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121.
122.
P. H.-S. Jen X. M. Zhou 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,185(5):471-478
This study examines the effect of temporally patterned pulse trains on duration tuning characteristics of inferior collicular
neurons of the big brown bat, Eptesicus fuscus, under free-field stimulation conditions. Using a 50% difference between maximal and minimal responses as a criterion, the
duration tuning characteristics of inferior collicular neurons determined with pulse trains of different pulse durations are
described as band-pass, long-pass, short-pass, and all-pass. Each band-pass neuron discharged maximally to a specific pulse
duration that was at least 50% larger than the neuron's responses to a long- and a short-duration pulse. In contrast, each
long- or short-pass neuron discharged maximally to a range of long- or short-duration pulses that were at least 50% larger
than the minimal responses. The number of impulses of an all-pass neuron never differed by more than 50%. When pulse trains
were delivered at different pulse repetition rates, the number of short-pass and band-pass neurons progressively increased
with increasing pulse repetition rates. The slope of the duration tuning curves also became sharper when determined with pulse
trains at high pulse repetition rates. Possible mechanisms underlying these findings are discussed.
Accepted: 25 August 1999 相似文献
123.
Song-Kun Shyue Stéphane Boissinot Horacio Schneider Iracilda Sampaio Maria Paula Schneider C.R. Abee Lawrence Williams David Hewett-Emmett Harry G. Sperling Jill A. Cowing Kanwaljit S. Dulai David M. Hunt Wen-Hsiung Li 《Journal of molecular evolution》1998,46(6):697-702
Although most New World monkeys have only one X-linked photopigment locus, many species have three polymorphic alleles at
the locus. The three alleles in the squirrel monkey and capuchin have spectral peaks near 562, 550, and 535 nm, respectively,
and the three alleles in the marmoset and tamarin have spectral peaks near 562, 556, and 543 nm, respectively. To determine
the amino acids responsible for the spectral sensitivity differences among these pigment variants, we sequenced all exons
of the three alleles in each of these four species. From the deduced amino acid sequences and the spectral peak information
and from previous studies of the spectral tuning of X-linked pigments in humans and New World monkeys, we estimated that the
Ala → Ser, Ile → Phe, Gly → Ser, Phe → Tyr, and Ala → Tyr substitutions at residue positions 180, 229, 233, 277, and 285,
respectively, cause spectral shifts of about 5, −2, −1, 8, and 15 nm. On the other hand, the substitutions His → Tyr, Met
→ Val or Leu, and Ala → Tyr at positions 116, 275, and 276, respectively, have no discernible spectral tuning effect, though
residues 275 and 276 are inside the transmembrane domains. Many substitutions between Val and Ile or between Val and Ala have
occurred in the transmembrane domains among the New World monkey pigment variants but apparently have no effect on spectral
tuning. Our study suggests that, in addition to amino acid changes involving a hydroxyl group, large changes in residue size
can also cause a spectral shift in a visual pigment.
Received: 17 July 1997 / Accepted: 7 December 1997 相似文献
124.
Michael T. V. Johnson Carolyn R. Mason Timothy J. Ebner 《Current opinion in neurobiology》2001,11(6):684-688
Recent single-unit recording studies have clarified how multiple parameters of movement are signaled by individual cortical and cerebellar neurons, and also that multiple coordinate frames are utilized. Cognitive processes also modulate the firing of these neurons. The various signals and coordinate systems vary in time and evolve throughout a behavioral sequence, consistent with the demands of the task and the required sensorimotor transformations. 相似文献
125.
Calì T Galli C Olivari S Molinari M 《Biochemical and biophysical research communications》2008,371(3):405-410
EDEM1 is a crucial regulator of endoplasmic reticulum (ER)-associated degradation (ERAD) that extracts non-native glycopolypeptides from the calnexin chaperone system. Under normal growth conditions, the intralumenal level of EDEM1 must be low to prevent premature interruption of ongoing folding programs. We report that in unstressed cells, EDEM1 is segregated from the bulk ER into LC3-I-coated vesicles and is rapidly degraded. The rapid turnover of EDEM1 is regulated by a novel mechanism that shows similarities but is clearly distinct from macroautophagy. Cells with defective EDEM1 turnover contain unphysiologically high levels of EDEM1, show enhanced ERAD activity and are characterized by impaired capacity to efficiently complete maturation of model glycopolypeptides. We define as ERAD tuning the mechanisms operating in the mammalian ER at steady state to offer kinetic advantage to folding over disposal of unstructured nascent chains by selective and rapid degradation of ERAD regulators. 相似文献
126.
