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   4283篇
  免费   200篇
  国内免费   46篇
耳鼻咽喉   41篇
儿科学   84篇
妇产科学   38篇
基础医学   580篇
口腔科学   86篇
临床医学   402篇
内科学   1349篇
皮肤病学   39篇
神经病学   174篇
特种医学   149篇
外科学   550篇
综合类   17篇
预防医学   75篇
眼科学   71篇
药学   295篇
中国医学   3篇
肿瘤学   576篇
  2022年   9篇
  2021年   27篇
  2020年   18篇
  2019年   34篇
  2018年   37篇
  2017年   30篇
  2016年   38篇
  2015年   41篇
  2014年   59篇
  2013年   99篇
  2012年   175篇
  2011年   202篇
  2010年   110篇
  2009年   103篇
  2008年   209篇
  2007年   220篇
  2006年   217篇
  2005年   237篇
  2004年   261篇
  2003年   256篇
  2002年   217篇
  2001年   233篇
  2000年   262篇
  1999年   210篇
  1998年   73篇
  1997年   50篇
  1996年   39篇
  1995年   42篇
  1994年   34篇
  1993年   25篇
  1992年   139篇
  1991年   84篇
  1990年   98篇
  1989年   114篇
  1988年   84篇
  1987年   86篇
  1986年   78篇
  1985年   60篇
  1984年   47篇
  1983年   46篇
  1982年   17篇
  1981年   17篇
  1980年   6篇
  1979年   17篇
  1978年   12篇
  1977年   12篇
  1976年   8篇
  1973年   5篇
  1969年   4篇
  1968年   4篇
排序方式: 共有4529条查询结果,搜索用时 0 毫秒
31.
We report an adult onset patient with moyamoya disease showing acute progress after contralateral vascular reconstructive surgery. A 47-year-old female developed cerebral infarction in the left corona radiata. A magnetic resonance (MR) angiography and a cerebral angiogram revealed severe stenosis extending from the terminal portion of left internal carotid artery (ICA) to the M1 portion. The right ICA showed slight stenosis. We performed direct bypass surgery (STA-MCA anastomosis) on the affected left side. MR angiography 1 month after surgery revealed the progressive stenosis of the C1 portion of the right ICA. While measurement of cerebral blood flow (CBF) showed a slight impairment of vascular reactivity to acetazolamide loading in the region of the right MCA, we continued without vascular reconstructive surgery for the right side because there was no ischemic attack. The patient had a transient sensory disturbance of the left upper extremity 16 months after surgery. MR angiography and a cerebral angiogram revealed more progressive stenosis extending from the right ICA to the M1 portion. CBF study showed a low CBF at rest and a negative response to acetazolamide loading in the region of the right MCA. Direct bypass surgery was performed on the right hemisphere. Follow-up study revealed an increment of rest CBF and improvement of vascular reactivity. We underlined the necessity for careful postoperation observation of progressive contralateral arterial stenosis using MR angiography and CBF study in adult onset patients with moyamoya disease.  相似文献   
32.
Allelotype and replication error phenotype of small cell lung carcinoma   总被引:3,自引:1,他引:3  
Allelotype and replication error (RER) phenotype analyses were performed to clarify the pathogenetic significance of inactivation of tumor suppressor genes and genomic instability in the genesis and progression of small cell lung carcinoma (SCLC). We examined 37 cases of SCLC for loss of heterozygosity (LOH) and microsatellite instability at 49 loci on all 39 nonacrocentric chromosomal arms. LOH was frequently (>70%) detected on chromosomes 3p (29/32, 90.6%), 5q (15/21, 71.4%), 13q (25/26, 96.2%), 17p (22/25, 88.0%), and 22q (24/33, 72.7%). Frequent LOH (>70%) on these loci was observed even among seven cases of stage I tumors. The incidence of LOH on all 39 nonacrocentric chromosomal arms was not significantly different between primary tumors and metastases. These results suggest that inactivation of multiple tumor suppressor genes accumulates relatively early during progression of SCLC and it may be responsible for clinically and biologically aggressive phenotype of SCLC. RER was observed in 6/37 (16.2%) of SCLC, however, RER at multiple loci was observed only in two cases. Therefore, it was indicated that genomic instability is uncommon, but might play a role in the genesis of a small subset of SCLC.   相似文献   
33.
