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   495651篇
  免费   51792篇
  国内免费   171篇
  2018年   5882篇
  2017年   5446篇
  2016年   7645篇
  2015年   9989篇
  2014年   11335篇
  2013年   15467篇
  2012年   17716篇
  2011年   17544篇
  2010年   11890篇
  2009年   10508篇
  2008年   15544篇
  2007年   15840篇
  2006年   15082篇
  2005年   14008篇
  2004年   14023篇
  2003年   13031篇
  2002年   12646篇
  2001年   18966篇
  2000年   18875篇
  1999年   15032篇
  1998年   5543篇
  1997年   5665篇
  1996年   5338篇
  1995年   5011篇
  1994年   4845篇
  1993年   4841篇
  1992年   12314篇
  1991年   12207篇
  1990年   11940篇
  1989年   11622篇
  1988年   11065篇
  1987年   10664篇
  1986年   9918篇
  1985年   9854篇
  1984年   8270篇
  1983年   7168篇
  1982年   5560篇
  1981年   4982篇
  1979年   7967篇
  1978年   6284篇
  1977年   5823篇
  1976年   5577篇
  1975年   6091篇
  1974年   6836篇
  1973年   6675篇
  1972年   6234篇
  1971年   5639篇
  1970年   5089篇
  1969年   5077篇
  1968年   4903篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
From six to 89 months after surgery 82 patients who had been treated by radical surgery (118 excisions) for intractable hidradenitis suppurativa were reviewed. Local recurrence rates varied greatly with the disease site, being low after axillary (3%) and perianal surgery (0%) and high after inguinoperineal (37%) and submammary (50%) excision. Recurrence results from inadequate excision or an unusually wide distribution of apocrine glands, but physical factors such as obesity, local pressure, and skin maceration played a part in a few patients. Recurrence due to inadequate surgery tended to be the most troublesome. At follow up 75 (91%) of the patients were pleased with the results of their operation. A quarter of the patients developed disease at a new anatomical site after operation. Radical surgery gives good symptomatic control of severe hidradenitis suppurativa of the axilla, inguinoperineal, and perianal regions but is less satisfactory for submammary disease.  相似文献   
942.
Stability of o-phthalaldehyde-derived isoindoles   总被引:1,自引:0,他引:1  
The degradation of 1-alkylthio-2-alkylisoindoles, generated in situ by reaction of o-phthalaldehyde with primary alkylamines in the presence of selected thiols, was studied under conditions typical of those used in precolumn derivatization applications. In all cases, loss of isoindole followed pseudo first order kinetics and was strongly accelerated by excess o-phthalaldehyde in the reaction mixture. Reactivity toward o-phthalaldehyde was found to be influenced by a number of experimental parameters including thiol structure, thiol concentration, amine structure, solvent composition, and pH. In the absence of excess o-phthalaldehyde, the stability of all derivatives examined was excellent. These results provide a basis for optimization of reaction conditions for maximum derivative stability.  相似文献   
943.
944.
Ovarian cancer G protein-coupled receptor 1 (OGR1) is a proton-sensing molecule that can detect decreases in extracellular pH that occur during inflammation. Although OGR1 has been shown to have pro-inflammatory functions in various diseases, its role in autoimmunity has not been examined. We therefore sought to determine whether OGR1 has a role in the development of T cell autoimmunity by contrasting the development of experimental autoimmune encephalomyelitis between wild type and OGR1-knockout mice. OGR1-knockout mice showed a drastically attenuated clinical course of disease that was associated with a profound reduction in the expansion of myelin oligodendrocyte glycoprotein 35-55-reactive T helper 1 (Th1) and Th17 cells in the periphery and a reduced accumulation of Th1 and Th17 effectors in the central nervous system. We determined that these impaired T cell responses in OGR1-knockout mice associated with a reduced frequency and number of dendritic cells in draining lymph nodes during EAE and a higher production of nitric oxide by macrophages. Our studies suggest that OGR1 plays a key role in regulating T cell responses during autoimmunity.  相似文献   
945.
Six peripheral blood lymphoid fractions (total lymphocytes, non-T, T, Tar (autologous rosette-forming T cells/precursor), T mu (helper), and T gamma (suppressor) lymphocytes) isolated through rosetting procedures were examined for the presence of ferritin by a direct immunofluorescence technique. Although ferritin was present in all lymphoid fractions studied, a significantly higher proportion of ferritin-containing cells were detected in the T-cell fraction than in the non-T-cell fraction, (mean +/- SD = 7.9 +/- 1.6% and 5.0 +/- 1.2%, respectively). T mu- and T gamma-cell fractions showed a twofold increase in the number of ferritin-positive cells (14.1 +/- 1.4% and 15.4 +/- 2.6%, respectively), as compared with Tar (7.0 +/- 0.9%)-and total lymphocyte (6.9 +/- 1.3%)-cell fractions. These results indicate that ferritin is preferentially distributed in T mu and T gamma lymphocytes and may constitute the basis for explaining some of the roles exercised by these cells in the control of other biological systems.  相似文献   
946.
In experiments on 56 healthy subjects (18-20 years old) the quality of their activity was determined during compensatory watching the mark at complicating regimes of work. Depending on the difficulty of the task five groups of subjects were singled out with optimum working capacity in one of four working conditions: normal, ordinary and strenuous work, model of stress situation. It is established that the change of the number of significant correlative connections between main parameters of psychophysiological state of man-operator reflects the condition of his functional systems. On the basis of computation of total range of organization values of both R-R intervals of the ECG and duration of expiration, the success of the man-operator work in complex conditions of activity is predicted.  相似文献   
947.
948.
949.
950.
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