全文获取类型
收费全文 | 2488篇 |
免费 | 154篇 |
国内免费 | 12篇 |
出版年
2023年 | 17篇 |
2022年 | 46篇 |
2021年 | 128篇 |
2020年 | 62篇 |
2019年 | 58篇 |
2018年 | 65篇 |
2017年 | 64篇 |
2016年 | 81篇 |
2015年 | 131篇 |
2014年 | 165篇 |
2013年 | 198篇 |
2012年 | 171篇 |
2011年 | 161篇 |
2010年 | 128篇 |
2009年 | 97篇 |
2008年 | 108篇 |
2007年 | 124篇 |
2006年 | 102篇 |
2005年 | 87篇 |
2004年 | 71篇 |
2003年 | 66篇 |
2002年 | 64篇 |
2001年 | 48篇 |
2000年 | 44篇 |
1999年 | 42篇 |
1998年 | 11篇 |
1997年 | 20篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1980年 | 9篇 |
1978年 | 11篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 9篇 |
1967年 | 9篇 |
排序方式: 共有2654条查询结果,搜索用时 453 毫秒
191.
Human amniotic epithelial cells (hAECs) are potentially one of the key players in tissue engineering due to their easy availability. The aim of the present study was to develop an optimal isolation and transportation technique, as well as to determine the immunophenotype and epithelial gene expression of hAECs. Amnion was mechanically peeled off from the chorion and digested with trypsin-ethylenediaminetetraacetic acid. The isolated hAECs were cultured in medium containing 10 ng/mL epidermal growth factor until P4. The epithelial gene expression, cell surface antigen and protein expression of hAECs were analyzed by quantitative polymerase chain reaction, flow cytometry and immunocytochemistry. hAECs were also cultured in adipogenic, osteogenic and neurogenic induction media. The best cell yield of hAECs was seen in the digestion of 15 pieces of amnion (2 × 2 cm) and isolated 30 min after digestion with trypsin. F12:Dulbecco's modified eagle medium was the best medium for short term storage at 4 °C. hAECs expressed CD9, CD44, CD73 and CD90, and negligibly expressed CD31, CD34, CD45 and CD117. After serial passage, CK3, CK19 and involucrin gene expressions were upregulated, while p63, CK1 and CK14 gene expressions were downregulated. Sustained gene expressions of integrin β1 and CK18 were observed. At initial culture, these cells might have stem-like properties. However, they differentiated after serial passage. Nonetheless, hAECs have epithelial stem cell characteristics and have the potential to differentiate into corneal epithelial cells. Further investigations are still needed to elucidate the mechanism of differentiation involved and to optimize the culture condition for long term in vitro culture. 相似文献
192.
Xiangdong Li Nafis Rahman 《The Journal of steroid biochemistry and molecular biology》2010,118(4-5):257-263
Increasing evidence indicates a direct interrelationship between benign prostatic hyperplasia and chronic non-bacterial prostatic inflammation in the development of human voiding dysfunction in aging male, which gradually transforms to bladder outlet obstruction (BOO). Increased prevalence of BOO along with the aging process further suggests that estrogen or more precisely decreased androgen to estrogen ratio in serum is involved in the pathogenesis of BOO. In this review, we will analyze the hormonal causes, clinical relevance, and biologically relevant estrogen-modulated animal models potential for BOO study. In light of the data presented in this review, it becomes apparent that direct inhibition of estrogen action may provide important pharmaceutical treatment of the BOO. 相似文献
193.
In this study, fatty acid methyl esters (FAME) have been successfully produced from transesterification reaction between triglycerides and methyl acetate, instead of alcohol. In this non-catalytic supercritical methyl acetate (SCMA) technology, triacetin which is a valuable biodiesel additive is produced as side product rather than glycerol, which has lower commercial value. Besides, the properties of the biodiesel (FAME and triacetin) were found to be superior compared to those produced from conventional catalytic reactions (FAME only). In this study, the effects of various important parameters on the yield of biodiesel were optimized by utilizing Response Surface Methodology (RSM) analysis. The mathematical model developed was found to be adequate and statistically accurate to predict the optimum yield of biodiesel. The optimum conditions were found to be 399 °C for reaction temperature, 30 mol/mol of methyl acetate to oil molar ratio and reaction time of 59 min to achieve 97.6% biodiesel yield. 相似文献
194.
Morshed A. Chowdhury Khaled R.A. Abdellatif Ying Dong Gang Yu Zhangjian Huang Moshfiqur Rahman Dipankar Das Carlos A. Velázquez Mavanur R. Suresh Edward E. Knaus 《Bioorganic & medicinal chemistry letters》2010,20(4):1324-1329
A new group of hybrid nitric oxide (NO) releasing anti-inflammatory (AI) coxib prodrugs (NO-coxibs) wherein the para-tolyl moiety present in celecoxib was replaced by a N-(4-nitrooxybutyl)piperidyl 15a–b, or N-(4-nitrooxybutyl)-1,2,3,6-tetrahydropyridyl 17a–b, NO-donor moiety was synthesized. All compounds released a low amount of NO upon incubation with phosphate buffered saline (PBS) at pH 7.4 (2.4–5.8% range). In comparison, the percentage NO released was higher (3.1–8.4% range) when these nitrate prodrugs were incubated in the presence of l-cysteine. In vitro COX-1/COX-2 isozyme inhibition studies showed this group of compounds are moderately more potent, and hence selective, inhibitors of the COX-2 relative to the COX-1 enzyme. AI structure–activity relationship data acquired showed that compounds having a MeSO2 COX-2 pharmacophore exhibited superior AI activity compared to analogs having a H2NSO2 substituent. Compounds having a MeSO2 COX-2 pharmacophore in conjunction with a N-(4-nitrooxybutyl)piperidyl (ED50 = 132.4 mg/kg po), or a N-(4-nitrooxybutyl)-1,2,3,6-tetrahydropyridyl (ED50 = 118.4 mg/kg po), moiety exhibited an AI potency profile that is similar to aspirin (ED50 = 128.7 mg/kg po) but lower than ibuprofen (ED50 = 67.4 mg/kg po). 相似文献
195.
