全文获取类型
收费全文 | 274篇 |
免费 | 22篇 |
国内免费 | 3篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 12篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 20篇 |
2013年 | 31篇 |
2012年 | 4篇 |
2011年 | 24篇 |
2010年 | 12篇 |
2009年 | 7篇 |
2008年 | 13篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 171 毫秒
131.
Excision and subsequent incubation of the apices (1 cm) of wheat (Triticum aestivum L.) seedling roots in simple media severely reduced elongation from 28 mm·(24 h)-1 in intact roots to a maximum of 2 mm·(24 h)-1 in excised roots. The reduction in growth was accompanied by a loss of cell turgor in the growing zone but was correlated with a hardening of the cell walls in this region. Rheological properties were measured as percent extensibility (both plastic and elastic) using a tensiometer, and as instantaneous volumetric elastic modulus (
i) using the pressure probe. Excision decreased plastic and elastic properties with a half-time of some 60 min. Plastic extension was reduced from 2.5% to 0.9% and elastic from 4.8% to 2.6% for an 8-g load. By contrast,
i was increased by excision. The observed reduction in root elongation rate was accompained by a reduction in mature cell length from 240 m to 40 m and a shortening of the zone of cell expansion.Symbol
i
instantaneous volumetric elastic modulus 相似文献
132.
目的:研究激光联合紫外线治疗II期和III期压疮患者的疗效。方法:回顾性分析2010 年7 月至2014 年7 月我科收治的59
例II期和III 期压疮患者的临床资料,按照护理方式的不同分为对照组(30 例)和联合组(29 例),对照组在基础治疗的基础上进
行传统护理,联合组在基础治疗的基础上加用激光联合紫外线护理,两组治疗14 天后,采用压疮愈合评估量表(PUSH)评分比较
两组疗效。结果:两组患者治疗后PUSH评分均降低,且联合组降低幅度显著高于对照组,差异均有统计学意义(P<0.001)。结论:
激光联合紫外线治疗对II期和III期压疮患者的恢复具有显著促进作用,值得推广使用。 相似文献
133.
Cardiovascular development is influenced by the flow-induced stress environment originating from cardiac biomechanics. To characterize the stress environment, it is necessary to quantify flow and pressure. Here, we quantify the flow field in a developing zebrafish heart during the looping stage through micro-particle imaging velocimetry and by analyzing spatiotemporal plots. We further build upon previous methods to noninvasively quantify the pressure field at a low Reynolds number using flow field data for the first time, while also comparing the impact of viscosity models. Through this method, we show that the atrium builds up pressure to ~0.25 mmHg relative to the ventricle during atrial systole and that atrial expansion creates a pressure difference of ~0.15 mmHg across the atrium, resulting in efficient cardiac pumping. With these techniques, it is possible to noninvasively fully characterize hemodynamics during heart development. 相似文献
134.
Yong Zhang Chul Koo Kim Kong-Ju-Bock Lee Youngah Park 《Journal of biological physics》2007,33(3):195-211
The cochlea is an important auditory organ in the inner ear. In most mammals, it is coiled as a spiral. Whether this specific
shape influences hearing is still an open problem. By employing a three-dimensional fluid model of the cochlea with an idealized
geometry, the influence of the spiral geometry of the cochlea is examined. We obtain solutions of the model through a conformal
transformation in a long-wave approximation. Our results show that the net pressure acting on the basilar membrane is not
uniform along its spanwise direction. Also, it is shown that the location of the maximum of the spanwise pressure difference
in the axial direction has a mode dependence. In the simplest pattern, the present result is consistent with the previous
theory based on the Wentzel–Kramers–Brillouin-like approximation (Manoussaki et al., Phys Rev Lett 96:088701, 2006). In this mode, the pressure difference in the spanwise direction is a monotonic function of the distance from the apex and
the normal velocity across the channel width is zero. Thus, in the lowest-order approximation, we can neglect the existence
of the Reissner’s membrane in the upper channel. However, higher responsive modes show different behavior and, thus, the real
maximum is expected to be located not exactly at the apex but at a position determined by the spiral geometry of the cochlea
and the width of the cochlear duct. In these modes, the spanwise normal velocities are not zero. Thus, it indicates that one
should take into account the detailed geometry of the cochlear duct for a more quantitative result. The present result clearly
demonstrates that the spiral geometry and the geometry of the cochlear duct play decisive roles in distributing the wave energy. 相似文献
135.
Luciana Morla Ga?lle Brideau Marc Fila Gilles Crambert Lydie Cheval Pascal Houillier Sureshkrishna Ramakrishnan Martine Imbert-Teboul Alain Doucet 《The Journal of biological chemistry》2013,288(14):10124-10131
Proteinase-activated receptor 2 (PAR2) is a G protein-coupled membrane receptor that is activated upon cleavage of its extracellular N-terminal domain by trypsin and related proteases. PAR2 is expressed in kidney collecting ducts, a main site of control of Na+ and K+ homeostasis, but its function remains unknown. We evaluated whether and how PAR2 might control electrolyte transport in collecting ducts, and thereby participate in the regulation of blood pressure and plasma K+ concentration. PAR2 is expressed at the basolateral border of principal and intercalated cells of the collecting duct where it inhibits K+ secretion and stimulates Na+ reabsorption, respectively. Invalidation of PAR2 gene impairs the ability of the kidney to control Na+ and K+ balance and promotes hypotension and hypokalemia in response to Na+ and K+ depletion, respectively. This study not only reveals a new role of proteases in the control of blood pressure and plasma potassium level, but it also identifies a second membrane receptor, after angiotensin 2 receptor, that differentially controls sodium reabsorption and potassium secretion in the late distal tubule. Conversely to angiotensin 2 receptor, PAR2 is involved in the regulation of sodium and potassium balance in the context of either stimulation or nonstimulation of the renin/angiotensin/aldosterone system. Therefore PAR2 appears not only as a new actor of the aldosterone paradox, but also as an aldosterone-independent modulator of blood pressure and plasma potassium. 相似文献
136.
