全文获取类型
收费全文 | 154978篇 |
免费 | 10042篇 |
国内免费 | 774篇 |
专业分类
耳鼻咽喉 | 2009篇 |
儿科学 | 3708篇 |
妇产科学 | 2288篇 |
基础医学 | 19323篇 |
口腔科学 | 3555篇 |
临床医学 | 15559篇 |
内科学 | 33430篇 |
皮肤病学 | 2510篇 |
神经病学 | 15106篇 |
特种医学 | 5751篇 |
外国民族医学 | 1篇 |
外科学 | 25737篇 |
综合类 | 1419篇 |
一般理论 | 259篇 |
预防医学 | 10889篇 |
眼科学 | 3083篇 |
药学 | 9390篇 |
3篇 | |
中国医学 | 192篇 |
肿瘤学 | 11582篇 |
出版年
2023年 | 1139篇 |
2022年 | 1965篇 |
2021年 | 4380篇 |
2020年 | 2466篇 |
2019年 | 3923篇 |
2018年 | 4652篇 |
2017年 | 3361篇 |
2016年 | 3691篇 |
2015年 | 4149篇 |
2014年 | 5803篇 |
2013年 | 7664篇 |
2012年 | 11744篇 |
2011年 | 12257篇 |
2010年 | 6731篇 |
2009年 | 6016篇 |
2008年 | 10394篇 |
2007年 | 10351篇 |
2006年 | 10064篇 |
2005年 | 10003篇 |
2004年 | 9196篇 |
2003年 | 8591篇 |
2002年 | 7835篇 |
2001年 | 1040篇 |
2000年 | 861篇 |
1999年 | 1200篇 |
1998年 | 1596篇 |
1997年 | 1290篇 |
1996年 | 1097篇 |
1995年 | 1072篇 |
1994年 | 863篇 |
1993年 | 807篇 |
1992年 | 649篇 |
1991年 | 547篇 |
1990年 | 511篇 |
1989年 | 449篇 |
1988年 | 503篇 |
1987年 | 438篇 |
1986年 | 468篇 |
1985年 | 473篇 |
1984年 | 566篇 |
1983年 | 539篇 |
1982年 | 655篇 |
1981年 | 622篇 |
1980年 | 486篇 |
1979年 | 246篇 |
1978年 | 319篇 |
1977年 | 294篇 |
1976年 | 199篇 |
1975年 | 183篇 |
1974年 | 185篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Patricia A Wilkosz Sachiko Miyahara Oscar L Lopez Steven T Dekosky Robert A Sweet 《The American journal of geriatric psychiatry》2006,14(4):352-360
BACKGROUND: Psychotic symptoms in Alzheimer disease (AD+P) identify a heritable phenotype associated with more rapid cognitive decline. The authors have proposed that AD+P is itself a composite of a misidentification and a paranoid subtype with increased cognitive impairment restricted to the misidentification type. Most prior studies of the clinical correlates of AD+P have been limited, however, by the inclusion of prevalent cases. METHODS: Subjects with possible or probable AD or mild cognitive impairment (MCI) without psychosis at study entry were assessed at the time of initial presentation and then annually. Psychotic symptoms were assessed using the CERAD Behavioral Rating Scale. Survival analyses used Cox proportional hazard models with time-dependent covariates to examine the predictors of psychosis onset. RESULTS: A total of 288 subjects completed at least one follow-up examination. Mean duration of follow-up was 22.1 months. The incidence of psychosis was 0.19 per person-year. Cognitive impairment was associated with onset of psychosis, largely as a result of its association with onset of the misidentification, but not the paranoid, subtype. Including psychotropic medication use in the model revealed an association of antidepressant use with the onset of psychosis. This latter association appeared to arise from an underlying association between depression and the risk of psychosis onset rather than from antidepressant treatment. CONCLUSION: These findings are consistent with the hypothesis that the misidentification and the paranoid subtypes each define a more biologically homogeneous group than AD+P as a whole. Further exploration of the relationship between depressive symptoms and psychosis in patients with AD is warranted. 相似文献
12.
13.
14.
