全文获取类型
收费全文 | 578篇 |
免费 | 72篇 |
国内免费 | 4篇 |
专业分类
耳鼻咽喉 | 2篇 |
儿科学 | 11篇 |
妇产科学 | 5篇 |
基础医学 | 35篇 |
口腔科学 | 2篇 |
临床医学 | 24篇 |
内科学 | 20篇 |
神经病学 | 55篇 |
特种医学 | 292篇 |
外科学 | 29篇 |
综合类 | 68篇 |
预防医学 | 16篇 |
药学 | 30篇 |
中国医学 | 3篇 |
肿瘤学 | 62篇 |
出版年
2023年 | 3篇 |
2022年 | 19篇 |
2021年 | 14篇 |
2020年 | 26篇 |
2019年 | 40篇 |
2018年 | 46篇 |
2017年 | 55篇 |
2016年 | 32篇 |
2015年 | 29篇 |
2014年 | 58篇 |
2013年 | 57篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 26篇 |
2009年 | 28篇 |
2008年 | 27篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1992年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有654条查询结果,搜索用时 31 毫秒
1.
It has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow (CBF) changes during brain activation. However, current ADC imaging techniques have an inherently low temporal resolution due to the requirement of multiple acquisitions with different b-factors, as well as potential confounds from cross talk between the deoxyhemoglobin-induced background gradients and the externally applied diffusion-weighting gradients. In this report a new method is proposed and implemented that addresses these two limitations. Specifically, a single-shot pulse sequence that sequentially acquires one gradient-echo (GRE) and two diffusion-weighted spin-echo (SE) images was developed. In addition, the diffusion-weighting gradient waveform was numerically optimized to null the cross terms with the deoxyhemoglobin-induced background gradients to fully isolate the effect of diffusion weighting from that of oxygenation-level changes. The experimental results show that this new single-shot method can acquire ADC maps with sufficient signal-to-noise ratio (SNR), and establish its practical utility in functional MRI (fMRI) to complement the blood oxygenation level-dependent (BOLD) technique and provide differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels. 相似文献
2.
3.
Xingchen Wu Seyoum Nerisho Prasun Dastidar Pertti Ryymin Ritva Järvenpää Hannu Pertovaara Hannu Eskola Pirkko‐Liisa Kellokumpu‐Lehtinen 《NMR in biomedicine》2013,26(9):1186-1194
To compare different MRI sequences for the detection of lesions and the evaluation of response to chemotherapy in patients with diffuse large B‐cell lymphoma (DLBCL), 18 patients with histology‐confirmed DLBCL underwent 3‐T MRI scanning prior to and 1 week after chemotherapy. The MRI sequences included T1‐weighted pre‐ and post‐contrast, T2‐weighted with and without fat suppression, and a single‐shot echo‐planar diffusion‐weighted imaging (DWI) with two b values (0 and 800 s/mm2). Conventional MRI sequence comparisons were performed using the contrast ratio between tumor and normal vertebral body instead of signal intensity. The apparent diffusion coefficient (ADC) of the tumor was measured directly on the parametric ADC map. The tumor volume was used as a reference for the evaluation of chemotherapy response. The mean tumor volume was 374 mL at baseline, and decreased by 65% 1 week after chemotherapy (p < 0.01). The T2‐weighted image with fat suppression showed a significantly higher contrast ratio compared with images from all other conventional MRI sequences, both before and after treatment (p < 0.01, respectively). The contrast ratio of the T2‐weighted image with fat suppression decreased significantly (p < 0.01), and that of the T1‐weighted pre‐contrast image increased significantly (p < 0.01), after treatment. However, there was no correlation between the change in contrast ratio and tumor volume. The mean ADC value was 0.68 × 10–3 mm2/s at baseline; it increased by 89% after chemotherapy (p < 0.001), and the change in ADC value correlated with the change in tumor volume (r = 0.66, p < 0.01). The baseline ADC value also correlated inversely with the percentage change in ADC after treatment (r = ?0.62, p < 0.01). In conclusion, this study indicates that T2‐weighted imaging with fat suppression is the best conventional sequence for the detection of lesions and evaluation of the efficacy of chemotherapy in DLBCL. DWI with ADC mapping is an imaging modality with both diagnostic and prognostic value that could complement conventional MRI. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
4.
《ACS medicinal chemistry letters》2021,12(3):404
A new series with the tetrahydroisoquinoline-fused benzodiazepine (TBD) ring system combined with the surrogates of (1-methyl-1H-pyrrol-3-yl)benzene (“MPB”) payloads were designed and executed for conjugation with a monoclonal antibody for anticancer therapeutics. DNA models helped in rationally identifying modifications of the “MPB” binding component and guided structure–activity relationship generation. This hybrid series of payloads exhibited excellent in vitro activity when tested against a panel of various cancer cell lines. One of the payloads was appended with a lysosome-cleavable peptide linker and conjugated with an anti-mesothelin antibody via a site-specific conjugation method mediated by the enzyme bacterial transglutaminase (BTGase). Antibody–drug conjugate (ADC) 50 demonstrated good plasma stability and lysosomal cleavage. A single intravenous dose of ADC 50 (5 or 10 nmol/kg) showed robust efficacy in an N87 gastric cancer xenograft model. 相似文献
5.
