全文获取类型
收费全文 | 5604篇 |
免费 | 419篇 |
国内免费 | 3篇 |
专业分类
6026篇 |
出版年
2023年 | 30篇 |
2022年 | 68篇 |
2021年 | 149篇 |
2020年 | 99篇 |
2019年 | 111篇 |
2018年 | 147篇 |
2017年 | 99篇 |
2016年 | 198篇 |
2015年 | 316篇 |
2014年 | 335篇 |
2013年 | 417篇 |
2012年 | 519篇 |
2011年 | 432篇 |
2010年 | 285篇 |
2009年 | 269篇 |
2008年 | 314篇 |
2007年 | 283篇 |
2006年 | 297篇 |
2005年 | 265篇 |
2004年 | 273篇 |
2003年 | 242篇 |
2002年 | 235篇 |
2001年 | 62篇 |
2000年 | 51篇 |
1999年 | 45篇 |
1998年 | 62篇 |
1997年 | 54篇 |
1996年 | 45篇 |
1995年 | 39篇 |
1994年 | 24篇 |
1993年 | 26篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有6026条查询结果,搜索用时 15 毫秒
131.
Miguel Pessanha Caroline S. Miles Stephen K. Chapman David L. Turner Carlos A. Salgueiro António V. Xavier 《BBA》2009,1787(2):113-301
The fumarate reductases from S. frigidimarina NCIMB400 and S. oneidensis MR-1 are soluble and monomeric enzymes located in the periplasm of these bacteria. These proteins display two redox active domains, one containing four c-type hemes and another containing FAD at the catalytic site. This arrangement of single-electron redox co-factors leading to multiple-electron active sites is widespread in respiratory enzymes. To investigate the properties that allow a chain of single-electron co-factors to sustain the activity of a multi-electron catalytic site, redox titrations followed by NMR and visible spectroscopies were applied to determine the microscopic thermodynamic parameters of the hemes. The results show that the redox behaviour of these fumarate reductases is similar and dominated by a strong interaction between hemes II and III. This interaction facilitates a sequential transfer of two electrons from the heme domain to FAD via heme IV. 相似文献
132.
133.
Michel de Bandt Bruno Fautrel Jean Francis Maillefert Jean Marie Berthelot Bernard Combe René-Marc Flipo Frédéric Lioté Olivier Meyer Alain Saraux Daniel Wendling Xavier Le Loët Francis Guillemin 《Arthritis research & therapy》2009,11(5):1-8
Introduction
The aim of this study was to determine a low disease activity threshold - a 28-joint disease activity score (DAS28) value - for the decision to maintain unchanged disease-modifying antirheumatic drug (DMARD) treatment in rheumatoid arthritis patients, based on expert opinion.Methods
Nine hundred and sixty-seven case scenarios with various levels for each component of the DAS28 (resulting in a disease activity score between 2 and 3.2) were presented to 44 panelists. For each scenario, panelists had to decide whether or not DMARD treatment (excluding steroids) could be maintained unchanged. In each scenario, for decision, the participants were given the DAS28 parameters, without knowledge of the resultant DAS28. The relationship between panelists' decision, DAS28 value, and components of the score were analysed by multiple logistic regression analysis. Each panelist analysed 160 randomised scenarios. Intra-rater and inter-rater reproducibility were assessed.Results
Forty-four panelists participated in the study. Inter-panelist agreement was good (κ = 0.63; 95% confidence interval = 0.61 to 0.65). Intra-panelist agreement was excellent (κ = 0.87; 95% confidence interval = 0.82 to 0.92). Quasi-perfect agreement was observed for DAS28 ≤ 2.4, less pronounced between 2.5 and 2.9, and almost no agreement for DAS28 > 3.0. For values below 2.5, panelists agreed to maintain unchanged DMARDs; for values above 2.5, discrepancies occurred more frequently as the DAS28 value increased. Multivariate analysis confirmed the relationship between panelist's decision, DAS28 value and components of the DAS28. Between DAS28 of 2.4 and 3.2, a major determinant for panelists' decision was swollen joint count. Female and public practice physicians decided more often to maintain treatment unchanged.Conclusions
As a conclusion, panelists suggested that in clinical practice there is no need to change DMARD treatment in rheumatoid arthritis patients with DAS28 ≤ 2.4. 相似文献134.
Danilo E Xavier Renata C Picão Raquel Girardello Lorena CC Fehlberg Ana C Gales 《BMC microbiology》2010,10(1):217
Background
Multi-drug efflux pumps have been increasingly recognized as a major component of resistance in P. aeruginosa. We have investigated the expression level of efflux systems among clinical isolates of P. aeruginosa, regardless of their antimicrobial susceptibility profile. 相似文献135.
One major challenge to industrial microalgal culturing is to devise and develop technical apparata, cultivation procedures and algal strains susceptible of undergoing substantial increases in efficiency of use of solar energy and carbon dioxide. Despite several research efforts developed to date, there is no such thing as "the best reactor system"- defined, in an absolute fashion, as the one able to achieve maximum productivity with minimum operation costs, irrespective of the biological and chemical system at stake. In fact, choice of the most suitable system is situation-dependent, as both the species of alga available and the final purpose intended will play a role. The need of accurate control impairs use of open-system configurations, so current investigation has focused mostly on closed systems. In this review, several types of closed bioreactors described in the technical literature as able to support production of microalgae are comprehensively presented and duly discussed, using transport phenomenon and process engineering methodological approaches. The text is subdivided into subsections on: reactor design, which includes tubular reactors, flat plate reactors and fermenter-type reactors; and processing parameters, which include gaseous transfer, medium mixing and light requirements. 相似文献
136.
