全文获取类型
收费全文 | 297篇 |
免费 | 12篇 |
专业分类
309篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 12篇 |
2012年 | 31篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 25篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有309条查询结果,搜索用时 15 毫秒
181.
This article describes the long-term trends in marital status mortality differences in the Netherlands using a unique dataset relating to the period 1850-1970. Poisson regression analysis was applied to calculate relative mortality risks by marital status. For two periods, cause-of-death by marital status could be used. Clear differences in mortality by marital status were observed, with strongly increasing advantages for married men and women and a relative increase in the mortality of widowed compared with non-married people. Excess mortality among single and formerly married men and women was visible in many cause-of-death categories, and this became more widespread during the last decades of the nineteenth century. Hypotheses are formulated that might explain why married men and women underwent a stronger decrease in mortality up until the end of World War II. 相似文献
182.
The distribution of IS231 has been analyzed in Bacillus thuringiensis serovars. A 723-bp HaeII conserved fragment from IS231M has been used as a probe against EcoRI-digested B. thuringiensis total DNA to yield serovar-specific hybridization profiles. The approach was useful at revealing the extent of distribution of IS231-like sequences between and within strains. Of the 88 B. thuringiensis strains tested, 70 showed hybridization banding patterns that comprised between one and 20 distinct bands. These 70 B. thuringiensis strains were grouped based on banding pattern similarities. Interestingly, intraserovar strains did not necessarily cluster together. 相似文献
183.
In an effort to determine the C-20 chirality effect on the antiinflammatory activity of 17beta-glycolate esters, methyl 11beta,17alpha,20-trihydroxy-3-oxo-1,4-pregnadien-21-oate and its 9alpha-fluoro analog, their acetonide and their carbonate derivatives were synthesized and evaluated. The agents were tested for their binding potency to the macrophage glucocorticoid receptor, and their effect on LPS-induced nitric oxide generation in RAW 264.7 cells. The acetonide derivatives showed the highest binding affinity while the triols and carbonates bound rather poorly to the receptors. With the exception of the triols, the alpha-isomer in each pair of the agents exhibited higher binding affinity to the receptor than its corresponding beta-isomer, clearly indicating that C-20 chirality has a significant effect on antiinflammatory activity. In addition, the alpha-isomers of the acetonides showed substantially higher binding affinity than the parent compound, prednisolone. In contrast to the high binding activity exhibited by some of the acetonides, all of the agents showed weak inhibitory effect on NO generation. Metabolic inactivation during assessment of NO inhibition may play a role in the divergence noted between receptor affinity and the measured biologic activity resulting from the binding. 相似文献
184.
AIMS: To assess the congruence between two earlier independent phylogenetic studies on Bacillus thuringiensis strains and on Bacillus-related species and the single, all-encompassing, phylogenetic tree presented here inferred from the combination of the two earlier datasets. METHODS AND RESULTS: A dendrogram was constructed using a combination of the data from our previous studies on 16S rRNA gene fingerprinting of 86 B. thuringiensis strains and of 77 species of Bacillus and related taxa. It revealed that all B. thuringiensis strains were clustered together in four distinct groups at a DNA similarity rate of 93%, except two serovars, bolivia and finitimus. Four bacilli species, Paenibacillus alvei, P. azotofixans, B. lentus and B. licheniformis, share a DNA similarity rate of 92% with Bt Group IV. CONCLUSIONS: Most, but not all, B. thuringiensis strains could be grouped together based on the DNA similarity rate. They were also very close to some other bacilli species. SIGNIFICANCE AND IMPACT OF THE STUDY: The combined phylogenetic study presented here, inferred from 16S rRNA gene restriction fragment length polymorphism, is congruent with two earlier independent phylogenetic studies, one on B. thuringiensis and the other on bacilli species. 相似文献
185.