Coassin S Schweiger M Kloss-Brandstätter A Lamina C Haun M Erhart G Paulweber B Rahman Y Olpin S Wolinski H Cornaciu I Zechner R Zimmermann R Kronenberg F 《PLoS genetics》2010,6(12):e1001239
Recent studies demonstrated a strong influence of rare genetic variants on several lipid-related traits. However, their impact on free fatty acid (FFA) plasma concentrations, as well as the role of rare variants in a general population, has not yet been thoroughly addressed. The adipose triglyceride lipase (ATGL) is encoded by the PNPLA2 gene and catalyzes the rate-limiting step of lipolysis. It represents a prominent candidate gene affecting FFA concentrations. We therefore screened the full genomic region of ATGL for mutations in 1,473 randomly selected individuals from the SAPHIR (Salzburg Atherosclerosis Prevention program in subjects at High Individual Risk) Study using a combined Ecotilling and sequencing approach and functionally investigated all detected protein variants by in-vitro studies. We observed 55 novel mostly rare genetic variants in this general population sample. Biochemical evaluation of all non-synonymous variants demonstrated the presence of several mutated but mostly still functional ATGL alleles with largely varying residual lipolytic activity. About one-quarter (3 out of 13) of the investigated variants presented a marked decrease or total loss of catalytic function. Genetic association studies using both continuous and dichotomous approaches showed a shift towards lower plasma FFA concentrations for rare variant carriers and an accumulation of variants in the lower 10%-quantile of the FFA distribution. However, the generally rather small effects suggest either only a secondary role of rare ATGL variants on the FFA levels in the SAPHIR population or a recessive action of ATGL variants. In contrast to these rather small effects, we describe here also the first patient with "neutral lipid storage disease with myopathy" (NLSDM) with a point mutation in the catalytic dyad, but otherwise intact protein. 相似文献
196.
Background
One of the major challenges in the field of vaccine design is to predict conformational B-cell epitopes in an antigen. In the past, several methods have been developed for predicting conformational B-cell epitopes in an antigen from its tertiary structure. This is the first attempt in this area to predict conformational B-cell epitope in an antigen from its amino acid sequence.Results
All Support vector machine (SVM) models were trained and tested on 187 non-redundant protein chains consisting of 2261 antibody interacting residues of B-cell epitopes. Models have been developed using binary profile of pattern (BPP) and physiochemical profile of patterns (PPP) and achieved a maximum MCC of 0.22 and 0.17 respectively. In this study, for the first time SVM model has been developed using composition profile of patterns (CPP) and achieved a maximum MCC of 0.73 with accuracy 86.59%. We compare our CPP based model with existing structure based methods and observed that our sequence based model is as good as structure based methods.Conclusion
This study demonstrates that prediction of conformational B-cell epitope in an antigen is possible from is primary sequence. This study will be very useful in predicting conformational B-cell epitopes in antigens whose tertiary structures are not available. A web server CBTOPE has been developed for predicting B-cell epitope http://www.imtech.res.in/raghava/cbtope/. 相似文献197.
Naz Chaibakhsh Mohd Basyaruddin Abdul Rahman Professor Mahiran Basri Abu Bakar Salleh Suraini Abd-Aziz 《Biotechnology journal》2010,5(8):848-855
Dimethyl adipate (DMA) was synthesized by immobilized Candida antarctica lipase B-catalyzed esterification of adipic acid and methanol. To optimize the reaction conditions of ester production, response surface methodology was applied, and the effects of four factors namely, time, temperature, enzyme concentration, and molar ratio of substrates on product synthesis were determined. A statistical model predicted that the maximum conversion yield would be 97.6%, at the optimal conditions of 58.5°C, 54.0 mg enzyme, 358.0 min, and 12:1 molar ratio of methanol to adipic acid. The R2 (0.9769) shows a high correlation between predicted and experimental values. The kinetics of the reaction was also investigated in this study. The reaction was found to obey the ping-pong bi-bi mechanism with methanol inhibition. The kinetic parameters were determined and used to simulate the experimental results. A good quality of fit was observed between the simulated and experimental initial rates. 相似文献
198.
Brian Sheng Xian Teo Mahiran Basri Mohd Rezuwan Shah Zakaria Abu Bakar Salleh Raja Noor Zaliha Raja Abdul Rahman Mohd Basyaruddin Abdul Rahman 《Journal of nanobiotechnology》2010,8(1):4
Background
Cosmeceuticals are cosmetic-pharmaceutical hybrids intended to enhance health and beauty of the skin. Nanocosmeceuticals use nano-sized system for the delivery of active ingredients to the targeted cells for better penetration. In this work, nanoemulsion from palm oil esters was developed as a delivery system to produce nanocosmeceuticals. The stability of the resulting formulation was tested using various methods. In addition, the effect of components i.e. Vitamin E and Pluronic F-68 on the formulation was also studied. 相似文献199.
Visvanathan S Rahman MU Keystone E Genovese M Klareskog L Hsia E Mack M Buchanan J Elashoff M Wagner C 《Arthritis research & therapy》2010,12(6):R211