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   16260篇
  免费   1257篇
  国内免费   6篇
  17523篇
  2023年   135篇
  2022年   114篇
  2021年   277篇
  2020年   214篇
  2019年   236篇
  2018年   420篇
  2017年   401篇
  2016年   478篇
  2015年   570篇
  2014年   655篇
  2013年   939篇
  2012年   1276篇
  2011年   1306篇
  2010年   775篇
  2009年   619篇
  2008年   1091篇
  2007年   1120篇
  2006年   1071篇
  2005年   962篇
  2004年   935篇
  2003年   882篇
  2002年   770篇
  2001年   183篇
  2000年   244篇
  1999年   184篇
  1998年   146篇
  1997年   93篇
  1996年   101篇
  1995年   110篇
  1994年   90篇
  1993年   80篇
  1992年   94篇
  1991年   74篇
  1990年   67篇
  1989年   50篇
  1988年   51篇
  1987年   48篇
  1986年   36篇
  1985年   44篇
  1984年   58篇
  1983年   37篇
  1982年   53篇
  1981年   48篇
  1980年   51篇
  1979年   41篇
  1978年   42篇
  1977年   35篇
  1976年   38篇
  1975年   38篇
  1974年   27篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
21.
Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,...  相似文献   
22.
Summary Observations in a family point to the existence of autosomal dominant inheritance for discrete subaortic stenosis (DSS), which made up part of a multisystem disorder. Both parents, offspring of two full siblings, had short stature, obstructive lung disease (OLD), hoarseness and upturned nose. The father alone had aortic stenosis and inguinal hernia.The six offspring, aged from 13 to 28 years, were followed up for up to 8 years. While one of them was virtually normal, and one had only minor abnormalities, four siblings displayed clinical signs of progressive aortic stenosis. Of the two eldest siblings who eventually died, necropsy in one showed a discrete subaortic stenosis, which was hemodynamically proven in one and surgically corrected in another sibling.Upturned nose was present in each examined member of the family, short stature and hoarseness in five of the siblings, DSS in four, OLD, inguinal hernia and congested episcleral veins in three, kyphoscoliosis in two, while epicanthus, strabismus, microphthalmos and widely spaced teeth were noted in the deceased female. The prevalence of some of these traits in roughly three-quarters of the sibship was consistent with an underlying single gene abnormality in affected heterozygous parents. We proposed that this constitutes a new syndrome.  相似文献   
23.
Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms.  相似文献   
24.
A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest.  相似文献   
25.
The xylanase gene from Cryptococcus albidus contains seven introns. Genomic and cDNA clones under the control of the CaMV 35S promoter were transferred into tobacco plants using Agrobacterium-mediated cell transformation. The genes were transcribed and the mRNAs were amplified by the polymerase chain reaction using primers on each side of the intron region. About 90% of the amplification products from plants transformed with the genomic clone corresponded to the size of the pre-mRNA (1.2 kb) and 10% represented the spliced product (0.85 kb). The 0.85 kb fragment was cloned and sequenced and the result indicated that the introns from the xylanase gene were accurately spliced by the plant cells.  相似文献   
26.
27.
28.
A new quantitative radiometric assay for adenosine deaminase is described. The reaction conditions are similar to those used in other radioassays and are shown to result in an activity which increases linearly with time and with enzyme concentration. An original feature of the technique resides in the use of reversed-phase thin-layer chromatography to separate adenosine from inosine. The separation is complete, fast, and reproducible. Both compounds can be recovered almost quantitatively from the plates. The assay is very simple and allows the determination of up to 36 samples in 3 h.  相似文献   
29.
30.
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