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   15484篇
  免费   928篇
  国内免费   93篇
耳鼻咽喉   93篇
儿科学   430篇
妇产科学   358篇
基础医学   2506篇
口腔科学   289篇
临床医学   1353篇
内科学   3766篇
皮肤病学   214篇
神经病学   1974篇
特种医学   388篇
外国民族医学   1篇
外科学   1311篇
综合类   35篇
一般理论   4篇
预防医学   783篇
眼科学   154篇
药学   1205篇
中国医学   30篇
肿瘤学   1611篇
  2024年   11篇
  2023年   119篇
  2022年   290篇
  2021年   470篇
  2020年   289篇
  2019年   384篇
  2018年   423篇
  2017年   379篇
  2016年   401篇
  2015年   503篇
  2014年   618篇
  2013年   734篇
  2012年   1222篇
  2011年   1236篇
  2010年   719篇
  2009年   632篇
  2008年   1057篇
  2007年   1062篇
  2006年   1025篇
  2005年   943篇
  2004年   895篇
  2003年   868篇
  2002年   767篇
  2001年   106篇
  2000年   91篇
  1999年   138篇
  1998年   153篇
  1997年   117篇
  1996年   100篇
  1995年   103篇
  1994年   74篇
  1993年   73篇
  1992年   59篇
  1991年   48篇
  1990年   44篇
  1989年   53篇
  1988年   28篇
  1987年   21篇
  1986年   34篇
  1985年   24篇
  1984年   32篇
  1983年   24篇
  1982年   21篇
  1981年   17篇
  1980年   16篇
  1979年   9篇
  1977年   8篇
  1976年   8篇
  1969年   6篇
  1968年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
 Soft tissue tumours represent a heterogeneous group of mesenchymal lesions, and their classification is the subject of continuous debate. Chromosome analysis, molecular cytogenetics and molecular assays may become increasingly useful in diagnosis, and this review summarises advances in the cytogenetic characterisation and classification of soft tissue tumours. Among the group of fibrous lesions, superficial fibromatosis exhibits trisomy 8. This genomic change is also observed in desmoid fibromatosis in association with trisomy 20. Trisomy 11 is the most frequently observed chromosomal aberration in congenital fibrosarcoma. Dermatofibrosarcoma protuberans and giant cell fibroblastoma share a translocation t(17;22), which supports the concept of the existence of a common differentiation pathway. Adipose tissue tumours is the group in which integration of genetics and pathology has been most fruitful. Ordinary lipomas cytogenetically show an abnormal karyotype in about half the cases. Genomic changes of the 11q13 region are observed in hibernoma. Lipoblastoma exhibits a specific 8q rearrangement in 8q11-q13. Loss of material from the region 16q13-qter and 13q deletions are observed in spindle cell/pleomorphic lipomas. The well-differentiated liposarcoma/atypical lipoma group is characterised karyotypically by the presence of one extra ring and/or extra giant chromosome marker. Myxoid and round cell liposarcoma share the same characteristic chromosome change: t(12;16)(q13;p11) in most cases. In the group of smooth muscle lesions most data are derived from uterine leiomyomas, which can be subclassified cytogenetically into seven different types. Half of all leiomyomas are chromosomally normal; the other half have one of six possible consistent chromosome changes. Alveolar rhabdomyosarcoma is characterised cytogenetically by two variant translocations t(2;13)(q35;q14) and t(1;13)(p36;q14). Among tenosynovial tumours, the localised type of giant cell tumour of tendon sheath exhibits two different karyotypic changes. One involves 1p11 in a translocation with chromosome 2 or with another chromosome. A second type involves 16q24. Synovial sarcoma is characterised cytogenetically by a translocation occurring between chromosome 18 and presumably two adjacent loci on the X chromosome. In neural tumours, abnormalities of chromosome 22 have been reported in benign schwannomas and perineuriomas. Malignant peripheral nerve sheath tumours exist in two main forms: sporadic and associated with the NF-1 syndrome. Karyotypes are very complex, but chromosomes 17q and 22q are very often involved. Clear cell sarcoma is characterised cytogenetically and molecularly by a translocation t(12;22)(q13;q12). The Ewing’s sarcoma/peripheral neuroectodermal tumour category shows a central karyotypic anomaly represented by the translocation t(11;22). The two variants t(21;22) and t(7;22) are found in some cases. Among cartilaginous lesion, the most frequently described anomaly is the t(9;22)(q22;q12) in extraskeletal myxoid chondrosarcoma. Intra-abdominal desmoplastic small round cell tumour is characterised by a t(11;22)(p13;q12). Received: 5 February 1997 / Accepted: 24 February 1997  相似文献   
2.
