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   2714篇
  免费   111篇
  国内免费   306篇
林业   341篇
农学   448篇
基础科学   245篇
  490篇
综合类   742篇
农作物   139篇
水产渔业   95篇
畜牧兽医   384篇
园艺   104篇
植物保护   143篇
  2024年   2篇
  2023年   28篇
  2022年   74篇
  2021年   121篇
  2020年   94篇
  2019年   96篇
  2018年   71篇
  2017年   106篇
  2016年   92篇
  2015年   127篇
  2014年   96篇
  2013年   146篇
  2012年   165篇
  2011年   185篇
  2010年   157篇
  2009年   145篇
  2008年   146篇
  2007年   141篇
  2006年   111篇
  2005年   143篇
  2004年   83篇
  2003年   47篇
  2002年   47篇
  2001年   43篇
  2000年   47篇
  1999年   83篇
  1998年   79篇
  1997年   54篇
  1996年   69篇
  1995年   59篇
  1994年   60篇
  1993年   49篇
  1992年   41篇
  1991年   37篇
  1990年   31篇
  1989年   17篇
  1988年   16篇
  1987年   10篇
  1986年   5篇
  1985年   4篇
  1984年   1篇
  1982年   3篇
排序方式: 共有3131条查询结果,搜索用时 15 毫秒
81.
In production industry ofAuricularia auricular, the varieties quality is most important impact factor on output. For evaluating the early quality of the edible fungus, 9 varieties ofAuricularia auricular (Au9, CF09, CF05, 29, 916, chang10, chang7, Au.Japanese and 8808) were cultured on the medium consists of potato dextrose agar (PDA) and sawdust to test their mycelium growth rate, endurance to high temperature, resistance to mildew, assimilation of nutriment, and resistance to drought. The result showed that the mycelium of Chang 10, CF09, 29 and Au.Japanese varieties had the eminent characteristics such as short lifespan, stronger assimilation of nutriment, and endurance to high temperature and steady growth. These four varieties are determined as superiority varieties ofAuricularia auricular in accordance with the research results. Foundation item: The research was supported by Science Fund of Northeast Forestry University (2004). Biography: Li Ling (1964-), female, Engineer in Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Zhu Hong  相似文献   
82.
After investigating and studying the vegetation, we have established that Makehe Forest, in Sanjiangyuan Nature Reserve, Qinghai Province, is host to a total of 364 different species, representing 173 “genera” in 55 different vegetative families. We propose five quantifiable indices for evaluating the level of threat to these plants: 1) the distribution frequency of the “line transect”; 2) the distribution frequency of sample plots; 3) the distribution density inside sample plots; 4) the existing abundance in the forest region; and 5) plant fidelity. The results show that there are two endangered species, six vulnerable species, 12 nearly threatened species and 344 safe species. The study tried to evaluate the urgency for conserving these plants, according to coefficients of closeness to disappearance, of genetic loss and of usefulness. Results also showed that the number of species of primary concern is two; of secondary concern, nine; of the third level, 23; and of least concern, 330 species. __________ Translated from Journal of Beijing Forestry University, 2006, 28(3): 20–25 [译自: 北京林业大学学报]  相似文献   
83.
The authors visited some deer farms in Northeastern China in 1991 and 1993. The seven subspecies of Asian Wapiti (Cervus elaphus) were detected by observing the animal’s appearance and analyzing the video information. The status of taxonomy research in China was also discussed.  相似文献   
84.
Heilongjing(China)and Alberta(Canada)provinces are situated at the same lati-tude,with similar nature conditions.Mammals in Alberta account for 87 species and in Heilongj-ing,97 spesics,among which a number of orders,families and species are in common.Continentsof Eurisia and North America histoi cally were connected and separated for several times,sothere are a number of animal forms in common,among them the similarity of herbivores is rath-er high.The similarity index of cervidae is 0.54.Other orders with comparatively similarcompiosition are Insevtivora,Chiroptera and Lagomorpha.In two orders,there are no commonspecies.In these two regions,duc to historical reasons,a number of specific genera and specieswere formed.  相似文献   
85.
