全文获取类型
收费全文 | 4760篇 |
免费 | 454篇 |
国内免费 | 351篇 |
出版年
2024年 | 14篇 |
2023年 | 74篇 |
2022年 | 121篇 |
2021年 | 256篇 |
2020年 | 175篇 |
2019年 | 258篇 |
2018年 | 221篇 |
2017年 | 139篇 |
2016年 | 240篇 |
2015年 | 353篇 |
2014年 | 342篇 |
2013年 | 360篇 |
2012年 | 430篇 |
2011年 | 362篇 |
2010年 | 259篇 |
2009年 | 230篇 |
2008年 | 255篇 |
2007年 | 231篇 |
2006年 | 193篇 |
2005年 | 138篇 |
2004年 | 126篇 |
2003年 | 129篇 |
2002年 | 97篇 |
2001年 | 87篇 |
2000年 | 57篇 |
1999年 | 73篇 |
1998年 | 42篇 |
1997年 | 35篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有5565条查询结果,搜索用时 93 毫秒
941.
942.
Liyuan Tian Xiaojie Wu Yanli Lin Zhuguo Liu Fuyin Xiong Zhengbin Han Yanrong Zhou Qiangcheng Zeng Yumin Wang Jixian Deng Hongxing Chen 《Molecular reproduction and development》2009,76(7):656-664
Members of the super‐class of zinc finger proteins are key regulators in early embryogenesis. Utilizing in silico mining of EST Databases for pre‐implantation Embryo‐Specific Zinc Finger Protein Genes, we characterized a novel zygotic mouse gene—tripartite motif family‐like 1 (TRIML1), which expresses in embryo before implantation. Knocking down of TRIML1 resulted in the fewer cell number of blastocysts and failture to give rise to neonates after embryo transfer. The binding partner of TRIML1, Ubiquitin‐specific protease 5 (USP5), was identified by yeast two‐hybrid screening assay. The interaction was confirmed by GST pull‐down and coimmunoprecipitation analysis. The role of TRIML1 in ubiquitin pathway during the development stage of mouse blastocyst was further discussed. Mol. Reprod. Dev. 76: 656–664, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
943.
Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall 总被引:6,自引:0,他引:6
To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl2 exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated
by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated
Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM
SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased
Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect
on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose
content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of
Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible
for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing
pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd
accumulation in soluble fraction of leaves. 相似文献
944.
Cadmium (Cd) is toxic to crown roots (CR), which are essential for maintaining normal growth and development in rice seedlings.
Nitric oxide (NO) is an important signaling molecule that plays a pivotal role in plant root organogenesis. Here, the effects
of Cd on endogenous NO content and root growth conditions were studied in rice seedlings. Results showed that similar to the
NO scavenger, cPTIO, Cd significantly decreased endogenous NO content and CR number in rice seedlings, and these decreases
were recoverable with the application of sodium nitroprusside (SNP, a NO donor). Microscopic analysis of root collars revealed
that treatment with Cd and cPTIO inhibited CR primordia initiation. In contrast, although SNP partially recovered Cd-caused
inhibition of CR elongation, treatment with cPTIO had no effect on CR elongation. l-NMMA, a widely used nitric oxide synthase (NOS) inhibitor, decreased endogenous NO content and CR number significantly, while
tungstate, a nitrate reductase (NR) inhibitor, had no effect on endogenous NO content and CR number. Moreover, enzyme activity
assays indicated that treatment with SNP inhibited NOS activity significantly, but had no effect on NR activity. All these
results support the conclusions that a critical endogenous NO concentration is indispensable for rice CR primordia initiation
rather than elongation, NOS is the main source for endogenous NO generation, and Cd decreases CR number by inhibiting NOS
activity and thus decreasing endogenous NO content in rice seedlings. 相似文献
945.
Zheng-Mei Xiong Kaori Kitagawa Yuji Nishiuchi Terutoshi Kimura Tomoyuki Nakamura Chiyoko Inagaki 《Life sciences》2009,84(5-6):132-138
AimsWe previously reported that the neurotoxicity of amyloid β protein (Aβ1–42, 10 nM) was blocked by an Aβ-derived tripeptide, Aβ32–34 (Ile-Gly-Leu, IGL), suggesting that IGL may be a lead compound in the design of Aβ antagonists. In the present study, three stable forms of IGL peptide with acetylation of its N-terminal and/or amidation of its C-terminal (acetyl-IGL, IGL-NH2 and acetyl-IGL-NH2) were synthesized and examined for their effects on Aβ-induced neurotoxicity.Main methodsPhosphatidylinositol 4-kinase type II (PI4KII) activity was measured using recombinant human PI4KIIα kinase and cell viability was assessed in primary cultured hippocampal neurons. To test effects in vivo, 1.5 μl of 100 nM Aβ and/or 100 nM acetyl-IGL was injected into the hippocampal CA1 region of right hemisphere in transgenic mice expressing V337M human tau protein. Four weeks later, behavior performance in the Morris water maze was tested and after another 2 weeks, sections of brain were prepared for immunohistochemistry.Key findingsAmong the three modified tripeptides, acetyl-IGL attenuated the Aβ-induced inhibition of PI4KII activity as well as enhancement of glutamate neurotoxicity in primary cultured rat hippocampal neurons. Injection of Aβ into the hippocampus of mice impaired spatial memory and increased the number of degenerating neurons in bilateral hippocampal regions. Co-injection of acetyl-IGL prevented the learning impairment as well as the neuronal degeneration induced by Aβ.SignificanceThese results suggest that a modified tripeptide, acetyl-IGL, may be effective in the treatment of Alzheimer's disease. 相似文献
946.
