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   5731篇
  免费   389篇
  国内免费   161篇
耳鼻咽喉   25篇
儿科学   14篇
妇产科学   9篇
基础医学   925篇
口腔科学   62篇
临床医学   510篇
内科学   1138篇
皮肤病学   19篇
神经病学   1201篇
特种医学   159篇
外科学   183篇
综合类   626篇
预防医学   434篇
眼科学   37篇
药学   714篇
  9篇
中国医学   186篇
肿瘤学   30篇
  2024年   34篇
  2023年   83篇
  2022年   154篇
  2021年   235篇
  2020年   176篇
  2019年   178篇
  2018年   148篇
  2017年   110篇
  2016年   139篇
  2015年   142篇
  2014年   255篇
  2013年   242篇
  2012年   253篇
  2011年   272篇
  2010年   271篇
  2009年   238篇
  2008年   282篇
  2007年   253篇
  2006年   232篇
  2005年   212篇
  2004年   225篇
  2003年   185篇
  2002年   150篇
  2001年   139篇
  2000年   123篇
  1999年   136篇
  1998年   154篇
  1997年   149篇
  1996年   110篇
  1995年   116篇
  1994年   114篇
  1993年   90篇
  1992年   72篇
  1991年   78篇
  1990年   65篇
  1989年   48篇
  1988年   56篇
  1987年   47篇
  1986年   39篇
  1985年   44篇
  1984年   36篇
  1983年   27篇
  1982年   37篇
  1981年   33篇
  1980年   25篇
  1979年   24篇
  1978年   13篇
  1977年   12篇
  1976年   10篇
  1975年   6篇
排序方式: 共有6281条查询结果,搜索用时 0 毫秒
11.
The actions of the nonsteroidal antiinflammatory drug niflumic acid were studied on frog neuromuscular preparations by conventional electrophysiological techniques. Niflumic acid reduced the amplitude and increased the latency of endplate potentials in a concentration-dependent manner. Neuromuscular junctions pretreated with niflumic acid (0.05–0.5 mM) showed much less depression than control when they were stimulated with trains of impulses. Inhibition of acetylcholine release was reverted by raising the extracellular Ca2+ concentration but not by simply washing out the preparations with niflumic acid-free solutions. Pretreatment with indomethacin (0.1 mM), another nonsteroidal antiinflamatory drug, did not affect the niflumic acid-induced inhibition of evoked responses. Niflumic acid (0.1 mM) did not change the amplitude of miniature endplate potentials and had a dual action on the frequency of miniatures: it decreased their frequency at 0.1 mM whereas it produced an enormous increase in the rate of spontaneous discharge at 0.5 mM. Niflumic acid (0.1–1 mM) reversibly increased the amplitude and affected the kinetics of presynaptic voltage-activated K+ current and Ca2+-activated K+ current in a concentration-dependent manner. Niflumic acid (0.1–1 mM) irreversibly decreased the amplitude and reversibly affected the kinetics of the nodal Na+ current. Indomethacin (0.1 mM) had no effect on presynaptic currents. In conclusion, niflumic acid reduces acetylcholine release by increasing presynaptic K+ currents. This may shorten the depolarizing phase of the presynaptic action potential and may reduce the entry of Ca2+ with each impulse.  相似文献   
12.
The effects of tetracaine (10–50 M) and ryanodine (0.1–10 M) were tested on the slow outward K+ current (I so) and the mechanical tension of isolated frog muscle fibres in a voltage-clamp device (double mannitol-gap) connected to a mechanoelectric transducer. In the concentration range tested, both drugs induced a simultaneous inhibition of tension and current. In all cases the effect on tension was twice that on current. The tetracaine-induced current and tension blocks were fully reversible and dose-dependent. In contrast the ryanodine effects on current and tension were not reversible and did not exhibit a dose dependence except for the delay before the onset of the response, which was shortened when the concentration was raised. Linear regression analysis of the time-dependent and dose-dependent effects of both drugs indicated a strong correlation between the decreases in tension and current. It is concluded that the slow outward current is partly under the control of the Ca2+ release from sarcoplasmic reticulum during contraction.  相似文献   
13.
A method to monitor contraction of isolated myocytes by transmicroscopic photometry is illustrated. Two photodiodes are mounted inside an inverse microscope used for visual control of a cell. Illumination of one diode varies in proportion to changes in cell length. The contraction signal is amplified in a comparator circuit. Spatial resolution of the device is in the order of 1 m which corresponds to about 5% of cell shortening in the fully activated state of contraction. The method was tested on isolated myocytes from guinea-pig ventricle. Optical records of contraction in response to action potentials or during voltage clamp compare well with the contractile behaviour of multicellular preparations.  相似文献   
14.
 The contribution of the Na/K ATPase (pump) current to the polarization of the Purkinje cell has been studied using slices of the rat cerebellum by blocking the pump with dihydro-ouabain (DHO) while recording the membrane potential with microelectrodes in the somata. From our recordings, it appeared that blocking the pump depolarized the Purkinje cells more rapidly than might be expected from shifts in Na+ and K+ concentrations, suggesting the removal of a hyperpolarizing current. Application of DHO, in the presence of tetrodotoxin (TTX), led to calcium spike firing and plateau-like discharges suggesting activation of voltage-dependent calcium channels in the dendrites. Adding 2 mM Co2+ to the medium did not prevent the depolarizations. Removing calcium from the bathing medium containing 2 mM Co2+ blocked the spiking activity but DHO application still produced a depolarization. Experiments to measure the current inhibited by DHO indicated that the Na/K pump supplies a constant current of 240 pA. Substitution of the sodium with choline produced a hyperpolarization, during which DHO had no effect on the membrane potential. Substitution of the sodium with lithium produced only a slowly developing depolarization. It is concluded that in the cerebellar Purkinje cell, a continuous sodium ion influx activates the pumps which produce a current that directly contributes to the membrane polarization. Possible pathways for this sodium influx are discussed. Received: 3 April 1997 / Received after revision and accepted: 12 May 1997  相似文献   
15.
