全文获取类型
收费全文 | 62104篇 |
免费 | 5303篇 |
国内免费 | 39篇 |
专业分类
67446篇 |
出版年
2023年 | 296篇 |
2022年 | 633篇 |
2021年 | 1167篇 |
2020年 | 827篇 |
2019年 | 918篇 |
2018年 | 1277篇 |
2017年 | 1052篇 |
2016年 | 1782篇 |
2015年 | 2639篇 |
2014年 | 2635篇 |
2013年 | 3309篇 |
2012年 | 3891篇 |
2011年 | 3621篇 |
2010年 | 2260篇 |
2009年 | 2155篇 |
2008年 | 2741篇 |
2007年 | 2697篇 |
2006年 | 2516篇 |
2005年 | 2806篇 |
2004年 | 2750篇 |
2003年 | 2381篇 |
2002年 | 1935篇 |
2001年 | 1563篇 |
2000年 | 1463篇 |
1999年 | 1353篇 |
1998年 | 698篇 |
1997年 | 617篇 |
1996年 | 667篇 |
1995年 | 529篇 |
1994年 | 522篇 |
1993年 | 508篇 |
1992年 | 1003篇 |
1991年 | 886篇 |
1990年 | 810篇 |
1989年 | 816篇 |
1988年 | 803篇 |
1987年 | 721篇 |
1986年 | 686篇 |
1985年 | 665篇 |
1984年 | 618篇 |
1983年 | 485篇 |
1982年 | 384篇 |
1981年 | 381篇 |
1980年 | 363篇 |
1979年 | 466篇 |
1978年 | 393篇 |
1977年 | 325篇 |
1975年 | 318篇 |
1974年 | 321篇 |
1973年 | 324篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Romain Guyot Marion de la Mare Véronique Viader Perla Hamon Olivier Coriton José Bustamante-Porras Valérie Poncet Claudine Campa Serge Hamon Alexandre de Kochko 《BMC plant biology》2009,9(1):22
Background
Coffea canephora, also called Robusta, belongs to the Rubiaceae, the fourth largest angiosperm family. This diploid species (2x = 2n = 22) has a fairly small genome size of ≈ 690 Mb and despite its extreme economic importance, particularly for developing countries, knowledge on the genome composition, structure and evolution remain very limited. Here, we report the 160 kb of the first C. canephora Bacterial Artificial Chromosome (BAC) clone ever sequenced and its fine analysis. 相似文献992.
993.
Paulo Cesar Gomes Bibiana Monson de Souza Nathalia Baptista Dias Patrícia Brigatte Danilo Mourelle Helen Andrade Arcuri Marcia Perez dos Santos Cabrera Rodrigo Guerino Stabeli João Ruggiero Neto Mario Sergio Palma 《Biochimica et Biophysica Acta (BBA)/General Subjects》2014
Background
The peptide Paulistine was isolated from the venom of wasp Polybia paulista. This peptide exists under a natural equilibrium between the forms: oxidised — with an intra-molecular disulphide bridge; and reduced — in which the thiol groups of the cysteine residues do not form the disulphide bridge. The biological activities of both forms of the peptide are unknown up to now.Methods
Both forms of Paulistine were synthesised and the thiol groups of the reduced form were protected with the acetamidemethyl group [Acm-Paulistine] to prevent re-oxidation. The structure/activity relationships of the two forms were investigated, taking into account the importance of the disulphide bridge.Results
Paulistine has a more compact structure, while Acm-Paulistine has a more expanded conformation. Bioassays reported that Paulistine caused hyperalgesia by interacting with the receptors of lipid mediators involved in the cyclooxygenase type II pathway, while Acm-Paullistine also caused hyperalgesia, but mediated by receptors involved in the participation of prostanoids in the cyclooxygenase type II pathway.Conclusion
The acetamidemethylation of the thiol groups of cysteine residues caused small structural changes, which in turn may have affected some physicochemical properties of the Paulistine. Thus, the dissociation of the hyperalgesy from the edematogenic effect when the actions of Paulistine and Acm-Paulistine are compared to each other may be resulting from the influence of the introduction of Acm-group in the structure of Paulistine.General significance
The peptides Paulistine and Acm-Paulistine may be used as interesting tools to investigate the mechanisms of pain and inflammation in future studies. 相似文献994.
