全文获取类型
收费全文 | 609篇 |
免费 | 52篇 |
国内免费 | 4篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 33篇 |
2020年 | 28篇 |
2019年 | 39篇 |
2018年 | 40篇 |
2017年 | 33篇 |
2016年 | 14篇 |
2015年 | 28篇 |
2014年 | 71篇 |
2013年 | 90篇 |
2012年 | 72篇 |
2011年 | 34篇 |
2010年 | 11篇 |
2009年 | 20篇 |
2008年 | 29篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 12篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
排序方式: 共有665条查询结果,搜索用时 15 毫秒
1.
Current MR methods use T2? relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T2? maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T2? values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T2? Two of these methods utilized a voxel-wise method to establish T2? maps: (1) a current “gold standard” method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T2? determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LSROI) instead of a voxel-wise basis. The resulting median T2? values of the PCL and computational time were compared. The median T2? values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T2? values between the 2MM and 6LS methods (R2=0.80). The median T2? values were not significantly different between the 6LS and 6LSROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LSROI (which efficiently provides the median T2? value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T2? maps to predict ligament structural properties as a patient outcome measure. 相似文献
2.
《Somatosensory & motor research》2013,30(1):51-67
We examined stimulus-response relationships of vibrissa-activated mechanosensory neurons of the rat's fifth (trigeminal) ganglion. Single-unit activity was recorded with tungsten microelectrodes. The vibrissae were deflected with a variety of parametrically controlled stimulus waveforms.We found that the receptive field of each vibrissa-activated neuron consisted of a single vibrissa. Few, if any, unambiguous examples of spontaneous activity were observed in these neurons. Even if true spontaneous activity was present, its observed incidence was low, as were the measured discharge rates.Thresholds of individual neurons were usually quite discrete; often a 1-2% increase in pulse magnitude (angular displacement) above a level to which the neuron did not respond caused it to discharge on every trial. The distribution of thresholds for the sample was continuous with a median of about 1° and a range of over three orders of magnitude. The most sensitive neurons responded to deflections of less than 0.1°. Many neurons responded to a single suprathreshold pulse with more than one spike. We found no consistent relationships among the thresholds of the additional evoked discharges of an individual neuron other than that the total number of evoked spikes either increased or stayed the same, but never decreased, as stimulus magnitude increased.About one-third of the neurons examined had velocity thresholds below 3°/sec. Above that value, thresholds were distributed continuously throughout a range of over three orders of magnitude. The median velocity threshold was about 100°/sec. The broad and continuous distributions of both magnitude and velocity thresholds suggest that a population of vibrissa-activated neurons can code stimulus strength smoothly and continuously over a wide range, even though individual neurons may be poorly suited to do so. 相似文献
3.
Cristiano Carlomagno Monia Cabinio Silvia Picciolini Alice Gualerzi Francesca Baglio Marzia Bedoni 《Journal of biophotonics》2020,13(3)
Alzheimer disease (AD) is the most common form of dementia in the elderly, progressively affecting the cognitive functions with a complex diagnostic procedure that limits the time for a prompt intervention. In this study we optimized a reliable protocol for the analysis of AD patients and healthy subjects' serum using the Surface Enhanced Raman Spectroscopy (SERS), taking into consideration the effect of different variables on the final spectra, analyzed and compared through multivariate analysis and correlated with hippocampus volume. As results, we demonstrated a statistical difference between the spectra collected from the two investigated groups, with an accuracy, precision and specificity of respectively 83%, 86%, and 86%. The correlation of these data with those obtained from MRI, demonstrated a direct correlation between Raman spectra and hippocampus degeneration showing the Raman Spectroscopy (RS) as a potential tool for the monitoring of AD progression and rehabilitation treatments. 相似文献
4.
5.
Veronika Zlatkina Michael Petrides 《Proceedings. Biological sciences / The Royal Society》2014,281(1797)
Distinct parts of the intraparietal sulcal cortex contribute to sensorimotor integration and visual spatial attentional processing. A detailed examination of the morphological relations of the different segments of the complex intraparietal sulcal region in the human brain in standard stereotaxic space, which is a prerequisite for detailed structure-to-function studies, is not available. This study examined the intraparietal sulcus (IPS) and the related sulcus of Jensen in magnetic resonance imaging brain volumes registered in the Montreal Neurological Institute stereotaxic space. It was demonstrated that the IPS is divided into two branches: the anterior ramus and the posterior ramus of the IPS, often separated by a submerged gyral passage. The sulcus of Jensen emerges between the anterior and posterior rami of the IPS, and its ventral end is positioned between the first and second caudal branches of the superior temporal sulcus. In a small number of brains, the sulcus of Jensen may merge superficially with the first caudal branch of the superior temporal sulcus. The above morphological findings are discussed in relation to previously reported functional neuroimaging findings and provide the basis for future exploration of structure-to-function relations in the posterior parietal region of individual subjects. 相似文献
6.
A novel multi-coaxial hollow fiber bioreactor for adherent cell types. Part 1: hydrodynamic studies.
Stephen P Wolfe Edward Hsu Lola M Reid Jeffrey M Macdonald 《Biotechnology and bioengineering》2002,77(1):83-90
A novel multi-coaxial bioreactor for three-dimensional cultures of adherent cell types, such as liver, is described. It is composed of four tubes of increasing diameter placed one inside the other, creating four spatially isolated compartments. Liver acinar structure and physiological parameters are mimicked by sandwiching cells in the space between the two innermost semi-permeable tubes, or hollows fibers, and creating a radial flow of media from an outer compartment (ECC), through the cell mass compartment, and to an inner compartment (ICC). The outermost compartment is created by gas-permeable tubing, and the housing is used to oxygenate the perfusion media to periportal levels in the ECC. Experiments were performed using distilled water to correlate the radial flow rate (Q(r)) with (1) the pressure drop (DeltaP) between the media compartments that sandwich the cell compartment and (2) the pressure in the cell compartment (P(c)). These results were compared with the theoretical profile calculated based on the hydraulic permeability of the two innermost fibers. Phase-contrast velocity-encoded magnetic resonance imaging was used to visualize directly the axial velocities inside the bioreactor and confirm the assumptions of laminar flow and zero axial velocity at the boundaries of each compartment in the bioreactor. Axial flow rates were calculated from the magnetic resonance imaging results and were similar to the measured axial flow rates for the previously described experiments. 相似文献
7.
《Free radical research》2013,47(3-6):391-397
Results are presented which illustrate the usefulness of Magnetic Resonance Imaging as applied to the study of living embryos. Nitroxide spin labels were employed as contrast agents to study the structure and properties of the embryos. These spin labels offer the additional advantage that they may potentially be bound to biologically important molecules thereby imparting the ability to produce contrast in the MR images to these new molecules.The horse conceptus was chosen over other embryos due to its large size. Whereas the embryos of cattle and swine are sub-millimetre in size, the horse conceptus is on the order of 10 millimetres in diameter. The availability of microscopic imaging gradient coils will allow the techniques developed in this study to be applied to the smaller embryos of other species. 相似文献
8.
A Special Issue of Physica Medica – European Journal of Medical Physics, focused on some important points of contact between the world of magnetic resonance and that of medical physics, was published during 2021. This Editorial describes and comments on the content of this Focus Issue, which contains articles from leading groups invited by the Guest Editors. 相似文献
9.
10.