Infantile hemangioendothelioma of the thymus is a rare disease. We describe a patient who developed a large anterior mediastinal mass, severe thrombocytopenia and massive pleural effusion at 1 month of age. Glucocorticosteroid and irradiation therapy had no effect on either the tumor size or clinical symptoms and the tumor was resected subtotally. Three months after the subtotal resection, the remaining tumor had almost disappeared and the symptoms had resolved. The patient has now been well for 1 year after surgery without evidence of recurrence. The tumor tissue was characterized by prominent vascular endothelial proliferation intermixed with a normal thymic structure, producing a picture consistent with that of an infantile hemangioendothelioma in the thymus, lmmunohistochemically, the tumor cells showed positive staining for vimentin, factor VIII and CD34. The DNA stemline and proliferative activity were examined by flow cytometry, which revealed a diploid stemline with a low growth fraction. DNA content and cell cycle analyses of the tumor tissue may be useful for predicting the biological behavior of the tumor.  相似文献   
34.
Cerebrospinal fluid (CSF) tau protein phosphorylated at both Thr231 and Ser235 sites (CSF/phospho-tau(231-235)) and total tau (CSF/total-tau) were quantified by sandwich ELISA in 20 patients with mild cognitive impairment (MCI) who eventually developed AD on follow-up as well as seven memory complainers with no objective memory loss. 13/20 (65%) of the MCI patients had high CSF/total-tau and detectable levels of CSF/phospho-tau(231-235), whereas these markers were low and under a detectable level in all of the memory complainers. Although either a total-tau, phospho-tau measurement or a combination of these can help in predicting if MCI will develop AD, our results suggest that the pathogenic steps of AD may be at the stage that finally leads to an accumulation of abnormally phosphorylated tau and neuron death, at least in some brain areas, when MCI patients present with the earliest detectable clinical symptoms of dementia.  相似文献   
35.
We examined photoparoxysmal responses (PPRs) elicited by half-field visual stimulation with deep-red flicker light to determine the neurophysiological features of photosensitive epilepsy (PSE). EEG revealed two types of PPRs. One had the focal spike in the occipital region and the other in the temporo-occipital region at the contralateral hemisphere. The equivalent current dipoles of these types were located at the occipital cortex and the inferior temporal (IT) cortex, respectively. These cortices comprise one of the main pathways in the visual system, and they play important roles in color discrimination. Thus, we propose that the visual system, especially the occipital cortex and the IT cortex, might be involved in the generator mechanism of PSE.  相似文献   
36.
BACKGROUND: The incidence of gastric neoplasm is increasing in the elderly population. Therefore, a rational method of treatment for gastric cancer in the elderly should be constituted to improve the survival. The purpose of the present study was to clarify whether the patient's age is an independent prognostic factor and to determine clinicopathological characteristics in the elderly. METHODS: Curative resection of gastric cancer was carried out on 601 patients who were 40 years or older. They were divided into the following two groups: younger patients (between 40 and 79 years old) and elderly patients (80 years or older). The clinicopathologic features of these patients were reviewed retrospectively and multivariate analysis was carried out. RESULTS: The distinguishing features of gastric cancer in the elderly patients were intestinal and mixed types of cancer, distal third stomach dominance in the tumour location, advanced stage of disease, and a low rate of extensive lymph node dissection (D3 or more). Regarding the recurrence site, the liver was the dominant site in the elderly group (25.3% in the younger group vs 54.5% in the elderly group). The 10-year disease-free survival rate of the elderly group was 53.2%, which was significantly worse than that (79.9%) of the younger patients (P = 0.0004). In multivariate analysis, an age of > or = 80 years is an independent prognostic factor, as well as stage, depth of tumour invasion, lymph node metastasis, scirrhous carcinoma, and blood transfusion. CONCLUSIONS: Results indicate that gastric cancer in elderly patients has a poorer prognosis than that in younger patients.  相似文献   
37.
