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   20028篇
  免费   2030篇
  国内免费   11篇
  22069篇
  2023年   80篇
  2022年   160篇
  2021年   343篇
  2020年   229篇
  2019年   253篇
  2018年   316篇
  2017年   334篇
  2016年   453篇
  2015年   807篇
  2014年   891篇
  2013年   985篇
  2012年   1389篇
  2011年   1344篇
  2010年   906篇
  2009年   825篇
  2008年   1123篇
  2007年   1231篇
  2006年   982篇
  2005年   1032篇
  2004年   1039篇
  2003年   976篇
  2002年   927篇
  2001年   338篇
  2000年   328篇
  1999年   299篇
  1998年   277篇
  1997年   176篇
  1996年   137篇
  1995年   134篇
  1994年   155篇
  1993年   132篇
  1992年   210篇
  1991年   201篇
  1990年   165篇
  1989年   169篇
  1988年   163篇
  1987年   161篇
  1986年   145篇
  1985年   171篇
  1984年   163篇
  1983年   127篇
  1982年   101篇
  1981年   114篇
  1980年   95篇
  1979年   101篇
  1978年   103篇
  1976年   85篇
  1974年   92篇
  1972年   74篇
  1971年   76篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
An automated follow-up register for the detection of iatrogenic thyroid disease has been established as a joint venture between the general practitioners in the north-east of Scotland and the thyroid clinic of Aberdeen General Hospitals.The data-processing operations in the system are handled by an International Computers Limited 4/50 computer. Patients are followed up at predetermined intervals and the system has been designed to process, screen, and store clinical and biochemical follow-up data and report results to the patients, general practitioners, and the hospital records department.  相似文献   
52.
53.
54.
55.
56.
57.
Binding of axial ligands to the nickel(II) of isolated factor F430 from the methyl reductase enzyme of Methanobacterium thermoautotrophicum is demonstrated. Evidence of bis-ligand coordination is obtained from the x-ray absorption, optical, and resonance Raman spectral characterization of F430 and its 12,13-diepimeric isomer in the presence of a large excess of cyanide, pyridine, or 1-methylimidazole. Significant broadening and 5-10-nm red shifts of the main 430-nm optical absorption band and shifts of up to 30 cm-1 for the high-frequency Raman lines are observed upon coordination of these axial ligands. The Raman spectra of native F430 and the diepimer with a particular axial ligand are nearly identical. Nickel x-ray absorption edge spectra of the diepimer in the absence and presence of these exogenous ligands are indicative of conversion from a square-planar to a tetragonally distorted octahedral geometry. Analyses of the nickel extended x-ray absorption fine structure data for the ligated diepimer complexes yield detailed structural information for these complexes. Implications of these data with respect to the enzymatic mechanism and the structure of the enzyme-bound factor are discussed.  相似文献   
58.
Plant hormone response mutants   总被引:4,自引:0,他引:4  
A variety of plant hormone response mutants has now been described, and is surveyed in this article. In addition to hormone-insensitive mutant phenotypes with defects in hormone-related features, there exist mutants apparently constitutive for the gibberellin responses, and also a mutant hyper-responsive to gibberellin. Although there is still little biochemical evidence on the nature of these mutants, the emerging picture of their genetic dominance relationships has given rise to tentative suggestions of the involvement of represser functions in hormonal control systems.  相似文献   
59.
The excavations at Christ Church, Spitalfields (1984-86) produced a sample of 968 human skeletons which were interred between 1729 and 1859. Of these, 387 were recovered in association with coffin plates stating name, age at death, and date of death. There are 138 adult females in the named sample and the obstetric histories of 94 have been reconstructed from historical documentation. Such variables as birth spacing, number of children, and age at first and last births are known for the majority of this sample. Any individual about whose history there is any doubt has been excluded from the analysis. A middle-class group, they were largely of high nutritional status and, by the standards of the day, lived in sanitary and comfortable conditions. Both males and females have a mean age at death of 56 years. The presence or absence, the typology, the severity, the width and the length of the preauricular sulcus, the presence or absence and the number of pits on the dorsal aspect of the pubic body, sulci along the anterior sacrum adjacent to the auricular facet, and the extension of the pubic tubercle were evaluated in relation to the obstetric histories of these females. Statistical analysis has demonstrated a relationship between the presence of pubic tubercle extension and parity status and between the degree of extension and the number of children borne (P < .02). Statistically there is no significant relationship (P > .05) between either the preauricular sulcus or pubic pitting and parity status. Sacral scarring is significantly associated (P < .05) with parity status, but as it was evident in only eight females it has little practical application. Sample sizes are small, and it must be considered that statistical evaluation of larger samples might detect associations between variables not demonstrated here. There is no significant relationship between any of the cortical variants under consideration and age at death.  相似文献   
60.
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