全文获取类型
收费全文 | 19483篇 |
免费 | 1959篇 |
国内免费 | 7篇 |
出版年
2023年 | 110篇 |
2022年 | 250篇 |
2021年 | 431篇 |
2020年 | 273篇 |
2019年 | 307篇 |
2018年 | 378篇 |
2017年 | 341篇 |
2016年 | 579篇 |
2015年 | 1057篇 |
2014年 | 1040篇 |
2013年 | 1291篇 |
2012年 | 1614篇 |
2011年 | 1561篇 |
2010年 | 1013篇 |
2009年 | 858篇 |
2008年 | 1149篇 |
2007年 | 1135篇 |
2006年 | 1064篇 |
2005年 | 1027篇 |
2004年 | 978篇 |
2003年 | 849篇 |
2002年 | 806篇 |
2001年 | 234篇 |
2000年 | 181篇 |
1999年 | 210篇 |
1998年 | 185篇 |
1997年 | 122篇 |
1996年 | 124篇 |
1995年 | 107篇 |
1994年 | 100篇 |
1993年 | 94篇 |
1992年 | 104篇 |
1991年 | 128篇 |
1990年 | 107篇 |
1989年 | 83篇 |
1988年 | 96篇 |
1987年 | 77篇 |
1986年 | 71篇 |
1985年 | 75篇 |
1984年 | 66篇 |
1983年 | 62篇 |
1982年 | 55篇 |
1981年 | 57篇 |
1980年 | 55篇 |
1979年 | 51篇 |
1978年 | 56篇 |
1977年 | 47篇 |
1975年 | 57篇 |
1974年 | 74篇 |
1971年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
1.
2.
3.
Edward Harrison 《BMJ (Clinical research ed.)》1916,1(2888):645-647
4.
Jennifer S. Lund 《Brain Cell Biology》2002,31(3-5):203-209
It is clear from reviewing the findings of our own studies and those of others that the cerebral cortex has combined two very different strategies of organisation. Firstly it has a strictly defined genetically determined substrate of specific neurons classes, specific rules for which kinds of cells interconnect, a laminar architecture where efferent and afferent relays and interlaminar links are predetermined. But, as well, a second strategy allows great developmental lability in the precise spatial patterns of intralaminar circuits of the excitatory neurons and in the actual weights of excitatory and inhibitory synapses that are contributed to each neuron. This second strategy presumably allows the cortex to be tailor-made to the early experience of each individual and, as well, allow for lability of responses to different conditions of stimulation and adjustment of the system to compensate to some degree for injuries affecting afferents and circuitry in the adult system. 相似文献
5.
6.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
7.
8.
Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme·substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans. 相似文献
9.
Robert Blake II Elizabeth A. Shute James Waskovsky Arthur P. Harrison JR. 《Geomicrobiology journal》2013,30(3-4):173-192
Abstract Microorganisms capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Phylogenetically distinct organisms were shown to express spectrally distinct redox‐active biomolecules during autotrophic growth on soluble iron. A new iron‐oxidizing eubacterium, designated as strain Funis, was investigated. Strain Funis was judged to be different from other known iron‐oxidizing bacteria on the bases of comparative lipid analyses, 16S rRNA sequence analyses, and cytochrome composition studies. When grown autotrophically on ferrous ions, Funis produced conspicuous levels of a novel acid‐stable, acid‐soluble yellow cytochrome with a distinctive absorbance peak at 579 nm in the reduced state. Stopped‐flow spectrophotometric kinetic studies were conducted on respiratory chain components isolated from cell‐free extracts of Thiobacillus ferrooxidans. Experimental results were consistent with a model where the primary oxidant of ferrous ions is a highly aggregated c‐type cytochrome that then reduces the periplasmic rusticyanin. The Fe(II)‐dependent, cytochrome c‐catalyzed reduction of the rusticyanin possessed three kinetic properties in common with corresponding intact cells that respire on iron: the same anion specificity, a similar dependence of the rate on the concentration of ferrous ions, and similar rates at saturating concentrations of ferrous ions 相似文献
10.
We previously reported that aged mice lacking complement factor H (CFH) exhibit visual defects and structural changes in the retina. However, it is not known whether this phenotype is age-related or is the consequence of disturbed development. To address this question we investigated the effect of Cfh gene deletion on the retinal phenotype of young and mid-age mice. Cfh
−/− mouse eyes exhibited thickening of the retina and reduced nuclear density, but relatively normal scotopic and photopic electroretinograms. At 12 months there was evidence of subtle astroglial activation in the Cfh
−/− eyes, and significant elevation of the complement regulator, decay-accelerating factor (DAF) in Müller cells. In the retinal pigment epithelium (RPE) of young control and Cfh
−/− animals mitochondria and melanosomes were oriented basally and apically respectively, whereas the apical positioning of melanosomes was significantly perturbed in the mid-age Cfh
−/− RPE. We conclude that deletion of Cfh in the mouse leads to defects in the retina that precede any marked loss of visual function, but which become progressively more marked as the animals age. These observations are consistent with a lifelong role for CFH in retinal homeostasis. 相似文献