全文获取类型
收费全文 | 28279篇 |
免费 | 1834篇 |
国内免费 | 3142篇 |
专业分类
林业 | 2088篇 |
农学 | 1703篇 |
基础科学 | 4775篇 |
9295篇 | |
综合类 | 9125篇 |
农作物 | 777篇 |
水产渔业 | 1668篇 |
畜牧兽医 | 958篇 |
园艺 | 494篇 |
植物保护 | 2372篇 |
出版年
2024年 | 170篇 |
2023年 | 516篇 |
2022年 | 770篇 |
2021年 | 883篇 |
2020年 | 966篇 |
2019年 | 1136篇 |
2018年 | 871篇 |
2017年 | 1284篇 |
2016年 | 1581篇 |
2015年 | 1153篇 |
2014年 | 1394篇 |
2013年 | 1721篇 |
2012年 | 2301篇 |
2011年 | 2121篇 |
2010年 | 1726篇 |
2009年 | 1586篇 |
2008年 | 1569篇 |
2007年 | 1770篇 |
2006年 | 1489篇 |
2005年 | 1260篇 |
2004年 | 1063篇 |
2003年 | 884篇 |
2002年 | 739篇 |
2001年 | 696篇 |
2000年 | 573篇 |
1999年 | 457篇 |
1998年 | 397篇 |
1997年 | 351篇 |
1996年 | 326篇 |
1995年 | 289篇 |
1994年 | 308篇 |
1993年 | 203篇 |
1992年 | 170篇 |
1991年 | 163篇 |
1990年 | 106篇 |
1989年 | 84篇 |
1988年 | 56篇 |
1987年 | 57篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1963年 | 1篇 |
1962年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
提高小麦单产的田间排水暗管规格模拟 总被引:1,自引:1,他引:0
改进内蒙古河套灌区田间排水系统的规格对灌区提升作物产量和保障粮食生产有重要现实意义,因此,在河套灌区对所构建的分布式SWAP-WOFOST模型进行了参数率定和验证,然后,对2000—2010年灌区春小麦种植条件下适宜的田间排水暗管规格进行探讨,并模拟评价了该条件下作物产量和水分生产力(WP)的时空分布特征。结果表明,所构建的分布式模型在河套灌区具有较高的适应性。春小麦种植条件下,灌区大部分耕地面积推荐采用田间排水暗管的规格为间距100.0m或75.0m,埋深为2.5m。相比现有排水系统,采用推荐的排水暗管规格,春小麦多年平均作物产量提高了18.5%,多年平均WP提高5.2%。研究结果为进一步改进灌区田间排水系统的效果提供了一定的参考。 相似文献
142.
143.
144.
青土湖水面形成区土壤颗粒组成与化学特性变化 总被引:2,自引:1,他引:1
青土湖输水作为石羊河流域治理的一项关键措施,对保护湖区水资源和生态环境具有重要意义。在距青土湖水面边缘东南方向0-450 m的10个样点中分3层取0-60 cm土样,测定土壤粒径的质量百分比与全氮、全磷、全钾和电导率,分析青土湖水面形成后土壤颗粒组成与化学特性变化。结果表明,随着离水面边缘距离的增加,土壤颗粒与化学特性呈有规律的增减变化,土壤粘粉粒组成与其全磷、全钾之间存在正线性相关。青土湖水面形成加剧了距水面边缘0-150 m处的土壤理化性质变化;土壤细粒及养分出现富集,分别在距水面边缘100-150 m和300 m处达到最大值。因此,土壤养分与土壤细物质的良好相关性表明,土壤粘粉粒变化可作为反映该区域土壤性状变化和评价衡量水面形成后土壤恢复程度的定量指标之一。 相似文献
145.
在分析水源地生态环境综合治理重要性的基础上,从把握水源地现状,分析水源地环境问题,合理划分保护区,确定治理规划内容及规模等方面,提出了水源地生态环境综合治理的步骤,并建立了综合治理方案。 相似文献
146.
Effects of cover crop growth and decomposition on the distribution of aggregate size fractions and soil microbial carbon dynamics
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)
D. Linsler M. Kaiser R. Andruschkewitsch C. Piegholdt B. Ludwig 《Soil Use and Management》2016,32(2):192-199
Although the effects of cover crops (CC) on various soil parameters have been fully investigated, less is known about the impacts at different stages in CC cultivation. The objective of this study was to quantify the influence of CC cultivation stages and residue placement on aggregates and microbial carbon (Cmic). Additionally, the influence of residue location and crop species on CO2 emissions and leached mineralized nitrogen (Nmin) during the plant degradation period was also investigated. Within an incubation experiment, four CC species were sown in soil columns, with additional columns being kept plant‐free. After plant growth, the columns were frozen (as occurs in winter under field conditions) and then incubated with the plant material either incorporated or surface‐applied. With CC, concentrations of large and medium macroaggregates were twice that of the fallow, confirming positive effects of root growth. Freezing led to a decrease in these aggregate size classes. In the subsequent incubation, the large macroaggregates decreased far more in the samples with CC than in the fallow, leading to similar aggregate size distributions. No difference in Cmic concentration was found among the CC cultivation stages. CO2 emissions were roughly equivalent to the carbon amounts added as plant residues. Comparison of columns with incorporated or surface‐applied residues indicated no consistent pattern of aggregate distribution, CO2 emission or Cmic and Nmin concentrations. Our results suggest that positive effects of CC cultivation are only short term and that a large amount of organic material in the soil could have a greater influence than CC cultivation. 相似文献
147.
