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   8078篇
  免费   790篇
  国内免费   604篇
耳鼻咽喉   60篇
儿科学   62篇
妇产科学   15篇
基础医学   791篇
口腔科学   127篇
临床医学   571篇
内科学   671篇
皮肤病学   83篇
神经病学   339篇
特种医学   456篇
外科学   223篇
综合类   1487篇
现状与发展   2篇
一般理论   2篇
预防医学   544篇
眼科学   64篇
药学   1850篇
  2篇
中国医学   1974篇
肿瘤学   149篇
  2024年   38篇
  2023年   148篇
  2022年   307篇
  2021年   302篇
  2020年   317篇
  2019年   265篇
  2018年   278篇
  2017年   352篇
  2016年   382篇
  2015年   335篇
  2014年   630篇
  2013年   688篇
  2012年   576篇
  2011年   648篇
  2010年   442篇
  2009年   457篇
  2008年   378篇
  2007年   411篇
  2006年   343篇
  2005年   258篇
  2004年   209篇
  2003年   215篇
  2002年   160篇
  2001年   152篇
  2000年   148篇
  1999年   125篇
  1998年   65篇
  1997年   101篇
  1996年   77篇
  1995年   89篇
  1994年   72篇
  1993年   44篇
  1992年   46篇
  1991年   44篇
  1990年   60篇
  1989年   43篇
  1988年   44篇
  1987年   28篇
  1986年   25篇
  1985年   33篇
  1984年   22篇
  1983年   17篇
  1982年   22篇
  1981年   16篇
  1980年   15篇
  1979年   10篇
  1978年   12篇
  1977年   9篇
  1976年   4篇
  1973年   4篇
排序方式: 共有9472条查询结果,搜索用时 62 毫秒
981.
The quasistatic and dynamic pressure volume characteristics of the lungs were measured in five anesthetized, paralyzed open-chest rats. Psuedo-random volume perturbations over a frequency range of 0.25 to 25 Hz and having peak-peak amplitudes of 1 to 4 ml were applied after the lungs were allowed to expire against 0.2, 0.4, 0.6, and 0.8 kPa positive endexpiratory pressure (PEEP). The lung mechanics were partitioned in two ways: a linear dynamic block followed by a static nonlinearity (Wiener model) and a static nonlinearity ahead of a linear dynamic block (Hammerstein model). It was found that a Hammerstein model featuring a third-order polynomial static nonlinearity and a linear impulse response function of 1-sec duration accounted for the greatest amount of the output variance (98.8±06%, mean±SD from perturbations of 4 ml amplitude and PEEP-0.8 kPa). The static nonlinear behavior matched the measured quasistantic pressure volume behavior obtained at the same amplitude and at the same level of PEEP, provided that all direct current gain of the model was located within the static nonlinearity. Under these conditions, the linear resistance was inversely dependent on the PEEP, whereas little PEEP or amplitude dependence of the linear compartment elastance was observed. Thus, of the two block-structured models tested, the Hammerstein model accounted better for the large amplitude nonlinear mechanical behavior. However, neither model could account for the dependence of the linear block resistance on PEEP.  相似文献   
982.
藏药如意珍宝丸的鉴别和含量测定   总被引:4,自引:2,他引:2  
目的 建立藏药如意珍宝丸的鉴别和含量测定方法。方法 采用薄层色谱法和高效液相色谱法。结果 如意珍宝丸中 ,在荜茇、红花、肉桂、黄葵子、丁香和决明子等药材与对照药材相应的色谱位置处各有相同的斑点 ;并采用HPLC法测定了制剂中诃子的有效成份没食子酸的含量 ,其回归方程为A =6× 10 5C +718 14 (r =0 9998) ,RSD =1 5 8%。结论 所建立的鉴别与含量测定方法简便、准确 ,可用于如意珍宝丸的质量控制。  相似文献   
983.
脊柱孤立性浆细胞瘤的临床及影像学特点分析   总被引:4,自引:0,他引:4  
目的:探讨脊柱孤立性浆细胞瘤的临床及影像学特点。方法:分析经手术病理检查证实的6例脊柱孤立性浆细胞瘤病例的临床特点及影像学特征。结果:病椎附近逐渐加重的疼痛是其共同首发临床表现。其X线片多表现为椎体的溶骨性破坏;ECT上表现不一;CT多为椎体骨质的虫嗜状破坏;MRI示病椎信号失均,T1WI低信号,T2WI等或稍高信号,增强扫描有不均匀强化。结论:CT及MRI可明确脊柱孤立性浆细胞瘤的形态特征及病灶范围,其确诊仍需借助骨髓活检或手术标本病理检查。但对颈背部疼痛的患者,早期行MRI检查有助于及时发现病变,避免严重脊柱脊髓损害的出现。  相似文献   
984.