Silber MV Gabriel G Strohmann B Garcia-Martin A Robert B Braun P 《Photosynthesis research》2008,96(2):145-151
The peripheral light-harvesting complex, LH2, of Rhodobacter sphaeroides consists of an assembly of membrane-spanning alpha and beta polypeptides which assemble the photoactive bacteriochlorophyll and carotenoid molecules. In this study we systematically investigated bacteriochlorophyll-protein interactions and their effect on functional bacteriochlorophyll assembly by site-directed mutations of the LH2 alpha-subunit. The amino acid residues, isoleucine at position -1 and serine at position -4 were replaced by 12 and 13 other residues, respectively. All residues replacing isoleucine at position -1 supported the functional assembly of LH2. The replacement of isoleucine by glycine, glutamine or asparagine, however, produced LH2 complex with significantly altered spectral properties in comparison to LH2 WT. As indicated by resonance Raman spectroscopy extensive rearrangement of the bacteriochlorophyll-B850 macrocycle(s) took place in LH2 in which isoleucine -1 was replaced by glycine. The replacement results in disruption of the H-bond between the C3 acetyl groups and the aromatic residues +13/+14 without affecting the H-bond involving the C13(1) keto group. In contrast, nearly all amino acid replacements of serine at position -4 resulted in shifting of the bacteriochlorophyll-B850 red most absorption maximum. Interestingly, the extent of shifting closely correlated with the volume of the residue at position -4. These results illustrate that fine tuning of the spectral properties of the bacteriochlorophyll-B850 molecules depend on their packing with single amino acid residues at distinct positions. 相似文献
127.
微RNA(MicroRNA,miRNA)是一类在转录后水平调节基因表达的大约22 nt的非编 码内源单链RNA.已经表明,它们与许多重要的生理和病理过程相关,包括发育、分化、细胞 凋亡、脂肪代谢、病毒感染和癌症.越来越多的证据表明,miRNA参与了获得性免疫的调节. 有趣的是,不同于开关式的调节,miRNA表现出定量的基因调节,它们能精细调节细胞免疫 反应以响应外界刺激.深入理解miRNAs对获得性免疫的调节作用有助于调节宿主免疫应答和 保护感染组织间的平衡,鉴定免疫调节新靶标和开发基于miRNA的有效疗法.本文综述了miRN A包括病毒miRNA对获得性免疫的调节作用,特别是miRNA在调节免疫活性细胞、T细胞功 能和抗体产生中的作用. 相似文献
128.
129.
本研究设计了一种新的自校正控制器——最小偏差超前控制器(MDAC)。MDAC在大于或等于纯时延的某一时刻使实际输出值与设定值的方差为最小。可用于控制带有未知或变化时延的Ⅰ、Ⅱ型非最小相位系统,具有快速、平滑、稳定的特点。用于控制家兔平均动脉压,可在95.8%时间内将其稳定于设定值±0.67kPa误差带内。 相似文献
130.
本工作应用背景光压抑闪光视网膜电图(FERG),考察对图形视网膜电图(PERG)的空间调谐特性的影响,并与无背景光时的结果进行比较。背景光使全屏幕闪光诱发的FERG基本压抑。在这种条件下,同屏幕的图形刺激所诱发的PERG的振幅显示一定的低空间频率衰减(LSFA)。FFT分析表明,当时间频率为3.91Hz时,PERG的二次谐波呈现十分明显的LS-FA,与无背景光时的结果吻合得很好;当时间频率为7.81Hz时,也表现出LSFA,而无背景光时则缺如。这些结果表明,无背景光时记录的PERG振幅在低空间频率区偏高确实是由于混杂有亮度特异性成分—FERG。但是,PERG振幅所显示的LSFA仍不如二次谐波那么明显,这可能是因为FERG中存在的非线性成分未为背景光所完全压抑,仍然混杂在低频区的PERG反应中。 相似文献