全文获取类型
收费全文 | 1661篇 |
免费 | 104篇 |
国内免费 | 2篇 |
专业分类
1767篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 53篇 |
2014年 | 76篇 |
2013年 | 93篇 |
2012年 | 135篇 |
2011年 | 126篇 |
2010年 | 71篇 |
2009年 | 70篇 |
2008年 | 118篇 |
2007年 | 113篇 |
2006年 | 117篇 |
2005年 | 111篇 |
2004年 | 115篇 |
2003年 | 94篇 |
2002年 | 83篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 29篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1973年 | 5篇 |
1972年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有1767条查询结果,搜索用时 15 毫秒
31.
Alternative pre-mRNA splicing is a major mechanism contributing to the proteome complexity of most eukaryotes, especially mammals. In less complex organisms, such as yeasts, the numbers of genes that contain introns are low and cases of alternative splicing (AS) with functional implications are rare. We report the first case of AS with functional consequences in the yeast Yarrowia lipolytica. The splicing pattern was found to govern the cellular localization of malate dehydrogenase, an enzyme of the central carbon metabolism. This ubiquitous enzyme is involved in the tricarboxylic acid cycle in mitochondria and in the glyoxylate cycle, which takes place in peroxisomes and the cytosol. In Saccharomyces cerevisiae, three genes encode three compartment-specific enzymes. In contrast, only two genes exist in Y. lipolytica. One gene (YlMDH1, YALI0D16753g) encodes a predicted mitochondrial protein, whereas the second gene (YlMDH2, YALI0E14190g) generates the cytosolic and peroxisomal forms through the alternative use of two 3'-splice sites in the second intron. Both splicing variants were detected in cDNA libraries obtained from cells grown under different conditions. Mutants expressing the individual YlMdh2p isoforms tagged with fluorescent proteins confirmed that they localized to either the cytosolic or the peroxisomal compartment. 相似文献
32.
Effect of acyl donor chain length and sugar/acyl donor molar ratio on enzymatic synthesis of fatty acid fructose esters 总被引:3,自引:0,他引:3
Samia Soultani Jean-Marc Engasser Mohamed Ghoul 《Journal of Molecular Catalysis .B, Enzymatic》2001,11(4-6):725-731
Lipase-catalyzed synthesis of fatty acid sugar esters through direct esterification was performed in 2-methyl 2-butanol as solvent. Fructose and saturated fatty acids were used as substrates and the reaction was catalyzed by immobilized Candida antarctica lipase. The effect of the initial fructose/acyl donor molar ratio and the carbon-chain length of the acyl donor as well as their reciprocal interactions on the reaction performance were investigated. For this purpose, an experimental design taking into account variations of the molar ratio (from 1:1 to 1:5) and the carbon-chain length of the fatty acid (from C8 to C18) was employed. Statistical analysis of the data indicated that the two factors as well as their interactions had significant effects on the sugar esters synthesis. The obtained results showed that whatever the molar ratio used, the highest concentration (73 g l−1), fructose and fatty acid conversion yields (100% and 80%, respectively) and initial reaction rate (40 g l−1 h−1) were reached when using the C18 fatty acid as acyl donor. Low molar ratios gave the best fatty acid conversion yields and initial reaction rates, whereas the best total sugar ester concentrations and fructose conversion yields were obtained for high molar ratios. 相似文献
33.
34.
Ten microsatellite loci were used to investigate the impact of human activity on the spatial and temporal genetic structure of Vitellaria paradoxa (Sapotaceae), a parkland tree species in agroforestry systems in southern Mali. Two stands (forest and fallow) and three cohorts (adults, juveniles and natural regeneration) in each stand were studied to: (i) compare their levels of genetic diversity (gene diversity, HE; allelic richness, Rs; and inbreeding, FIS); (ii) assess their genetic differentiation (FST); and (iii) compare their levels of spatial genetic structuring. Gene diversity parameters did not vary substantially among stands or cohorts, and tests for bottleneck events were nonsignificant. The inbreeding coefficients were not significantly different from zero in most cases (FIS = -0.025 in forest and 0.045 in fallow), suggesting that the species is probably outbreeding. There was a weak decrease in F(IS) with age, suggesting inbreeding depression. Differentiation of stands within each cohort was weak (FST = 0.026, 0.0005, 0.010 for adults, juveniles and regeneration, respectively), suggesting extensive gene flow. Cohorts within each stand were little differentiated (FST = -0.001 and 0.001 in forest and fallow, respectively). The spatial genetic structure was more pronounced in fallow than in forest where adults showed no spatial structuring. In conclusion, despite the huge influence of human activity on the life cycle of Vitellaria paradoxa growing in parkland systems, the impact on the pattern of genetic variation at microsatellite loci appears rather limited, possibly due to the buffering effect of extensive gene flow between unmanaged and managed populations. 相似文献
35.
36.
37.
The use of fluctuating asymmetry (FA) for biomonitoring environmental stress is limited by the lack of work on how FA in particular traits responds to specific stresses. Here, by manipulating the number of individuals in an enclosed fallow deer (Dama dama) population, we describe, for the first time, clear density dependence in the FA of juvenile jaw morphology. The impact of high population density on FA was strong for both sexes, supporting the use of FA for indexing environmental stress. In addition, there was some indication that the change in FA was greater in males (43.6%) than females (28.5%). Finally, the ability to buffer density-dependent stress was independent of body condition. We suggest that, under highly limiting conditions, whole cohorts may be unable to buffer against developmental error, irrespective of individual quality. 相似文献
38.