图像分割技术在木材表面缺陷识别中的应用   总被引:3,自引:3,他引:3  
阐述了图像分割技术在图像处理及分析中重要意义,以及主要的图像分割技术。以木材表面缺陷为主要研究对象,利用微分算子边缘检测、最优迭代阈值分割及形态学方法针对具有代表性缺陷死节和虫眼进行分割处理。  相似文献   
86.
内蒙古可持续发展指标体系设计及评价方法研究   总被引:2,自引:0,他引:2  
通过对内蒙古可持续发展评价指标体系和方法的初步研究,设计出了包括可持续发展综合指数1个目标层、人口状况等5个准则层和人口自然增长率等28个评价指标的层次性指标体系,并利用均方差权数决策方法,对区域可持续发展进行全面分析和定量评价。  相似文献   
87.
Fe and Zn deficiencies are global nutritional problems. N supply could increase Fe and Zn concentrations in wheat grain. This study was conducted to determine the impacts of different N rates (0, 122, 174, and 300 kg/ha) on the distribution and speciation of Fe and Zn in wheat grain milling fractions under field conditions. Zn and protein concentrations were increased, whereas Fe was less affected in the flour fractions with increasing N rates. Further analysis with size‐exclusion chromatography coupled with inductively coupled plasma mass spectrometry revealed that Fe and Zn bound to low‐molecular‐weight (LMW) compounds in the flour fractions (probably Fe‐nicotianamine [NA], Fe‐deoxymugineic acid, or Zn‐NA) were less affected by increasing N supply, representing 3.5–10.9% of total Fe and 2.5–56.6% of total Zn. In the shorts fraction, LMW‐Fe was absent, and LMW‐Zn with higher N supply was over twice as high as that in control and 3–27 times as high as that in the other milling fractions. In the flour fractions, the molar ratios of phytic acid (PA)/Fe and PA/Zn (both less than 30.5) decreased, whereas soluble LMW‐Fe/Zn was not affected with increasing N rates.  相似文献   
88.
本文分析了影响培育落叶松人工林的不利因素,提出落叶松发展需要注意的问题及对策,使落叶松在培育过程中能充分发挥短期效益。  相似文献   
89.
不同方法提取三种生态型沙地云杉总DNA的比较   总被引:1,自引:0,他引:1  
沙地云杉为内蒙古特有树种,干旱适应性强,是我国西部重要造林树种。在长期适应干旱生态条件的过程中沙地云杉形成了紫果型、绿果型和红果型3种生态型。前期研究证明:紫果型沙地云杉有更强的抗旱能力,绿果型抗旱能力弱,红果型处于二者之间,是一个比较典型的过渡类型。本文从分子生物学的角度,详细叙述了沙地云杉总DNA的提取过程、方法,并对已知的植物DNA提取方法作了针对性的改良;对实验过程提取DNA的影响作了分析。为今后针对进行沙地云杉的植物基因研究和生物工程打下基础,对扩大沙地云杉造林面积和西部大开发的生态环境建设具有重要的指导意义。  相似文献   
90.
Root mat method described by Kuchenbuch and Jungk was used to study the rhizosphere processes. The experiment was carried out on two years oldPinus koraiensis seedlings. Soil samples collected from the upper 20-cm soil layer in Changbai Mountain were treated with three different forms of nitrogen fertilizers: NO3 −N, NH4 +−N and NH4NO3. The results showed that the soil pH and available P near the roots were all lower than in the bulk soil in control treatment. NH4 +−N application greatly decreased the soil pH near the roots compared to the control treatment and promoted the absorption of phosphorus, which led to a more remarkable depletion region of available P. On the contrary, the rhizosphere soil pH was higher than in the bulk soil in treatments with NO3 −N and retarded the P absorption, which led to a nearly equal available P contents to the bulk soil. In treatment with NH4NO3, the rhizosphere soil pH was only a little lower than that in the control treatment and its effects on P absorption is mediate between the treatments with NH4 +−N and NO3 −N. Foundation item: This paper was supported by National Natural Science Foundation of China (Grant No. 30170167). Biography: Chen Yong-liang (1969-), male, Ph. Doctor, lecture of Northeast Forestry University, Harbin 150040, Post-doctor in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P.R. China. E-mail: ylchin@sohu.com Responsible editor: Seng Funan  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