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   30498篇
  免费   1938篇
  国内免费   3404篇
林业   2216篇
农学   1878篇
基础科学   4827篇
  9727篇
综合类   10204篇
农作物   977篇
水产渔业   1794篇
畜牧兽医   1235篇
园艺   548篇
植物保护   2434篇
  2024年   225篇
  2023年   571篇
  2022年   851篇
  2021年   972篇
  2020年   1071篇
  2019年   1196篇
  2018年   935篇
  2017年   1377篇
  2016年   1704篇
  2015年   1244篇
  2014年   1522篇
  2013年   1854篇
  2012年   2466篇
  2011年   2310篇
  2010年   1861篇
  2009年   1746篇
  2008年   1678篇
  2007年   1902篇
  2006年   1559篇
  2005年   1337篇
  2004年   1117篇
  2003年   931篇
  2002年   770篇
  2001年   738篇
  2000年   610篇
  1999年   484篇
  1998年   428篇
  1997年   373篇
  1996年   351篇
  1995年   307篇
  1994年   335篇
  1993年   225篇
  1992年   186篇
  1991年   182篇
  1990年   117篇
  1989年   97篇
  1988年   64篇
  1987年   66篇
  1986年   19篇
  1985年   13篇
  1984年   7篇
  1983年   8篇
  1982年   2篇
  1981年   5篇
  1980年   4篇
  1979年   5篇
  1978年   3篇
  1976年   2篇
  1963年   3篇
  1962年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
分析了当前绿色环保的循环冷却水的处理工艺、现状、机理和应用情况,指出了绿色环保型循环冷却水的重要性,以期引起业内的重视并提供参考。  相似文献   
122.
近年来我国的水环境持续恶化,尤其农村的饮用水安全问题令人堪忧。文章从我国农村饮用水安全的现状以及存在的主要问题出发,着重探析造成现阶段我国农村饮用水安全种种问题的根源,基于法律保障的视角,注重法律制度诸项功能在具体操作层面上的充分发挥,指出我国农村饮用水安全保护的重要意义,提出合理的建议,希望能够对进一步探索和研究有所启示。  相似文献   
123.
田丰 《湖南农机》2016,(7):173-174
随着国内城市化的推进,市政工程的给排水工程越发显得重要。传统的给排水施工技术已经无法满足城市发展要求,社会对给排水的施工质量提出了更高地要求。文章结合当前给排水施工管理现状,对给排水施工的施工管理各方面进行简要探析。  相似文献   
124.
为了筛选适宜曲周县后老营村农业生产的较优种植体系并设计更好的种植体系,采用随机抽样调查的方法,对该村主要作物的种植体系及其水肥资源利用状况和经济效益进行了详细调查。结果表明:棉花-西瓜套作体系的水肥资源利用率最高,小麦-西瓜-玉米间套作体系的经济效益最好,棉花-西瓜套作体系次之,二者差异不显著。未来可以基于这2种种植体系重新设计新的种植体系,从而在生态、经济、环境等方面取得较好的综合效益。  相似文献   
125.
本文在对白石水库水源富营养化进行评价的基础上,对水库供水可靠性进行了分析.从现状水质评价结果看,白石水库的水质满足《地表水环境质量标准》(GB 3838-2002)中的Ⅲ类用水水质要求,可以作为集中式生活饮用水水源地和工业用水水源地.经过水量调节计算,可知白石水库供水水质是可靠的.  相似文献   
126.
We previously reported an alfalfa half‐sib family, HS‐B, with improved salt tolerance, compared to parental plants, P‐B. In this study, we conducted additional experiments to address potential physiological mechanisms that may contribute to salt tolerance in HS‐B. Vegetatively propagated HS‐B and P‐B plants were treated with a nutrient solution (control) or a nutrient solution containing NaCl (EC = 12 dS/m). Shoots and roots were harvested at various time points after treatment for quantification of proline, soluble sugar, and H2O2 using spectrophotometers. Subcellular localization and quantification of Na in roots were conducted using a Na+‐specific dye under a confocal microscope. HS‐B produced 86 and 89% greater shoot and root dry biomass, respectively, compared to parental plants, P‐B, under salinity in the greenhouse. Under saline conditions the HS‐B shoots accumulated 115% and roots 55% more soluble sugars than P‐B counterparts. The non‐saline HS‐B shoots, however, showed 72% less soluble sugars than the non‐saline P‐B plants. Under saline conditions HS‐B accumulated 39% less proline in shoots, while roots accumulated 56% more proline, compared to their P‐B parents. HS‐B plants also showed a greater reduction of stomatal conductance under mild saline stress. HS‐B shoots and roots contained 3–4 times less reactive oxygen species (H2O2) after salt treatment compared to P‐B plants. Sodium localization and distribution analysis using Na+‐specific dye revealed HS‐B plants accumulated 88% and 48% less Na+ in stele and xylem vessels compared to P‐B. The study provides insights into the potential mechanisms that may contribute to salt tolerance in HS‐B: maintaining RWC by accumulating soluble sugars while reducing transpiration, maintaining healthy status by reducing oxidative stresses, and preventing salt toxicity by reducing accumulation of Na+ inside root cells and xylem.  相似文献   
127.