Delbosc S Alsac JM Journe C Louedec L Castier Y Bonnaure-Mallet M Ruimy R Rossignol P Bouchard P Michel JB Meilhac O 《PloS one》2011,6(4):e18679
Background
Abdominal Aortic Aneurysms (AAAs) represent a particular form of atherothrombosis where neutrophil proteolytic activity plays a major role. We postulated that neutrophil recruitment and activation participating in AAA growth may originate in part from repeated episodes of periodontal bacteremia.Methods and Findings
Our results show that neutrophil activation in human AAA was associated with Neutrophil Extracellular Trap (NET) formation in the IntraLuminal Thrombus, leading to the release of cell-free DNA. Human AAA samples were shown to contain bacterial DNA with high frequency (11/16), and in particular that of Porphyromonas gingivalis (Pg), the most prevalent pathogen involved in chronic periodontitis, a common form of periodontal disease. Both DNA reflecting the presence of NETs and antibodies to Pg were found to be increased in plasma of patients with AAA. Using a rat model of AAA, we demonstrated that repeated injection of Pg fostered aneurysm development, associated with pathological characteristics similar to those observed in humans, such as the persistence of a neutrophil-rich luminal thrombus, not observed in saline-injected rats in which a healing process was observed.Conclusions
Thus, the control of periodontal disease may represent a therapeutic target to limit human AAA progression. 相似文献39.
Jernej Jakse Natasa Stajner Zlata Luthar Jean-Marc Jeltsch Branka Javornik 《Molecular breeding : new strategies in plant improvement》2011,28(2):227-239
Data mining of gene sequences available from various projects dealing with the development of expressed sequence tags (ESTs)
can contribute to the discovery of new microsatellite markers. Our aim was to develop new microsatellite markers in hop isolated
from an enriched cDNA library and from coding GenBank sequences and to test their suitability in hop diversity studies and
for construction of a linkage map. In a set of 614 coding GenBank sequences, 72 containing microsatellites were found (11.7%);
the most frequent were trinucleotide repeats (54.0%) followed by dinucleotide repeats (34.5%). Additionally, 11 sequences
containing microsatellites were isolated from an enriched cDNA library. A total of 34 primer pairs were designed, 29 based
on GenBank sequences and five on sequences from the cDNA enriched library. Twenty-seven (79.4%) coding microsatellites were
successfully amplified and used in diversity and linkage mapping studies. Eleven primer pairs amplified 12 coding microsatellite
loci suitable for mapping and were placed on female and male linkage maps. We were able to extend previous simple sequence
repeat (SSR) female, male and integral maps by 38.8, 25.8 and 40.0 cM, respectively. In the diversity study, 36 diverse hop
genotypes were analyzed. Twenty-four coding microsatellites were polymorphic, 17 showing co-dominant behavior and 7 primer
pairs amplifying three or more bands in some hop genotypes. Altogether, 143 microsatellite DNA fragments were amplified and
they revealed a clear separation of hop genotypes according to geographical region, use or breeding history. In addition,
a discussion and comparison of results with other plant coding/EST SSR studies is presented. Our results showed that these
microsatellite markers can enhance hop diversity and linkage mapping studies and are a comparable marker system to non-coding
SSRs. 相似文献
40.
Galina K. Vasilyeva Byung-Taek Oh Patrick J. Shea Rhae A. Drijber Vladimir D. Kreslavski Robert Minard Jean-Marc Bollag 《Bioremediation Journal》2000,4(2):111-124
Bioremediation of munitions-contaminated soil requires effective transformation and detoxification of high concentrations of 2,4,6-trinitrotoluene (TNT). Pseudomonas aeruginosa strain MX, isolated from munitions-contaminated soil, aerobically transformed TNT (100 mg/L) in culture medium within 15 h, causing transient accumulation of hydroxylaminodinitrotoluenes (HADNTs). The predominance of 2-hydroxylamino-4,6-dinitrotoluene (2HADNT), as well as 2-amino-4,6-dinitrotoluene (2ADNT) and 4,4' ,6,6' -tetranitro-2,2' -azoxytoluene (2,2'AZT), indicated preferential reduction of the TNT ortho nitro group. While only 12% of the TNT was transformed to 2ADNT, up to 65% was transformed to tetranitroazoxytoluenes (AZTs), which accumulated as a precipitate. The precipitate was formed by microscopic particles adhering to bacterial cells, which subsequently formed clusters containing lysed cells. Toxicity toward bacteria was primarily attributed to 2ADNT, because pure AZTs preincubated with sterile medium had little effect on the strain. While the culture medium containing TNT exhibited toxicity toward corn (Zea mays L.) and witchgrass (Panicum capillare L.), little phytotoxicity was observed after incubating with P. aeruginosa strain MX for 4 d. Strong binding of HADNTs to soil and low AZT bioavailability may further promote the detoxification of TNT in soil. 相似文献