全文获取类型
收费全文 | 12980篇 |
免费 | 898篇 |
出版年
2024年 | 16篇 |
2023年 | 96篇 |
2022年 | 96篇 |
2021年 | 199篇 |
2020年 | 169篇 |
2019年 | 215篇 |
2018年 | 421篇 |
2017年 | 415篇 |
2016年 | 565篇 |
2015年 | 757篇 |
2014年 | 742篇 |
2013年 | 1013篇 |
2012年 | 1279篇 |
2011年 | 1157篇 |
2010年 | 664篇 |
2009年 | 535篇 |
2008年 | 768篇 |
2007年 | 715篇 |
2006年 | 704篇 |
2005年 | 601篇 |
2004年 | 589篇 |
2003年 | 526篇 |
2002年 | 474篇 |
2001年 | 122篇 |
2000年 | 112篇 |
1999年 | 96篇 |
1998年 | 69篇 |
1997年 | 48篇 |
1996年 | 55篇 |
1995年 | 51篇 |
1994年 | 30篇 |
1993年 | 39篇 |
1992年 | 48篇 |
1991年 | 42篇 |
1990年 | 43篇 |
1989年 | 37篇 |
1988年 | 35篇 |
1987年 | 21篇 |
1986年 | 32篇 |
1985年 | 35篇 |
1984年 | 40篇 |
1983年 | 20篇 |
1982年 | 24篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 15篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The E. coli dnaY gene encodes an arginine transfer RNA 总被引:21,自引:0,他引:21
132.
J T Lecomte G N La Mar J D Smit K H Winterhalter K M Smith K C Langry H K Leung 《Journal of molecular biology》1987,197(1):101-110
Reconstitution of liver fluke (Dicrocoelium dendriticum) apo-hemoglobin with hemins selectively deuterated at specific positions has permitted the assignment of several heme resonances in the proton nuclear magnetic resonance spectrum of the Met-aquo and Met-cyano forms of the holoprotein. It was established that in the Met-aquo form the meso protons resonate at positions characteristic of a six-co-ordinated in-plane iron. From this, we deduced that the Met-aquo species retains a bound water molecule at pH values as low as 4.5. The orientation of the proximal histidine imidazole ring with respect to the heme group in the cavity was determined through the identification of the heme methyl signals and the analysis of the hyperfine shift pattern in the Met-cyano hemoglobin proton nuclear magnetic resonance spectrum. Compared to sperm whale myoglobin, the heme appears to be rotated by 180 degrees about the alpha, gamma meso-axis. Protein isomers with the heme group in a reversed orientation were not detected, even shortly after reconstitution. In the Met-cyano form, the resonances most affected by the Bohr transition were shown to arise from the heme propionates. 相似文献
133.
A mandible from the Middle Pleistocene Hexian site and its significance in relation to the variability of Asian Homo erectus
下载免费PDF全文
![点击此处可从《American journal of physical anthropology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
134.
Fontán-Lozano A López-Lluch G Delgado-García JM Navas P Carrión AM 《Molecular neurobiology》2008,38(2):167-177
Aging is associated with the decline of cognitive properties. This situation is magnified when neurodegenerative processes
associated with aging appear in human patients. Neuronal synaptic plasticity events underlie cognitive properties in the central
nervous system. Caloric restriction (CR; either a decrease in food intake or an intermittent fasting diet) can extend life
span and increase disease resistance. Recent studies have shown that CR can have profound effects on brain function and vulnerability
to injury and disease. Moreover, CR can stimulate the production of new neurons from stem cells (neurogenesis) and can enhance
synaptic plasticity, which modulate pain sensation, enhance cognitive function, and may increase the ability of the brain
to resist aging. The beneficial effects of CR appear to be the result of a cellular stress response stimulating the production
of proteins that enhance neuronal plasticity and resistance to oxidative and metabolic insults; they include neurotrophic
factors, neurotransmitter receptors, protein chaperones, and mitochondrial biosynthesis regulators. In this review, we will
present and discuss the effect of CR in synaptic processes underlying analgesia and cognitive improvement in healthy, sick,
and aging animals. We will also discuss the possible role of mitochondrial biogenesis induced by CR in regulation of neuronal
synaptic plasticity. 相似文献
135.
María?F.?MonteroEmail author Manuela?Aristizábal Guillermo?García Reina 《Journal of applied phycology》2011,23(6):1053-1057
Biodiesel from algae is considered an alternative for a third generation of biofuels. However, most microalgae are not lipogenic
during fast growth periods, but high-lipid content occurs at resting stages. Microalgae biomass production for biodiesel needs
continuous high volumetric and aerial yields and large amount of neutral lipid in the biomass. These requirements are similar
to demanding a marathon runner to be obese. We show that by using cell sorting capabilities of flow cytometers, in combination
with the lipid-soluble fluorescent dye Nile Red, we can isolate and select cells with a high and stable lipid content. In
our study, we were able to select the equivalent of a stable “fat marathon runner” through three sorting events obtained from
wild populations of Tetraselmis suecica. 相似文献
136.
