全文获取类型
收费全文 | 32812篇 |
免费 | 2953篇 |
国内免费 | 4063篇 |
出版年
2024年 | 55篇 |
2023年 | 438篇 |
2022年 | 619篇 |
2021年 | 1788篇 |
2020年 | 1260篇 |
2019年 | 1588篇 |
2018年 | 1446篇 |
2017年 | 1086篇 |
2016年 | 1419篇 |
2015年 | 2173篇 |
2014年 | 2622篇 |
2013年 | 2752篇 |
2012年 | 3345篇 |
2011年 | 2921篇 |
2010年 | 1896篇 |
2009年 | 1753篇 |
2008年 | 1893篇 |
2007年 | 1722篇 |
2006年 | 1436篇 |
2005年 | 1285篇 |
2004年 | 1044篇 |
2003年 | 927篇 |
2002年 | 764篇 |
2001年 | 544篇 |
2000年 | 446篇 |
1999年 | 462篇 |
1998年 | 292篇 |
1997年 | 250篇 |
1996年 | 231篇 |
1995年 | 189篇 |
1994年 | 162篇 |
1993年 | 124篇 |
1992年 | 136篇 |
1991年 | 123篇 |
1990年 | 114篇 |
1989年 | 98篇 |
1988年 | 77篇 |
1987年 | 59篇 |
1986年 | 47篇 |
1985年 | 58篇 |
1984年 | 23篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 7篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1973年 | 9篇 |
1971年 | 9篇 |
1968年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
21.
22.
23.
Yunhe Meng Xixi Shao Yan Wang Yumei Li Xiaojian Zheng Gongyuan Wei Seon-Won Kim Chonglong Wang 《Biotechnology and bioengineering》2020,117(11):3499-3507
Squalene is a lipophilic and non-volatile triterpene with many industrial applications for food, pharmaceuticals, and cosmetics. Metabolic engineering focused on optimization of the production pathway suffer from little success in improving titers because of a limited space of the cell membrane accommodating the lipophilic product. Extension of cell membrane would be a promising approach to overcome the storage limitation for successful production of squalene. In this study, Escherichia coli was engineered for squalene production by overexpression of some membrane proteins. The highest production of 612 mg/L was observed in the engineered E. coli with overexpression of Tsr, a serine chemoreceptor protein, which induced invagination of inner membrane to form multilayered structure. It was also observed an increase in unsaturated fatty acid in membrane lipids composition, suggesting cellular response to maintain membrane fluidity against squalene accumulation in the engineered strain. This study potentiates the capability of E. coli for squalene production and provides an effective strategy for the enhanced production of such compounds. 相似文献
24.
Xin Deng Guoli Zhang Ling Zhang Yan Feng Zehong Li GuangMou Wu Yuhuan Yue Gensong Li Yu Cao Ping Zhu 《PloS one》2015,10(11)
Non-viral gene delivery system with many advantages has a great potential for the future of gene therapy. One inherent obstacle of such approach is the uptake by endocytosis into vesicular compartments. Receptor-mediated gene delivery method holds promise to overcome this obstacle. In this study, we developed a receptor-mediated gene delivery system based on a combination of the Pseudomonas exotoxin A (PE), which has a receptor binding and membrane translocation domain, and the hyperthermophilic archaeal histone (HPhA), which has the DNA binding ability. First, we constructed and expressed the rPE-HPhA fusion protein. We then examined the cytotoxicity and the DNA binding ability of rPE-HPhA. We further assessed the efficiency of transfection of the pEGF-C1 plasmid DNA to CHO cells by the rPE-HPhA system, in comparison to the cationic liposome method. The results showed that the transfection efficiency of rPE-HPhA was higher than that of cationic liposomes. In addition, the rPE-HPhA gene delivery system is non-specific to DNA sequence, topology or targeted cell type. Thus, the rPE-HPhA system can be used for delivering genes of interest into mammalian cells and has great potential to be applied for gene therapy. 相似文献
25.
Plasmonics - We investigate aluminum nanopatch/nanohole arrays surrounded by a dielectric material on plastic substrates for large area color printing. In this specific arrangement, metallic... 相似文献
26.
Xiao-Long Lin Yan-Min Zhao Li-Ping Yan Wen-Bin Liu Wen-Jun Bu Xin-Hua Wang Chen-Guang Zheng 《Zoologica scripta》2022,51(1):119-132
Evolutionary analysis of Prodiamesinae has long been impeded by lack of information, and its phylogenetic relationship with Orthocladiinae remains questionable. Here, ten complete mitochondrial genomes (mitogenomes) of Orthocladiinae sensu lato were newly sequenced, including three Prodiamesinae species and seven Orthocladiinae species. Coupled with published mitogenomes, a total of 12 mitogenomes of Orthocladiinae sensu lato were selected for a comparative mitogenomic analysis and phylogenetic reconstruction. Mitogenomes of Orthocladiinae sensu lato are conserved in structure, and all genes arrange the same gene order as the ancestral insect mitogenome. Nucleotide composition is highly biased, and the control region displayed the highest A + T content. All protein-coding genes are under purifying selection, and the ATP8 evolves at the fastest rate. In addition, the mitogenomes of Orthocladiinae sensu lato are highly conserved, and they are practically useful for phylogenetic inference, suggesting a re-classification of Orthocladiinae by sinking Prodiamesinae as a subgroup of Orthocladiinae. 相似文献
27.
由于圆锥角膜疾病导致越来越多的人患有近视,常见的矫正方法有佩戴近视眼镜、隐形眼镜等.随着科技的进步,利用光对近视等眼科疾病进行屈光矫正已经成为当前临床中常用的方法.使用光诱导角膜胶原蛋白发生交联,从而达到治疗圆锥角膜疾病、提高患者视力水平的目的,这是一种新型的光治疗眼睛疾病的方法.同时这种方法由于无侵入性、对操作者能力依赖性小等优势成为新的研究热点.本文阐述光诱导角膜交联的基本原理,并介绍其发展历程,分析现有的各种交联方法和角膜检测技术的原理,并对现有交联方法和检测方法的优缺点进行讨论.最后,本文对光诱导角膜交联和检测技术的最新进展进行系统的论述,并对未来的发展趋势进行展望. 相似文献
28.
29.