全文获取类型
收费全文 | 50883篇 |
免费 | 16838篇 |
国内免费 | 29篇 |
专业分类
67750篇 |
出版年
2023年 | 225篇 |
2022年 | 455篇 |
2021年 | 1063篇 |
2020年 | 2608篇 |
2019年 | 4146篇 |
2018年 | 4511篇 |
2017年 | 4655篇 |
2016年 | 4906篇 |
2015年 | 5170篇 |
2014年 | 5000篇 |
2013年 | 5752篇 |
2012年 | 3650篇 |
2011年 | 3354篇 |
2010年 | 4139篇 |
2009年 | 2805篇 |
2008年 | 2033篇 |
2007年 | 1606篇 |
2006年 | 1503篇 |
2005年 | 1401篇 |
2004年 | 1286篇 |
2003年 | 1129篇 |
2002年 | 1060篇 |
2001年 | 715篇 |
2000年 | 619篇 |
1999年 | 483篇 |
1998年 | 218篇 |
1997年 | 163篇 |
1996年 | 148篇 |
1995年 | 170篇 |
1994年 | 155篇 |
1993年 | 129篇 |
1992年 | 218篇 |
1991年 | 182篇 |
1990年 | 182篇 |
1989年 | 149篇 |
1988年 | 142篇 |
1987年 | 118篇 |
1986年 | 105篇 |
1985年 | 113篇 |
1984年 | 98篇 |
1983年 | 103篇 |
1982年 | 80篇 |
1981年 | 86篇 |
1980年 | 55篇 |
1979年 | 91篇 |
1978年 | 88篇 |
1976年 | 52篇 |
1975年 | 73篇 |
1974年 | 65篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
211.
212.
Organic Solar Cells: Following the Morphology Formation In Situ in Printed Active Layers for Organic Solar Cells (Adv. Energy Mater. 1/2016) 下载免费PDF全文
213.
Zhenwen Cui Zhihong Zhong Yong Yang Baofeng Wang Yuhao Sun Qingfang Sun Guo‐yuan Yang Liuguan Bian 《Journal of biochemical and molecular toxicology》2016,30(8):396-403
Free radical damage caused by ferrous iron is involved in the pathogenesis of secondary brain injury after intracerebral hemorrhage (ICH). NF‐E2‐related factor 2 (Nrf2), a major phase II gene regulator that binds to antioxidant response element, represents an important cellular cytoprotective mechanism against oxidative damage. We hypothesized that Nrf2 might protect astrocytes from damage by Fe2+. Therefore, we examined cytotoxicity in primary astrocytes induced by iron overload and evaluated the effects of Fe2+ on Nrf2 expression. The results demonstrated that 24‐h Fe2+ exposure exerted time‐ and concentration‐dependent cytotoxicity in astrocytes. Furthermore, Fe2+ exposure in astrocytes resulted in time‐ and concentration‐dependent increases in Nrf2 expression, which preceded Fe2+ toxicity. Nrf2‐specific siRNA further knocked down Nrf2 levels, resulting in greater Fe2+‐induced astrocyte cytotoxicity. These data indicate that induction of Nrf2 expression could serve as an adaptive self‐defense mechanism, although it is insufficient to completely protect primary astrocytes from Fe2+‐induced neurotoxicity. 相似文献
214.
We herein report the joint occurrence of an autistic disorder (AD) and X-linked hypophosphatemia. X-linked hypophosphatemia (XLH), an X-linked dominant disorder, is the most common of the inherited renal phosphate wasting disorders. Autism is a pervasive developmental disorder that occurs mainly due to genetic causes. In approximately 6-15% of cases, the autistic phenotype is a part of a broader genetic condition called syndromic autism.Therefore, reports of cases with the joint occurrence of a known genetic syndrome and a diagnosis of ASD by a child psychiatrist are relevant. A joint occurrence does not, however, mean that there is always a causal link between the genetic syndrome and the autistic behavioural phenotype. In this case, there are a number of arguments countering a causal link. 相似文献
215.
