全文获取类型
| 收费全文 | 40149篇 |
| 免费 | 15451篇 |
| 国内免费 | 463篇 |
专业分类
| 林业 | 3286篇 |
| 农学 | 2379篇 |
| 基础科学 | 2620篇 |
| 24377篇 | |
| 综合类 | 16494篇 |
| 农作物 | 1138篇 |
| 水产渔业 | 59篇 |
| 畜牧兽医 | 1826篇 |
| 园艺 | 547篇 |
| 植物保护 | 3337篇 |
出版年
| 2025年 | 814篇 |
| 2024年 | 1808篇 |
| 2023年 | 2050篇 |
| 2022年 | 1899篇 |
| 2021年 | 1894篇 |
| 2020年 | 2009篇 |
| 2019年 | 2222篇 |
| 2018年 | 1824篇 |
| 2017年 | 2493篇 |
| 2016年 | 2881篇 |
| 2015年 | 1996篇 |
| 2014年 | 2262篇 |
| 2013年 | 3197篇 |
| 2012年 | 4010篇 |
| 2011年 | 2917篇 |
| 2010年 | 2297篇 |
| 2009年 | 2349篇 |
| 2008年 | 2116篇 |
| 2007年 | 2301篇 |
| 2006年 | 2000篇 |
| 2005年 | 1688篇 |
| 2004年 | 1295篇 |
| 2003年 | 1125篇 |
| 2002年 | 881篇 |
| 2001年 | 850篇 |
| 2000年 | 731篇 |
| 1999年 | 535篇 |
| 1998年 | 470篇 |
| 1997年 | 489篇 |
| 1996年 | 415篇 |
| 1995年 | 438篇 |
| 1994年 | 406篇 |
| 1993年 | 305篇 |
| 1992年 | 258篇 |
| 1991年 | 253篇 |
| 1990年 | 178篇 |
| 1989年 | 155篇 |
| 1988年 | 95篇 |
| 1987年 | 76篇 |
| 1986年 | 41篇 |
| 1985年 | 13篇 |
| 1984年 | 6篇 |
| 1983年 | 2篇 |
| 1982年 | 2篇 |
| 1981年 | 2篇 |
| 1980年 | 4篇 |
| 1976年 | 1篇 |
| 1963年 | 1篇 |
| 1962年 | 5篇 |
| 1955年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 20 毫秒
311.
Zhuoxiao Wang;Daming Yang;Xin Peng;Heng Chang;Wei Dai;Yi Zeng;Lingshan Ni;Lei Deng;Nufang Fang; 《Land Degradation u0026amp; Development》2024,35(9):3181-3190
The widespread adoption of large-scale machines has led to a significant shift in terrace construction methods, transitioning from manual labor to mechanical processes. Mechanical terracing, by deeply disturbing the surface and compaction of the soil, has resulted in significant variations in both the soil physicochemical properties (SPCs) and soil infiltration properties (SIPs). However, few studies have been carried out to investigate the impact mechanisms of mechanical terracing on soils. In this study, we conducted detailed field experiments to determine the effects of mechanical terracing on SPCs and SIPs. The results showed that mechanical terracing increased soil compaction and decreased soil porosity and organic matter compared to manual terracing. Moreover, mechanical terracing had lower initial and steady infiltration rates than manual terracing (decreasing by 2.60% and 18.59%, respectively). However, initial and steady infiltration rates significantly improved compared to sloped land, increasing by 20.82% and 54.68%, respectively. The partial least squares path model indicated that bulk weight, organic matter content, and soil texture were the dominant influencing factors of SIPs. The results underscore the critical need to incorporate distinctions between various terrace construction methods into hydrological models for more accurate predictions. 相似文献
312.
