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   93466篇
  免费   8122篇
  国内免费   1828篇
耳鼻咽喉   681篇
儿科学   1518篇
妇产科学   1282篇
基础医学   5173篇
口腔科学   1255篇
临床医学   20752篇
内科学   10600篇
皮肤病学   635篇
神经病学   10280篇
特种医学   23818篇
外国民族医学   18篇
外科学   6918篇
综合类   10005篇
现状与发展   2篇
预防医学   1936篇
眼科学   1527篇
药学   2881篇
  64篇
中国医学   549篇
肿瘤学   3522篇
  2024年   314篇
  2023年   1485篇
  2022年   2917篇
  2021年   3784篇
  2020年   3580篇
  2019年   3308篇
  2018年   3261篇
  2017年   3583篇
  2016年   3798篇
  2015年   3714篇
  2014年   6411篇
  2013年   5794篇
  2012年   5478篇
  2011年   5987篇
  2010年   5006篇
  2009年   5120篇
  2008年   5089篇
  2007年   4895篇
  2006年   4438篇
  2005年   3906篇
  2004年   3330篇
  2003年   2571篇
  2002年   2110篇
  2001年   2045篇
  2000年   1672篇
  1999年   1400篇
  1998年   1320篇
  1997年   1230篇
  1996年   1065篇
  1995年   962篇
  1994年   773篇
  1993年   650篇
  1992年   532篇
  1991年   434篇
  1990年   315篇
  1989年   215篇
  1988年   202篇
  1987年   170篇
  1986年   128篇
  1985年   119篇
  1984年   82篇
  1983年   53篇
  1982年   61篇
  1981年   33篇
  1980年   22篇
  1979年   12篇
  1978年   16篇
  1977年   8篇
  1976年   11篇
  1974年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Transitional progressive multiple sclerosis: MRI and MTI findings   总被引:1,自引:0,他引:1  
Transitional progressive multiple sclerosis (MS) is quite an unusual form of presentation and course of the disease. A case with this progressive form is presented and brain MRI and MTI findings are discussed in relation to the possible insight they may provide for understanding the mechanisms that determine progressive disability in MS.  相似文献   
22.
Summary— The influence of local resistance and cardiac performance on peripheral blood acceleration was investigated in 14 healthy male volunteers. Steady and pulsatile flow was studied in the brachial and in the common carotid arteries, ie, two territories that exhibit marked differences in resistive characteristics. Instantaneous blood velocity (V), mean blood velocity (Vm) and artery diameter (D) were evaluated at rest by an ultrasonic range-gated pulsed Doppler flowmeter using a double transducer probe, thus allowing the calculation of mean blood flow (Q). Mean local resistance (R) was obtained by dividing the mean arterial pressure by Q. The peak value of the local acceleration of the blood was obtained by computer-assisted calculation of the first derivative of instantaneous blood velocity (Gmax = +dV/dtmax). Peak aortic blood acceleration (GAo) was simultaneously measured from the suprasternal notch using a pulsed Doppler velocity meter. In the brachial and the common carotid arteries, Gmax was of a similar magnitude (551 ±30 and 555 ± 44 cm/s2, respectively) despite major differences in the respective D, Vm, Q and R values. In neither artery was there a relationship between Gmax and either resting Q or R. At the brachial artery level, Gmax was positively related to GAo ( r = 0.79, P = 0.0008). At the common carotid artery level, there was a weak, although non significant relationship between Gmax and GAo ( P = 0.08). Our results indicate that the local acceleration of peripheral blood flow in the brachial artery is related rather to upstream central impulse than to downstream hemodynamics, and suggest some regional differences in the hemodynamic determinants of the local acceleration of peripheral blood flow.  相似文献   
23.
To elucidate the pathogenesis of mitral regurgitation (MR) after myocardial infarction (MI), the incidence of papillary muscle dysfunction (PMD), mitral annular size, and the extent of wall-motion abnormalities were examined in 81 patients with previous MI by two-dimensional echocardiography and real-time two-dimensional Doppler flow imaging. The prevalence of pathological MR was lower in patients with anterior MI (36%) than in those with inferior (65%) or anterior and inferior MI (88%) (P < 0.01 vs anterior MI group). The incidence of PMD in patients with MR in the anterior MI group (15%) was lower than that in the inferior (50%, P < 0.01) or anterior and inferior MI group (43%, P < 0.05). The mitral annular dimension in patients with MR was significantly greater than in those without MR, but it was similar among the three groups. The extent of wall-motion abnormality correlated significantly with the area of MR jet in the anterior MI group (y = 3.1x + 15.5, r = 0.52, P < 0.01) and in the inferior MI group (y = 8.3x + 32.7, r = 0.57, P < 0.01). However, the slope of this relationship was significantly steeper in the inferior MI group than in the anterior MI group (P < 0.05). These results indicated that the degree of MR with inferior MI was greater than with anterior MI for a given MI area. PMD may play an important role in the higher prevalence and greater degree of MR in inferior MI.  相似文献   
24.
