全文获取类型
收费全文 | 6627篇 |
免费 | 254篇 |
国内免费 | 78篇 |
专业分类
耳鼻咽喉 | 15篇 |
儿科学 | 186篇 |
妇产科学 | 42篇 |
基础医学 | 956篇 |
口腔科学 | 402篇 |
临床医学 | 1582篇 |
内科学 | 746篇 |
皮肤病学 | 36篇 |
神经病学 | 239篇 |
特种医学 | 144篇 |
外科学 | 973篇 |
综合类 | 806篇 |
预防医学 | 252篇 |
眼科学 | 19篇 |
药学 | 440篇 |
1篇 | |
中国医学 | 71篇 |
肿瘤学 | 49篇 |
出版年
2024年 | 6篇 |
2023年 | 98篇 |
2022年 | 237篇 |
2021年 | 275篇 |
2020年 | 240篇 |
2019年 | 200篇 |
2018年 | 239篇 |
2017年 | 175篇 |
2016年 | 224篇 |
2015年 | 205篇 |
2014年 | 456篇 |
2013年 | 439篇 |
2012年 | 431篇 |
2011年 | 491篇 |
2010年 | 334篇 |
2009年 | 352篇 |
2008年 | 347篇 |
2007年 | 310篇 |
2006年 | 283篇 |
2005年 | 264篇 |
2004年 | 211篇 |
2003年 | 160篇 |
2002年 | 97篇 |
2001年 | 104篇 |
2000年 | 80篇 |
1999年 | 89篇 |
1998年 | 65篇 |
1997年 | 60篇 |
1996年 | 65篇 |
1995年 | 52篇 |
1994年 | 50篇 |
1993年 | 39篇 |
1992年 | 36篇 |
1991年 | 11篇 |
1990年 | 31篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有6959条查询结果,搜索用时 796 毫秒
51.
Although it has been recognized for many years that arteries in vivo exist under significant axial strain, studies of the adaptation of arteries to elevated axial strain have only recently been conducted. To determine the effects of sustained elevation of axial loading on arterial structure and function, axial stresses of 250 kPa or greater were applied to porcine common carotid arteries maintained in a perfusion organ culture system for 7 days at physiologic pressure and flow conditions. Our results demonstrated that axial stretch could lead to an increase in unloaded length that was proportional to the axial stretch ratio (stretched length divided by unloaded length) when the axial stretch ratio was above a threshold value of 2.14. Below this threshold, no significant length change occurred. Above this threshold, a significant increase in unloaded length (13 ± %,) and the number of smooth muscle cell nuclei (20 ± 7%) was observed. Permanent length change was associated with a significant decrease in axial stiffness, and the maximum elongation achieved was limited by rupture of the arterial wall. All tested arteries demonstrated good viability and strong vasomotor responses. These results show that arteries in organ culture can elongate under sustained axial loading. 相似文献
52.
The mechanical impedance of the ankle joint during electrical stimulation of the soleus is studied by applying constant-velocity
10° angular perturbations to the ankle and measuring the resultant torque. Both neurologically intact subjects and spinal
cord injured subjects are tested. Lumped, piecewise linear models are developed to predict the torque from the measured displacement
and acceleration signals. The commonly used second-order mass-spring-dashpot model fails to predict the changes in torque
that occur following imposed movements. A fiveelement, directionally-dependent piecewise linear model is much better at predicting
the measured responses for velocities up to 50° s−1. Numerical least squared error indentification techniques are used to estimate the model parameters for three neurologically
intact and three spinal cord injured subjects. The average error between the model’s response and the measured response across
all subjects is 10·9%. There is some evidence that a velocity-dependent non-linear model could produce better results than
the directionally-dependent piecewise linear model. 相似文献
53.
