全文获取类型
收费全文 | 1459篇 |
免费 | 105篇 |
专业分类
耳鼻咽喉 | 11篇 |
儿科学 | 131篇 |
妇产科学 | 20篇 |
基础医学 | 168篇 |
口腔科学 | 32篇 |
临床医学 | 157篇 |
内科学 | 300篇 |
皮肤病学 | 16篇 |
神经病学 | 191篇 |
特种医学 | 91篇 |
外科学 | 184篇 |
综合类 | 28篇 |
一般理论 | 2篇 |
预防医学 | 105篇 |
眼科学 | 6篇 |
药学 | 99篇 |
1篇 | |
中国医学 | 4篇 |
肿瘤学 | 18篇 |
出版年
2021年 | 15篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 26篇 |
2014年 | 22篇 |
2013年 | 34篇 |
2012年 | 33篇 |
2011年 | 57篇 |
2010年 | 40篇 |
2009年 | 32篇 |
2008年 | 37篇 |
2007年 | 34篇 |
2006年 | 60篇 |
2005年 | 56篇 |
2004年 | 58篇 |
2003年 | 39篇 |
2002年 | 54篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 43篇 |
1998年 | 22篇 |
1997年 | 33篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 34篇 |
1989年 | 44篇 |
1988年 | 50篇 |
1987年 | 32篇 |
1986年 | 19篇 |
1985年 | 34篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 26篇 |
1976年 | 29篇 |
1975年 | 22篇 |
1974年 | 16篇 |
1973年 | 22篇 |
1971年 | 11篇 |
1970年 | 10篇 |
1968年 | 12篇 |
1967年 | 10篇 |
排序方式: 共有1564条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
D A Patterson R Rapoport M A Patterson B M Freed N Lempert 《Archives of surgery (Chicago, Ill. : 1960)》1988,123(3):300-304
Hydrogen peroxide, a reactive oxygen intermediate produced by activated neutrophils, has been shown to inhibit the response of human T lymphocytes to mitogens and alloantigens. Since hydrogen peroxide is known to react with iron and to induce lipid peroxidation, we compared the effects of hydrogen peroxide and a lipid peroxidation product, malondialdehyde, on the response of human peripheral blood mononuclear cells to T-cell mitogens. Peripheral blood mononuclear cells pretreated with 1 mmol/L of malondialdehyde, washed, and resuspended in fresh medium exhibited no inhibition of phytohemagglutinin responsiveness. Peripheral blood mononuclear cells treated in the same manner but with 200 mumol/L of hydrogen peroxide were inhibited by more than 95%. The addition of ferric edetate did not alter the inhibitory effects of 50 to 100 mumol/L of hydrogen peroxide, nor did the addition of deferoxamine, an iron chelator. These studies suggest that exogenous lipid peroxidation does not affect lymphocyte activation but that hydrogen peroxide has a direct inhibitory effect. Although monocytes are necessary for T-cell mitogenic responses, the effect of hydrogen peroxide was found to be directed at T lymphocytes. Exposure of T cells to a single dose of 200 mumol/L of hydrogen peroxide resulted in more than 71% suppression of the proliferative response measured 48 hours later, but the effect was spontaneously reversed by 72 to 96 hours. Repeated exposure of the cells to hydrogen peroxide resulted in continued inhibition of the proliferative response. These findings suggest that hydrogen peroxide produced by inflammatory phagocytic cells might be capable of suppressing the immune response of nearby T lymphocytes. 相似文献
5.
6.
7.
Maciej Poltorak John J. Hemperly Jamesine R. Williams Rif El-Mallakh William J. Freed 《Experimental neurology》1995,131(2):266-272
Although the pathogenesis of schizophrenia is unknown, there are data which indicate that the disease may be due to neurodevelopmental disturbances. Cell recognition molecules such as N-CAM and L1 antigen are involved in cell-cell interactions during development and in plasticity of the nervous system and could therefore be altered in relation to ongoing or established pathological processes. Using the Western blot technique, we found significant increases in N-CAM immunoreactive proteins and decreases in L1 antigen in the CSF of schizophrenic patients as compared to normal controls. The decrease in L1 antigen was observed in the 140-kDa band, and N-CAM was increased only in the 120-kDa band. The 120-kDa band of N-CAM and the 140-kDa band of L1 antigen were prominent components of CSF, but in serum these bands were minor or not detectable. Neuroleptic treatment did not significantly change either N-CAM or L1 antigen concentrations in CSF. It is possible that these CSF proteins are derived from CNS cells as secreted soluble N-CAM isoforms and L1 peptides. Our results suggest the possibility of a specific pattern of abnormal cellular function in the CNS in schizophrenia. 相似文献
8.
9.
Computational model of the on-alpha ganglion cell receptive field based on bipolar cell circuitry. 下载免费PDF全文
M A Freed R G Smith P Sterling 《Proceedings of the National Academy of Sciences of the United States of America》1992,89(1):236-240
The on-alpha ganglion cell in the area centralis of the cat retina receives approximately 450 synapses from type b1 cone bipolar cells. This bipolar type forms a closely spaced array (9 microns), which contributes from 1 to 7 synapses per b1 cell throughout the on-alpha dendritic field. Here we use a compartmental model of an on-alpha cell, based on a reconstruction from electron micrographs of serial sections, to compute the contribution of the b1 array to the on-alpha receptive field. The computation shows that, for a physiologic range of specific membrane resistance (9500-68,000 omega.cm2) and a linear synapse, inputs are equally effective at all points on the on-alpha dendritic tree. This implies that the electrotonic properties of the dendritic tree contribute very little to the domed shapes of the receptive field center and surround. Rather, these shapes arise from the domed distribution of synapses across the on-alpha dendritic field. Various sources of "jitter" in the anatomical circuit, such as variation in bipolar cell spacing and fluctuations in the number of synapses per bipolar cell, are smoothed by the overall circuit design. However, the computed center retains some minor asymmetries and lumps, due to anatomical jitter, as found in actual alpha-cell receptive fields. 相似文献
10.
Different modulation by histamine of IL-4 and interferon-gamma (IFN-γ) release according to the phenotype of human Th0, Th1 and Th2 clones 下载免费PDF全文
Histamine, an important inflammatory mediator in allergic diseases and asthma, has been reported to have modulator effects on T cells, suggesting that the bronchial microenvironment may regulate the function of resident T cells. We examined the effect of histamine on the release of the Th2-associated cytokines IL-4 and IL-5 and the Th1-associated cytokine IFN-γ by 30 CD4+ T cell clones from peripheral blood or bronchial biopsy of one atopic subject. Based on the IL-4/IFN-γ ratio, the clones were ascribed to the Th2 (ratio >1), Th0 (ratio 0.1 and 1) or Th1 (ratio <0.1) phenotype. Histamine inhibited IFN-γ production by Th1-like cells (P<0.02, Kruskall–Wallis), especially from bronchial biopsy, but had no effect on IL-4 release. Regarding Th0 clones, histamine inhibited IL-4 production (P<0.02) in a dose-dependent manner and slightly inhibited IFN-γ production, but had no effect on Th2-like cells. Histamine had a heterogeneous and insignificant effect on IL-5 production. The H2-receptor antagonist ranitidine completely reversed the inhibition of IL-4 and IFN-γ production, whereas the agonist dimaprit mimicked this effect. In contrast, H1- and H3-receptor agonists and antagonists had no significant effect. These data demonstrate that histamine has different effects on IL-4 and IFN-γ release by T helper cells according to their phenotype via H2-receptors. This study extends the immunomodulatory effects of histamine which may contribute to the perpetuation of airway inflammation in asthma. 相似文献