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   14003篇
  免费   1113篇
  国内免费   187篇
耳鼻咽喉   36篇
儿科学   183篇
妇产科学   42篇
基础医学   2001篇
口腔科学   39篇
临床医学   1224篇
内科学   1202篇
皮肤病学   375篇
神经病学   7004篇
特种医学   615篇
外科学   552篇
综合类   653篇
现状与发展   1篇
预防医学   310篇
眼科学   224篇
药学   629篇
中国医学   126篇
肿瘤学   87篇
  2024年   14篇
  2023年   237篇
  2022年   199篇
  2021年   478篇
  2020年   501篇
  2019年   554篇
  2018年   622篇
  2017年   571篇
  2016年   510篇
  2015年   435篇
  2014年   748篇
  2013年   1274篇
  2012年   567篇
  2011年   671篇
  2010年   528篇
  2009年   641篇
  2008年   712篇
  2007年   621篇
  2006年   571篇
  2005年   457篇
  2004年   437篇
  2003年   365篇
  2002年   310篇
  2001年   291篇
  2000年   250篇
  1999年   253篇
  1998年   223篇
  1997年   251篇
  1996年   252篇
  1995年   216篇
  1994年   150篇
  1993年   154篇
  1992年   130篇
  1991年   107篇
  1990年   124篇
  1989年   68篇
  1988年   80篇
  1987年   89篇
  1986年   68篇
  1985年   90篇
  1984年   82篇
  1983年   69篇
  1982年   76篇
  1981年   49篇
  1980年   60篇
  1979年   46篇
  1978年   25篇
  1977年   25篇
  1976年   24篇
  1975年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
结节性硬化症的磁共振影像学表现   总被引:14,自引:3,他引:11  
目的 分析结节性硬化症TSC的MRI表现。方法  13例经临床证实的TSC病例 ,分析其头部MRI特征性改变。结果 MRI主要征象包括 :①室管膜下结节 :13例均发现病灶 ,T1WI发现 71个 ,T2 WI 39个 ,PDWI 5 6个 ;②皮层及皮层下结节 :11例有阳性发现 ,T2 WI和PDWI各发现 114个病灶 ,T1WI 72个 ;③脑白质异常信号 :5例发现白质病变 ,T2 WI和PDWI各发现 10个病灶 ,T1WI无明确显示 ;④室管膜下巨细胞星形细胞瘤 :仅 1例发现。结论 MRI对TSC的中枢神经系统改变敏感 ,是诊断此病的首选影像学检查方法 ,其中T1WI观察室管膜下结节敏感 ,T2 WI和PDWI观察皮层下及白质病变敏感  相似文献   
62.
熊升远  鞠富霞 《河北医学》2003,9(3):241-243
目的:探讨如何准确评价膀胱颈硬化症逼尿肌功能。方法:对78例膀胱颈硬化症患者进行了尿动力学检查。结果:单纯性逼尿肌收缩力增高者39例,术后疗效不佳的发生率为0;逼尿肌不稳定者31例,术后疗效不佳的发生率为46%;逼尿肌收缩无力者8例,术后疗效不佳的发生率为100%。结论:应用尿动力学检查来评价膀胱颈硬化症逼尿肌功能,对合理选择病倒,指导临床治疗,提高疗效有重要的价值。  相似文献   
63.
Abstract The issue of fertility in patients with multiple sclerosis (MS) has not been exhaustively studied. Epidemiological data have suggested that spontaneous fecundity might be reduced; several endocrine and sexual disturbances potentially interfering with reproduction have been evidenced in MS patients of both sexes. Moreover, some medical treatments used in MS (e. g., mitoxantrone, cyclophosphamide) may exert detrimental effects on spermatozoa as well as on oocytes, leading to early impairment of fertility. This review illustrates the factors potentially interfering with fertility in MS and discusses the therapeutic tools that may be used to promote fertility in these patients. The safety of hormonal therapies in MS is also examined. The current applications of assisted reproductive technology (ART) are discussed, including in vitro fertilisation (IVF) techniques. Currently available methods to preserve fertility in patients that undergo cytotoxic treatments by means of sperm/oocyte cryostorage or by ovarian fragment cryopreservation and autografting are considered.  相似文献   
64.
