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   25850篇
  免费   1250篇
  国内免费   176篇
耳鼻咽喉   199篇
儿科学   529篇
妇产科学   447篇
基础医学   2832篇
口腔科学   618篇
临床医学   2061篇
内科学   6781篇
皮肤病学   486篇
神经病学   2972篇
特种医学   777篇
外科学   3902篇
综合类   44篇
一般理论   5篇
预防医学   1088篇
眼科学   451篇
药学   1459篇
中国医学   30篇
肿瘤学   2595篇
  2024年   26篇
  2023年   173篇
  2022年   389篇
  2021年   750篇
  2020年   444篇
  2019年   618篇
  2018年   692篇
  2017年   552篇
  2016年   620篇
  2015年   692篇
  2014年   1013篇
  2013年   1275篇
  2012年   2002篇
  2011年   1991篇
  2010年   1164篇
  2009年   1069篇
  2008年   1756篇
  2007年   1812篇
  2006年   1668篇
  2005年   1651篇
  2004年   1628篇
  2003年   1354篇
  2002年   1319篇
  2001年   193篇
  2000年   113篇
  1999年   150篇
  1998年   252篇
  1997年   212篇
  1996年   195篇
  1995年   170篇
  1994年   132篇
  1993年   134篇
  1992年   116篇
  1991年   92篇
  1990年   89篇
  1989年   67篇
  1988年   69篇
  1987年   65篇
  1986年   60篇
  1985年   57篇
  1984年   80篇
  1983年   46篇
  1982年   45篇
  1981年   43篇
  1980年   34篇
  1979年   20篇
  1978年   17篇
  1977年   30篇
  1976年   17篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We investigated the effect of 10 months ovariectomy and a correction therapy, 2 weeks before the rats were killed, of oestradiol, progesterone or their combination on NMDA and AMPA receptor binding in the hippocampus, dentate gyrus, striatum, nucleus accumbens and frontal cortex of the rat brain as well as on amino acid levels in frontal cortex. NMDA and AMPA binding densities were assayed by autoradiography using, respectively, L-[3H]glutamate and [3H]AMPA; amino acid concentrations were measured by high performance liquid chromatograhy (HPLC) coupled with UV detection. Ovariectomy was without effect on NMDA and AMPA binding density in all brain regions assayed except in the hippocampal CA1 region and dentate gyrus where it decreased NMDA binding density compared to intact rats values. Oestradiol restored and increased NMDA binding density in the CA1 subfield and the dentate gyrus of ovariectomized rats but, by contrast, it decreased binding density in the striatum and in the frontal cortex while having no effect in the CA2/3 subfield of the hippocampus and in the nucleus accumbens. Oestradiol was without effect on AMPA binding density in the hippocampus and the dentate gyrus but it reduced AMPA binding density in the striatum, the frontal cortex and the nucleus accumbens. Progesterone, and oestradiol combined with progesterone, decreased NMDA but not AMPA binding density in the frontal cortex of ovariectomized rats, and they were without effect on these receptors in the other brain regions assayed. Amino acid concentrations in the frontal cortex were unchanged after ovariectomy or steroid treatments. The effect of oestradiol in the hippocampus confirmed in the present study and our novel findings in the frontal cortex, striatum and nucleus accumbens may have functional significance for schizophrenia and neurodegenerative diseases.  相似文献   
92.
PURPOSE: Recently, we reported that a large number of human hepatocellular cancer (HCC) cell lines were auxotrophic for arginine. Here we report the results obtained with the amino acid-degrading enzyme arginine deiminase (ADI) conjugated to polyethylene glycol (ADI-SS PEG 20,000 mw) as a means of lowering plasma arginine to treat HCC. The study was a cohort dose-escalation phase I/II study. PATIENTS AND METHODS: Pharmacodynamic studies indicated an ADI-SS PEG 20,000 mw dose level of 160 U/m(2) was sufficient to lower plasma arginine from a resting level of approximately 130 micromol/L to below the level of detection (< 2 micromol/L) for more than 7 days, a dose later defined as the optimal biologic dose. All patients were to receive three cycles at the optimum biologic dose. RESULTS: This therapy was well tolerated, even in patients who had no detectable plasma arginine for 3 continuous months of therapy. Of the 19 patients enrolled, two had a complete response, seven had a partial response, seven had stable disease, and three had progressive disease. The median survival for the 19 patients enrolled on this study was 410 days, with four patients still alive at present (> 680 days). CONCLUSION: Elimination of all detectable plasma arginine in patients with HCC was well tolerated and seemed to be effective in the treatment of some patients with HCC. Further testing of ADI-SS PEG 20,000 mw in a larger population of individuals with HCC as well as other human tumors auxotrophic for arginine is warranted.  相似文献   
93.
