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   2142篇
  免费   148篇
  国内免费   57篇
耳鼻咽喉   26篇
儿科学   51篇
妇产科学   33篇
基础医学   232篇
口腔科学   55篇
临床医学   204篇
内科学   546篇
皮肤病学   28篇
神经病学   75篇
特种医学   224篇
外科学   289篇
综合类   95篇
预防医学   122篇
眼科学   44篇
药学   123篇
中国医学   26篇
肿瘤学   174篇
  2023年   15篇
  2022年   22篇
  2021年   42篇
  2020年   34篇
  2019年   30篇
  2018年   55篇
  2017年   35篇
  2016年   34篇
  2015年   80篇
  2014年   82篇
  2013年   112篇
  2012年   104篇
  2011年   127篇
  2010年   71篇
  2009年   70篇
  2008年   88篇
  2007年   131篇
  2006年   104篇
  2005年   82篇
  2004年   105篇
  2003年   105篇
  2002年   68篇
  2001年   60篇
  2000年   58篇
  1999年   45篇
  1998年   28篇
  1997年   35篇
  1996年   28篇
  1995年   27篇
  1994年   22篇
  1993年   21篇
  1992年   29篇
  1991年   35篇
  1990年   30篇
  1989年   40篇
  1988年   35篇
  1987年   27篇
  1986年   30篇
  1985年   16篇
  1984年   14篇
  1983年   17篇
  1982年   10篇
  1981年   10篇
  1980年   12篇
  1979年   8篇
  1977年   9篇
  1976年   10篇
  1972年   7篇
  1971年   10篇
  1947年   6篇
排序方式: 共有2347条查询结果,搜索用时 15 毫秒
11.
12.
An RNA-binding motif (RBM) gene family has been identified on the human Y chromosome that maps to the same deletion interval as the 'azoospermia factor' (AZF). We have identified the homologous gene family (Rbm) on the mouse Y with a view to investigating the proposal that this gene family plays a role in spermatogenesis. At least 25 and probably >50 copies of Rbm are present on the mouse Y chromosome short arm located between Sry and the centromere. As in the human, a role in spermatogenesis is indicated by a germ cell-specific pattern of expression in the testis, but there are distinct differences in the pattern of expression between the two species. Mice carrying the deletion Yd1, that maps to the proximal Y short arm, are female due to a position effect resulting in non-expression of Sry ; sex-reversing such mice with an Sry transgene produces males with a high incidence of abnormal sperm, making this the third deletion interval on the mouse Y that affects some aspect of spermatogenesis. Most of the copies of Rbm map to this deletion interval, and the Yd1males have markedly reduced Rbm expression, suggesting that RBM deficiency may be responsible for, or contribute to, the abnormal sperm development. In man, deletion of the functional copies of RBM is associated with meiotic arrest rather than sperm anomalies; however, the different effects of deletion are consistent with the differences in expression between the two species.   相似文献   
13.
Purpose To characterize and predict cycles generating slowcleaving embryos in in vitro fertilization, 86 cycles were retrospectively divided into two groups (slow, n=41, and fast, n=45 according to whether the number of blastomeres per embryo on day 3 was or > than the mean of the distribution, respectively.Results Cycles generating slowcleaving embryos were treated with luteinizing hormonereleasing hormone agonist before ovarian stimulation for a shorter period (12.1±0.5 versus 15.6±1.1 days; P0.01) and had higher immaturity grade of oocyte-corona-cumulus complexes which resulted in embryos (1.6±0.1 vs 1.3±0.1; P0.05) when compared to cycles producing fastcleaving embryos. Both variables entered in a logistic regression model applied in order to predict the probability of a cycle generating slowcleaving embryos (goodness-of-fit chisquare=180.0, degrees of freedom (df)=80, P=0.4786. This model predicted correctly 86.7% (13 of 15) of cycles generating slowcleaving embryos and 83.3% (10 of 12) of cycles producing fastcleaving embryos when the estimated probability of a cycle producing slowcleaving embryos was 0.7 or 0.3, respectively.Conclusion Shorter treatment with hormone-releasing hormone agonist before ovarian stimulation and higher immaturity grade of oocyte-corona-cumulus complexes which result in embryos are predictive characteristics of in vitro fertilization cycles generating slow-cleaving embryos.  相似文献   
14.