Prevalence of isolated left ventricular (LV) diastolic dysfunction has been reported to be as high as one-third of all heart failure (HF) cases, with an increasing prevalence in the elderly population. However, there is a paucity of prospective data about the prevalence and prognosis of isolated LV diastolic dysfunction in an unselected population of patients hospitalized with HF. Therefore, we prospectively evaluated 179 consecutive patients discharged from our hospital with HF to assess the prevalence of systolic versus diastolic LV dysfunction among patients hospitalized with HF and to compare their demographics, clinical features, self-perceived quality of life (QOL), and 6-month readmission rate and mortality. Among them, 133 (59% men, median age 74 years) showed in sinus rhythm and had no significant primary valvular disease. LV diastolic dysfunction was diagnosed on the basis of the European Study Group on Diastolic HF echocardiographic criteria. QOL was assessed at hospital discharge and 6-month follow-up visit using the Minnesota Living with HF questionnaire. Survival of patients with HF was compared with that of age- and sex-matched general population. In all, 29 patients (22%) had isolated LV diastolic dysfunction and 102 (78%) had prevalent LV systolic dysfunction (ie, LV ejection fraction 相似文献   
3.
Insulin-like growth factor II (IGF-II) is a mitogen for manycell types and an important modulator of muscle growth and differentiation.IGF-II gene is prevalently expressed during prenatal developmentand its gene activity is regulated by genomic imprinting, inthat the allele inherited from the father is active and theallele inherited from the mother is inactive in most normaltissues. IGF-II expression is activated in several types ofhuman neoplasms and an alteration of IGF-II imprinting has beendescribed in Beckwith–Wiedemann syndrome and Wilms' tumour.Here we show that monoallelic expression of IGF-II gene is conservedin normal adult muscle tissue whereas two or more copies ofactive IGF-II alleles, arising by either relaxation of imprintingor duplication of the active allele, are found in 9 out of 11(82%) rhabdomyo-sarcomas retaining heterozygosity at 11p15,regardless of the histological subtype. Since IGF-II has beenindicated as an autocrine growth factor for rhabdomyosarcomacells, these findings strongly suggest that acquisition of adouble dosage of active IGF-II gene is an important step forthe initiation or progression of rhabdomyosarcoma tumorigenesis.Among different types of muscle tumors, relaxation of imprintingseems to arise prevalently in rhabdomyosarcomas, since we havedetected only one case of partial reactivation of the maternalIGF-II allele out of 7 lelomyosarcomas tested.  相似文献   
4.
There is a need for consistent definition of human immunodeficiency virus (HIV)-associated cases of progressive multifocal leukoencephalopathy (PML), especially following the profound disease changes that have resulted from the use of highly active antiretroviral therapy (HAART). According to the criteria used for diagnosis, PML cases should be either referred to as “histology-confirmed,” with evidence of JC virus (JCV) infection in brain, “laboratory-confirmed,” with detection of JCV DNA in cerebrospinal fluid (CSF), or “possible,” in the presence of typical clinical and radiological picture, but no demonstration of JCV infection. Disease outcome should be defined by the evidence or lack of evidence of disease activity, rather than using survival or other variables. Disease activity should be based on clinical (scored neurological examination), radiological (magnetic resonance imaging), and virological (JCV DNA levels in CSF) indicators, to be assessed regularly, e.g., every 3 months until evidence of disease arrest or death. Furthermore, parallel assessments of other HIV-associated manifestations, including CD4+ cell counts and viral load, are required. A standard patient classification would be helpful for clinical management of PML patients, for their inclusion in clinical studies, and also will increase our current knowledge of PML and its evolution in relation with HAART.  相似文献   
5.
