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   3763篇
  免费   168篇
  国内免费   270篇
林业   317篇
农学   317篇
基础科学   157篇
  534篇
综合类   1888篇
农作物   243篇
水产渔业   165篇
畜牧兽医   331篇
园艺   169篇
植物保护   80篇
  2024年   8篇
  2023年   35篇
  2022年   56篇
  2021年   100篇
  2020年   89篇
  2019年   106篇
  2018年   52篇
  2017年   113篇
  2016年   159篇
  2015年   140篇
  2014年   220篇
  2013年   220篇
  2012年   331篇
  2011年   347篇
  2010年   258篇
  2009年   287篇
  2008年   252篇
  2007年   278篇
  2006年   238篇
  2005年   174篇
  2004年   135篇
  2003年   114篇
  2002年   65篇
  2001年   61篇
  2000年   45篇
  1999年   61篇
  1998年   45篇
  1997年   38篇
  1996年   27篇
  1995年   26篇
  1994年   21篇
  1993年   30篇
  1992年   13篇
  1991年   17篇
  1990年   9篇
  1989年   6篇
  1988年   6篇
  1987年   11篇
  1986年   4篇
  1985年   2篇
  1981年   1篇
  1978年   1篇
排序方式: 共有4201条查询结果,搜索用时 46 毫秒
991.
黎雪萍 《青海草业》2002,11(4):31-34
青海地处青藏高原生态脆弱区 ,青海经济发展必须以保护和治理环境为根本出发点。根据青海农牧业经济现状和社会经济发展的客观要求 ,必须依靠先进技术为根本手段 ,生态保护为基本目标 ,即走“生态—技术”农牧业发展道路。  相似文献   
992.
赤霉素和2,4—D对猴头菇的效应及其机制研究   总被引:4,自引:0,他引:4  
用赤霉素和2,4-D处理猴头菇,对改善猴头菇品质,提高其维生素及微量元素含量,增强猴头菇菌丝体酶活性,促进猴头菇子实层细胞分裂、伸长、分化均具有明显效应。  相似文献   
993.
用酶标抗体法检测蚕微粒子孢子   总被引:6,自引:0,他引:6  
用酶标抗体间接法和酶标抗体PAP法检测蚕微粒子孢子,二种方法检测结果一致,被检材料与阳性对照中的孢子被染成褐色,从而可以确定为蚕微粒子孢子。二种方法比较,间接法相对简单,PAP法敏感性更高,均为重要的蚕微粒子孢子的鉴别诊断方法。  相似文献   
994.
Influences of upland and riparian land use patterns on stream biotic integrity   总被引:11,自引:2,他引:11  
Snyder  C.D.  Young  J.A.  Villella  R.  Lemarié  D.P. 《Landscape Ecology》2003,18(7):647-664
We explored land use, fish assemblage structure, and stream habitat associations in 20 catchments in Opequon Creek watershed, West Virginia. The purpose was to determine the relative importance of urban and agriculture land use on stream biotic integrity, and to evaluate the spatial scale (i.e., whole-catchment vs riparian buffer) at which land use effects were most pronounced. We found that index of biological integrity (IBI) scores were strongly associated with extent of urban land use in individual catchments. Sites that received ratings of poor or very poor based on IBI scores had > 7% of urban land use in their respective catchments. Habitat correlations suggested that urban land use disrupted flow regime, reduced water quality, and altered stream channels. In contrast, we found no meaningful relationship between agricultural land use and IBI at either whole-catchment or riparian scales despite strong correlations between percent agriculture and several important stream habitat measures, including nitrate concentrations, proportion of fine sediments in riffles, and the abundance of fish cover. We also found that variation in gradient (channel slope) influenced responses of fish assemblages to land use. Urban land use was more disruptive to biological integrity in catchments with steeper channel slopes. Based on comparisons of our results in the topographically diverse Opequon Creek watershed with results from watersheds in flatter terrains, we hypothesize that the potential for riparian forests to mitigate effects of deleterious land uses in upland portions of the watershed is inversely related to gradient.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   
995.