In order to examine the mechanism by which the oral carbonaceousadsorbent, AST-120 delays the appearance of glomerular sclerosis,experiments were carried out in 120 male Sprague-Dawley ratsweighing 285–320 g. The rats were first subjected to 2/3,3/4, and 4/5 nephrectomy (n=40). The experiments were begunat 2 weeks after the surgery, and were performed over an 8-weekperiod. Half of each group (n=20) was administered 1 g/day ofliquid AST-120, and the other half received liquid vehicle solutionwith pair feeding in each group. In the 2/3 nephrectomized groupthe administration of AST-120 delayed the occurrence of glomerularhypertrophy and prevented the appearance of glomerular sclerosiswithout any significant differences in renal function, systemicblood pressure (SBP), and urinary protein excretion (U-P). Inthe 3/4 nephrectomized group the administration of AST-120 delayedthe appearance of glomerular hypertrophy and sclerosis withsignificant decreases in SBP and U-P. In the 4/5 nephrectomizedgroup the administration of AST-120 delayed the appearance ofglomerular sclerosis and prevented a decrease in renal function.It is concluded that administration of the oral adsorbent AST-120delays the occurrence of glomerular sclerosis by delaying theappearance of glomerular hypertrophy, systemic hypertension,and the increase in proteinuria. It can be therefore mentionedthat the accumulating substances in the digestive tract worsenthe abnormal milieu of chronic renal failure.  相似文献   
65.
采用临床流行病学方法对IgG指数和IgG合成率的实用价值进行评价。结果发现:在对多发性硬化(MS)的诊断中,IgG指数的敏感性、特异性和阳性结果似然比分别是60%、65%和1.80,而IgG合成率分别为50%,65%和1.43。在排除皮质类固醇激素的影响后,IgG指数的敏感性和阳性结果似然比分别是84%和2.4,IgG合成率则分别是79%和2.26。此外,IgG指数和IgG合成率对于判断是否存在中枢神经系统器质性损害有较大的意义  相似文献   
66.
Autoantibodies to centromere proteins (anti-CENPs) and to topoisomerase-I are highly specific for scleroderma. Unlike most autoantibodies in other diseases, these autoantibodies are mutually exclusive. We have analysed the idiotypes (Ids) expressed by anti-CENP-B, antitopoisomerase-I, and IgGs from 20 scleroderma patients. Rabbit anti-Ids were prepared to antitopoisomerase-I from two scleroderma patients, and to anti-CENP-B from four patients. These six anti-Ids were used to study the purified autoantibodies from 20 scleroderma patients: four antitopoisomerase-I, 10 anti-CENP-B, and six purified IgG from scleroderma patients who were negative for both autoantibodies. In addition, we studied sera from 40 normal autoantibody-negative controls, and sera and purified immunoglobulins from 17 systemic lupus erythematosus (SLE) patients containing high titres of anti-double-stranded DNA, and/or autoantibodies to extractable nuclear antigens (ENA). Using direct binding, and competitive inhibition ELISAs and immunoblots, we identified an Id present in the heavy chains of all the affinity-purified antitopoisomerase-I, and anti-CENP-B. Interestingly, this Id was also present in the immunoglobulins of the scleroderma patients who had neither of the two autoantibodies. By contrast, cross-reactive Id-EM was not found in the sera or immunoglobulins from 17 SLE patients, or in the sera from 40 normal subjects. Several samples from two patients showed that this cross-reactive Id-EM was stable over time. The scleroderma disease-specific autoantibodies may be identified through a common structural feature at the variable region of the heavy chain: cross-reactive Id-EM.  相似文献   
67.
Long repetition time (TR) spin-echo (SE) with T2- or proton density weighting is the sequence of choice to detect the brain lesions of multiple sclerosis (MS). Fast spin-echo (FSE) permits the generation of T2-weighted images with similar contrast to SE but in a fraction of the time. We compared the sensitivity of FSE and SE in the detection of the brain lesions of MS. Six patients with clinically definite MS underwent brain imaging with both dual echo (long TR, long and short echo time (TE) SE and dual echo FSE. The SE and FSE images were first reviewed independently and then compared. A total of 404 lesions was detected on SE and 398 on FSE. Slightly more periventricular lesions were detected using SE than FSE (145 vs 127), whereas more posterior cranial fossa lesions were detected by FSE (77 vs 57). With both SE and FSE the short TE images revealed more lesions than the long echo. These results suggest that FSE could replace SE as the long TR sequence of choice in the investigation of MS.  相似文献   
68.
