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171.
Delocalization of charges thorough DNA occurs due to the natural and continuous movements of molecule which stimulates the charge transfer through the molecule. A model is presented showing that the mechanism of electrical conduction occurs mainly by thermally-activated drift motion of holes under control of the localized carriers; where electrons are localized in the conduction band. These localized (stationary-trapped) electrons control the movements of the positive charges and do not play an effective role in the electrical conduction itself. It is found that the localized charge-carriers in the bands have characteristic relaxation times at 5×10(^-2)s, 1.94×10(^-4)s, 5×10(^-7)s, and 2×10(^-11)s respectively which are corresponding to four intrinsic thermal activation energies 0.56eV, 0.33eV, 0.24eV, and 0.05eV respectively. The ac-conductivity of some published data are well fitted with the presented model and the total charge density in DNA molecule is calculated to be n=1.88×10(^19)cm(^-3) at 300K which is corresponding to a linear electron density n=8.66×10(^3)cm(^-1) at 300K. The model shed light on the role of transfer and/or localization of charges through DNA which has multiple applications in medical, nano-technical, bio-sensing and different domains. So, repair DNA by adjusting the charge transport through the molecule is future challenges to new medical applications. 相似文献
172.
The mechanisms underlying cyclic AMP modulation of action potential-dependent and -independent (spontaneous) release of glycine from terminals synapsing onto sacral dorsal commissural nucleus neurons of lamina X were studied in spinal cord slices using conventional patch-clamp recordings. 3-Isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, and forskolin increased the amplitude of evoked inhibitory postsynaptic currents (eIPSCs) in a sensitive manner to protein kinase A (PKA) inhibition (with KT-5720). Direct activation (with adenosine 3',5'-cyclic-monophosphothioate, Sp-isomer) and inhibition (with adenosine 3',5'-cyclic-monophosphothioate, Rp-isomer) of PKA increased and decreased the eIPSC amplitude, respectively. Paired pulse experiments and direct injection of PKA inhibitor fragment 6-22 amide (PKI(6-22)) into the recording neuron revealed that these effects on eIPSC amplitude occurred presynaptically, indicating that evoked glycine release is regulated by presynaptic cAMP via changes in PKA activity. Increasing cAMP also increased spontaneous release of glycine, causing an increased frequency of miniature IPSCs (mIPSCs). In contrast to the effects on evoked release, this response was not solely mediated via PKA, as it was not occluded by PKA inhibition, and both direct inhibition and direct activation of PKA actually enhanced mIPSC frequency. Direct inhibition of cAMP (with SQ 22536) did, however, reduce mIPSC frequency. These results suggest cAMP modulation of evoked and spontaneous release involves different presynaptic mechanisms and proteins. 相似文献
173.
M. J. Katkowska 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,177(4):519-526
The membrane potential of ventral longitudinal muscles of Tenebrio molitor larvae was studied as a function of time and of cesium substituted for all or part of external potassium. The conventional microelectrode technique was applied. The mean value of resting potential was — 47.4 mV in standard physiological saline which did not change significantly with time (90 min). Cesium caused, almost immediately, a significant hyperpolarization of membrane potential the magnitude of which depended on cesium concentration. The presence of external potassium enhanced the effectiveness of cesium action, resulting in more pronounced hyperpolarization. The effect of Cs ions was fully reversible upon washing. These data support the idea that inward potassium current can be activated at resting potential level, at least in some cells, including the muscles studied. It is presumed that this potassium current might have some contribution to the resting membrane potential generation in mealworm larva muscles.Abbreviations [K
+]0
extracellular concentration of K ions
-
E
m
resting membrane potential of a cell when bathed in normal saline
-
E
K
K
+
equilibrium potential
-
MP
membrane potential
-
RP
resting potential
-
SD
standard deviation
-
SEM
standard error of the mean 相似文献
174.
175.
176.
文县疣螈资源现状、威胁因素及保护对策 总被引:2,自引:2,他引:2
文县疣螈Tylototriton wenxianensis分布在文县、平武、青川、阆中、奉节和雷山,但只有文县、青川、平武3县相连成片,为岷山栖息地,面积约1800km2,数量约30000条。文县疣螈对海拔1000~1400m的潮湿陆地森林或泥底的水域环境选择较强,以森林或林缘地带积水不深、植被良好、基底多泥的小水塘为繁殖发育场所。文县疣螈面临茶园扩张、薪柴、干旱和分布区狭窄的威胁。调整茶叶发展战略,加强林地保护,推动茶叶集约化加工,研制并推广小型节能炒茶炉,人工增建小泥塘,保护和扩大最适栖息地,资助社区保护组织是缓解这些威胁的有效对策。 相似文献
177.
