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   7462篇
  免费   393篇
  国内免费   44篇
耳鼻咽喉   102篇
儿科学   102篇
妇产科学   101篇
基础医学   901篇
口腔科学   118篇
临床医学   454篇
内科学   1857篇
皮肤病学   109篇
神经病学   530篇
特种医学   351篇
外科学   1544篇
综合类   42篇
预防医学   175篇
眼科学   74篇
药学   572篇
中国医学   20篇
肿瘤学   847篇
  2023年   50篇
  2022年   92篇
  2021年   213篇
  2020年   112篇
  2019年   167篇
  2018年   195篇
  2017年   186篇
  2016年   194篇
  2015年   193篇
  2014年   250篇
  2013年   323篇
  2012年   455篇
  2011年   551篇
  2010年   310篇
  2009年   283篇
  2008年   442篇
  2007年   519篇
  2006年   491篇
  2005年   467篇
  2004年   493篇
  2003年   480篇
  2002年   479篇
  2001年   59篇
  2000年   61篇
  1999年   87篇
  1998年   95篇
  1997年   81篇
  1996年   77篇
  1995年   52篇
  1994年   60篇
  1993年   53篇
  1992年   37篇
  1991年   27篇
  1990年   23篇
  1989年   23篇
  1988年   20篇
  1987年   24篇
  1986年   18篇
  1985年   18篇
  1984年   19篇
  1983年   11篇
  1982年   11篇
  1981年   8篇
  1980年   10篇
  1978年   10篇
  1977年   6篇
  1976年   8篇
  1975年   7篇
  1974年   13篇
  1973年   6篇
排序方式: 共有7899条查询结果,搜索用时 375 毫秒
71.
This study was undertaken to determine whether the specific Th1- or Th2-cell response to varicella-zoster virus was induced predominantly by a mucosal adjuvant, cholera toxin, in mice. A commercially available live varicella vaccine (Oka strain) and cholera toxin or its B subunit were administered simultaneously via the nasal route. Delayed-type hypersensitivity to the Oka vaccine was induced, but the systemic neutralizing antibody response was low. The delayed-type hypersensitivity evoked after a single administration was relatively higher than that on administration three times. When spleen cells from mice immunized once with the vaccine and cholera toxin or its B subunit were restimulated with the live vaccine in vitro, there was greater thymidine uptake and production of interleukin- 2 (IL-2) than controls, but only a low level of IL-4 production. The production of IL-2 induced by the B subunit of cholera toxin was less than that by cholera toxin and a mutant of Escherichia coli enterotoxin on co-immunization with the vaccine in mice. Cholera toxin and its B subunit have been reported to induce predominantly a specific Th2-type T-cell response to various antigens. However, the Oka vaccine is an antigen that polarizes the activation of specific Th1/Th2-type T cells by cholera toxin or its B subunit to the Th1-type side. Cholera toxin and its B subunit are thus useful mucosal adjuvants for inducing cellular immunity to the Oka vaccine similar to Escherichia coli enterotoxin.  相似文献   
72.
73.
The p16INK4a tumour suppressor gene, encoding p16 protein, plays a crucial role in regulation of the G1 cell-cycle phase. To investigate the potential role of p16 in soft tissue leiomyosarcoma (LMS), an immunohistochemical analysis was performed of 77 LMSs for p16 expression. Decreased expression of the p16 protein was identified in 25 of 77 LMSs (32%). Decreased expression of p16 correlated significantly with large tumour size (p=0.0038). In a univariate analysis, large tumour size and decreased expression of p16 were statistically significant adverse prognostic factors (p=0.025 and p=0.0021, respectively). In a multivariate analysis including conventional clinicopathological parameters, decreased expression of p16 protein was revealed as the only independent unfavourable prognostic factor (p=0.012). To elucidate the mechanisms of inactivation of the p16INK4a gene, 49 LMSs for which genomic DNA was available were examined; analysis for homozygous deletion, mutation, and promoter hypermethylation was conducted using differential PCR, PCR-SSCP, and methylation-specific PCR, respectively. Promoter hypermethylation was detected in 11 of 49 LMS cases (22%); homozygous deletion was detected in 3 of 49 cases (6%); and mutation was not recognized in any of the cases studied. Eight of 15 cases (53%) with decreased expression of p16 protein revealed methylation of the p16INK4a gene promoter. Promoter hypermethylation correlated closely with decreased expression and poor prognosis (p=0.0014 and p=0.0088, respectively). These results suggest that decreased expression of p16 protein can be considered as an independent reliable prognostic parameter in patients with soft tissue LMS. Furthermore, promoter methylation was more frequent than either homozygous deletion or mutation in this tumour, and promoter methylation was also shown to have a strong association with inactivation of the p16INK4a gene.  相似文献   
74.
