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   24908篇
  免费   1851篇
  国内免费   110篇
耳鼻咽喉   420篇
儿科学   875篇
妇产科学   392篇
基础医学   2530篇
口腔科学   551篇
临床医学   2270篇
内科学   5559篇
皮肤病学   656篇
神经病学   1309篇
特种医学   1308篇
外国民族医学   1篇
外科学   4657篇
综合类   354篇
一般理论   15篇
预防医学   1230篇
眼科学   826篇
药学   2068篇
中国医学   41篇
肿瘤学   1807篇
  2023年   226篇
  2022年   401篇
  2021年   990篇
  2020年   478篇
  2019年   823篇
  2018年   949篇
  2017年   622篇
  2016年   661篇
  2015年   692篇
  2014年   1035篇
  2013年   1244篇
  2012年   1753篇
  2011年   1722篇
  2010年   914篇
  2009年   868篇
  2008年   1297篇
  2007年   1235篇
  2006年   1148篇
  2005年   1006篇
  2004年   894篇
  2003年   760篇
  2002年   666篇
  2001年   606篇
  2000年   562篇
  1999年   508篇
  1998年   243篇
  1997年   207篇
  1996年   214篇
  1995年   191篇
  1994年   175篇
  1993年   148篇
  1992年   281篇
  1991年   299篇
  1990年   269篇
  1989年   253篇
  1988年   250篇
  1987年   251篇
  1986年   218篇
  1985年   203篇
  1984年   134篇
  1983年   138篇
  1982年   106篇
  1981年   88篇
  1980年   71篇
  1979年   146篇
  1978年   91篇
  1977年   85篇
  1975年   70篇
  1974年   71篇
  1973年   102篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Prospective observations on 442 consecutive samples have confirmed that pregnancies with CNS malformations are regularly associated with an abnormal cellular content of amniotic fluid. A crude semiquantitative test of the cell content can give valuable clinical information in relation to borderline amniotic fluid alpha-fetoprotein values, and help to detect false positive AFP's.  相似文献   
72.
73.
Pre-B cell acute lymphoblastic leukaemia (cALL) commonly occurs in young patients and although successful conventional therapies are available (such as cytotoxic drugs and bone marrow transplantation) for a proportion of patients (approximately 30%) these are ultimately unsuccessful. Recurrence of disease is a result of the failure of the immune system to recognize these abnormal cells and down-regulation of crucial molecules required for cognate CD4(+) T cell recognition has been postulated as a means of immune escape. In this study we show that an embryonic kidney cell line (293 cells) transfected with CD154 (40 L.1) are capable of not only maintaining the viability of primary ALL cells in culture but can also up-regulate the expression of a number of crucial molecules involved in antigen recognition. We show that 40 L.1 cell stimulation of primary ALL cell cultures can not only enhance the allogeneic and autologous MLR response to such cells but will also induce CTL effectors which are capable of lysing wild-type autologous ALL cells. It is therefore conceivable that such an approach could be used to generate an active anti-tumour response in patients, following conventional therapy, reducing the incidence of recurrence.  相似文献   
74.
Cetirizine, a derivative of hydroxyzine, is a new compound with potent antihistaminic property without antiserotonin and anticholinergic activities. The effect of both a single dose (15 mg) and 7 days of treatment (15 mg twice daily) with cetirizine, a potent H1 antagonist on bronchoconstriction induced by histamine and leukotriene D4 (LTD4) has been examined in 10 patients with mild atopic asthma in a placebo-controlled, double-blind, crossover study. Cetirizine, after a single dose and 7 days of treatment with placebo, the geometric mean values of the provocative concentration of histamine causing a 20% fall in FEV1 (millimolars) were 1.60 (95% confidence interval, 0.82 to 3.11) and 1.67 (0.77 to 3.65), compared with 118.07 (77.22 to 180.54) (p less than 0.0001) and 53.16 (20.50 to 137.84) after cetirizine administration (p less than 0.0002). The mean inhibition after a single dose was twofold higher than after 1 week of treatment (p less than 0.05). After a single dose and 7 days of treatment with placebo, the geometric mean values of the provocative concentration of LTD4 causing a 20% fall in FEV1 (micromolars) were 2.26 (1.74 to 2.94) and 2.37 (1.77 to 3.17), compared with 3.90 (2.60 to 5.86) (p less than 0.05) and 3.21 (2.28 to 4.52) after cetirizine administration. This result suggests that cetirizine is a potent H1 antagonist in the human airways. Diminished activity after 1 week of treatment suggests subsensitivity of H1 receptors developing in human airways. The small protective effect after a single dose against LTD4-induced bronchoconstriction indicates a nonspecific rather than a specific receptor antagonism.  相似文献   
75.
