
2017年 | 9915篇 |
2016年 | 7206篇 |
2015年 | 11027篇 |
2014年 | 11304篇 |
2013年 | 13408篇 |
2012年 | 17978篇 |
2011年 | 18751篇 |
2010年 | 18291篇 |
2009年 | 16400篇 |
2008年 | 15895篇 |
2007年 | 15094篇 |
2006年 | 12777篇 |
2005年 | 10419篇 |
2004年 | 6127篇 |
2003年 | 4439篇 |
2002年 | 4087篇 |
2001年 | 3999篇 |
2000年 | 3848篇 |
1999年 | 2694篇 |
1998年 | 1776篇 |
1997年 | 1592篇 |
1996年 | 1432篇 |
1995年 | 1307篇 |
1994年 | 1128篇 |
1993年 | 1149篇 |
1992年 | 922篇 |
1991年 | 771篇 |
1990年 | 645篇 |
1989年 | 512篇 |
1988年 | 390篇 |
1987年 | 257篇 |
1986年 | 151篇 |
1985年 | 67篇 |
1984年 | 45篇 |
1983年 | 40篇 |
1982年 | 48篇 |
1981年 | 68篇 |
1980年 | 32篇 |
1979年 | 14篇 |
1965年 | 18篇 |
1962年 | 36篇 |
1956年 | 47篇 |
1955年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
41.
42.
Paddy and Water Environment - Water adaptation strategies are necessary for decreasing climate change impacts on local societies. This study models a community water supply system as a distributed... 相似文献
43.
44.
我国社会救助体系不断完善的过程中涉及主体更多元、方式更多样。当前社会救助面临相关部门和组织多、信息复杂、经办分散、分类精准施救难度大等问题。基于我国社会救助模式的合理价值选择,提出管理服务体系建设的重要意义。进而分析社会救助在管理服务上面临的挑战和难题,从组织协调管理、信息网络系统、基层经办机构、社会参与机制四个方面提出构建多层次管理服务体系的思路。力求提高管理服务的效率和效能,促进互助共济社会救助共同体的形成,提升公众满意度,夯实我国民生保障基础。 相似文献
45.
46.
Impact of grassland contract policy on soil organic carbon losses from alpine grassland on the Qinghai–Tibetan Plateau
下载免费PDF全文
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J. Cao Y. Gong E. T. Yeh N. M. Holden J. F. Adamowski R. C. Deo M. Liu J. Zhou J. Zhang W. Zhang S. Zhang D. Sheng S. Yang X. Xu M. Li Q. Feng 《Soil Use and Management》2017,33(4):663-671
Carbon storage in the soils on the Qinghai–Tibetan Plateau plays a very important role in the global carbon budget. In the 1990s, a policy of contracting collective grasslands to smaller units was implemented, resulting in a change from the traditional collective grassland management to two new management patterns: a multi‐household management pattern (MMP: grassland shared by several households without enclosures) and a single‐household management pattern (SMP: grassland enclosed and used by only one household). In 2016, 50 MMP and 54 SMP winter pastures on the Qinghai–Tibetan Plateau were sampled to assess the differences in soil organic carbon (SOC) between the two management patterns. Results showed that average SOC was significantly greater under MMP than under SMP, with an estimated 0.41 Mg C/ha/yr lost due to SMP following the new grassland contract. Based on the government's grassland policy, four grassland utilization scenarios were developed for both summer and winter pastures. We found that if the grassland were managed under SMP, likely C losses ranged between 0.31 × 107 and 6.15 × 107 Mg C/yr across the Qinghai–Tibetan Plateau relative to MMP, which more closely resembles pre‐1990s grassland management. Previous estimates of C losses have only considered land use change (with cover change) and ignored the impacts driven by land management pattern changes (without cover change). The new data suggest that C losses from the Qinghai–Tibetan Plateau are greater than previously estimated, and therefore that the grassland contract policy should be reviewed and SMP households should be encouraged to reunite into the MMP. These findings have potential implications for land management strategies not only on the Qinghai–Tibetan Plateau but also other grazing regions globally where such practices may exist. 相似文献
47.
Sheng-cai QIANG Fu-cang ZHANG Miles Dyck Yan ZHANG You-zhen XIANG Jun-liang FAN 《农业科学学报》2019,18(10):2369-2380
Excessive use of nitrogen(N) fertilizers in agricultural systems increases the cost of production and risk of environmental pollution. Therefore, determination of optimum N requirements for plant growth is necessary. Previous studies mostly established critical N dilution curves based on aboveground dry matter(DM) or leaf dry matter(LDM) and stem dry matter(SDM), to diagnose the N nutrition status of the whole plant. As these methods are time consuming, we investigated the more rapidly determined leaf area index(LAI) method to establish the critical nitrogen(N_c) dilution curve, and the curve was used to diagnose plant N status for winter wheat in Guanzhong Plain in Northwest China. Field experiments were conducted using four N fertilization levels(0, 105, 210 and 315 kg ha-1) applied to six wheat cultivars in the 2013–2014 and 2014–2015 growing seasons. LAI, DM, plant N concentration(PNC) and grain yield were determined. Data points from four cultivars were used for establishing the N_c curve and data points from the remaining two cultivars were used for validating the curve. The N_c dilution curve was validated for N-limiting and non-N-limiting growth conditions and there was good agreement between estimated and observed values. The N nutrition index(NNI) ranged from 0.41 to 1.25 and the accumulated plant N deficit(N_(and)) ranged from 60.38 to –17.92 kg ha~(-1) during the growing season. The relative grain yield was significantly affected by NNI and was adequately described with a parabolic function. The N_c curve based on LAI can be adopted as an alternative and more rapid approach to diagnose plant N status to support N fertilization decisions during the vegetative growth of winter wheat in Guanzhong Plain in Northwest China. 相似文献
48.
以菠萝蜜种子淀粉为壁材,采用饱和水溶液法制备香草兰精油微胶囊,以包埋产率为指标,采用响应面分析法对微胶囊的包埋条件进行优化探讨。结果表明:5个单因素中,影响最显著的因素为壁芯材比例、包埋温度和包埋时间。响应面优化得到香草兰精油微胶囊的最佳工艺条件为壁芯材比例为7.5∶1;包埋时间72 min;包埋温度54℃,此条件下的包埋产率为(95.46±0.2)%,包埋率为(76.35±0.6)%,载油量为(27.73±0.3)%。试验证明,此条件结果与模型预测值相吻合,此工艺条件可为菠萝蜜种子淀粉包埋香草兰精油微胶囊工艺提供理论依据。 相似文献
49.
不同秧龄对沿江地区双季晚稻秧苗素质及产量的影响 总被引:1,自引:0,他引:1
以早熟高产品种上农粳2号和镇稻18为材料,采用常规毯苗机械栽插,分别设置20 d、24 d、28 d、32 d等4个秧龄处理,研究不同秧龄对沿江地区双季晚稻秧苗素质、生育进程、茎蘖动态及产量构成的影响。结果表明,随秧龄天数增加,参试品种的绿叶数、茎基宽和根系盘结力均逐渐升高;与20 d、24 d和28 d秧龄的处理相比,32 d秧龄处理的成熟期提前4~5 d,茎蘖高峰期提早15 d左右,结实率显著升高;与24 d秧龄处理相比,上农粳2号和镇稻18在32 d秧龄处理下的产量分别提高10.26%和20.82%。在秧苗强化化控和苗床管理的条件下,安徽沿江地区常规毯苗机插的栽插秧龄可延长至32 d。 相似文献
50.