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   745篇
  免费   54篇
  国内免费   50篇
林业   73篇
农学   31篇
基础科学   15篇
  62篇
综合类   252篇
农作物   44篇
水产渔业   111篇
畜牧兽医   182篇
园艺   30篇
植物保护   49篇
  2024年   5篇
  2023年   8篇
  2022年   21篇
  2021年   33篇
  2020年   22篇
  2019年   42篇
  2018年   40篇
  2017年   36篇
  2016年   52篇
  2015年   32篇
  2014年   32篇
  2013年   51篇
  2012年   49篇
  2011年   51篇
  2010年   43篇
  2009年   45篇
  2008年   31篇
  2007年   18篇
  2006年   30篇
  2005年   24篇
  2004年   10篇
  2003年   26篇
  2002年   24篇
  2001年   18篇
  2000年   11篇
  1999年   15篇
  1998年   12篇
  1997年   4篇
  1996年   8篇
  1995年   4篇
  1994年   6篇
  1993年   7篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   5篇
  1987年   3篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1982年   6篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有849条查询结果,搜索用时 15 毫秒
1.
用台盼兰—姬姆萨染色检测家畜精子顶导反应的研究   总被引:1,自引:0,他引:1  
本文探讨了用台盼兰—姬姆萨染色检测家畜精子顶体反应的可行性。用肝素或钙离子载体诱发精子顶体反应。根据染色结果将精子分为四类:a)核后帽部不着色或淡青色,顶体不着色或部分紫红色(有顶体反应活精子);b)核后帽部暗青色.顶体部不着色或部分暗红色(有顶体反应死精子);c)核后帽部不着色或淡青色,顶体部紫红色(无顶体反应活精子);d)核后帽部暗青色,顶体部暗紫红色(无顶体反应死精子)。有顶体反应活精子百分率与仓鼠卵穿透率呈强正相关。从而证明台盼兰—姬姆萨染色是检测家畜精子顶体反应的有效手段,并能预测获能处理后精子的受精能力。  相似文献   
2.
丝核菌细胞核染色技术的研究   总被引:16,自引:0,他引:16  
比较了5种不同的染色方法对丝核菌(Rhizoctonia)菌株细胞核的染色效果。结果表明,番红O-KOH的染色效果最好,Giemsa、苯胺蓝-甘油次之,染色效果最差的是苯胺蓝-乳酚油及曲利苯蓝-乳酚油。用番红O-KOH染色方法对分离自13种作物的57个丝核菌菌株进行细胞核染色,其中3个菌株为双核丝核菌,其余54个菌株为多核丝核菌。  相似文献   
3.
对5例巴氏杆菌感染家兔的空肠与圆小囊肥大细胞(mast cell,MC)进行了组织化学与电镜的观察,发现在细菌感染导致的病变组织边缘、病变组织内血管附近结缔组织中及变性细胞周围组织的上皮下与黏膜下层都出现了大量甲苯胺蓝(Toluidine Blue,TB)阳性肥大细胞。电镜下,MC有的直接与变性细胞密切接触,有的则和血管内皮紧密相触,在此部位的血管内可见有淋巴细胞贴附填充。MC胞浆内充盈大量的特征性颗粒,有时这些颗粒向细胞表面突出形成边缘空隙,即形成所谓的脱颗粒管道,将颗粒内容物逐渐排除细胞外,遗留空腔。  相似文献   
4.
Systemic acquired resistance (SAR) is induced following inoculation of Peronospora tabacina sporangia into the stems of Nicotiana tabacum plants highly susceptible to the pathogen. Previous results have shown that accumulation of acidic β-1,3-glucanases (PR-2's) following induction of SAR by P. tabacina may contribute to resistance to P. tabacina. We showed that up-regulation of the PR-2 gene, PR-2d, following stem inoculation with P. tabacina, is associated with SAR. Studies using plants transformed with GUS constructs containing the full length promoter from PR-2d or promoter deletions, provided evidence that a previously characterized regulatory element that is involved in response to salicylic acid (SA), may be involved in regulation of PR-2d following induction of SAR with P. tabacina. This work provides evidence that regulation of PR-2 genes during P. tabacina-induced SAR may be similar to regulation of these genes during infection of N-gene tobacco by TMV or following exogenous application of SA, and provides further support for the role of SA in regulation of genes during P. tabacina-induced SAR.  相似文献   
5.
