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   4453篇
  免费   294篇
  国内免费   85篇
耳鼻咽喉   38篇
儿科学   34篇
妇产科学   57篇
基础医学   356篇
口腔科学   163篇
临床医学   962篇
内科学   231篇
皮肤病学   36篇
神经病学   172篇
特种医学   202篇
外国民族医学   1篇
外科学   401篇
综合类   888篇
预防医学   350篇
眼科学   96篇
药学   408篇
  3篇
中国医学   242篇
肿瘤学   192篇
  2023年   51篇
  2022年   136篇
  2021年   143篇
  2020年   124篇
  2019年   110篇
  2018年   118篇
  2017年   107篇
  2016年   150篇
  2015年   127篇
  2014年   321篇
  2013年   273篇
  2012年   298篇
  2011年   296篇
  2010年   252篇
  2009年   198篇
  2008年   224篇
  2007年   268篇
  2006年   236篇
  2005年   183篇
  2004年   155篇
  2003年   100篇
  2002年   96篇
  2001年   110篇
  2000年   88篇
  1999年   79篇
  1998年   60篇
  1997年   57篇
  1996年   42篇
  1995年   47篇
  1994年   43篇
  1993年   30篇
  1992年   28篇
  1991年   21篇
  1990年   17篇
  1989年   13篇
  1988年   14篇
  1987年   10篇
  1986年   18篇
  1985年   20篇
  1984年   16篇
  1983年   11篇
  1982年   22篇
  1981年   21篇
  1980年   17篇
  1979年   17篇
  1978年   21篇
  1976年   9篇
  1975年   9篇
  1974年   7篇
  1973年   7篇
排序方式: 共有4832条查询结果,搜索用时 15 毫秒
31.
The asymmetry of the spectral distribution of ultrasonic Doppler flow velocity signals, assessed using the coefficient of skewness, is discussed as a criterion of stenosis differentiation. Its performance is compared with that of the index of turbulence intensity for both in vitro and in vivo flow Doppler signals, recorded distal to a stenosis. The power spectral distributions are computed using the direct Fourier transform and maximum likelihood method. The asymmetry of spectral distribution has proved to be a more efficient criterion than the turbulence intensity. The maximum likelihood method ensures better stenosis differentiation than the direct FFT method.  相似文献   
32.
通过对乳腺肿瘤边界特征的分析,得到边界的特征量似圆度,面积比率,长宽比组成的特征矢量,最后用反向传播人工神经网络(BP)的算法对经病理证实的119幅乳腺良、恶性肿块超声图像进行分类识别。BP神经网络对良、恶性肿瘤正确识别率分别为89.7%、73.5N。量化后的乳腺超声图像肿瘤轮廓特征结合BP神经网络可以比较有效的用于肿瘤的良、恶性识别。  相似文献   
33.
中药雾化对慢性单纯性鼻炎鼻腔粘膜微循环血流量的影响   总被引:1,自引:0,他引:1  
目的:探讨中药雾化吸入对慢性单纯性鼻炎患者鼻腔粘膜微循环血流量的影响。方法:60例患者采用复方丹参、鱼腥草注射液超声雾化治疗3疗程。分别于治疗前后采用吸入性氢气清除法测定鼻粘膜微循环血流量的变化。结果:慢性单纯性鼻炎鼻粘膜微循环血流量较健康对照组明显减低,经雾化治疗后得到明显改善,其差异有极显著性意义(P<0.01)。结论:慢性单纯性鼻炎患者经中药雾化治疗后鼻粘膜微循环血流量明显增加,临床效果较好。  相似文献   
34.
We report on a newborn infant with clinical and radiological manifestations of some type of short rib-polydactyly syndrome who died soon after birth. Chromosomal studies on peripheral blood lymphocytes and chondrocytes demonstrated an apparently balanced pericentric inversion of chromosome 4 (present in the mother also). This association may have occurred by chance but, if not, the chromosomal breakpoints could interrupt the gene responsible for short rib-polydactyly syndromes, or else be related to the mechanism of short rib-polydactyly syndromes. © 1994 Wiley-Liss, Inc.  相似文献   
35.
超声手术刀组织切割的实验研究   总被引:1,自引:0,他引:1  
用国产超声手术刀,在大白兔活体上进行切割实验.并与普通手术刀和高频电刀进行了比较.结果显示超声手术刀的组织切割速度和切缘整齐情况不及普通手术刀,但有一定的止血功能,组织损伤不如高额电刀大,也不引起肌肉收缩,无组织烧焦气味;术后切缘愈合良好.认为超声手术刀更适合于肝、脾等实质性组织的切割.如在操作柄、刀具、仪器性能等方面能进一步改进,应用效果会更好。  相似文献   
36.