94.
Prognostic value of CD40 in adult soft tissue sarcomas.   总被引:4,自引:0,他引:4  
PURPOSE: The purpose is to evaluate the expression of CD40, a membrane protein predominantly expressed on B cells, dendritic cells, and macrophages, in a series of adult soft tissue sarcomas and to test its possible prognostic value. EXPERIMENTAL DESIGN: CD40 expression was studied by immunohistochemistry. Correlations with other baseline characteristics of patients and tumors were analyzed with chi(2) test. The prognostic value was studied with univariable and multivariable analysis adjusted by age, sex, tumor size, grade, location, and distant metastases. RESULTS: Eighty-two patients, between January 1994 and May 2001, were analyzed. Membrane or cytoplasmic staining for CD40 protein was absent in 30% of the tumors but present in <10% of cells in 22 (27%), in 10% to 50% in 23 (28%), and in >50% of cells in 12 (15%) tumors. There was no correlation between CD40 expression and age, sex, size, grade, and location of the primary tumor and distant metastases. With 61 patients (74.4%) progressed and 31 (37.8%) dead, CD40 expression was a significant prognostic factor for disease-free and overall survival at univariable and multivariable analysis. Patients with tumors expressing CD40 in >50% of cells had a dramatically unfavorable prognosis with median disease-free and overall survival of 7 and 17 months, respectively, and hazard ratios of relapse and death as compared with patients with CD40-negative tumors of 2.89 (95% confidence interval: 1.26-6.60) and 6.92 (95% confidence interval: 2.18-22.0), respectively. CONCLUSIONS: These data suggest that expression of CD40 protein in >50% of cells might indicate an unfavorable prognosis in adult soft tissue sarcomas.  相似文献   
95.
OBJECTIVE: To determine the relationship between p53 overexpression and vascular endothelial growth factor (VEGF) upregulation in liver and abdominal metastases from colon cancer. The analysis in the two metastatic sites was carried out to evaluate the potential role of microenvironment in the molecular regulation of VEGF. METHODS: Bioptic specimens of liver and abdominal metastases from colon carcinomas were examined by immunohistochemistry for p53 and VEGF expressions. Consecutive cases with assessable tumor tissue were selected. RESULTS: The study population consisted of 24 cases having liver metastases and 34 cases having abdominal metastases. Abdominal metastases showed a higher number of VEGF-positive cases and a higher intensity of VEGF immunoreactivity than liver metastases did (p = 0.01). The combined analysis of p53 and VEGF showed a strong association between the two markers in the 24 liver metastases; 9 cases were VEGF positive/p53 positive and 15 cases were VEGF negative/p53 negative. This relationship was not found in the 34 abdominal metastases, which showed concordance between the two markers in 9 VEGF-positive/p53-positive cases only. CONCLUSIONS: Microenvironment factors like hypoxia may have a predominant role in inducing VEGF expression and they can override the molecular control of p53 on VEGF.  相似文献   
96.
We have shown previously that melanoma cells in culture release heavy-chain ferritin (H-Ferritin) into supernatants and that this is responsible for the suppression of responses of peripheral blood lymphocytes stimulated by anti-CD3. These effects were mediated by activation of regulatory T cells to produce interleukin (IL)-10. In the present study, we examined whether a similar relation might exist between levels of H-Ferritin and activation of regulatory T cells in patients with melanoma. Ferritin levels were evaluated by ELISA and regulatory T-cell numbers were assessed by three-color flow cytometry to identify CD4(+) CD25(+) CD69(-) T cells. CD69 positive cells were excluded to avoid inclusion of normal activated CD4, CD25 expressing T cells. Measurements of H- and light-chain (L)-Ferritin by ELISA revealed that H- but not L-Ferritin was elevated in the circulation of melanoma patients. In addition, these studies revealed a marked increase in the number of CD4(+) CD25(+) CD69(-) T cells in such patients, compared with age-matched controls. The ratio of H-Ferritin:L-Ferritin correlated with the levels of regulatory T cells consistent with a causal relation between unbound H-Ferritin levels and the activation of regulatory T cells. H-Ferritin or regulatory T cells did not, however, correlate with the stage of the melanoma. These results provide evidence for the importance of H-Ferritin in the induction of regulatory T cells in patients with melanoma and provide additional insight into the suppression of immune responses in such patients.  相似文献   
97.
