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   297866篇
  免费   18216篇
  国内免费   841篇
耳鼻咽喉   4321篇
儿科学   10196篇
妇产科学   7541篇
基础医学   39689篇
口腔科学   6633篇
临床医学   26215篇
内科学   60682篇
皮肤病学   6236篇
神经病学   27235篇
特种医学   11451篇
外国民族医学   45篇
外科学   45825篇
综合类   3944篇
现状与发展   3篇
一般理论   231篇
预防医学   19519篇
眼科学   8258篇
药学   19983篇
中国医学   529篇
肿瘤学   18387篇
  2021年   3431篇
  2020年   2188篇
  2019年   3546篇
  2018年   4340篇
  2017年   3288篇
  2016年   4009篇
  2015年   4730篇
  2014年   6766篇
  2013年   10352篇
  2012年   14620篇
  2011年   15545篇
  2010年   8905篇
  2009年   8316篇
  2008年   14968篇
  2007年   15975篇
  2006年   15595篇
  2005年   16067篇
  2004年   15385篇
  2003年   14757篇
  2002年   14307篇
  2001年   8626篇
  2000年   8206篇
  1999年   7596篇
  1998年   3986篇
  1997年   3597篇
  1996年   3072篇
  1995年   2811篇
  1994年   2562篇
  1993年   2502篇
  1992年   4896篇
  1991年   4615篇
  1990年   4468篇
  1989年   4260篇
  1988年   3911篇
  1987年   3712篇
  1986年   3728篇
  1985年   3629篇
  1984年   3214篇
  1983年   2824篇
  1982年   2616篇
  1981年   2457篇
  1980年   2206篇
  1979年   2666篇
  1978年   2309篇
  1977年   1951篇
  1976年   1689篇
  1975年   1787篇
  1974年   1844篇
  1973年   1707篇
  1972年   1453篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
BACKGROUND: Improved prognosis can be achieved in selected patients with peritoneal carcinomatosis (PC) by major surgery and hyperthermic intraperitoneal chemotherapy (HIPEC). METHOD: Sixty seven patients with PC were operated with the aim of complete macroscopical cytoreduction followed by HIPEC (using cisplatin, mitomycin or mitoxantrone). Quality of life was assessed with the EORTC QLQ-C30 questionnaire. RESULTS: The patients had a variety of primary tumours, including appendix carcinomas (22/67). Mean operating time was 7 hours and complete cytoreduction was achieved in 58% of the patients. Overall morbidity was 34%. Post-operative mortality was 4.5%. The mean score for global health status of long-term survivors (20 questionnaires/25 patients) was 62.6 (73.3 for the control population, p=0.07). Functional status, particularly the role (56.4) and the social functioning (53.9) were impaired. CONCLUSION: Cytoreductive surgery combined with HIPEC is associated with an increased morbidity and mortality. Complications are predominantly related to major surgery. Following this aggressive treatment, survivors may achieve a satisfactory quality of life.  相似文献   
993.
Dysplasia is the only marker for malignant potential in Barrett's esophagus. The histologic interpretation of dysplasia is sometimes difficult, particularly when attempting to distinguish dysplastic changes from those of a regenerating and inflammatory mucosa. In order to find an objective marker to identify patients with high risk of malignant transformation, the authors evaluated 497 biopsies from 66 patients with Barrett's esophagus with flow cytometry. The aim of the study was to correlate DNA content and proliferative abnormalities with histology. All biopsies classified histologically as negative for dysplasia had a diploid DNA content. The percentage of biopsies with an aneuploid DNA content increased with the histologic grade of dysplasia: 2 percent of indefinite dysplasia, 11 percent of low grade dysplasia, 44 percent of high grade dysplasia and 78 percent of biopsy specimens with cancer biopsies were aneuploid. Mean S and G2M fractions of diploid biopsy specimens increased with the severity of histologic changes. The S and G2M fraction threshold values that could differentiate patients that were negative for dysplasia from those with high grade dysplasia or cancer were 9 percent and 6 percent, respectively. Aneuploidy or G2M fraction greater than 6 percent was the best discriminating criteria between those two distinct groups of patients. All 6 patients with high grade dysplasia or cancer had aneuploid cell populations or increased G2M fraction, whereas none of the 35 patients whose biopsies were histologically negative for dysplasia had evidence of genomic instability or increased G2M fraction. Flow cytometric abnormalities were found in 10 out of 25 patients whose biopsies were classified as indefinite for dysplasia or low grade dysplasia.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
994.
