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   5393篇
  免费   273篇
  国内免费   36篇
耳鼻咽喉   14篇
儿科学   181篇
妇产科学   169篇
基础医学   782篇
口腔科学   131篇
临床医学   380篇
内科学   1211篇
皮肤病学   62篇
神经病学   612篇
特种医学   282篇
外国民族医学   10篇
外科学   537篇
综合类   25篇
预防医学   333篇
眼科学   41篇
药学   328篇
中国医学   25篇
肿瘤学   579篇
  2023年   43篇
  2022年   123篇
  2021年   186篇
  2020年   121篇
  2019年   125篇
  2018年   140篇
  2017年   108篇
  2016年   138篇
  2015年   136篇
  2014年   199篇
  2013年   237篇
  2012年   381篇
  2011年   390篇
  2010年   210篇
  2009年   211篇
  2008年   299篇
  2007年   307篇
  2006年   320篇
  2005年   255篇
  2004年   181篇
  2003年   226篇
  2002年   204篇
  2001年   108篇
  2000年   105篇
  1999年   105篇
  1998年   45篇
  1997年   30篇
  1996年   31篇
  1995年   37篇
  1994年   23篇
  1993年   24篇
  1992年   74篇
  1991年   52篇
  1990年   72篇
  1989年   44篇
  1988年   44篇
  1987年   42篇
  1986年   33篇
  1985年   33篇
  1984年   33篇
  1983年   18篇
  1982年   12篇
  1981年   13篇
  1980年   16篇
  1979年   23篇
  1978年   13篇
  1977年   13篇
  1976年   17篇
  1975年   17篇
  1972年   15篇
排序方式: 共有5702条查询结果,搜索用时 27 毫秒
11.
Between March 1976 and June 1985, 1,000 consecutive adults with asymptomatic gross or microscopic hematuria in the absence of proteinuria were evaluated urologically. Lesions that could account for the hematuria were detected in 88.3 per cent of the patients. Life-threatening lesions were diagnosed in 9.1 per cent of the patients, while lesions requiring at least observation were present in 22.8 per cent. The incidence of life-threatening lesions increased with age, with a sharp increase after age 50 years. Life-threatening lesions were more common in men (13.6 per cent) than in women (4.9 per cent). In general, as the degree of hematuria increased so did the yield of life-threatening lesions; however, there was no "safe" lower limit of hematuria. Of the patients with life-threatening lesions 18.6 per cent had at least 1 urinalysis with less than 3 red blood cells per high power field within 6 months of the diagnosis. The direct medical cost of a hematuria evaluation was $777. The difference in direct medical costs to diagnose and treat localized versus metastatic genitourinary cancer was $48,070 in 3 matched pairs of patients. In this study group 77 of 84 patients (92 per cent) diagnosed with genitourinary cancer had localized disease. A hematuria evaluation was cost-effective for all groups studied. A literature-based estimate of the life-threatening risks of diagnostic studies applied to the study data resulted in a 1.1 per cent life-threatening risk per hematuria evaluation. For all categories studied, except for women less than 40 years old with microscopic hematuria, the risk of a hematuria evaluation was less than the incidence of life-threatening lesions discovered as a result of the evaluation. Asymptomatic hematuria, whether gross or microscopic, is a significant finding and warrants evaluation from a risk-benefit and cost-effectiveness standpoint.  相似文献   
12.
13.
14.
15.
Exercise induces free oxygen radicals that cause oxidative stress, and metallothioneins (MTs) are increased in states of oxidative stress and possess anti-apoptotic effects. We therefore studied expression of the antioxidant factors metallothionein I and II (MT-I + II) in muscle biopsies obtained in response to 3 h of bicycle exercise performed by healthy men and in resting controls. Both MT-I + II proteins and MT-II mRNA expression increased significantly in both type I and II muscle fibres after exercise. Moreover, 24 h after exercise the levels of MT-II mRNA and MT-I + II proteins were still highly increased and the MT-II mRNA expression reached a 15-fold increase. As expected, immunohistochemical detection of malondialdehyde (MDA) and nitrotyrosine (NITT) showed that formation of free radicals and oxidative stress were clearly increased in exercising muscle peaking shortly after the end of exercise in both type I and II muscle fibres. This is the first report demonstrating that MT-I + II are significantly induced in human skeletal muscle fibres following exercise. As MT-I + II are antioxidant factors that protect various tissues during pathological conditions, the MT-I + II increases post exercise may represent a mechanism whereby contracting muscle fibres are protected against cellular stress and injury.  相似文献   
16.