 Reduction of an inwardly rectifying K+ current by thyrotropin-releasing hormone (TRH) and caffeine has been considered to be an important determinant of electrical activity increases in GH3 rat anterior pituitary cells. However, the existence of an inwardly rectifying K+ current component was recently regarded as a misidentification of an M-like outward current, proposed to be the TRH target in pituitary cells, including GH3 cells. In this report, an inwardly rectifying component of K+ current is indeed demonstrated in perforated-patch voltage-clamped GH3 cells. The degree of rectification varied from cell to cell, but both TRH and caffeine specifically blocked a fraction of current with strong rectification in the hyperpolarizing direction. Use of ramp pulses to continuously modify the membrane potential demonstrated a prominent blockade even in cells with no current reduction at voltages at which M-currents are active. Depolarization steps to positive voltages at the maximum of the inward current induced a caffeine-sensitive instantaneous outward current followed by a single exponential decay. The magnitude of this current was modified in a biphasic way according to the duration of the previous hyperpolarization step. The kinetic characteristics of the current are compatible with the possibility that removal from inactivation of a fast-inactivating delayed rectifier causes the hyperpolarization-induced current. Furthermore, the inwardly rectifying current was blocked by astemizole, a potent and selective inhibitor of human ether-á-go-go -related gene (HERG) K+ channels. Along with other pharmacological and kinetic evidence, this indicates that the secretagogue-regulated current is probably mediated by a HERG-like K+ channel. Addition of astemizole to current-clamped cells induced clear increases in the frequency of action potential production. Thus, an inwardly-rectifying K+ current and not an M-like outward current seems to be involved in TRH and caffeine modulation of electrical activity in GH3 cells. Received: 15 May 1997 / Received after revision and accepted: 24 July 1997  相似文献   
16.
The amiloride-sensitive epithelial sodium channel (ENaC) is the rate-limiting step for sodium reabsorption in the distal segments of the nephron, in the colon and in the airways. Its activity is regulated by intracellular and extracellular factors but the mechanisms of this regulation are not yet completely understood. Recently, we have shown that the fast regulation of ENaC by the extracellular [Na+], a phenomenon termed self-inhibition, is temperature dependent. In the present study we examined the effects of temperature on the single-channel properties of ENaC. Single-channel recordings from excised patches showed that the channel open probability (P o, estimated from the number of open channels N·P o, where N is the total number of channels) increased on average two- to threefold while the single-channel conductance decreased by about half when the temperature of the perfusion solution was lowered from ~30 to ~15 °C. The effects of temperature on the single-channel conductance and P o explain the changes of the macroscopic current that can be observed upon temperature changes and, in particular, the paradoxical effect of temperature on the current carried by ENaC.  相似文献   
17.
The paper presents an evaluation of the possibility of using fetal magnetocardiogram (FMCG) signals to estimate and classify the accessory pathway in fetal Wolff-Parkinson-White (WPW) syndrome. The FMCG signals of two fetuses with WPW syndrome (type A) were detected using a 64-channel superconducting quantum-interference device system. An average across the cycles of these signals was taken to obtain clear WPW signals. To determine the direction and position of the accessory pathway in a fetal heart accurately, the accessory pathway and activated pathway at the peak of the QRS complex thus obtained were estimated for each fetus, using a single-dipole model. The phase angle (about 90o) between the equivalent current dipoles (ECDs) was the same for both fetuses. This angle suggested that the accessory pathway is in the left side of the heart, i.e. that the pathway exists in the position of the accessory pathway in a fetus with WPW syndrome from the angle between the ECD of the accessory pathway and the ECD of the peak in the QRS complex was thus demonstrated.  相似文献   
18.
人体神经定量电流感觉检测系统的研制   总被引:3,自引:0,他引:3  
电流感觉阈值测试是人体神经感觉功能的定量感觉测试方法的一种.它采用特定频率的正弦恒电流刺激人体神经末梢感受器,检测人体对电流刺激的最小感受量,用于定量评估神经功能。本文回顾了国际上电流感觉阈值测试技术的发展与现状,介绍了我们开发的人体神经定量电流感觉检测系统。该系统采用生理心理统计算法过滤人体主观感受的影响,具有双盲全自动测量功能,测量结果具有很好的重复性。  相似文献   
19.
A wireless power transfer system for endoscopic micro-robot operating at 36 kHz is presented in this paper. The issue of patient' s health and safety regarding exposure to the electromagnetic field is addressed. The specific absorption rate and current density can be used to investigate the electromagnetic influences on the biological tissues surrounded by the wireless power launching coil. In view of this purpose, the limited close-ound solenoid electromagnetic model is built, the relationship between the electric intensity and the specific absorption rate and current density is deduced, and the simulation experiments are done. Experimental results show that the values of SAR and current density related to different tissue catalogs are all very small and do not exceed their own limits respectively when the resonance frequency of operation is 36 kHz.  相似文献   
20.
A circuit is described which allows the input capacitance of an f.e.t. input integrated circuit to be used both as the feedback capacitance to neutralise the total input capacitance and to inject current pulses into the input. Compared with the conventional method of adding discrete capacitors to perform these functions, this design results in a lower total capacitance at the input, which reduces the high-frequency noise generated by the amplifier and facilitates the achievement of a low effective capacitance. A modified version having an ultralow (0·1pA) input current, for use with ion-sensitive microelectrodes, is also described.  相似文献   
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