A marine microalga Gyrodinium impudicum strain KG03 produced sulfated exopolysaccharide designated as p-KG03, which showed a strong antiviral activity against encephalomyocarditis virus (EMCV). To optimize culture conditions for the production of p-KG03, mineral salts, vitamins, plant growth hormones, temperature, pH and light conditions were examined. From this study, M-KG03 medium for the maximum production of p-KG03 was suggested as follows; NH(4)Cl 75 microM, NaH(3)PO(4) 200 microM, NaHCO(3) 50 microM, Na(2)SO(4) 10 microM, FeCl(2) x 6H(2)O 10 microM, MnCl(2) x 4H(2)O 0.1 microM, vitamin B(12) 0.75 microg, naphthalene acetic acid (NAA) 7.5 microg and myo-inositol 200 mg per liter of aged sea water. The optimal temperature and pH were 22.5 degrees C and 8.0, respectively. The optimal light conditions of intensity and period were 150 microE m(-2) s(-1) and 16:8 h light:dark cycle. Finally, the cell growth and p-KG03 production were measured in one liter of M-KG03 medium with 1% CO(2) and 50 ml min(-1) of airflow using two liters airlift balloon type photobioreactor (ABTPR). At these optimal conditions, p-KG03 production and cell growth were 134.6+/-5.9 mg l(-1) and 123,076+/-1,597 cells ml(-1), respectively, representing a 7.7 and 5.1 times compared with f/2 medium with Erlenmeyer flask culture (p-KG03 production 17.5+/-1.3 mg l(-1) and cell growth 24,311+/-1,291 cells ml(-1)). 相似文献
186.
Effective Gene Transfer into Regenerating Sciatic Nerves by Adenoviral Vectors: Potentials for Gene Therapy of Peripheral Nerve Injury 总被引:8,自引:0,他引:8
Replication defective adenoviral vectors have been demonstrated as an effective method for delivering genes into a variety of cell types and tissues both in vivo and in vitro. Transfecting genes into neuronal cells has proven to be difficult because of their lack of cell division. Since the major problem in neurological disease is the degeneration of the terminally differentiated neuronal cells, the adenoviral vectors ability to transfer genes into differentiated post-mitotic cells makes them advantageous for a gene delivery system for the nervous system. Here we showed that a replication defective recombinant adenovirus carrying the lacZ gene could infect the neuronal stem cells and even the differentiated neuronal cells derived from the central nervous system. The lacZ gene delivered into the neuronal cells was expressed efficiently. In addition, the recombinant virus also infected Schwann cells in intact and injured nerves in vivo. The expression of the lacZ gene lasted for 5 weeks, within which nerve regeneration is accomplished in the rat. Adenoviral vectors might thus be used to modulate Schwann cell gene expression for treating peripheral nerve injury or peripheral neuropathy. 相似文献
187.
Lahjouji K Storms R Xiao Z Joung KB Zheng Y Powlowski J Tsang A Varin L 《Applied microbiology and biotechnology》2007,75(2):337-346
A cellobiohydrolase-encoding cDNA, Tvcel7a, from Trametes versicolor has been cloned and expressed in Aspergillus niger. The deduced amino acid sequence shows that Tvcel7a encodes a 456-amino acid polypeptide belonging to glycosyl hydrolase family 7. TvCel7a possesses a 19-amino acid secretion
signal but does not possess a linker region nor a carbohydrate-binding domain. Two peaks of activity were obtained after TvCel7a
was purified to apparent homogeneity by gel-filtration followed by anion-exchange chromatography. Mass spectrometry performed
on the purified proteins confirmed that both peaks corresponded to the predicted sequence of the T. versicolor cellulase. The biochemical properties of the purified TvCel7a obtained from both peaks were studied in detail. The pH and
temperature optima were 5.0 and 40°C, respectively. The enzyme was stable over a pH range extending from pH 3.0 to 9.0 and
at temperatures lower than 50°C. The kinetic parameters with the substrate p-nitrophenyl β-d-cellobioside (pNPC) were 0.58 mM and 1.0 μmol/min/mg protein for the purified TvCel7a found in both peaks 1 and 2. TvCel7a
catalyzes the hydrolysis of pNPC, filter paper, β-glucan, and avicel to varying extents, but no detectable hydrolysis was
observed when using the substrates carboxymethylcellulose, laminarin and pNPG. 相似文献
188.
