全文获取类型
收费全文 | 7333篇 |
免费 | 801篇 |
国内免费 | 3篇 |
专业分类
8137篇 |
出版年
2022年 | 66篇 |
2021年 | 98篇 |
2020年 | 73篇 |
2019年 | 88篇 |
2018年 | 108篇 |
2017年 | 120篇 |
2016年 | 162篇 |
2015年 | 272篇 |
2014年 | 290篇 |
2013年 | 370篇 |
2012年 | 501篇 |
2011年 | 528篇 |
2010年 | 320篇 |
2009年 | 304篇 |
2008年 | 437篇 |
2007年 | 420篇 |
2006年 | 385篇 |
2005年 | 377篇 |
2004年 | 325篇 |
2003年 | 327篇 |
2002年 | 338篇 |
2001年 | 103篇 |
2000年 | 80篇 |
1999年 | 112篇 |
1998年 | 120篇 |
1997年 | 67篇 |
1996年 | 72篇 |
1995年 | 67篇 |
1994年 | 55篇 |
1993年 | 58篇 |
1992年 | 65篇 |
1991年 | 54篇 |
1990年 | 57篇 |
1989年 | 56篇 |
1988年 | 55篇 |
1987年 | 60篇 |
1986年 | 53篇 |
1985年 | 63篇 |
1984年 | 50篇 |
1983年 | 45篇 |
1982年 | 45篇 |
1981年 | 51篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 46篇 |
1977年 | 33篇 |
1975年 | 35篇 |
1974年 | 52篇 |
1973年 | 41篇 |
1972年 | 33篇 |
排序方式: 共有8137条查询结果,搜索用时 15 毫秒
991.
Vera-Garcia FJ Moreside JM McGill SM 《Journal of electromyography and kinesiology》2011,21(6):893-903
The aim of this study was to compare trunk muscular recruitment and lumbar spine kinematics when motion was constrained to either the thorax or the pelvis. Nine healthy women performed four upright standing planar movements (rotations, anterior–posterior translations, medial–lateral translations, and horizontal circles) while constraining pelvis motion and moving the thorax or moving the pelvis while minimizing thorax motion, and four isometric trunk exercises (conventional curl-up, reverse curl-up, cross curl-up, and reverse cross curl-up). Surface EMG (upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, and latissimus dorsi) and 3D lumbar displacements were recorded. Pelvis movements produced higher EMG amplitudes of the oblique abdominals than thorax motions in most trials, and larger lumbar displacements in the medial–lateral translations and horizontal circles. Conversely, thorax movements produced larger rotational lumbar displacement than pelvis motions during rotations and higher EMG amplitudes for latissimus dorsi during rotations and anterior–posterior translations and for lower rectus abdominis during the crossed curl-ups. Thus, different neuromuscular compartments appear when the objective changes from pelvis to thorax motion. This would suggest that both movement patterns should be considered when planning spine stabilization programs, to optimize exercises for the movement and muscle activations desired. 相似文献
992.
993.
Trepanowski JF Farney TM McCarthy CG Schilling BK Craig SA Bloomer RJ 《Journal of strength and conditioning research / National Strength & Conditioning Association》2011,25(12):3461-3471
Trepanowski, JF, Farney, TM, McCarthy, CG, Schilling, BK, Craig, SA, and Bloomer, RJ. The effects of chronic betaine supplementation on exercise performance, skeletal muscle oxygen saturation, and associated biochemical parameters in resistance trained men. J Strength Cond Res 25(12): 3461-3471, 2011-We examined the effects of chronic betaine supplementation on exercise performance and associated parameters in resistance trained men. Men were randomly assigned in a double-blind manner using a crossover design to consume betaine (2.5 g of betaine mixed in 500 ml of Gatorade?) or a placebo (500 ml of Gatorade?) for 14 days, with a 21-day washout period. Before and after each treatment period, tests of lower- and upper-body muscular power and isometric force were conducted, including a test of upper-body muscular endurance (10 sets of bench press exercise to failure). Muscle tissue oxygen saturation (StO2) during the bench press protocol was measured via near infrared spectroscopy. Blood samples were collected before and after the exercise test protocol for analysis of lactate, nitrate/nitrite (NOx), and malondialdehyde (MDA). When analyzed using a repeated measures analysis of variance, no significant differences were noted between conditions for exercise performance variables (p > 0.05). However, an increase in total repetitions (p = 0.01) and total volume load (p = 0.02) in the 10-set bench press protocol was noted with betaine supplementation (paired t-tests), with values increasing approximately 6.5% from preintervention to postintervention. Although not of statistical significance (p = 0.14), postexercise blood lactate increased to a lesser extent with betaine supplementation (210%) compared with placebo administration (270%). NOx was lower postintervention as compared with preintervention (p = 0.06), and MDA was relatively unchanged. The decrease in StO2 during the bench press protocol was greater with betaine vs. placebo (p = 0.01), possibly suggesting enhanced muscle oxygen consumption. These findings indicate that betaine supplementation results in a moderate increase in total repetitions and volume load in the bench press exercise, without favorably impacting other performance measures. 相似文献
994.