Gene deletions in spinal muscular atrophy.   总被引:7,自引:0,他引:7       下载免费PDF全文
Two candidate genes (NAIP and SMN) have recently been reported for childhood onset spinal muscular atrophy (SMA). Although affected subjects show deletions of these genes, these deletions can lead to either a very mild or a severe phenotype. We have analysed a large number of clinically well defined patients, carriers, and normal controls to assess the frequency and extent of deletions encompassing both of these genes. A genotype analysis indicates that more extensive deletions are seen in the severe form of SMA than in the milder forms. In addition, 1 center dot 9% of phenotypically normal carriers are deleted for the NAIP gene; no carriers were deleted for the SMN gene. Our data suggest that deletions in both of these genes, using the currently available assays, are associated with both a severe and very mild phenotype.  相似文献   
76.
Spinal bulbar muscular atrophy is a neurodegenerative disorder caused by a polyglutamine expansion in the androgen receptor (AR). We show in transiently transfected HeLa cells that an AR containing 48 glutamines (ARQ48) accumulates in a hormone-dependent manner in both cytoplasmic and nuclear aggregates. Electron microscopy reveals both types of aggregates to have a similar ultrastructure. ARQ48 aggregates sequester mitochondria and steroid receptor coactivator 1 and stain positively for NEDD8, Hsp70, Hsp90 and HDJ-2/HSDJ. Co-expression of HDJ-2/HSDJ significantly represses aggregate formation. ARQ48 aggregates also label with antibodies recognizing the PA700 proteasome caps but not 20S core particles. These results suggest that ARQ48 accumulates due to protein misfolding and a breakdown in proteolytic processing. Furthermore, the homeostatic disturbances associated with aggregate formation may affect normal cell function.  相似文献   
77.
Determination of T lymphocyte subsets using monoclonal antibodies revealed a deficiency of suppressor cells and an elevated helper:suppressor T cell ratio in 7 patients with untreated idiopathic immune complex glomerulonephritis and nephrotic syndrome. Possible pathogenetic mechanisms of immunoregulatory cell imbalance and their implications specifically in reference to idiopathic glomerulonephritis are discussed.  相似文献   
78.
Monoclonal antibodies were raised against pregnancy-associated endometrial alpha 1-globulin (alpha 1-PEG), a 32 KD insulin-like growth factor binding protein (IGF-BP), which represents a major secretory product of the human decidualized endometrium during pregnancy. This class of IGF-BP has been implicated in the modulation of action, inhibitory and stimulatory, of insulin-like growth factors. Immunization with the protein purified from pregnancy endometrium resulted after myeloma fusion in the isolation of six hybridoma clones and the antibodies produced were characterized. The Ka of the antibodies ranged between 4.75 x 10(9) M-1 and 0.7 x 10(8) M-1. In Western blots all monoclonal antibodies reacted with purified protein of molecular weight 32 KD and specifically detected this IGF-BP species in culture medium and cytosolic extracts of pregnancy endometrium and amniotic fluid. The monoclonal antibodies appear to define three epitope-bearing regions as evidenced by their reactivity to polypeptide fragments of the protein. After synthesis and secretion by tissue explants in vitro the protein is susceptible to cleavage into fragments possessing different monoclonal antibody-defined reactivity. Employing immunohistochemical techniques the protein was principally localized to decidual cells in tissue sections of pregnancy endometrium and solely to these cells after enzymic digestion of the tissue. The implications of these results are discussed with respect to potential role of IGF-BP in the action of IGF upon the IGF-1 receptor-bearing populations, including lymphocytes and trophoblast cells, D in the decidua.  相似文献   
79.
In 4 patients with neuronal ceroid-lipofuscinoses (NCL) (3 patients with the junvenile type, 1 patient with the late infantile type), the ultrastructural spectrum of residual bodies in the central and peripheral nervous system presented curvilinear profiles in all cases and regions investigated and many more ultrastructural patterns within and beyond regions commonly accessible to biopsy, probably due to age dependence, local tissue and cellular biochemical factors. Sampling from basal ganglia especially yielded combined curvilinear-fingerpint bodies, from peripheral ganglia additional membranous bodies. Residual bodies in NCL were present in almost every cell type, similar to the distribution of regular lipofuscin. Although the classical subgroups of NCL contain electronmicroscopically well defined residual bodies, permitting distinction of the late infantile type from the juvenile type, the ultrastructural differences are more of a quantitative than of a qualitative nature. However, they are not pathognomonic. N.m.r. spectra of ceroid and lipofuscin support the concept of their biochemical similarity, and argue against the proposition that they contain a single major component.  相似文献   
80.
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