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   24862篇
  免费   1354篇
  国内免费   49篇
耳鼻咽喉   398篇
儿科学   735篇
妇产科学   485篇
基础医学   3469篇
口腔科学   402篇
临床医学   2366篇
内科学   4961篇
皮肤病学   930篇
神经病学   2496篇
特种医学   922篇
外国民族医学   2篇
外科学   3653篇
综合类   224篇
一般理论   6篇
预防医学   1706篇
眼科学   398篇
药学   1647篇
  1篇
中国医学   38篇
肿瘤学   1426篇
  2023年   138篇
  2022年   134篇
  2021年   373篇
  2020年   241篇
  2019年   310篇
  2018年   663篇
  2017年   450篇
  2016年   566篇
  2015年   622篇
  2014年   615篇
  2013年   981篇
  2012年   1640篇
  2011年   1692篇
  2010年   820篇
  2009年   662篇
  2008年   1298篇
  2007年   1436篇
  2006年   1383篇
  2005年   1285篇
  2004年   1221篇
  2003年   1110篇
  2002年   1075篇
  2001年   612篇
  2000年   590篇
  1999年   576篇
  1998年   176篇
  1997年   137篇
  1996年   111篇
  1995年   129篇
  1994年   127篇
  1993年   102篇
  1992年   273篇
  1991年   317篇
  1990年   258篇
  1989年   248篇
  1988年   217篇
  1987年   236篇
  1986年   221篇
  1985年   220篇
  1984年   148篇
  1983年   148篇
  1979年   143篇
  1978年   102篇
  1977年   97篇
  1975年   120篇
  1974年   125篇
  1973年   105篇
  1972年   115篇
  1971年   105篇
  1968年   97篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Part 5 is the final part of a series of five articles reporting on an international, multicenter clinical audit of treatment outcome for complete UCLP. A number of recommendations for the methodology of future studies is made especially with respect to entry criteria, sample size, assumptions of homogeneity, and the reproducibility and validity of outcome measures. The findings of the present study regarding clinical procedures are presented tentatively, and improvement and extension of the methodology are required. It appears, however, that acceptable results can be achieved by different programs and ultimately clinical choices may be based on factors such as complexity, costs, and demands of treatment. Standardization, centralization, and the participation of high volume operators were associated with good outcomes, and nonstandardization and the participation of low volume operators with poor outcomes. Therapeutic factors associated with good outcomes were the employment of a vomer flap to close the anterior palate, and poor outcomes with primary bone grafting and with active presurgical orthopedics.  相似文献   
12.
The dental response to repeated antimicrobial and antihistamine medications was studied by comparing the dental health of 64 adenoidectomized children 5 years after surgery to that of 212 untreated controls. Annual dental recordings starting from the age of 3 years were obtained from health care centers. As expected, the proportion of children who had several (> or = 11) syrup medications was significantly higher (p < 0.001) in the adenoidectomized than in the control group. Sucrose-containing syrup medications were prescribed twice as often for the children of the adenoidectomized as for the control group (p < 0.001). However, the average amount of antimicrobial syrup medications prescribed was 19.2 +/- (SD) 13.0 per child for the adenoidectomized as compared to 8.5 +/- 8.3 for the control children (p < 0.001). The dmf value of the adenoidectomized children at the age of 3 years (mean +/- SEM: 0.5 +/- 0.1) was significantly (p < 0.005) lower than that of the controls (1.1 +/- 0.2). The difference was still significant (p < 0.01) at the age of 4 years, but disappeared thereafter. In conclusion, the antibacterial syrup medication seemed to be associated with a significant decline in dental caries at first. The simultaneous use of antihistamines was, however, thought to delay normal tooth maturation, so that after discontinuation of the antimicrobial medication, accelerated formation of new carious lesions took place.  相似文献   
13.
From the culture medium of the Bacillus subtilis strain ATCC 6633 the proteolytic enzyme activity was isolated by ammonium sulphate precipitation and acetone treatment. In the case of the isolated activity it is a question of a serine protease with a pH optimum of 10, which is inhibited by diisopropyl fluoro-phosphate and sodium ethylene diamine tetra-acetic acid and is not influenced by o-phenanthroline. With the enzyme preparations thus obtained, decalcified sections of caries-free human teeth were incubated at pH 7.0 and 37 °C both with and without di-isopropyl fluoro-phosphate. Under the influence of the enzyme action there were changes in the matachromatic structures and finally the disintegration of the decalcified dental tissue. Propitious points of attack are the cement-dentine boundary and the central sections of the globuli. The isolated enzyme thus leads to the same decomposition phenomena as the direct incubation with Bacillus subtilis. With this enzymatic decomposition of the dental tissue, determinable quantities of nitrogen are released biochemically in the incubation solution. It is assumed that the hydrolysed substance is a glycoproteid with a non-collagenic protein component.  相似文献   
14.
15.