MRI同层动态增强对垂体微腺瘤的诊断价值   总被引:3,自引:0,他引:3  
目的:分析垂体微腺瘤的MPd同层动态增强特征。方法:对40例临床怀疑为垂体微腺瘤的病人行同层动态增强MPd扫描,并绘出时间一信号强度曲线图。结果:40例病人中共检出垂体微腺瘤26例。同层动态增强后垂体微腺瘤的MPd表现为圆或椭圆形的低或稍低信号,似“充盈缺损”;垂体微腺瘤的最大信号强度多出现在注入造影剂后32~96s,以64s最明显。结论:同层MPd动态增强对垂体微腺瘤的诊断有较高价值。  相似文献   
25.
OBJECTIVE: To indicate whether the double peaked N(1) to gaps in continuous white noise is a composite of onset and offset responses to transients or whether it reflects higher processing such as change or mismatch detection and to assess the role of attention in this process. METHODS: Evoked potentials were recorded to two binaural stimulus types: (1) gaps of different durations randomly distributed in continuous white noise; and (2) click pairs at intervals identical to those between gap onsets and offsets in the continuous noise stimulus. Potentials to these stimuli were recorded while subjects read a text and while detecting gaps in noise or click pairs. RESULTS: Potentials were detected to all click pairs and to gaps of 5 ms or longer, corresponding to the subjects' psychoacoustic gap detection threshold. With long gap durations of 200-800 ms, distinct potentials to gap onset and gap offset were observed. The waveforms to all click pairs and to offsets of long gaps were similar and single-peaked, while potentials to gaps of 10 ms and longer, and potentials to onsets of long gaps were double-peaked, consisting of two N(1) negativities, 60 ms apart, irrespective of gap duration. The first (N(1a)), was more frontal in its distribution and similar to that of clicks. The second (N(1b)) peak's distribution was more central/temporal and its source locations and time course of activity were distinct. No effects of attention on any of the varieties and constituents of N(1) were observed. CONCLUSIONS: Comparing potentials to gap onsets, to click pairs and to gap offsets, suggests that potentials to gap onsets involve not only sound onset/offset responses (N(1), N(1a)) but also the subsequent pre-attentive perception of the cessation of an ongoing sound (N(1b)). We propose that N(1b) is distinct from change or mismatch detection and is associated with termination of an ongoing continuous stimulus. We propose to call it the N(egation)-process. SIGNIFICANCE: A constituent of the N(1) complex is shown to be associated with the pre-attentive perception of termination of an ongoing stimulus and to have distinct scalp distribution and intracranial sources.  相似文献   
26.
Summary Seventy-five diabetic and 40 nondiabetic subjects who where suffering from peripheral vascular disease were studied in order to determine whether the degree of the severity of their disease can be better calculated by Doppler ultrasound examinations of the peak velocity than by the systolic pressure of the peripheral bloodstream. In 46 examinations of normal controls the mean value of the peak velocity was 13.3±3.3 cm/s with a standard deviation of 15.4%±13.2% on one day and 16.1%±15.9% on different days. Considering patients with or without diabetes mellitus the velocity was significantly decreased in correlation to an increasing degree of severity of the vascular disease (P<0.001); however, the decrease was lower in diabetic than in nondiabetic subjects (6.9±2.8 vs 4.6±6.2,P<0.05). The systolic pressure hardly decreased, but remained higher in all stages of peripheral vascular disease of diabetics than in the nondiabetic subject (P<0.05 toP<0.005). There was a significant decrease of the systolic pressure only in diabetic subjects with the most advanced degree of the disease, i.e. stage IV (P<0.05).It is concluded from this study that Doppler ultrasound measurements of the peak velocity of the peripheral bloodstream are a useful parameter to calculate the degree of severity of the peripheral vascular disease. In addition, it is concluded than peak velocity is an even better prognostic indicator of peripheral vascular disease than is measurement of the systolic blood pressure at the feet.

Abkürzungen AVK periphere arterielle Verschlußkrankheit - USDI Ultraschall-Doppler-Index - MSBG maximale Blutströmungsgeschwindigkeit - HFV Herzfrequenzvariation  相似文献   
27.
