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   814篇
  免费   18篇
  国内免费   69篇
  901篇
  2015年   10篇
  2013年   17篇
  2012年   20篇
  2011年   27篇
  2010年   33篇
  2009年   46篇
  2008年   33篇
  2007年   53篇
  2006年   42篇
  2005年   35篇
  2004年   28篇
  2003年   35篇
  2002年   29篇
  2001年   14篇
  1999年   7篇
  1998年   8篇
  1997年   13篇
  1996年   16篇
  1995年   17篇
  1993年   14篇
  1992年   16篇
  1991年   11篇
  1990年   14篇
  1989年   13篇
  1988年   12篇
  1987年   11篇
  1986年   8篇
  1985年   10篇
  1984年   7篇
  1983年   7篇
  1981年   6篇
  1980年   9篇
  1978年   10篇
  1977年   8篇
  1976年   10篇
  1975年   7篇
  1974年   15篇
  1973年   6篇
  1972年   7篇
  1971年   11篇
  1966年   6篇
  1959年   9篇
  1958年   18篇
  1957年   18篇
  1956年   10篇
  1955年   16篇
  1954年   17篇
  1953年   11篇
  1952年   8篇
  1951年   9篇
排序方式: 共有901条查询结果,搜索用时 0 毫秒
31.
32.
33.
(一)乙型脑炎疫苗在用每分钟2,000转的速度沉澱20分钟後,疫苗中的总氮含量此较不沉澱的减少50%以上,但是疫苗的效价不论在其制成时或在保存一年的各时期 内,都没有比不沉澱的低。 (二)用含有5%的乳醣和一些鹽灰的溶液裂偏的疫苗的免疫效僵在各保存时期内都比用普通的生理鹽水制偏的疫苗为高,而且比较稳定。 (三)本文同时讨论了福尔马林的使用量和疫苗中蛋白質的含量的关系。  相似文献   
34.
The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC50), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1‐ and 833.3‐fold differences, followed by etofenprox with RRs of 138.4‐ and 224.1‐fold differences in values of LC50 and concentration that produced 90% mortality (LC90), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020‐, 0.019‐ and 0.001‐fold differences in resistance ratios (RRLC50), respectively.  相似文献   
35.
36.
An ecotope (spatial eco-space) map that considers topography and bio-organism-relevant variables emerges as an important basic framework when landscape-scale characteristics for ecosystem management and wildlife conservation are needed. A spatio-geoecological framework based on geographic information systems (GIS) and a vegetation survey were developed for wildlife habitat evaluation of national parks and applied to a representative rugged valley area of Mt. Sorak National Park in Korea. An ecotope map was classified into hundreds of types and dozens of groups by combining biological and geophysical variables. Variables included: forest vegetation type, topographic solar radiation, normalized difference vegetation index (NDVI), elevation, and anthropogenic factors, such as, streams and roads. Layers of GIS variables were produced by field surveys, modeling, satellite images, or digitalization. Vegetation surveys were carried out to identify finer-scale distribution of vegetation types in the rugged valley area. Digital forest vegetation maps from the Forestry Administrator were then modified using the field-surveyed vegetation maps. Topographic solar radiation was predicted with a daily topographic radiation model. The NDVI was calculated from the satellite imagery of a Landsat Thematic Mapper. A digital elevation model (DEM) was used and the other layers were digitized using topographical maps with a scale of 1:25000. The aim of this study is to determine the geoecological factors relating to the spatial pattern of plant community. It was cleared by the spatial pattern of environmental variables and vegetation characteristics by detrended correspondence analysis using plant species and the environmental variables of each plot. The ordination component value of the first axis shows significant regression to some environmental variables. A case study of habitat evaluation was carried out using the resultant ecotope map. The spatial distribution of potential goral habitat and vegetation characteristics were predicted and the impact of human trails on the neighboring vegetation was also examined for restoration planning. The GIS-based framework developed for wildlife habitat evaluation is useful for natural resource management and human activity control in national parks in Korea.  相似文献   
37.
38.
39.
Calreticulin (CRT) plays pivotal roles in Ca2+ homeostasis, molecular chaperoning, infection, inflammation and innate immunity. In an attempt to study the involvement of CRT in innate immunity, the full-length cDNA of calreticulin (PxCRT) was cloned from the diamondback moth, Plutella xylostella. It consists of 1674 bp (excluding poly-A tail) with a longest open reading frame (ORF) of 1197 bp encoding 398 amino acids. In silico analysis of PxCRT ORF reveals that it has various repeat motifs and endoplasmic reticulum retention signal found in all the calreticulin proteins. As expected, high amino acid sequence identities were found from other CRTs identified from Bombyx mori (87%), Galleria mellonella (87%), Apis mellifera (74%), Anopheles gambiae (74%), Tribolium castaneum (73%), Culex quinquefasciatus (73%), Rhodnius prolixus (72%), Nasonia vitripennis (71%), Drosophila melanogaster (71%) and Haemaphysalis qinghaiensis (68%). During development, P. xylostella expressed PxCRT predominantly in the pupal stage. In addition, spatial expression pattern analysis indicates that PxCRT was highly expressed in the silk gland. PxCRT mRNA, furthermore, was strongly induced 3 to 6 h after laminarin treatment, suggesting that PxCRT appears to be involved in immune responses and also plays an important role in the silk gland.  相似文献   
40.
任信在  李新宇 《兽类学报》2002,22(2):108-115
1997 年至1999 年间, 在韩国智异山国家公园选取生境相似, 但片断化和未片断化不同的调查地。设置8 条2 km 长截线, 调查记录了黄鼬( Mustela sibirica) 、黄喉貂(青鼬) ( Martes lavigula) 、狗獾(Meles meles) 、豹猫( Felis bengalensis) 、野猪( Sus scrofa) 、獐( Hydropotes inermis) 、狍( Capreolus) 、朝鲜兔(Lepus coreanus) 和松鼠的数量, 并对影响动物数量的相关因子进行回归分析。结果表明, 8 块样地虽属两大类不同景观且具有相似植被特征, 但在片断化和未片断化中, 枯折木, 胸高直径(dbh)6~10 cm的树及50 cm的巨树密度, 树冠盖度及灌木被度均有明显差异。3 年内在8 块样地共记录到9种兽类在雪被上留下的足迹, 其中5 种兽的密度在片断化和未片断化生境中差异明显。9 种兽的渐近多元回归中, 6 种兽的密度同景观和植被变量密切相关, 但如果不增加当地生境条件, 则足迹链丰富度同植被构成的简单相关性表现得很微弱。在片断化和未片断化的不同景观林区, 对兽类的分布及其动态还要做进一步详细研究。  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