We present the clinical, radiographical and pathological features of low-grade fibrosarcoma of the left proximal humerus in a 23-year-old man in whom it was necessary to distinguish the tumor from desmoplastic fibroma, malignant fibrous histiocytoma and intramedullary well-differentiated osteosarcoma. The patient presented with a 10-day history of pain in his left upper arm sustained when trying to break his fall with his left hand when slipping in the street. Plain radiography revealed an expanding multilobular osteolytic lesion from the proximal metaphysis to the diaphysis of his left humerus, accompanied by a pathological fracture at the distal portion of the lesion. Open biopsy of the lesion was performed twice; however, a conclusive diagnosis could not be obtained. The patient underwent wide excision and prosthetic replacement of the left proximal humerus. Histologically, the resected tumor was composed of both cellular areas and hypocellular areas. Cellular areas revealed a proliferation of bundles of uniform fibroblastic spindle-shaped cells with minimal cellular atypia, mixed with abundant intercellular collagenization. Mitotic figures were occasionally seen. Hypocellular areas showed myxoid features with loose bundles of collagen fibers. The patient demonstrates no evidence of disease 42 months after surgery. It is important to detect the scant atypical cells for the differential diagnosis of low-grade fibrosarcoma and desmoplastic fibroma of bone.  相似文献   
75.
The PTEN/MMAC1 ( PTEN ) gene was identified as a tumor suppressor gene encoding a cytoplasmic protein that controls cellular processes. To investigate the potential role and the alteration of the PTEN gene in soft tissue sarcomas (STSs), we searched for homozygous deletion and promoter hypermethylation in a series of 48 STSs that was composed of malignant fibrous histiocytoma, leiomyosarcoma, malignant peripheral nerve sheath tumor, including 2 cases with a mutation that we previously reported; differential polymerase chain reaction and methylation-specific polymerase chain reaction, respectively, were used for the analyses. Furthermore, to determine whether PTEN gene alterations are involved in the down-regulation of PTEN expression, we examined the expression of PTEN protein in 38 cases in which paraffin-embedded tissues were available for immunohistochemical analysis. In addition to our previous results showing that 2 (4%) of 51 cases had a PTEN mutation, promoter methylation was recognized in 6 (13%) of 48 cases, and homozygous deletion was detected in 1 (2%) of 48 cases in the current study. Of 6 cases with promoter methylation of PTEN gene, 5 were malignant peripheral nerve sheath tumor. Decreased expression of PTEN protein was recognized in 11 (29%) of 38 STS cases. Of 9 cases with PTEN alterations (6 cases with promoter methylation, 2 with mutation, and 1 with homozygous deletion), 3 (33%) showed decreased expression of PTEN protein. Furthermore, decreased expression of the PTEN gene showed a statistically significant correlation with high MIB-1 labeling index in 38 STS cases examined ( P = .0441). In conclusion, promoter methylation and homozygous deletion of the PTEN gene were found to be relatively rare events in cases of STS, as is mutation of the gene. Of 9 cases with a PTEN alteration, 3 (33%) showed a decrease in PTEN expression, indicating that PTEN gene alterations seem to play a minor role in the inactivation of PTEN in these tumors. Furthermore, although a further detailed analysis of a larger number of cases is still necessary, the present results suggest that PTEN expression may be a useful indicator of cell proliferation in patients with STS.  相似文献   
76.
