全文获取类型
收费全文 | 13670篇 |
免费 | 720篇 |
国内免费 | 1073篇 |
专业分类
15463篇 |
出版年
2024年 | 38篇 |
2023年 | 157篇 |
2022年 | 234篇 |
2021年 | 248篇 |
2020年 | 329篇 |
2019年 | 426篇 |
2018年 | 330篇 |
2017年 | 268篇 |
2016年 | 301篇 |
2015年 | 290篇 |
2014年 | 637篇 |
2013年 | 904篇 |
2012年 | 554篇 |
2011年 | 495篇 |
2010年 | 438篇 |
2009年 | 506篇 |
2008年 | 551篇 |
2007年 | 632篇 |
2006年 | 629篇 |
2005年 | 530篇 |
2004年 | 511篇 |
2003年 | 490篇 |
2002年 | 505篇 |
2001年 | 401篇 |
2000年 | 327篇 |
1999年 | 358篇 |
1998年 | 350篇 |
1997年 | 287篇 |
1996年 | 297篇 |
1995年 | 277篇 |
1994年 | 246篇 |
1993年 | 220篇 |
1992年 | 242篇 |
1991年 | 269篇 |
1990年 | 216篇 |
1989年 | 164篇 |
1988年 | 184篇 |
1987年 | 150篇 |
1986年 | 158篇 |
1985年 | 174篇 |
1984年 | 152篇 |
1983年 | 103篇 |
1982年 | 160篇 |
1981年 | 133篇 |
1980年 | 141篇 |
1979年 | 95篇 |
1978年 | 81篇 |
1977年 | 61篇 |
1976年 | 51篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R2 > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes. 相似文献
994.
云开脊蛇(Achalinus yunkaiensis)之前仅在广东和广西有分布报道。本文基于形态比较及线粒体COI基因序列分子系统关系分析结果,确定采集于湖南省新宁县的1号雌性脊蛇标本(CIB 119041)为云开脊蛇,为湖南省新记录种。该标本鼻间鳞沟约等于前额鳞沟,上颔齿24枚;背鳞通身23行,腹鳞150枚,尾下鳞55枚;尾长与体长之比为0.203。至此共有4种脊蛇分布于湖南省。此外,本文还报道了棕脊蛇(A. rufescens)1号雄性地模标本(CIB 119042),该标本鼻间鳞沟长于前额鳞沟;背鳞通身23行,腹鳞153枚,尾下鳞62枚;尾长与体长之比0.201。分子系统发育结果显示,棕脊蛇种组各支系的系统地位还需进一步研究厘定。 相似文献
995.
为了培养学生的自主学习能力和实践创新能力,按照工程教育专业认证要求基于成果导向教育(outcome based education, OBE)理念设计课程教学,将制药工程微生物学实验课实验教学项目设置成入门、进阶和自主3种项目等级。实验项目内容由浅入深、逐级递进、层层相关,教学过程以学生为中心,并结合线上教学手段和竞赛机制的支持。实践结果表明,经过项目化教学改革,在教师教学和学生学习成效两个方面均得到明显提升,学生在论文撰写能力、动手能力等方面也有了明显的进步,值得后续进一步总结和推广。 相似文献
996.
We investigated emotional intimacy with nature and life, and intellectual interest in life among South Korean pre-service teachers (N = 114) training in biology education, analysing the differences between these two constructs as well as their relationship to environmental behaviour and sensitivity. In addition, differences in the respondents’ experiences of nature, concerns about environmental problems and willingness to perform environmental education were explored. Four groups of pre-service biology teachers, categorised by the two investigated personal variables, showed different responses for the environment-related characteristics and other variables. Our results suggest that biology teachers should have higher emotional and intellectual interest in nature and life, and a balance between emotional intimacy with nature and life, and intellectual interest in life is needed to prepare them. 相似文献
997.
