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   15230篇
  免费   919篇
  国内免费   92篇
耳鼻咽喉   90篇
儿科学   427篇
妇产科学   359篇
基础医学   2494篇
口腔科学   276篇
临床医学   1344篇
内科学   3729篇
皮肤病学   212篇
神经病学   1938篇
特种医学   338篇
外科学   1283篇
综合类   35篇
一般理论   4篇
预防医学   773篇
眼科学   129篇
药学   1193篇
中国医学   30篇
肿瘤学   1587篇
  2024年   11篇
  2023年   117篇
  2022年   285篇
  2021年   462篇
  2020年   284篇
  2019年   378篇
  2018年   418篇
  2017年   368篇
  2016年   400篇
  2015年   496篇
  2014年   611篇
  2013年   729篇
  2012年   1215篇
  2011年   1217篇
  2010年   711篇
  2009年   627篇
  2008年   1048篇
  2007年   1043篇
  2006年   1011篇
  2005年   936篇
  2004年   884篇
  2003年   860篇
  2002年   758篇
  2001年   96篇
  2000年   86篇
  1999年   130篇
  1998年   151篇
  1997年   111篇
  1996年   100篇
  1995年   101篇
  1994年   74篇
  1993年   72篇
  1992年   56篇
  1991年   43篇
  1990年   38篇
  1989年   51篇
  1988年   25篇
  1987年   20篇
  1986年   30篇
  1985年   22篇
  1984年   32篇
  1983年   23篇
  1982年   19篇
  1981年   17篇
  1980年   14篇
  1979年   8篇
  1977年   8篇
  1976年   7篇
  1974年   5篇
  1963年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Well-differentiated thyroid neoplasms may be included among the most frequently occurring thyroid carcinomas. Papillary ca. is without doubt the best behaved type. The aim of the present work is to perform a retrospective case history study to assess patients with con papillary ca. who have been treated surgically over the last 17 years and have been subjected to periodic checks. A sample of patients was therefore extrapolated who had all undergone total thyroidectomy for papillary ca. of the thyroid. The incidence of local recurrence of the disease was verified, together with the results at distance. Furthermore, the assessments performed were evaluated and compared. From the sample of patients observed we inferred that papillary carcinoma of the thyroid can have a good prognosis over time provided periodic random checks are carried out.  相似文献   
992.
Gambaccini M  Baldelli P 《La Radiologia medica》2003,106(5-6):454-64; quiz 465-6
Mammography is currently considered the best tool for the detection of breast cancer, pathology with a rate of incidence in constant increase. To produce the radiological picture a screen film combination is conventionally used. One of the inherent limitations of screen- film combination is the fact that the detection, display and storage processes are one and the same, making it impossible to separately optimize each stage. These limitations can be overcome with digital systems. In this work we evaluate the main characteristics of digital detectors available on the market and we compare the performance of digital and conventional systems. Digital mammography, due to the possibility to process images, offers many potential advantages, among these the possibility to introduce the dual-energy technique which employs the composition of two digital images obtained with two different energies to enhance the inherent contrast of pathologies by removing the uniform background. This technique was previously tested by using synchrotron monochromatic beam and a digital detector, and then the Senographe 2000D full-field digital system manufactured by GE Medical Systems. In this work we present preliminary results and the future applications of this technique.  相似文献   
993.
PURPOSE: To assess the role of magnetic resonance enteroclysis (MRE) in patients with Crohn's disease, in order to identify involved segments, define the extension and evaluate transmural alterations. MATERIALS AND METHODS: Eighteen patients with known Crohn's disease were studied with MR (1.5 T), with breath-hold T2-weighted TSE, T2-weighted TSE SPIR and 3D T1-weighted sequences before and after gadolinium injection (0.2 mmol/kg) in the coronal and axial planes. The small bowel was distended by the administration of 2 l of methylcellulose through a nasojejunal tube and drug induced hypotony. Typical patterns of Crohn's disease, such as mucosal abnormalities, parietal thickening and narrowing of the bowel, prestenotic dilation, fibrofatty proliferation and enlarged lymph nodes were analysed on radiological and MRE images. MRE was performed within 30 days from conventional radiological studies (conventional enteroclysis and small bowel follow-through). RESULTS: Good distension of the bowel wall was obtained in all cases. MRE assessed the presence of parietal thickening and narrowing of the bowel wall (14/18 cases) and the presence of prestenotic dilatation (12/18 cases). Vascular enhancement (14/18 cases), transmural abnormalities (8/18 cases), fibrofatty proliferation (3/18 cases), abscess formation (2/18 cases) and enlarged mesenteric lymph nodes (6/18 cases) were also observed. MRE missed small fistulas which were visible in radiological studies in two patients. CONCLUSIONS: MRE appears to be a promising technique in patients with Crohn's disease. Due to limited spatial resolution MRE could be a useful adjunct to radiological studies and in following up selected groups of patients with prior known disease.  相似文献   
994.