Sang Joon Son Kang Soo Lee Ji Hyung Chung Ki Jung Chang Hyun Woong Roh Soo Hyun Kim Taewon Jin Joung Hwan Back Hyun Jung Kim Yunhwan Lee Seong Hye Choi Jai Sung Noh Ki Young Lim Young Ki Chung Chang Hyung Hong Byoung Hoon Oh 《PloS one》2015,10(3)
Background and Aims
Heat shock proteins (HSPs) have been regarded as cytoprotectants that protect brain cells during the progression of neurodegenerative diseases and from damage resulting from cerebral ischemia. In this study, we assessed the association between plasma HSP 70/27 levels and cognitive decline.Methods
Among participants in the community-based cohort study of dementia called the Gwangju Dementia and Mild Cognitive Impairment Study, subjects without cognitive impairment at baseline, who then either remained without impairment (non-conversion group), or suffered mild cognitive impairment (MCI) (conversion group) (non-conversion group, N = 36; conversion group, N = 30) were analyzed.Results
After a five to six year follow-up period, comparison of the plasma HSP 70 and HSP 27 levels of the two groups revealed that only the plasma HSP 70 level was associated with a conversion to MCI after adjustments for age, gender, years of education, follow-up duration, APOE e4, hypertension, and diabetes (repeated measure analysis of variance: F = 7.59, p = 0.008). Furthermore, an increase in plasma HSP 70 level was associated with cognitive decline in language and executive function (linear mixed model: Korean Boston Naming Test, -0.426 [-0.781, -0.071], p = 0.019; Controlled Oral Word Association Test, -0.176 [-0.328, -0.023], p = 0.024; Stroop Test, -0.304 [-0.458, -0.150], p<0.001).Conclusions
These findings suggest that the plasma HSP 70 level may be related to cognitive decline in the elderly. 相似文献189.
Whi-An Kwon Sung Han Kim Sohee Kim Jae Young Joung Jinsoo Chung Kang Hyun Lee Sang-Jin Lee Ho Kyung Seo 《PloS one》2015,10(5)
ObjectiveThe sound of running water (SRW) has been effectively used for toilet training during toddlerhood. However, the effect of SRW on voiding functions in adult males with lower urinary tract symptoms (LUTS) has not been evaluated. To determine the effect of SRW on urination in male patients with LUTS, multiple voiding parameters of uroflowmetry with postvoid residual urine (PVR) were assessed according to the presence of SRW played by a mobile application.MethodsEighteen consecutive male patients with LUTS were prospectively enrolled between March and April 2014. Uroflowmetry with PVR measured by a bladder scan was randomly performed once weekly for two consecutive weeks with and without SRW in a completely sealed room after pre-checked bladder volume was scanned to be more than 150 cc. SRW was played with river water sounds amongst relaxed melodies from a smartphone mobile application.ResultsThe mean age of enrolled patients and their mean International Prostate Symptom Score (IPSS) were 58.9 ± 7.7 years (range: 46–70) and 13.1 ± 5.9, respectively. All patients had not been prescribed any medications, including alpha-blockers or anti-muscarinic agents, in the last 3 months. There was a significant increase in mean peak flow rate (PFR) with SRW in comparison to without SRW (15.7 mL/s vs. 12.3 mL/s, respectively, p = 0.0125). However, there were no differences in other uroflowmetric parameters, including PVR.ConclusionsThe study showed that SRW from a mobile phone application may be helpful in facilitating voiding functions by increasing PFR in male LUTS patients. 相似文献
190.
Tsujimoto K Hayashi A Ha TJ Kubo I 《Zeitschrift für Naturforschung. C, Journal of biosciences》2007,62(9-10):710-716
6-Pentadeca(e)nylsalicylic acids isolated from the cashew Anacardium occidentale L. (Anacardiaceae), commonly known as anacardic acids, inhibited the linoleic acid peroxidation catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, type 1) competitively without prooxidant effects. Their parent compound, salicylic acid, did not have this inhibitory activity up to 800 pm, indicating that the pentadeca(e)nyl group is an essential element to elicit the activity. The inhibition is attributed to its ability to chelate iron in the enzyme. Thus, anacardic acids chelate iron in the active site of the enzyme and then the hydrophobic tail portion slowly begins to interact with the hydrophobic domain close to the active site. Formation of the anacardic acids-ferric ion complex was detected in the ratio of 2:1 as the base peak in the negative ion electrospray ionization mass spectrometry. Hence, anacardic acids inhibit both Eox and Ered forms. 相似文献