Rajpaul Attariwala MD PhD FRCPC FANM Wayne Picker M. Hlth. Sc. 《Journal of magnetic resonance imaging : JMRI》2013,38(2):253-268
Diffusion‐weighted imaging (DWI) is an established functional imaging technique that interrogates the delicate balance of water movement at the cellular level. Technological advances enable this technique to be applied to whole‐body MRI. Theory, b‐value selection, common artifacts and target to background for optimized viewing will be reviewed for applications in the neck, chest, abdomen, and pelvis. Whole‐body imaging with DWI allows novel applications of MRI to aid in evaluation of conditions such as multiple myeloma, lymphoma, and skeletal metastases, while the quantitative nature of this technique permits evaluation of response to therapy. Persisting signal at high b‐values from restricted hypercellular tissue and viscous fluid also permits applications of DWI beyond oncologic imaging. DWI, when used in conjunction with routine imaging, can assist in detecting hemorrhagic degradation products, infection/abscess, and inflammation in colitis, while aiding with discrimination of free fluid and empyema, while limiting the need for intravenous contrast. DWI in conjunction with routine anatomic images provides a platform to improve lesion detection and characterization with findings rivaling other combined anatomic and functional imaging techniques, with the added benefit of no ionizing radiation. J. Magn. Reson. Imaging 2013;38:253–268. © 2013 Wiley Periodicals, Inc. 相似文献
6.
Apparent diffusion coefficients in prostate cancer: correlation with molecular markers Ki‐67, HIF‐1α and VEGF
下载免费PDF全文
![点击此处可从《NMR in biomedicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Teng Ma Shaolin Yang Haiyan Jing Lin Cong Zhixin Cao Zhiling Liu Zhaoqin Huang 《NMR in biomedicine》2018,31(3)
Prostate cancer (PCa) is the second most common cancer in men. The Gleason score (GS) and biomarkers play important roles in the diagnosis and treatment of patients with PCa. The purpose of this study was to investigate the relationship between the apparent diffusion coefficient (ADC) and the molecular markers Ki‐67, hypoxia‐inducible factor‐1α (HIF‐1α) and vascular endothelial growth factor (VEGF) in PCa. Thirty‐nine patients with 39 lesions, who had been diagnosed with PCa, were enrolled in this study. All patients underwent diffusion‐weighted magnetic resonance imaging (DW‐MRI) (b = 800 s/mm2). The expression of Ki‐67, HIF‐1α and VEGF was assessed by immunohistochemistry. Statistical analysis was applied to analyze the association between ADC and prostate‐specific antigen (PSA), GS and the expression of Ki‐67, HIF‐1α and VEGF. The group differences in ADC among different grades of Ki‐67, HIF‐1α and VEGF were also analyzed. The mean ± standard deviation of ADC was (0.76 ± 0.27) × 10?3 mm2/s. ADC correlated negatively with PSA and GS (p < 0.05). The Ki‐67 staining index (SI), HIF‐1α expression and VEGF expression in PCa were correlated inversely with ADC, controlling for age (r = –0.332, p < 0.05; r = ?0.662, p < 0.0005; and r = ?0.714, p < 0.0005, respectively). ADC showed a significant difference among different grades of Ki‐67 (F = 9.164, p = 0.005), HIF‐1α (F = 40.333, p < 0.0005) and VEGF (F = 22.048, p < 0.0005). In conclusion, ADC was correlated with PSA, GS, and Ki‐67, HIF‐1α and VEGF expression in patients with PCa. ADC may be used to evaluate tumor proliferation, hypoxia and angiogenesis in PCa. 相似文献
7.
Lise Vejby Søgaard Franz Schilling Martin A. Janich Marion I. Menzel Jan Henrik Ardenkjær‐Larsen 《NMR in biomedicine》2014,27(5):561-569
The combination of hyperpolarized MRS with diffusion weighting (dw) allows for determination of the apparent diffusion coefficient (ADC), which is indicative of the intra‐ or extracellular localization of the metabolite. Here, a slice‐selective pulsed‐gradient spin echo sequence was implemented to acquire a series of dw spectra from rat muscle in vivo to determine the ADCs of multiple metabolites after a single injection of hyperpolarized [1‐13C]pyruvate. An optimal control optimized universal‐rotation pulse was used for refocusing to minimize signal loss caused by B1 imperfections. Non‐dw spectra were acquired interleaved with the dw spectra and these were used to correct for signal decay during the acquisition as a result of T1 decay, pulse imperfections, flow etc. The data showed that the ADC values for [1‐13C]lactate (0.4–0.7 µm2/ms) and [1‐13C]alanine (0.4–0.9 µm2/ms) were about a factor of two lower than the ADC of [1‐13C]pyruvate (1.1–1.5 µm2/ms). This indicates a more restricted diffusion space for the former two metabolites consistent with lactate and alanine being intracellular. The higher ADC for pyruvate (similar to the proton ADC) reflected that the injected substance was not confined inside the muscle cells but also present extracellular. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
8.