Introduction

Piezoosteotomy was assessed as alternative osteotomy method in orthognathic surgery regarding handling, time requirement, nerve and vessel impairment.

Materials and methods

In this comparative clinical experience, 90 patient’s orthognathic surgery procedures were performed in typical distribution prospectively by piezoosteotomy: 34 (38%) monosegment, 47 (52%) segmented LeFortI osteotomies, 94 (52%) sagittal split osteotomies, 11 (12%) symphyseal, and 4 (2%) mandibular body osteotomies. As controls served 90 retrospective patients with conventional saw and chisel osteotomy: 58 (64%) monosegment, 27 (30%) segmented LeFortI osteotomies, 130 (72%) sagittal split, and 4 (4%) symphyseal osteotomies.

Results and discussion

Piezoosteotomies were individually designed to interdigitate the jaw segments after repositioning. The pterygomaxillary suture weakened angulated tools; auxiliary chisels were required in 100% of cases for the nasal septum and lateral nasal walls, in 33% for pterygoid processes. The dorsal maxilla as the pterygoid process were easily reduced; 15% mandibular osteotomies required sawing, while the lingual dorsal osteotomy was performed by manual feedback due to limited visibility. Bloodloss decreased from average 537?±?208 ml vs. 772?±?338 ml (p?=?0.0001). Operation time remained unchanged: 223?±?70 min vs. 238?±?60 min (p?=?0.2) for a conventional bimaxillary procedure. Clinical courses and reossification were unobtrusive. Alveolar inferior nerve sensitivity was retained in 98% of the piezoosteotomy collective versus 84% of controls (p?=?0.0001) at 3 months postoperative testing.

Conclusion

Piezoelectric osteotomy did not prolong the operation and reduced blood loss as alveolar nerve impairment. A few patients required additional sawing or chisel. Piezoelectric screw insertion as complex osteotomies may be initiated to simplify the procedure and increase segment interdigitation after repositioning as to minimize the osteofixation time and dimensions.  相似文献   
16.
Although thoracic duct injury is an uncommon complication of neck dissection, it can have a significant physiological and immunological impact on the patient's recovery as well as having more serious effects. We report a novel technique of using cyanoacrylate tissue glue for managing thoracic duct damage when this is noted at the time of neck dissection surgery.We have used this technique in four patients with no post-operative chyle leak or added complications.  相似文献   
17.

Objectives

To provide fractographic analysis of clinically fractured zirconia implants recovered with their cemented crown. To calculate bending moments, corresponding stress and crack onset location on the implant’s fracture surface using a mathematical model integrating spatial coordinates of the crown-implant part and occlusal loading obtained from 2D and 3D images.

Methods

15 fractured zirconia implants parts (11 posterior and 4 anterior) with their all- ceramic crowns still cemented on it were recovered. The implants were first generations from four manufacturers (AXIS Biodental, Z-Systems, Straumann, Swiss Dental Solutions). The time-to-failure varied between 2 weeks and 9 years. Fractography was performed identifying the failure origin and characteristic surface crack features. From 2D and 3D digital images of the crown-implant part, spatial coordinates anchoring the crown’s occlusal contacts with the implant’s central axis and reference plane were integrated in a mathematical model spreadsheet. Loads of 500 N in total were selectively distributed over identified occlusal contacts from wear patterns. The resultant bending and torsion moments, corresponding shear, tensile, maximum principal stress and von Mises stress were calculated. The fracture crack onset location on the implant’s fracture surface was given by an angular position with respect to an occlusal reference and compared with the location of the fracture origin identified from fractographic analysis.

Results

Implants fractured from the periphery of the smaller inner diameter between two threads at the bone-entrance level except for one implant which failed half-way within the bone. The porous coating (AXIS Biodental) and the large grit alumina sandblasting (Z-System) created surface defects directly related to the fracture origin. The model spreadsheet showed how occlusal loading with respect to the implant’s central axis affects bending moments and crack onset. Dominant loads distributed on contacts with important wear pattern provided a calculated crack onset location in good agreement with the fractographic findings of the fracture origin.

