全文获取类型
收费全文 | 730篇 |
免费 | 37篇 |
国内免费 | 4篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 34篇 |
2020年 | 11篇 |
2019年 | 40篇 |
2018年 | 35篇 |
2017年 | 13篇 |
2016年 | 29篇 |
2015年 | 37篇 |
2014年 | 41篇 |
2013年 | 35篇 |
2012年 | 50篇 |
2011年 | 57篇 |
2010年 | 36篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 41篇 |
2006年 | 28篇 |
2005年 | 26篇 |
2004年 | 25篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 16篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1966年 | 2篇 |
1962年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有771条查询结果,搜索用时 31 毫秒
151.
The gene encoding the extracellular lipase of Staphylococcus xylosus (SXL) was cloned using PCR technique. The sequence corresponding to the mature lipase was subcloned in the pET-14b expression vector, with a strong T7 promoter, to construct a recombinant lipase protein containing six histidine residues at the N-terminal. High level expression of the lipase by Escherichia coli BL21 (DE3) cells harbouring the lipase gene containing expression vector was observed upon induction with 0.4 mM IPTG at 37 degrees C. One-step purification of the recombinant lipase was achieved with Ni-NTA resin. The specific activity of the purified His-tagged SXL was 1500 or 850 U/mg using tributyrin or olive oil emulsion as substrate, respectively. It has been proposed that the region near the residue Asp290 could be involved in the selection of the substrate. Therefore, we also mutated the residue Asp 290 by Ala using site-directed mutagenesis. The mutant SXL-D290A was overexpressed in E. coli BL21 (DE3) and purified with the same nickel metal affinity column. The specific activity of the purified His-tagged SXL-D290A mutant was 1000 U/mg using either tributyrin or olive oil emulsion as substrate. A comparative study of the wild type (His(6)-SXL) and the mutant (His(6)-SXL-D290A) proteins was carried out. Our results confirmed that Asp290 is important for the chain length specificity and catalytic efficiency of the enzyme. 相似文献
152.
Synthesis and structure of proteoglycan core protein 总被引:2,自引:0,他引:2
N B Schwartz G Habib S Campbell D D'Elvlyn M Gartner R Krueger C Olson L Philipson 《Federation proceedings》1985,44(2):369-372
Studies of the structure and synthesis of cartilage proteoglycan core protein have been carried out. Deglycosylation of completed, secreted proteoglycan by HF-pyridine treatment yielded an intact homogeneous core protein of approximately 210,000 daltons, with a blocked amino-terminus. Greater than 95% of chondroitin sulfate chains and 80% of N- and O-linked oligosaccharides were removed by the procedure, which made the product an excellent xylosyltransferase acceptor. Little alteration of core protein structure occurred during the HF-pyridine treatment as shown by complete immunoreactivity with antiserums prepared against hyaluronidase-digested proteoglycan. In other studies, the initially synthesized precursor for proteoglycan core protein was found to be approximately 376,000 daltons and localized to the rough membrane fractions. This precursor already contained N-linked oligosaccharides, and was also able to accept xylose, thereby initiating chondroitin sulfate chains. The precursor was translocated intact in an energy-dependent manner to smooth membrane-Golgi fractions where further processing of high mannose type of oligosaccharides and addition of glycosaminoglycan chains occurred. The subcellular distribution pattern of the chondroitin sulfate-synthesizing enzymes corroborated the proposed topological modifications of the proteoglycan core protein precursor. 相似文献
153.
J T Saari F D Dickerson M P Habib 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1990,195(1):30-33
Evidence is accumulating which indicates that copper-deficient animals are prone to oxidative damage. To investigate this possibility further, we measured the production of breath ethane, a hydrocarbon by-product of lipid peroxidation, in copper-deficient rats. Male, weanling Sprague-Dawley rats were fed either a purified diet which was deficient in copper (CuD) or the same diet made sufficient with 5 ppm of copper (CuS). After 33 to 34 days the rats were placed individually in gastight metabolic cages through which ethane-free air or 100% O2 was passed. Expired ethane was absorbed onto cold, activated charcoal, liberated by heating, and measured by gas chromatography. Ethane production rates (pmoles/min/100 g +/- SD) were 3.3 +/- 0.8 (CuS-air), 4.3 +/- 1.4 (CuD-air), 8.3 +/- 2.5 (CuS-O2), and 12.2 +/- 4.3 (CuD-O2). Repeated measures analysis of variance indicated that both copper deficiency (P less than 0.01) and breathing 100% O2 (P less than 0.0001) enhanced ethane production, with no interaction between treatments. This finding complements previous evidence that increased lipid peroxidation occurs in copper-deficient rats. 相似文献
154.