Timing of precipitation in an arid environment: Effects on population performance of a large herbivore 下载免费PDF全文
Levi J. Heffelfinger Kelley M. Stewart Anthony P. Bush James S. Sedinger Neal W. Darby Vernon C. Bleich 《Ecology and evolution》2018,8(6):3354-3366
Climate models predict that shifts in temperature and precipitation patterns are likely to occur across the globe. Changing climate will likely have strong effects on arid environments as a result of increased temperatures, increasing frequency and intensity of droughts, and less consistent pulses of rainfall. Therefore, understanding the link between patterns of precipitation, temperature, and population performance of species occupying these environments will continue to increase in importance as climatic shifts occur within these natural ecosystems. We sought to evaluate how individual, maternal, population, and environmental, particularly temperature and precipitation, level factors influence population performance of a large herbivore in an arid environment. We used mule deer (Odocoileus hemionus) as a representative species and quantified juvenile survival to test hypotheses about effects of environmental factors on population performance. Precipitation events occurring in mid‐ to late‐pregnancy (January–April) leading to spring green‐up, as indexed by normalized difference in vegetation index, had the strongest positive effect on juvenile survival and recruitment. In addition, larger neonates had an increased probability of survival. Our findings indicate that timing and amount of precipitation prior to parturition have strong influences on maternal nutritional condition, which was passed on to young. These results have important implications for understanding how animal populations may benefit from timing of precipitation during spring and prior to parturition, especially in arid environments. 相似文献
998.
Front Cover: Spectrally encoded coherence tomography and reflectometry: Simultaneous en face and cross‐sectional imaging at 2 gigapixels per second (J. Biophotonics 4/2018) 下载免费PDF全文
SECTR is a novel multimodal imaging platform for combined volumetric optical coherence tomography (OCT) and en face spectrally encoded reflectometry (SER). The authors demonstrate three‐dimensional motion‐tracking with millisecond temporal and micron spatial resolution using complementary data from OCT and SER, and preliminary algorithms and results showing real‐time image aiming and multi‐volumetric mosaicking for reconstruction of wide‐field composites. The image shows a noninvasively imaged nine‐field mosaic of in vivo human retina and depth‐resolved visualization of tissue microstructures. Further details can be found in the article by Mohamed T. El‐Haddad, Ivan Bozic, and Yuankai K. Tao ( e201700268 )
999.
W.F. Theeuwes H.R. Gosker R.C.J. Langen N.A.M. Pansters A.M.W.J. Schols A.H.V. Remels 《生物化学与生物物理学报:疾病的分子基础》2018,1864(9):2913-2926
Background
Mitochondrial biogenesis is crucial for myogenic differentiation and regeneration of skeletal muscle tissue and is tightly controlled by the peroxisome proliferator-activated receptor-γ co-activator 1 (PGC-1) signaling network. In the present study, we hypothesized that inactivation of glycogen synthase kinase (GSK)-3β, previously suggested to interfere with PGC-1 in non-muscle cells, potentiates PGC-1 signaling and the development of mitochondrial biogenesis during myogenesis, ultimately resulting in an enhanced myotube oxidative capacity.Methods
GSK-3β was inactivated genetically or pharmacologically during myogenic differentiation of C2C12 muscle cells. In addition, m. gastrocnemius tissue was collected from wild-type and muscle-specific GSK-3β knock-out (KO) mice at different time-points during the reloading/regeneration phase following a 14-day hind-limb suspension period. Subsequently, expression levels of constituents of the PGC-1 signaling network as well as key parameters of mitochondrial oxidative metabolism were investigated.Results
In vitro, both knock-down as well as pharmacological inhibition of GSK-3β not only increased expression levels of important constituents of the PGC-1 signaling network, but also potentiated myogenic differentiation-associated increases in mitochondrial respiration, mitochondrial DNA copy number, oxidative phosphorylation (OXPHOS) protein abundance and the activity of key enzymes involved in the Krebs cycle and fatty acid β-oxidation. In addition, GSK-3β KO animals showed augmented reloading-induced increases in skeletal muscle gene expression of constituents of the PGC-1 signaling network as well as sub-units of OXPHOS complexes compared to wild-type animals.Conclusion
Inactivation of GSK-3β stimulates activation of PGC-1 signaling and mitochondrial biogenesis during myogenic differentiation and reloading of the skeletal musculature. 相似文献1000.
Milan Höfer Klaas Nicolay George Robillard 《Journal of bioenergetics and biomembranes》1985,17(3):175-182
The electrochemical gradient of protons,
, was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH0 range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP+) for negative above pH0 4.5, and thiocyanate (SCN–) for positive below pH0 4.5. The chemical gradient of H+ was determined by measuring the chemical shift of intracellular Pi by31P-NMR at given pH0 values. The values of pHi increased almost linearly from 7.3 at pH0 3 to 7.8 at pH0 8.5. In the physiological pH0 range from 3.5 to 6,
was fairly constant at values between 17–18 KJ mol–1, gradually decreasing at pH0 above 6. In deenergized cells, the intracellular pHi decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH0 4.5 or 7.5. There was no membrane potential detectable in deenergized cells. 相似文献