A nonlinear dynamic morphometric model of breathing mechanics during artificial ventilation is described. On the basis of the Weibel symmetrical representation of the tracheobronchial tree, the model accurately accounts for the geometrical and mechanical characteristics of the conductive zone and packs the respiratory zone into a viscoelastic Voigt body. The model also accounts for the main mechanisms limiting expiratory flow (wave speed limitation and viscous flow limitation), in order to reproduce satisfactorily, under dynamic conditions, the expiratory flow limitation phenomenon occurring in normal subjects when the difference between alveolar pressure and tracheal pressure (driving pressure) is high. Several expirations characterized by different levels of driving pressure are simulated and expiratory flow limitation is detected by plotting the isovolume pressure–flow curves. The model is used to study the time course of resistance and total cross-sectional area as well as the ratio of fluid velocity to wave speed (speed index), in conductive airway generations. The results highlight that the coupling between dissipative pressure losses and airway compliance leads to onset of expiratory flow limitation in normal lungs when driving pressure is increased significantly by applying a subatmospheric pressure to the outlet of the ventilator expiratory channel; wave speed limitation becomes predominant at still higher driving pressures. 相似文献
54.
Does a torn anterior cruciate ligament lead to change in the central nervous drive of the knee extensors? 总被引:2,自引:0,他引:2
Lars -Gunnar Elmqvist Ronny Lorentzon Christer Johansson Axel R. Fugl-Meyer 《European journal of applied physiology》1988,58(1-2):203-207
Summary Integrated surface electromyograms of the three superficial parts of the quadriceps and isokinetic knee extensor maximum torque and power production were recorded simultaneously and at different angular velocities in both legs in 11 male subjects with unilateral tear of the anterior cruciate ligament. The cross-sectional area (CSA) of the thigh and its muscular components were measured by computerized tomography. The principal findings were a small but significant decrease in quadriceps CSA on the affected side; a decreased active, but not passive, range of movement; decreased mechanical output, whether or not corrected for differences in CSA; and decreased electrornyographic activity — particularly in rectus femoris. These findings suggest that the reason for the decreased maximum and total knee extensor performance seen in these patients is a change in knee joint receptor afferent inflow. 相似文献
55.
Paolo Cerretelli Pietro Enrico di Prampero 《Pflügers Archiv : European journal of physiology》1988,412(3):270-276
Frog (Rana esculenta, L.) gastrocnemii (161 pairs) or sartorii (8 pairs) were stimulated by intermittent tetani at 10°C (20 Hz, supramaximal intensity, N2 atmosphere) isometrically (IM) or isotonically (IT) for various durations (6–30 s) at different tensions (0.05–1.00 P0=maximal IM tension at resting length,l
o). The energy expenditure (E) was measured from ATP and phosphocreatine breakdown and the high energy phosphate equivalent of lactic acid production. Both in IM and IT conditions,E was found to be a linear function of the summated tetanus duration (t):E=a+b t, whereb is the energy cost of tension maintenance. For the gastrocnemius, both in IM and IT,b was independent of the tension developed and equal to 0.45 mol P · g–1 · s–1, whereas for the sartoriusb was tension-dependent, varying between 0.58 and 0.28 mol P · g–1 · s–1 for P0 and 0.18 P0, respectively. The constancy of theb value in muscles with pennate structure may be tentatively attributed, at least in part, to the greater internal energy dissipation, regardless of the tension developed. The terma of the above equation is due to all time-independent processes of muscle contraction, i.e.: (1) activation energy; (2) internal work and (3) external work (in IT only). Based on the measured value ofa and on the work performed, the mechanical equivalent of P splitting was calculated as 17.7 kJ · mol–1, a figure close to that previously obtained on frog sartorius (16.7 kJ · mol–1) and dog gastrocnemius (19.2 kJ · mol–1) When taking into account the energy due to the activation processes, the calculated net mechanical equivalent of P splitting amounted to 25.5 kJ · mol–1. 相似文献
56.
