全文获取类型
收费全文 | 6585篇 |
免费 | 895篇 |
出版年
2021年 | 80篇 |
2020年 | 54篇 |
2019年 | 80篇 |
2018年 | 76篇 |
2017年 | 86篇 |
2016年 | 140篇 |
2015年 | 222篇 |
2014年 | 235篇 |
2013年 | 321篇 |
2012年 | 367篇 |
2011年 | 364篇 |
2010年 | 221篇 |
2009年 | 181篇 |
2008年 | 306篇 |
2007年 | 283篇 |
2006年 | 268篇 |
2005年 | 244篇 |
2004年 | 276篇 |
2003年 | 213篇 |
2002年 | 236篇 |
2001年 | 182篇 |
2000年 | 171篇 |
1999年 | 157篇 |
1998年 | 96篇 |
1997年 | 75篇 |
1996年 | 72篇 |
1995年 | 82篇 |
1994年 | 77篇 |
1993年 | 76篇 |
1992年 | 138篇 |
1991年 | 127篇 |
1990年 | 139篇 |
1989年 | 142篇 |
1988年 | 122篇 |
1987年 | 120篇 |
1986年 | 105篇 |
1985年 | 74篇 |
1984年 | 90篇 |
1983年 | 80篇 |
1982年 | 73篇 |
1981年 | 61篇 |
1979年 | 78篇 |
1978年 | 55篇 |
1977年 | 61篇 |
1976年 | 60篇 |
1975年 | 72篇 |
1974年 | 58篇 |
1973年 | 52篇 |
1972年 | 53篇 |
1971年 | 51篇 |
排序方式: 共有7480条查询结果,搜索用时 31 毫秒
1.
In a typical auditory scene, sounds from different sources and reflective surfaces summate in the ears, causing spatial cues to fluctuate. Prevailing hypotheses of how spatial locations may be encoded and represented across auditory neurons generally disregard these fluctuations and must therefore invoke additional mechanisms for detecting and representing them. Here, we consider a different hypothesis in which spatial perception corresponds to an intermediate or sub-maximal firing probability across spatially selective neurons within each hemisphere. The precedence or Haas effect presents an ideal opportunity for examining this hypothesis, since the temporal superposition of an acoustical reflection with sounds arriving directly from a source can cause otherwise stable cues to fluctuate. Our findings suggest that subjects’ experiences may simply reflect the spatial cues that momentarily arise under various acoustical conditions and how these cues are represented. We further suggest that auditory objects may acquire “edges” under conditions when interaural time differences are broadly distributed. 相似文献
2.
This is the first report of the growth in culture of Porphyra subtumens J. Agardh ex Laing (Bangiales, Rhodophyta), an obligate epiphyte of Durvillaea species and endemic to New Zealand waters. Archeospores, previously observed on field material, develop directly into the blade phase. Spores released from field collected blades form conchocelis. Conchospores develop into new blades, completing the life history in culture. Earlier reports of reproduction in P. subtumens gave conflicting accounts with some authors citing this species as having an asexual, monophasic life history with an unusual form of spore production, while others described spermatangia and carposporangia on the blade phase. 相似文献
3.
4.
5.
6.
7.
Reuben S.E. Young Andrew P. Bowman Kaylyn D. Tousignant Berwyck L.J. Poad Jennifer H. Gunter Lisa K. Philp Colleen C. Nelson Shane R. Ellis Ron M.A. Heeren Martin C. Sadowski Stephen J. Blanksby 《Journal of lipid research》2022,63(6):100223
The cellular energy and biomass demands of cancer drive a complex dynamic between uptake of extracellular FAs and their de novo synthesis. Given that oxidation of de novo synthesized FAs for energy would result in net-energy loss, there is an implication that FAs from these two sources must have distinct metabolic fates; however, hitherto, all FAs have been considered part of a common pool. To probe potential metabolic partitioning of cellular FAs, cancer cells were supplemented with stable isotope-labeled FAs. Structural analysis of the resulting glycerophospholipids revealed that labeled FAs from uptake were largely incorporated to canonical (sn-) positions on the glycerol backbone. Surprisingly, labeled FA uptake also disrupted canonical isomer patterns of the unlabeled lipidome and induced repartitioning of n-3 and n-6 PUFAs into glycerophospholipid classes. These structural changes support the existence of differences in the metabolic fates of FAs derived from uptake or de novo sources and demonstrate unique signaling and remodeling behaviors usually hidden from conventional lipidomics. 相似文献
8.
Etiology and modification of gait instability in older adults: a randomized controlled trial of exercise. 总被引:2,自引:0,他引:2
J M Hausdorff M E Nelson D Kaliton J E Layne M J Bernstein A Nuernberger M A Singh 《Journal of applied physiology》2001,90(6):2117-2129
Increased gait instability is common in older adults, even in the absence of overt disease. The goal of the present study was to quantitatively investigate the factors that contribute to gait instability and its potential reversibility in functionally impaired older adults. We studied 67 older men and women with functional impairment before and after they participated in a randomized placebo-controlled, 6-mo multimodal exercise trial. We found that 1) gait instability is multifactorial; 2) stride time variability is strongly associated with functional status and performance-based measures of function that have previously been shown to predict significant clinical outcomes such as morbidity and nursing home admission; 3) neuropsychological status and health-related quality of life play important, independent roles in gait instability; and 4) improvement in physiological capacity is associated with reduced gait instability. Although the etiology of gait instability in older persons with mild-moderate functional impairment is multifactorial, interventions designed to reduce gait instability may be effective in bringing about a more consistent and more stable walking pattern. 相似文献
9.
10.
Nelson OE 《Genetics》1952,37(2):101-124