全文获取类型
收费全文 | 1755篇 |
免费 | 58篇 |
国内免费 | 51篇 |
专业分类
1864篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 33篇 |
2021年 | 58篇 |
2020年 | 67篇 |
2019年 | 98篇 |
2018年 | 94篇 |
2017年 | 68篇 |
2016年 | 56篇 |
2015年 | 42篇 |
2014年 | 121篇 |
2013年 | 202篇 |
2012年 | 39篇 |
2011年 | 114篇 |
2010年 | 41篇 |
2009年 | 87篇 |
2008年 | 92篇 |
2007年 | 57篇 |
2006年 | 60篇 |
2005年 | 59篇 |
2004年 | 59篇 |
2003年 | 25篇 |
2002年 | 35篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 34篇 |
1998年 | 18篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 5篇 |
排序方式: 共有1864条查询结果,搜索用时 15 毫秒
991.
Elisabeth Eckert Hans DrexlerThomas Göen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(27):2506-2514
Mercapturic acids are increasingly used as biomarkers for exposure to certain carcinogenic substances. Glycidol, ethylene oxide, propylene oxide, acrolein and 1,3-butadiene are important intermediates of toxicological concern used in the industrial production of various chemicals. The main urinary metabolites of these alkylating substances are hydroxyalkyl mercapturic acids. Therefore, we developed and validated an analytical method for the simultaneous determination of six hydroxyalkyl mercapturic acids in human urine after solid phase extraction. The mercapturic acids were separated using hydrophilic interaction liquid chromatography (HILIC) and quantified by tandem mass spectrometry using isotopically labelled internal standards. The developed method enables for the first time the determination of 2,3-dihydroxypropyl mercapturic acid (DHPMA), a metabolite of glycidol, in human urine. Additionally, the mercapturic acids of ethylene oxide (hydroxyethyl mercapturic acid, HEMA), propylene oxide (2-hydroxypropyl mercapturic acid, 2-HPMA), acrolein (3-hydroxypropyl mercapturic acid, 3-HPMA) as well as of 1,3-butadiene(3,4-dihydroxybutyl mercapturic acid, DHBMA and monohydroxy-3-butenyl mercapturic acid, MHBMA) can be determined. The limits of detection range from 3.0 to 7.0 μg/L. Intra- and inter-day precision was determined to range from 1% to 9%. Due to the good accuracy and precision and the low limits of detection the developed method is well suited for the determination of occupational exposure to alkylating substances as well as for the determination of background concentrations of the respective mercapturic acids in the general population. 相似文献
992.
Fungicidal effect of human lactoferrin against Candida albicans 总被引:3,自引:0,他引:3
Human lactoferrin (LF) in its iron-free state (apo LF), killed Candida albicans in a time- and dose-dependent way. The lethal effect was stronger at pH 7.0 than at pH 5.5 and maximum inhibition at neutral pH was achieved in 25 min when the fungal cells were exposed to LF in 0.05 mM KCl at 37 degrees C. Fe(3+)-saturated LF had no fungicidal activity. Apo LF-mediated killing was also temperature-dependent with enhanced inhibition at higher temperatures (37 degrees, 42 degrees C). The presence of 1 mM D-glucose did not affect the candidacidal activity of apo LF but both phosphate and bicarbonate ions at physiological salivary concentrations completely blocked the anti-fungal effect. Therefore it seems unlikely that LF belongs to the major host defence factors against oral candidosis. 相似文献
993.
Lei Y Mulchandani P Chen W Wang J Mulchandani A 《Biotechnology and bioengineering》2004,85(7):706-713
In this paper, we reported the construction of a hybrid biosensor for direct, highly selective, sensitive, and rapid quantitative determination of organophosphate pesticides with p-nitrophenyl substituent using purified organophosphorus hydrolase (OPH) for the initial hydrolysis and Arthrobacter sp. JS443 for subsequent p-nitrophenol oxidation. The biocatalytic layer was prepared by co-immobilizing Arthrobacter sp. JS443 and OPH on a carbon paste electrode. OPH catalyzed the hydrolysis of organophosphorus pesticides with p-nitrophenyl substituent such as paraoxon and methyl parathion to release p-nitrophenol that was oxidized by the enzymatic machinery of Arthrobacter sp. JS443 to carbon dioxide through electroactive intermediates 4-nitrocatechol and 1,2,4-benzenetriol. The oxidization current of the intermediates was measured and correlated to the concentration of organophosphates. The best sensitivity and response time were obtained using a sensor constructed with 0.06 mg dry weight of cell and 965 IU of OPH operating at 400 mV applied potential (vs. Ag/AgCl reference) in 50 mM citrate-phosphate pH 7.5 buffer at room temperature. Using these conditions, the biosensor measured as low as 2.8 ppb (10 nM) of paraoxon and 5.3 ppb (20 nM) of methyl parathion without interference from phenolic compounds, carbamate pesticides, triazine herbicides, and organophosphate pesticides that do not have the p-nitrophenyl substituent. The biosensor had excellent operational life-time stability with no decrease in response for more than 40 repeated uses over a 12-h period when stored at room temperature, while its storage life was approximately 2 days when stored in the operating buffer at 4 degrees C. 相似文献
994.