Misra S Sahu NP Pal AK Xavier B Kumar S Mukherjee SC 《Fish & shellfish immunology》2006,21(4):346-356
The combined effect of dietary carbohydrate type and n-3 PUFA (EPA+DHA) on pre- and post-challenge haemato-immunological responses in Labeo rohita juveniles was studied. Fish were fed for 67days with six different test diets containing either gelatinised (G) or non-gelatinised (NG) corn (43%) with three levels of n-3 PUFA (0.5%, 1.0% and 2.0%). During the pre-challenge period, significantly higher (P<0.05) NBT, serum lysozyme activity, total protein and globulin content was recorded in the NG carbohydrate fed groups. Highest NBT value was recorded in the groups fed with 1.0% n-3 PUFA, whereas the highest serum lysozyme activity (P<0.05) was recorded at either 0.5% or 2.0% n-3 PUFA fed groups in both the pre- and post-challenge period. Feeding of NG corn significantly increased the total leucocyte count, lysozyme activity, A/G ratio and decreased the total erythrocyte count, haemoglobin, serum total protein and globulin content of L. rohita juveniles during the post-challenge period. Similarly, feeding of n-3 PUFA at any level significantly increased the immunological parameters like lysozyme activity or A/G ratio, whereas total leukocyte count increased due to feeding of either 0.5% or 1.0% n-3 PUFA. The NBT and albumin values remained similar in both the pre- and post-challenge period. After challenge with Aeromonas hydrophila, the highest survival was recorded in the NG carbohydrate fed groups, whereas the lowest survival was recorded in the highest level of n-3 PUFA fed group irrespective of dietary carbohydrate type. Thus, a high level of G carbohydrate as well as n-3 PUFA is found to be immunosuppressive in L. rohita juveniles. NG carbohydrate supplemented with 1.0% n-3 PUFA is found to be optimum to enhance the immunity in L. rohita juveniles. 相似文献
137.
Josiane Ribolli Evoy Zaniboni Filho Bianca Maria Soares Scaranto Oscar Akio Shibatta Carolina Barros Machado 《Genetics and molecular biology》2021,44(3)
The wide distribution of the Neotropical freshwater catfish Rhamdia offers an excellent opportunity to investigate the historical processes responsible for modeling South America’s hydrogeological structure. We used sequences from cis-Andean and Mesoamerican Rhamdia species to reconstruct and estimate divergence times among cis-Andean lineages, correlating the results with known geological events. Species delimitation methods based on distance (DNA barcoding and BIN) and coalescence (GMYC) approaches identified nine well-supported lineages from the cis-Andean region from sequences available in the BOLD dataset. The cis-Andean Rhamdia lineages diversification process began in Eocene and represented the split between cis-Andean and Mesoamerican clades. The cis-Andean clade contains two principal groups: Northwest clade (MOTUs from Amazon, Essequibo, Paraguay, and Itapecuru basins) and Southeast clade (Eastern Brazilian shield basins (Paraná, Uruguay, Iguaçu, and São Francisco) plus eastern coastal basins). The diversification of the cis-Andean Rhamdia lineages results from vicariance and geodispersion events, which played a key role in the current intricate distribution pattern of the Rhamdia lineages. The wide geographical distribution and large size of the specimens make it attractive to cultivate in different countries of the Neotropical region. The lineages delimitation minimizes identification mistakes, unintentional crossings by aquaculture, and reduces natural stocks contamination. 相似文献
138.
139.
Baohua Wang Xavier Draye Zhimin Zhuang Zhengsheng Zhang Min Liu Edward L. Lubbers Don Jones O. Lloyd May Andrew H. Paterson Peng W. Chee 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2017,130(6):1297-1308
Key message
QTLs for fiber length mapped in three generations of advanced backcross populations derived from crossing Gossypium hirsutum and Gossypium mustelinum showed opportunities to improve elite cottons by introgression from wild relatives.Abstract
The molecular basis of cotton fiber length in crosses between Gossypium hirsutum and Gossypium mustelinum was dissected using 21 BC3F2 and 12 corresponding BC3F2:3 and BC3F2:4 families. Sixty-five quantitative trait loci (QTLs) were detected by one-way analysis of variance. The QTL numbers detected for upper-half mean length (UHM), fiber uniformity index (UI), and short fiber content (SFC) were 19, 20, and 26 respectively. Twenty-three of the 65 QTLs could be detected at least twice near adjacent markers in the same family or near the same markers across different families/generations, and 32 QTLs were detected in both one-way variance analyses and mixed model-based composite interval mapping. G. mustelinum alleles increased UHM and UI and decreased SFC for five, one, and one QTLs, respectively. In addition to the main-effect QTLs, 17 epistatic QTLs were detected which helped to elucidate the genetic basis of cotton fiber length. Significant among-family genotypic effects were detected at 18, 16, and 16 loci for UHM, UI, and SFC, respectively. Six, two, and two loci showed genotype?×?family interaction for UHM, UI and SFC, respectively, illustrating complexities that might be faced in introgression of exotic germplasm into cultivated cotton. Co-location of many QTLs for UHM, UI, and SFC accounted for correlations among these traits, and selection of these QTLs may improve the three traits simultaneously. The simple sequence repeat (SSR) markers associated with G. mustelinum QTLs will assist breeders in transferring and maintaining valuable traits from this exotic source during cultivar development.140.
Efficacy of three‐in‐one capsule bismuth quadruple therapy for Helicobacter pylori eradication in clinical practice in a multinational patient population 下载免费PDF全文