目的探讨豚鼠皮肤黑色素细胞在大黄有效成分的作用下,一氧化氮合酶(Nitric OxideSynthse;NOS)表达的变化,阐明大黄在活体皮肤中对黑素细胞的有效作用浓度和作用机制.方法将21只雄性豚鼠随机分成对照组及5个实验组,用芦荟大黄素5种浓度对局部皮肤皮下注射处理,48小时后取材,免疫组织化学方法(SABC)法显示NOS的表达,用光学显微镜和图象分析仪对结果进行统计分析.结果芦荟大黄素作用下,表皮黑素细胞NOS表达明显减少,光密度明显下降(P<0.05);不同浓度药物作用之间无显着差异(P>0.05),加注侧与未加注侧之间无显著差异.结论芦荟大黄素对黑色素细胞NOS的表达具有调节作用,提示大黄对黑素细胞的调节是经NO信号介导途径,为大黄的临床应用提供实验依据.  相似文献   
37.
Previously, our laboratory has shown that androgen receptors in the medial preoptic area (MPOA) and ventromedial nucleus (VMN) are necessary for copulation in male rats. The present study examined whether these receptors are required for other sociosexual behaviors. In Experiment 1, different regions of the VMN were implanted with the antiandrogen hydroxyflutamide (OHF). We found that implants located in anterodorsal portions of the VMN were more effective at inhibiting the restoration of copulation than implants in the posteroventral VMN. In Experiment 2, a second set of male rats was pretested for copulation and other sociosexual behaviors and was castrated. Experimental animals then received Silastic capsules filled with testosterone (T) plus intracranial (IC) implants filled with OHF to selectively block androgen receptors in either the MPOA or VMN. We found that androgen receptor blockade in the MPOA inhibited the restoration of copulation but had no effect on other sociosexual behaviors. OHF directed at the VMN inhibited the restoration of copulation and 50-kHz vocalizations but had no effect on scent marking. Two tests were used to assay sexual motivation: partner preference and conditioned place preference (CPP). Both methods revealed impairments in sexual motivation in the VMN group but not in animals receiving OHF in the MPOA. Taken together, these data suggest that androgen receptors in the MPOA are essential for copulatory performance, while androgen receptors in the VMN are important for copulation, sexual motivation, and androgen-dependent vocalizations.  相似文献   
38.
Adult rats emit 22 kHz ultrasonic vocalizations (USVs) in response to aversive stimuli, and these sounds are suggested to have communicative information among conspecifics. It is conceivable that social environment during development of rats has relevance to the emission of 22 kHz USVs. To examine the effects of social environment after weaning on production of stress-induced USVs, we compared the amount of emission of USVs among three groups of rats reared under different conditions after weaning. One group of rats was housed individually, and the other two groups were housed in pairs, in which social hierarchy of the pair was determined by social dominance-subordination relationships. The USVs were induced by acute mild somatic stimuli on the back and neck. Individually reared rats emitted much fewer USVs than pair-reared rats. In addition, socially subordinate rats emitted more USVs compared with socially dominant ones. These results suggest that not only social interaction but also the status in social hierarchy may play an important role in the process of the development of USVs induced by somatic stimuli.  相似文献   
39.
彩色多普勒超声诊断胎盘绒毛膜血管瘤   总被引:2,自引:0,他引:2  
目的探讨彩色多普勒超声(CDFI)对胎盘绒毛膜血管瘤的诊断价值及其临床意义。方法回顾性分析了6例胎盘绒毛膜血管瘤的CDFI表现及妊娠结果。结果6例患者肿瘤均为单发,2例瘤体直径>5.0 cm,有羊水过多,新生儿窒息等不良并发症。4例直径<5.0 cm,随访至分娩,未发生明显并发症。结论CDFI是产前诊断胎盘血管瘤惟一有效的辅助手段,对于瘤体较大,CDFI的监测和随诊对临床具有重要的指导意义。  相似文献   
40.
To localize the gene encoding the 60 kD glycoprotein (gp60) of infectious laryngotracheitis virus (ILTV), a library of the ILTV genome was constructed in the gt11 expression vector. Twelve recombinant bacteriophages expressing gp60 epitopes as fusion products with -galactosidase were detected by immunoscreening with monoclonal antibodies specific for gp60. The ILTV DNA sequence contained in one of these recombinants 24-4 was used as a hybridization probe for mapping the insert sequence on the viral genome. The gene for the gp60 was located at map unit 0.72–0.77 in the unique long region (UL) of the ILTV genome. The DNA sequence of the 1.2 kb insert of 24-4 containing the gp60 epitope was determined. The majority of deduced gp60 amino acid sequence has no homology with any of the known alphaherpesvirus glycoproteins.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number X 121209.  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