Real-time PCR with fluorogenic hydrolysis probes (5' nuclease assay) is increasingly used for the detection of pathogens for diagnostic purposes. Nevertheless, the size of the probes, usually 25–40 nucleotides, might limit their use to detect pathogens with high genome variability between isolates, where an identical sequence cannot be found without multiple mismatches. In this report, we describe a 5' nuclease assay, to detect Apple stem pitting virus, based on the use of a shorter probe which is chemically modified with a minor groove binder in order to increase duplex stability and raise the melting temperature to a value suitable for real-time analysis. The short size of the probe, which is critical to target a conserved cluster sequence of 14 nucleotides in the RNA polymerase gene, circumvents the genome variability of the virus. The assay correlates at 96 percent with gel analysis and is more reliable than biological indexing to detect Apple stem pitting virus field isolates. It is fast and fully compatible with automation, and therefore particularly suitable for plant certification.  相似文献   
996.
通过比较,研究了粗状假丝酵母诱变株产脂肪酶催化水解不同底物的相对活力,包括低级酯、脂肪酸甘油酯和天然油脂。并对粗状假丝酵母产脂肪酶催化水解猪油反应中的pH值、温度、时间、加酶量、乳化剂用量和Ca2+浓度等因素进行了研究,得出pH值为7.5、温度为45℃、水解反应时间为72h、加8ml粗酶液、2%油的乳化剂、Ca2+浓度为75mmol/l时,猪油有最佳水解率。通过对该酶反应动力学进行研究得出其水解反应的米氏常数Km为12.25×10-3mol/l和最大反应速率Vmax为11.14μmol/min。  相似文献   
997.
朱孝霖  Li Huan  韦萍 《饲料工业》2008,29(12):39-42
为探讨耐热木聚糖酶水解自制甘蔗渣木聚糖制备木寡糖的工艺条件和分析水解液的寡糖成分,试验以产耐热木聚糖酶的基因工程菌1020为原料,水解自制的甘蔗渣木聚糖,分别研究水解过程中酶的用量、木聚糖的浓度及酶解温度对酶解反应的影响,并采用高压液相色谱和质谱联用技术对水解液成分进行分析。试验结果表明,2%的木聚糖浓度,水解温度95℃,酶液用量100U/g,酶解3h后DP值可降至2.94,满足生产木寡糖对聚合度的要求;并且水解液的成分主要为木糖、木二糖和木三糖,没能检测到木四糖。耐热木聚糖酶在高温下酶解木聚糖对酶法制备木寡糖具有重要的应用价值。  相似文献   
998.
An experiment was undertaken to evaluate the protective role of boron on the serum profile of buffalo calves fed a high fluoride ration. Twelve male Murrah buffalo (Bubalus bubalis) calves of 6–8 months age, divided into three groups of four calves in each, were fed basal diets and supplemented with sodium fluoride (NaF, 60 ppm) alone or in combination with borax (Na2B4O7.10H2O, 140 ppm) for 90 days. Boron (B) was added in the ration as borax to make @140 ppm boron (elemental B) on DM basis in treatment II. Dietary F caused a significant (p < 0.05) depressing effect on serum Ca and Zn on day 90 which was improved with B supplementation. However, serum Fe and Cu did not show any significant change on F or F+B supplementation. The serum ALP and phosphorus level were increased significantly (p < 0.05) on F feeding but declined significantly (p < 0.05) when B was fed. The findings suggested beneficial effect of boron on serum minerals and ALP in buffalo calves fed high fluoride ration.  相似文献   
999.
无公害平菇代料栽培标准化生产技术   总被引:2,自引:0,他引:2  
本文提出了平菇无公害生产技术及栽培措施,包括母种、原种及栽培种、栽培袋的无公害生产技术,出菇管理技术,病虫害的物理防治与生物防治,产品采收要求,开发的技术完全符合国家相关无公害农产品标准。  相似文献   
1000.
谈红松人工林改培果林技术   总被引:1,自引:0,他引:1  
从3个方面分析论述了红松人工林的改培适宜的林分和采取的技术措施。  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