BACKGROUND: Under particular conditions a patent foramen ovale (PFO) can potentially give rise to ischemic stroke by means of paradoxic embolization. In obstructive sleep apnea syndrome (OSAS) right to left shunting (RLSh) can occur through PFO during periods of nocturnal apnea. Our study aimed to evaluate the prevalence of PFO diagnosed by means of transcranial Doppler (TcD) in subjects with OSAS. METHODS: Seventy-eight consecutive subjects with OSAS (mean age 53+/-12 years) and 89 normal controls (mean age 48+/-9 years) underwent TcD with intravenous application of agitated physiological saline solution. The test was performed on patients at rest and during Valsalva maneuver. RESULTS: PFO was present in 21 out of 78 patients with OSA (27%) and in 13 out of 89 control patients (15%). Seventeen out of 21 patients with OSA showed PFO only during Valsalva maneuver (85%) with respect to 12 out of 13 subjects of the control group (92%). Prevalence of PFO in OSAS was statistically different with respect to the control group (P<0.05). However, no statistically significant differences could be found for the prevalence of provocative-only shunting PFO with respect to already at rest shunting PFO in patients with OSAS with respect to the control group. CONCLUSIONS: Prevalence of PFO in subjects with OSA is significantly higher than in normal controls. The shunt is frequently present only during Valsalva maneuver.  相似文献   
995.
BACKGROUND: End-stage cholestatic liver disease (ESCLD) is the main indication for liver replacement in children. Pediatric cadaver-organ-donor shortage has prompted the most important evolutions in the technique of liver transplantation, in particular living-donor liver transplantation (LDLT) and split-liver transplantation (SLT). METHODS: Between November 1997 and June 2001, 127 children with ESCLD were evaluated for liver transplantation, and 124 underwent 138 liver transplantations after a median time of 40 days. Causes of liver disease were congenital biliary atresia (n=96), Alagille's syndrome (n=12), Byler's disease (n=8), and other cholestatic diseases (n=8). RESULTS: Ninety (73%) patients received a split-liver graft, 28 (23%) a whole liver, and 6 (4%) a reduced-size liver. Overall 2- and 4-year patient survival rates were 93% and 91%, respectively; the 2- and 4-year graft-survival rates were 84% and 80%, respectively. In split-liver recipients, 4-year patient and graft-survival rates were 91% and 83%, respectively; these were 93% and 78%, respectively, in whole-liver recipients and 67% and 63%, respectively, in reduced-size liver recipients. Retransplantation rate was 11%, whereas mortality rate was 8%. Overall incidence of vascular and biliary complication were 16% and 27%, respectively. CONCLUSIONS: SLT can provide liver grafts for children with ESCLD with an outcome similar to the one reported following LDLT, eliminating mortality while they are on a transplantation wait list. The need for pediatric LDLT should be reevaluated and programs of SLT strongly encouraged and supported at a national and international level.  相似文献   
996.
Rapamycin impairs antigen uptake of human dendritic cells   总被引:16,自引:0,他引:16  
BACKGROUND: Rapamycin is a recently introduced immunosuppressive agent. Its effect on lymphocytes has been extensively studied. Whether it can also modulate dendritic cell (DC) function is unknown. METHODS: The effect of rapamycin on differentiation, antigen uptake, and the immunostimulatory capacity of human DC was examined. DC were derived from monocytes upon culture with interleukin (IL)-4 and granulocyte-macrophage colony-stimulating factor in the presence or absence of rapamycin (0.1-100 ng/mL). Surface phenotype and antigen uptake capacity of DC were assessed by flow cytometry. Immunostimulatory capacity was measured by mixed lymphocyte culture. RESULTS: Rapamycin reduced DC recovery and increased DC apoptosis. DC differentiated in the presence of rapamycin (rapa-DC) had increased expression of CD1a, CD1b, and CD1c and decreased expression of MHC I, MHC II, CD80, CD86, and CD40. Antigen uptake receptor expression (mannose receptor, CD32, CD91, CD46) was decreased, and receptor-mediated endocytosis of fluorescein isothiocyanate-dextran was markedly impaired in rapa-DC, as were fluid phase endocytosis of Lucipher Yellow and phagocytic activity of bacteria and dead or apoptotic cells. CD40 ligand-induced production of both IL-12 and IL-10 was reduced in rapa-DC, and allogeneic T lymphocyte responses were moderately impaired when rapa-DC were used as stimulator cells. Neither cyclosporine nor FK506 affected DC function. However, the effects of rapamycin on DC could be completely inhibited by a 10-fold excess of FK506 but not by up to 100-fold excess of cyclosporine. CONCLUSION: Rapamycin has a unique and profound inhibitory effect on DC function, which seems to be at least in part mediated by the FKBP immunophilins.  相似文献   
997.