Red/ET同源重组技术(Red/ET recombineering)是由来源于大肠杆菌λ噬菌体的蛋白对Redα/Redβ或来源于Rac原噬菌体的蛋白对Rec E/Rec T所介导的基于短同源臂(40–50 bp)的同源重组技术,能对宿主DNA序列进行快速、高效、精确的修饰和操作。本文主要综述了2010年以来Red/ET同源重组技术在大肠杆菌及其他细菌中的研究进展,同时简要介绍了该技术在微生物基因组挖掘,尤其是在微生物基因簇的异源表达领域的应用进展。 相似文献
178.
Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders 总被引:7,自引:0,他引:7
Chippindale PT Bonett RM Baldwin AS Wiens JJ 《Evolution; international journal of organic evolution》2004,58(12):2809-2822
The transition from aquatic to terrestrial eggs is a key evolutionary change that has allowed vertebrates to successfully colonize and exploit the land. Although most amphibians retain the primitive biphasic life cycle (eggs deposited in water that hatch into free-living aquatic larvae), direct development of terrestrial eggs has evolved repeatedly and may have been critical to the evolutionary success of several amphibian groups. We provide the first conclusive evidence for evolutionary reversal of direct development in vertebrates. The family Plethodontidae (lungless salamanders) contains the majority of salamander species, including major radiations of direct developers. We reconstruct the higher level phylogenetic relationships of plethodontid salamanders using molecular and morphological data and use this phylogeny to examine the evolution of direct development. We show that the predominantly biphasic desmognathines, previously considered the sister group of other plethodontids, are nested inside a group of direct-developing species (Plethodontini) and have re-evolved the aquatic larval stage. Rather than being an evolutionary dead end, the reversal from direct developing to biphasic life history may have helped communities in eastern North America to achieve the highest local diversity of salamander species in the world. 相似文献
179.
Jacques Danielle Bkaily Ghassan Jasmin Gaétan Ménard Daniel Proschek Libuse 《Molecular and cellular biochemistry》1997,176(1-2):249-256
Using the whole-cell voltage-clamp technique, early embryonic tetrodotoxin (TTX) and Mn2+-insensitive slow Na+ current was detected in 10-22 week old fetal human heart cells as well as in 1-day-old and young cardiomyopathic hamster myocytes. This slow Na+ current in both heart cell preparations has the same kinetics and pharmacology. This type of slow Na+ current was absent in heart cells of newborn and young normal hamsters and became less present in myocytes of 19 and 22 week old human heart myocytes. Our results demonstrate that the slow Na+ channel does exist in early fetal human life and this type of channel continues to be functional after birth in myocytes of the hereditary cardiomyopathic hamster. 相似文献
180.
Composite particles of rice starch (RS) and microcrystalline cellulose were fabricated by spray-drying technique to be used
as a directly compressible excipient. Two size fractions of microcry stalline cellulose, sieved (MCS) and jet milled (MCJ),
having volumetric mean diameter (D50) of 13.61 and 40.51 μm, respectively, were used to form composite particles with RS in various mixing ratios. The composite
particles produced were evaluated for their powder and compression properties. Although an increase in the microcrystalline
cellulose proportion imparted greater compressibility of the composite particles, the shape of the particles was typically
less spherical with rougher surface resulting in a decrease in the degree of flowability. Compressibility of composite particles
made from different size fractions of microcrystalline cellulose was not different; however, using MCJ, which had a particle
size range close to the size of RS (D50=13.57 μm), provided more spherical particles than using MCS. Spherical composite particles between RS and MCJ in the ratio
of 7∶3 (RS-MCJ-73) were then evaluated for powder properties and compressibility in comparison with some marketed directly
compressible diluents. Compressibility of RS-MCJ-73 was greater than commercial spray-dried RS (Eratab), coprocessed lactose
and microcrystalline cellulose (Cellactose), and agglomerated lactose (Tablettose), but, as expected, lower than microcrystalline
cellulose (Vivapur 101). Flowability index of RS-MCJ-73 appeared to be slightly lower than Eratab but higher than Vivapur
101, Cellactose, and Tablettose. Tablets of RS-MCJ-73 exhibited low friability and good self-disintegrating property. It was
concluded that these developed composite particles could be introduced as a new coprocessed direct compression excipient. 相似文献