Shahenda M. El-Messery El-Sayed E. Habib Sarah T. A. Al-Rashood 《Journal of enzyme inhibition and medicinal chemistry》2018,33(1):818-832
A series of amide chalcones conjugated with different secondary amines were synthesised and characterised by different spectroscopic techniques 1H NMR, 13C NMR, and ESI-MS. They were screened for in vitro antibacterial activity. Compounds 36, 37, 38, 42, and 44 are the most active among the synthesised series exhibiting MIC value of 2.0–10.0?µg/ml against different bacterial strains. Compound 36 was equipotent to the standard drug Ampicillin displaying MBC value of 2.0?µg/ml against the bacterial strain Staphylococcus aureus. The products were screened for anti-biofilm activity. Compounds 36, 37, and 38 exhibited promising anti-biofilm activity with IC50 value ranges from 2.4 to 8.6?µg. Molecular modelling was performed suggesting parameters of signalling anti-biofilm mechanism. AspB327 HisB340 (arene–arene interaction) and IleB328 amino acid residues seemed of higher importance to inhibit c-di-GMP. Hydrophobicity may be crucial for activity. ADME calculations suggested that compounds 36, 37, and 38 could be used as good orally absorbed anti-biofilm agents. 相似文献
155.
Sayed M. Riyadh Shojaa A. El‐Motairi Hany E. A. Ahmed Khaled D. Khalil EL‐Sayed E. Habib 《化学与生物多样性》2018,15(9)
2‐(1‐{4‐[(4‐Methylphenyl)sulfonamido]phenyl}ethylidene)thiosemicarbazide ( 3 ) was exploited as a starting material for the synthesis of two novel series of 5‐arylazo‐2‐hydrazonothiazoles 6a – 6j and 2‐hydrazono[1,3,4]thiadiazoles 10a – 10d , incorporating sulfonamide group, through its reactions with appropriate hydrazonoyl halides. The structures of the newly synthesized products were confirmed by spectral and elemental analyses. Also, the antimicrobial, anticancer, and DHFR inhibition potency for two series of thiazoles and [1,3,4]thiadiazoles were evaluated and explained by molecular docking studies and SAR analysis. 相似文献
156.
Kifayat Ullah Khan Maqarab Shah Habib Ahmad Shujaul Mulk Khan Inayat Ur Rahman Zafar Iqbal Raees Khan Elsayed Fathi Abd_Allah Abdulaziz Abdullah Alqarawi Abeer Hashem Abdullah Aldubise 《Saudi Journal of Biological Sciences》2018,25(2):326-331
In the study area, the traditional knowledge regarding the uses of local wild medicinal plants for the health care of human and domestic animals is totally in hold of old people. The young ones are unaware about such an indispensable practices. The objective of the current study was to transfer this sort of precious knowledge from old members of the community to young generations in documented form. 相似文献
157.
Waqas Khan Shujaul Mulk Khan Habib Ahmad Abdulaziz A. Alqarawi Ghulam Mujtaba Shah Manzoor Hussain E.F. Abd_Allah 《Saudi Journal of Biological Sciences》2018,25(1):94-100
The life form and leaf size spectra of plant species of the Thandiani forests, district Abbottabad, were studied during the summer of 2013. These forests host 252 plant species of 97 families. Biological spectra showed that Hemicryptophytes (80 spp., 31.74%) were dominant followed by Megaphanerophytes (51 spp., 20.24%), Therophytes (49 spp., 19.44%) and Nanophanerophytes (45 spp., 17.86). Hemicryptophytes are the indicators of cold temperate vegetation. At the lower elevations, Megaphanerophytes and Nanophanerophytes were dominant which confirm trees as dominant habit form due to high soil depth, moisture and temperature factors. Data on Leaf spectra in the area showed that Microphyllous (88 spp., 34.92%) species were dominant followed by Leptophyllous (74 spp., 29.36%) and Nanophyllous (60 spp., 23.80%). The Microphyllous plants again are the indicator of cold temperate zone as the area is situated at an elevation of 1191–2626 m. Similarly, Nanophylls were dominant at lower elevations. Data on family importance values and diversity among various communities were also recorded. Life form and Leaf spectra studies could be used to understand the micro climatic variation of the region. 相似文献
158.
