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   720360篇
  免费   82936篇
  国内免费   422篇
  2018年   6231篇
  2016年   8333篇
  2015年   10689篇
  2014年   13011篇
  2013年   18555篇
  2012年   20471篇
  2011年   21193篇
  2010年   14150篇
  2009年   13163篇
  2008年   18793篇
  2007年   19714篇
  2006年   18465篇
  2005年   17844篇
  2004年   17685篇
  2003年   17172篇
  2002年   16587篇
  2001年   31628篇
  2000年   32080篇
  1999年   25492篇
  1998年   8674篇
  1997年   9125篇
  1996年   8825篇
  1995年   8388篇
  1994年   8355篇
  1993年   8158篇
  1992年   21639篇
  1991年   21421篇
  1990年   21189篇
  1989年   20624篇
  1988年   19255篇
  1987年   18513篇
  1986年   17099篇
  1985年   17496篇
  1984年   14490篇
  1983年   12657篇
  1982年   9553篇
  1981年   8892篇
  1980年   8366篇
  1979年   14137篇
  1978年   10979篇
  1977年   10122篇
  1976年   9661篇
  1975年   10886篇
  1974年   11369篇
  1973年   11219篇
  1972年   10411篇
  1971年   9255篇
  1970年   8122篇
  1969年   7601篇
  1968年   7060篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity.  相似文献   
922.
923.
924.
Fractions containing macrophage migration inhibition factor (MIF) and leucocyte migration inhibition factor (LIF) were obtained using Sephadex G-200 filtration from supernatant fluids of human lymphocyte cultures stimulated by PHA. The fractions were tested for the ability to affect migration and phagocytic activity of target cells. Peripheral blood leucocyte migration capacity was inhibited by the fraction with the molecular mass of 60,000-70,000 D (LIF), while migration activity of mouse peritoneal exudate cells was suppressed by the fraction with the molecular mass of 20,000-30,000 D (MIF). MIF- and LIF-containing fractions increased almost three-fold Fc-receptor-mediated phagocytic activity of neutrophils.  相似文献   
925.
Several phenotypic and functional defects have been described within the residual T-lymphocyte population of patients with B-cell chronic lymphocytic leukemia (B-CLL), particularly in those in the more advanced stages of the disease. In this study, we review these abnormalities and discuss their possible effects on the course of the illness. Particular emphasis is devoted to the role of interleukin 2 (IL-2) in B-CLL. Evidence is provided that the IL-2 released by B-CLL T-lymphocytes may be utilized by the neoplastic B-cell clone that expresses the IL-2 receptor and that decreased availability of IL-2 may play a contributory role in some of the T-cell defects encountered in B-CLL.  相似文献   
926.
The isolation of spirochaetes from the rat caecum   总被引:1,自引:1,他引:0  
Spirochaetes indigenous to the conventional rat caecum were cultivated on agar medium using selective isolation techniques. The 27 axenic isolates represented four morphological types of spirochaetes differing in cell size, cell coiling pattern and number of protoplasmic flagella.  相似文献   
927.
928.
Plasma concentrations of adrenaline and noradrenaline were measured at rest from cannulated fish and following net capture. Adrenaline and noradrenaline concentrations in capture-stressed fish averaged 36,740 pmol l-1 and 38,860 pmol l-1 respectively, whereas resting values were less than 200 pmol l-1 for both amines. Erythrocyte swelling and raised blood lactate were evident in stressed fish. In vitro effects of 5 mmol l-1 adrenaline on erythrocyte suspensions suggested that the catecholamine had a direct effect on erythrocyte volume. The significance of these results is discussed in relation to the oxygen transport properties of the blood.  相似文献   
929.
C L Rümke 《Blood cells》1985,11(1):137-140
Ratios of two percentages observed in differential counts of leukocytes or lymphocytes are very imprecise if they are based on relatively small numbers of cells. This is shown by the length of the 95% confidence intervals for such ratios. A formula is given for computing the limits of such intervals. They should accompany each observed value for a ratio.  相似文献   
930.
Antigen inoculated intratracheally (IT) into animals can induce primary immune responses and selectively recruit specific T cells to the lung. In the current study, the role of alveolar macrophages (AM) in these two responses was investigated. Antigen-pulsed bronchoalveolar cells (BAC) inoculated IT into guinea pigs generated a population of immune T cells that proliferated in vitro on reexposure to antigen-pulsed macrophages (M?). The possibility that antigen-pulsed donor BAC shed antigen that was subsequently processed and presented by host M? was ruled out by genetic experiments. Thus, peritoneal exudate lymphocytes (PEL) from (2 X 13)F1 guinea pigs primed with antigen-pulsed BAC from strain 2 animals responded preferentially to antigen-pulsed strain 2 M? rather than to antigen-pulsed strain 13 M?. In a second set of studies, antigen-pulsed BAC inoculated IT into guinea pigs selectively recruited antigen-specific T cells to the lung. Genetic experiments verified that inoculated BAC were the source of the antigen-presenting cells responsible for selective recruitment. Thus, antigen-pulsed strain 2 BAC inoculated IT recruited a greater proportion of (2 X 13)F1 T cells that recognized antigen in the context of strain 2 M? than F1 T cells that recognized antigen on strain 13 M?. Taken together, these studies suggest that AM contribute to the regulation of pulmonary immunity by both inducing T lymphocyte immunity and selectively recruiting specific T cells to the lung.  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