Examined the changing profiles of intelligence in males with fragile X syndrome as these individuals increased in chronological age. Using a psychometric instrument designed to measure styles of information processing, 21 males aged 4 to 27 years were examined cross-sectionally in sequential processing, simultaneous processing, and achievement. The age of the subject was associated with age-equivalent levels of both simultaneous processing and achievement, but fragile X males did not show higher levels of sequential processing with increasing chronological age. Compared to younger fragile X males, the older subjects were more delayed in sequential processing skills relative to their abilities in other areas. A smaller longitudinal study confirmed the presence of a plateau in sequential processing among those subjects tested two times after the age of 10 years. Implications are discussed for diagnosis, intervention, and the matching of subject groups in mental retardation research.This research was supported in part by the John Merck Fund, the Joseph P. Kennedy, Jr. Foundation, NIH grants RR00125 and HD03008, and NIMH grants MH18268 and MH30929. We thank Wendy Marans and Joel Bregman for their comments on an earlier draft of this paper.  相似文献   
995.
This paper describes the implementation of an ultraviolet (UV) laser (Spectra Physics 171-18 with 3 lines: 334, 351 and 364 nm in UV) as light source for fluorescence confocal scanning microscopy. With this instrument it is possible to use fluorophores not previously available for confocal laser microscopical imaging of fluorophores such as fluoro-gold and AMCA. In the study we show confocal laser microscopical imaging of fluorescent motoneurons labelled by retrograde transport of fluoro-gold and AMCA-fluorescent axon terminals labelled with antisera against immunogenes as thyrotropin-releasing hormone (TRH) and calcitonin gene-related peptide (CGRP). These two fluorophores may be recorded simultaneously or separately by using a filter that suppresses the emission of one of the fluorophores. The described instrument should also be useful in applications involving detection of monoamines by the Falck-Hillarp technique, as well as measurements of cytosolic free calcium by indicators such as Fura-2 and Indo-1. Measurements performed in reflected and fluorescence light indicated that the resolution along the optical axis improved by about 25% when UV (351 nm) is used instead of visible light (514 nm). This figure is close to that expected on theoretical basis. There are, however, also serious problems related to the use of UV excitation. Firstly, objectives must be selected based on their UV transmission properties. Secondly, chromatic aberration may cause a substantial focal shift between illuminating and emitted light, calling for a flexible instrumental design in order to allow for compensation. As shown here, this problem can be circumvented by using reflecting objectives but at a price of lower resolution compared with high-aperture refracting objectives.  相似文献   
996.
Summary The influence of mediolateral deformity, tibial torsion, and different centers of foot support was studied with a three-dimensional computer model that incorporates the significant muscles of the lower extremities needed for quasi-static walking. This theoretical method avoids the variability in gait pattern from the pain and discomfort associated with deformity in patients. The study illustrates the possible importance of the muscle force on the load across the knee and ankle. High strains in the medial gastrocnemius and the medial hamstring created particularly high loads in the medial compartment of the knee. Internal torsion and varus deformity were associated with the highest loads in the medial compartment of the knee, although the peak load for each deformity occurred in different phases of the gait cycle. Both external torsion and valgus deformity generally decreased the load in the medial compartment, but early in the gait cycle external torsion increased the loads on the medial side. In addition, when the center of support of the body was in the forefoot, the loads through the knee were lower than when foot support was at the heel. As expected, if the center of support was on the lateral foot line, the lateral compartment was subjected to more load and, conversely, when the center of support was on the medial part of the foot the medial compartment of the knee was more loaded. Although the predicted forces agree well with those found with other methods, we think that the model is best used to measure the direction of influence of specific factors.  相似文献   
997.
998.
The incidence of cervical myelopathy and subluxation was investigatedin 48 patients with rheumatoid disease who had three or moremajor lower limb joint replacements. Eight (17%) developed cervicalmyelopathy requiring cervical fusion. This was the subsequentcause of death in two. Four further patients demonstrated clinicalfeatures of myelopathy. Cervical subluxation was present in29 of 44 (66%) in whom adequate radiographs were available.The development of cervical symptoms and signs could not havebeen predicted from the sex, age of onset, duration of diseaseor steriod therapy. Radiographic changes in the cervical spinewere independent of major lower limb joint destruction and wereoften not present when planning a programme of joint replacement.Fifty-one control patients were studied. Cervical myelopathyoccurred in 2 (4%) and subluxation in 24 (47%). The developmentof rheumatoid changes in the cervical spine was unrelated toinvolvement of the hip or knee joints in the control group. There was a significant (p<0.05) increase in the incidenceof cervical myelopathy in patients with multiple lower limbjoint replacements compared with the control population. KEY WORDS: Rheumatoid arthritis, Cervical myelopathy, Cervical subluxation, Arthroplasty  相似文献   
999.
A direct solution is proposed to an optimal control problem of linear econometric systems with a quadratic welfare loss function when there are linear equality constraints on the control variables. The direct solution proposed here eliminates the problem of non-uniqueness of the optimal solution, which is present when this optimal control problem is solved using the recursive algorithm proposed by Chow,1 Pindyck2 and Tan.3 If a unique solution to the optimal control problem exists, then the direct solution and the recursive solution coincide.  相似文献   
1000.
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