全文获取类型
收费全文 | 719篇 |
免费 | 60篇 |
专业分类
779篇 |
出版年
2023年 | 11篇 |
2022年 | 17篇 |
2021年 | 31篇 |
2020年 | 14篇 |
2019年 | 29篇 |
2018年 | 34篇 |
2017年 | 24篇 |
2016年 | 25篇 |
2015年 | 28篇 |
2014年 | 49篇 |
2013年 | 55篇 |
2012年 | 72篇 |
2011年 | 83篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 32篇 |
2007年 | 27篇 |
2006年 | 41篇 |
2005年 | 23篇 |
2004年 | 18篇 |
2003年 | 13篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有779条查询结果,搜索用时 15 毫秒
91.
Empathy, the capacity to recognize and share feelings experienced by another individual, is an important trait in humans, but is not the same as pro-sociality, the tendency to behave so as to benefit another individual. Given the importance of understanding empathy''s evolutionary emergence, it is unsurprising that many studies attempt to find evidence for it in other species. To address the question of what should constitute evidence for empathy, we offer a critical comparison of two recent studies of rescuing behaviour that report similar phenomena but are interpreted very differently by their authors. In one of the studies, rescue behaviour in rats was interpreted as providing evidence for empathy, whereas in the other, rescue behaviour in ants was interpreted without reference to sharing of emotions. Evidence for empathy requires showing that actor individuals possess a representation of the receiver''s emotional state and are driven by the psychological goal of improving its wellbeing. Proving psychological goal-directedness by current standards involves goal-devaluation and causal sensitivity protocols, which, in our view, have not been implemented in available publications. Empathy has profound significance not only for cognitive and behavioural sciences but also for philosophy and ethics and, in our view, remains unproven outside humans. 相似文献
92.
Vasconcelos AF Monteiro NK Dekker RF Barbosa AM Carbonero ER Silveira JL Sassaki GL da Silva R de Lourdes Corradi da Silva M 《Carbohydrate research》2008,343(14):2481-2485
Four exopolysaccharides (EPS) obtained from Botryosphaeria rhodina strains isolated from rotting tropical fruit (graviola, mango, pinha, and orange) grown on sucrose were purified on Sepharose CL-4B. Total acid hydrolysis of each EPS yielded only glucose. Data from methylation analysis and (13)C NMR spectroscopy indicated that the EPS from the graviola isolate consisted of a main chain of glucopyranosyl (1-->3) linkages substituted at O-6 as shown in the putative structure below: [carbohydrate structure: see text]. The EPS of the other fungal isolates consisted of a linear chain of (1-->6)-linked glucopyranosyl residues of the following structure: [carbohydrate structure: see text]. FTIR spectra showed one band at 891 cm(-1), and (13)C NMR spectroscopy showed that all glucosidic linkages were of the beta-configuration. Dye-inclusion studies with Congo Red indicated that each EPS existed in a triple-helix conformational state. beta-(1-->6)-d-Glucans produced as exocellular polysaccharides by fungi are uncommon. 相似文献
93.
94.
95.
Yunjiao Wang Pawel Paszek Caroline A Horton Douglas B Kell Michael RH White David S Broomhead Mark R Muldoon 《BMC systems biology》2011,5(1):23
Background
Sustained stimulation with tumour necrosis factor alpha (TNF-alpha) induces substantial oscillations—observed at both the single cell and population levels—in the nuclear factor kappa B (NF-kappa B) system. Although the mechanism has not yet been elucidated fully, a core system has been identified consisting of a negative feedback loop involving NF-kappa B (RelA:p50 hetero-dimer) and its inhibitor I-kappa B-alpha. Many authors have suggested that this core oscillator should couple to other oscillatory pathways. 相似文献96.
The production of food supplements containing cyanobacteria is a growing worldwide industry. While there have been several
reports of health benefits that can be gained from the consumption of these supplements, there have also been a growing number
of studies showing the presence of toxins some of which (for example microcystins) are known to affect human health. In this
paper, we report a multiplex polymerase chain reaction (PCR) technique that can be used to identify microcystin contamination
in dietary supplements produced for human consumption. This method involves a PCR reaction containing three primer pairs,
the first of which is used to amplify a 220-bp fragment of 16s rDNA specific to Microcystis, the most common microcystin-producing cyanobacterium. The second primer pair is used to amplify a 300-bp fragment of the
mcyA gene, linked to microcystin biosynthesis in Anabaena, Microcystis, and Planktothrix. A third primer pair, used as a positive control, results in the amplification of a 650-bp fragment from the phycocyanin
operon common to all cyanobacteria. This technique was found to be useful for detecting the presence of toxigenic Microcystis in all dietary supplements produced from the nontoxic cyanobacterium Aphanizomenon flos-aquae. 相似文献
97.