Rômulo Sátiro De Medeiros Ana Maria Camêlo Da Silva Francisco De Sousa Ramalho José Eduardo Serrão Paulo Roberto Cecon 《Biocontrol Science and Technology》2004,14(5):487-498
The daily reproductive rate of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) fed with Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) larvae was studied at constant temperatures of 20, 23, 25, 28, 30 and 33±0.2°C, relative humidity of 60±10% and photoperiod of L:D 14:10. Daily reproductive rate of P. nigripinus was affected by age of this predator. Each P. nigrispinus female laid 5.3 (20°C) to 19.9 eggs/day (28°C) which developed into 4.3–16.5 nymphs, respectively. Highest daily reproductive rate of P. nigrispinus was recorded at 28 and 30°C for 5–30-day-old females. This predator showed higher daily reproductive rate than its prey A. argillacea at 25°C. It was also able to reproduce at temperatures from 20 to 33°C with maximum daily reproductive rate between 25 and 30°C. These results are important for optimizing mass rearing of P. nigrispinus in the laboratory. 相似文献
216.
Characterization of phytoplankton assemblages in a tropical coastal environment using Kohonen self‐organizing map 下载免费PDF全文
Isimemen Osemwegie Julie E. Niamien‐Ebrottié Mathieu Y. J. Koné Allassane Ouattara Jean Biemi Barbara Reichert 《African Journal of Ecology》2017,55(4):487-499
This study was aimed at understanding the main abiotic environmental factors controlling the distribution patterns of abundance and composition of phytoplankton (size less than 10 μm) assemblages in the coastal waters of south‐eastern Côte d'Ivoire. Data were collected during two cruises, in January (low‐water period) and October (high‐water period) of 2014. A total of 67 species were identified and assigned to Bacillariophyceae (49%), Cyanophyceae (21%), Chlorophyceae (13%), Euglenophyceae (10%), Dinophyceae (4%) and Chrysophyceae (3%). Three biotic zones (I, IIA and IIB) were distinguishable on a Kohonen self‐organizing map after an unsupervised learning process. The diatom genera Eunotia sp., Navicula sp. and Actinoptychus senarius are significantly associated with I, IIA and IIB biotic zones, respectively. A clear seasonal cum salinity trend was apparent in phytoplankton distribution patterns. Turbidity and nitrate levels were the main abiotic factors controlling phytoplankton distribution in I, the upland tidal regions of the lagoon. In regions along the lagoon–sea continuum, phosphate and turbidity exert the most control during the low‐water season (IIA), while total dissolved solids control phytoplankton distribution during the high‐water season (IIB). These are climate‐sensitive parameters whose concentrations depend on prevailing hydroclimatic processes. Therefore, seasonality can have important consequences on phytoplankton community and inadvertently the productivity of these systems. 相似文献
217.
Background and Aims
Several widespread tree species of temperate forests, such as species of the genus Quercus, produce recalcitrant (desiccation-sensitive) seeds. However, the ecological significance of seed desiccation sensitivity in temperate regions is largely unknown. Do seeds of such species suffer from drying during the period when they remain on the soil, between shedding in autumn and the return of conditions required for germination in spring?Methods
To test this hypothesis, the Mediterranean holm oak (Quercus ilex) forest was used as a model system. The relationships between the climate in winter, the characteristics of microhabitats, acorn morphological traits, and the water status and viability of seeds after winter were then investigated in 42 woodlands sampled over the entire French distribution of the species.Key Results
The percentages of germination and normal seedling development were tightly linked to the water content of seeds after the winter period, revealing that in situ desiccation is a major cause of mortality. The homogeneity of seed response to drying suggests that neither intraspecific genetic variation nor environmental conditions had a significant impact on the level of desiccation sensitivity of seeds. In contrast, the water and viability status of seeds at the time of collection were dramatically influenced by cumulative rainfall and maximum temperatures during winter. A significant effect of shade and of the type of soil cover was also evidenced.Conclusions
The findings establish that seed desiccation sensitivity is a key functional trait which may influence the success of recruitment in temperate recalcitrant seed species. Considering that most models of climate change predict changes in rainfall and temperature in the Mediterranean basin, the present work could help foresee changes in the distribution of Q. ilex and other oak species, and hence plant community alterations. 相似文献218.
219.