In the normal, healthy lung, elastin production is restricted to periods of development and growth. However, elastin expression in the adult lung has been observed in some forms of pulmonary injury, including pulmonary fibrosis. Here, we report that elastin production is significantly increased within precise interstitial compartments of the lung in an experimental model of granulomatous lung disease. An increase in the number and volume of elastic fibers within the alveolar walls was apparent on histological examination of Verhoeff-van Gieson-stained sections of silicotic rat lungs. Quantitation of mature elastin cross-links indicated that silicosis was accompanied by a 17-fold increase in lung elastin content when compared with values from saline-treated controls. In situ hybridization for tropoelastin mRNA revealed that elastin production was absent from granulomatous lesions yet was prominent at nonfibrotic alveolar septal tips, where a high density of elastic fibers is seen in the normal lung. Immunohistochemistry indicated tropoelastin was being expressed by alpha-smooth muscle actin-containing cells. Transforming growth factor-beta was immunolocalized to granulomatous regions of the silicotic lung but was absent from regions showing increased tropoelastin expression. These data indicate that the reinitiation of tropoelastin gene expression is associated with granulomatous lung disease, and this expression leads to the aberrant accumulation of mature elastin in the lung.  相似文献   
17.
Over the past decade extracorporeal shock-wave therapy (ESWT) has been increasingly applied to orthopaedic and musculoskeletal pathologies, the aim of this study was to assess how the energy density of the shock waves and the number of impulses affect viability, differentiation and synthetic activity of osteoblasts. Primary sheep osteoblasts cultures were treated with ESWT with an electro-hydraulic shock wave generator by selecting three different energy levels (14-21-28 kV corresponding at 0.15-0.31-0.40 mJ/mm2) and two different total numbers of impulses (500, 1000) for each level. At the end of treatment, cell counts and viability were recorded. Cells were then cultivated for 48 hours starting from a concentration of 1 x 10(4) cells/ml. The biological activity and viability were evaluated at 24 and 48 hours after treatment. No cytodestructive effects were observed in Group A, while a cytodestructive effect of ESWT was seen in cultures receiving the highest energy treatments. The different shock wave treatment induced differences in MTT assays after 24 and 48 hours, in particular the highest level showed a detrimental effect on cell respiration at both experimental times as compared to the Control Group and the protein metabolism was generally depressed by ESWT with impulses at the highest energy level. After 24 hours such effect further increased with the growing number of impulses. The lowest energy level appeared to significantly improve the metabolic parameter in primary cell cultures as compared to controls when 500 impulses were selected. The current study has demonstrated that one of the most important aspects to be considered is not the total number of impulses used but the energy level of the shock waves, thus confirming that ESWT has a dose-dependent effect on cells.  相似文献   
18.
Natural killer (NK) cell function is largely modulated by growth factors and cytokines. In particular, interleukin (IL)-2, IL-12, and IL-15 have major effects on the proliferative and cytotoxic activities of NK cells against tumor and virus-infected cells. It is thought that the members of the protein kinase C (PKC) family of serine/threonine kinases play an important role in mediating the pleiotropic effects of cytokines on their target cells. We have investigated the downstream effects generated in purified human NK cells by IL-2, IL-12, and IL-15 on PKCalpha and PKCepsilon--a canonical and a novel isoform of PKC, respectively. By means of Western blotting, PKC activity assays, and immunofluorescence performed on highly purified preparations of primary human NK cells, we demonstrate that: 1) the three cytokines have similar effects on PKCalpha and PKCepsilon activities; 2) whereas PKCepsilon activity is induced by cytokine stimulation, PKCalpha activity is inhibited; and 3) both the induction of PKCepsilon and the inhibition of PKCalpha functional activity are relatively early events in NK cells, while longer cytokine stimulations do not generate significant variations in enzyme activity, suggesting that the activation of both the canonical and novel isoforms of PKC are events required in the early phases of cytokine-induced NK cell stimulation.  相似文献   
19.
Several studies indicate that cyclooxygenase-2 (COX-2) is overexpressed in human malignancies, where it produces high levels of prostaglandins and contributes to tumor growth. In this study we have analyzed the expression of COX-2 in a series of 48 skeletal osteosarcomas of different subtypes by immunohistochemistry. In addition, we examined the effects of the specific COX-2 inhibitor Celecoxib on the growth of the human osteosarcoma cell line SaOS-2. Immunoreactivity for COX-2 was observed in 39 out of 48 tumors (81.2%), 30 (76.9%) of which showed a moderate or diffuse immunostaining. Considering the group of 42 primary osteosarcomas, COX-2 immunoreactivity was significantly higher in high grade osteosarcomas, where moderate or diffuse expression was detected in 23 out of 32 cases (71.8%), than in low grade osteosarcomas, where moderate or diffuse expression was detected in 2 out of 10 cases (20%) (P = 0.008, Fisher exact test). In addition, low COX-2 expression was always associated with a good response to chemotherapy (5 out of 5 cases), whereas moderate or diffuse COX-2 expression was associated with a good response in 11 out of 20 cases (55%) (P = 0.12, Fisher exact test). In SaOS-2 osteosarcoma cells, which express COX-2, treatment with Celecoxib determined inhibition of cell proliferation and induction of apoptosis. These results indicate that COX-2 is expressed at high levels in high grade osteosarcomas and support the use of COX-2 inhibitors to improve both the tumor response to chemotherapy and the outcome of osteosarcoma patients.  相似文献   
20.
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