Moreira JS Almeida RG Tavares LS Santos MO Viccini LF Vasconcelos IM Oliveira JT Raposo NR Dias SC Franco OL 《The protein journal》2011,30(1):32-38
Heavy agricultural losses are closely related to attacks by insect-pests and phytopathogens such as bacteria and fungi. Among
them, the fungus Botrytis cinerea can cause gray mold in more than 200 different species of plants, and is considered a challenging problem for agribusiness.
Fungicides are commonly used to control this pathogen because they are fast-working and easy to apply. However, the continuous
use of fungicides may promote the selection of resistant fungi and can also cause profound contamination in ecosystems. Aiming
to find alternative strategies to solve these problems, several studies have focused on searching for plant proteins and peptides
with antifungal activities (AFPs). With this in mind, this report shows the isolation and characterization of two novels antifungal
proteins from flowers of rosemary pepper (Lippia sidoides Cham.) with 10 and 15 kDa. Isolation was performed by using an Octyl-Sepharose hydrophobic column. In vitro bioassays indicated
that isolated proteins were able to inhibit B. cinerea development, but were not effective against all bacteria tested. Moreover, N-termini sequences indicate that both proteins
showed sequence homology with NBS–LRR R proteins with a lower molecular mass, suggesting possible protein fragmentation. Data
reported here could help in the development of biotechnological products for crop protection against phytopathogenic fungi
in the near future. 相似文献
98.
99.
Daniel D. R. Arcanjo Ana Carolina Mafud Andreanne G. Vasconcelos José Couras da Silva-Filho Maurício P. M. Amaral Lucas M. Brito Marcelo P. Bemquerer Selma A. S. Kückelhaus Alexandra Plácido Cristina Delerue-Matos Nuno Vale Yvonne P. Mascarenhas Fernando Aécio A. Carvalho Aldeidia P. Oliveira José Roberto Souza Almeida Leite 《International journal of peptide research and therapeutics》2017,23(3):323-331
BPP-BrachyNH2 is a proline-rich oligopeptide (PRO) firstly identified in skin secretion of the frog Brachycephalus ephippium, which possess in vitro inhibitory activity of angiotensin-I converting enzyme (ACE) and endothelium-dependent vasorelaxant activity. Considering its potential application in the treatment of cardiovascular diseases, the present work assessed the toxicological profile of the BPP-BrachyNH2. The in silico toxicity prediction was performed from the best model obtained through the optimization of the FASTA query peptide. This prediction study revealed that BPP-BrachyNH2 induced high predicted LD50 values for both humans and rats, and then is well-tolerated in the recommended range. The MTT assay was applied for the in vitro cytotoxic evaluation in murine macrophages. In this assay, a decrease of cell viability was not observed. The in vivo acute toxicological study was performed after the intraperitoneal administration of BPP-BrachyNH2 at doses of 5 and 50 mg/kg. After intraperitoneal administration, no death, alterations in behavioral parameters or weight gain curve was observed, as well as none in the serum biochemical parameters, and gross pathological and histopathological analyses. These observations demonstrates an acceptable safety profile for BPP-BrachyNH2, leading towards further studies focused on investigation of pharmacological and therapeutical applications for this peptide. 相似文献
100.
Wool and silk were dissolved and used for the preparation of blended films. Two systems are proposed: (1) blend films of silk fibroin and keratin aqueous solutions and (2) silk fibroin and keratin dissolved in formic acid. The FTIR spectra of pure films cast from aqueous solutions indicated that the keratin secondary structure mainly consists of alpha-helix and random coil conformations. The IR spectrum of pure SF is characteristic of films with prevalently amorphous structure (random coil conformation). Pure keratin film cast from formic acid shows an increase in the amount of beta-sheet and disordered keratin structures. The FTIR pattern of SF dissolved in formic acid is characteristic of films with prevalently beta-sheet conformations with beta-sheet crystallites embedded in an amorphous matrix. The thermal behavior of the blends confirmed the FTIR results. DSC curve of pure SF is typical of amorphous SF and the curve of pure keratin show the characteristic melting peak of alpha-helices for the aqueous system. These patterns are no longer observed in the films cast from formic acid due to the ability of formic acid to induce crystallization of SF and to increase the amount of beta-sheet structures on keratin. The nonlinear trend of the different parameters obtained from FTIR analysis and DSC curves of both SF/keratin systems indicate that when proteins are mixed they do not follow additives rules but are able to establish intermolecular interactions. Degradable polymeric biomaterials are preferred candidates for medical applications. It was investigated the degradation behavior of both SF/keratin systems by in vitro enzymatic incubation with trypsin. The SF/keratin films cast from water underwent a slower biological degradation than the films cast from formic acid. The weight loss obtained is a function of the amount of keratin in the blend. This study encourages the further investigation of the type of matrices presented here to be applied whether in scaffolds for tissue engineering or as controlled release drug delivery vehicles. 相似文献