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   497篇
  免费   28篇
  国内免费   15篇
耳鼻咽喉   26篇
儿科学   31篇
妇产科学   82篇
基础医学   59篇
口腔科学   8篇
临床医学   44篇
内科学   117篇
皮肤病学   1篇
神经病学   18篇
特种医学   16篇
外科学   29篇
综合类   10篇
预防医学   17篇
眼科学   48篇
药学   9篇
肿瘤学   25篇
  2024年   3篇
  2022年   5篇
  2021年   4篇
  2020年   8篇
  2019年   6篇
  2018年   10篇
  2017年   3篇
  2016年   12篇
  2015年   4篇
  2014年   15篇
  2013年   27篇
  2012年   24篇
  2011年   38篇
  2010年   19篇
  2009年   17篇
  2008年   26篇
  2007年   32篇
  2006年   32篇
  2005年   20篇
  2004年   24篇
  2003年   24篇
  2002年   27篇
  2001年   20篇
  2000年   17篇
  1999年   14篇
  1998年   19篇
  1997年   12篇
  1996年   7篇
  1995年   7篇
  1994年   9篇
  1993年   6篇
  1992年   9篇
  1991年   6篇
  1990年   5篇
  1989年   3篇
  1988年   4篇
  1987年   3篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1983年   3篇
  1981年   2篇
  1980年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1970年   1篇
  1954年   1篇
排序方式: 共有540条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
ObjectiveAdvanced placental maturation (Grannum [G] grade 3) before term is associated with adverse perinatal outcomes associated with placental insufficiency. The nature and timing of the underlying pathology of this process is presently unclear. We hypothesized that advanced placental maturation at 30 to 34 weeks’ gestation is not associated with established second trimester markers of severe placental dysfunction.MethodsIn a cohort study of 1238 low-risk Caucasian women with singleton pregnancies who had sonographic assessment of placental maturation and fetal growth at 34 weeks, the results of maternal serum screening (MSS) and uterine artery Doppler (UtAD) flow studies at 16 weeks were related to adverse perinatal outcomes associated with placental insufficiency: antepartum hemorrhage, preeclampsia, preterm birth < 37 weeks, small for gestational age (< 10th percentile), or postnatal evidence of intrauterine growth restriction (IUGR; ponderal index < 5th percentile).ResultsG1 was found in 127 women (10.3%), G2 was found in 18 women (1.5%), and no cases of G3 were observed. Advanced Grannum grading was significantly associated with IUGR (48 [4.4%] in G0, 9 [7.1%] in G1, 5 [27.8%] in G2; P < 0.001), but was dependent on smoking status. IUGR was not predicted by abnormal MSS or abnormal UtAD findings at either the second or third trimester ultrasounds.ConclusionG2 maturation at 30 to 34 weeks’ gestation is associated with mild IUGR at delivery in low-risk women and with smoking. IUGR was not predicted by either second or third trimester markers of severe placental dysfunction. Future studies directly observing the placenta in the late third trimester may aid the elusive diagnosis of “late-onset” mild IUGR.  相似文献   
95.
NOV, located on human chromosome 8q24.1, was originally cloned following discovery of its avian homolog as a consequence of over-expression in virally induced nephroblastoma. The gene product is a secreted, modular, protein and a member of the CCN gene family. Evidence to date indicates that the expression of the wild type protein is associated with cellular quiescence in normal embryonic fibroblasts yet produces growth stimulatory effects on established murine NIH 3T3 cells. Here we report the expression of NOV in the first trimester of human embryogenesis, between 5 and 10 weeks. In situ hybridisation and immunohistochemistry reveal widespread expression in derivatives of all three germ layers. The most abundant sites of expression are in the motor neurons and floor plate of the spinal cord, adrenal cortex, fusing skeletal, and smooth muscle, the urogenital system and the developing heart. Additionally, expression is seen in the cranial ganglia, differentiating chondrocytes, gonads, and lung. The sites of expression suggest strongly that autocrine or paracrine expression of NOV is associated with the process of cell differentiation. Accepted: 28 February 2001  相似文献   
96.
Natural scenes contain localized variations in both first-order (luminance) and second-order (contrast and texture) information. There is much evidence that first- and second-order stimuli are detected by distinct mechanisms in the mammalian visual system. However, in natural scenes the two kinds of information tend to be spatially correlated. Do correlated and uncorrelated combinations of first- and second-order stimuli differentially affect perception? To address this question we employed orientation-modulated textures in which observers were required to discriminate the spatial frequency of the texture modulation. The textures consisted of micropatterns defined as either local variations in luminance (first-order) or luminance contrast (second-order). Performance was robust with textures composed of only first-order micropatterns, but impossible with only second-order micropatterns. However, when the second-order micropatterns were combined with the first-order micropatterns, they enhanced performance when the two were spatially correlated, but impaired performance when the two were spatially uncorrelated. We conclude that local second-order information may enhance texture modulation discrimination provided it is combined with first-order information in an ecologically valid manner.  相似文献   
97.

