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   44614篇
  免费   4939篇
  国内免费   874篇
耳鼻咽喉   312篇
儿科学   1041篇
妇产科学   599篇
基础医学   3358篇
口腔科学   1592篇
临床医学   4211篇
内科学   5994篇
皮肤病学   490篇
神经病学   3527篇
特种医学   1276篇
外国民族医学   3篇
外科学   3531篇
综合类   4788篇
现状与发展   5篇
一般理论   2篇
预防医学   7802篇
眼科学   584篇
药学   3419篇
  25篇
中国医学   4421篇
肿瘤学   3447篇
  2024年   111篇
  2023年   1020篇
  2022年   1076篇
  2021年   1987篇
  2020年   1927篇
  2019年   1865篇
  2018年   1831篇
  2017年   1772篇
  2016年   1587篇
  2015年   1442篇
  2014年   3248篇
  2013年   3306篇
  2012年   2630篇
  2011年   2763篇
  2010年   2128篇
  2009年   2055篇
  2008年   2306篇
  2007年   2396篇
  2006年   2132篇
  2005年   1776篇
  2004年   1460篇
  2003年   1389篇
  2002年   1079篇
  2001年   996篇
  2000年   793篇
  1999年   688篇
  1998年   503篇
  1997年   538篇
  1996年   416篇
  1995年   425篇
  1994年   366篇
  1993年   304篇
  1992年   302篇
  1991年   264篇
  1990年   229篇
  1989年   210篇
  1988年   197篇
  1987年   159篇
  1986年   128篇
  1985年   117篇
  1984年   101篇
  1983年   70篇
  1982年   65篇
  1981年   61篇
  1980年   58篇
  1979年   32篇
  1978年   29篇
  1977年   27篇
  1976年   18篇
  1975年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Population-based association studies are powerful tools for the genetic mapping of complex diseases. However, this method is sensitive to potential confounding by population structure. While statistical methods that use genetic markers to detect and control for population structure have been the focus of current literature, the utility of self-defined race/ethnicity in controlling for population structure has been controversial. In this study of 1334 individuals, who self-identified as either African American, European American or Hispanic, we demonstrated that when the true underlying genetic structure and the self-defined racial/ethnic groups were roughly in agreement with each other, the self-defined race/ethnicity information was useful in the control of population structure.  相似文献   
72.
In a long-term follow-up study of 44 female alcoholics, a family history of alcoholism was related to younger age of onset of problem drinking, but did not necessarily imply a poorer outcome within this highly selected group of individuals. Alcoholism in father and his family was not related to either antisocial or borderline personality disorder nor outcome. However, alcoholism in mother and her family correlated with both borderline personality disorder and a significantly poorer outcome. The findings are discussed within different frames of reference, considering genetic mechanisms, psychodynamic factors and family systems theory.  相似文献   
73.
舒经汤治疗痛经及对患者血液流变学的影响   总被引:2,自引:0,他引:2  
目的探讨舒经汤治疗原发性痛经的疗效及安全性。方法将62例原发性痛经患者随机分为3组,其中治疗组21例(口服舒经汤)、中药对照组21例(口服痛经宝颗粒)、西药对照组20例(口服双氯芬酸),观察各组的临床疗效、血液流变学变化及不良反应。结果治疗组、中药对照组及西药对照组的总有效率分别为95.2%、90.5%及77.8%。治疗前治疗组的血浆粘度(1.60±0.23)mPa·s,纤维蛋白原(4.40±1.18)g/L,均值略高于健康组,其中血沉均值与健康组比有非常显著差异(P<0.01)。而治疗后血浆粘度(1.34±0.18)mPa·s,纤维蛋白原(3.32±1.27)g/L,均值与健康组比无差异,其中血沉与健康组比较无显著性差异(P>0.05)。治疗组和中药对照组均未见明显不良反应,西药对照组主要表现为消化道反应。结论舒经汤治疗原发性痛经疗效确定,且远期疗效及安全性均优于西药对照组。  相似文献   
74.