Boxiang Zhang;Yanfeng Jia;Haoming Fan;Chengjiu Guo;Juan Fu;Shuang Li;Mengyuan Li;Bo Liu;Renming Ma; 《Land Degradation u0026amp; Development》2024,35(10):3256-3273
Soil compaction is generally viewed as one of the most serious soil degradation problems and a determining factor in crop productivity worldwide. It is imperative to understand the processes involved in soil compaction to meet the future global challenges of food security. In this work, we used co-occurring keyword analysis to summarize 3491 papers on soil compaction over the past 40 years, elaborating on the main research focuses such as the causes, influencing factors, and effects of soil compaction on crops, and the mitigation and prevention of soil compaction. This review provides a comprehensive discussion of the effects of soil compaction, including altering soil structure, increasing bulk density (BD) and penetration resistance (PR), and reducing porosity and soil hydraulic properties. Notably, based on the 387 data points of 11 papers about BD, our results demonstrated soil compaction on average, increased BD by 7.6%, 6.9%, and 3.2% in the medium-, coarse-, and fine-textured soils, respectively. Based on the 264 data points of 18 papers, in the 0–30 cm soil layer, compaction increased penetration resistance (by 91% in the coarse-textured, 84.2% in the medium-textured, and 8.8% in the fine-textured soils). Compacted soil limits the access of crop roots to water and nutrients, leading to poor root development and reduced crop productivity. There was a difference in soil compaction sensitivity between the different crops, but crop growth and yield showed an overall worsening trend with increasing degrees of compaction. This review collected data points on 142 crop yields and found that wheat, barley, corn, and soybean yields decreased by an average of 4.1%, 15.1%, 37.7%, and 22.7%, respectively, in the BD range of 1.1–1.8 Mg/cm3 after compaction. Additionally, the effectiveness of different compaction mitigation measures, including natural, tillage, and biological, is systematically discussed. Compared with soil compaction mitigation measures, prevention should be the top priority although there is still a lack of practical prevention methods. Soil conditions and agricultural machinery type are the main factors affecting the risk of soil compaction in the process of soil compaction. Therefore, it is particularly important to optimize the soil working conditions in the field and the type of farm machinery used to reduce the risk of soil compaction. This initiative is pivotal for ensuring sustainable systems for food production and recovering crop productivity from compacted soil. 相似文献
313.
水土资源是农业可持续发展的核心,水资源的合理利用会影响到土地的利用方式。为了分析新疆农业水土资源匹配状况,本文采用农业水土资源匹配系数对2008-2017年新疆14个地、州、市的水土资源时空匹配程度进行研究。研究结果表明:从时间上看,2008年到2017年,新疆农业水土资源匹配系数呈现出增加的趋势。从空间分布上看,北疆地区的农业水土资源匹配系数整体较低,南疆地区的农业水土资源匹配系数较高。通过对2008年和2017年新疆农业水土资源匹配系数的差值对比发现,克孜勒苏柯尔克孜自治州、阿勒泰地区、伊犁哈萨克自治州(直属)、乌鲁木齐市和和田地区的农业水土资源匹配系数的变化较明显;博尔塔拉蒙古自治州和喀什地区农业水土资源匹配系数降低最明显。 相似文献
314.
315.
《Communications in Soil Science and Plant Analysis》2012,43(22):2741-2764
ABSTRACT The present study aimed to evaluate the effect of biochar derived from the distilled waste of Cymbopogon winterianus at two different pyrolysis temperatures (450°C and 850°C) on the chemical and biological properties of sandy loamy soil (SLS) and its subsequent impact on plant growth. Pot experiments utilizing Bacopa monnieri were performed in a greenhouse with four different application rates of biochar (2%, 4%, 6%, and 8% (w/w)) for 120 days. Biochar induced alterations in soil properties (nutrients, enzymes, and microbes) and plant responses (yield, biocide and antioxidant content) to biochar addition were measured. Biochar application, notably improved the soil carbon, cation exchange capacity, and the availability of NH4 + and phosphorus. Initially, biochar produced at the lower temperature had more effect on the available nitrogen, phosphorus, soil enzymatic properties, and plant biomass growth. After 120 days, the pyrolysis temperature had only a marginal influence on biochar-induced effects on soil pH, WHC, and soil enzymatic activities. Our results suggest that C. winterianus derived biochar amendment leads to an overall amelioration of soil fertility and plant growth improvement. In specific biochar produced at lower temperatures (450°C) was more effective for improvement of plant biomass and soil characteristics. 相似文献
316.
A. I. KR
PFL G. A. Cecchi N. M. Villasuso R. A. Distel 《Land Degradation u0026amp; Development》2013,24(4):393-399
Vegetation in many arid and semi‐arid shrublands frequently occurs in patches with high plant cover (shrub patches) interspersed in a low‐cover herbaceous matrix (inter‐shrub areas). We hypothesized that (a) livestock grazing is an important determinant of such spatial patterns of vegetation, and (b) redistribution of soil resources associated with shrub patches helps in the recovery of vegetation in inter‐shrub areas. To test these hypotheses, we (a) used line transects to compare spatial variations in vegetation, soil microtopography, and soil physicochemical properties in grazed areas and areas protected from grazing since 1970, (b) added sediment and seeds to inter‐shrub areas, and (c) measured resource redistribution after a wildfire. Results were consistent with the hypotheses. They indicated greater spatial heterogeneity in vegetation, soil microtopography and soil physicochemical properties in grazed areas than in protected areas, and that addition of sediment and seeds or redistribution of soil resources from shrub patches after a wildfire enhanced re‐establishment of vegetation in degraded inter‐shrub areas. As a synthesis, a conceptual model of degradation and recovery processes in semi‐arid shrublands of Northern Patagonia is presented. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
317.
