全文获取类型
收费全文 | 7354篇 |
免费 | 682篇 |
国内免费 | 6篇 |
专业分类
8042篇 |
出版年
2023年 | 51篇 |
2022年 | 116篇 |
2021年 | 232篇 |
2020年 | 153篇 |
2019年 | 183篇 |
2018年 | 180篇 |
2017年 | 157篇 |
2016年 | 210篇 |
2015年 | 355篇 |
2014年 | 380篇 |
2013年 | 461篇 |
2012年 | 548篇 |
2011年 | 543篇 |
2010年 | 321篇 |
2009年 | 288篇 |
2008年 | 380篇 |
2007年 | 391篇 |
2006年 | 328篇 |
2005年 | 336篇 |
2004年 | 315篇 |
2003年 | 279篇 |
2002年 | 272篇 |
2001年 | 67篇 |
2000年 | 43篇 |
1999年 | 64篇 |
1998年 | 83篇 |
1997年 | 38篇 |
1996年 | 32篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 42篇 |
1992年 | 44篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 23篇 |
1982年 | 43篇 |
1981年 | 44篇 |
1980年 | 42篇 |
1979年 | 23篇 |
1978年 | 39篇 |
1977年 | 29篇 |
1975年 | 33篇 |
1974年 | 30篇 |
1973年 | 29篇 |
排序方式: 共有8042条查询结果,搜索用时 15 毫秒
991.
Background
We aimed to evaluate the incidence of type 1 diabetes mellitus in children <15 years of age (yr) in the Auckland region (New Zealand) over 20 years (1990–2009).Methods
We performed a retrospective review of all patients <15 yr diagnosed with type 1 diabetes, from an unselected complete regional cohort.Results
There were 884 new cases of type 1 diabetes, and age at diagnosis rose from 7.6 yr in 1990/1 to 8.9 yr in 2008/9 (r2 = 0.31, p = 0.009). There was a progressive increase in type 1 diabetes incidence among children <15 yr (p<0.0001), reaching 22.5 per 100,000 in 2009. However, the rise in incidence did not occur evenly among age groups, being 2.5-fold higher in older children (10–14 yr) than in the youngest group (0–4 yr). The incidence of new cases of type 1 diabetes was highest in New Zealand Europeans throughout the study period in all age groups (p<0.0001), but the rate of increase was similar in New Zealand Europeans and Non-Europeans. Type 1 diabetes incidence and average annual increase were similar in both sexes. There was no change in BMI SDS shortly after diagnosis, and no association between BMI SDS and age at diagnosis.Conclusions
There has been a steady increase in type 1 diabetes incidence among children <15 yr in Auckland over 20 years. Contrary to other studies, age at diagnosis has increased and the greatest rise in incidence occurred in children 10–14 yr. There was little change in BMI SDS in this population, providing no support for the ‘accelerator hypothesis’. 相似文献992.
Building cognitive abilities often requires sustained engagement with effortful tasks. We demonstrate that beliefs about willpower-whether willpower is viewed as a limited or non-limited resource-impact sustained learning on a strenuous mental task. As predicted, beliefs about willpower did not affect accuracy or improvement during the initial phases of learning; however, participants who were led to view willpower as non-limited showed greater sustained learning over the full duration of the task. These findings highlight the interactive nature of motivational and cognitive processes: motivational factors can substantially affect people's ability to recruit their cognitive resources to sustain learning over time. 相似文献
993.
994.
Westerterp M Gourion-Arsiquaud S Murphy AJ Shih A Cremers S Levine RL Tall AR Yvan-Charvet L 《Cell Stem Cell》2012,11(2):195-206
Intact cholesterol homeostasis helps to maintain hematopoietic stem and multipotential progenitor cell (HSPC) quiescence. Mice with defects in cholesterol efflux pathways due to deficiencies of the ATP binding cassette transporters ABCA1 and ABCG1 displayed a dramatic increase in HSPC mobilization and extramedullary hematopoiesis. Increased extramedullary hematopoiesis was associated with elevated serum levels of G-CSF due to generation of IL-23 by splenic macrophages and dendritic cells. This favored hematopoietic lineage decisions toward granulocytes rather than macrophages in the bone marrow leading to impaired support for osteoblasts and decreased Cxcl12/SDF-1 production by mesenchymal progenitors. Greater HSPC mobilization and extramedullary hematopoiesis were reversed by raising HDL levels in Abca1(-/-)Abcg1(-/-) and Apoe(-/-) mice or in a mouse model of myeloproliferative neoplasm mediated by Flt3-ITD mutation. Our data identify a role of cholesterol efflux pathways in the control of HSPC mobilization. This may translate into therapeutic strategies for atherosclerosis and hematologic malignancies. 相似文献
995.
996.
Dana M. Blumenthal Andrew P. Norton Samuel E. Cox Erik M. Hardy Glen E. Liston Lisa Kennaway D. Terrance Booth Justin D. Derner 《Biological invasions》2012,14(2):395-404
Identifying environments where invasive plants are most invasive is key to understanding causes of invasion and developing
effective management strategies. In mixed-grass prairie, invasive plants are often successful in relatively wet, nitrogen-rich
areas, and areas protected from grazing. Dalmatian toadflax, a common invader of mixed-grass prairie, can also be favored
by high water and nitrogen availability, but is thought to be relatively unpalatable to cattle, and therefore favored by grazing.