Elisabet Barbero-Camps Vicente Roca-Agujetas Isabel Bartolessis Cristina de Dios Jose C. Fernández-Checa Montserrat Marí 《Autophagy》2018,14(7):1129-1154
Macroautophagy/autophagy failure with the accumulation of autophagosomes is an early neuropathological feature of Alzheimer disease (AD) that directly affects amyloid beta (Aβ) metabolism. Although loss of presenilin 1 function has been reported to impair lysosomal function and prevent autophagy flux, the detailed mechanism leading to autophagy dysfunction in AD remains to be elucidated. The resemblance between pathological hallmarks of AD and Niemann-Pick Type C disease, including endosome-lysosome abnormalities and impaired autophagy, suggests cholesterol accumulation as a common link. Using a mouse model of AD (APP-PSEN1-SREBF2 mice), expressing chimeric mouse-human amyloid precursor protein with the familial Alzheimer Swedish mutation (APP695swe) and mutant presenilin 1 (PSEN1-dE9), together with a dominant-positive, truncated and active form of SREBF2/SREBP2 (sterol regulatory element binding factor 2), we demonstrated that high brain cholesterol enhanced autophagosome formation, but disrupted its fusion with endosomal-lysosomal vesicles. The combination of these alterations resulted in impaired degradation of Aβ and endogenous MAPT (microtubule associated protein tau), and stimulated autophagy-dependent Aβ secretion. Exacerbated Aβ-induced oxidative stress in APP-PSEN1-SREBF2 mice, due to cholesterol-mediated depletion of mitochondrial glutathione/mGSH, is critical for autophagy induction. In agreement, in vivo mitochondrial GSH recovery with GSH ethyl ester, inhibited autophagosome synthesis by preventing the oxidative inhibition of ATG4B deconjugation activity exerted by Aβ. Moreover, cholesterol-enrichment within the endosomes-lysosomes modified the levels and membrane distribution of RAB7A and SNAP receptors (SNAREs), which affected its fusogenic ability. Accordingly, in vivo treatment with 2-hydroxypropyl-β-cyclodextrin completely rescued these alterations, making it a potential therapeutic tool for AD. 相似文献
137.
Linda H Münger Mar Garcia-Aloy Rosa Vázquez-Fresno Doreen Gille Albert Remus R Rosana Anna Passerini María-Trinidad Soria-Florido Grégory Pimentel Tanvir Sajed David S Wishart Cristina Andres Lacueva Guy Vergères Giulia Praticò 《Genes & nutrition》2018,13(1):26
Dairy and egg products constitute an important part of Western diets as they represent an excellent source of high-quality proteins, vitamins, minerals and fats. Dairy and egg products are highly diverse and their associations with a range of nutritional and health outcomes are therefore heterogeneous. Such associations are also often weak or debated due to the difficulty in establishing correct assessments of dietary intake. Therefore, in order to better characterize associations between the consumption of these foods and health outcomes, it is important to identify reliable biomarkers of their intake. Biomarkers of food intake (BFIs) provide an accurate measure of intake, which is independent of the memory and sincerity of the subjects as well as of their knowledge about the consumed foods. We have, therefore, conducted a systematic search of the scientific literature to evaluate the current status of potential BFIs for dairy products and BFIs for egg products commonly consumed in Europe. Strikingly, only a limited number of compounds have been reported as markers for the intake of these products and none of them have been sufficiently validated. A series of challenges hinders the identification and validation of BFI for dairy and egg products, in particular, the heterogeneous composition of these foods and the lack of specificity of the markers identified so far. Further studies are, therefore, necessary to validate these compounds and to discover new candidate BFIs. Untargeted metabolomic strategies may allow the identification of novel biomarkers, which, when taken separately or in combination, could be used to assess the intake of dairy and egg products. 相似文献
138.
Isolation of plant DNA: A fast,inexpensive, and reliable method 总被引:46,自引:2,他引:46
We describe here a simple method to isolate DNA of high molecular weight from a wide variety of plant materials, such as trees,
herbaceous plants, cell suspension cultures, calli, seeds, dried embryos, ferns and lichens. The crucial step of the extraction
is the use of an acidic extraction medium. When necessary, the sample was separated on a fast RPC-5 column providing us with
highly purified DNA suitable not only for restriction endonuclease analyses but also for PCR experiments, RLFP analyses, or
detection of adducts. 相似文献
139.
140.
Rojas P Garduño B Rojas C Vigueras RM Rojas-Castañeda J Rios C Serrano-Garcia N 《Neurochemical research》2001,26(11):1245-1251
EGb761 has been suggested to be an antioxidant and free radical scavenger. Excess generation of free radicals, leading to lipid peroxidation (LP), has been proposed to play a role in the damage to striatal neurons induced by 1-methyl-4-phenylpyridinium (MPP+). We investigated the effects of EGb761 pretreatment on MPP+ neurotoxicity. C-57 black mice were pretreated with EGb761 for 17 days at different doses (0.63, 1.25, 2.5, 5 or 10 mg/kg) followed by administration of MPP+, (0.18, 0.36 or 0.72 mg/kg). LP was analyzed in corpus striatum at 30 min, 1 h, 2 h and 24 h after MPP+ administration. Striatal dopamine content was analyzed by HPLC at the highest EGb761 dose at 2 h and 24 h after MPP+ administration. MPP+-induced LP was blocked (100%) by EGb761 (10 mg/kg). Pretreatment with EGb761 partially prevented (32%) the dopamine-depleting effect of MPP+ at 24 h. These results suggest that supplements of EGb761 may be effective at preventing MPP+-induced oxidative stress. 相似文献