Background/Objectives
Due to its rarity, epidermoid cyst in intrapancreatic accessory spleen (ECIPAS) is still a diagnostic dilemma during clinical practice. The aim of this review was to summarize the epidemiologic features and management of ECIPAS.Methods
MEDLINE and EMBASE were searched for English articles reporting on ECIPAS up to April 30th, 2018 following the methodology suggested by the PRISMA guidelines. Categorical variables were reported as frequency and percentage. Continuous variables were reported as median (range).Results
A total of 56 patients from 47 full articles were included for the final data synthesis. More than half of the ECIPASs (59%) were found incidentally. The female/male ratio was 1.33. ECIPAS is typically a single mono-/multi-lobular cystic lesions in the pancreatic tail with thickened cystic wall or various amount of solid component which had identical density/signal to the spleen on imaging examinations. The cyst is filled with serous or non-serous fluid. Recognition of the surrounding ectopic splenic tissue is the key point to diagnose ECIPAS. However, no preoperative examination was able to make a definite diagnosis. Almost all the patients (96%) received surgical treatment, due to the suspicion of pancreatic malignant or potentially malignant cystic tumor, especially mucinous cystic neoplasm (MCN).Conclusions
Although seldom encountered, ECIPAS should be considered as a differential diagnosis for pancreatic cystic lesions, especially when solid component was detected. As a benign disease, unnecessary surgery should be avoided. Because it is difficult to make a definite diagnosis preoperatively by one single examination, multiple modalities may be required. 相似文献9.
模数转换器(Analog-to-Digital Converter,ADC)是片上集成系统的关键部件,通过对逐次逼近逻辑电路和三值逻辑原理的研究,提出了一种基于碳纳米场效应晶体管(Carbon Nanotube Field Effect Transistor,CNFET)的三值逐次逼近ADC设计方案。该方案首先控制三值电容阵列的底板电压,逐次逼近其模拟量值,产生由高位到低位的二值信号,然后由编码器将二值转换为三值信号,完成整个转换过程,最后实验证明了所设计的电路逻辑功能正确,并具有明显的高速、低功耗特性。 相似文献
10.
Rishabh Kumar Prachi Kala Geeta S. Narayanan Bhaskar Vishwanathan Sowmya Narayanan Sanjeet Mandal Arpitha Rao Gangadharappa Gowda 《Brachytherapy》2021,20(1):112-117
PURPOSEImage-guided adaptive brachytherapy (IGABT) recently has shown excellent clinical outcomes with superior local control and less toxicity. For IGABT, T2W (T2-weighted) MRI is the gold standard. However, studies have shown that target delineation with the same results in uncertainties, poor interobserver variabilities, and low conformity indices for high-risk clinical target volume contours. In this study, we investigate the role of diffusion-weighted imaging–derived apparent diffusion coefficient (ADC) maps to aid in IGABT. We also evaluated ADC from the baseline to brachytherapy.Methods and MaterialsThirty selected patients were enrolled for this study, and two MRIs were taken at diagnosis and before brachytherapy. Patients were divided into two groups, Group 1 being patients with parametrial involvement before external beam radiotherapy and no parametrial involvement before brachytherapy. Group 2 included patients with parametrial involvement before external beam radiotherapy and persistent parametrial involvement before brachytherapy. ADC was measured at the center, edge, and 1 cm from the edge.ResultsThe measured ADC increased from diagnosis to brachytherapy, and this increase was more for the patients in Group 1 than in Group 2. The mean TDadc (diagnosis ADC, center), TEadc (tumor edge ADC diagnosis), and T1cmDadc (1 cm from edge at diagnosis) were 0.884, 1.45, and 1.9 × 10?3 mm2/s, respectively. The TBadc (ADC at brachytherapy, center), TEBadc (tumor edge ADC at brachytherapy), and TE1cmBadc (1 cm from edge brachytherapy) were 1.2, 1.8, and 2.3 × 10?3 mm2/s, respectively, p-value <0.00001. No abnormal ADC was present outside the high-risk clinical target volume contours.ConclusionMRI-based IGABT using T2W imaging essentially covers all functionally abnormal zones at brachytherapy. Diffusion-weighted imaging, along with ADC maps, should only be used as a supplement for target delineation. 相似文献