首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   10925篇
  免费   579篇
  国内免费   1414篇
林业   412篇
农学   1886篇
基础科学   530篇
  1809篇
综合类   4455篇
农作物   1279篇
水产渔业   390篇
畜牧兽医   1429篇
园艺   222篇
植物保护   506篇
  2024年   63篇
  2023年   204篇
  2022年   354篇
  2021年   416篇
  2020年   407篇
  2019年   422篇
  2018年   367篇
  2017年   501篇
  2016年   578篇
  2015年   478篇
  2014年   575篇
  2013年   762篇
  2012年   764篇
  2011年   753篇
  2010年   564篇
  2009年   559篇
  2008年   510篇
  2007年   593篇
  2006年   526篇
  2005年   451篇
  2004年   344篇
  2003年   305篇
  2002年   280篇
  2001年   268篇
  2000年   222篇
  1999年   219篇
  1998年   160篇
  1997年   156篇
  1996年   140篇
  1995年   129篇
  1994年   105篇
  1993年   129篇
  1992年   126篇
  1991年   107篇
  1990年   72篇
  1989年   92篇
  1988年   45篇
  1987年   53篇
  1986年   28篇
  1985年   18篇
  1984年   12篇
  1983年   7篇
  1982年   10篇
  1981年   7篇
  1980年   8篇
  1979年   6篇
  1977年   6篇
  1976年   5篇
  1962年   5篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
991.
Fertilization of grain legumes with zinc (Zn) can affect both marketable yield and Zn content of the grain, which is important in addressing human nutritional deficiencies in certain regions of the world. A pot experiment was conducted to determine the response of three different market classes of lentil to Zn fertilization using ten surface soils from Saskatchewan (Canada). The distribution of Zn among labile and stable fractions chemically separated from the soil was also determined in the ten prairie soils and related to the lentil responses observed. The three market classes of lentils (large and small green, small red) were grown without Zn (control), and with 2.5 and 5 kg Zn ha?1 added as zinc sulfate to each soil prior to planting. Zinc fertilizer application significantly influenced grain yield and was soil dependent. A significant increase in grain yield over the control was observed from application of Zn on some low organic matter, high pH Brown Chernozem soils whereas a decrease in grain yield over control was observed in other soils such as a Black Chernozem of high organic matter content and low (<7) pH. Lack of positive yield response to addition of Zn were related to measured high diethylene triamine pentaacetic acid (DTPA) extractable and plant root simulator (PRS) resin membrane probe Zn, and large amounts of native Zn in exchangeable and iron/manganese (Fe/Mn) oxide bound fractions. Application of Zn fertilizer generally increased the grain concentration of Zn. For example, an increase of ~20% in Zn concentration over control was observed when 5 kg Zn ha?1 was added to a loamy textured low organic matter Brown Chernozem soil. Overall, small green lentil was more consistent in producing a positive response to Zn fertilizer application on soils with low plant available Zn compared to large green lentil and small red lentil.  相似文献   
992.
In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L?1 and urea 0 and 2 g L?1 concentrations. Results indicated that nickel (Ni; 300 mg L?1) plus urea (2 g L?1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L?1and urea (2 g L?1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L?1 without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L?1 without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L?1 along with urea at 2 g L?1 were the best treatments.  相似文献   
993.
ABSTRACT

Field experiments were conducted for 2 years in sandy loam soil, to study the direct effect of organic manures i.e. sewage sludge (SS), vermicompost (VC) and sesbania (SB) and chemical fertilizers on rice (Oryza sativa) and their residual effect on wheat (Triticum aestivum) grown in sequence in winter (Rabi) and summer (Kharif) season during 2015–2016 to 2016–2017 at Varanasi, Uttar Pradesh. Residual effect of organic sources of nutrients as SS, VC and SB were monitored up to fourth crop (II wheat) in sequence applied in conjunction with 75% recommended dose of fertilize (RDF). Among the nutrient sources, the maximum grain yield in I rice (4.89 t ha?1), II rice (4.95 t ha?1), was recorded in treatment T3 (100% RDF with S, Zn, B) whereas in I wheat (4.68 t ha?1) and II wheat (4.59 t ha?1), it was recorded in T4 (customized fertilizer). The maximum straw yield during all four crops was recorded in T3 (100% RDF with S, Zn, B) in rice and T4 (customized fertilizer) in wheat crop, which showed 25, 32, 23 and 28% increase over 100% RDF (T2). Application of 100% RDF along with S, Zn, B and customized fertilizer increased the total uptake of N, P, K, S and B and also in net returns and B:C ratio followed by organic treatments.  相似文献   
994.
