全文获取类型
收费全文 | 114006篇 |
免费 | 1791篇 |
国内免费 | 1758篇 |
出版年
2024年 | 54篇 |
2023年 | 295篇 |
2022年 | 636篇 |
2021年 | 1029篇 |
2020年 | 676篇 |
2019年 | 907篇 |
2018年 | 12489篇 |
2017年 | 11133篇 |
2016年 | 8251篇 |
2015年 | 1908篇 |
2014年 | 1789篇 |
2013年 | 2042篇 |
2012年 | 6079篇 |
2011年 | 14433篇 |
2010年 | 12870篇 |
2009年 | 9030篇 |
2008年 | 10693篇 |
2007年 | 12189篇 |
2006年 | 1095篇 |
2005年 | 1218篇 |
2004年 | 1578篇 |
2003年 | 1532篇 |
2002年 | 1243篇 |
2001年 | 561篇 |
2000年 | 479篇 |
1999年 | 305篇 |
1998年 | 183篇 |
1997年 | 182篇 |
1996年 | 192篇 |
1995年 | 162篇 |
1994年 | 142篇 |
1993年 | 131篇 |
1992年 | 171篇 |
1991年 | 187篇 |
1990年 | 131篇 |
1989年 | 104篇 |
1988年 | 115篇 |
1987年 | 110篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 57篇 |
1983年 | 70篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1975年 | 34篇 |
1972年 | 258篇 |
1971年 | 292篇 |
1962年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Michael Denker Alexa Riehle Markus Diesmann Sonja Grün 《Journal of computational neuroscience》2010,29(3):599-613
The hypothesis that cortical networks employ the coordinated activity of groups of neurons, termed assemblies, to process
information is debated. Results from multiple single-unit recordings are not conclusive because of the dramatic undersampling
of the system. However, the local field potential (LFP) is a mesoscopic signal reflecting synchronized network activity. This
raises the question whether the LFP can be employed to overcome the problem of undersampling. In a recent study in the motor
cortex of the awake behaving monkey based on the locking of coincidences to the LFP we determined a lower bound for the fraction
of spike coincidences originating from assembly activation. This quantity together with the locking of single spikes leads
to a lower bound for the fraction of spikes originating from any assembly activity. Here we derive a statistical method to
estimate the fraction of spike synchrony caused by assemblies—not its lower bound—from the spike data alone. A joint spike
and LFP surrogate data model demonstrates consistency of results and the sensitivity of the method. Combining spike and LFP
signals, we obtain an estimate of the fraction of spikes resulting from assemblies in the experimental data. 相似文献
982.
983.
A strain of canine parvovirus (CPV) was isolated from feces of an ill puppy in an animal hospital in Wuhan, China. It was designated as CPV/WH02/06. This isolate was identified as serotype CPV-2a by the hemagglutination test, CPV Ag detection strip, electron microscopy, and PCR. The vp2 gene was cloned and sequenced and assigned GenBank accession number EU377537. A 1242 bp segment of the 5' region of the vp2 gene was cloned and inserted into the binary vector pBI121 and used for Agrobacterium-mediated tobacco transformation. Transgenic tobacco plants were selected on MS medium supplemented with 100 μg/mL kanamycin and 100 μg/mL timentin. Integration of the vp2 gene into the tobacco genome was confirmed by PCR using T1 progeny plants, and the expression of the VP2 protein was confirmed by Western blotting. 相似文献
984.
985.
Current knowledge of microbial community structures in landfills and its cover soils 总被引:2,自引:0,他引:2
Semrau JD 《Applied microbiology and biotechnology》2011,89(4):961-969
Landfills are a vital component of our waste handling processes. Our lack of knowledge on the microbial processes in these
systems, however, hampers our ability to design the next generation of landfills that: (1) enhance the rate and extent of
waste decomposition, (2) produce byproducts of some value (e.g., methane that can be used for energy generation), and, (3)
minimize their overall impact on driving climate change through the emission of greenhouse gases. In this review, the current
state of knowledge the microbial community structure and activity in both the refuse and overlying cover soils is discussed,
and suggestions provided for future research in this critical aspect of our infrastructure. 相似文献
986.
Nostoc flagelliforme, which is distributed on arid and semi-arid steppes of northwestern parts of China, has attracted increasing interest for
its stress tolerance. In order to gain more insight into the genetic background of N. flagelliforme, we sequenced its partial genomic DNA for similarity analyses against current public databases, followed by phylogenetic
comparison of N. flagelliforme and the potentially related species deduced from the similarity analyses. Approximately 430 kb genomic sequence (~5% of genome
as a rough estimate) was determined from 106 distinct genomic clones. Nucleotide BLAST showed that ~23.1% of the partial genomic
sequence was similar to N. punctiforme genomic DNA and ~12.4% to its plasmid DNA. Similar protein search by online FASTA-protein program showed 46.2% of the similar
proteins had their corresponding orthologs in N. punctiforme genome. Furthermore, phylogenetic comparison based on 16S rRNA sequences showed N. flagelliforme and N. punctiforme clustered closer among the deduced related species. These results indicated that N. punctiforme might also be potentially close neighbor species of N. flagelliforme, in addition to the formerly regarded close neighbor species N. commune and N. sphaeroids. In general, these data enriched our recognition of the evolutionary relationship between N. flagelliforme and other Nostoc species, especially N. punctiforme. 相似文献
987.
988.
It is well-known that there is a large amount of antimicrobial peptides in amphibian skins but few antimicrobial peptides are found in amphibian brains. Twenty-two and four antimicrobial peptides were purified and characterized from the brain homogenate of Bombina maxima and B. microdeladigitora, respectively. One hundred fifty-eight cDNA clones encoding 79 antimicrobial peptides were isolated from brain cDNA libraries of B. maxima and B. microdeladigitora. These antimicrobial peptides belong to two peptide groups (maximin and maximin-H). Twenty of them are identical to previously reported antimicrobial peptides (maximin 1-8, 10, 11, maximin H1, 3-5, 7, 9, 10, 12, 15, 16) from B. maxima skin secretions. Fifty-nine of them are novel antimicrobial peptides. Some of these antimicrobial peptides showed strong antimicrobial activities against tested microorganism strains including Gram-positive and -negative bacteria and fungi. The current diversity in peptide coding cDNA sequences is, to our knowledge, the most extreme yet described for any animal brains. The extreme diversity may give rise to interest to prospect the actual functions of antimicrobial peptides in amphibian brains. 相似文献
989.
虹鳟生长激素cDNA在酵母中的表达 总被引:10,自引:0,他引:10
采用聚合酶链式反应( P C R) 技术对虹鳟生长激素c D N A 进行改造。将改造后的基因克隆到含酵母 P G K 启动子的大肠杆菌酵母穿梭质粒p M A91 ,转化酿酒酵母 Y33 ,构建表达鱼生长激素的酵母工程菌 Y33(p M Ar G H16) ,并在酵母中获得表达,表达量约占细胞可溶性蛋白总量的3 % 。表达产物作为饲料添加剂投喂罗非鱼,具有明显的促进生长作用 相似文献
990.
几种木本植物的N2O释放与某些生理活动的关系 总被引:16,自引:4,他引:16
使用带有开放气路的气体交换测定系统,同步测定了几种针、阔叶树种的光合作用、呼吸作用及气孔导度.结果表明,低光下树木针叶或叶片释放N2O的速率与光合速率无显著相关.伴随根、茎、叶的呼吸,检测到有N2O吸收现象,其通量与温度及呼吸强度呈正相关.气孔导度明显影响N2O的通量,表明气孔可能是木本植物释放N2O的主要途径. 相似文献