全文获取类型
收费全文 | 1335篇 |
免费 | 98篇 |
国内免费 | 34篇 |
专业分类
1467篇 |
出版年
2024年 | 9篇 |
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 8篇 |
2020年 | 21篇 |
2019年 | 44篇 |
2018年 | 45篇 |
2017年 | 25篇 |
2016年 | 26篇 |
2015年 | 21篇 |
2014年 | 53篇 |
2013年 | 66篇 |
2012年 | 34篇 |
2011年 | 57篇 |
2010年 | 36篇 |
2009年 | 50篇 |
2008年 | 62篇 |
2007年 | 74篇 |
2006年 | 62篇 |
2005年 | 53篇 |
2004年 | 55篇 |
2003年 | 47篇 |
2002年 | 49篇 |
2001年 | 34篇 |
2000年 | 38篇 |
1999年 | 39篇 |
1998年 | 49篇 |
1997年 | 41篇 |
1996年 | 37篇 |
1995年 | 30篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 24篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 7篇 |
1967年 | 2篇 |
排序方式: 共有1467条查询结果,搜索用时 15 毫秒
1.
2.
《FEBS letters》1988,240(1-2):88-94
Four subtypes of muscarinic acetylcholine receptor (mAChR) were stably expressed in neuroblastoma-glioma hybrid cells (NG108-15). By combining fluorescent indicator dye (fura-2) studies with electrophysiological measurements it is shown that stimulation of mAChR I and mAChR III readily leads to release of calcium from intracellular stores and to associated conductance changes, whereas stimulation of mAChR II and mAChR IV exerts no such effect. Dose-response curves describing the amplitude or the delay of the calcium rise induced by acetylcholine suggest that the apparent affinity of mAChR III for its agonist is higher by about one order of magnitude than that of mAChR I. Ionic substitution experiments and current fluctuation analysis indicate that calcium activates a K+-specific conductance of ‘small’ single-channel amplitude similar to the SK type [1]. Furthermore, an outward current (M current) suppressed by activation of mAChR I and mAChR III has a single-channel amplitude corresponding to a conductance of approximately 3 pS. 相似文献
3.
With the help of a ribonucleoprotein it is possible to precipitate collagen in a layer of fibers with a 700 Å period. As collagen is a constituent of many membrane systems in the body, it seemed interesting to investigate the permeability of ions and water through a native collagen membrane.The experiments were carried out with the help of an acryl glass apparatus, where an osmotic pressure, a hydrostatic pressure difference or both can be maintained between the two bulk phases separated by the membrane. The diffusion coefficients for NaCl and KCl were found to be comparable with those in other biological membranes (Ds = 9 · 10−7cm2 · s−1) whereas there is difference of more than three orders of magnitude in the hydraulic permeability (Lp = 6 cm4 · J−1 · s−1).Volume flow measurements caused by an osmotic gradient indicated that the reflection coefficient for NaCl and KCl is very small. In hydrostatic pressure experiments, the membrane shows a preferred direction for volume flows which seems to have something to do with the mode of preparation of the membrane. 相似文献
4.
The current induced in a human exposed to radio frequency electric fields has been studied by the use of a stripline, in which whole body exposure to vertical electric fields (3-27 MHz) can be produced. We have examined two different techniques to measure the induced current; parallel plate meters and current probes. When the subject has good connection to the ground, the choice of measurement technique is not crucial, since there are only minor differences in readings between the instruments. But when the subject is wearing shoes and/or standing on a wooden plate, the difference between the instruments increases considerably. The difference can mainly be explained by the capacitive coupling between the parallel plate meters and the ground; therefore, the current probes are preferred when the subject does not have perfect contact with the ground. Since the International Commission on Non-Ionizing Radiation Protection guidelines demand measurements of induced current in humans exposed to radio frequency fields in the range of 10-110 MHz, the importance of finding an appropriate measurement procedure becomes apparent. 相似文献
5.
Caryn C. Vaughn 《Hydrobiologia》1987,154(1):201-205
The position of Helicopsyche borealis (Hagen) (Trichoptera: Helicopsychidae) larvae on the substratum surface is dependent on the current regime but varies with larval size. All size classes of larvae chose significantly different positions on the substratum under high versus low current velocities. All size classes preferred exposed surfaces under low current velocities. Small larvae preferred the upper surfaces of substrata under low current velocities and were physically displaced under high current velocities. Larger larvae also occurred on upper surfaces, but were more evenly dispersed over all surfaces than smaller larvae, and tended to aggregate on down-stream faces of rocks during high flow. 相似文献
6.