38.
Background: The usefulness of transthoracoscopic needle biopsy for preoperatively indeterminate intrapulmonary nodules was evaluated. Methods: Thoracoscopy was performed on 38 patients with pulmonary solitary nodules suspected to be primary lung carcinomas. When the nodule was localized by simple observation or tactile sensor, a biopsy specimen of the tumor was obtained by a biopsy needle introduced through a trocar. Results: The nodules were 7 to 55 mm in diameter. All were located in the peripheral region of the lung. Biopsy specimens were obtained even from 17 nodules with no associated pleural changes. By cytology, all the malignant tumors were precisely diagnosed, 29 as primary lung cancers and 3 as metastatic lung neoplasms. Five of the remaining six benign nodules were not precisely diagnosed. However, they were cytologically classified as class I. Conclusions: Transthoracoscopic needle biopsy is feasible for diagnosing small intrapulmonary nodules, particularly those of malignant neoplasms. As compared with thoracoscopic excisional biopsy, transthoracoscopic needle biopsy saves time and may reduce the possibility of tumor dissemination during the procedure. Received: 14 March 1997/Accepted: 31 May 1997  相似文献   
39.
OBJECTIVE: The maximal period of cryopreservation for the trachea is still unsolved. We assessed the maximal period of cryopreservation using the Bicell biofreezing vessel as an easy and cheap slow-freezing instrument for viable tracheal grafts in 95 rats. METHODS: Each isograft was harvested from 17 donor rats, immersed in the preservative solution, and stored in a Bicell device in a deep freezer at -80 degrees C. The tracheal isografts were then randomly assigned to 9 groups according to cryopreservation periods ranging from 0 to 12 months. Included in the 9 groups were 2 subgroups (n = 6 per subgroup) that were observed immediately after being thawed and 1 month after heterotopic transplantation into the omentum after being thawed. Four subgroups (n = 6 per subgroup) were added according to the cryopreservation period for 1, 3, 6, and 12 months to evaluate the graft morphology 3 months after being thawed and transplanted heterotopically. RESULTS: A prolonged period of cryopreservation had a degenerative effect on both the epithelium and cartilage. One month after transplantation, degeneration was more pronounced in the cartilage than in the epithelium, as characterized by the viable chondrocyte ratio and the epithelial score of isografts undergoing cryopreservation for more than 9 months. Three months after transplantation, the morphology of the epithelium and cartilage in isografts undergoing cryopreservation for less than 3 months was better preserved, whereas the morphology of both deteriorated in isografts undergoing cryopreservation for more than 6 months. CONCLUSIONS: We conclude that the permissible period of cryopreservation to maintain tracheal isograft viability in this simple system using a Bicell biofreezing vessel is 3 months.  相似文献   
40.
Chordoid meningioma is a very rare variant, especially in adults. We report an adult case of chordoid meningioma. A 52-year-old man was admitted to our hospital due to right hemiparesis. MRI revealed a left temporal convexity mass that showed two structures; the cerebral layer was shown as an isointensity area on T1WI and T2WI, and the dural layer seemed relatively hypointense on T1WI and hyperintense on T2WI. The tumor was well enhanced with gadolinium, especially on the dural side. A left external carotid arteriogram showed tumor stains with feeding vessels from the left middle meningeal artery. The tumor was totally removed via fronto-temporal craniotomy. Histological examination of the surgical specimen revealed two different structural components, meningothelial meningioma on the cerebral side, and chordoid meningioma on the dural side, consisting of clustering spindled cells and partly vacuolated ones in the mucoid stroma. In immunohistochemical examination, tumor cells showed positive staining for vimentin and epithelial membrane antigen (EMA), and negative for cytokeratin. From the above findings, this case was diagnosed as chordoid meningioma in an adult, a very rare variant of meningioma.  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