全文获取类型
收费全文 | 10169篇 |
免费 | 1405篇 |
国内免费 | 292篇 |
专业分类
耳鼻咽喉 | 30篇 |
儿科学 | 115篇 |
妇产科学 | 27篇 |
基础医学 | 1133篇 |
口腔科学 | 181篇 |
临床医学 | 995篇 |
内科学 | 974篇 |
皮肤病学 | 49篇 |
神经病学 | 1580篇 |
特种医学 | 2573篇 |
外国民族医学 | 2篇 |
外科学 | 448篇 |
综合类 | 1026篇 |
预防医学 | 737篇 |
眼科学 | 130篇 |
药学 | 1279篇 |
1篇 | |
中国医学 | 322篇 |
肿瘤学 | 264篇 |
出版年
2024年 | 16篇 |
2023年 | 156篇 |
2022年 | 237篇 |
2021年 | 578篇 |
2020年 | 490篇 |
2019年 | 583篇 |
2018年 | 528篇 |
2017年 | 578篇 |
2016年 | 528篇 |
2015年 | 500篇 |
2014年 | 770篇 |
2013年 | 815篇 |
2012年 | 636篇 |
2011年 | 662篇 |
2010年 | 480篇 |
2009年 | 514篇 |
2008年 | 492篇 |
2007年 | 396篇 |
2006年 | 362篇 |
2005年 | 323篇 |
2004年 | 304篇 |
2003年 | 226篇 |
2002年 | 198篇 |
2001年 | 144篇 |
2000年 | 103篇 |
1999年 | 99篇 |
1998年 | 81篇 |
1997年 | 92篇 |
1996年 | 89篇 |
1995年 | 98篇 |
1994年 | 82篇 |
1993年 | 67篇 |
1992年 | 58篇 |
1991年 | 54篇 |
1990年 | 53篇 |
1989年 | 58篇 |
1988年 | 51篇 |
1987年 | 39篇 |
1986年 | 28篇 |
1985年 | 50篇 |
1984年 | 46篇 |
1983年 | 22篇 |
1982年 | 44篇 |
1981年 | 20篇 |
1980年 | 30篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 19篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 121 毫秒
31.
目的:探讨PHILIPSGyroscanIntera1.5TMRI成像仪正常腹部实质脏器表观弥散系数(ADC)值范围并研究适合本扫描仪腹部弥散加权成像的最佳b值。材料和方法:对30例健康志愿者行磁共振弥散加权成像。在ADC图上直接测量ADC值。结果:所有检查均一次成功得到弥散加权成像(DWI)和ADC图。正常肝脏、胰腺、肾脏、脾脏在b值分别为300、1000、1500s/mm2时的ADC值分别为(10-3mm2/s)1.520±0.169、1.937±0.370、2.632±0.258、1.163±0.188,1.200±0.132、1.484±0.272、2.016±0.178、0.840±0.117,1.068±0.118、1.321±0.149、1.659±0.169、0.747±0.102。不同b值时同一脏器ADC值有统计学差异;四种实质性脏器在同一b值时ADC值有统计学差异。结论:正常腹部不同脏器的ADC值有明显差异。腹部弥散加权成像的b值为300s/mm2和1000s/mm2时,DWI和ADC图像可以互相补充。 相似文献
32.
Leonardo Bonilha MD PhD Paulien M. de Vries Diana J. Vincent MD PhD Chris Rorden MD PhD Paul S. Morgan Mark W. Hurd PhD Nada Besenski MD Kenneth J. Bergmann MD Vanessa K. Hinson MD PhD 《Movement disorders》2007,22(8):1110-1116
We investigated whether structural white matter abnormalities, in the form of disruption of axonal coherence and integrity as measured with diffusion tensor imaging (DTI), constitute an underlying pathological mechanism of idiopathic dystonia (ID), independent of genotype status. We studied seven subjects with ID: all had cervical dystonia as their main symptom (one patient also had spasmodic dysphonia and two patients had concurrent generalized dystonia, both DYT1‐negative). We compared DTI MR images of patients with 10 controls, evaluating differences in mean diffusivity (MD) and fractional anisotropy (FA). ID was associated with increased FA values in the thalamus and adjacent white matter, and in the white matter underlying the middle frontal gyrus. ID was also associated with increase in MD in adjacent white matter to the pallidum and putamen bilaterally, left caudate, and in subcortical hemispheric regions, including the postcentral gyrus. Abnormal FA and MD in patients with ID indicate that abnormal axonal coherence and integrity contribute to the pathophysiology of dystonia. These findings suggest that ID is not only a functional disorder, but also associated with structural brain changes. Impaired connectivity and disrupted flow of information may contribute to the impairment of motor planning and regulation in dystonia. © 2006 Movement Disorder Society 相似文献
33.