Significance

Recovered broken zirconia implant parts with their restorative crowns can provide not only information regarding the failure origin using fractography but also knowledge regarding occlusal crown loading with respect to the implant’s axis. The mathematical model was helpful in showing how occlusal loading affects the location of the fracture initiation site on clinical zirconia implant fracture cases.  相似文献   
18.
Neuregulin 1 (NRG1) and v-erb-a erythroblastic leukemia viral oncogene homolog 4 (ErbB4) have been extensively studied in schizophrenia susceptibility because of their pivotal role in key neurodevelopmental processes. One of the reasons for the inconsistencies in results could be the fact that the phenotype investigated has mostly the diagnosis of schizophrenia per se, which is widely heterogeneous, both clinically and biologically. In the present study we tested, in a large cohort of 461 schizophrenia patients recruited in Scotland, whether several SNPs in NRG1 and/or ErbB4 are associated with schizophrenia symptom dimensions as evaluated by the Positive and Negative Syndrome Scale (PANSS). We then followed up nominally significant results in a second cohort of 439 schizophrenia subjects recruited in Germany. Using linear regression, we observed two different groups of polymorphisms in NRG1 gene: one showing a nominal association with higher scores of the PANSS positive dimension and the other one with higher scores of the PANSS negative dimension. Regarding ErbB4, a small cluster located in the 5′ end of the gene was detected, showing nominal association mainly with negative, general and total dimensions of the PANSS. These findings suggest that some regions of NRG1 and ErbB4 are functionally involved in biological processes that underlie some of the phenotypic manifestations of schizophrenia. Because of the lack of significant association after correction for multiple testing, our analyses should be considered as exploratory and hypothesis generating for future studies.  相似文献   
19.

Background

The study explores whether the cerebral biochemical pattern in patients treated with hemicraniectomy after large middle cerebral artery infarcts reflects ongoing ischemia or non-ischemic mitochondrial dysfunction.

Methods

The study includes 44 patients treated with decompressive hemicraniectomy (DCH) due to malignant middle cerebral artery infarctions. Chemical variables related to energy metabolism obtained by microdialysis were analyzed in the infarcted tissue and in the contralateral hemisphere from the time of DCH until 96 h after DCH.

Results

Reperfusion of the infarcted tissue was documented in a previous report. Cerebral lactate/pyruvate ratio (L/P) and lactate were significantly elevated in the infarcted tissue compared to the non-infarcted hemisphere (p < 0.05). From 12 to 96 h after DCH the pyruvate level was significantly higher in the infarcted tissue than in the non-infarcted hemisphere (p < 0.05).

Conclusion

After a prolonged period of ischemia and subsequent reperfusion, cerebral tissue shows signs of protracted mitochondrial dysfunction, characterized by a marked increase in cerebral lactate level with a normal or increased cerebral pyruvate level resulting in an increased LP-ratio. This biochemical pattern contrasts to cerebral ischemia, which is characterized by a marked decrease in cerebral pyruvate. The study supports the hypothesis that it is possible to diagnose cerebral mitochondrial dysfunction and to separate it from cerebral ischemia by microdialysis and bed-side biochemical analysis.  相似文献   
20.
Surgery remains the mainstay of potentially curative treatment of esophageal cancer; however, esophageal resection is still associated with a relevant morbidity and mortality. Furthermore, patients frequently suffer from concomitant comorbidities and present in a reduced nutritional status. The rationale of minimally invasive surgery is the reduction of surgical trauma with subsequent minimization of (pulmonary) complications and mortality without compromising oncological quality. Minimally invasive esophageal resection was established nearly two decades ago and since then some centers worldwide have adopted this approach as the preferred option for surgical treatment of esophageal cancer. Minimally invasive esophageal resection can be safely performed and provides excellent results in experienced hands. Currently, there is only one randomized trial available comparing open and minimally invasive resection. It was demonstrated that the latter significantly reduced pulmonary complications with comparable mortality and oncological outcome. However, in the majority of studies these convincing results could not be confirmed. Reduced blood loss and a shortened hospital stay were shown to be the main advantages of the minimally invasive approach. Due to technical modifications, patient selection and a remarkable heterogeneity of current studies, a final conclusion on the value of minimally invasive esophagectomy is difficult to be drawn. Based on the current evidence, a noncritical use of minimally invasive resection for esophageal cancer cannot be recommended; however, in selected patients and with appropriate expertise this approach is at least comparable to open esophagectomy.  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