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1.
为研究气固两相流中固体颗粒间碰撞对冲蚀的影响,提出一种利用直接模拟蒙特卡罗(Direct Simulation Monte Carlo,DSMC)方法和计算流体力学(CFD)计算颗粒间碰撞的冲蚀预测方法。使用Eulerian-Lagrangian方法,将气相作为连续相,通过Navier-Stokes方程求解,颗粒平移运动由离散相模型(DPM)求解。颗粒平移运动由Eulerian-Lagrangian框架下的DPM求解,计算颗粒间碰撞运动时采用DSMC方法以少量采样颗粒代替真实颗粒,碰撞的发生条件通过修正的Nanbu方法判定。分析气固两相流中颗粒间碰撞对弯管冲蚀速率和颗粒分布的影响,结果表明:使用DSMC方法计算颗粒间碰撞,Oka模型的平均百分误差从39.2%降低至27.4%;计算颗粒间碰撞时弯管内拱侧的无颗粒区变小,最大冲蚀位置沿外拱轴线后移5°,同时V形冲蚀痕迹的两翼向外侧扩大。使用DSMC方法计算颗粒间碰撞可以明显降低模型误差,考虑颗粒间碰撞的Oka模型与实验结果偏差最小,是冲蚀预测的最佳模型。  相似文献   
2.
稀土元素示踪法从上世纪90年代开始逐渐被相关学者重视,并在坡面土壤侵蚀的研究中得到越来越广泛的应用。笔者采用CiteSpace软件和文献计量学方法,以Web of Science数据库核心合集和中国知网(CNKI)数据库核心期刊为数据源,分析了近30年国内外稀土元素示踪法在坡面侵蚀研究的发展历程。研究发现:①总体而言,国内稀土元素示踪法在坡面侵蚀中的应用在理论和实践层面已经从初步探索走向了成熟;②随着研究的深入,稀土元素示踪法的研究与相关学科交叉更加密切,并在微观探索和宏观调控方面取得一定进展;③未来发展趋势来看,宏观方面趋向和生态系统、气候变化等互相作用机理的研究,微观方向趋向对团聚体等微观颗粒的迁移研究;④在国际相关研究方面,对于稀土元素示踪法在坡面侵蚀的应用从多个方面和角度做了大量的研究,我国的相关研究相较于国外顶尖水平的研究仍存在一定差距。  相似文献   
3.
This research aims to improve erosion control practice in the Loess Plateau, by studying the surface erosion processes, including splash, sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity (120 mm h−1) with three-scale indoor artificial experiments. Four contrasting soils as sandy loam, sandy clay loam, clay loam and loamy clay were collected from different parts of the Loess Plateau. The results showed that sediment load was significantly impacted by soil properties in all three sub-processes. Splash rate (4.0–21.6 g m−2∙min−1) was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration. The average sediment load by sheet/interrill erosion (6.94–42.86 g m−2∙min−1) was highest in clay loam from middle part of the Loess Plateau, and the stable sediment load after 20 min showed a positive power relation with the silt content in soil. The average sediment load increased dramatically by rill and interrill erosion (21.03–432.16 g m−2∙min−1), which was highest in loamy clay from south part of the Loess Plateau. The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content. The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties. The critical factors varied for different processes, which were the aggregate size for splash erosion, the content of silt particles and slope gradient for sheet/interrill erosion, and the content of clay particles, soil organic matter and slope gradient for rill erosion. Based on the results of the experiments, specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient. The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.  相似文献   
4.
张菲  管曦  朱荣军 《茶叶科学》2021,41(3):430-438
基于时变随机前沿引力模型和贸易非效率模型,运用37个代表性国家和地区2001—2017年面板数据,实证分析了中国茶叶出口的影响因素与贸易效率。结果显示,我国茶叶出口贸易效率呈现随时间递增的趋势,但是总体上我国茶叶出口效率处于较低水平,且呈现区域不平衡,对发达经济体的出口贸易效率相对较高,与“一带一路”沿线国家的茶叶贸易效率比较低;我国茶叶出口效率无法完全实现主要是由于技术效率损失;国内供给增加、进口市场容量扩大以及贸易成本降低均对茶叶贸易效率有促进作用;进口市场营商环境改善一定程度上能够抵消贸易非效率的影响,提升我国茶叶出口效率;自由贸易协定对于我国茶叶出口尚未发挥作用。  相似文献   
5.
Identifying land management practices (LMPs) that enhance on-site sediment management and crop productivity is crucial for the prevention, reduction, and restoration of land degradation and contributing to achieving land degradation neutrality (LDN). We reviewed studies in Ethiopia to assess the effects of LMPs on soil loss (84 studies) and crop productivity (34 studies) relative to control practice. Yield variability on conserved lands was assessed using 12,796 fixed plot data. Effects of LMP on soil loss were 0.5–55 t ha−1y−1 compared to control practices yielding 50 to 140 t ha−1y−1. More than 55% of soil loss records revealed soil loss less than the tolerable rate (10 t ha−1). Area closure, perennial vegetation cover, agronomic practices, mechanical erosion control practices, annual cropland cover, and drainage groups of practices led to 74.0 ± 18.3%, 69.0 ± 24.6%, 66.2 ± 30.5%, 66.1 ± 18.0%, 63.5 ± 20.0%, and 40 ± 11,1% soil loss reduction, respectively. A yield increase of 25.2 ± 15.0%, 37.5 ± 28.0%, and 75.4 ± 85.0% was found from drainage, agronomy, and mechanical erosion control practices, respectively. The average yield loss by erosion on fields without appropriate land management practice and on conserved fields was 26.5 ± 26.0% and 25 ± 3.7%, respectively. The findings suggest that practices that entail a continuous presence of soil cover during the rainy season, perennial vegetation, retention of moisture, and barriers for sediment transport were most effective at decreasing soil loss and increasing productivity. This review provides evidence to identify the best LMP practices for wider adoption and inform decision-making on LMP investments towards achieving sustainable solutions to reverse land degradation.  相似文献   
6.
