全文获取类型
收费全文 | 1851篇 |
免费 | 97篇 |
专业分类
1948篇 |
出版年
2024年 | 6篇 |
2023年 | 12篇 |
2022年 | 47篇 |
2021年 | 70篇 |
2020年 | 43篇 |
2019年 | 47篇 |
2018年 | 72篇 |
2017年 | 59篇 |
2016年 | 80篇 |
2015年 | 106篇 |
2014年 | 105篇 |
2013年 | 119篇 |
2012年 | 143篇 |
2011年 | 146篇 |
2010年 | 88篇 |
2009年 | 79篇 |
2008年 | 82篇 |
2007年 | 100篇 |
2006年 | 107篇 |
2005年 | 77篇 |
2004年 | 70篇 |
2003年 | 49篇 |
2002年 | 49篇 |
2001年 | 11篇 |
2000年 | 18篇 |
1999年 | 7篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有1948条查询结果,搜索用时 15 毫秒
1.
2.
Swida A Czarna M Woyda-Płoszczyca A Kicinska A Sluse FE Jarmuszkiewicz W 《Journal of bioenergetics and biomembranes》2007,39(1):109-115
A profile of free fatty acid (FFA) specificity in Acanthamoeba castellanii mitochondrial uncoupling is described. The FFA uncoupling specificity was observed as different abilities to stimulate resting
respiration, to decrease resting membrane potential, and to decrease oxidative phosphorylation efficiency. Tested unsaturated
FFA (C18–20) were more effective as uncouplers and protonophores when compared to tested saturated FFA (C8–18), with palmitic
acid (C16:0) as the most active. As FFA efficiency in mitochondrial uncoupling is related to physiological changes of fatty
acid composition (and thereby FFA availability) during growth of amoeba cells, it could be a way to regulate the activity
of an uncoupling protein and thereby the efficiency of oxidative phosphorylation during a cell life of this unicellular organism.
Aleksandra Swida and Małgorzata Czarna contributed equally to this work. 相似文献
3.
4.
Aleksandra Szczepankiewicz Anna Bręborowicz Paulina Sobkowiak Anna Popiel 《Clinical and molecular allergy : CMA》2010,8(1):1-6
Background
Histamine-metabolizing enzymes (N-methyltransferase and amiloride binding protein 1) are responsible for histamine degradation, a biogenic amine involved in allergic inflammation. Genetic variants of HNMT and ABP1 genes were found to be associated with altered enzyme activity. We hypothesized that alleles leading to decreased enzyme activity and, therefore, decreased inactivation of histamine may be responsible for altered susceptibility to asthma.Methods
The aim of this study was to analyze polymorphisms within the HNMT and ABP1 genes in the group of 149 asthmatic children and in the group of 156 healthy children. The genetic analysis involved four polymorphisms of the HNMT gene: rs2071048 (-1637T/C), rs11569723 (-411C/T), rs1801105 (Thr105Ile = 314C/T) and rs1050891 (1097A/T) and rs1049793 (His645Asp) polymorphism for ABP1 gene. Genotyping was performed with use of PCR-RFLP. Statistical analysis was performed using Statistica software; linkage disequilibrium analysis was done with use of Haploview software.Results
We found an association of TT genotype and T allele of Thr105Ile polymorphism of HNMT gene with asthma. For other polymorphisms for HNMT and ABP1 genes, we have not observed relationship with asthma although the statistical power for some SNPs might not have been sufficient to detect an association. In linkage disequilibrium analysis, moderate linkage was found between -1637C/T and -411C/T polymorphisms of HNMT gene. However, no significant differences in haplotype frequencies were found between the group of the patients and the control group.Conclusions
Our results indicate modifying influence of histamine N-methyltransferase functional polymorphism on the risk of asthma. The other HNMT polymorphisms and ABP1 functional polymorphism seem unlikely to affect the risk of asthma. 相似文献5.
6.
