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   7487篇
  免费   271篇
  国内免费   49篇
耳鼻咽喉   255篇
儿科学   295篇
妇产科学   359篇
基础医学   450篇
口腔科学   407篇
临床医学   622篇
内科学   1677篇
皮肤病学   71篇
神经病学   455篇
特种医学   390篇
外科学   1639篇
综合类   112篇
预防医学   178篇
眼科学   265篇
药学   243篇
中国医学   9篇
肿瘤学   380篇
  2024年   3篇
  2023年   52篇
  2022年   82篇
  2021年   192篇
  2020年   119篇
  2019年   128篇
  2018年   189篇
  2017年   160篇
  2016年   252篇
  2015年   268篇
  2014年   336篇
  2013年   411篇
  2012年   556篇
  2011年   505篇
  2010年   306篇
  2009年   273篇
  2008年   504篇
  2007年   632篇
  2006年   564篇
  2005年   552篇
  2004年   521篇
  2003年   354篇
  2002年   374篇
  2001年   105篇
  2000年   60篇
  1999年   63篇
  1998年   33篇
  1997年   24篇
  1996年   22篇
  1995年   16篇
  1994年   13篇
  1993年   7篇
  1992年   16篇
  1991年   16篇
  1990年   3篇
  1989年   7篇
  1988年   8篇
  1987年   11篇
  1985年   9篇
  1984年   5篇
  1983年   4篇
  1981年   4篇
  1979年   4篇
  1972年   5篇
  1970年   2篇
  1969年   4篇
  1968年   2篇
  1967年   2篇
  1966年   4篇
  1955年   2篇
排序方式: 共有7807条查询结果,搜索用时 15 毫秒
981.
The aim of this study was to investigate the effects of the vertical chincap on mandibular morphology and also on the dentoalveolar structures in patients with high-angle open-bite malocclusions. We examined 35 children with high-angle skeletal Class I or II open-bite malocclusions. Eighteen subjects were selected as the treatment group, and 17 were the controls. Vertical chincaps, applying 400 g on each side from beneath the anterior part of the mandibular corpus in an upward direction, were used in the treatment group for 16 hours per day over a mean period of 9 months. We studied 70 lateral cephalograms taken before and after the treatment and the control periods. The changes of 7 linear and 8 angular parameters were evaluated statistically in both groups with paired and Student t tests, respectively. Eruption of the mandibular incisors, decrease of the ramal inclination, decrease of the mandibular plane, and increase of the overbite in the treatment group compared with the control group were found to be statistically significant. Intrusion of the first molars, decrease of the gonial angle, and increase of the mandibular corpus inclination in the treatment group were contrary to the results observed in the control group; these comparisons were also found to be statistically significant. It appears that the vertical chincap is effective in treating skeletal open bite and in decreasing the gonial angle and ramus/corpus relationship.  相似文献   
982.
The present study is focused on spectrum analysis as a useful method of processing the PCG in order to obtain the frequency spectral distribution of normal heart sounds. Thirty normal subjects aged from 17 to 34 were studied. PCG was recorded on the fourth intercostal space at the left sternal border using a sound level meter coupled with a standard 6 ml cavity. The microphone had a linear response from 0.2 to 8,000 Hz. The signal was filtered with the standard B network according to the ANSI specifications and was registered on a four track FM tape recorder. A four channel analyzer with a microprocessor for off-line elaborations was used with 10 KHz sampling frequency. The PCG signal was triggered by a QRS detector on the R wave of the simultaneously recorded ECG. Fast Fourier transform was performed employing either a four channel analyzer with a microprocessor, or an A/D converter with a computer. Finally the results of the analysis were statistically elaborated. The described procedures permit to obtain a direct and exact tracing of the acoustic features of the heart, thus representing an attempt to come closer to the standardization and automatic analysis of the phonocardiographic technique.  相似文献   
983.
The clinical and radiological features of one case of renal hydatid disease communicating with collecting system are described. Introduction of hydatid elements into the renal pelvis due to rupture was accompanied by six episodes of renal colic. Although the sonographic features of renal hydatid disease have been described extensively, direct demonstration by ultrasonography of hydatid cyst ruptured into the renal pelvis has not, to our knowledge, been previously reported. The diagnosis has also been confirmed at surgery. Received 12 October 1995; Revision received 25 March 1996; Accepted 4 April 1996  相似文献   
984.
