全文获取类型
收费全文 | 35610篇 |
免费 | 3237篇 |
国内免费 | 5268篇 |
专业分类
44115篇 |
出版年
2024年 | 122篇 |
2023年 | 505篇 |
2022年 | 1175篇 |
2021年 | 1881篇 |
2020年 | 1366篇 |
2019年 | 1743篇 |
2018年 | 1593篇 |
2017年 | 1230篇 |
2016年 | 1666篇 |
2015年 | 2417篇 |
2014年 | 2916篇 |
2013年 | 3011篇 |
2012年 | 3639篇 |
2011年 | 3295篇 |
2010年 | 2111篇 |
2009年 | 1877篇 |
2008年 | 2107篇 |
2007年 | 1894篇 |
2006年 | 1655篇 |
2005年 | 1356篇 |
2004年 | 1109篇 |
2003年 | 1040篇 |
2002年 | 872篇 |
2001年 | 547篇 |
2000年 | 474篇 |
1999年 | 436篇 |
1998年 | 283篇 |
1997年 | 259篇 |
1996年 | 231篇 |
1995年 | 183篇 |
1994年 | 179篇 |
1993年 | 123篇 |
1992年 | 132篇 |
1991年 | 104篇 |
1990年 | 78篇 |
1989年 | 76篇 |
1988年 | 61篇 |
1987年 | 40篇 |
1986年 | 51篇 |
1985年 | 60篇 |
1984年 | 23篇 |
1983年 | 29篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Effects of long-term environmental flow releases on the restoration and preservation of Baiyangdian Lake,a regulated Chinese freshwater lake 总被引:1,自引:0,他引:1
Environmental flow releases provide the water regime required to maintain the aquatic ecosystem health, which are subject to intensive human disturbance. We used decades of data to determine whether the long-term use of flow releases had successfully restored China’s Baiyangdian Lake ecosystem. We used fuzzy-logic inference and field data to compare the water level regime, water quality, and ecological variables before and after the releases. Critical components of the water level regime, including the annual mean, the 7-day low, and the 30-day low and high water levels, differed significantly before and after the releases. The releases slightly improved water quality compared with the pre-1997 level, except in 2003. The reed area and fish yield have been greatly increased by these flows since 1997, but changes in the reed yield and fish species were not significant. We discuss the advantages and drawbacks of the current environmental flow releases for Baiyangdian Lake, and propose that the release patterns have adversely affected the lake’s natural level regime from an ecological perspective. Therefore, we suggest that accounting for recent research on environmental flows, including the implementation of adaptive management, will be required to implement more sustainable and ecologically effective releases of environmental flows. 相似文献
982.
983.
984.
We address how spatial frequency selectivity arises in Macaque primary visual cortex (V1) by simulating V1 with a large-scale
network model consisting of O(104) excitatory and inhibitory integrate-and-fire neurons with realistic synaptic conductances. The new model introduces variability
of the widths of subregions in V1 neuron receptive fields. As a consequence different model V1 neurons prefer different spatial
frequencies. The model cortex has distributions of spatial frequency selectivity and of preference that resemble experimental
findings from the real V1. Two main sources of spatial frequency selectivity in the model are the spatial arrangement of feedforward
excitation, and cortical nonlinear suppression, a result of cortical inhibition.
Action Editor: Jonathan D. Victor 相似文献
985.
