全文获取类型
收费全文 | 8326篇 |
免费 | 547篇 |
国内免费 | 5篇 |
专业分类
8878篇 |
出版年
2023年 | 89篇 |
2022年 | 196篇 |
2021年 | 312篇 |
2020年 | 240篇 |
2019年 | 294篇 |
2018年 | 361篇 |
2017年 | 310篇 |
2016年 | 415篇 |
2015年 | 483篇 |
2014年 | 546篇 |
2013年 | 583篇 |
2012年 | 650篇 |
2011年 | 572篇 |
2010年 | 346篇 |
2009年 | 326篇 |
2008年 | 368篇 |
2007年 | 389篇 |
2006年 | 314篇 |
2005年 | 294篇 |
2004年 | 268篇 |
2003年 | 218篇 |
2002年 | 194篇 |
2001年 | 122篇 |
2000年 | 114篇 |
1999年 | 85篇 |
1998年 | 49篇 |
1997年 | 30篇 |
1996年 | 41篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 16篇 |
1992年 | 45篇 |
1991年 | 48篇 |
1990年 | 26篇 |
1989年 | 39篇 |
1988年 | 32篇 |
1987年 | 39篇 |
1986年 | 33篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1973年 | 18篇 |
1972年 | 14篇 |
1970年 | 14篇 |
排序方式: 共有8878条查询结果,搜索用时 15 毫秒
101.
102.
Colussi F Serpa V Delabona Pda S Manzine LR Voltatodio ML Alves R Mello BL Pereira N Farinas CS Golubev AM Santos MA Polikarpov I 《Journal of microbiology and biotechnology》2011,21(8):808-817
Because of its elevated cellulolytic activity, the filamentous fungus Trichoderma harzianum has a considerable potential in biomass hydrolysis applications. Trichoderma harzianum cellobiohydrolase I (ThCBHI), an exoglucanase, is an important enzyme in the process of cellulose degradation. Here, we report an easy single-step ion-exchange chromatographic method for purification of ThCBHI and its initial biophysical and biochemical characterization. The ThCBHI produced by induction with microcrystalline cellulose under submerged fermentation was purified on DEAE-Sephadex A-50 media and its identity was confirmed by mass spectrometry. The ThCBHI biochemical characterization showed that the protein has a molecular mass of 66 kDa and pI of 5.23. As confirmed by smallangle X-ray scattering (SAXS), both full-length ThCBHI and its catalytic core domain (CCD) obtained by digestion with papain are monomeric in solution. Secondary structure analysis of ThCBHI by circular dichroism revealed alpha- helices and beta-strands contents in the 28% and 38% range, respectively. The intrinsic fluorescence emission maximum of 337 nm was accounted for as different degrees of exposure of ThCBHI tryptophan residues to water. Moreover, ThCBHI displayed maximum activity at pH 5.0 and temperature of 50 degrees C with specific activities against Avicel and p-nitrophenyl-β-D-cellobioside of 1.25 U/mg and 1.53 U/mg, respectively. 相似文献
103.
Marcelo F. da Silva Diehgo T. da Silva Elane G. Giese Igor G. Hamoy Edilson R. Matos 《The Journal of eukaryotic microbiology》2019,66(4):608-616
The coccidians of the family Calyptosporidae are parasites of the tissue and organs of fish and aquatic invertebrates, in particular in the tropical region. In contrast with other apicomplexans of the suborder Eimeriorina, the diversity and ecology of the species of the genus Calyptospora have been poorly investigated, resulting in a lacuna that restricts the understanding of the distribution and prevalence of this group of eukaryote microparasites in the Amazon region. In the present study, the integrated comparative analysis of morphological characteristics, histological and structural traits, and the sequences of a fragment of the 18S rRNA gene, provides support for the identification of a new species of Calyptospora, found parasitizing the hepatic tissue of the piscivorous blue peacock bass, Cichla piquiti, captured in the reservoir of the Estreito hydroelectric dam on the middle Tocantins River in northern Brazil. This new species was named Calyptospora paranaidji n. sp. 相似文献
104.
Fiuza SM Gomes C Teixeira LJ Girão da Cruz MT Cordeiro MN Milhazes N Borges F Marques MP 《Bioorganic & medicinal chemistry》2004,12(13):3581-3589
The antiproliferative and cytotoxic properties of polyphenolic acid derivatives, structurally related with the natural models caffeic and gallic acids, have been tested in human cervix adenocarcinoma cells (HeLa). Simultaneous structural information was obtained for these compounds through theoretical ab initio methods. This study was conducted for the following esters: methyl caffeate (MC, 1), propyl caffeate (PC, 2), octyl caffeate (OC, 3), methyl gallate (MG, 4), propyl gallate (PG, 5) and octyl gallate (OG, 6). A significant growth-inhibition effect was assessed for some of these compounds, clearly dependent on their structural characteristics. Marked structure-activity relationships (SARs)--namely the number of hydroxyl ring substituents--were found to rule the biological effect of such systems. 相似文献
105.
