全文获取类型
收费全文 | 3815篇 |
免费 | 227篇 |
专业分类
4042篇 |
出版年
2024年 | 6篇 |
2023年 | 42篇 |
2022年 | 59篇 |
2021年 | 124篇 |
2020年 | 89篇 |
2019年 | 100篇 |
2018年 | 129篇 |
2017年 | 120篇 |
2016年 | 150篇 |
2015年 | 193篇 |
2014年 | 263篇 |
2013年 | 266篇 |
2012年 | 288篇 |
2011年 | 331篇 |
2010年 | 202篇 |
2009年 | 145篇 |
2008年 | 221篇 |
2007年 | 164篇 |
2006年 | 161篇 |
2005年 | 150篇 |
2004年 | 120篇 |
2003年 | 109篇 |
2002年 | 103篇 |
2001年 | 54篇 |
2000年 | 65篇 |
1999年 | 43篇 |
1998年 | 25篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 8篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 6篇 |
1971年 | 9篇 |
排序方式: 共有4042条查询结果,搜索用时 0 毫秒
101.
Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend. 相似文献
102.
Endoplasmic reticulum (ER)-resident mannosidases generate asparagine-linked oligosaccharide signals that trigger ER-associated protein degradation (ERAD) of unfolded glycoproteins. In this study, we provide in vitro evidence that a complex of the yeast protein disulfide isomerase Pdi1p and the mannosidase Htm1p processes Man(8)GlcNAc(2) carbohydrates bound to unfolded proteins, yielding Man(7)GlcNAc(2). This glycan serves as a signal for HRD ligase-mediated glycoprotein disposal. We identified a point mutation in PDI1 that prevents complex formation of the oxidoreductase with Htm1p, diminishes mannosidase activity, and delays degradation of unfolded glycoproteins in vivo. Our results show that Pdi1p is engaged in both recognition and glycan signal processing of ERAD substrates and suggest that protein folding and breakdown are not separated but interconnected processes. We propose a stochastic model for how a given glycoprotein is partitioned into folding or degradation pathways and how the flux through these pathways is adjusted to stress conditions. 相似文献
103.
Santos ME das C L E Silva F Gomes KB Fernandes AP Freitas FR Faria MC Mota AP Carvalho MG 《Molecular biology reports》2011,38(5):3361-3366
Peripheral arterial disease (PAD) is an atherosclerotic disturbance characterized by a progressive obstruction of lower limb
arteries. Many risk factors associated with PAD development have being reported in the literature. The present study aimed
to investigate whether mutations in the methylenetetrahydrofolate reductase (MTHFR) or in the cystathionine beta synthase
(CBS) genes are associated with higher levels of homocysteine and the risk of PAD in patients from Brazil. This study analyzed
39 patients with PAD and 32 without PAD in whom risk factors and C677T mutations in the MTHFR gene and both 844ins68 and T833C
mutations in the CBS gene were investigated. Although higher levels of homocysteine could be observed in patients with PAD
compared to controls, no association between the increase of homocysteine and the frequency of C677T, 844ins68, and T833C
mutations could be observed. The results suggest that these mutations do not appear to be related to either homocysteine levels
or the development of the disease. However, hyperhomocysteinemia and smoking are important factors in PAD development. 相似文献
104.
This paper refers to a case of polymorphism in the desmid genus Xanthidium Ehr. It is based on material from Lake Dais Irmaios, the main body of water in the Zoological and Botanical Garden in Recife, Pernambuco, northeastern Brazil, collected at 4 different times of the year during 1967 and 1968. A detailed examination of almost 1300 specimens showed an enormous variety in form of Xanthidium regulare Nordst., X. fragile Borge, and X. pseudoregulare Borge, thus allowing the authors to draw the following conclusions: (1) the name X. regulare Nordst. should be retained until further and more detailed studies on form variation within the species are available; (2) the names X. regulare Nordst. var. asteptum Nordst. in Borge, X. regulare Nordst. var. sexangulare Grönbl., X. regulare Nordst. var. sexangulare Grönbl. f. robustior Grönbl., X. fragile Borge, X. fragile Borge forma, and X. fragile Borge var. depauperatum Borge should be considered synonymous, all referring to a single variety of X. regulare Nordst., var. asteptum Nordst. in Borge emend. C. Bic. & L. M. Carv.; (3) X. pseudoregulare Borge must be treated as a variety of X. regulare Nordst. and must be called X. regulare Nordst. var. pseudoregulare (Barge) C. Bic. & L. M. Carv. Finally, a key is given to the 3 varieties of X. regulare Nordst. proposed in the present paper. 相似文献
105.
106.
107.
Felipe Luiz Pereira Lucas Amorim Gonçalves Guilherme Campos Tavares Siomar de Castro Soares Fernanda Alves Dorella Alex Fiorini de Carvalho Márcia Pimenta Leibowitz Carlos Augusto Gomes Leal Vasco Ariston de Carvalho Azevedo Henrique César Pereira Figueiredo 《Genomics》2018,110(6)
Francisella noatunensis subsp. orientalis (FNO) is an important emerging pathogen associated with disease outbreaks in farm-raised Nile tilapia. FNO genetic diversity using PCR-based typing, no intra-species discrimination was achieved among isolates/strains from different countries, thus demonstrating a clonal behaviour pattern. In this study, we aimed to evaluate the population structure of FNO isolates by comparing whole-genome sequencing data. The analysis of recombination showed that Brazilian isolates group formed a clonal population; whereas other lineages are also supported by this analysis for isolates from foreign countries. The whole-genome multilocus sequence typing (wgMLST) analysis showed varying numbers of dissimilar alleles, suggesting that the Brazilian clonal population are in expansion. Each Brazilian isolate could be identified as a single node by high-resolution gene-by-gene approach, presenting slight genetic differences associated to mutational events. The common ancestry node suggests a single entry into the country before 2012, and the rapid dissemination of this infectious agent may be linked to market sales of infected fingerlings. 相似文献
108.
109.
110.