R. Y. K. Pun 《Molecular and cellular biochemistry》1989,80(1-2):109-120
Summary The voltage clamp technique is a powerful method for studying the physiology of excitable membrane. This technique has made possible the determination of ionic responses generated by activation of either receptor-mediated or voltage-dependent processes. The development of the whole-cell, tight-seal voltage clamp method has allowed the analysis and examination of membrane physiology at the single cell level. The method allows the characterization of voltage-dependent ionic conductances both at the macroscopic (whole-cell) and at the microscopic (unitary conductance or single channel) level in cells less than 10 µm in diameter, a feat difficult to achieve with conventional fine-tipped micropipettes.In this paper, several methologies used for culturing neuronal and non-neuronal cells in the laboratory are described. A comparison between the two modes of voltage clamp using blunt-tipped patch-microelectrodes, the switching (discontinuous) and the non-switching (continuous) modes, of the Axoclamp-2A amplifier is made. Some results on membrane currents obtained from neuronal and non-neuronal cells using the single electrode whole-cell tight-seal voltage clamp is illustrated. The possible existence of two inactivating K+ currents, one dependent on Ca++ the other is not, is discussed. 相似文献
7.
The effect of the organic compound l-cis-diltiazem on the light-sensitive current of isolated rods of the tiger salamander was analysed by rapidly changing the extracellular medium using the method of Hodgkin et al. (1985). Addition to the extracellular medium of small amounts of l-cis-diltiazem rapidly inhibits the photocurrent. Complete suppression of the current was observed with 1 mM l-cis-diltiazem. Half blockage of the photocurrent occurred with about 150 M l-cis-diltiazem. The blocking effect of l-cis-diltiazem was enhanced by light and by a reduction of extracellular Na. A concentration of l-cis-diltiazem of 140 M, which suppresses one third of the photocurrent, was able to completely suppress the photocurrent carried by Ba. It is suggested that l-cis-diltiazem blocks the light-sensitive channel, possibly competing with cyclic guanosine-3-5-monophosphate (cGMP) for an internal regulatory site. 相似文献
8.
1. Two mutants of the sodium channel II have been expressed inXenopus oocytes and have been investigated using the patch-clamp technique. In mutant E387Q the glutamic acid at position 387 has been replaced by glutamine, and in mutant D384N the aspartic acid at position 384 has been replaced by asparagine.2. Mutant E387Q, previously shown to be resistant to block by tetrodotoxin (Noda et al. 1989), has a single-channel conductance of 4 pS, that can be easily measured only using noise analysis. At variance with the wild-type, the openchannel current-voltage relationship of mutant E387Q is linear over a wide voltage range even under asymmetrical ionic conditions.3. Mutant D384N has a very low permeability for any of the following ions: Cl–, Na+, K+, Li+, Rb+, Ca2+, Mg2+, NH4
+ , TMA+, TEA+. However, asymmetric charge movements similar to the gating currents of the Na+-selective wild-type are still observed.4. These results suggest that residues E387 and D384 interact directly with the pathway of the ions permeating the open channel.Abbreviations TTX
tetrodotoxin; Na+, sodium; K+, potassium;
- NFR
normal frog Ringer
- HEPES
N-2-hydroxylethyl piperazine-N-2-ethanesulfonic acid
- EGTA
ethyleneglycol-bis(-amino-ethyl ether) N,N,N',N'-tetra acetic acid
- TEA
tetraethylammonium
- TMA
tetramethylammonium;I
g
, gating current; , single-channel conductance 相似文献
9.
A. Wenning R. L. Calabrese 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,168(1):53-61
Summary The nephridial nerve cells of the leech, Hirudo medicinalis, 34 sensory cells, each associated with one nephridium, are sensitive to changes in extracellular Cl- concentration, an important factor in ion homeostasis. Using single-electrode current- and voltage clamp and ion substitution techniques, the specificity and mechanism of Cl- sensitivity of the nephridial nerve cell was studied in isolated preparations. Increase of the normally low external Cl- concentration leads to immediate and sustained hyperpolarization, decrease of the frequency of bursts and decrease of membrane conductance. The response is halogen specific: Cl- can be replaced by Br–, but not by organic mono- or divalent anions or inorganic divalent anions.At physiological Cl- concentrations (36mM extra-cellular Cl-), the nephridial nerve cell has a high resting conductance for Cl- and the membrane potential is governed by Cl-. In high extracellular Cl- concentrations (110–130 mM), membrane conductance is low, most likely due to the gating off of Cl- channels. Under these conditions, membrane potential is dominated by the K+ distribution and the nephridial nerve cell hyperpolarizes towards EK.Abbreviations
NNC
nephridial nerve cell
-
V
m
membrane potential
-
E
Cl(k)
equilibrium potential for Cl (K)
-
IV-curve
current-voltage relationship 相似文献
10.
R. S. Wotton 《Hydrobiologia》1985,123(3):215-218
Larvae of Simulium noelleri Friederichs aggregate at high population densities (more than 102 cm–2) on sluices, dams, and spillways. Experiments were conducted in a laboratory trough to assess the reaction of larvae to different current velocities (velocities ranged from 5–49 cm s–1). In the lower part of the range of water velocities used, larvae moved a greater distance upstream from where they had been located. Larger larvae always showed a greater tendency to move than did smaller larvae, whatever the velocity. This intraspecific variation in reaction to different current velocities allows the aggregation of larvae of mixed sizes at suitable sites, smaller individuals being occluded by those that are larger. 相似文献