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   100920篇
  免费   10362篇
  国内免费   6679篇
耳鼻咽喉   804篇
儿科学   1669篇
妇产科学   1014篇
基础医学   9601篇
口腔科学   2047篇
临床医学   13318篇
内科学   12448篇
皮肤病学   1066篇
神经病学   3856篇
特种医学   3833篇
外国民族医学   27篇
外科学   9898篇
综合类   20834篇
现状与发展   28篇
一般理论   6篇
预防医学   8572篇
眼科学   2295篇
药学   11148篇
  135篇
中国医学   7969篇
肿瘤学   7393篇
  2025年   28篇
  2024年   1464篇
  2023年   2131篇
  2022年   4330篇
  2021年   5288篇
  2020年   4286篇
  2019年   3081篇
  2018年   3100篇
  2017年   3386篇
  2016年   2998篇
  2015年   4547篇
  2014年   5619篇
  2013年   5916篇
  2012年   8110篇
  2011年   9053篇
  2010年   6725篇
  2009年   5534篇
  2008年   6293篇
  2007年   6038篇
  2006年   5525篇
  2005年   4907篇
  2004年   3451篇
  2003年   3129篇
  2002年   2566篇
  2001年   1983篇
  2000年   1707篇
  1999年   1393篇
  1998年   757篇
  1997年   830篇
  1996年   586篇
  1995年   504篇
  1994年   423篇
  1993年   287篇
  1992年   322篇
  1991年   275篇
  1990年   257篇
  1989年   204篇
  1988年   172篇
  1987年   177篇
  1986年   128篇
  1985年   90篇
  1984年   55篇
  1983年   32篇
  1982年   17篇
  1981年   20篇
  1980年   28篇
  1979年   48篇
  1978年   22篇
  1975年   18篇
  1974年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Fu SL  Ma ZW  Yin L  Iannotti C  Lu PH  Xu XM 《Neuroscience》2005,135(3):851-862
To determine whether neural precursor cells have region-specific growth properties, we compared the proliferation, mitogenicity, and differentiation of these cells isolated from the embryonic day 16 rat forebrain and spinal cord. Neural precursor cells isolated from both regions were cultured in growth medium supplemented with epidermal growth factor, basic fibroblast growth factor, or epidermal growth factor+basic fibroblast growth factor. Under all three conditions, both neural precursor cell populations proliferated for multiple passages. While spinal cord-derived neural precursor cells proliferated moderately faster in epidermal growth factor-enriched growth medium, brain-derived cells proliferated much faster in basic fibroblast growth factor-enriched growth medium. When exposed to both epidermal growth factor and basic fibroblast growth factor, the two neural precursor cell populations expanded and proliferated more rapidly than when exposed to a single factor, with brain-derived neural precursor cells expanding significantly faster than spinal cord-derived ones (P<0.0001). Differentiation studies showed that both neural precursor cell populations were multi-potent giving rise to neurons, astrocytes, and oligodendrocytes. However, neuronal differentiation from brain-derived neural precursor cells was greater than spinal cord-derived ones (11.95+/-5.00% vs 1.92+/-1.13%; passage 2). Further, the two neural precursor cell populations differentiated into a similar percentage of oligodendrocytes (brain: 8.66+/-5.85%; spinal cord: 7.69+/-3.91%; passage 2). Immunofluorescence and Western blot studies showed that neural precursor cells derived from both regions expressed receptors for basic fibroblast growth factor and epidermal growth factor. However, brain-derived neural precursor cells expressed higher levels of the two receptors than spinal cord-derived ones in growth medium containing epidermal growth factor+basic fibroblast growth factor. Thus, our results showed that neural precursor cells isolated from the two regions of the CNS have distinct properties and growth requirements. Identifying phenotypic differences between these neural precursor cell populations and their growth requirements should provide new insights into the development of cell therapies for region-specific neurological degenerative diseases.  相似文献   
62.