BACKGROUND: Oncocytic carcinoma is a rare tumor of major salivary glands. Despite being described 5 decades ago, not much is known about these rare tumors. Histochemical or electron microscopic confirmation of the oncocytic nature of the tumor cell is needed for differential diagnosis. The main treatment modality is surgery with or without adjuvant radiotherapy. Malignant oncocytomas have the potential risk of developing distant metastases and demand long term follow-up after therapy. CASE REPORT: A 58-year old man presented with a recurrent mass in the left parotid gland with a prior diagnosis of monomorphic adenoma in the same localization which had been treated by tumor excision in July 2002. Left superficial parotidectomy followed by radiotherapy into tumor bed and upper neck were carried out in September 2004. To date, he has had no evidence of recurrence for 14 months. CONCLUSION: For an accurate approach in the management of patients, oncocytic adenocarcinoma should be considered in the differential diagnosis of lesions of the parotid gland, most of which are benign.  相似文献   
985.
The characteristic changes in cancer process are assumed to be genetic alterations about the imbalance of cell proliferation and apoptotic cell death. This study was conducted to determine the value of the circulating vascular endothelial growth factor (VEGF) and Bcl-2 in patients with advanced stage non-small cell lung cancer (NSCLC). These serum factors were measured of 52 NSCLC patients pathologically verified on before and after chemotherapy in comparison with 16 healthy controls by using ELISA method. Both of the serum levels of VEGF (p = 0.015) and Bcl-2 (p < 0.001) were increased significantly in NSCLC patients compared with the healthy controls. No statistically significant relationships between investigated elevated serum parameters and various characteristics of patients and disease such as stage and tumor burden were determined. Likewise, we also found no correlation between serum VEGF and Bcl-2. Cytotoxic therapy of patients was accompanied by unchanged serum levels of serum factors. The median survival of all patients was 27 weeks and one-year survival rate was 22.4 percent. With the median serum levels as the cut-off value, patients were divided into high- and low-serum parameter groups. While we found that patients' performance status (p < 0.0001), serum LDH level (p = 0.0002), response to chemotherapy (p = 0.0023), and stage of the disease (p = 0.0085) were prognostic factors for survival, serum VEGF (p = 0.48) and Bcl-2 (p = 0.91) levels were determined as ineffective on survival in patients with advanced NSCLC. In conclusion, our data suggest that these serum factors, VEGF and Bcl-2, are useful diagnostic factors, not predictive and prognostic markers for overall survival in advanced NSCLC patients.  相似文献   
986.
Angiogenesis is essential for tumor progression and metastasis; however, the angiogenesis regulators that are biologically relevant for melanoma are still unknown. In this study, we analyzed the circulating serum levels of potent angiogenic factors, including vascular endothelial growth factor (VEGF), angiogenin, transforming growth factor-beta1 and VEGF receptors, VEGFR1 and VEGFR2, in human melanoma patients. One hundred and fourteen patients with histopathologically verified cutaneous melanoma at different stages and 30 healthy controls were investigated. Serum levels of angiogenic factors and VEGF receptors were quantitatively analyzed by solid-phase enzyme-linked immunosorbent assay. The age of the patients (61 men and 53 women) ranged from 18 to 80 years; median age was 51 years. Serum transforming growth factor-beta1 (P < 0.001), VEGF (P = 0.006) and VEGFR1 (P = 0.007) levels were significantly higher in patients with melanoma than in the control group. No significant differences, however, exist in the serum angiogenin and VEGFR2 levels between melanoma patients and the controls. The positive correlations of elevated serum levels of transforming growth factor-beta1, VEGF and VEGFR1 with advanced stages of disease were found. Significant relationship was found only between serum levels of VEGF and VEGFR2. Elevated serum transforming growth factor-beta1 (P < 0.001) and VEGF levels (P = 0.0012) were found to be poor prognostic factors. Serum level of angiogenin and VEGF receptors, however, had no effect on survival. Our data suggest that the angiogenic serum factors, including VEGF, transforming growth factor-beta1 and VEGFR1, but not angiogenin and VEGFR2 were increased in melanoma patients, especially associated with advanced disease stages. The mechanism of VEGF regulation of angiogenesis may in part be due to enhanced proliferation of VEGFRs, especially VEGFR1.  相似文献   
987.