BACKGROUND: The optimal projection data acquisition strategy for myocardial perfusion (MP) single photon emission computed tomography (SPECT) remains controversial. METHODS: We compared MP SPECT using 180 degrees and 360 degrees projection data obtained with the same acquisition time, reconstructed either with filtered back projection (FBP) or the iterative ordered-subsets expectation maximization (OS-EM) algorithm with various combinations of attenuation, detector response, and scatter compensation using mathematical observers and a myocardial defect detection task. We used Monte Carlo-simulated projection data from a population of 3-dimensional nurbs-based cardiac-torso (NCAT) phantoms with ranges of variability in patient anatomy, organ uptake, defect location, defect size, and noise level based on clinical data. Projection data from 180 degrees and 360 degrees acquisitions were generated by assuming the same acquisition time. After iterative or FBP reconstruction, standard postprocessing methods were applied. For each acquisition and reconstruction method, we optimized the number of iterations and cut-off frequency of the Butterworth filter using the Channelized Hotelling Observer methodology. The optimum set of parameters was that which gave the maximum area under the curve. RESULTS: For both acquisition protocols, OS-EM with compensations provided better performance than FBP or OS-EM without compensation. For FBP, the optimized 180 degrees acquisition provided a statistically significant increase in AUC as compared with optimized 360 degrees acquisition. For OS-EM, the AUCs for 180 degrees were slightly larger than for 360 degrees acquisitions when comparing images reconstructed with the same compensations. However, the differences were smaller and not statistically significant. CONCLUSION: With optimized reconstruction and filtering parameters, 180 degrees acquisition provided a statistically significant improvement over 360 degrees acquisition for FBP reconstruction. However, for OS-EM the differences were small and not statistically significant.  相似文献   
75.
Summary We prospectively examined bone growth patterns in 894 children aged 6–17 years at the baseline visit, with a 6-year follow-up. Results show bone “tracking” over a six-year interval and sexual dimorphism of bone attained levels and timing of peak bone growth. Our findings underscore childhood and adolescence as critical periods for building bone and developing gender differences. Introduction Bone growth patterns were prospectively examined in 894 Chinese children (496 males), aged 6–17 yrs, from a population-based twin cohort. Whole-body bone area (BA), bone mineral content (BMC), and bone mineral density (BMD) were measured by DEXA at baseline and a 6-yr follow-up. Methods Graphic smoothing plots and generalized estimating equations were used to model bone attained levels, growth, and “tracking”. Results Attained levels of BMC and BA increased curvilinearly with age. Male attained levels were higher than females after age ∼15 yr, but BMD was lower between 13–17 yrs (Tanner stage I to IV). In both genders, peak BMC and BMD growth lagged ∼2 yrs behind peak BA growth, which lagged 2 yrs behind peak height growth. Peak bone growth occurred 1–3 yrs later in males. Over the 6-yr follow-up, all bone measurements “tracked”, but “shifting” across ranks also occurred, and baseline tertile ranking influenced bone growth. Females with early menarche had higher attained levels than females with late menarche at age 12–13 yrs. Conclusion Our findings confirm and expand previous studies on peak bone growth conducted in Caucasian cohorts, particularly sexually dimorphic and maturational effects. The significant “tracking” of bone measurements in this 6-yr follow-up study underscores the importance that osteoporosis prevention should begin in childhood and adolescence. Fengxiu Ouyang and Binyan Wang contributed equally to this article. Source(s) of support: This study is supported in part by grant R01 HD049059, R01 HL0864619 and R01 AR045651 from the National Institute of Health and by the Food Allergy Project.  相似文献   
76.
目的:探讨子宫内膜萎缩疗法治疗青春期功血(DUB)的止血效果。方法:将362例平均分为观察组(采用炔诺酮、戊酸雌二醇联合疗法止血)和对照组(单用炔诺酮子宫内膜萎缩疗法止血),两组各181例,比较两组的止血效果。结果:观察组和对照组止血有效率分别为96.13%(174/181)和92.27%(167/181),两组比较差异无统计学意义(踟105);观察组和对照组控制出血时间分别为(28.69±14.87)h和(29.72±15.34)h,两组比较差异无统计学意义(踟.05)。观察组和对照组的完全止血时间分别为(32.80±19.10)h和(47.30±18.60)h,两组比较差异有统计学意义(/9〈0.05)。观察组和对照组的住院天数平均为(6.10±2.80)d和(6.9±2.60)d,观察组住院时间短于对照组(P〈0.01)。结论:炔诺酮止血疗法和炔诺酮、戊酸雌二醇联合疗法治疗青春期功血效果均较好,但炔诺酮、戊酸雌二醇联合疗法治疗效果更佳。  相似文献   
77.