《Bioorganic & medicinal chemistry letters》2014,24(5):1261-1264
Ten natural compounds are successfully identified as falcipain-2 (FP-2) inhibitors from our in-house natural products database using structure-based virtual screening, which show moderate inhibitory activities against FP-2 with IC50 values ranging from 3.18 to 68.19 μM. While one of the inhibitors (compound 5) also exhibits in vitro antiplasmodial activity against chloroquine sensitive strain (3D7) and chloroquine resistant strain (Dd2) of Plasmodium falciparum in the micromolar range (IC50s = 5.54 μM and 4.05 μM against 3D7 cells and Dd2 cells, respectively). Furthermore, the predicted binding poses are analyzed to explain the structure–activity relationships, which will be helpful for further structural modifications. 相似文献
995.
蛋白质的错误折叠与疾病 总被引:10,自引:0,他引:10
周筠梅 《生物化学与生物物理进展》2000,27(6):579-584
蛋白质是生物体内一切功能的执行者.人体内的任何功能,从催化化学反应到抵御外来侵略都是蛋白质作用的结果.蛋白质折叠是生命活动的最基本过程,近年发现蛋白质的错误折叠可以导致一些疾病.蛋白质的错误折叠与疾病的关系已成为分子生物学新的研究前沿.介绍了细胞内保证蛋白质正常功能的“质量控制”系统,重点讨论了翻译后的质量控制、与蛋白质错误折叠有关的一些疾病和治疗这一类疾病的原则方法. 相似文献
996.
In silico target fishing approach using PharmMapper server identified c-Met kinase as the selective target for our previously synthesized compound NCI 748494/1. This approach was validated by in vitro kinase assay which showed that NCI 748494/1 possessed promising inhibitory activity against c-Met kinase (IC50 = 31.70 μM). Assessment of ADMET profiling, drug-likeness, drug score as well as docking simulation for the binding pose of that compound in the active site of c-Met kinase domain revealed that NCI 748494/1 could be considered as a promising drug lead. Based on target identification and validation, it was observed that there is structure similarity between NCI 748494/1 and the reported type II c-Met kinase inhibitor BMS-777607. Optimization of our lead NCI 748494/1 furnished newly synthesized 1,2,4-triazine derivatives based on well-established structure-activity relationships, whereas three compounds namely; 4d, 7a and 8c displayed excellent in vitro cytotoxicity against three c-Met addicted cancer cell lines; A549 (lung adenocarcinoma), HT-29 (colon cancer) and MKN-45 (gastric carcinoma); with IC50 values in the range 0.01–1.86 µM. In vitro c-Met kinase assay showed 8c to possess the highest c-Met kinase inhibition profile (IC50 = 4.31 µM). Docking of the active compounds in c-Met kinase active site revealed strong binding interactions comparable to the lead NCI 748494/1 and BMS-777607, suggesting that c-Met inhibition is very likely to be the mechanism of the antitumor effect of these derivatives. 相似文献
997.
Yihui Shi Jaehyeon Park Chandraiah Lagisetti Wei Zhou Lidia C. Sambucetti Thomas R. Webb 《Bioorganic & medicinal chemistry letters》2017,27(3):406-412
The splicing of pre-mRNA is a critical process in normal cells and is deregulated in cancer. Compounds that modulate this process have recently been shown to target a specific vulnerability in tumors. We have developed a novel cell-based assay that specifically activates luciferase in cells exposed to SF3B1 targeted compounds, such as sudemycin D6. This assay was used to screen a combined collection of approved drugs and bioactive compounds. This screening approach identified several active hits, the most potent of which were CGP-74514A and aminopurvalanol A, both have been reported to be cyclin-dependent kinases (CDKs) inhibitors. We found that these compounds, and their analogs, show significant cdc2-like kinase (CLK) inhibition and clear structure-activity relationships (SAR) at CLKs. We prepared a set of analogs and were able to ‘dial out’ the CDK activity and simultaneously developed CLK inhibitors with low nanomolar activity. Thus, we have demonstrated the utility of our exon-skipping assay and identified new molecules that exhibit potency and selectivity for CLK, as well as some structurally related dual CLK/CDK inhibitors. 相似文献
998.