In order to perform a molecular dynamics (MD) simulation of the incommensurate crystalline structure hexamethylenetetramine suberate (C 6 H 12 N 4 )(HOOC-(CH 2 ) 6 -COOH), we present in a first step the separate simulations of the crystalline structure of each of the two pure components, hexamethylenetetramine (HMT) and suberic acid. The domain decomposition parallel MD program ddgmq is used for this purpose. A second-generation consistent force field (CFF91) is employed to describe the interactions between atoms. Starting from experimental crystal structures, both pure components were heated from low to high temperatures. Our MD results show that the HMT system can be well represented by CFF91. In the case of suberic acid the layered structure of the crystal is largely preserved although deviations in the unit cell lengths from the experimental values are ~10%. Rather than attempt a complex re-parametrisation of CFF91 we chose to impose a fixed compensating external pressure tensor to correct for the deficiencies of the chosen force field. After optimising this compensating external pressure tensor at one temperature we find that experimental lattice constants and angles can be well reproduced over a range of temperatures. 相似文献
137.
The decision to perform intervention on a patient with coronary stenosis is often based on functional diagnostic parameters obtained from pressure and flow measurements using sensor-tipped guidewire at maximal vasodilation (hyperemia). Recently, a rapid exchange Monorail Pressure Sensor catheter of 0.022″ diameter (MPS22), with pressure sensor at distal end has been developed for improved assessment of stenosis severity. The hollow shaft of the MPS22 is designed to slide over any standard 0.014″ guidewire (G14). Hence, influence of MPS22 diameter on coronary diagnostic parameters needs investigation. An in vitro experiment was conducted to replicate physiologic flows in three representative area stenosis (AS): mild (64% AS), intermediate (80% AS), and severe (90% AS), for two arterial diameters, 3 mm (N2; more common) and 2.5 mm (N1). Influence of MPS22 on diagnostic parameters: fractional flow reserve (FFR) and pressure drop coefficient (CDP) was evaluated both at hyperemic and basal conditions, while comparing it with G14. The FFR values decreased for the MPS22 in comparison to G14, (Mild: 0.87 vs 0.88, Intermediate: 0.68 vs 0.73, Severe: 0.48 vs 0.56) and CDP values increased (Mild: 16 vs 14, Intermediate: 75 vs 56, Severe: 370 vs 182) for N2. Similar trend was observed in the case of N1. The FFR values were found to be well above (mild) and below (intermediate and severe) the diagnostic cut-off of 0.75. Therefore, MPS22 catheter can be used as a possible alternative to G14. Further, irrespective of the MPS22 or G14, basal FFR (FFRb) had overlapping ranges in close proximity for clinically relevant mild and intermediate stenoses that will lead to diagnostic uncertainty under both N1 and N2. However, CDPb had distinct ranges for different stenosis severities and could be a potential diagnostic parameter under basal conditions. 相似文献
138.
目的:神经调节蛋白2( neuregulin-2, NRG2)可促进神经系统发育,基因缺失表现早期生长延迟, NRG2在心脏中也有表达,但其在心脏发育尤其是病理刺激时对心脏结构及功能的影响尚未见报道。本文目的是建立心脏组织特异性表达NRG2转基因小鼠,分析其在正常及压力负荷刺激时对心脏结构及功能的影响。方法将人NRG2基因插入到心脏特异性启动子α-MHC下游,构建转基因表达载体,显微注射法建立NRG2转基因小鼠,PCR鉴定转基因小鼠基因型,western blot鉴定NRG2蛋白在心脏中的表达并筛选高表达的转基因品系,主动脉缩窄术( transverse aortic constriction , TAC)制备压力负荷诱导的心肌肥厚小鼠模型。利用超声影像分析和病理学观察小鼠心脏结构和功能改变。结果建立了心脏组织特异性高表达NRG2转基因小鼠品系。与同窝阴性转基因小鼠相比,转基因小鼠左心室舒张末期后壁厚度(LVPWD)明显增加,3月龄时可达15.6%(P<0.05),经压力负荷刺激后,NRG2转基因手术小鼠心室壁增厚程度显著下降,心室腔增大,同时心肌排列紊乱程度和纤维化程度明显比NTG手术小鼠严重。结论在压力负荷下,转基因表达NRG2缩短了肥厚过程,同时加速了心衰进程。 相似文献
139.
Pressure drop (△p) estimations in human coronary arteries have several important applications, including determination of appropriate boundary conditions for CFD and estimation of fractional flow reserve (FFR). In this study a △p prediction was made based on geometrical features derived from patient-specific imaging data. 相似文献
140.
The relaxation kinetics of aqueous lipid dispersions after a pressure jump (p-jump) were investigated using time-resolved
FTIR spectroscopy. The methylene stretching vibrational band and the carbonyl band were analyzed to detect changes in conformational
order of the hydrocarbon chains and to follow the degree of hydration of the head group, respectively. The kinetics of the
transition was found to consist of multiple processes with relaxation constants from seconds down to milliseconds. Faster
processes are also present, but could not be resolved by our instrument. This is the first investigation showing directly
the time resolved change in chain order in lipid bilayers induced by a p-jump. The results obtained with this IR detection
method support previous results that the change in chain order after a perturbation is a multi-step process with the initial
molecular events occurring with time constants shorter than milliseconds. 相似文献