Milner TE 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2004,159(2):172-184
This study investigated the ability to use an internal model of the environmental dynamics when the dynamics were predictable but unstable. Subjects performed goal-directed movements using a robot manipulandum while counteracting a force field, which created instability by assisting the movement in proportion to hand velocity. Subjects performance was better on the last trial than on the first trial in the force field for all four movement directions tested: out, in, right and left. Subjects adapted to the force field primarily by increasing muscle co-contraction, compared to null field movements, during all phases of movement. This co-contraction generally declined for both the deceleration and stabilization phases during the course of the first 25 movements in each direction, but tended not to decrease significantly thereafter. Catch trials at the end of the learning period suggested that increased viscoelastic impedance due to muscle co-contraction was used to counteract the force field. Only in the case of outward movements were aftereffects observed that were consistent with formation of an accurate internal model of the force field dynamics. Stabilization of the hand for outward movements required less muscle co-contraction than for movements in other directions due to stability conferred by the geometry of the arm. The results suggest that the accuracy of an internal model depends critically on the stability of the coupled dynamics of the limb and the environment. 相似文献
57.
Mohammad Sotoudeh Shila Jalali Shunichi Usami John Y-J. Shyy Shu Chien 《Annals of biomedical engineering》1998,26(2):181-189
The objective of this study is to design a new apparatus to allow the control of the magnitude and frequency of dynamic stretch applied uniformly to cells cultured on a silicon elastic membrane. The apparatus is designed to produce equi-biaxial dynamic stretches with area changes ranging from 0% to 55% and frequencies ranging from 0 to 2 Hz. Homogeneous finite strain analysis using triangles of markers was performed to compute the symmetric two-dimensional Lagrangian strain tensor on the membrane. Measurements of strain in both static and dynamic conditions showed that the shear component of the strain tensor (Erc) was near zero, and that there was no significant difference between radial (Err) and circumferential (Ecc) components, indicating the attainment of equi-biaxial strain. Bovine aortic endothelial cells were transiently transfected with a chimeric construct in which the luciferase reporter is driven by TPA-responsive elements (TRE). The transfected cells cultured on the membrane were stretched. The luciferase activity increased significantly only when the cells were stretched by 15% or more in area. Cells in different locations of the membrane showed similar induction of luciferase activities, confirming that strain is uniform and equi-biaxial across the membrane. © 1998 Biomedical Engineering Society.
PAC98: 8780+s, 8745-k, 8722-q 相似文献
58.
Christophe Cornu Maria-Izabel Almeida Silveira F. Goubel 《European journal of applied physiology》1997,76(3):282-288
The objective of this work was to study the effects of plyometric training on the mechanical properties of the ankle joint
in humans. Changes in the mechanical parameters of this musculo-articular structure were quantified with the aid of a sinusoidal
perturbation technique. This technique allowed the expression of the mechanical impedance of the musculo-articular system
in terms of stiffness, viscosity and inertia. Measurements were performed under passive conditions and when the subject performed
plantar flexion. A 7-week period of training induced a decrease in the slope of the relationship between stiffness and plantar
flexion torque, whereas passive stiffness was increased. A slight decrease in viscosity and an invariability in inertia were
also found. These results are interpreted in terms of the possible adaptations of the musculo-articular structure and ultrastructure
involved in the performance of plantar flexion.
Accepted: 11 April 1997 相似文献
59.
计算机辅助全膝置换中股骨力线定位精度的实验研究 总被引:3,自引:0,他引:3
摘要利用光学定位追踪仪确定全膝置换中患者的股骨头中心从而确定其股骨力线,在力线的定位精度分析中,首次采用股骨的三维重建模型进行精度校验。实验结果表明通过追踪固定于股骨末端的刚性定位器即能确定精确的股骨力线,与传统的髓内定位相比,不仅可重复性好,而且大大地提高了术中股骨力线的位置精度,将其位置偏差减小到10以内。 相似文献
60.
Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface
of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation,
performance and limitations. Examples of capacitive, piezoelectric, optical, conductive and resistive types of transducer
are presented. Where available, the current clinical status is specified. 相似文献