从多孢木霉(Trichoderma polysporum)的发酵液中,分离到一组具有免疫抑制作用的物质-G-18-Ⅰ、G-18-Ⅱ、G-18-Ⅲ、G-18-Ⅳ,其中G-18-Ⅳ为在红外光谱2100cm~(-1)具有强吸收的异腈类化合物,基于理化性质及光谱数据,已鉴别G-18-Ⅳ为异腈素酸E(木菌素)甲酯。  相似文献   
985.
心率与血压变异性的多变量、多维信号分析进展   总被引:9,自引:2,他引:7  
心率变异性与血压变异性反映心血管系统自主神经的调制活动,近年研究已向多变量、多维、动态分析方向发展。心率与血压变异性的多变量系统辨识、时频分析及非线性动力学分析等技术方法,将在心血管疾病的危险性预报、病情评估、疗效评价及特种环境医学等领域有更多应用。  相似文献   
986.
ObjectiveThis article proposes a method to automatically identify and label event-related potential (ERP) components with high accuracy and precision.MethodsWe present a framework, referred to as peak-picking Dynamic Time Warping (ppDTW), where a priori knowledge about the ERPs under investigation is used to define a reference signal. We developed a combination of peak-picking and Dynamic Time Warping (DTW) that makes the temporal intervals for peak-picking adaptive on the basis of the morphology of the data. We tested the procedure on experimental data recorded from a control group and from children diagnosed with developmental dyslexia.ResultsWe compared our results with the traditional peak-picking. We demonstrated that our method achieves better performance than peak-picking, with an overall precision, recall and F-score of 93%, 86% and 89%, respectively, versus 93%, 80% and 85% achieved by peak-picking.ConclusionWe showed that our hybrid method outperforms peak-picking, when dealing with data involving several peaks of interest.SignificanceThe proposed method can reliably identify and label ERP components in challenging event-related recordings, thus assisting the clinician in an objective assessment of amplitudes and latencies of peaks of clinical interest.  相似文献   
987.
988.
This article reports a longitudinal study of the communicative and linguistic development of five infants, identified as having severe or profound bilateral sensorineural hearing loss, and using amplification consistently, by 3-6 months of age. Each hearing impaired infant was carefully matched for chronolgical age, social and cultural background with a normally hearing infant. The parents of each of the infants had normal hearing and spoken English was the first language of the home. Video recorded social interaction took place over a variety of semi-structured contexts and occurred at six-weekly intervals from 6 to 21 months. The pattern of gestural and vocal communication and the transition to symbolic language by each hearing impaired and hearing infant forms the focus of this report. It is concluded that severely and profoundly hearing impaired infants can follow a normal pattern of communicative and linguistic development (albeit sometimes delayed) when hearing impairment is identified within the first months of life and appropriate interventions are in place.  相似文献   
989.
A comparison of six deconvolution techniques   总被引:1,自引:0,他引:1  
We present results for the comparison of six deconvolution techniques. The methods we consider are based on Fourier transforms, system identification, constrained optimization, the use of cubic spline basis functions, maximum entropy, and a genetic algorithm. We compare the performance of these techniques by applying them to simulated noisy data, in order to extract an input function when the unit impulse response is known. The simulated data are generated by convolving the known impulse response with each of five different input functions, and then adding noise of constant coefficient of variation. Each algorithm was tested on 500 data sets, and we define error measures in order to compare the performance of the different methods. The work described in this paper was carried out as part of Grant GR/J67130 “Identifiability and Indistinguishability of Nonlinear Dynamic Systems” from the U.K. Engineering and Physical Sciences Research Council.  相似文献   
990.
We have evaluated a multiplex STR system for routine forensic use, which co-amplifies six short tandem repeat (STR) loci; HUMTH01, D21S11, D18S51, D8S1179, HUMVWF31/A and HUMFIBRA (FGA), in conjunction with the X-Y homologous gene Amelogenin. Analysis of PCR products employs denaturing polyacrylamide gels coupled with fluorescentlabelled primers and detection is undertaken on ABD 373A automated sequencers. The technique was shown to be robust and reproducible when samples were analysed under conditions consistent with those encountered in a forensic environment.The system was demonstrated to be human specific and is suitable for use with both aged and degraded material. Somatic stability was proven with a wide range of tissue types and we were able to detect mixtures at ratios between 1:10 and 10: 1. During this study no incidence of sample mis-typing due to allelic or locus drop-out was observed. Furthermore, although additional artefact bands were occasionally encountered these did not interfere with the interpretation of results. The performance of the system with poor quality samples demonstrated its suitability as a powerful tool in forensic investigation.  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