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   1156197篇
  免费   132014篇
  国内免费   678篇
  1288889篇
  2018年   9853篇
  2016年   13755篇
  2015年   19125篇
  2014年   22444篇
  2013年   32102篇
  2012年   36029篇
  2011年   36371篇
  2010年   24676篇
  2009年   23115篇
  2008年   32718篇
  2007年   33697篇
  2006年   31549篇
  2005年   30443篇
  2004年   30097篇
  2003年   28926篇
  2002年   28199篇
  2001年   51199篇
  2000年   51595篇
  1999年   41126篇
  1998年   15108篇
  1997年   15958篇
  1996年   15109篇
  1995年   14080篇
  1994年   13892篇
  1993年   13723篇
  1992年   34555篇
  1991年   33371篇
  1990年   32629篇
  1989年   31706篇
  1988年   29287篇
  1987年   28262篇
  1986年   26158篇
  1985年   26186篇
  1984年   21791篇
  1983年   18784篇
  1982年   14669篇
  1981年   13203篇
  1980年   12557篇
  1979年   20913篇
  1978年   16606篇
  1977年   15102篇
  1976年   14065篇
  1975年   15346篇
  1974年   16655篇
  1973年   16335篇
  1972年   14747篇
  1971年   13660篇
  1970年   11751篇
  1969年   11090篇
  1968年   10101篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
841.
842.
1. Experiments were performed on six dogs to determine the rate of penetration of Cl(33) and Na(24) across the blood-aqueous humor and blood-cerebrospinal fluid barriers after intravenous injection of the radioactive ions. The radioactivity measurements were made with an immersion type of Geiger-Müller counter. 2. The concentrations of the labelled ions in the anterior chamber and the cisterna magna increase slowly to approach that of plasma. The rate of penetration k is calculated from a simple exponential equation with the half-value interval t(0.5) or the time required for the labelled-ion concentration in the fluid to reach 50 per cent of that of plasma. The average t(0.5) for Cl(38) and Na(24) in aqueous humor are 34.3 +/- 9 and 27.3 +/- 9 minutes, respectively, while those for cerebrospinal fluid are 90 +/- 6 and 95 +/- 6 minutes, respectively. 3. A study of the radioactivity in plasma was made to determine the per cent remaining after a steady state was reached. By means of this determination the sodium and chloride space was calculated to be 33 +/- 5 per cent.  相似文献   
843.
844.
845.
C-Type Virus Released from Cultured Human Rhabdomyosarcoma Cells   总被引:44,自引:0,他引:44  
RD-114 virus, released from human rhabdomyosarcoma cells, has all the characteristics of a mammalian C-type virus. Immunological tests indicate that it differs from all known C-type viruses and is the most likely candidate for a human C-type virus yet described.  相似文献   
846.
847.
848.
849.
C57BL/6 nude beige mice (B6 nubq; no T cell, no NK activity) were used as recipients for the adoptive transfer of thymocytes from B6 gld mice (generalized lymphoproliferative disease) which are a model of systemic lupus erythematous. The [gld----nubg] chimeras showed several similarities with gld control mice including the T cell disorders (lymphoproliferation and Con A-response deficiency of splenocytes) and B cell disorders (hyperglobulinemia and elevated anti-single-stranded DNA antibody titers). This suggests that the gld lymphoproliferative disorder has a thymic origin (and does not result from an abnormally extrathymic T cell development) and that the gld T cells have an essential role for the emergence of the disorders of both the T and B cells.  相似文献   
850.
The non-newtonian viscous and elasto-thixotropic properties of native and lyophilized pathological bronchial mucus and of polymer solutions (3% and 6% PIB in decalin) used as mucus analogs were analyzed using a cone-plate Carri-Med rheometer and a Couette viscoelastometer that we have specifically developed for measuring the rheological properties of bronchial mucus in clinical practice. The master curves obtained for apparent viscosity under steady conditions as a function of shear rates (gamma: 2.6 X 10(-3) to 6.9 X 10(1) sec-1) were fairly similar, whatever the apparatus used. Under transient conditions, at low shear rate (gamma less than 1.4 sec-1), PIB and mucus exhibited a typical viscoelastic behavior: the shear stress increased slightly up to a steady-state value. At higher gamma, a transitory overshoot of sigma characteristic of the elastothixotropic systems appeared. Such a behavior can be interpreted as resulting from structural changes such as formation and rupture of the three-dimensional network present in bronchial mucus as in polymer solutions.  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