Effects of CO2 Enrichment and Drought on Photosynthesis,Growth and Yield of an Old and a Modern Barley Cultivar
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
I. Schmid J. Franzaring M. Müller N. Brohon O. C. Calvo P. Högy A. Fangmeier 《Journal of Agronomy and Crop Science》2016,202(2):81-95
Susceptibility of crops to drought may change under atmospheric CO2 enrichment. We tested the effects of CO2 enrichment and drought on the older malting barley cultivar Golden Promise (GP) and the recent variety Bambina (BA). Hypothesizing that CO2 enrichment mitigates the adverse effects of drought and that GP shows a stronger response to CO2 enrichment than BA, plants of both cultivars were grown in climate chambers. Optimal and reduced watering levels and two CO2 concentrations (380 and 550 ppm) were used to investigate photosynthetic parameters, growth and yield. In contrast to expectations, CO2 increased total plant biomass by 34 % in the modern cultivar while the growth stimulation was not significant in GP. As a reaction to drought, BA showed reduced biomass under elevated CO2, which was not seen in GP. Grain yield and harvest index (HI) were negatively influenced by drought and increased by CO2 enrichment. BA formed higher grain yield and had higher water‐use efficiency of grain yield and HI compared to GP. CO2 fertilization compensated for the negative effect of drought on grain yield and HI, especially in GP. Stomatal conductance proved to be the gas exchange parameter most sensitive to drought. Photosynthetic rate of BA showed more pronounced reaction to drought compared to GP. Overall, BA turned out to respond more intense to changes in water supply and CO2 enrichment than the older GP. 相似文献
148.
Foliage‐applied sodium nitroprusside and hydrogen peroxide improves resistance against terminal drought in bread wheat
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. Farooq A. Nawaz M. A. M. Chaudhary A. Rehman 《Journal of Agronomy and Crop Science》2017,203(6):473-482
Terminal drought is threatening the wheat productivity worldwide, which is consumed as a staple food by millions across the globe. This study was conducted to examine the influence of foliage‐applied stress signalling molecules hydrogen peroxide (H2O2; 50, 100, 150 μm ) and nitric oxide donor sodium nitroprusside (SNP; 50, 100, 150 μm ) on resistance against terminal drought in two bread wheat cultivars Mairaj‐2008 and BARS‐2009. These stress signalling molecules were applied at anthesis stage (BBCH 61); drought was then imposed by maintaining pots at 35% water holding capacity. Terminal drought caused significant reduction in grain yield of both tested bread wheat cultivars; however, foliage application of both stress signalling molecules at either concentration improved the performance of both bread wheat cultivars. Maximum improvement in 100‐grain weight (12.2%), grains per spike (19.7%), water‐use efficiency (WUE; 19.8%), chlorophyll content index (10.7%), total soluble phenolics (21.6%) and free leaf proline (34.3%), and highest reduction in leaf malondialdehyde contents (20.4%) was recorded when H2O2 was foliage‐applied at 100 μm . Foliage application of SNP enhanced the grains per spike, 100‐grain weight and grain yield by 14.9%, 11.3% and 20.1%, respectively, than control. The foliage‐applied stress signalling molecules improved the accumulation of soluble phenolics, proline and glycine betaine with simultaneous reduction in malondialdehyde contents, which enabled wheat plants to sustain the biological membranes under stress resulting in better stay green (high chlorophyll contents) under drought. This helped improving the grain number, grain weight, grain yield, WUE and transpiration efficiency. In crux, foliage‐applied H2O2 and SNP, at pre‐optimized rate, may be opted to lessen the drought‐induced yield losses in bread wheat in climate change conditions. 相似文献
149.
王彪东 《国际沙棘研究与开发》2016,(4)
葫芦岛市建昌县2014年国家农业综合开发大凌河流域生态综合治理项目分布在建昌县新开岭乡新开岭村、贺杖子乡碾房村、素珠营子乡梁杖子村.通过该项目治理后,生态环境得到明显改善,经济效益十分显著,社会效益巨大,促进了区域经济社会发展.同时工程建设也起到了科技示范作用,为推动生态环境建设奠定了坚实基础保障. 相似文献
150.
为促进设施农业的稳步发展,对设施农业水利配套现状与使用情况进行了调查,认真分析了“十一五”期间水利设施现状,水力工程实施及运行情况,人员情况,信息化建设和工程管理办法,并充分结合实际,提出了水利保障体系发展的目标和保障措施. 相似文献