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   17896篇
  免费   979篇
  国内免费   76篇
耳鼻咽喉   134篇
儿科学   420篇
妇产科学   257篇
基础医学   2242篇
口腔科学   470篇
临床医学   1250篇
内科学   4318篇
皮肤病学   860篇
神经病学   1293篇
特种医学   435篇
外科学   3182篇
综合类   68篇
一般理论   1篇
预防医学   480篇
眼科学   487篇
药学   1148篇
中国医学   46篇
肿瘤学   1860篇
  2023年   73篇
  2022年   188篇
  2021年   313篇
  2020年   171篇
  2019年   234篇
  2018年   321篇
  2017年   273篇
  2016年   327篇
  2015年   303篇
  2014年   430篇
  2013年   478篇
  2012年   750篇
  2011年   775篇
  2010年   544篇
  2009年   440篇
  2008年   748篇
  2007年   809篇
  2006年   880篇
  2005年   904篇
  2004年   821篇
  2003年   811篇
  2002年   799篇
  2001年   680篇
  2000年   686篇
  1999年   646篇
  1998年   206篇
  1997年   149篇
  1996年   171篇
  1995年   138篇
  1994年   98篇
  1993年   113篇
  1992年   420篇
  1991年   361篇
  1990年   385篇
  1989年   402篇
  1988年   362篇
  1987年   326篇
  1986年   325篇
  1985年   275篇
  1984年   217篇
  1983年   163篇
  1982年   70篇
  1979年   147篇
  1978年   103篇
  1977年   106篇
  1974年   105篇
  1973年   82篇
  1972年   95篇
  1971年   84篇
  1970年   87篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper examines a case of pleomorphic primitive neuroectodermal tumor (PNET) with glial and neuronal differentiation in a 7-year-old girl who was clinicopathologically reported with immunohistochemical and chromosomal analysis. Clinically, a highly aggressive behavior leading to early recurrence with cerebrospinal fluid seedings was characteristic despite total removal and chemoradiation therapy. Pathologically, severe pleomorphism was noted and large ganglioid cells were predominant.Immunohistochemically, the expression of low-molecular neurofilament was recognized in the surgical specimens and increased in the recurrence. Coexpression of vimentin and neurofilament/GFAP was recognized in the culture. Chromosomal analysis showed near-diploidy, but different karyotype from that PNETs previously reported. These findings suggested that PNETs with pleomorphism and differentiation into both glial and neuronal lineages may show aggressiveness and require more aggressive therapy.  相似文献   
992.
BACKGROUND: Hypoxia is important in cancer progression, and at the stage of detachment of the cancer cells from the primary lesion. This study was undertaken to analyze the effect of hypoxia on angiogenesis and cell proliferation in ovarian cancer. MATERIALS AND METHODS: We first used immunohistochemistry to examine the expression of VEGF in 42 cases of ovarian carcinoma, with relevance to the p53 expression. Then, the expression of VEGF, HIF-1 alpha, cell cycle-related molecules and cell numbers were examined in 4 ovarian cancer cell lines with various p53 gene status. RESULTS: Immunohistochemistry showed that there was no significant correlation between VEGF and p53 expression. Moreover, hypoxia increased the expression of VEGF via up-regulation of HIF-1 alpha irrespective of p53 gene status. However hypoxia did not change the cell numbers, but influenced the expression of cell cycle-related molecules (increased p27 and decreased cyclin D1 and Rb). CONCLUSION: Hypoxia increased VEGF expression in ovarian cancer cells irrespective of p53 gene status.  相似文献   
993.
994.
Bcl-2 family of proteins regulates apoptosis by controlling mitochondrial membrane permeability. We have previously shown that the voltage-dependent anion channel (VDAC) plays a crucial role in apoptotic changes of the mitochondria and its activity is directly regulated by some Bcl-2 family members, including Bcl-2/Bcl-x(L) and Bax/Bak but not Bid. Here, we showed that in isolated mitochondria, Bim induced loss of membrane potential and cytochrome c release like Bax/Bak, with these changes being inhibited by an anti-VDAC antibody. In addition, microinjection of the anti-VDAC antibody significantly reduced Bim-induced apoptosis. Study using purified proteins indicated that Bim directly interacts with the VDAC. Immunoprecipitation analysis revealed that Bim interacts with the VDAC and the interaction is remarkably enhanced during apoptosis. An experiment using liposomes indicated that Bim enhanced VDAC activity, as did Bax/Bak. Furthermore, Bim (but not tBid) was able to induce apoptotic changes of yeast mitochondria in a VDAC-dependent manner, and also induced the lysis of red blood cells, with this effect being inhibited by the anti-VDAC antibody. These results indicate that Bim has an ability to activate directly the VDAC, which plays an important role in apoptosis of mammalian cells.  相似文献   
995.