We used spatially-adjusted model selection techniques to quantify relationships between toadflax cover (measured using very
high-resolution aerial imagery), and relative snow deposition (estimated with a blowing snow model), slope, aspect, soil texture,
and grazing intensity (estimated by proximity to water tanks). Toadflax was common throughout the 400 ha study site, occurring
in 742 of 1,861 images. Toadflax cover was high on steeper slopes, particularly those with southern aspects. These two topographic
variables were more effective in explaining toadflax distribution than modeled snow deposition, suggesting that factors other
than snow deposition cause toadflax invasion on south-facing slopes. Toadflax cover was also high in areas further from water
tanks, indicating that grazing may inhibit toadflax invasion. More broadly, this result suggests that grazing can reduce invasion
of even relatively unpalatable species in ecosystems with long evolutionary histories of grazing. 相似文献
997.
998.
Jean-Malo Couzigou Vladimir Zhukov Samuel Mondy Ghada Abu el Heba Viviane Cosson T.H. Noel Ellis Mike Ambrose Jiangqi Wen Million Tadege Igor Tikhonovich Kirankumar S. Mysore Joanna Putterill Julie Hofer Alexei Y. Borisov Pascal Ratet 《The Plant cell》2012,24(11):4498-4510
During their symbiotic interaction with rhizobia, legume plants develop symbiosis-specific organs on their roots, called nodules, that house nitrogen-fixing bacteria. The molecular mechanisms governing the identity and maintenance of these organs are unknown. Using Medicago truncatula nodule root (noot) mutants and pea (Pisum sativum) cochleata (coch) mutants, which are characterized by the abnormal development of roots from the nodule, we identified the NOOT and COCH genes as being necessary for the robust maintenance of nodule identity throughout the nodule developmental program. NOOT and COCH are Arabidopsis thaliana BLADE-ON-PETIOLE orthologs, and we have shown that their functions in leaf and flower development are conserved in M. truncatula and pea. The identification of these two genes defines a clade in the BTB/POZ-ankyrin domain proteins that shares conserved functions in eudicot organ development and suggests that NOOT and COCH were recruited to repress root identity in the legume symbiotic organ. 相似文献
999.
Jones MT Ambegaonkar JP Nindl BC Smith JA Headley SA 《Journal of strength and conditioning research / National Strength & Conditioning Association》2012,26(4):1094-1100
Unilateral and bilateral lower-body heavy resistance exercises (HREs) are used for strength training. Little research has examined whether muscle activation and testosterone (TES) responses differ between these exercises. Our purpose was to compare the effects of unilateral and bilateral lower-body HRE on muscle activity using surface electromyography (sEMG) and TES concentrations. Ten resistance-trained, college-aged male athletes (football, track and field) completed 5 testing sessions in which bilateral (back squat [BS]) and unilateral (pitcher squat [PS]) exercises were performed using a counterbalanced design. Sessions 1 and 2 determined estimated maximum strength (10 repetition maximum [10RM]) in the BS and PS. During testing session 3, muscle activation (sEMG) was measured in the right vastus lateralis, biceps femoris, gluteus maximus, and erector spinae (ES) during both BS and PS (stance leg) exercises. In sessions 4 and 5, total TES concentrations (nanomoles per liter) were measured via blood draws at baseline (preexercise), 0, 5, 10, 15, and 30 minutes postexercise after 4 sets of 10 repetitions at the 10RM. Separate repeated-measures analyses of variance examined differences in sEMG and TES between BS and PS (p < 0.05). The sEMG amplitudes were similar (p = 0.80) for BS (0.22 ± 0.06 mV) and PS (0.20 ± 0.07 mV). The TES responses were also similar (p = 0.15) between BS (21.8 ± 6.9 nmol·L(-1)) and PS (26.2 ± 10.1 nmol·L(-1)). The similar lower limb and back sEMG and TES responses may indicate that the neuromuscular and hormonal demands were comparable for both the BS and PS exercises despite the absolute work being less in the PS. The PS exercise may be an effective method for including unilateral exercise into lower-body resistance training when designing training programs for ground-based activities. 相似文献
1000.
The Revised Classification of Eukaryotes 总被引:1,自引:0,他引:1
Sina M. Adl Alastair G. B. Simpson Christopher E. Lane Julius Lukeš David Bass Samuel S. Bowser Matthew W. Brown Fabien Burki Micah Dunthorn Vladimir Hampl Aaron Heiss Mona Hoppenrath Enrique Lara Line le Gall Denis H. Lynn Hilary McManus Edward A. D. Mitchell Sharon E. Mozley‐Stanridge Laura W. Parfrey Jan Pawlowski Sonja Rueckert Laura Shadwick Conrad L. Schoch Alexey Smirnov Frederick W. Spiegel 《The Journal of eukaryotic microbiology》2012,59(5):429-514
This revision of the classification of eukaryotes, which updates that of Adl et al. [J. Eukaryot. Microbiol. 52 (2005) 399], retains an emphasis on the protists and incorporates changes since 2005 that have resolved nodes and branches in phylogenetic trees. Whereas the previous revision was successful in re‐introducing name stability to the classification, this revision provides a classification for lineages that were then still unresolved. The supergroups have withstood phylogenetic hypothesis testing with some modifications, but despite some progress, problematic nodes at the base of the eukaryotic tree still remain to be statistically resolved. Looking forward, subsequent transformations to our understanding of the diversity of life will be from the discovery of novel lineages in previously under‐sampled areas and from environmental genomic information. 相似文献