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   1507篇
  免费   89篇
  国内免费   19篇
耳鼻咽喉   22篇
儿科学   33篇
妇产科学   67篇
基础医学   187篇
口腔科学   45篇
临床医学   137篇
内科学   417篇
皮肤病学   48篇
神经病学   114篇
特种医学   36篇
外科学   155篇
综合类   5篇
预防医学   76篇
眼科学   32篇
药学   85篇
中国医学   1篇
肿瘤学   155篇
  2023年   15篇
  2022年   31篇
  2021年   61篇
  2020年   40篇
  2019年   51篇
  2018年   62篇
  2017年   50篇
  2016年   41篇
  2015年   44篇
  2014年   67篇
  2013年   85篇
  2012年   110篇
  2011年   94篇
  2010年   52篇
  2009年   45篇
  2008年   95篇
  2007年   80篇
  2006年   77篇
  2005年   66篇
  2004年   58篇
  2003年   71篇
  2002年   57篇
  2001年   20篇
  2000年   17篇
  1999年   25篇
  1998年   16篇
  1997年   14篇
  1996年   16篇
  1995年   6篇
  1994年   9篇
  1993年   11篇
  1992年   18篇
  1991年   9篇
  1990年   10篇
  1989年   6篇
  1988年   7篇
  1987年   5篇
  1986年   5篇
  1985年   5篇
  1984年   7篇
  1983年   3篇
  1982年   4篇
  1981年   5篇
  1979年   8篇
  1978年   7篇
  1977年   3篇
  1975年   4篇
  1972年   3篇
  1971年   6篇
  1966年   2篇
排序方式: 共有1615条查询结果,搜索用时 996 毫秒
131.
PURPOSE: To evaluate the current role of small bowel (SB) radiologic barium examinations in adult celiac disease (ACD). MATERIALS AND METHODS: Retrospective review of 61 SB barium examinations in 280 ACD patients. Sixty-one examinations in 61 patients were performed: 7/61 with small bowel 'follow-through' (SBFT) method, and 54/61 with small bowel double-contrast enteroclysis (SBE). Radiological criteria for ACD diagnosis were divided in four groups: 1) definite ACD (reversal of jejuno-ileal fold pattern); 2) possible ACD (malabsorption pattern and ileal jejunization); 3) malabsorption (fluid, dilatation, 'moulage', flocculation); 4) complicated ACD (irregular, thickened, nodular folds; wall thickening; masses). RESULTS: In 49/61 patients RX examinations were performed before ACD diagnosis. In this group, clinical presentations included one or more of the following: diarrhea, weight loss, malabsorption, anemia, abdominal pain; 7/49 had a SBFT, and 42/49 a SBE. All 7 SBFTs showed pattern 3, and 8/42 SBEs showed pattern 2 (suspected ACD). In 34/42 patients SBE allowed a definite ACD diagnosis (pattern 1); however, 6/34 were also false-positive for complicated ACD (pattern 4). Ten out of sixty-one patients were clinically suspected of having complicated ACD, correctly excluded (8/8) or confirmed (2/2) by SBE. None of these 59/61 patients had a radiologic diagnosis of normal' SB. The last 2/61 patients with ACD, examined for persisting chronic anemia, had a normal SBE. CONCLUSIONS: This study confirm that SB radiology may be of value either in ACD diagnosis or in excluding complications: SBE is currently the most accurate examination. SBE alone is however less accurate in confirming complicated ACD; further imaging techniques are always needed in this clinical context.  相似文献   
132.
AIM: Prostaglandin analogues provide an effective method for induction of abortion in the second trimester of pregnancy. The clinical outcome and the risk of complications were evaluated in a group of women having a medical termination of pregnancy with gemeprost. METHODS: Three-hundred and six women undergoing second trimester termination of pregnancy, between January 1998 and July 2002 in our center, were studied. All women were given 1 mg vaginal gemeprost every 3 h up to a maximum of 3 doses in the first 24 hours. If the abortion did not occur within the first 24 hours after initiation of treatment, they were given a 2(nd) course of gemeprost. Outcome measures included failure of the 1st course of gemeprost, length of hospital stay after expulsion of conceptus, heavy blood loss with or without necessity of uterine packing or blood transfusion, and failure of induction. RESULTS: There was a significant difference, with better results in women with previous deliveries (vaginal or abdominal), as to the failure to abort after the 1(st) course of PG (P<0.01). Length of hospital stay, complications and failure of induction were independent from parity. Twelve (3.9%) women failed to abort with gemeprost and required other methods for abortion. CONCLUSIONS: The study confirms the efficacy of gemeprost for mid-trimester termination of pregnancy, although it is a risky and costly procedure, requiring hospitalisation and is associated with higher complication rate than the first trimester surgical abortion.  相似文献   
133.