Ullah Habib Khan Adnan Daud Noman Muhammad Rehman Anees Ur 《Plasmonics (Norwell, Mass.)》2018,13(2):591-597
Plasmonics - We numerically analyzed a simple and novel design of multi-broadband plasmonic absorber which consists of a planar array of thin gold square ring structures on dielectric/metal... 相似文献
159.
Manel B. Hammouda Ichrak Riahi-Chebbi Soumaya Souid Houcemeddine Othman Zohra Aloui Najet Srairi-Abid Habib Karoui Ammar Gasmi Edith M. Magnenat Timothy N.C. Wells Kenneth J. Clemetson José Neptuno Rodríguez-López Khadija Essafi-Benkhadir 《Biochimica et Biophysica Acta (BBA)/General Subjects》2018,1862(3):600-614
Background
The resistance of melanoma cells to cisplatin restricts its clinical use. Therefore, the search for novel tumor inhibitors and effective combination treatments that sensitize tumor cells to this drug are still needed. We purified macrovipecetin, a novel heterodimeric C-type lectin, from Macrovipera lebetina snake venom and investigated its anti-tumoral effect on its own or combined with cisplatin, in human melanoma cells.Methods
Biochemical characterization, in vitro cells assays such as viability, apoptosis, adhesion, migration, invasion, Western blotting and in silico analysis were used in this study.Results
Macrovipecetin decreased melanoma cell viability 100 times more than cisplatin. Interestingly, when combined with the drug, macrovipecetin enhanced the sensitivity of SK-MEL-28 cells by augmenting their apoptosis through increased expression of the apoptosis inducing factor (AIF) and activation of ERK1/2, p38, AKT and NF-κB. Moreover, macrovipecetin alone or combined with cisplatin induced the expression of TRADD, p53, Bax, Bim and Bad and down-regulated the Bcl-2 expression and ROS levels in SK-MEL-28 cells. Interestingly, these treatments impaired SK-MEL-28 cell adhesion, migration and invasion through modulating the function and expression of αvβ3 integrin along with regulating E-cadherin, vimentin, β-catenin, c-Src and RhoA expression. In silico study suggested that only the α chain of macrovipecetin interacts with a region overlapping the RGD motif binding site on this integrin.Conclusions
We validated the antitumor effect of macrovipecetin when combined, or not, with cisplatin on SK-MEL-28 cells.General significance
The presented work proposes the potential use of macrovipecetin and cisplatin in combination as an effective anti-melanoma treatment. 相似文献160.
Arik Kershenbaum Éloïse C. Déaux Bilal Habib Brian Mitchell Vicente Palacios Holly Root-Gutteridge 《Bioacoustics.》2018,27(3):215-229
Communicative complexity is a key behavioural and ecological indicator in the study of animal cognition. Much attention has been given to measures such as repertoire size and syntactic structure in both bird and mammal vocalizations, as large repertoires and complex call combinations may give an indication of the cognitive abilities both of the sender and receiver. However, many animals communicate using a continuous vocal signal that does not easily lend itself to be described by concepts such as ‘repertoire’. For example, dolphin whistles and wolf howls both have complex patterns of frequency modulation, so that no two howls or whistles are quite the same. Is there a sense in which some of these vocalizations may be more ‘complex’ than others? Can we arrive at a quantitative metric for complexity in a continuously varying signal? Such a metric would allow us to extend familiar analyses of communicative complexity to those species where vocal behaviour is not restricted to sequences of stereotyped syllables. We present four measures of complexity in continuous signals (Wiener Entropy, Autocorrelation, Inflection Point Count, and Parsons Entropy), and examine their relevance using example data from members of the genus Canis. We show that each metric can lead to different conclusions regarding which howls could be considered complex or not. Ultimately, complexity is poorly defined and researchers must compare metrics to ensure that they reflect the properties for which the hypothesis is being tested. 相似文献