Agostinho AM Hartman A Lipp C Parker AE Stewart PS James GA 《Journal of applied microbiology》2011,111(5):1275-1282
Aims: To develop an in vitro model (Colony/drip‐flow reactor – C/DFR) for the growth and analysis of methicillin‐resistant Staphylococcus aureus (MRSA) biofilms. Methods and Results: Using the C/DFR model, biofilms were grown on the top of polycarbonate filter membranes inoculated with a clinical isolate of MRSA, placed on absorbent pads in the DFR and harvested after 72 h. The biofilms varied from 256 to 308 μm in thickness with a repeatability standard deviation of 0·22. Testing of antimicrobial agents was also performed where C/DFR biofilms were grown in parallel with conventional colony biofilms. A saline solution (control), 1% silver sulfadiazine solution, and 0·25% Dakin’s solution were used to treat the biofilms for 15 min. Microscopic evaluation of biofilm morphology and thickness was conducted. The Dakins solution in both models produced statistically significantly higher log reductions than silver sulfadiazine treatment. Conclusions: The C/DFR biofilms were thick and repeatable and exhibited higher resistance to Dakins solution than the treated colony biofilms. Significance and Impact of the Study: The C/DFR can be used as a tool for examining complex biofilm physiology as well as for performing comparative experiments that test wound care products and novel antimicrobials. 相似文献
999.
Raid A Al-akeel Talat A El-kersh Yazeed A Al-Sheikh Ziab Zakey Al-Ahmadey 《Bioinformation》2013,9(7):357-362
Biofilm formation by Candida species is a major contribute to their pathogenic potential.The aim of this study was to determine in
vitro effects of EDTA, cycloheximide, and heparin-benzyl alcohol preservative on C. albicans (126) and non-albicans (31)vaginal
yeast isolates biofilm formations and their susceptibility against three antifungal Etest strips. Results of the crystal violet-assay,
indicated that biofilms formation were most commonly observed [100%] for C. kefyr, C. utilis, C. famata, and Rhodotorula
mucilaginosa, followed by C. glabrata [70%], C. tropicalis [50%], C. albicans [29%], Saccharomyces cerevisiae [0.0%]. EDTA (0.3mg/ml)
significantly inhibited biofilm formation in both C. albicans and non-albicans isolates (P=0.0001) presumably due to chelation of
necessary metal cations for the process-completion. In contrast, heparin (-benzyl alcohol preservative) stimulated biofilm formation
in all tested isolates, but not at significant level (P=0.567). Conversely, cycloheximide significantly (P=0.0001) inhibited biofilm
formation in all C. albicans strains(126) and its effect was even 3 fold more pronounced than EDTA inhibition, probably due to its
attenuation of proteins (enzymes) and/or complex molecules necessary for biofilm formation. Results also showed that all nonalbicans
yeasts isolates were susceptible to 5-flucytosine (MIC50, 0.016 µg/ml; MIC90, 0.064 µg/ml), but 14% of C. albicans isolates
were resistant (MIC50, 0.064 µg/ml; MIC90 >32 µg/ml). The MIC50 value of amphotricin B for all C. albicans and non-albicans isolates
was at a narrow range of 0.023 µg /ml, and the MIC90 values were 0.047 µg/ml and 0.064 µg/ml respectively, thereby confirming
its efficacy as a first line empiric- treatment of Candida spp infections. 相似文献
1000.
《化学与生物多样性》2018,15(2)
Thanks to the understanding of the relationships between the residence lifetime τM of the coordinated water molecules to macrocyclic Gd‐complexes and the rotational mobility τR of these structures, and according to the theory for paramagnetic relaxation, it is now possible to design macromolecular contrast agents with enhanced relaxivities by optimizing these two parameters through ligand structural modification. We succeeded in accelerating the water exchange rate by inducing steric compression around the water binding site, and by removing the amide function from the DOTA‐AA ligand [1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid mono(p‐aminoanilide)] ( L ) previously designed. This new ligand 10[2(1‐oxo‐1‐p‐propylthioureidophenylpropyl]‐1,4,7,10‐tetraazacyclodecane‐1,4,7‐tetraacetic acid ( L 1 ) was then covalently conjugated to API [O‐(aminopropyl)inulin] to get the complex API ‐(GdL 1 )x with intent to slow down the rotational correlation time (τR) of the macromolecular complex. The evaluation of the longitudinal relaxivity at different magnetic fields and the study of the 17O‐NMR at variable temperature of the low‐molecular‐weight compound ( GdL 1 ) showed a slight decrease of the τM value ( = 331 ns vs. = 450 ns for the Gd L complex). Consequently to the increase of the size of the API ‐(GdL 1 )x complex, the rotational correlation time becomes about 360 times longer compared to the monomeric GdL 1 complex (τR = 33,700 ps), which results in an enhanced proton relaxivity. 相似文献