On December 31, 2001, 2486 patients with terminal renal failure received dialysis treatment in Croatia. Only one third of the patients are registered on the national waiting list for cadaveric kidney transplant. In most of the others, transplantation is impossible because of comorbidity. This is mainly due to the steadily growing age of the dialytic population and therefore a higher incidence of cardiovascular disease and diabetes. Still, evaluation of the potential recipients of cadaveric kidney transplant, registered on the waiting list, often reveals contraindications for transplantation. The aim of this study was to determine the incidence and type of contraindications in transplant candidates, found during immediate preoperative evaluation. Analysis of these data should help in determining how contraindications can be early detected and prevented. Before registering onto the national waiting list transplant candidates need to be thoroughly investigated including detailed history, physical examination, routine diagnostic procedures and additional examinations, if needed, to exclude or evaluate the possibly existing contraindications for transplantation. During the period from January 1997 until June 2002, 145 potential recipients from the national waiting list were referred to the Rijeka University Hospital Center and evaluated for kidney transplantation. Eighty-eight patients underwent transplantation. Preoperative evaluation revealed contraindications for transplantation in 52 (35.9%) candidates. Twenty-two (15.2%) patients had a positive cross-match with donor lymphocytes, 6 (4.1%) patients refused transplantation, and in 24 (16.6%) patients serious comorbidity was the reason for not being accepted for transplantation and for their withdrawal from the national waiting list. Comorbidity was mainly due to cardiovascular disease (12 patients--8.3%) and infection (8 patients--5.5%). These data show a high incidence of contraindications found during the immediate preoperative evaluation of potential kidney recipients. It was the case in more than one third of patients. During the evaluation of potential candidates for kidney transplantation special attention should be addressed to the presence of cardiovascular morbidity and infection. Peripheral vascular occlusive disease, cardiac status and/or cerebrovascular disease should be evaluated. Measures used to treat or reduce the development of complications include an optimal control of blood pressure, serum phosphate, hyperparathyroidism, dyslipidemia, and renal anemia. The sites of infection must be treated and eradicated, because immunosuppressive treatment is a threat to the transplant recipient's life. The second most common cause of refusal of potential candidates was a positive cross-match with donor lymphocytes. Sensitization to human leukocyte antigens can be prevented by the avoiding of blood transfusions and use of erythopoietin in treating renal anemia. To minimize the morbidity and mortality, the potential kidney recipients should undergo rigorous selection and thorough evaluation before including them into the waiting list for kidney transplantation. Afterwards, regular examinations are obligatory to reveal contraindications, proceed to medical interventions and treat concomitant diseases in time, which can influence the patient's survival. In case that contraindications for transplantation arise, the patient must be temporarily or definitely removed from the waiting list.  相似文献   
63.
64.
LJM, a 41-year-old schizophrenic Chinese man with bilateral anterior cingulate gyrus (Brodmann's area 24) lesions and also a small lesion in right amygdala after an operation, was compared with normal as well as brain-damaged and schizophrenic controls in identification of morphed facial expressions of six basic emotions. In repeated administrations of the test for recognition of facial emotions, over a 1- year period, LJM performed significantly worse for expressions of fear compared with the three groups of controls. Recognition of other emotions was not significantly different from that of the controls, except that his recognition of disgust during the first session (but not in two subsequent sessions) was worse than normal and brain-damaged controls but not worse than schizophrenic controls. The dissociation between recognition of fear and other emotions supported the view that the brain has separable networks for processing different emotions, and that the right amygdala as well as the anterior part of bilateral cingulate gyrus are possible substrates involved in the special network for perception of fear. The results from the various groups of Chinese subjects indicate that they perceive emotions in a categorical manner, and that the six basic emotions are likely to be cross-cultural universals.  相似文献   
65.
Endothelial precursor cells (EPCs) cultured from adult bone marrow (BM) have been shown to mediate neovasculogenesis in murine models of vascular injury. We sought to directly compare umbilical cord blood (UCB)- and BM-derived EPC surface phenotypes and in vivo functional capacity. UCB and BM EPCs derived from mononuclear cells (MNC) were phenotyped by surface staining for expression of stromal (Stro-1, CXCR4, CD105, and CD73), endothelial (CD31, CD146, and vascular endothelial [VE]-cadherin), stem cell (CD34 and CD133), and monocyte (CD14) surface markers and analyzed by flow cytometry. The nonobese diabetic/severe combined immunodeficiency murine model of hind-limb ischemia was used to analyze the potential of MNCs and culture-derived EPCs from UCB and BM to mediate neovasculogenesis. Histologic evaluation of the in vivo studies included capillary density as a measure of neovascularization. Surface CXCR4 expression was notably higher on UCB-derived EPCs (64.29%+/-7.41%) compared with BM (19.69%+/-5.49%; P=.021). Although the 2 sources of EPCs were comparable in expression of endothelial and monocyte markers, BM-derived EPCs contained higher proportions of cells expressing stromal cell markers (CD105 and CD73). Injection of UCB- or BM-derived EPCs resulted in significantly improved perfusion as measured by laser Doppler imaging at days 7 and 14 after femoral artery ligation in nonobese diabetic/severe combined immunodeficiency mice compared with controls (P<.05). Injection of uncultured MNCs from BM or UCB showed no significant difference from control mice (P=.119; P=.177). Tissue samples harvested from the lower calf muscle at day 28 demonstrated increased capillary densities in mice receiving BM- or UCB-derived EPCs. In conclusion, we found that UCB and BM-derived EPCs differ in CXCR4 expression and stromal surface markers but mediate equivalent neovasculogenesis in vivo as measured by Doppler flow and histologic analyses.  相似文献   
66.