Genomes of some parasites contain dozens of alternative and highly diverged surface antigens, of which only a single one is expressed in any cell. Individual cells occasionally change expression of their surface antigen, allowing them to escape immune surveillance. These switches appear to occur in a partly random way, creating a diverse set of antigenic variants. In spite of this diversity, the parasitemia develops as a series of outbreaks, in which each outbreak is dominated by relatively few antigenic types. Host-specific immunity eventually clears the dominant antigenic types, and a new outbreak follows from antigenic types that have apparently been present all along at low frequency. This pattern of sequential dominance by different antigenic types remains unexplained. We review the five most prominent theories, which have developed mainly from studies of the protozoans Trypanosoma and Plasmodium, and the bacterial spirochete Borrelia. The most promising theories depend on some combination of mechanisms to create favored connectivity pathways through the matrix of transitions between variants. Favored pathways may arise from biased switches at the molecular level of gene expression or from biases imposed by immune selection. We illustrate the concept of connectivity pathways by reanalysis of data on transitions between variants from Borrelia hermsii. 相似文献
15.
16.
17.
We evaluated the acquisition and performance of a high-precision locomotor task in patients with Parkinson's disease (PD) and healthy subjects. All subjects walked on a treadmill and had to step repetitively as low as possible over an obstacle without touching it. During blocks 1 and 2, the subjects had full vision and received additional acoustic warning and feedback signals. During block 3, vision became restricted. Changes in foot clearance and the number of obstacle hits were evaluated. Initially, PD patients performed poorer and improved foot clearance slower. After task repetition, the groups performed similarly. Restricting vision deteriorated performance in both groups. The similar performance of PD patients after task repetition might indicate that adequate training could improve adaptive locomotor behavior in PD patients. 相似文献
18.
19.
Validation of a simplified technique for using the POPQ pelvic organ prolapse classification system 总被引:3,自引:2,他引:1
Steven Swift Sarah Morris Vikki McKinnie Robert Freeman Eckhard Petri Richard J. Scotti Peter Dwyer 《International urogynecology journal》2006,17(6):615-620
Our objective was to determine the inter-examiner agreement of a simplified pelvic organ prolapse quantification (POPQ) exam and to assess its correlation with the standard POPQ exam. This study consists of two parts; both were preformed in a prospective, randomized, blinded fashion on women presenting with complaints attributed to pelvic organ support defects. The first study was done to determine the inter-examiner reliability of a simplified POPQ exam. The simplified POPQ exam is based on the POPQ with similar ordinal staging but with only four points measured instead of nine. Forty-eight women underwent exams by five different investigators. The order of exams was randomized and the examiners were blinded to the results of each other’s findings. The results of these two exams were compared using weighted kappa statistics. The second part of the study was done to determine the inter-system agreement between the simplified vs standard POPQ exam. A group of 49 women were examined by four different investigators: one using the simplified and the other using standard POPQ exams. The order of the exams was randomized and the examiners were blinded to the results of each other’s exam. Kendall’s tau-b statistics were used to determine the inter-system agreement. For the inter-examiner reliability of the POPQ exam, the average age was 60±13 years. The weighted kappa statistics for the inter-examiner reliability of the simplified prolapse classification system were 0.86 for the overall stage, 0.89 and 0.86 for the anterior and posterior vaginal walls, respectively, 0.82 for the apex/cuff, and 0.72 for the cervix. All demonstrate significant agreement. For the inter-system association between the simplified POPQ and standard POPQ, the average age was 61±15 year. The Kendall’s tau-b value for overall stage was 0.90, 0.83, and 0.87 for the anterior and posterior walls respectively, and 0.78 for the cuff/apex and 0.98 for the cervix. There is good inter-examiner agreement of a simplified POPQ classification system and it appears to have good inter-system association with the POPQ.IUGA Standardization of Terminology Committee members: Robert Freeman MD (chairman), Steven Swift, Eckhard Petri MD, Richard J. Scotti MD, and Peter Dwyer MD. 相似文献
20.
Steven M Shechter Andrew J Schaefer R Scott Braithwaite Mark S Roberts 《Medical decision making》2006,26(5):550-553
The authors discuss techniques for Monte Carlo (MC) cohort simulations that reduce the number of simulation replications required to achieve a given degree of precision for various output measures. Known as variance reduction techniques, they are often used in industrial engineering and operations research models, but they are seldom used in medical models. However, most MC cohort simulations are well suited to the implementation of these techniques. The authors discuss the cost of implementation versus the benefit of reduced replications. 相似文献