Yiping Zhu Kun Xiao Lanping Ma Bin Xiong Yan Fu Haiping Yu Wei Wang Xin Wang Dingyu Hu Hongli Peng Jingya Li Qi Gong Qian Chai Xican Tang Haiyan Zhang Jia Li Jingkang Shen 《Bioorganic & medicinal chemistry》2009,17(4):1600-1613
To explore novel effective drugs for the treatment of Alzheimer’s disease (AD), a series of dual inhibitors of acetylcholineterase (AChE) and β-secretase (BACE-1) were designed based on the multi-target-directed ligands strategy. Among them, inhibitor 28 exhibited good dual potency in enzyme inhibitory potency assay (BACE-1: IC50 = 0.567 μM; AChE: IC50 = 1.83 μM), and also showed excellent inhibitory effects on Aβ production of APP transfected HEK293 cells (IC50 = 98.7 nM) and mild protective effect against hydrogen peroxide (H2O2)-induced PC12 cell injury. Encouragingly, intracerebroventricular injection of 28 into amyloid precursor protein (APP) transgenic mice caused a 29% reduction of Aβ1–40 production. Therefore, 28 was demonstrated as a good lead compound for the further study and more importantly, the strategy of AChE and BACE-1 dual inhibitors might be a promising direction for developing novel drugs for AD patients. 相似文献
947.
Bacterial decolorization and degradation of the reactive dye Reactive Red 180 by Citrobacter sp. CK3
Hui Wang Jian Qiang Su Xiao Wei Zheng Yun Tian Xiao Jing Xiong Tian Ling Zheng 《International biodeterioration & biodegradation》2009,63(4):395-399
A bacterial strain, CK3, with remarkable ability to decolorize the reactive textile dye Reactive Red 180, was isolated from the activated sludge collected from a textile mill. Phenotypic characterization and phylogenetic analysis of the 16S rDNA sequence indicated that the bacterial strain belonged to the genus Citrobacter. Bacterial isolate CK3 showed a strong ability to decolorize various reactive textile dyes, including both azo and anthraquinone dyes. Anaerobic conditions with 4 g l?1 glucose, pH = 7.0 and 32 °C were considered to be the optimum decolorizing conditions. Citrobacter sp. CK3 grew well in a high concentration of dye (200 mg l?1), resulting in approximately 95% decolorization extent in 36 h, and could tolerate up to 1000 mg l?1 of dye. UV–vis analyses and colorless bacterial cells suggested that Citrobacter sp. CK3 exhibited decolorizing activity through biodegradation, rather than inactive surface adsorption. It is the first time that a bacterial strain of Citrobacter sp. has been reported with decolorizing ability against both azo and anthraquinone dyes. High decolorization extent and facile conditions show the potential for this bacterial strain to be used in the biological treatment of dyeing mill effluents. 相似文献
948.
"现代生态学讲座"系列会议是由国内外华人生态学家联合发起、为加强现代生态学的新理论、新观点、新方法和热点问题的交流与合作的国际会议.总结了2009年6月27~29日在兰州大学举行的第五届现代生态学讲座国际会议的全部二十五场报告,围绕"宏观生态学和可持续发展科学"的会议主题,分别从森林生态学、草地生态学、全球变化生态学、根际和土壤生态学、分子和行为生态学以及农业生态学等角度进行了分类总结.全部报告可归纳为"生态系统服务功能的物质基础"和"生态系统服务的生态学机制"两个大的基础理论问题,而解决问题的途径必须在人类-自然耦合生态系统的大框架下进行探索.对该会议的进一步改善提出了一些建议. 相似文献
949.
Feng Wang Xue-Rong Xiong Chun-Zhao Liu 《In vitro cellular & developmental biology. Plant》2009,45(3):342-349
With rapid economic development, energy consumption in China has tripled in the past 20 yr, exceeding 2.4 billion tons of
standard coal in 2006. The search for new green energy as substitutes for the nonrenewable energy resources has become an
urgent task. China has a variety of climates and is rich in potential biofuel plant species. Corn and cassava are used as
the main raw materials for bioethanol production in China. At the end of 2005, bioethanol productivity had increased to 1.02
million tons produced by four companies, and bioethanol-blended petrol accounted for 20% of the total petrol consumption in
China. According to the Mid- and Long-term Development Plan for Renewable Energy, the consumption of biodiesel in China will
reach 0.2 million tons in 2010 and 2.0 million tons in 2020. This review is intended to provide an introduction to the distribution
and development of biofuel crops and biofuel industry in China. 相似文献