Long-chain omega-3 polyunsaturated fatty acids (LC-O3PUFAs) exhibit therapeutic potential for the treatment and prevention of the neurological deficits associated with spinal cord injury (SCI). However, the mechanisms implicated in these protective responses remain unclear. The objective of the present functional metabolomics study was to identify and define the dominant metabolic pathways targeted by dietary LC-O3PUFAs. Sprague-Dawley rats were fed rodent purified chows containing menhaden fish oil-derived LC-O3PUFAs for 8 weeks before being subjected to sham or spinal cord contusion surgeries. We show, through untargeted metabolomics, that dietary LC-O3PUFAs regulate important biochemical signatures associated with amino acid metabolism and free radical scavenging in both the injured and sham-operated spinal cord. Of particular significance, the spinal cord metabolome of animals fed with LC-O3PUFAs exhibited reduced glucose levels (?48 %) and polar uncharged/hydrophobic amino acids (less than ?20 %) while showing significant increases in the levels of antioxidant/anti-inflammatory amino acids and peptides metabolites, including β-alanine (+24 %), carnosine (+33 %), homocarnosine (+27 %), kynurenine (+88 %), when compared to animals receiving control diets (p?0.05). Further, we found that dietary LC-O3PUFAs impacted the levels of neurotransmitters and the mitochondrial metabolism, as evidenced by significant increases in the levels of N-acetylglutamate (+43 %) and acetyl CoA levels (+27 %), respectively. Interestingly, this dietary intervention resulted in a global correction of the pro-oxidant metabolic profile that characterized the SCI-mediated sensorimotor dysfunction. In summary, the significant benefits of metabolic homeostasis and increased antioxidant defenses unlock important neurorestorative pathways of dietary LC-O3PUFAs against SCI. 相似文献
995.
de Chaumont F Dallongeville S Chenouard N Hervé N Pop S Provoost T Meas-Yedid V Pankajakshan P Lecomte T Le Montagner Y Lagache T Dufour A Olivo-Marin JC 《Nature methods》2012,9(7):690-696
Current research in biology uses evermore complex computational and imaging tools. Here we describe Icy, a collaborative bioimage informatics platform that combines a community website for contributing and sharing tools and material, and software with a high-end visual programming framework for seamless development of sophisticated imaging workflows. Icy extends the reproducible research principles, by encouraging and facilitating the reusability, modularity, standardization and management of algorithms and protocols. Icy is free, open-source and available at http://icy.bioimageanalysis.org/. 相似文献
996.
997.
Despite increasing awareness of the ways in which non-epistemic values play roles in science, many scientists remain reluctant to acknowledge values at stake in their own work. Even when research clearly relates to risk assessment and establishing public policy, contexts in which the presence of values is less likely to be contentious, scientists tend to present such research as merely involving empirical questions about what the evidence is. As a result, debates over policy-related science tend to be framed as purely epistemic debates over the state of the evidence. We argue that this neglects the important ways that ethical and social values play legitimate roles in judgments about what we take to be evidence for a particular policy. Using the case of recent disputes about the relative safety of home birth, we argue that although the debate has been framed as a purely scientific one about the empirical evidence for home birth, it actually involves disagreements about underlying value assumptions. If our claims are correct, then in order to move the debate forward, scientists will need to engage in a critical discussion about the values at stake. 相似文献
998.
Buket Aksu Anant Paradkar Marcel de Matas ?zgen ?zer Tamer Güneri Peter York 《AAPS PharmSciTech》2012,13(4):1138-1146
The publication of the International Conference of Harmonization (ICH) Q8, Q9, and Q10 guidelines paved the way for the standardization of quality after the Food and Drug Administration issued current Good Manufacturing Practices guidelines in 2003. “Quality by Design”, mentioned in the ICH Q8 guideline, offers a better scientific understanding of critical process and product qualities using knowledge obtained during the life cycle of a product. In this scope, the “knowledge space” is a summary of all process knowledge obtained during product development, and the “design space” is the area in which a product can be manufactured within acceptable limits. To create the spaces, artificial neural networks (ANNs) can be used to emphasize the multidimensional interactions of input variables and to closely bind these variables to a design space. This helps guide the experimental design process to include interactions among the input variables, along with modeling and optimization of pharmaceutical formulations. The objective of this study was to develop an integrated multivariate approach to obtain a quality product based on an understanding of the cause–effect relationships between formulation ingredients and product properties with ANNs and genetic programming on the ramipril tablets prepared by the direct compression method. In this study, the data are generated through the systematic application of the design of experiments (DoE) principles and optimization studies using artificial neural networks and neurofuzzy logic programs.KEY WORDS: artificial neural networks (ANNs), gene expression programming (GEP), optimization, quality by design (QbD) 相似文献
999.
1000.