The quality of health care systems and processes is becoming a prominent problem and more and more efforts are devoted to define methodologies and tools to measure and assure quality of care. New methods are required to optimize health care processes to guarantee high quality standards within (limited) available resources. Resource optimizations able to preserve the quality of treatments require good models of medical processes. This paper presents LEMMA, a new notation to model medical processes. LEMMA provides physicians with intuitive graphical elements to design their models. At the same time a high level timed Petri net corresponding to the designed model is built automatically. In this way, LEMMA models are ascribed formal semantics and can be executed and analyzed automatically. The dual language approach followed in this paper allows physicians to gain all the benefits of formal methods without being proficient in them. Medical users manage simple graphical elements, while Petri nets ensure formality and validation capabilities. In this way LEMMA mixes formal and informal notations, overcoming the problems of both the approaches. The definition of the notation has been supported by the development of an environment to design LEMMA models. The environment, besides letting us experiment with the notation, has been employed to define and analyze real case studies.  相似文献   
6.
7.
Scatter correction in scintigraphy: the state of the art   总被引:3,自引:3,他引:0  
In scintigraphy, the detection of scattered photons degrades both visual image analysis and quantitative accuracy. Many methods have been proposed and are still under investigation to cope with scattered photons. The main features of the problem of scattering in radionuclide imaging are presented first, to provide a sound foundation for a critical review of the existing scatter correction techniques. These are described using a classification relating to their aims and principles. Their theoretical potentials are analysed, as well as the difficulties of their practical implementation. Finally, the problems of their evaluation and comparison are discussed. Correspondence to: I. Buvat  相似文献   
8.
We report the results of a retrospective review of the outpatient pretransplantation workup for United Network for Organ Sharing (UNOS) 3 patients adopted at a liver transplantation (LT) center and illustrate the efficiency indicators used for quality evaluation and cost-analysis. A single-center, pre-LT evaluation workup was performed on an outpatient basis at a cost per patient evaluation of 2,770 Euros (). Objective measures were: the number of patients admitted to and excluded from each phase of the algorithm; the rate of patients admitted to pre-LT evaluation out of the total of referred patients (the referral efficiency rate); the rate of waitlisted patients out of those admitted to pre-LT evaluation (the evaluation efficiency rate); the rate of waitlisted patients out of those referred for LT (the process efficiency rate); and the cost per waitlisted patient, as the ratio of the cost per patient evaluation to the evaluation efficiency rate. From January 1, 1996, to October 1, 2004, 1,837 patients were referred for LT on an outpatient basis. Based on preemptive evaluation of the available clinical data, 412 patients (22.4%) were excluded from pre-LT evaluation and 1,425 (77.6%) were admitted to preliminary consultation. Among these, 603 (42.3%) were excluded from and 822 (57.7%) were admitted to pre-LT evaluation with a referral efficiency rate of 44.7% (822 of 1,837). Out of the patients evaluated for LT, 484 were waitlisted with a cost-utility and evaluation efficiency rate of 58.8% each (484 of 822). Of the 1,837 patients originally addressed for LT 484 were waitlisted, yielding a process efficiency rate of 26.3% (484 of 1,837) and a cost per waitlisted patient of 4,710.8. In conclusion, the 3 indicators allowed monitoring of the efficiency of the pre-LT evaluation algorithm. The current process efficiency rate at our center is low (26.3%), but avoiding early referrals we might increase it to 31.6%, with a 12% net saving on costs per waitlisted patient (from 4,710.8 to 4,165.4).  相似文献   
9.
10.
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