7.
采用黄河流域(片)国家级防治区中部分县级行政区2020年度水土流失动态监测成果及对应的平均土壤侵蚀模数,建立了不同县级行政区县域面积、各侵蚀强度等级面积与其平均土壤侵蚀模数之间的关系,进而推算不同区域的土壤流失量。结果表明,临界土壤侵蚀模数与平均土壤侵蚀模数之间存在较好的线性关系。根据建立的拟合关系,推算出不同时期黄土高原多沙区土壤流失量,1990—2019年黄土高原多沙区累积保土量为213.44亿t。  相似文献   
8.
[目的] 精确评估皖南山区土壤侵蚀量并分析其时空变化特征,为区域水土流失综合治理提供科学依据。[方法] 在GIS技术的支持下,利用研究区日降雨数据,30 m分辨率DEM,土壤数据和土地利用等数据,采用中国土壤流失方程(CSLE)估算皖南山区土壤侵蚀模数,并分析2000,2010和2018年近20 a研究区土壤侵蚀时空变化特征。[结果] 2000—2010年土壤侵蚀模数增加了963.96 t/(km2·a),土壤侵蚀强度面积向高强度等级转移;2010—2018年土壤侵蚀模数减少了781.22 t/(km2·a),土壤侵蚀强度面积由高向低转移,总体上土壤侵蚀变化呈先增后减的趋势。皖南山区3期土壤侵蚀空间分布格局基本一致,池州市和铜陵市东南侧以及黄山市周边区域是水土流失重点防治区域。研究区内耕地以微度和轻度侵蚀为主,林地以中度及以下侵蚀为主,2010—2018年耕地和林地中度及以上侵蚀面积减小,水土保持措施成效显著。[结论] 近年来皖南山区土壤侵蚀强度呈先增加后减少的趋势,总体上以轻度侵蚀为主,后续的水土流失治理仍需要加强。  相似文献   
9.
土壤有机碳(SOC)作为陆地碳库的重要组成部分,不仅对土壤肥力产生重要影响,而且在一定程度上影响着全球变暖趋势,为了深入探究土壤侵蚀与有机碳的关系,利用137 Cs核示踪法,以黄土丘陵沟壑区典型流域王茂沟坡耕地、林地、草地和梯田四种土地利用为研究对象,分析了不同坡面下土壤侵蚀对SOC迁移和沉积的影响规律。结果表明:与该流域137 Cs面积浓度背景值相比(1237 Bq/m2),坡耕地平均137 Cs面积浓度最小,平均137 Cs流失率最大,达到95.86%。根据侵蚀速率,四种坡面景观侵蚀速率大小依次为:坡耕地>草地>林地>梯田。根据土壤有机碳空间分布特征发现,除坡耕地外,林地、草地和梯田土壤沉积与土壤侵蚀同时发生,并且土壤137 Cs面积浓度与有机碳面积浓度呈现显著相关关系(p<0.05)。研究结果表明采用137 Cs核示踪法可以较为科学的解释该区域土壤侵蚀作用对坡面有机碳迁移-沉积的影响规律。  相似文献   
10.
Barchan dunes are among the most common accumulative phenomena made by wind erosion, which are usually formed in regions where the prevailing wind direction is almost constant throughout the year and there is not enough sand to completely cover the land surface. Barchans are among the most common windy landscapes in Pashoueyeh Erg in the west of Lut Desert, Iran. This study aims to elaborate on morphological properties of barchans in this region using mathematical and statistical models. The results of these methods are very important in investigating barchan shapes and identifying their behavior. Barchan shapes were mathematically modeled by simulating them in the coordinate system through nonlinear parabolic equations, so that two separate equations were calculated for barchan windward and slip-face parabolas. The type and intensity of relationships between barchan morphology and mathematical parameters were determined by the statistical modeling. The results indicated that the existing relationships followed the power correlation with the maximum coefficient of determination and minimum error of estimate. Combining the above two methods is a powerful basis for stimulating barchans in virtual and laboratory environments. The most important result of this study is to convert the mathematical and statistical models of barchan morphology to each other. Focal length is one of the most important parameters of barchan parabolas, suggesting different states of barchans in comparison with each other. As the barchan's focal length decreases, its opening becomes narrower, and the divergence of the barchan's horns reduces. Barchans with longer focal length have greater width, dimensions, and volume. In general, identifying and estimating the morphometric and planar parameters of barchans is effective in how they move, how much they move, and how they behave in the environment. These cases play an important role in the management of desert areas.  相似文献   
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