Cavada BS da Silva LI Ramos MV Galvani FR Grangeiro TB Leite KB Assreuy AM Cajazeiras JB Calvete JJ 《Protein and peptide letters》2003,10(6):607-617
A glucose/mannose lectin was purified by affinity chromatography from Pisum arvense seeds (PAL) and the 50 kDa molecular mass in solution determined by size exclusion chromatography. SDS-PAGE and electrospray ionization mass spectrometry showed two distinct polypeptide chains: alpha (Mr. 5591 Da) and beta (19986 Da). The lectin was extensively characterized in terms of its biochemical and biological aspects. The amino acid sequence was established by Edman degradation of overlapping peptides. PAL in solution behaves as a dimer and has its monomeric structure formed by two distinct polypeptide chains named alpha (Mr. 5591 Da) and beta (19986 Da) by Electrospray ionization (ESI) mass spectrometry. PAL possesses identical amino acid sequences to that of pea seed lectin but undoubtedly does not exhibit sequence heterogeneity. It is discussed that P. arvense should be considered as a synonym of P. sativum. Furthermore, like pea lectin, PAL discriminates biantennary fucosylated glycan, determined by surface plasmon resonance. 相似文献
106.
Text-mining in molecular biology - defined as the automatic extraction of information about genes, proteins and their functional relationships from text documents - has emerged as a hybrid discipline on the edges of the fields of information science, bioinformatics and computational linguistics. A range of text-mining applications have been developed recently that will improve access to knowledge for biologists and database annotators. 相似文献
107.
Ana Paula de Araújo Maria Alice Varjal de Melo-Santos Sidney de Oliveira Carlos Eugênia Maria Mariz Maranho Rios Lêda Regis 《Biological Control》2007,41(3):339-347
The larvicidal activity of an experimental formulation of Bacillus thuringiensis israelensis (Bti) against Aedes aegypti larvae was evaluated under laboratory and simulated field conditions (SFC). Samples of technical powder (TP) were assayed to establish the LC50 and the potency of the product. The larvicidal activity of the TP and the tablet (T) were evaluated under SFC to assess the efficacy and the residual activity, measured against Ae. aegypti larvae. Either a T or 250 mg of TP were added to 50 L of water in plastic containers. Containers were exposed to sunlight or kept in the shade. Results showed a LC50 of 0.26 mg/L and a potency of 750 ITU/mg. In spite of differences in the toxicity amongst TP and T samples, all of them killed 98–100% of the larvae and the mortality remained high for six months, in the shade. The replacement of 20% or 60% of the water volume did not affect the activity of the product. Seasonal differences influenced the persistence of the product in containers exposed to sunlight. Both formulations showed an excellent performance, especially when kept in the shade. The Bti tablet evaluated in this study is potentially very useful in programs to control dengue vectors. 相似文献
108.
109.
Carbon concentration and oxygen availability affect lipid and carotenoid production by carob pulp syrup‐grown Rhodosporidium toruloides NCYC 921
下载免费PDF全文
![点击此处可从《Engineering in Life Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Teresa Margarida Parreira Claudia Freitas Alberto Reis José Roseiro Teresa Lopes da Silva 《Engineering in Life Science》2015,15(8):815-823
The simultaneous effect of oxygen availability and carbon source concentration on yeast lipid and carotenoid production has never been studied before. In this work, a Doehlert distribution design was used to study the simultaneous effect of carbon concentration and oxygen availability on Rhodosporidium toruloides NCYC 921 carotenoid and lipid production. A cheap industrial byproduct was used as carbon source (carob pulp syrup). A total sugar concentration of 106.3 g/L and a medium volume of 0.120 L induced the highest total carotenoid and total fatty acid productivities (4.60 μg/Lh and 0.029 g/Lh, respectively). Flow cytometry was used to assess yeast stress response under different cultivation conditions. The highest proportion of cells with permeabilised membrane (>20%) was induced when the cultivations were carried out at the highest sugar concentration studied (130.0 g/L) or when the culture reached the minimum final medium pH (4.60). The results showed that the total sugar concentration had a positive influence on the yeast biomass and carotenoid content, while the oxygen availability had little influence on the biomass concentration, but had a slight positive influence on the carotenoid content. Regarding the fatty acids, the two factors had a negative impact on the synthesis of these compounds. 相似文献
110.
Luís Fernando Parizi Kiyoko Uemura Utiumi Saiki Imamura Misao Onuma Kazuhiko Ohashi Aoi Masuda Itabajara da Silva Vaz Jr. 《Experimental parasitology》2011,(1):113-118
Recombinant Glutathione S-transferase of Haemaphysalis longicornis (rGST-Hl) was expressed in Escherichia coli, purified by affinity chromatography and used in the immunization of cattle. Western blot analysis showed positive antibody response in cattle immunized with rGST-Hl. The tests also showed that immunized bovine sera recognize native Rhipicephalus microplus proteins in different tissue extracts. Furthermore, the vaccine potential of rGST-Hl was investigated against infestation of Hereford cattle by R. microplus. Vaccination of cattle with rGST-Hl conferred partial cross-protection immunity against R. microplus. Considering the effect on number of engorged ticks, egg laying capacity and egg fertility, the overall efficacy of vaccination was of 57%, as compared with control group. 相似文献