全文获取类型
收费全文 | 6783篇 |
免费 | 679篇 |
国内免费 | 3篇 |
出版年
2023年 | 43篇 |
2022年 | 113篇 |
2021年 | 215篇 |
2020年 | 118篇 |
2019年 | 131篇 |
2018年 | 171篇 |
2017年 | 126篇 |
2016年 | 228篇 |
2015年 | 429篇 |
2014年 | 437篇 |
2013年 | 522篇 |
2012年 | 658篇 |
2011年 | 586篇 |
2010年 | 342篇 |
2009年 | 296篇 |
2008年 | 431篇 |
2007年 | 399篇 |
2006年 | 389篇 |
2005年 | 322篇 |
2004年 | 304篇 |
2003年 | 260篇 |
2002年 | 212篇 |
2001年 | 54篇 |
2000年 | 48篇 |
1999年 | 39篇 |
1998年 | 59篇 |
1997年 | 37篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 19篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1973年 | 12篇 |
1971年 | 9篇 |
1970年 | 12篇 |
1969年 | 8篇 |
排序方式: 共有7465条查询结果,搜索用时 175 毫秒
1.
2.
Sheep are used as models for the human spine, yet comparative in vivo data necessary for validation is limited. The purpose of this study was therefore to compare spinal motion and trunk muscle activity during active trunk movements in sheep and humans. Three-dimensional kinematic data as well as surface electromyography (sEMG) of spinal flexion and extension was compared in twenty-four humans in upright (UR) and 4-point kneeling (KN) postures and in 17 Austrian mountain sheep. Kinematic markers were attached over the sacrum, posterior iliac spines, and spinous and transverse processes of T5, T8, T11, L2 and L5 in humans and over the sacrum, tuber sacrale, T5, T8, T12, L3 and L7 in sheep. The activity of erector spinae (ES), rectus abdominis (RA), obliquus externus (OE), and obliquus internus (OI) were collected. Maximum sEMG (MOE) was identified for each muscle and trial, and reported as a percentage (MOE%) of the overall maximally observed sEMG from all trials. Spinal range of motion was significantly smaller in sheep compared to humans (UR / KN) during flexion (sheep: 6–11°; humans 12–34°) and extension (sheep: 4°; humans: 11–17°). During extension, MOE% of ES was greater in sheep (median: 77.37%) than UR humans (24.89%), and MOE% of OE and OI was greater in sheep (OE 76.20%; OI 67.31%) than KN humans (OE 21.45%; OI 19.34%), while MOE% of RA was lower in sheep (21.71%) than UR humans (82.69%). During flexion, MOE% of RA was greater in sheep (83.09%) than humans (KN 47.42%; UR 41.38%), and MOE% of ES in sheep (45.73%) was greater than KN humans (14.45%), but smaller than UR humans (72.36%). The differences in human and sheep spinal motion and muscle activity suggest that caution is warranted when ovine data are used to infer human spine biomechanics. 相似文献
3.
Relation of precipitation and temperature with yield of herbaceous plants in eastern Oregon 总被引:2,自引:0,他引:2
Forrest A. Sneva 《International journal of biometeorology》1982,26(4):263-276
Eighteen years of herbage yields of range grasses and concomitant precipitation and temperature fluctuations were examined with correlation and regression techniques. Antecedent precipitation was the dominant factor influencing yield of perennial herbaceous species, while both temperature and precipitation were important for prediction of yield of downy bromegrass, a winter annual. Total yield of the herbaceous community was closely correlated with precipitation received during the September to June period (r = 0.92); however, September to March precipitation was also highly correlated (r = 0.89). These correlations provide timely and useful estimates of native range production on eastern Oregon ranges. Sixty to 92% of yield variation was accounted for by the regression models for 9 of the 12 species or species groups examined. 相似文献
4.
Abhishek Chatterjee Celia Caballero-Franco Dannika Bakker Stephanie Totten Armando Jardim 《The Journal of biological chemistry》2015,290(42):25579-25594
Enterohemorrhagic Escherichia coli is a causative agent of gastrointestinal and diarrheal diseases. Pathogenesis associated with enterohemorrhagic E. coli involves direct delivery of virulence factors from the bacteria into epithelial cell cytosol via a syringe-like organelle known as the type III secretion system. The type III secretion system protein EspD is a critical factor required for formation of a translocation pore on the host cell membrane. Here, we show that recombinant EspD spontaneously integrates into large unilamellar vesicle (LUV) lipid bilayers; however, pore formation required incorporation of anionic phospholipids such as phosphatidylserine and an acidic pH. Leakage assays performed with fluorescent dextrans confirmed that EspD formed a structure with an inner diameter of ∼2.5 nm. Protease mapping indicated that the two transmembrane helical hairpin of EspD penetrated the lipid layer positioning the N- and C-terminal domains on the extralumenal surface of LUVs. Finally, a combination of glutaraldehyde cross-linking and rate zonal centrifugation suggested that EspD in LUV membranes forms an ∼280–320-kDa oligomeric structure consisting of ∼6–7 subunits. 相似文献
5.
Household‐level correlates of children's physical activity levels in and across 12 countries
下载免费PDF全文
![点击此处可从《Obesity (Silver Spring, Md.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Deirdre M. Harrington Fiona Gillison Stephanie T. Broyles Jean‐Philippe Chaput Mikael Fogelholm Gang Hu Rebecca Kuriyan Anura Kurpad Allana G. LeBlanc Carol Maher Jose Maia Victor Matsudo Timothy Olds Vincent Onywera Olga L. Sarmiento Martyn Standage Mark S. Tremblay Catrine Tudor‐Locke Pei Zhao Peter T. Katzmarzyk for the ISCOLE Research Group 《Obesity (Silver Spring, Md.)》2016,24(10):2150-2157
6.
7.
8.
9.
Stephanie Herzfeld 《Plant Systematics and Evolution》1912,62(8-9):289-303
Ohne Zusammenfassung 相似文献
10.