Objective.The aim of this study was to define the clinical–therapeutical approach to endometrial cancer now being followed in some of the most important centers of reference for gynecological cancer in North America by means of a questionnaire.Study design.The questionnaire focused on four principal areas: (1) surgical staging and therapy; (2) adjuvant treatment; (3) treatment modifications; and (4) management of advanced stages (FIGO III–IV).Results.There were 48 evaluable responses (77%) received by the end of December 1994 which were considered for this analysis. Lymphadenectomy is utilized routinely in 26/48 centers (54.2%) and in selective clinical–pathological conditions in another 21/48 centers (43.5%). In the majority of centers (31/48; 64.6%) radical surgery is utilized for selected indications such as cervical involvement. Only 3/48 (6.2%) centers consider the vaginal approach totally inappropriate. The great majority (40/48; 83.3%) of the centers considered postsurgical adjuvant therapy to be necessary in FIGO Stage Ic. Brachytherapy is routinely performed in 3 centers (6.2%) in postsurgical management of Stage I endometrial cancer, while the majority of the centers (31/48; 64.6%) perform brachytherapy of the vaginal vault in certain clinical–pathological conditions. A wide variety of treatments are used for advanced stages (FIGO III–IV).Conclusions.It emerges that some controversial aspects exist on endometrial cancer treatment, and these conflicting data need a large-scale multicenter randomized clinical trial.  相似文献   
98.
We report the case of a young girl with recurrent sharp pain in the outer aspect of the ankle. She had no previous trauma. High-resolution US (HRUS) showed a complete intermittent dislocation of the peroneal tendons. Post-traumatic chronic peroneal instability is quite common, whereas complete dislocation is rare. HRUS is an important adjunct to clinical examination and radiographic evaluation of patients with musculoskeletal disorders of the foot and ankle [1]. This paper reports its value in non-traumatic recurrent dislocation of the peroneal tendons. Received: 23 May 1997 Accepted: 1 December 1997  相似文献   
99.
OBJECTIVE: To present our experience with permanent preoperative balloon occlusion of the internal carotid artery while dealing with different abnormalities of the lateral skull base and a comparison with the results mentioned in the literature. STUDY DESIGN: Retrospective case review. SETTING: Private neurotologic and skull base tertiary referral center. PATIENTS: Fifteen patients who underwent preoperative balloon occlusion of the internal carotid artery and surgery subsequently for various abnormalities of the lateral skull base between 1989 and 2002. INTERVENTIONS: Each patient was subjected to four-vessel angiography along with the manual cross-compression test and balloon test occlusion to assess the efficacy of the collateral circulation. After angiography, each patient underwent a preoperative balloon occlusion, after which a lateral skull base procedure was performed for removal of the abnormality. MAIN OUTCOME MEASURES: Only those patients showing evidence of adequate collateral cerebral circulation and a less than 1-second delay between the angiographic phases of the two cerebral hemispheres on angiography were considered fit for preoperative balloon occlusion. While under going the preoperative balloon occlusion, the patients were clinically assessed for the development of any neurologic symptoms and signs. Long-term follow-up after surgery was also based on the development of symptoms and signs of neurovascular compromise. RESULTS: A major complication in the form of long-lasting hemiplegia occurred in one patient (6.7%). This complication was the result of technical factors rather than an effect of cerebral ischemia, because it was caused by an intimal dissection produced by the catheter. A defect in the visual field occurred in one patient (6.7%) that resolved partially after antiplatelet therapy. There was no mortality in our series related to preoperative balloon occlusion of the internal carotid artery. CONCLUSION: Preoperative balloon occlusion of the internal carotid artery can still be considered a viable option for the management of the internal carotid artery during lateral skull base surgery. Proper preoperative evaluation of the adequacy and efficacy of the collateral cerebral circulation reduces the chances of postoperative neurovascular complications.  相似文献   
100.
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