全文获取类型
收费全文 | 357篇 |
免费 | 45篇 |
出版年
2021年 | 11篇 |
2020年 | 3篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1970年 | 4篇 |
1969年 | 7篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1965年 | 5篇 |
1964年 | 5篇 |
1961年 | 3篇 |
1933年 | 2篇 |
1931年 | 3篇 |
1923年 | 2篇 |
1912年 | 2篇 |
排序方式: 共有402条查询结果,搜索用时 15 毫秒
41.
Tkačik G Garrigan P Ratliff C Milčinski G Klein JM Seyfarth LH Sterling P Brainard DH Balasubramanian V 《PloS one》2011,6(6):e20409
Here we introduce a database of calibrated natural images publicly available through an easy-to-use web interface. Using a Nikon D70 digital SLR camera, we acquired about six-megapixel images of Okavango Delta of Botswana, a tropical savanna habitat similar to where the human eye is thought to have evolved. Some sequences of images were captured unsystematically while following a baboon troop, while others were designed to vary a single parameter such as aperture, object distance, time of day or position on the horizon. Images are available in the raw RGB format and in grayscale. Images are also available in units relevant to the physiology of human cone photoreceptors, where pixel values represent the expected number of photoisomerizations per second for cones sensitive to long (L), medium (M) and short (S) wavelengths. This database is distributed under a Creative Commons Attribution-Noncommercial Unported license to facilitate research in computer vision, psychophysics of perception, and visual neuroscience. 相似文献
42.
Local anesthetics (LAs) are compounds that inhibit the propagation of action potentials in excitable tissues by blocking voltage-gated Na+ channels. Mutagenesis studies have demonstrated that several amino acid residues are important sites of LA interaction with the channel, but these studies provide little information regarding the molecular forces that govern drug-binding interactions, including the binding orientation of drugs. We used computational methods to construct a simple model of benzocaine analog binding with the D4S6 segment of rat skeletal muscle (NaV4.1) sodium channels. The model revealed that four hydrophobic residues form a binding cavity for neutral LAs, and docking studies indicated that increasing hydrophobicity among the benzocaine analogs allowed a better fit within the binding cavity. The similarities between our simple model and published experimental data suggested that modeling of LA interactions with sodium channels, along with experimental approaches, could further enhance our understanding of LA interactions with sodium channels. 相似文献
43.
Michael?A?Ward Cynthia?M?Carlsson Mehul?A?Trivedi Mark?A?Sager Sterling?C?JohnsonEmail author 《BMC neurology》2005,5(1):23
Background
Obesity causes or exacerbates a host of medical conditions, including cardiovascular, pulmonary, and endocrine diseases. Recently obesity in elderly women was associated with greater risk of dementia, white matter ischemic changes, and greater brain atrophy. The purpose of this study was to determine whether body type affects global brain volume, a marker of atrophy, in middle-aged men and women. 相似文献44.
Direct evidence of prey choice in carnivorous dinosaurs is rare in the fossil record. The most celebrated example pertains to purported stomach contents in the carnivorous dinosaur Coelophysis bauri, which besides revealing prey choice, also points to cannibalistic behaviour as being commonplace (Colbert 1989, 1995). Here, we test this hypothesis by conducting the first comprehensive anatomical and histological examination of the famed Coelophysis 'cannibals'. The results unequivocally show that the gut contents derive from early crocodylomorphs rather than juveniles of Coelophysis. These findings suggest that this taxon is not cannibalistic and bring into question the commonality of this behaviour among non-avian dinosaurs. 相似文献
45.
Tennakoon DK Mehta RS Ortega SB Bhoj V Racke MK Karandikar NJ 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(11):7119-7129
In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease. 相似文献
46.
Carr PA Wang HH Sterling B Isaacs FJ Lajoie MJ Xu G Church GM Jacobson JM 《Nucleic acids research》2012,40(17):e132
Genome-scale engineering of living organisms requires precise and economical methods to efficiently modify many loci within chromosomes. One such example is the directed integration of chemically synthesized single-stranded deoxyribonucleic acid (oligonucleotides) into the chromosome of Escherichia coli during replication. Herein, we present a general co-selection strategy in multiplex genome engineering that yields highly modified cells. We demonstrate that disparate sites throughout the genome can be easily modified simultaneously by leveraging selectable markers within 500 kb of the target sites. We apply this technique to the modification of 80 sites in the E. coli genome. 相似文献
47.
48.
Bendlin BB Carlsson CM Johnson SC Zetterberg H Blennow K Willette AA Okonkwo OC Sodhi A Ries ML Birdsill AC Alexander AL Rowley HA Puglielli L Asthana S Sager MA 《PloS one》2012,7(6):e37720
Cerebrospinal fluid (CSF) biomarkers T-Tau and Aβ(42) are linked with Alzheimer's disease (AD), yet little is known about the relationship between CSF biomarkers and structural brain alteration in healthy adults. In this study we examined the extent to which AD biomarkers measured in CSF predict brain microstructure indexed by diffusion tensor imaging (DTI) and volume indexed by T1-weighted imaging. Forty-three middle-aged adults with parental family history of AD received baseline lumbar puncture and MRI approximately 3.5 years later. Voxel-wise image analysis methods were used to test whether baseline CSF Aβ(42), total tau (T-Tau), phosphorylated tau (P-Tau) and neurofilament light protein predicted brain microstructure as indexed by DTI and gray matter volume indexed by T1-weighted imaging. T-Tau and T-Tau/Aβ(42) were widely correlated with indices of brain microstructure (mean, axial, and radial diffusivity), notably in white matter regions adjacent to gray matter structures affected in the earliest stages of AD. None of the CSF biomarkers were related to gray matter volume. Elevated P-Tau and P-Tau/Aβ(42) levels were associated with lower recognition performance on the Rey Auditory Verbal Learning Test. Overall, the results suggest that CSF biomarkers are related to brain microstructure in healthy adults with elevated risk of developing AD. Furthermore, the results clearly suggest that early pathological changes in AD can be detected with DTI and occur not only in cortex, but also in white matter. 相似文献
49.
50.