Paolo Martinelli Giovanni Rizzo David Manners Caterina Tonon Fabio Pizza Claudia Testa Cesa Scaglione Bruno Barbiroli Raffaele Lodi 《Movement disorders》2007,22(8):1182-1185
The pathophysiology of essential tremor (ET) is unknown. PET and fMRI studies have revealed bilateral activation and (1)H-MRS studies metabolic abnormalities in the cerebellum and other functionally related brain structures in ET. Diffusion-weighted imaging (DWI) was used to search for evidence of tissue integrity abnormalities in these areas in ET patients and 10 matched controls by calculating water apparent diffusion coefficients (ADCs). Regions of interest included the left and right cerebellum, red nucleus, thalamus, caudate, putamen, pallidum, and frontal white matter. Histograms of ADCs were generated for all pixels in the infratentorial compartment and manually segmented areas corresponding to brainstem, vermis, and cerebellar hemispheres. ADC values were similar in all brain areas in patients and controls. Our study did not detect changes affecting the investigated brain regions in ET patients. These findings argue against major structural damage in the ET brain, although more subtle neurodegenerative changes cannot be ruled out. 相似文献
34.
35.
In this paper, a vertical distribution of 137Cs in undisturbed soil was investigated experimentally and theoretically. Soil samples were taken from the surroundings of the city of Kragujevac in central Serbia during spring-summer of 2001. The sampling locations were chosen in such a way that the influence of soil characteristics on depth distribution of 137Cs in soil could be investigated. Activity of 137Cs in soil samples was measured using a HpGe detector and multi-channel analyzer. Based on vertical distribution of 137Cs in soil which was measured for each of 10 locations, the diffusion coefficient of 137Cs in soil was determined. In the next half-century, 137Cs will remain as the source of the exposure. Fifteen years after the Chernobyl accident, and more than 30 years after nuclear probes, the largest activity of 137Cs is still within 10 cm of the upper layer of the soil. This result confirms that the penetration of 137Cs in soil is a very slow process. Experimental results were compared with two different Green functions and no major differences were found between them. While both functions fit experimental data well in the upper layer of soil, the fitting is not so good in deeper layers. Although the curves obtained by these two functions are very close to each other, there are some differences in the values of parameters acquired by them. 相似文献
36.
带状灰质异位的磁共振弥散张量白质束成像研究 总被引:2,自引:0,他引:2
目的采用磁共振弥散张量白质束成像技术,观察带状灰质异位脑白质异常分布情况,探讨异位灰质的神经病理机制以及弥散张量白质束成像技术的应用价值。方法采用磁共振弥散张量白质束成像技术,对1例癫痫症状的带状灰质异位患者进行白质束描绘,观察其不同灰、白质的分布情况,并和1例正常人进行对比研究。结果弥散张量白质束成像技术很好地描绘了白质束结构。整体观察发现带状灰质异位患者脑白质整体结构紊乱,与正常人相比其联络弓状纤维稀疏、大部缺失,胼胝体纤维稀疏不整;局部分析发现内层灰质为主要的白质纤维发出处,而外层灰质仅发出细碎短小的纤维。结论对于带状灰质异位,异位的内层灰质不仅具有神经生理功能,并且可能起着主要作用,外层"正常"的灰质由于脑结构紊乱而丧失主要功能地位;灰质结构的紊乱导致白质纤维结构的缺失;弥散张量白质束成像技术可以很好地应用于带状灰质异位的神经机制研究。 相似文献
37.
The effects of various metal cations and pH on the adsorption of uranium(VI) on strongly acidic cation exchanger Amberlite IR-118H (AIR-118H) were studied. The metal cations suppress U(VI) adsorption differently depending on their ionic radii. Adsorption of U(VI) on AIR-118H peaks at pH 3.4, which was attributed to the occurrence of different forms of U(VI) at different pH values. The adsorption data were then processed using the Frumkin–Fowler–Guggenheim equation, and the standard free energy of adsorption was calculated. 相似文献
38.
39.
选用昆明种小鼠60只,体重18~24克,随机分成三组,每组20只,雌雄各半。通过饮水染毒。一组正常对照,饮自来水,二组饮30ppm含镉水,三组饮300ppm含镉水,染毒时间三个半月。观察指标:体重增长速度、脏器系数、肝肾中镉含量、重点病理形态学改变(光镜和电镜)。结果,30ppm组小鼠肝肾组织有一定病变,300ppm组小鼠的光镜和电镜的病理形态学改变更为明显。提示,小鼠长期摄入镉可引起一定的损害。 相似文献
40.
李英 《中华流行病学杂志》1988,9(5):265-268
本文应用1974~1976年浙江省肿瘤死亡回顾调查和1975~1978年中国恶性肿瘤调查研究的资料以及中华人民共和国血吸虫病地图集,探讨了血吸虫病与大肠癌之间的统计学关系。地区相关分析结果表明,在我国和浙江省的血吸虫病流行区,血吸虫病发病率与大肠癌死亡率高低变化呈直线相关关系。我国南方12个省市自治区和浙江省嘉兴地区10个县的血吸虫病发病率与大肠癌死亡率间的等级相关系数分别为0.706和0.903,都具有非常显著的相关性,说明在我国血吸虫病严重流行地区血吸虫病可能是大肠癌高发的一个危险因素。 相似文献