Huang Z Lin L Gao Y Chen Y Yan X Xing J Hang W 《Molecular & cellular proteomics : MCP》2011,10(10):M111.007922
The purpose of this study was to use metabonomic profiling to identify a potential specific biomarker pattern in urine as a noninvasive bladder cancer (BC) detection strategy. A liquid chromatography-mass spectrometry based method, which utilized both reversed phase liquid chromatography and hydrophilic interaction chromatography separations, was performed, followed by multivariate data analysis to discriminate the global urine profiles of 27 BC patients and 32 healthy controls. Data from both columns were combined, and this combination proved to be effective and reliable for partial least squares-discriminant analysis. Following a critical selection criterion, several metabolites showing significant differences in expression levels were detected. Receiver operating characteristic analysis was used for the evaluation of potential biomarkers. Carnitine C9:1 and component I, were combined as a biomarker pattern, with a sensitivity and specificity up to 92.6% and 96.9%, respectively, for all patients and 90.5% and 96.9%, respectively for low-grade BC patients. Metabolic pathways of component I and carnitine C9:1 are discussed. These results indicate that metabonomics is a practicable tool for BC diagnosis given its high efficacy and economization. The combined biomarker pattern showed better performance than single metabolite in discriminating bladder cancer patients, especially low-grade BC patients, from healthy controls. 相似文献
986.
987.
A biosensor based on bovine serum albumin (BSA) for the detection of lead (Pb(2+)) ion was developed and characterized. BSA was immobilized onto a colloidal Au-modified piezoelectric quartz crystal (PQC) as a biosensor for the detection of Pb(2+) ion by piezoelectric quartz crystal impedance (PQCI). Calibration curves for the quantification of Pb(2+) ion showed excellent linearity throughout the concentration range from 1.0 x 10(-7) to 3.0 x 10(-9)mol/L. The interaction between the Pb(2+) ions and the sensor chip is influenced significantly by the pH of the reaction buffer, and the optimal pH for the experiment was 5.4. Under the optimal conditions, the detection limit of 1.0 x 10(-9)mol/L for Pb(2+) was obtained. Kinetic parameters of the Pb(2+)-BSA interactions were also determined by using this chip. The sensor chip could be regenerated for use by dipping in the ethylenediaminetetraacetic acid (EDTA) solution for approximately 2h, and the chip was used to detect Pb(2+) ion for eight times without obvious signal attenuation. 相似文献
988.
Yuhao Liu Ziyi Wang Chao Ma Zhenquan Wei Kai Chen Chao Wang Chi Zhou Leilei Chen Qingwen Zhang Zhenqiu Chen Wei He Jiake Xu 《Journal of cellular and molecular medicine》2020,24(6):3303-3313
Osteolytic skeletal disorders are caused by an imbalance in the osteoclast and osteoblast function. Suppressing the differentiation and resorptive function of osteoclast is a key strategy for treating osteolytic diseases. Dracorhodin perchlorate (D.P), an active component from dragon blood resin, has been used for facilitating wound healing and anti-cancer treatments. In this study, we determined the effect of D.P on osteoclast differentiation and function. We have found that D.P inhibited RANKL-induced osteoclast formation and resorbed pits of hydroxyapatite-coated plate in a dose-dependent manner. D.P also disrupted the formation of intact actin-rich podosome structures in mature osteoclasts and inhibited osteoclast-specific gene and protein expressions. Further, D.P was able to suppress RANKL-activated JNK, NF-κB and Ca2+ signalling pathways and reduces the expression level of NFATc1 as well as the nucleus translocation of NFATc1. Overall, these results indicated a potential therapeutic effect of D.P on osteoclast-related conditions. 相似文献
989.
990.
The advancement of leaf senescence is accompanied by a reduction in cellular protein content together with the induction of specific proteins which are probably involved in the process. In the present study, with parsley, we followed the changes in the levels of proteins functionally and immunogenically related to pathogenesis‐related proteins during both senescence of detached leaves and natural senescence of attached leaves. Both chitinase activity and protein level were found to be induced during senescence, as was the level of two other proteins immunologically related to β‐1,3‐glucanase and P4 pathogenesis‐related proteins of citrus and tomato, respectively. A high correlation between the advancement of senescence and the induction of these proteins was demonstrated. Treatments with CO2 or gibberellic acid, which retard senescence, reduced both chitinase activity and the level of the pathogenesis‐related proteins, whereas enhancement of senescence with ethylene induced them further. The induction of pathogenesis‐related proteins during senescence suggests that these proteins may have a primary role in this process. 相似文献