Background  

Selection of patients with local failure of nasopharyngeal carcinoma (NPC) for appropriate type of salvage treatment can be difficult due to the lack of data on comparative efficacy of different salvage treatments. The purpose of the present study was to validate a previously published prognostic scoring system for local failures of NPC treated by radiosurgery based on reported results in the literature.  相似文献   
98.

Background

Oral submucous fibrosis is a common oral health problem in India. This study was conducted to correlate the histopathological diagnosis with habits and clinical findings in patients suffering from oral submucous fibrosis (OSF).

Methods

Patients suffering from oral submucous fibrosis from the Departments of Otorhinolayngology and Pathology, Moti Lal Nehru Medical College, Allahabad, India were studied from 2004–2008. Detailed information was gathered in a pretested proforma. Emphasis was given to the various addictions, clinical findings and histological examination was done.

Results

Two hundred and thirty nine patients were studied, yielding a male to female ratio of 6.8:1. Maximum patients were in the 21–30 years age group with a marked male predominance. Of these, 197 (82.4%) patients chewed areca nut/dohra, 14 (5.8%) were smokers and 2 (0.8%) patients were habituated to alcohol. 89(37.2%) patients reported difficulty in opening of the mouth (trismus). 51 (57.4%) patients were found to have stage II (2–3 cm) trismus while rest had stage I and III. The buccal mucosa was found to be the most commonly involved site. On the basis of histopathological examination, 52(21.7%) were classified as OSF grade I, 75(31.3%) patients as grade II and 112(46.8%) had grade III disease.

Conclusion

The widespread habit of chewing dohra/paan masala is a major risk factor of OSF, especially in the younger age group. In this study, an increase in histopathological grading was found with severity and duration of addiction habit. However no significant correlation was found between clinical staging and histopathological grading.  相似文献   
99.
We have employed the shape frequency and shape-amplitude after-effects (SFAE and SAAE) to investigate: (i) whether the shapes of illusory and real curves are processed by the same or different mechanisms, and (ii) the carrier-tuning properties of illusory curvature mechanisms. The SFAE and SAAE are the phenomena in which adaptation to a sinusoidal-shaped contour results in a shift in, respectively, the perceived shape-frequency and perceived shape-amplitude of a test contour in a direction away from that of the adapting stimulus. Both after-effects are believed to be mediated by mechanisms sensitive to curvature ( [Gheorghiu and Kingdom, 2007a] and [Gheorghiu and Kingdom, 2009]; see also Hancock & Peirce, 2008). We observed both shape after-effects in sinusoidally-shaped illusory contours defined by phase-shifted line-grating carriers. We tested whether illusory and real contours were mediated by the same or different mechanisms by comparing same adaptor-and-test with different adaptor-and-test combinations of real and illusory contours. Real contour adaptors produced after-effects in illusory contour tests that were as great as, or even greater than those produced by illusory contour adaptors. However, illusory contour adaptors produced much weaker after-effects in real contour tests than did real contour adaptors. This asymmetry suggests that illusory contour curves are encoded by a sub-set of mechanisms sensitive to real contour curves. We also examined the carrier-tuning properties of illusory-contour curvature processing using adaptor and test illusory contours that differed in the luminance contrast-polarity, luminance scale and orientation of the carriers. We found no selectivity to any of these dimensions for either even-symmetric or odd-symmetric line-gratings carriers, even though selectivity to these dimensions was found for real contours.  相似文献   
100.
OBJECTIVE: To evaluate the relationship among peripheral eosinophilia, total IgE, and paranasal sinus mucosal disease based on computed tomography (CT) of the sinus. DESIGN: Retrospective review of a large medical information database from a tertiary referral medical center. SETTING: Tertiary referral medical center specializing in respiratory disorders. PATIENTS: Consecutive patients having total IgE and peripheral eosinophil levels and sinus CT imaging available for review. Patients 18 years or older were included; subjective or objective evidence of chronic rhinosinusitis was not used as selection criteria. A total of 303 patients were found to have peripheral eosinophil levels and CT imaging for review; 288 patients had total IgE levels and CT imaging. MAIN OUTCOME MEASURES: Linear regression analysis was used to evaluate (1) the correlation between peripheral eosinophil level and CT stage of sinus disease and (2) the correlation between total IgE level and CT stage of sinus disease. The CT scans were graded using the Lund-MacKay scoring system. RESULTS: There was a significant positive correlation between sinus CT stage and peripheral eosinophil levels (r=0.60, P<.05). Eighty-nine percent of the abnormal eosinophil counts (>550 cells/microL) were associated with CT scores higher than 12. Total IgE did not correlate with CT stage of disease (r=0.05, P>.05). CONCLUSIONS: The presence of peripheral eosinophilia indicates a high likelihood of mucosal sinus disease based on CT imaging. No correlation was noted between total IgE levels and CT stage of mucosal disease. These data support a link between eosinophilia and the presence of paranasal sinus mucosal inflammation.  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