Twenty-four Mediterranean fin whales were tracked in open sea with a method based on the assessment of the animal differential position in respect of the observer's absolute position aboard a vessel, with the concomitant recording of the respiratory activity. Short distance video recording was also performed in two whales, permitting the simultaneous determination of single breath expiratory (TE) and inspiratory (TI) durations. In the 24 whales swimming at an average velocity of 1.39 (0.47) m·s–1 [mean (SD), range: 0.62–2.44 m·s–1], 2068 breaths organized in 477 respiratory cycles were observed. Each cycle entailed a prolonged apnoea dive phase [225 (91) s, Tdive) followed by a period near the surface [62 (28) s, surfacing], during which a series of breaths [4.6 (1.8)] was performed at short intervals. On the basis of track length and swimming velocity, two groups of animals were devised differing for convolution of the course (p<0.001), extension of ranging territory (p<0.01) and horizontal swimming velocity (p<0.05), which may represent two distinct behaviours. A possibly general mechanism of control of breathing in cetaceans was found, consistent with a model of constant tidal volume and variable respiratory frequency. Coherently with this model, TE was independent of TI or Tdive, in line with a passive expiration, while TI appeared to be negatively correlated with Tdive (p<0.05), otherwise suggesting, similarly with terrestrial mammals, a significant role of hypercapnic stimulation. The estimated O2 consumption of about 150 l·min–1 is in line with the general allometric regression for mammals and corresponds to an energetic expenditure of 85–95 kJ·kg–1·day–1.Partially presented as a poster at The World Marine Mammal Science Conference and 12th Annual Conference of the European Cetacean Society, Monaco (Montecarlo), 20–24 January 1998.Angelo Colombini provided technical assistance.  相似文献   
134.
Previous studies have shown a high incidence (77%) of isolation of Candida spp. from the oral cavities of patients with type 1 diabetes mellitus. The aim of the present study was to assess the prevalence of yeast in the oral cavities of patients suffering from type 1 and type 2 diabetes mellitus. The patients were classified according to the level of diabetic control (HbA1c), and further stratified on the presence or absence of dental prosthesis. Oral rinse samples were assessed for the growth of yeast and the degree of colonization. Oral isolates were defined to the species level by both phenotypic and novel molecular methods. The overall proportion (60%) of diabetic patients who had Candida spp. isolated from the oral cavity was similar to that previously reported. Local oral factors, such as the presence of dentures, seemed to have a greater influence than diabetic status on the amount and species of Candida isolated from the oral cavities of diabetic patients. Diabetic patients with dentures had more non-albicans Candida isolated from their mouths than dentate diabetic patients. Candida dubliniensis was isolated from diabetic patients and may have a predilection for dentate patients.  相似文献   
135.
Aim of this study was to evaluate the results in 6 patients undergoing laparoscopic adrenalectomy for the treatment of solitary adrenal gland metastases. One hundred forty-five patients underwent laparoscopic adrenalectomy by transperitoneal anterior approach. In 6 patients the indication was the presence of a solitary adrenal gland metastasis. Primary tumors were the following: truncal melanoma, gastric cancer, renal cancer, lung cancer, and breast cancer. Mean age was 57 years (range 44-70 years). Three patients underwent right adrenalectomy and 3 patients a left adrenalectomy. No conversion to open surgery occurred. No mortality or intraoperative complications were observed. Mean operative time was 103 minutes (range 70-150) for right adrenalectomy and 170 minutes (range 90-280) for left adrenalectomy. No postoperative complications occurred. Mean diameter of the tumor was 3.5 cm (range 2-5 cm). Tumor free margins were obtained in every case. Mean hospital stay was 2 days (range 2-3 days). At follow-up, 2 patients have died of systemic dissemination of the disease, one 15 months and one 24 months after the operation. The remaining 4 patients are alive and disease free at a mean follow-up of 7 months (range 4-11 months). So far, no port site metastases or local recurrence have been observed. In our experience adrenal gland metastasis can be treated safely and effectively by the laparoscopic transperitoneal anterior approach.  相似文献   
136.