本试验旨在研究饲粮中添加银杏-杜仲叶发酵物(FGEL)对脂多糖(LPS)应激肉仔鸡的生长性能、肠道结构、消化吸收功能和免疫反应的影响,并与未发酵银杏-杜仲叶(GEL)进行比较。采用2×3双因子试验设计,即2种免疫应激处理(腹腔注射LPS或注射等量生理盐水)和3种饲粮处理(基础饲粮及在基础饲粮中添加0.40%GEL或0.40%FGEL的试验饲粮)。选取1日龄健康爱拔益加(AA)肉仔鸡360只,随机分为6个处理,每个处理均设6个重复,每个重复10只鸡。试验期为21 d。在试验第13、15、17、19和21天,3个应激处理的试鸡腹腔注射500μg/kg BW的LPS,其他3个处理注射等量的生理盐水。在试验第21天最后1次注射后2~4 h进行屠宰取样。结果表明:1)与对照饲粮相比,饲粮添加FGEL的肉仔鸡料重比(F/G)有显著改善(P=0.024),饲粮添加FGEL显著缓解了LPS应激肉仔鸡平均日增重(ADG)(P=0.023)和血清D-木糖的含量(P=0.011)的降低。2)与对照饲粮相比,饲粮添加FGEL显著缓解了LPS应激肉仔鸡十二指肠(P=0.011)和空肠(P=0.030)的相对重量...  相似文献   
128.
湛江市园林水景的水生植物配置现状及分析   总被引:1,自引:0,他引:1  
通过对湛江市几个滨水绿地的实地调查,详细研究了湛江市主要园林水景中水生植物的主要形态特性及其在园林中的应用,并讨论了其应用现状及存在的不足。  相似文献   
129.
Brassica rapa L. is a genetically diverse parent species of the allotetraploid species, oilseed rape (B. napus) and a potential source of drought tolerance for B. napus. We examined the effect of a 13‐day drought stress period during the early reproductive phase, relative to a well‐watered (WW) control, on subsequent growth and development in nine accessions of B. rapa and one accession of Brassica juncea selected for their wide morphological and genetic diversity. We measured leaf water potential, stomatal conductance, water use, and leaf and bud temperatures during the stress period and aboveground dry weight of total biomass at maturity. Dry weight of seeds and reproductive tissue were not useful measures of drought tolerance due to self‐incompatibility in B. rapa. The relative total biomass (used as the measure of drought tolerance in this study) of the 10 accessions exposed to drought stress ranged from 47 % to 117 % of the WW treatment and was negatively correlated with leaf‐to‐air and bud‐to‐air temperature difference when averaged across the 13‐day stress period. Two wild‐type (B. rapa ssp. sylvestris) accessions had higher relative total and non‐reproductive biomass at maturity and cooler leaves and buds than other types. We conclude that considerable genotypic variation for drought tolerance exists in B. rapa and cooler leaves and buds during a transient drought stress in the early reproductive phase may be a useful screening tool for drought tolerance.  相似文献   
130.
The physiological response of multiple rice cultivars, eighteen initially and eight cultivars later on, to suboptimal temperatures (ST) conditions was investigated in laboratory and outdoor experimental conditions. Treatment with ST decreased growth in different extents according to the cultivar and affected the PSII performance, determined by chlorophyll fluorescence fast‐transient test, and stomatal conductance, regardless the experimental condition. Two groups of cultivars could be distinguished on the base of their growth and physiological parameters. The group of cultivars presenting higher growths displayed optimal JIP values, and higher instantaneous water use efficiency (WUEi), due to a lower Gs under ST, unlike cultivars showing lower growth values, which presented worse JIP values and could not adjust their Gs and hence their WUEi. In this work, we detected at least two cultivars with superior tolerance to ST than the cold tolerant referent Koshihikari. These cultivars could be used as parents or tolerance donors in breeding for new crop varieties. On other hand, positive and significant correlations between data obtained from laboratory and outdoor experiments suggest that laboratory measurements of most of the above mentioned parameters would be useful to predict the response of rice cultivars to ST outdoor.  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