We present an unusual case of a drug-related hemorrhagic diathesis. One month prior to admission, the patient was diagnosed at another medical center as having Graves' disease and propylthiouracil therapy (PTU) was initiated. Since clinical recovery was not achieved, the PTU was quickly increased to an unconventional daily dose of 1,000 mg. The patient was referred to our hospital because of spontaneous epistaxis, multiple ecchymoses and prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT), which developed soon after the increase in PTU dose. Drug-related hemorrhagic diathesis was considered, after other possible causes had been eliminated. To the best of our knowledge, this is the first reported case of spontaneous hemorrhage due to PTU use.  相似文献   
988.
The p53 family comprises the tumor suppressor p53 and the structural homologs p63 and p73. How the three family members cooperate in tumor suppression remains unclear. Here, we report different but complementary functions of the individual members for regulating retinoblastoma protein (RB) function during myogenic differentiation. Whereas p53 transactivates the retinoblastoma gene, p63 and p73 induce the cyclin-dependent kinase inhibitor p57 to maintain RB in an active, hypophosphorylated state. DeltaNp73 inhibits these functions of the p53 family in differentiation control, prevents myogenic differentiation, and enables cooperating oncogenes to transform myoblasts to tumorigenicity. DeltaNp73 is frequently overexpressed in rhabdomyosarcoma and essential for tumor progression in vivo. These findings establish differentiation control as a key tumor suppressor activity of the p53 family.  相似文献   
989.
The aim of this study was to assess the in vitro activity of a number of non-traditional antibiotics (colistin, azithromycin, doxycycline and rifampicin) against multidrug-resistant (MDR) strains of Pseudomonas aeruginosa and Acinetobacter baumannii isolated from Intensive Care Units (ICUs). We also used the checkerboard method to determine whether combinations of colistin with another non-traditional antibiotic or meropenem act synergistically against these strains. Thirty-five P. aeruginosa and 25 A. baumannii strains that were found to be MDR were included the study. Isolates were collected from the specimens of patients in ICUs from 2001 to 2003. All isolates were identified by standard methods and stored at -20 degrees C until use. Antibiotic powders of azithromycin, doxycycline, rifampicin, meropenem and colistin were obtained from their manufacturers. Minimum inhibitory concentrations (MICs) were determined by the agar dilution method on Mueller-Hinton agar. Five strains of A. baumannii and five strains of P. aeruginosa, all of which had different MIC values for colistin, were selected for the synergy study using the checkerboard titration method. The susceptibility results for doxycycline and meropenem were interpreted according to National Committee for Clinical Laboratory Standards guidelines. The susceptibility breakpoints for colistin and rifampicin were established as 4 mg/L and 2 mg/L, respectively, based on previous studies. Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 were used as control strains. Testing against the P. aeruginosa strains revealed high MIC50 values for all the drugs except colistin. Doxycycline and colistin were both effective against the A. baumannii strains, with high susceptibility rates of 92% and 100%, respectively. Azithromycin had a high MIC50 value against these strains, whilst rifampicin had a moderate effect (susceptibility rate 64%). The combination of colistin and rifampicin was fully synergistic against four A. baumannii and two P. aeruginosa strains. Combinations of colistin with meropenem and of colistin with azithromycin each showed synergistic activity against three A. baumannii isolates, whilst the same combinations resulted in generally additive or indifferent effects against P. aeruginosa strains. The colistin and doxycycline combination was generally partially synergistic or additive against all the isolates. MDR strains of P. aeruginosa and A. baumannii, which cause nosocomial infections with an increasing ratio in recent years, have limited treatment options. According to our in vitro study results, non-traditional antibiotics such as doxycycline and colistin can be an alternative for the treatment of infections caused by these strains. Combinations of colistin with non-traditional antibiotics or meropenem could be promising alternatives for the treatment of infections due to MDR strains of A. baumannii and P. aeruginosa.  相似文献   
990.
Cefoperazone is a third-generation cefalosporin that contains the N-methyl- thio-tetrazole (NMTT) side chain, which inhibits vitamin K-dependent carboxylation. Administration of NMTT-containing cefalosporins can cause alterations in the hepatic glutathione redox state, resulting in a dose-related increase in oxidised glutathione, which is responsible for the inhibition of microsomal reduction of vitamin K epoxide. In addition, cefoperazone is not metabolised and is excreted predominantly through the bile. In patients with hepatic impairment, the clearance of cefoperazone has been shown to be significantly reduced and the half-life prolonged. We report a case of choledocholithiasis related to a prolonged prothrombin time and INR secondary to cefoperazone therapy.  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