Beta-interferon (IFN-β) is a promising treatment in multiple sclerosis (MS), reducing the exacerbation rate and MRI lesion burden, as well as the disease progression in relapsing-remitting MS. IFN-β was originally defined by its antiviral effects, but the interest has recently been focused on its immunomodulatory properties. Myelin basic protein (MBP) is one of several autoantigens considered to be the target for autoaggressive immune responses, which eventually might lead to the development of MS. To study in-vitro effects of IFN-β1b on MBP induced cytokine expression, mRNA for the Th1 cytokines IFN-γ and TNF-α, the Th2 related IL-4 and IL-6, the cytolytic perforin and the immune response downregulating TGF-β was measured with in situ hybridization after culture of blood mononuclear cells (MNC) in the presence and absence of MBP. Numbers of cells expressing IFN-γ, TNF-α, perforin and IL-4 mRNA were significantly suppressed after culture with 10 U/ml IFN-β1b. No such effect was seen on MBP induced IL-6 or TGF-β mRNA expression. These observations suggest that one of the major effects of IFN-β1b is the induction of a shift in the cytokine mRNA profile towards a more immunosuppressive pattern. In parallel in vitro tests, the control substance dexametasone (40 μg/ml) reduced the numbers of cells expressing mRNA for all cytokines under study with the exception of TGF-β, to an extent equal to or even more pronounced than IFN-β1b.  相似文献   
69.
Summary Histological, ultrastructural and morphometrical observations on Clarke's column were carried out in 18 patients with sporadic amyotrophic lateral sclerosis (ALS) and 15 age-matched control subjects. Of the 18 ALS patients 6 had been on a respirator before death. Bunina bodies were found in the neuronal cytoplasm in 7 of the 12 non-respirator-supported ALS patients and in 3 of the 6 respirator-supported patients. The number of spheroids was significantly higher in the non-respirator-supported patients (P<0.01) than in the control subjects; however, the number in the respirator-supported patients was about equal to that in the controls. The number of neurons in Clarke's column in the non-respirator-supported ALS patients was not reduced, but in the respirator-supported patients they tended to disappear with time after respiratory support. These findings suggest that Clarke's column neurons are also involved primarily in the disease process in sporadic ALS. However, they may begin to disappear only after the patients require respiratory support.Supported in part by a research grant for CNS degenerative diseases from the Ministry of Health and Welfare, Japan  相似文献   
70.
Our aim was to develop an accurate multispectral tissue segmentation method based on 3D feature maps. We utilized proton density (PD), T2-weighted fast spin-echo (FSE), and T1-weighted spin-echo images as inputs for segmentation. Phantom constructs, cadaver brains, an animal brain tumor model and both normal human brains and those from patients with either multiple sclerosis (MS) or primary brain tumors were analyzed with this technique. Initially, misregistration, RF inhomogeneity and image noise problems were addressed. Next, a qualified observer identified samples representing the tissues of interest. Finally, k-nearest neighbor algorithm (k-NN) was utilized to create a stack of color-coded segmented images. The inclusion of T1 based images, as a third input, produced significant improvement in the delineation of tissues. In MS, our 3D technique was found to be far superior to that based on any combination of 2D feature maps (P < 0.001). We identified at least two distinctly different classes of lesions within the same MS plaque, representing different stages of the disease process. Further, we obtained the regional distribution of MS lesion burden and followed its changes over time. Neuropsychological aberrations were the clinical counterpart of the structural changes detected in segmentation. We could also delineate the margins of benign brain tumors. In malignant tumors, up to four abnormal tissues were identified: 1) a solid tumor core, 2) a cystic component, 3) edema in the white matter, and 4) areas of necrosis and hemorrhage. Subsequent neurosurgical exploration confirmed the distribution of tissues as predicted by this analysis.  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