995.
996.
Genetic analysis of abiotic stress tolerance in crops 总被引:1,自引:0,他引:1
Abiotic stress tolerance is complex, but as phenotyping technologies improve, components that contribute to abiotic stress tolerance can be quantified with increasing ease. In parallel with these phenomics advances, genetic approaches with more complex genomes are becoming increasingly tractable as genomic information in non-model crops increases and even whole crop genomes can be re-sequenced. Thus, genetic approaches to elucidating the molecular basis to abiotic stress tolerance in crops are becoming more easily achievable. 相似文献
997.
Dodd KA Bird BH Khristova ML Albariño CG Carroll SA Comer JA Erickson BR Rollin PE Nichol ST 《PLoS neglected tropical diseases》2011,5(10):e1352
Background
Alkhurma hemorrhagic fever virus (AHFV) and Kyasanur forest disease virus (KFDV) cause significant human disease and mortality in Saudi Arabia and India, respectively. Despite their distinct geographic ranges, AHFV and KFDV share a remarkably high sequence identity. Given its emergence decades after KFDV, AHFV has since been considered a variant of KFDV and thought to have arisen from an introduction of KFDV to Saudi Arabia from India. To gain a better understanding of the evolutionary history of AHFV and KFDV, we analyzed the full length genomes of 16 AHFV and 3 KFDV isolates.Methodology/Principal Findings
Viral genomes were sequenced and compared to two AHFV sequences available in GenBank. Sequence analyses revealed higher genetic diversity within AHFVs isolated from ticks than human AHFV isolates. A Bayesian coalescent phylogenetic analysis demonstrated an ancient divergence of AHFV and KFDV of approximately 700 years ago.Conclusions/Significance
The high sequence diversity within tick populations and the presence of competent tick vectors in the surrounding regions, coupled with the recent identification of AHFV in Egypt, indicate possible viral range expansion or a larger geographic range than previously thought. The divergence of AHFV from KFDV nearly 700 years ago suggests other AHFV/KFDV-like viruses might exist in the regions between Saudi Arabia and India. Given the human morbidity and mortality associated with these viruses, these results emphasize the importance of more focused study of these significant public health threats. 相似文献998.
Hu J Nudelman G Shimoni Y Kumar M Ding Y López C Hayot F Wetmur JG Sealfon SC 《PloS one》2011,6(2):e16614
In the first few hours following Newcastle disease viral infection of human monocyte-derived dendritic cells, the induction of IFNB1 is extremely low and the secreted type I interferon response is below the limits of ELISA assay. However, many interferon-induced genes are activated at this time, for example DDX58 (RIGI), which in response to viral RNA induces IFNB1. We investigated whether the early induction of IFNBI in only a small percentage of infected cells leads to low level IFN secretion that then induces IFN-responsive genes in all cells. We developed an agent-based mathematical model to explore the IFNBI and DDX58 temporal dynamics. Simulations showed that a small number of early responder cells provide a mechanism for efficient and controlled activation of the DDX58-IFNBI positive feedback loop. The model predicted distributions of single cell responses that were confirmed by single cell mRNA measurements. The results suggest that large cell-to-cell variation plays an important role in the early innate immune response, and that the variability is essential for the efficient activation of the IFNB1 based feedback loop. 相似文献
999.
Identifying priority areas for conservation: a global assessment for forest-dependent birds 总被引:1,自引:0,他引:1
Limited resources are available to address the world's growing environmental problems, requiring conservationists to identify priority sites for action. Using new distribution maps for all of the world's forest-dependent birds (60.6% of all bird species), we quantify the contribution of remaining forest to conserving global avian biodiversity. For each of the world's partly or wholly forested 5-km cells, we estimated an impact score of its contribution to the distribution of all the forest bird species estimated to occur within it, and so is proportional to the impact on the conservation status of the world's forest-dependent birds were the forest it contains lost. The distribution of scores was highly skewed, a very small proportion of cells having scores several orders of magnitude above the global mean. Ecoregions containing the highest values of this score included relatively species-poor islands such as Hawaii and Palau, the relatively species-rich islands of Indonesia and the Philippines, and the megadiverse Atlantic Forests and northern Andes of South America. Ecoregions with high impact scores and high deforestation rates (2000-2005) included montane forests in Cameroon and the Eastern Arc of Tanzania, although deforestation data were not available for all ecoregions. Ecoregions with high impact scores, high rates of recent deforestation and low coverage by the protected area network included Indonesia's Seram rain forests and the moist forests of Trinidad and Tobago. Key sites in these ecoregions represent some of the most urgent priorities for expansion of the global protected areas network to meet Convention on Biological Diversity targets to increase the proportion of land formally protected to 17% by 2020. Areas with high impact scores, rapid deforestation, low protection and high carbon storage values may represent significant opportunities for both biodiversity conservation and climate change mitigation, for example through Reducing Emissions from Deforestation and Forest Degradation (REDD+) initiatives. 相似文献
1000.