A mononucleotide repeat (D310) in mitochondrial DNA has been recently identified as a mutational hot spot in primary tumors. We analyzed 56 tumors for insertion/deletion mutations in the D310 repeat. A total of 13 mutations were detected. The highest frequency of mutations was found for cervical cancer, followed by bladder tumors, breast cancer and endometrial neoplasia. No alterations were observed in four patients suspected of malignancy but without evidence of malignant tumor. We detected identical changes in four of four urine sediments from patients with bladder cancer and in three of three fine needle aspirates of patients with breast cancer. Our results indicate that D310 abnormalities are detectable in cytology specimens from patients with cancer and support the notion that D310 analysis may represent a new molecular tool for cancer detection.  相似文献   
998.
999.
We report that cyclin D3 is rate limiting for G1 progression in thyroid follicular cells and that its constitutive upregulation by chronic stimulation of the TSH/cAMP pathway plays a role in human and experimental hyperproliferative diseases of the thyroid gland. These conclusions are supported by in vitro and in vivo studies. In rat thyrocytes (PC Cl 3 cells), cyclin D3 expression is enhanced in response to activation of the TSH/cAMP pathway. Interference with the expression of G1 cyclins (in particular cyclin D3) by the antisense methodology strongly reduced TSH-dependent proliferation of PC Cl 3 cells, indicating that proper progression through G1 requires cyclin D3. Accordingly, PC Cl 3 cells engineered to overexpress cyclin D3 (PC-D3 cells) show enhanced growth rate and elude hormone-dependence and contact inhibition. Using an animal experimental model of thyroid stimulation, we demonstrate that cyclin D3 is a key mediator of TSH-dependent proliferation of thyroid follicular cells also in vivo. Cyclin D3 protein levels were higher in the thyrocytes from glands of propylthiouracil-treated rats compared with control animals. The increase in cyclin D3 expression occurred after the propylthiouracil-induced increase in TSH levels and preceded the burst of cell proliferation. Finally, we found that cyclin D3 protein is expressed in a fraction of human goiters but it is strongly overexpressed in most follicular adenomas.  相似文献   
1000.
Lonidamine, a derivate of indazole-3-carboxylic acid, is an antineoplastic drug with a typical mechanism of action. Lonidamine has no function on cellular nucleic acids or protein synthesis, whereas it exerts a powerful inhibitory effect on oxygen consumption, aerobic glycolysis and lactate transport and accumulation of neoplastic cells. Nevertheless, its proven ability to modify the permeability of membranes is consistent with the possible increase of drug uptake, reverse of drug resistance and triggering of apoptotic pathway. Lonidamine has been experimentally shown to potentiate the cytotoxic effects of anthracyclines in human breast cancer cell lines and cisplatin activity in both platinum-sensitive and platinum-resistant human ovarian carcinoma cell lines. Since the specific mechanism of action and side effects are not overlapping with those of standard antineoplastic agents, combination of lonidamine with standard chemotherapy has been widely investigated for the treatment of solid tumors. Additionally, the enhancement of radiotherapy activity by lonidamine has been considered for palliative therapy of lesions from metastatic cancers. The encouraging results of phase II-III trials for the treatment of advanced breast, ovarian and lung cancer must be confirmed by larger studies. Specifically designed studies to address the role of lonidamine in the adjuvant setting are warranted. Lonidamine, a dechlorinate derivative of indazole-3-carboxylic acid, has proved to exert a powerful antiproliferative effect and to impair the energy metabolism of neoplastic cells. Herein we review the current experience on combining lonidamine and chemotherapy and/or radiation therapy in the treatment of solid tumors. Several studies have been published on this topic. The total number of trials reported in literature and length of follow-up are still insufficient to draw a firm conclusion. However, the available data demonstrate a significant role of lonidamine in modulating anthracycline and platinum compound activity.  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