Abstract

Maize response to deficit water and nitrogen for assessing phenological development and yield was studied under semi-arid conditions. Experiment consisting three drip irrigation levels, replenish 60 (DI60), 80 (DI80) and 100 percent (DI100) of cumulative pan evaporation, and four nitrogen doses 50 (RN50), 75 (RN75), 100 (RN100) and 125 (RN125) per cent of recommended nitrogen. A Furrow irrigated treatment was kept as control/check. Significant earliness in visibility of collar of 8th leaf, tasseling, silking and significant delay in dough stage and physiological maturity was recorded under well water treatment DI100 as compared to DI60. Days to collar of 8th leaf, tasseling and silking had significant negative correlation, and duration of yield formation phase and days to physiological maturity had significant positive correlation with grain yield. Higher DM production, longer yield formation phase and late physiological maturity led to significantly higher grain yield under DI100. In case of nitrogen levels, phonological characteristics like collar of 8th leaf, tasseling and silking were significantly delayed, and dough stage and physiological maturity were advanced under nitrogen deficit treatment RN50 as compared to RN100 and RN125. Significantly higher dry matter production and longer yield formation phase observed led to significant higher SCY under RN100 and RN125 as compared to RN50. Yield formation phase was significantly longer under drip irrigated crop as compared to control during 2nd year of study. Crop phenological development significantly affected by drip irrigation regimes and nitrogen levels, and there was significant correlation between phenological stages development and grain yield.  相似文献   
995.
郑雪  姚顺波  鲁亚楠 《水土保持通报》2020,40(2):239-246,254
[目的]研究退耕还林工程对粮食生产的影响,为深入开展退耕还林工程提供科学依据。[方法]以山西省的117个县域为研究单位,基于1990,2000,2005,2010和2015年5期土地利用数据和社会经济统计数据,分析耕地和粮食生产时空变化,并通过建立生产函数分析退耕还林工程对粮食生产的影响。[结果]①山西省生态环境重点治理区域的退耕效果显著,黄土丘陵沟壑区耕地转林草地的类型尤为明显;②退耕15 a期间,山西省粮食总产量及粮食单位面积产量总体呈上升趋势,其中重点退耕县的粮食总产量与粮食单产水平都一定程度的提高,且粮食单产增幅高于全省平均水平;③退耕对粮食总产量及粮食单位面积产出均有显著的正向影响。[结论]在省级层面,退耕还林工程不会对粮食生产造成负面影响,反而通过促进农业集约化生产等方式,提高粮食单产水平,进而带动粮食产量的提高。  相似文献   
996.
采用针型电容传感器和测量电路,并采取减小介质损耗的有效措施,研制了测量谷物含水率的针型电容法。实验结果表明,在谷物含水率与输出电压间具有良好的线性关系。该方法具有较高灵敏度、稳定性和良好的动态特性,完全可以满足谷物含水率的测量要求,为谷物含水率的准确、快速和在线测量提供了一种有效的方法。  相似文献   
997.
山东省粮食作物的化肥施用状况分析   总被引:14,自引:0,他引:14  
在农户抽样调查数据的基础上,分析了山东省粮食作物上施用化肥的状况。通过对山东省不同地区2003年施肥状况调查并结合统计资料分析表明,粮食作物上施肥占化肥总投入的比例逐年在下降,但单位面积化肥投入量却稳步提高。在氮肥的品种构成中,低浓度的碳酸氢铵提供了46.8%的施氮量,仍占有重要地位。山东省粮食作物单位面积化肥平均用量为251.1kg/hm^2,其中小麦平均施肥量最高,达到277.6kg/hm^2;另外就施氮量来说,玉米施氮量最高,平均用量为175.2kg/hm^2;小麦施磷量最高,平均用量为97.6kg/hm^2;薯类施钾量最高,平均用量为55.7kg/hm^2。从施肥的氮磷比例来看,小麦上施用化肥的氮磷比例为1:0.7,高于推荐施肥比例,玉米上施用化肥的氮磷比例为1:0.25,低于推荐施肥比例。  相似文献   
998.
气候生态因子对冬小麦粒重影响规律的探讨   总被引:5,自引:0,他引:5  
运用统计学原理和分析计算方法,较系统地分析了西藏山南地区冬小麦主要发育阶段气象因子对小麦灌浆时间、灌浆速度、千粒重的影响规律,得出小麦开花—黄熟期平均气温低、降水总量为171.6mm左右,是延长灌浆时间的有利条件;平均气温低、气温日较差小,对提高小麦千粒重最为有利,其中气温日较差是主要因子。  相似文献   
999.
中国稻谷干燥现状和稻谷干燥设备的开发   总被引:9,自引:8,他引:9  
介绍了我国稻谷干燥技术和干燥设备的现状,重点探讨了稻谷干燥的特点,如低温、大风量和干燥后必须缓苏等。对稻谷干燥中的爆腰问题作了深入的分析,对影响稻谷品质的主要因素如干燥速率、缓苏时间和爆腰率的测定时间和方法进行了讨论。对进一步发展我国的稻谷干燥技术提出了建议。  相似文献   
1000.
基于灰色聚类法的乌鲁木齐市空气质量状况研究   总被引:1,自引:0,他引:1  
《水土保持研究》2007,14(6):137-139
采用灰色聚类分析方法,对乌市2000~2004年和2005年12个月的大气污染物进行多因子污染等级评价。结果表明2000年至2004年乌市大气质量状况变化总体较稳定并向清洁程度发展;2005年12个月的大气质量状况受到采暖期和非采暖期的影响较大。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号