为探讨细胞外间质主要成分透明质酸(HA)与层粘连蛋白(LN)在缺血性股骨头坏死(INFH)中的生理病理过程及临床价值,采用放射免疫分析法对45例不同病因的INFH患者进行了血清HA与LN的定量分析,并与30例正常人对照。结果显示,INFH患者血清HA含量极显著地高于对照组(t=3-29;P<0-01)。尤以激素性INFN增高最为显著(t=3-62;P<0-01)。INFH患者LN含量亦明显高于对照组(t=2-84;P<0-01)。同时,HA与LN含量增高与病程发展密切相关。故定量检测HA与LN可作为INFH早期诊断及判断预后的良好指标  相似文献   
67.
Evaluation of endothelial cell migration with a novel in vitro assay system   总被引:1,自引:0,他引:1  
In this study we introduce a novel in vitro 'oil-drop' assay system for the measurement of endothelial cell (EC) migration, based on the original concept of the Teflon fence assay (Pratt et al., 1984; Am. J. Pathol. 117: 349–354). An aliquot of 15–20,000 human umbilical vein EC (HUVEC) is pipetted through a layer of mineral oil. The cells readily attach, spread and migrate on the surface of a matrix-coated tissue culture dish as a confluent circular monolayer. Migration is measured as the net increase in the total area covered at 24 hours. We have used this system to quantify EC migration on matrices composed of a mixture of type I collagen and either von Willebrand factor (vWF) or fibronectin (FN) in the presence or absence of tumor necrosis factor (TNF). Plating efficiency on both vWF/collagen and FN/collagen, measured by counting cells after attachment and spreading, is about 80%. With this method, migration on vWF/collagen was about 6.4 mm2 and 5.3 mm2 for TNF-treated and untreated HUVEC, respectively. HUVEC migration on FN/collagen was slightly greater – 6.4 mm2 and 6.5 mm2 with and without TNF treatment, respectively. During the 24 hour time period, HUVEC numbers increased 30–40% on vWF/collagen, and 60–80% on FN/collagen, with increased proliferation observed with TNF- treatment. EC proliferation could be completely inhibited by 2 mM hydroxyurea. This assay system has proven useful in our studies to quantify cell migration and proliferation.  相似文献   
68.
Wang ZH  Liao YH  Fu M 《Autoimmunity》2001,34(4):241-245
The aim of this study was to examine the frequency of occurrence of autoantibodies against beta1-adrenoceptors in patients with hepatitis virus myocarditis (HVM) and its possible correlation with clinical characteristics. A total of 103 patients with viral myocarditis were divided into a positive group (HVM group, n=29) and a negative group (Non-HVM group, n=74) according to the laboratory findings regarding their type of hepatitis virus. The study parameters included UCG, ECG, biochemical findings and screening of autoantibodies against beta1-adrenoceptor. It was shown that the positive rate of the hepatitis virus was 28.16% (29/103) in patients with viral myocarditis. The severity of myocardial or liver injuries and the frequency of occurrence of autoantibodies against beta1-adrenoceptors in patients with viral myocarditis were more pronounced, before treatment, in the HVM group than in the Non-HVM group. The positive rates of the antibodies against the hepatitis virus and the autoantibodies against beta1-adrenoceptors were highly consistent in patients with HVM (p<0.05). In conclusion, the frequency of occurrence of the autoantibodies against beta1-adrenoceptors may be one important marker of HVM and, thus, possibly involved in the pathogenesis of the HVM.  相似文献   
69.
Intending to clarify the true Incidence of Invasive lobular carcinoma of the breast In Japanese women as well as the frequency of unilateral multlcentriclty, 362 cases of clinically defined monocentrlc breast cancer without pre-operative biopsy (previously fine needle aspiration or needle biopsy were routinely carried out for every case) were examined by whole mammary gland serial sectioning. On the basis of pathology and the World Health Organization classification of breast tumors, each case was assigned to one of two main histologlc types: Invasive lobular carcinoma (ILC) or Invasive ductal carcinoma (IDC). Invasive lobular carcinoma was further separated into classic and variant types by employing previously published criteria. Twenty-one cases of ILC (5.8%) were diagnosed, which Is more than In most previous Japanese studies. Unilateral multicentric breast carcinoma was detected In 9.5% of ILC and 16.1% of IDC (the difference was found not significant). Microscopically, ILC tumors were found to be, on average, larger than IDC. Patients with classic type ILC tended to be younger than those with variant type or IDC. Estrogen receptor expression was found more frequently In variant type ILC than in classic type. These results suggest that the incidence of invasive lobular carcinoma of the breast In Japanese women is low and that unilateral multicentricity Is not significantly higher in ILC than in IDC.  相似文献   
70.
胃动素对血管灌流大鼠离体胃运动的作用   总被引:8,自引:1,他引:8  
通过血管灌流大鼠离体胃,探讨胃动素对胃运动的影响。结果表明:(1)胃动素可以明显地兴奋胃窦自发的胃运动;(2)胃动素抗血清可以完全消除胃动素兴奋胃窦运动的作用;(3)阿托品可以阻断胃动素兴奋胃窦运动的作用。上述结果提示,胃动素可特异性兴奋血管灌流大鼠胃窦收缩运动,该作用通过壁内胆碱能神经介导。  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