Erosion and soil degradation are environmental impacts recognized worldwide. The degraded areas in the Guarapuava region are small (patchy). However, these areas are important sources of sediment that affects water quality in rural catchments and could threaten farm sustainability because farmers in this region generally have only a small area for cultivation. This paper presents a case study at a field scale that explores key questions concerning the evaluation of soil erosion, the appraisal of soil degradation and area recovery. This study was carried out over seven years (2002–2008). Several different measurement procedures were employed including assessment of soil loss, aggregation distribution, bulk density, total porosity, aggregate water retention and palisade efficiency. The degraded area displayed a very high soil loss (165.2–217.7 t ha−1 y−1). The palisades were efficient for sediment retention because they were able to trap 62–88 per cent of the total sediment that originated in the area during the first year when this management technique was applied. After their installation, the retained sediment was gradually enhanced with respect to its physical, chemical and biological characteristics. The palisades promoted efficient soil recuperation in spite of the degraded conditions of the degraded area (shallow rills and cohesive soil). The use of palisades together with enclosure of the area was the most efficient method for promoting soil recovery and plant succession. These techniques allowed transformation of the area from a loss system towards an accumulation system with respect to sediment, water, nutrients, organic matter and seeds. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
318.
V. Barbera I. Poma L. Gristina A. Novara M. Egli 《Land Degradation u0026amp; Development》2012,23(1):82-91
A calcareous and clayey xeric Chromic Haploxerept of a long‐term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual‐layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75‐times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. The differences in SOC concentrations between NT and CT were surprisingly small. Cumulative C input of all cropping and tillage systems and the annually sequestered SOC indicated that a steady state occurred at a sequestration rate of 7·4 Mg C ha−1 y−1. Independent of the CSs, most of the SOC was stored in the silt and clay fraction. This fraction had a high N content which is typical for organic matter interacting with minerals. Macroaggregates (>250 µm) and large microaggregates (75–250 µm) were influenced by the treatments whereas the finest fractions were not. DL reduced the SOC in macroaggregates while NT and CT gave rise to higher SOC contents. In Mediterranean areas with Vertisols, agricultural strategies aimed at increasing the SOC contents should probably consider enhancing the proportion of coarser soil fractions so that, in the short‐term, organic C can be accumulated. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
319.
D. Dimoyiannis 《Land Degradation u0026amp; Development》2012,23(5):450-455
Aggregate stability is a fundamental property influencing soil erodibility and hydraulic characteristics. Knowledge of soil components controlling aggregate stability is very important to soil structure conservation. The objective of this study, which was carried out in surface soils from central Greece, was to relate wet aggregate stability to selected soil properties, with emphasis on excessive free carbonate content. The wet‐sieving technique of air‐dried aggregates was used for structural stability evaluation, according to a test that calculates an instability index. The soils studied were developed on Tertiary marly parent material and ranged in calcium carbonate content from 5 to 641 g kg−1. From the texture analysis before and after removal of carbonates, it was concluded that carbonates mainly contributed to total silt and sand fractions, that is to the mechanical fractions which, as a rule, negatively affect aggregate stability. The results of the correlation analysis showed that aggregate stability was positively affected by aluminosilicate clay content, cation exchange capacity (CEC) and Al‐containing sesquioxides. Clay fraction from carbonates and total sand and silt negatively affected aggregate stability. CEC has been proved a very significant determinant of aggregate stability, which in a hyperbolic form relationship with instability index explained 78·9 per cent of aggregate stability variation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
320.
本文调查了蛋鸡养殖场粪便产生量及处理利用现状等基本资料,选点采集养殖场配套龙眼园的土壤样品,通过分析测定有机质、全氮、全磷、铜、锌等指标,探讨了施用蛋鸡粪对龙眼园土壤质量的影响,并对龙眼园土壤环境现状进行评价。结果表明,该养殖场龙眼园土壤粪便当量负荷为19.14t·hm-2,未超过以氮计的土壤粪便当量负荷警戒值。四个季节施用蛋鸡粪的龙眼园土壤中有机质、全氮、全磷、铜、锌等指标均高于未施用蛋鸡粪的橡胶园土壤,但无显著差异;施用过蛋鸡粪的龙眼园土壤有机质、全氮、全磷、铜、锌全年平均含量分别为18.71g·kg-1、0.97g·kg-1、0.79g·kg-1、19.65mg·kg-1和43.05mg·kg-1,均显著高于未施用过蛋鸡粪的橡胶园土壤。四个季节龙眼园土壤和橡胶园土壤铜、锌单项污染指数均小于1,属于安全级别。由于龙眼园施用的蛋鸡粪仅占养殖场蛋鸡粪产生总量的2%,而且采用直接施用鲜鸡粪的方式,因此仍存在环境污染的隐患。本文所得结果可为评估蛋鸡养殖场环境污染风险及与果园结合的蛋鸡养殖模式的合理性提供依据。 相似文献