Epstein-Barr (EB) virus-associated primary smooth muscle tumors have been reported in immunosuppressed young patients with acquired immunodeficiency syndrome (AIDS) and young people who have undergone liver transplantation. An autopsy case of EB virus-associated smooth muscle cell tumor in a 21 year old female who received immunosuppres-sive therapy following renal transplantation Is repotted. Multiple tumor nodules were present in the liver, but no primary lesion was found in any other organ. Histologically, the nodules were composed of spindle cells, positive for α-smooth muscle action, which were arranged in fascicles and closely associated with vascular channels, thereby suggesting a vascular smooth muscle cell origin. EB virus infection of the tumor cells was clearly demonstrated by in situ hybridization with an EB virus-encoded RNA 1 (EBER-1) probe. The present case illustrates that EB virus infection may play some role in the development of smooth muscle tumors not only in immunocompromised young patients with liver allo-grafts, but also in those with renal allografts.  相似文献   
77.
We describe a case of hepatocellular carcinoma in which a tumor embolus in the portal vein and 3 of 4 intrahepatic metastases were necrosed completely by Lipiodol transcatheter chemo-embolization (Lipiodol-TCE). Tumor emboli in the portal vein and intrahepatic metastases usually cannot be necrosed by conventional transcatheter chemo-embolization alone, because small nodules such as intrahepatic metastases and tumor emboli in the portal vein are supplied blood from the portal vein. However, in this case, Lipiodol-TCE was effective against tumor emboli in the portal vein and intrahepatic metastases. ACTA PATHOL JPN 38: 1363-1367, 1988.  相似文献   
78.
We report on a female baby with Fryns syndrome who died soon after birth. The patient had short limbs, coarse face, hypoplastic lungs, diaphragmatic hernia, and acral hypoplasia. Literature review disclosed varying degrees of skeletal manifestations in Fryns syndrome; short limbs may be a component of Fryns syndrome. © 1995 Wiley-Liss, Inc.  相似文献   
79.
Formalin-fixed paraffin-embedded hippocampal sections of brains with early-onset and late-onset Alzheimer's disease were studied immunohistochemically with antisera against cathepsin D and cathepsin B. In addition to the staining of neuronal perikarya, some of the senile plaques visualized by Bielshowsky silver staining and some of reactive astrocytes were positively stained with the antisera against cathepsin D and cathepsin B in brains with Alzheimer's disease. Abnormal localization of cathepsin D and cathepsin B immunoreactivity in neuronal perikarya was observed in brains with early-onset Alzheimer's disease. These findings demonstrate that the distribution of lysosomal proteases was altered in brains with Alzheimer's disease, suggesting the primary and/or secondary involvement of the lysosomal proteases in the pathological process of Alzheimer's disease.  相似文献   
80.
A rare variant of dedifferentiated chondrosarcoma wlth malignant mesenchymomatous component in a 57-year-old male is reported. The patient presented with a posterior mediastinal mass arising from the left eighth and ninth ribs showing well differentiated, low-grade chondrosarcoma. Five years later, local recurrence occurred and an excised specimen also showed the same histological features as the primary tumor. Another 6 years later, the tumor recurred and metastasized to the multiple organs, the patient dying 4 months later. Autopsy revealed that the recurrent and metastatic tumors showed malignant mesenchymomatous 'dedifferentiation' of chondrosarcoma composed of rhab domyosarcoma, angiosarcoma, chondrosarcoma, osteosarcoma, and leiomyosarcoma, in addition to fibrosarcomatous areas. Although the less differentiated component of dedifferentiated chondrosarcoma usually shows the histological features of malignant fibrous histiocytoma and fibrosarcoma, multilineage differentiation can occur in that component. The phenomenon of 'dedifferentiation' in chondrosarcoma and the relationship to and distinction from malignant mesenchymoma of soft tissue and bone are discussed.  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