996.
 Intravenous digital subtraction angiography (IV-DSA) was performed before and after neoadjuvant chemotherapy (NACT) in five patients with locally advanced breast cancer, and the efficacy of NACT was evaluated on the basis of the results of IV-DSA and histopathological examination. Following NACT, the maximum density of tumor enhancement (MAX) in the IV-DSA image decreased by 61.6% in case 1, 50% in case 2, 58.1% in case 3, 90.8% in case 4, and 97.2% in case 5. In all five patients, the efficacy of chemotherapy was rated as a partial response in terms of tumor size, while histological efficacy was rated as slightly effective in cases 1–4 and moderately effective in case 5. The pathological efficacy of NACT was highest in case 5, which showed the greatest decrease in MAX. These results indicate that variations in MAX reflect clinical efficacy, and, to some extent, also permit prediction of pathological efficacy. Received: March 4, 2002 / Accepted: June 10, 2002 Correspondence to:O. Watanabe  相似文献   
997.
Induction of vasculogenesis in breast cancer models   总被引:4,自引:0,他引:4  
Recently, there have been reports of postnatal vasculogenesis in cases of ischaemia models. The aim of the present study is to provide evidence of postnatal vasculogenesis in breast-cancer-bearing mice. Based on cell surface antigen expression, we isolated endothelial precursor cells from bone marrow, peripheral blood and tumour-infiltrating cells from mice that had received six human breast cancer xenografts. In all three areas (bone marrow, peripheral blood and tumour-infiltrating cells), endothelial precursor cell population was elevated in all transplanted mice. Differentiation and migration activities of endothelial precursor cells were measured by comparing levels of the endothelial precursor cell maturation markers Flk-1, Flt-1, Tie2, VE-cadherin and CD31 among these three areas. The endothelial precursor cell population was 14% or greater in the gated lymphocyte-size fraction of the inflammatory breast cancer xenograft named WIBC-9, which exhibits a hypervascular structure and de novo formation of vascular channels, namely vasculogenic mimicry (Shirakawa et al, 2001). In vitro, bone marrow-derived endothelial precursor cells from four human breast cancer xenografts proliferated and formed multiple clusters of spindle-shaped attaching cells on a vitronectin-coated dish. The attaching cells, which incorporated DiI-labelled acetylated low-density lipoprotein (DiI-acLDL) and were negative for Mac-1. The putative bone marrow derived endothelial precursor cell subset, which was double positive of CD34 and Flk-1, and comparative bone marrow derived CD34 positive with Flk-1 negative subset were cultured. The former subset incorporated DiI-acLDL and were integrated with HUVECs. Furthermore, they demonstrated significantly higher levels of murine vascular endothelial growth factor and interleukin-8 in culture supernatant on time course by enzyme-linked immunosorbent assay. These findings constitute direct evidence that breast cancer induces postnatal vasculogenesis in vivo.  相似文献   
998.
BACKGROUND: Numerous reports have examined the relationship between hepatocyte growth factor (HGF) and either the facilitation or suppression of the occurrence of hepatocellular carcinoma (HCC). METHODS: In this study, we measured serum HGF concentrations of blood samples and conducted prospective studies to examine the long-term outcome of C-viral chronic hepatitis (CH) and cirrhosis in patients. The subjects examined in this study include 99 patients with C-viral CH, cirrhosis, and HCC. The serum HGF level was measured in blood samples within 48 hours of collection using enzyme-linked immunosorbent assay kits. RESULTS: The serum concentrations of HGF were significantly higher in patients with HCC than in patients with CH or cirrhosis. The detection rate of HGF and its mean serum level were significantly higher in patients with a low platelet count than in patients with a high platelet count. All of the patients with serum HGF concentrations of more than 0.6 ng/mL had HCC, irrespective of the levels of alpha-fetoprotein, vitamin K absence, or antagonist-II in the blood. Serum HGF concentrations increased concomitantly with increases in areas occupied by HCC. The cumulative incidence of occurrence of HCC was significantly higher in patients with high HGF concentrations than in patients with low HGF concentrations. Multivariate analysis revealed that the elevation in serum HGF level is the most important risk factor for the occurrence of HCC. CONCLUSIONS: The serum level of HGF represents the degree of the carcinogenic state in the liver of patients with C-viral CH and cirrhosis. Therefore, the determination of serum HGF concentrations may be useful as a third tumor marker of HCC in detection as well as follow-up therapy.  相似文献   
999.