Olivier Véron Jean-Philippe Blondeau Michał Grabiec Aleksandra Wolak Krzystof Dzierżęga Nadège Ollier François Goutaland Mohamed Chérif Sow Stéphane Pellerin Nadia Pellerin 《Plasmonics (Norwell, Mass.)》2013,8(1):93-103
Silver-exchanged silicate glass has been irradiated by 532-nm pulsed Nd:YAG laser in order to locally form metallic nanoparticles. The particular interest of this process is to locally control the silver nanoparticles (NPs) growth. Silver ions are exchanged with sodium ions near the glass surface after dumping of a silicate glass few minutes in silver and sodium nitrates molten salt. A low-energy density laser exposure (0.239 J/cm2) chosen at the ablation threshold allows to observe the kinetics of the silver NPs growth according to the increasing shots number. An on-line optical measurement is carried out after each shot to identify the most important steps during the irradiation process. According to this measurement, we have determined four steps highlighted by UV/Visible spectrophotometry and we have identified the influence of located surface plasmon resonance. Three combined material analysis methods were used to understand the glass/laser interaction mechanism: we outlined the material volume variations by profilometric method, the element distribution by scanning electron microscopy and finally the structural distribution of the irradiated region by a local infrared investigation. The trend for NPs formation revealed by the UV/Visible spectrophotometry is thus explained by the formation of a ring expelled from a central hole. We highlight that the on-line extinction measurement can be used to data process the NPs evolution. 相似文献
7.
Aleksandra Włodarczyk Claudia Elsner Alexandra Schmitterer Annie E. Wertz 《Evolution and human behavior》2018,39(6):583-593
Plants produce dangerous chemical and physical defenses that have shaped the physiology and behavior of the herbivorous predators that feed on them. Here we explore the impact that these plant defenses may have had on humans by testing infants' responses to plants with and without sharp-looking thorns. To do this, we presented 8- to 18-month-olds with plants and control stimuli and measured their initial reaching behavior and subsequent object exploration behavior. Half of the stimuli had sharp-looking thorns or pointed parts while the other half did not. We found that infants exhibited both an initial reluctance to touch and minimized subsequent physical contact with plants compared to other object types. Further, infants treated all plants as potentially dangerous, whether or not they possessed sharp-looking thorns. These results reveal novel dimensions of a behavioral avoidance strategy in infancy that would mitigate potential harm from plants. 相似文献
8.
9.
Marek Gołębiowski Magdalena Cerkowniak Aleksandra Ostachowska Aleksandra M. Naczk Mieczysława I. Boguś Piotr Stepnowski 《化学与生物多样性》2016,13(8):982-989
Conidiobolus coronatus is an entomopathogenic fungus which has a potential as a biological control agent of insects. The cuticular and internal lipid composition of infected and noninfected Tettigonia viridissima males were analyzed by GC/MS. A total of 49 compounds were identified in the infected and noninfected males, including fatty acids, fatty acid methyl esters (FAMEs), n‐alkanes, alcohols, sterols, and other organic compounds. The most abundant components of the cuticular and internal lipids of the insects were fatty acids. After exposure to C. coronatus, the cuticular lipids of the T. viridissima males contained 17 free fatty acids from C(8) to C(22), while the cuticular lipids of the noninfected insects contained only 15 fatty acids from C(12) to C(24). The cuticular and internal lipids of both the infected and the noninfected males also contained five FAMEs from C(15) to C(19), seven n‐alkanes from C(25) to C(34), five alcohols from C(16) to C(25), five sterols, and the following six other organic compounds: azelaic acid, phenylacetic acid, glutaric acid, benzoic acid, sebacic acid, and glycerol. The compounds which were present only in the cuticular lipids of the infected males could be due to fungal infection. 相似文献
10.
Decoding of the UGA selenocysteine codon for selenoprotein translation requires the SECIS element, a stem-loop motif in the 3'-UTR of the mRNA carrying short or large apical loops. In previous structural studies, we derived a secondary structure model for SECIS RNAs with short apical loops. Work from others proposed that intra-apical loop base pairing can occur in those SECIS that possess large apical loops, yielding form 2 SECIS versus the form 1 with short loops. In this work, SECIS elements arising from eight different selenoprotein mRNAs were assayed by enzymatic and/or chemical probing showing that seven can adopt form 2. Further, database searches led to the discovery in drosophila and zebrafish of SECIS elements in the selenophosphate synthetase 2, type 1 deiodinase and SelW mRNAs. Alignment of SECIS sequences not only highlighted the predominance of form 2 but also made it possible to classify the SECIS elements according to the type of selenoprotein mRNA they belong to. Interestingly, the alignment revealed that an unpaired adenine, previously thought to be invariant, is replaced by a guanine in four SECIS elements. Tested in vivo, neither the A to G nor the A to U changes at this position greatly affected the activity while the most detrimental effect was provided by a C. The putative contribution of the various SECIS motifs to function and ligand binding is discussed. 相似文献