Serum MMP-2 and MMP-9 are elevated in different multiple sclerosis subtypes   总被引:7,自引:0,他引:7  
In multiple sclerosis (MS), matrix metalloproteinase (MMP) activity in tissues is the result of a balance between MMPs and their tissue inhibitors (TIMPs). MMP-9 predominates in acute MS lesions and is inhibited by TIMP-1, while MMP-2 may participate in the remodeling of the extracellular matrix (ECM) such as in chronic disease and is inhibited by TIMP-2. These differences may be reflected in serum and cerebrospinal fluid (CSF). We have tried to characterize MMP-2 and MMP-9 activities, in relation to their respective TIMPs, 2 and 1, as a factor of different types of the disease, as this information was not previously clearly stated. We found the MMP-2/TIMP-2 ratio in serum to show higher values in secondary progressive (SP, p=0.02) and primary progressive (PP, p=0.01) MS than short disease duration (SDD) relapsing-remitting (RR) MS, but not different from the healthy control (HC) group. Whereas the MMP-9/TIMP-1 ratio in serum showed higher (p=0.04) values in SDD RR MS than PP but also in active patients, evaluated either clinically (p=0.006) or from the magnetic resonance imaging (MRI, p<0.05), compared to inactive disease. CSF MMP to TIMP ratios did not differ between MS subtypes, suggesting systemic rather CNS-restricted changes. These results show that an increase in MMP-2/TIMP-2 ratio marks chronic progression in MS, but it is as high as in HC, and also confirm that high MMP-9 activity characterizes short duration relapsing and active forms of the disease.  相似文献   
137.
138.
In Germany the dD by Feldmann is a frequently used test in child assessment. Unknown, however, is the validity of the dD in the assessment of children with specific developmental language disorders. The dD by Feldmann are pairs of three-syllable content words which are presented dichotically. In this controlled cross-sectional study 65 children took the dichotic listening test by Feldmann (dD). The experimental group comprised 34 children with developmental reading and spelling disorders. The control group comprised 31 children with normal reading and spelling development. Age and nonverbal IQ were matched in both groups. The mean age was 9.8 years (range 7 - 11 years). The dichotic listening performance of right and left ear was registered separately. Twenty word pairs were presented dichotically at a constant amplitude of 65 dB. Memorisation of word pairs was tested under free recall conditions. A score of 100 % can be attained, if all word pairs are repeated correctly. Results demonstrated that no child attained a score of 100 %. As expected, the children with the developmental reading and spelling disorders attained significantly lower scores than the children in the control group (42.4 % versus 64 %). The reason for the lower results in the experimental group was left ear dichotic listening performance. There were no significant differences in right dichotic listening performance. Raw score overlaps occurred to some extent in both groups, but scores of 30 % or less were only observed in the experimental group. Scores correlated significantly with age, but not with nonverbal IQ. However, dD performance significantly correlated with several measures of phonological and syntactic language development as well as with auditory working memory. Based on these results it is our opinion that performance scores of the dD by Feldmann should be interpreted cautiously until validation studies have been carried out.  相似文献   
139.
Two and a half millennia ago Pythagoras initiated the scientific study of the pitch of sounds; yet our understanding of the mechanisms of pitch perception remains incomplete. Physical models of pitch perception try to explain from elementary principles why certain physical characteristics of the stimulus lead to particular pitch sensations. There are two broad categories of pitch-perception models: place or spectral models consider that pitch is mainly related to the Fourier spectrum of the stimulus, whereas for periodicity or temporal models its characteristics in the time domain are more important. Current models from either class are usually computationally intensive, implementing a series of steps more or less supported by auditory physiology. However, the brain has to analyze and react in real time to an enormous amount of information from the ear and other senses. How is all this information efficiently represented and processed in the nervous system? A proposal of nonlinear and complex systems research is that dynamical attractors may form the basis of neural information processing. Because the auditory system is a complex and highly nonlinear dynamical system, it is natural to suppose that dynamical attractors may carry perceptual and functional meaning. Here we show that this idea, scarcely developed in current pitch models, can be successfully applied to pitch perception.The pitch of a sound is where we perceive it to lie on a musical scale. For a pure tone with a single frequency component, pitch rises monotonically with frequency. However, more complex signals also elicit a pitch sensation. Some instances are presented in Fig. Fig.1.1. These are sounds produced by the nonlinear interaction of two or more periodic sources, by amplitude or frequency modulation. All such stimuli, which may be termed complex tones, produce a definite pitch sensation, and all of them exhibit a certain spectral periodicity. Many natural sounds have this quality, including vowel sounds in human speech and vocalizations of many other animals. Evidence for the importance of spectral periodicity in sound processing by humans is that noisy stimuli exhibiting this property also elicit a pitch sensation. An example is repetition pitch: the pitch of ripple noise (1), which arises naturally when the sound from a noisy source interacts with a delayed version of itself, produced, for example, by a single or multiple echo. It is clear that an efficient mechanism for the analysis and recognition of complex tones represents an evolutionary advantage for an organism. In this light, the pitch percept may be seen as an effective one-parameter categorization of sounds possessing some spectral periodicity (25). Figure 1Stimuli: waveforms, Fourier spectra, and pitches. (a) A 1-kHz pure tone; the pitch coincides with the frequency ω0. (b) Complex tone formed by 200-Hz fundamental plus overtones; the pitch is at the frequency of the fundamental ω0. ...  相似文献   
140.
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