BACKGROUND: It is a common observation that superficial freezing of normal skin and skin tumors may create a transient superficial whitening effect. In this respect, cryoscopy refers to the direct observation by dermoscopy, with or without digital recording, of the visual alterations of the frozen tissues. AIMS: To define the optimal method of cryoscopy and to describe the cryoscopy patterns of normal skin and selected skin lesions. MATERIALS AND METHODS: The influence of (a) different cryogenic sources [solid carbon dioxide (-78.5 degrees C), liquid nitrogen (N(2), -196 degrees C), and a mixture of dimethyl ether and propane (-57 degrees C)], (b) various application methods (spraying, cotton chill tips, copper plate), and (c) freezing time was assessed with regard to clinical feasability, visualization quality, and persistance time of the whitening effect. Cryoscopy patterns of normal skin, callosities and of histologically proven seborrheic keratoses, verrucous hamartomas, molluscum contagiosum, keratoacanthomas, viral warts, condylomas, actinic keratoses, dermatofibromas, skin tags, basal cell carcinomas, angiomas, and melanocytic naevi were assessed. RESULTS: The cryoscopy images of skin highlighted the skin lines. They appeared similar regardless of the freezing source and the application method. The aspects differed according to the nature of the lesions. The cotton chill tip method provided a longer whitening period compared with the other cold sources, both in normal and lesional skin. Hence, it represented the most convenient way for performing digital recording cryoscopy. On normal skin, cryoapplication was limited to about 1.5 s due to pain, resulting in whitening times ranging from 6 to 9 s, which was too short for easy digital recording. On all studied skin tumors, a 10-s N(2) freezing time was not experienced as painful, and blanching time persisted for 20-34 s, allowing easy digital recording. The whitening time was longer with increasing freezing time on both normal and lesional skin. Every single examined normal skin site and all the skin lesions showed a strong whitening effect, except heavily cornified structures, including some keratoses, callosities, and viral warts. Increased contrast of the skin surface texture was observed in almost every studied lesion. CONCLUSION: The N(2) cotton chill tip technique appeared to be the most convenient technique for cryoscopy and provided longer whitening periods compared with the other freezing sources. Pain prevented its use on normal skin, but a series of exophytic skin lesions was conveniently accessible to cryoscopy. The differences in whitening periods of various epidermal components resulted in increased visual contrast, creating typical cryoscopy images for the different exophytic skin tumors. Cryoscopy represents a novel in vivo skin imaging technique that is rapid, non-invasive, cost-effective, and easily performed. It shows both investigative and diagnostic potentials. It is remarkable that cryoscopy pictures closely resemble those yielded by skin capacitance imaging.  相似文献   
28.
OBJECTIVE: The purpose of this presentation is to show the imaging findings of the common and uncommon variants of adenomyosis as seen on sonography and magnetic resonance imaging (MRI). METHODS: A 3-year database search was performed to identify women who had pelvic sonography and pelvic MRI within a 6-month interval. Images of these cases were retrospectively reviewed. RESULTS: Eighty women were identified. Adenomyosis was diagnosed on MRI, which was used as the reference standard, in 45 of these women. The correct diagnosis was made on sonography in 73% of the cases. CONCLUSIONS: Awareness of the spectrum of imaging features of adenomyosis is important to use sonography effectively for diagnosing this entity and to help avoid misdiagnosis.  相似文献   
29.
Objectives To develop a simple image viewer that utilizes image files in general-purpose formats that are written from the original 3DX volume data. Methods We used FLASH MX2004 for Macintosh to develop a simple image viewer. In developing the software for the simple image viewer, we decided that the viewer should provide the following features: (1) be available to both Windows OS and Mac OS, (2) allow interlocking of the 3D images, (3) display image enlargement, and (4) allow distance measurements. The accuracy of the distance measurements was evaluated. Results The procedure was as follows: (1) write 3D images in jpeg format to a folder on i-VIEW; (2) place the folder containing the 3D images into the directory of the simple image viewer software on a PC; (3) start the software and open the window to input the folder name containing the 3D images; and (4) display the 3D images. Our viewer had features such as image enlargement, interlocking 3D images, drawing, and distance measurements. No significant differences were shown between the measurements made by our simple viewer and the actual values of the images in any direction. Conclusions Our image-viewing software for 3DX is beneficial for clinical use.  相似文献   
30.
Introduction: One of the causes of pain during insertion of the colonoscope is stretching of the mesenterium by loop formation. The degree of pain differs according to the type of loop formation. Our aims were to study the accuracy of the colonoscopist’s assessment of the presence and type of loop formation and to study the degree of pain in relation to the type of loop by administering the visual analog scale (VAS). Methods: Two hundred and fifty‐seven consecutive patients were enrolled. All procedures were performed by two experienced colonoscopists who were blind to magnetic endoscope imaging view. After the colonoscopy, the colonoscopist was asked to assess the presence and type of loop formation. The degree of pain was assessed using the VAS. Results: The accuracy of estimating N loop, alpha loop, absence of loop formation and U loop was each over 70%. The accuracy of estimating gamma and splenic loop was significantly lower than the accuracy of estimating U loop. Colonoscopy was significantly more painful in women than in men. The degree of pain was significantly higher upon formation of reverse alpha loop and gamma and splenic loop than upon formation of N loop and U loop. Conclusions: Upon formation of reverse alpha loop or gamma and splenic loop, patients experienced more pain and it was difficult for the endoscopists to assess these loops. As women had severe pain compared with men, the use of a pediatric colonoscope or higher dosage of sedation in women should be considered.  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