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   350篇
  免费   7篇
林业   26篇
农学   4篇
  11篇
综合类   184篇
水产渔业   8篇
畜牧兽医   116篇
园艺   1篇
植物保护   7篇
  2019年   1篇
  2018年   3篇
  2017年   1篇
  2016年   5篇
  2015年   3篇
  2014年   2篇
  2013年   17篇
  2012年   15篇
  2011年   23篇
  2010年   12篇
  2009年   13篇
  2008年   12篇
  2007年   18篇
  2006年   16篇
  2005年   12篇
  2004年   8篇
  2003年   13篇
  2002年   18篇
  2001年   8篇
  2000年   12篇
  1999年   6篇
  1998年   5篇
  1997年   4篇
  1996年   7篇
  1995年   5篇
  1994年   7篇
  1993年   4篇
  1992年   15篇
  1991年   20篇
  1990年   23篇
  1989年   3篇
  1988年   4篇
  1986年   3篇
  1984年   7篇
  1983年   4篇
  1982年   4篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1974年   2篇
  1973年   1篇
  1972年   3篇
  1970年   1篇
  1969年   2篇
  1967年   1篇
  1963年   1篇
  1942年   1篇
  1941年   1篇
排序方式: 共有357条查询结果,搜索用时 500 毫秒
81.
82.
We describe a pathogenetic mechanism underlying a variant form of the inherited blood disorder alpha thalassemia. Association studies of affected individuals from Melanesia localized the disease trait to the telomeric region of human chromosome 16, which includes the alpha-globin gene cluster, but no molecular defects were detected by conventional approaches. After resequencing and using a combination of chromatin immunoprecipitation and expression analysis on a tiled oligonucleotide array, we identified a gain-of-function regulatory single-nucleotide polymorphism (rSNP) in a nongenic region between the alpha-globin genes and their upstream regulatory elements. The rSNP creates a new promoterlike element that interferes with normal activation of all downstream alpha-like globin genes. Thus, our work illustrates a strategy for distinguishing between neutral and functionally important rSNPs, and it also identifies a pathogenetic mechanism that could potentially underlie other genetic diseases.  相似文献   
83.
84.
85.
86.
87.
The Paisley Caves in Oregon record the oldest directly dated human remains (DNA) in the Western Hemisphere. More than 100 high-precision radiocarbon dates show that deposits containing artifacts and coprolites ranging in age from 12,450 to 2295 (14)C years ago are well stratified. Western Stemmed projectile points were recovered in deposits dated to 11,070 to 11,340 (14)C years ago, a time contemporaneous with or preceding the Clovis technology. There is no evidence of diagnostic Clovis technology at the site. These two distinct technologies were parallel developments, not the product of a unilinear technological evolution. "Blind testing" analysis of coprolites by an independent laboratory confirms the presence of human DNA in specimens of pre-Clovis age. The colonization of the Americas involved multiple technologically divergent, and possibly genetically divergent, founding groups.  相似文献   
88.
Cholangitis is a common inflammatory disorder of the biliary system in cats. There are two major forms based on the predominate type of inflammatory cell infiltrates: lymphocytic or neutrophilic. Ultrasound is a common imaging modality used in these patients. This retrospective study evaluated the ultrasound examinations of 26 cats with a histologic diagnosis of cholangitis. Most cats with cholangitis had sonographically normal liver size, echogenicity, and normal biliary systems. Statistically significant sonographic changes for cats with cholangitis included hyperechoic liver parenchyma, hyperechoic gallbladder contents, and increased pancreatic size. No statistically significant changes were noted to distinguish lymphocytic and neutrophilic forms of cholangitis. Cats with the sonographic features of diffuse liver hyperechogenicity, gallbladder contents and enlarged pancreas may suggest cholangitis.  相似文献   
89.
Objective To document an ovine disease attributed to the consumption of Lythrum hyssopifolia (lesser loosestrife). Procedures Historical and histological review of field and experimental cases. Results 1–20% mortality occurred in sheep flocks grazing paddocks where L. hyssopifolia was the predominant green vegetation. Well‐documented disease outbreaks occurred in summer on nine farms across Victoria between 1974 and 2002. Liver damage occurred in all nine outbreaks, with kidney damage in at least eight. Hepatocyte necrosis was usually zonal to midzonal (zone 2) in the liver samples from four farms and periacinar (zone 3) in those from three farms, but some livers showed only single‐cell necrosis. Multinucleate hepatocytes near necrotic areas were a feature in six cases. Proximal tubular epithelium appeared to be the primary renal target and brown granules were often present in renal tubules. Biochemical and histological evidence of liver and kidney damage was obtained from two sheep experimentally pen‐fed harvested L. hyssopifolia. Conclusion Chemicals in L. hyssopifolia are toxic to ovine hepatocytes and renal tubular epithelial cells.  相似文献   
90.
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