BACKGROUND: beta-Catenin has been shown to function as a Wnt signaling molecule to stimulate cyclin D1 expression and cell growth in several kinds of tumors. METHODS: The authors immunohistochemically examined specimens of 217 surgically resected primary nonsmall cell lung carcinomas (NSCLCs) for beta-catenin expression and classified them semiquantitatively into three categories, including those with high, moderate, and low scores of expression. RESULTS: High, moderate, and low scores of expression were found in 37 (17.1%), 145 (66.8%), and 35 (16.1%) tumors, respectively. beta-Catenin expression was not correlated with cyclin D1 expression, but was positively correlated with the Ki-67 cell growth fraction (P = 0.04). The direct sequencing analysis for the beta-catenin gene mutation of 13 specimens of 217 tumors for the current study revealed no mutations. The relation between survival and beta-catenin expression was evaluated in 148 potentially curatively resected tumors with pathologic Stages I-IIIA. A trend toward better survival was found in patients with tumors having higher scores. In multivariate analysis, high beta-catenin expression was a significant and independent favorable prognostic factor (hazards ratio, 0.31; P = 0.007) as was pathologic stage. Analyzed by cell type, in nonsquamous cell carcinomas, patients with tumors having high scores survived a significantly longer time than those with tumors having moderate or low scores (5-year survival rates, 84%, 55%, and 32%, respectively; P = 0.02), and high beta-catenin expression tended to be a favorable prognostic factor (hazards ratio, 0.32; P = 0.052). CONCLUSIONS: These results indicate that, in NSCLCs, increased expression of beta-catenin can predict favorable prognosis of patients with resected tumors, suggesting that accumulation of beta-catenin has no or little oncogenic effect via activation of the Wnt pathway, unlike in colon carcinomas or hepatomas.  相似文献   
1000.
To quantify three-dimensional (3D) movement of the prostate gland with the patient in the supine and prone positions and to analyze the movement frequency for each treatment position.

The real-time tumor-tracking radiotherapy (RTRT) system was developed to identify the 3D position of a 2-mm gold marker implanted in the prostate 30 times/s using two sets of fluoroscopic images. The linear accelerator was triggered to irradiate the tumor only when the gold marker was located within the region of the planned coordinates relative to the isocenter. Ten patients with prostate cancer treated with RTRT were the subjects of this study. The coordinates of the gold marker were recorded every 0.033 s during RTRT in the supine treatment position for 2 min. The patient was then moved to the prone position, and the marker was tracked for 2 min to acquire data regarding movement in this position. Measurements were taken 5 times for each patient (once a week); a total of 50 sets for the 10 patients was analyzed. The raw data from the RTRT system were filtered to reduce system noise, and the amplitude of movement was then calculated. The discrete Fourier transform of the unfiltered data was performed for the frequency analysis of prostate movement.

No apparent difference in movement was found among individuals. The amplitude of 3D movement was 0.1–2.7 mm in the supine and 0.4–24 mm in the prone positions. The amplitude in the supine position was statistically smaller in all directions than that in the prone position (p < 0.0001). The amplitude in the craniocaudal and AP directions was larger than in the left-right direction in the prone position (p < 0.0001). No characteristic movement frequency was detected in the supine position. The respiratory frequency was detected for all patients regarding movement in the craniocaudal and AP directions in the prone position. The results of the frequency analysis suggest that prostate movement is affected by the respiratory cycle and is influenced by bowel movement in the prone position.

The results of this study have confirmed that internal organ motion is less frequent in the supine position than in the prone position in the treatment of prostate cancer. RTRT would be useful in reducing uncertainty due to the effects of the respiratory cycle, especially in the prone position.  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