全文获取类型
收费全文 | 3506篇 |
免费 | 368篇 |
出版年
2021年 | 46篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 36篇 |
2017年 | 51篇 |
2016年 | 76篇 |
2015年 | 112篇 |
2014年 | 142篇 |
2013年 | 158篇 |
2012年 | 224篇 |
2011年 | 198篇 |
2010年 | 127篇 |
2009年 | 114篇 |
2008年 | 158篇 |
2007年 | 212篇 |
2006年 | 167篇 |
2005年 | 134篇 |
2004年 | 140篇 |
2003年 | 146篇 |
2002年 | 114篇 |
2001年 | 66篇 |
2000年 | 58篇 |
1999年 | 47篇 |
1998年 | 49篇 |
1997年 | 41篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 57篇 |
1991年 | 32篇 |
1990年 | 49篇 |
1989年 | 46篇 |
1988年 | 57篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 49篇 |
1983年 | 31篇 |
1982年 | 22篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 32篇 |
1978年 | 31篇 |
1977年 | 23篇 |
1976年 | 25篇 |
1975年 | 18篇 |
1974年 | 37篇 |
1972年 | 18篇 |
1968年 | 17篇 |
排序方式: 共有3874条查询结果,搜索用时 15 毫秒
1.
G Henderson A Duncan M Kromberg J Roberts F Sim G Vafidis 《BMJ (Clinical research ed.)》1990,300(6731):1076
2.
Calcium-induced degradation of the lens cytoskeleton. 总被引:1,自引:0,他引:1
3.
4.
Summary The steroid 21-hydroxylase enzyme (P450c21) is a member of the cytochrome P450 gene superfamily and is essential in the synthesis of cortisol and aldosterone. Defects in the P450c21B gene cause congenital adrenal hyperplasia (CAH), a common genetic disorder leading to virilization of newborn females. To avoid the standard cloning of mutant P450c21 genes from genomic libraries, we amplified the full-length genomic P450c21 genes by polymerase chain reaction (PCR). The amplification was followed by cloning and sequencing of a defective P450c21B gene. The strategy described here is generally applicable, thus making a simple characterization of the complete P450c21B gene possible. The method was tested in one patient suffering from the simple virilizing form of CAH. The sequence of three independent clones originating from the defective P450c21B showed that Ile at position 172 in exon 4 was substituted by Asn. The identical mutation also has been found in other patients with CAH. 相似文献
5.
6.
7.
Elizabeth Storer Scholl Antonella Pirone Daniel H Cox R Keith Duncan Michele H Jacob 《Channels (Austin, Tex.)》2014,8(1):62-75
Small conductance Ca2+-sensitive potassium (SK2) channels are voltage-independent, Ca2+-activated ion channels that conduct potassium cations and thereby modulate the intrinsic excitability and synaptic transmission of neurons and sensory hair cells. In the cochlea, SK2 channels are functionally coupled to the highly Ca2+ permeant α9/10-nicotinic acetylcholine receptors (nAChRs) at olivocochlear postsynaptic sites. SK2 activation leads to outer hair cell hyperpolarization and frequency-selective suppression of afferent sound transmission. These inhibitory responses are essential for normal regulation of sound sensitivity, frequency selectivity, and suppression of background noise. However, little is known about the molecular interactions of these key functional channels. Here we show that SK2 channels co-precipitate with α9/10-nAChRs and with the actin-binding protein α-actinin-1. SK2 alternative splicing, resulting in a 3 amino acid insertion in the intracellular 3′ terminus, modulates these interactions. Further, relative abundance of the SK2 splice variants changes during developmental stages of synapse maturation in both the avian cochlea and the mammalian forebrain. Using heterologous cell expression to separately study the 2 distinct isoforms, we show that the variants differ in protein interactions and surface expression levels, and that Ca2+ and Ca2+-bound calmodulin differentially regulate their protein interactions. Our findings suggest that the SK2 isoforms may be distinctly modulated by activity-induced Ca2+ influx. Alternative splicing of SK2 may serve as a novel mechanism to differentially regulate the maturation and function of olivocochlear and neuronal synapses. 相似文献
8.
Duncan T. Patten 《American journal of botany》1978,65(8):891-895
During years with good winter rainfall, ephemeral plants can contribute considerably to primary production in the upper Sonoran Desert. This study was designed to compare ephemeral community productivity and production efficiency within the different microhabitats created by trees, shrubs and open spaces in a Sonoran Desert ecosystem. Ephemerals were periodically harvested in the different habitats and dried for biomass and caloric determinations. The caloric data were compared to total solar input into the different microhabitats in order to determine production efficiencies of each stand. Productivity rates were also determined for the total community for the sample period, winters of 1972-74. Both productivity and production efficiency were highest under the shade of Cercidium. The highest production efficiency occurring in the shaded sites was 5.03% which approaches the theoretical maximum photosynthetic efficiency level. The production efficiency of the entire ephemeral community for the whole growing season was only 0.17% during an optimal year, demonstrating the influence of the environment in the interspaces on productivity and solar conversion in the desert. 相似文献
9.
10.