Sperm DNA fragmentation is a condition that interferes directly in the reproductive efficiency. Currently, there are several methods for assessing the sperm DNA integrity, such as Alkaline Comet, TUNEL and Sperm Chromatin Structure Assay. However, many of these techniques are laborious and require high‐precision equipment. Thus, the development of new techniques can optimize the evaluation of sperm DNA damage. Therefore, the aim of this study was to standardize the toluidine blue (TB) stain technique for the analysis of DNA fragmentation of dog, cat, bull, stallion and ram spermatozoa. For this purpose, we used six animals of each specie (n = 30), in reproductive age. Sperm was collected by different methods according to the particularities of each species, and such samples were divided into two aliquots: a sperm sample was kept at 5°C (considered as intact sperm DNA), and the remaining samples were submitted to the induction of DNA fragmentation by exposure to ultraviolet light for 4 hr. Samples were then mixed with the intact sample to obtain known and progressive proportions of sperm with fragmented DNA (0%, 25%, 50%, 75% and 100%). Semen smears were performed and subjected to staining with TB. Blue‐stained spermatozoa were considered to have DNA fragmentation. We observed high linear regression coefficients between the expected proportion of damaged DNA and the results of TB for dog, cat, ram, bull and stallion samples. In conclusion, TB stain was considered a fast and effective technique for the study of spermatozoa DNA in several species.  相似文献   
6.
随着人们生活方式的变化,养猪户也变得越来越多,不仅能为其带来更多的经济收入,也可提高其生活质量和水平。调查数据显示,很多养殖户在养猪中通常会因很多因素致使猪群感染疾病,倘若不能及时处理,势必会对自身带来较为严重的经济损失,甚至会加大疫病的扩散。该文主要对高致病性猪蓝耳病防控新理念展开分析,并提出一些可行的对策。  相似文献   
7.
8.
以笃斯越橘(Vaccinium uliginosum)成熟果实为试材,以钼蓝比色法测定笃斯越橘果实还原型抗坏血酸(Reduced ascorbic acid,As A)含量进行条件优化。结果表明,3%偏磷酸-乙酸用量为100μL、5%硫酸和5%钼酸铵用量均为200μL、以去离子水补充至1 500μL,30℃干热恒温浴显色40 min,取出室温下放置1 h后,在700 nm下测定,所得数据稳定,准确性适合用于笃斯越橘果实As A含量的测定;测得含量为(40.20±6.23)mg/100 g FW。  相似文献   
9.
The northern Chilean Patagonia region is a key feeding ground and a nursing habitat in the southern hemisphere for blue whales (Balaenoptera musculus). From 2014 to 2019, during 6 separate research cruises, the dive behavior of 28 individual blue whales was investigated using bio-logging tags (DTAGs), generating ≈190 h of data. Whales dove to significantly greater depths during the day compared to nighttime (day: 32.6 ± 18.7 m; night: 6.2 ± 2.7 m; P < 0.01). During the night, most time was spent close to the surface (86% ± 9.4%; P < 0.01) and at depths of less than 12 m. From 2016 to 2019, active acoustics (scientific echosounders) were used to record prey (euphausiids) density and distribution simultaneously with whale diving data. Tagged whales appeared to perform dives relative to the vertical migration of prey during the day. The association between diurnal prey migration and shallow nighttime dive behavior suggests that blue whales are at increased risk of ship collisions during periods of darkness since the estimated maximum ship draft of vessels operating in the region is also ≈12 m. In recent decades, northern Chilean Patagonia has seen a large increase in marine traffic due to a boom in salmon aquaculture and the passenger ship industry. Vessel strike risks for large whales are likely underestimated in this region. Results reported in this study may be valuable for policy and mitigation decisions regarding conservation of the endangered blue whale.  相似文献   
10.
Abstract

The bismuth sulfide and methylene blue colorimetric finishes for soil sulfate determination by the Johnson‐Nishita distillation method were examined and compared. Both procedures gave comparable results when applied to soils and soil extracts, but the bismuth method was more rapid and more reliable. Nitrogen flow rate over the range 100–500 ml/min was not critical for the bismuth method, provided appropriate distillation times were employed. However, the release and transfer of hydrogen sulfide in the bismuth method was effected in one‐third of the time required for the méthylène blue finish, largely due to the elimination of a gas‐washing step. Predrying of soil extract samples increased recovery of hydrogen sulfide with the bismuth procedure arid could be used to increase sensitivity. Nitrate interference was observed with the bismuth procedure but attributed to interference during the reduction step. The bismuth procedure can readily be adapted for microdetermination in the 0–40 ppm sulfate‐S range.  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