全文获取类型
收费全文 | 13445篇 |
免费 | 1061篇 |
国内免费 | 12篇 |
出版年
2024年 | 12篇 |
2023年 | 67篇 |
2022年 | 58篇 |
2021年 | 360篇 |
2020年 | 188篇 |
2019年 | 230篇 |
2018年 | 304篇 |
2017年 | 236篇 |
2016年 | 405篇 |
2015年 | 610篇 |
2014年 | 679篇 |
2013年 | 818篇 |
2012年 | 1125篇 |
2011年 | 1124篇 |
2010年 | 701篇 |
2009年 | 646篇 |
2008年 | 900篇 |
2007年 | 877篇 |
2006年 | 868篇 |
2005年 | 757篇 |
2004年 | 720篇 |
2003年 | 697篇 |
2002年 | 615篇 |
2001年 | 148篇 |
2000年 | 90篇 |
1999年 | 159篇 |
1998年 | 163篇 |
1997年 | 110篇 |
1996年 | 109篇 |
1995年 | 67篇 |
1994年 | 72篇 |
1993年 | 77篇 |
1992年 | 41篇 |
1991年 | 48篇 |
1990年 | 36篇 |
1989年 | 49篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 30篇 |
1982年 | 21篇 |
1981年 | 31篇 |
1980年 | 28篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
61.
62.
63.
Some properties of monolayers of (POPG) alone or of POPG in mixtures with (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm2·s?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m?1 in the presence of Na+, Ca2+ or low pH (2.0) in the subphase. (3) The presence of Ca2+ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na+ or Ca2+ in the subphase. 相似文献
64.
The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime (“dwarfing” phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by O2 uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity. 相似文献
65.
Kevin D. Reilly 《Bulletin of mathematical biology》1968,30(4):565-579
A mathematical model for learning of a conditioned avoidance behavior is presented. An identification of the net excitation
of a neural model (Rashevsky, N., 1960.Mathematical Biophysics. Vol. II. New York: Dover Publications, Inc.) with the instantaneous probability of response is introduced and its usefulness
in discussing block-trial learning performances in the conditioned avoidance situation is outlined for normal and brain-operated
animals, using experimental data collected by the author. Later, the model is applied to consecutive trial learning and connection
is made with the approach of H. D. Landahl (1964. “An Avoidance Learning Situation. A Neural Net Model.”Bull. Math. Biophysics,26, 83–89; and 1965, “A Neural Net Model for Escape Learning.”Bull. Math. Biophysics,27, Special Edition, 317–328) wherein lie further data with which the model can be compared. 相似文献
66.
67.
Summary Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated. ATP-sensitive K+ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pH
i
. (1) The time course of K+(ATP) channel activity during exposure to and washout of NH4Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH4Cl entry and inhibition of the Na
o
+
H
i
+
exchanger, resembles the time course of pH
i
measured in other cell types that have been similarly treated. (2) Increasing pH
o
over the range 6.25–7.9 increases K+(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H+ by the application of the K+/H+ exchanger nigericin. (3) Increasing pH
i
over a similar range produces similar effects on K+(ATP) channels in inside-out excised patches exposed to small concentrations of ATP
i
. The physiological role of pH
i
in the metabolic gating of this channel remains to be explored. 相似文献
68.
We have previously demonstrated that most isolates of C. albicans are hydrophobic when grown at room temperature (RT, ca. 22-24 degrees C) and hydrophilic when grown at 37 degrees C. Variants of our standard strain LGH1095 were isolated that are hydrophobic at 37 degrees C and hydrophilic at RT. After repeated phase partitioning with cyclohexane-water cell populations that were 6-16% hydrophobic at RT and 66-80% hydrophobic at 37 degrees C were obtained. Subsequent limiting dilution experiments provided clones which were more hydrophobic at RT or hydrophilic at 37 degrees C. These were then recloned until the resultant populations were consistently under 5% cell surface hydrophobicity (CSH) at RT or over 95% at 37 degrees C. Treatment with several detergents as well as sugars did not decrease the CSH of these cells. Lipase and several proteases also had no effect. When treated with trypsin at a concentration twice that used to lower CSH of normal cells to less than 5%, the hydrophobic variant only decreased in CSH by 50%. Both variants were capable of germinating, although at different levels depending on prior growth temperature. Sensitivity to the germination inhibitor morphogenic autoregulatory substance (MARS) was similar to that of the parent strain. 相似文献
69.
Characterization of the solubilized and reconstituted ATP-dependent vesicular glutamate uptake system 总被引:1,自引:0,他引:1
We have previously provided evidence for ATP-dependent glutamate uptake into synaptic vesicles, and, based upon the unique properties of the vesicular uptake system, we have proposed that the vesicular glutamate translocator plays a crucial role in selecting glutamate for neurotransmission. In this study, we have solubilized the vesicular glutamate uptake system, proposed to consist of at least a glutamate translocator and a proton pump Mg-ATPase, from rat brain synaptic vesicles, and reconstituted the functional ATP-dependent glutamate uptake system into liposomes. The glutamate uptake in the reconstituted system is dependent upon ATP, markedly potentiated by low millimolar concentrations of chloride and inhibited by agents known to dissipate electrochemical proton gradients. Moreover, it exhibited low affinity for glutamate (Km = 2 mM), yet high specificity for glutamate; thus, it did not recognize aspartate and other agents known to interact with glutamate receptors. These properties are indistinguishable from those observed in intact synaptic vesicles. The solubilized functional components of the glutamate uptake system, alone or as a complex, have been estimated to have a Stokes radius in the range of 69 to 84 A. The reconstitution experiments described here provide a functional assay for the solubilized vesicular glutamate uptake system and represent an initial step towards the purification of the glutamate translocator. 相似文献
70.
Down''s Syndrome Individuals Begin Life with Normal Levels of Brain Cholinergic Markers 总被引:3,自引:1,他引:2
Stephen Kish Harry Karlinsky Lawrence Becker Joseph Gilbert Michelle Rebbetoy Li-Jan Chang Linda DiStefano Oleh Hornykiewicz 《Journal of neurochemistry》1989,52(4):1183-1187
We measured the activities of the cholinergic marker enzymes choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in autopsied brains of seven infants (age range 3 months to 1 year) with Down's syndrome (DS), a disorder in which virtually all individuals will develop by middle age the neuropathological changes of Alzheimer's disease accompanied by a marked brain cholinergic reduction. When compared with age-matched controls cholinergic enzyme activity was normal in all brain regions of the individuals with infant DS with the exception of above-normal activity in the putamen (ChAT) and the occipital cortex (AChE). Our neurochemical observations suggest that DS individuals begin life with a normal complement of brain cholinergic neurons. This opens the possibility of early therapeutic intervention to prevent the development of brain cholinergic changes in patients with DS. 相似文献