Nitschke JE  Nattrass CL  Disler PB  Chou MJ  Ooi KT 《Spine》1999,24(3):262-268
STUDY DESIGN: Repeated measures design for intra- and interrater reliability. OBJECTIVES: To determine the intra- and interrater reliability of the lumbar spine range of motion measured with a dual inclinometer, and the thoracolumbar spine range of motion measured with a long-arm goniometer, as recommended in the American Medical Association Guides. SUMMARY OF BACKGROUND DATA: The American Medical Association Guides (2nd and 4th editions) recommend using measurements of thoracolumbar and lumbar range of movement, respectively, to estimate the percentage of permanent impairment in patients with chronic low back pain. However, the reliability of this method of estimating impairment has not been determined. METHODS: In all, 34 subjects participated in the study, 21 women with a mean age of 40.1 years (SD, +/- 11.1) and 13 men with a mean age of 47.7 years (SD, +/- 12.1). Measures of thoracolumbar flexion, extension, lateral flexion, and rotation were obtained with a long-arm goniometer. Lumbar flexion, extension, and lateral flexion were measured with a dual inclinometer. Measurements were taken by two examiners on one occasion and by one examiner on two occasions approximately 1 week apart. RESULTS: The results showed poor intra- and interrater reliability for all measurements taken with both instruments. Measurement error expressed in degrees showed that measurements taken by different raters exhibited systematic as well as random differences. As a result, subjects measured by two different examiners on the same day, with either instrument, could give impairment ratings ranging between 0% and 18% of the whole person (excluding rotation), in which percentage impairment is calculated using the average range of motion and the average systematic and random error in degrees for the group for each movement (flexion, extension, and lateral flexion). CONCLUSIONS: The poor reliability of the American Medical Association Guides' spinal range of motion model can result in marked variation in the percentage of whole-body impairment. These findings have implications for compensation bodies in Australia and other countries that use the American Medical Association Guides' procedure to estimate impairment in chronic low back pain patients.  相似文献   
15.
Two new antiviral flavan derivatives were isolated from a methanol extract of leaves of Pithecellobium clypearia as guided by antiviral assays. The structures were characterized, by spectroscopic analyses, as 7-O-galloyltricetifavan (1) and 7,4'-di-O-galloyltricetifavan (2). Cytopathic effect (CPE) reduction assay showed that both compounds 1 and 2 possess antiviral activity against respiratory syncytial virus (RSV), with 50% inhibition concentration (IC(50)) values of 5 and 10 microg/mL, respectively; influenza A (H1N1) virus, with IC(50) values of 15.7 and 30 microg/mL; Coxsackie B3 (Cox B3) virus, with IC(50) values of 12.5 and 25 microg/mL, respectively; and Herpes simplex virus type 1 (HSV-1) with IC(50) values of 30 and 20 microg/mL, respectively. Cytotoxicity evaluation using the MTT assay showed that both compounds 1 and 2 were also moderately toxic to several cultured cell lines.  相似文献   
16.
[Purpose] To consider the effective rehabilitation approaches for locomotive syndrome (LS) and pre-frailty, we examined the characteristics of physical function and health-related quality of life (HRQoL) in community-dwelling older adults. [Participants and Methods] Eighty-three individuals (age 71.8 ± 5.5 years, 29 males and 54 females) were divided into robust (R), LS, and locomotive syndrome with pre-frailty (LSP) groups. We compared the subscale and summary scores of the 36-Item Short-Form Health Survey (SF-36) as HRQoL indices. The grip strength, five-chair stand up test (SS-5), and normal walking speed were the physical function indices. [Results] The LS group had lower two-step scores and normal walking speed but there was no significant difference in the SF-36. The two-step score and 25-question geriatric locomotive function scale, SS-5, seven SF-36 subscales, and mental component summary (MCS) scores were lower in the LSP group. Compared to that of the LS group, the LSP group did not show significant difference in physical function but showed lower values in overall health, vitality, mental health, and MCS in the SF-36 subscales. [Conclusion] The subjective evaluation of one’s health was lower than that of the deterioration of physical function as a characteristic of the LSP.  相似文献   
17.
18.
19.
20.
End-stage periventricular leukomalacia: MR evaluation   总被引:3,自引:0,他引:3  
Baker  LL; Stevenson  DK; Enzmann  DR 《Radiology》1988,168(3):809-815
A prospective study was performed to assess the capabilities of magnetic resonance (MR) imaging in evaluation of end-stage periventricular leukomalacia (PVL) in six children, aged 31-54 months, in whom PVL had been documented by neurologic ultrasonography during the neonatal period. Eight children of similar age (four premature infants and four full-term infants) with normal neurologic development served as controls. A characteristic triad of PVL abnormalities was seen on MR images: (a) abnormally increased periventricular white-matter signal intensity on the first and second echo images of a T2-weighted sequence (repetition time = 2,000-2,400 msec, echo times = 20 or 30 and 80 msec), most commonly observed in the trigone regions of the lateral ventricles bilaterally; (b) marked loss of periventricular white matter in these regions of abnormal signal intensity, predominantly in the periatrial regions; and (c) compensatory focal ventricular enlargement adjacent to regions of abnormal signal intensity. In patients with the classic periatrial distribution of PVL lesions, general correlation between the degree of neurologic impairment and the severity of MR abnormalities was demonstrated. MR imaging was useful in detecting subtle forms of PVL in cases in which neurologic damage was subclinical.  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