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   44641篇
  免费   4192篇
  国内免费   34篇
  48867篇
  2022年   273篇
  2021年   606篇
  2020年   339篇
  2019年   412篇
  2018年   555篇
  2017年   514篇
  2016年   927篇
  2015年   1598篇
  2014年   1742篇
  2013年   2210篇
  2012年   2771篇
  2011年   2845篇
  2010年   1864篇
  2009年   1801篇
  2008年   2615篇
  2007年   2635篇
  2006年   2568篇
  2005年   2538篇
  2004年   2470篇
  2003年   2435篇
  2002年   2382篇
  2001年   518篇
  2000年   412篇
  1999年   587篇
  1998年   676篇
  1997年   482篇
  1996年   437篇
  1995年   423篇
  1994年   405篇
  1993年   410篇
  1992年   353篇
  1991年   323篇
  1990年   339篇
  1989年   261篇
  1988年   308篇
  1987年   278篇
  1986年   272篇
  1985年   335篇
  1984年   383篇
  1983年   344篇
  1982年   440篇
  1981年   438篇
  1980年   419篇
  1979年   272篇
  1978年   302篇
  1977年   266篇
  1976年   277篇
  1975年   210篇
  1974年   286篇
  1973年   253篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Increased longevity and recently intensified emphasis on gerodontology mandate that dental students'exposure to clinical care of the elderly be enhanced. The extent to which individual students can be exposed to geriatric dental care depends on the availability of elderly patients to dental school clinics and the treatment needs of these patients. The purposes of this study were (1) to determine the dental treatment needs of geriatric patients who seek care at a dental school, and (2) to ascertain if differences exist between the needs of older versus relatively young geriatric patients. Data collected on 128 elderly patients during a three month period indicate that 57% of the aged were either edentulous at examination or treatment planned to become edentulous and receive two full dentures. The remaining 43% were treatment planned to remain dentulous and receive therapies other than full upper and lower dentures. More older geriatric patients required full dentures than their younger cohorts. More young elderly required prophylaxes, scalings, root planing therapy, dental restorations, and partial dentures. Additional to their denture requirements, aged patients appear to have sufficient non-prosthetic needs to allow for meaningful gerodontic experience by students.  相似文献   
102.
103.
Starch gel electrophoretic studies of 16 enzymes encoded by 34 Loci were performed on six brown trout populations. One new polymorphism is described at the Pmi-2 locus. Breeding data were analysed for both single and joint segregation of six loci: Aat-1, Cpk-1, G3p-2, Mdh-2, Mdh-3, and Pmi-2. All the loci are shown to segregate in simple mendelian ratios and one nonrandom joint segregation was observed. The polymorphism level, heterozygosities, and genetic distances were estimated and compared with those reported in other studies on brown trout and closely related salmonid species. The polymorphism level (25%) and average heterozygosity (9%) were high. Significant genetic distances were observed, but the average degree of differentiation between populations appeared to be small (9% of the total heterozygosity).  相似文献   
104.
Translation of encephalomyocarditis virus RNA in rabbit reticulocyte lysates in the presence of N-formyl-[(35)S]methionine-tRNA(f) (Met) revealed that a small polypeptide is cleaved from the N-terminus of the capsid protein precursor, preA, by virus-coded protease activity. Therefore, this N-terminal segment comprising the translation initiation site is not conserved in any of the mature capsid proteins.  相似文献   
105.
Abstract: The combined techniques of HPLC and radioimmunoassay were used to identify and quantitate enkephalin-related peptides in the guinea pig hippocampus. Both met- and leu-enkephalin were identified, in approximately a 2:1 ratio, as well as a third enkephalin-like molecule that is neither met- nor leu-enkephalin. The third enkephalin elutes earlier than met- or leu-enkephalin from a reversed-phase column, has a molecular weight similar to the other enkephalins, and is as active as these enkephalins are in inhibiting binding of labeled opiates to rat brain membranes. All regions of the hippocampus (dentate gyrus, CA1–2, CA3–4, and subiculum) contain all three immunoreactive peptides. Immunocytochemical techniques, using antisera raised against met-enkephalin, show with one antiserum immunoreactivity in the granule cell-mossy fiber system, and with the other scattered immunoreactive cells mostly in the CA2 region. Enkephalins are not confined to the mossy fiber system, as previously suggested, but may be a component of another hippocampal innervation.  相似文献   
106.
107.
Inbred mice and lines congenic to them for the major histocompatibility complex were similar in susceptibility to EAE except for moderate differences in two pairs. TheH-2 haplotypesq, s, andb occurred in inbred strains and in congenic lines of high, medium, or low susceptibility. It is concluded that the major histocompatibility complex does not control susceptibility to EAE in mice. Furthermore, the low susceptibility of DBA/1J mice was not enhanced by poly A-U.  相似文献   
108.
109.
110.
That the uptake of glucose by the parasitic amoeba Entamoeba histolytica occurs by an equilibrative transport system is supported by the following observations. 1. The rate of glucose uptake is several orders of magnitude greater than the uptake by pinocytosis. 2. The uptake of glucose exhibits saturation kinetics, with K(m)=1.6mm and V(max.) ranging from 2 to 5mumol/min per ml of cells at 37 degrees C. 3. The glucose analogues 2-deoxyglucose, 3-O-methylglucose and d-xylose are transported by the glucose system although with much less affinity. Competitive inhibition was observed between pairs of substrates, with K(i) values for any sugar closely coincident with the corresponding K(m). 4. d-Xylose, a sugar not metabolized by the cells, equilibrated with 80% of the amoebal cell water. 5. Cells equilibrated with xylose exhibited countertransport of this sugar against its concentration gradient when another substrate was added to the medium. 6. Blocking of glycolysis by iodoacetate or F(-) has no immediate effect on transport. The presence of a glucose-transport system in E. histolytica contrasts with the situation found in the non-parasitic amoeba, where pinocytosis seems to be the only mechanism of solute uptake.  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