Reduced bone mineral density (BMD) was sporadically reported in patients with Marfan syndrome. This may or may not place the Marfan patient at increased risk for bone fracture. In comparing the BMDs of our patients with those reported in the literature, it seemed that agreement between values, and hence the degree of osteoporosis or osteopenia reported, was dependent on the instrumentation used. The objective of this study was to statistically assess this impression. Bone mineral density measurements from our previously published study of 30 adults with Marfan syndrome performed on a Lunar DPXL machine were compared with studies published between 1993–2000 measured using either Lunar or Hologic bone densitometry instruments. The differences of our measurements compared with those made on other Lunar machines were not statistically significant, but did differ significantly with published results from Hologic machines (P < 0.001). Before progress can be made in the assessment of BMD and fracture risk in Marfan patients and in the evidence-based orthopedic management of these patients, standardization of instrumental bone density determinations will be required along with considerations of height, obesity, age, and sex.  相似文献   
78.
目的:研究腹腔镜全腹膜外腹股沟疝修补术(totally extraperitoneal prosthetic,TEP)在临床应用中的价值。方法:71例成人腹股沟疝患者前瞻性随机分成两组,分别进行TEP和无张力疝修补术(Lichtenstein)。TEP组35例,Lichtenstein组36例。手术后1周和1年内对患者作出临床观察和评估,并在3个月和1年时进行电话及门诊随访。观察指标为:手术时间、使用镇痛药物的频率、下床活动时间、住院天数、并发症、暂时性神经感觉异常、正常活动时间、腹股沟疼痛持续时间、疝复发。将两组数据进行统计学处理和分析。结果:使用镇痛药物的频率、下床活动时间、住院天数、恢复正常活动时间、腹股沟疼痛持续时间、并发症方面TEP组优于Lichtenstein组,有显著性差异(P〈0.05)。手术时间、复发例数TEP组少于Lichtenstein组,但无统计学差异。结论:TEP对于复发疝、老年人疝以及双侧疝更加具有优势。但TEP手术费用较高、需要腹腔镜等设备、学习曲线较长,这些可能是目前TEP尚未广泛开展的主要原因。我们认为,缩短TEP学习曲线的关键在于掌握手术空间的建立,腹白线中隔是影响手术空间建立的主要因素,打开下方部分腹白线中隔是手术的要点。  相似文献   
79.
80.
The aim of the study was to assess if lung function at birth predicts lung function at 2 yr and secondly, if lung function development was influenced by the common phenotypes of recurrent bronchial obstruction (rBO) or atopic eczema (AE) by 2 yr. Lung function was assessed at birth (n = 802) and at 2 yr within the prospective birth cohort study 'the Environment and Childhood Asthma Study' in Oslo. The 135 children with lung function measured at birth by tidal flow volume (TFV) loops and passive respiratory mechanics, who were included in a nested case-control study were reinvestigated at 2 yr with clinical examination, TFV loops (n = 90) (mean age 26.6 (3.7 s.d.) months), skin prick test and parental interview. Children were categorized into quartiles (lower, middle two, upper) according to time to peak tidal expiratory flow/total expiratory time (t(PTEF)/t(E)) at birth as well as clinical phenotype based on the presence of rBO and/or AE (ever) by 2 yr. The observed reduction in mean t(PTEF)/t(E) from birth to 2 yr within the quartiles, were not significantly different after controlling for 'regression to the mean'. t(PTEF)/t(E) at birth correlated significantly with t(PTEF)/t(E) at 2 yr, (r = 0.475, p < 0.001). Children with both rBO and AE by 2 yr had significantly lower t(PTEF)/t(E) at 2 yr (p = 0.002) and at birth (p = 0.027), compared with children with no rBO or AE. Clinical phenotype at 2 yr did not influence the change in t(PTEF)/t(E) from birth to 2 yr. This study demonstrates a clear tracking of lung function from birth, not influenced by rBO or AE by 2 yr.  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