全文获取类型
收费全文 | 2765篇 |
免费 | 198篇 |
国内免费 | 2篇 |
专业分类
2965篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 73篇 |
2020年 | 43篇 |
2019年 | 48篇 |
2018年 | 62篇 |
2017年 | 59篇 |
2016年 | 87篇 |
2015年 | 138篇 |
2014年 | 158篇 |
2013年 | 184篇 |
2012年 | 253篇 |
2011年 | 202篇 |
2010年 | 143篇 |
2009年 | 137篇 |
2008年 | 155篇 |
2007年 | 174篇 |
2006年 | 173篇 |
2005年 | 126篇 |
2004年 | 119篇 |
2003年 | 117篇 |
2002年 | 96篇 |
2001年 | 25篇 |
2000年 | 30篇 |
1999年 | 34篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 20篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1968年 | 4篇 |
排序方式: 共有2965条查询结果,搜索用时 3 毫秒
141.
Jose P. Garcia-Sabater Julien Maheut Julio J. Garcia-Sabater 《Flexible Services and Manufacturing Journal》2012,24(2):171-209
This paper presents an operations planning scheme based on mathematical programming models (specifically, Mixed-Integer Linear Programming (MILP) models) integrated into a web-enabled Advanced Planning and Scheduling System (APS), developed for and implemented in an engine assembler that supplies the car industry. One objective of this paper is to provide empirical insights into some operations planning characteristics in the automotive industry. The other main objective is to show MILP models and their use to create plans that enable the coordination of different planning levels (mid-term and short-term) and planning domains (procurement, production and distribution). The APS fulfills the requirements of an engine assembler in the automotive sector (namely lean-type constraints and objectives). The system is based on two MILP models, which have been purposely developed together along with their relations. The models presented herein provide a solution that considers supply chain objectives and constraints, and are integrated by means of data and constraints which have proven sufficient to fulfill users?? and stakeholders?? requirements. This case study presents the models?? most relevant aspects and their implementation. 相似文献
142.
143.
144.
Reggies/flotillins regulate E-cadherin-mediated cell contact formation by affecting EGFR trafficking
Solis GP Schrock Y Hülsbusch N Wiechers M Plattner H Stuermer CA 《Molecular biology of the cell》2012,23(10):1812-1825
The reggie/flotillin proteins are implicated in membrane trafficking and, together with the cellular prion protein (PrP), in the recruitment of E-cadherin to cell contact sites. Here, we demonstrate that reggies, as well as PrP down-regulation, in epithelial A431 cells cause overlapping processes and abnormal formation of adherens junctions (AJs). This defect in cell adhesion results from reggie effects on Src tyrosine kinases and epidermal growth factor receptor (EGFR): loss of reggies reduces Src activation and EGFR phosphorylation at residues targeted by Src and c-cbl and leads to increased surface exposure of EGFR by blocking its internalization. The prolonged EGFR signaling at the plasma membrane enhances cell motility and macropinocytosis, by which junction-associated E-cadherin is internalized and recycled back to AJs. Accordingly, blockage of EGFR signaling or macropinocytosis in reggie-deficient cells restores normal AJ formation. Thus, by promoting EGFR internalization, reggies restrict the EGFR signaling involved in E-cadherin macropinocytosis and recycling and regulate AJ formation and dynamics and thereby cell adhesion. 相似文献
145.
Lima G Furuzawa-Carballeda J Ramos-Bello D Jakez-Ocampo J Pascual-Ramos V Núñez-Alvarez CA Granados J Llorente L 《European cytokine network》2012,23(2):25-28
The aim of this study was to investigate the possible role of the CCR5 59029 A→G promoter point mutation polymorphism in determining the susceptibility to rheumatoid factor-positive and rheumatoid factor-negative rheumatoid arthritis. This polymorphism was assessed in 85 seropositive and 39 seronegative rheumatoid arthritis patients and in 126 healthy individuals of the same geographic and ethnic origin. We found an increase in the genetic frequency of the A allele in the 59029 A→G promoter region of the CCR5 receptor in patients with rheumatoid arthritis compared with healthy controls (p = 0.01; OR = 1.5, 95% CI (1.0-2.2). Likewise, the homozygous state for the A allele was found to be more frequent in rheumatoid arthritis patients, again when compared with healthy controls (p = 0.03; OR = 1.8, 95% CI 1.0-3.0). The increased frequency of the A allele was more evident in the more benign, seronegative rheumatoid arthritis group when compared with controls (p = 0.003; OR 2.4 95% CI 1.3-4.4), and when combining the A homozygous and the AG heterozygous patients compared with healthy subjects. These results suggest that this CCR5 promoter polymorphism seems to play an important role in determining different clinical courses in both forms of rheumatoid arthritis. 相似文献
146.
Aranda F Wingeyer SP Muñoz SA Allievi A Orden A Trobo R Alvarez A Eimon A Barreira JC Schneeberger E Sarano J Hofman J de Larrañaga G 《European cytokine network》2012,23(1):7-11
Systemic lupus erythematosus (SLE) is a systemic, autoimmune disorder. Monocyte chemoattractant protein 1 (MCP-1), a chemokine involved in the recruitment and migration of monocytes/macrophages, has been shown to be increased in the plasma of SLE patients. The aim of our study was to evaluate the possible association of the polymorphism -2518 of the MCP-1 gene with the risk of developing SLE, manifesting lupus nephritis (LN) and with other clinical features of SLE in an Argentinean population. A group of 171 SLE patients and 120 control subjects were examined. Genotypic and allelic frequencies of the MCP-1 -2518 A/G polymorphism showed significant differences between the SLE and the control groups (p=0.001 and p=0.01, respectively). However, the polymorphism showed no association with LN or with the other clinical variables studied. Our results suggest that the presence of the MCP-1 -2518 A/G polymorphism might be a risk factor for developing SLE in genetically predisposed individuals, but it does not seem to have a role in the evolution of the disease in the Argentinean population. 相似文献
147.
Sandra López Beatriz Lima Liliana Aragón Luis Ariza Espinar Alejandro Tapia Susana Zacchino Julio Zygadlo Gabriela Egly Feresin María Liza López 《化学与生物多样性》2012,9(8):1452-1464
The essential oils (EOs) of two populations of Azorella cryptantha (Clos) Reiche , a native species from San Juan Province, were obtained by hydrodistillation in a Clevenger‐type apparatus and characterized by GC‐FID and GC/MS analyses. The compounds identified amounted to 92.3 and 88.7% of the total oil composition for A. cryptantha from Bauchaceta (Ac‐BAU) and Agua Negra (Ac‐AN), respectively. The EO composition for the two populations was similar, although with differences in the identity and content of the main compounds and also in the identity of minor components. The main compounds of the Ac‐BAU EO were α‐pinene, α‐thujene, sabinene, δ‐cadinene, δ‐cadinol, trans‐β‐guaiene, and τ‐muurolol, while α‐pinene, α‐thujene, β‐pinene, γ‐cadinene, τ‐cadinol, δ‐cadinene, τ‐muurolol, and a not identified compound were the main constituents of the Ac‐AN EO, which also contained 3.0% of oxygenated monoterpenes. The repellent activity on Triatoma infestans nymphs was 100 and 92% for the Ac‐AN and Ac‐BAU EOs, respectively. Regarding the toxic effects on Ceratitis capitata, the EOs were very active with LD50 values lower than 11 μg/fly. The dermatophytes Microsporum gypseum, Trichophyton rubrum, and T. mentagrophytes and the bacterial strains Escherichia coli LM1, E. coli LM2, and Yersinia enterocolitica PI were more sensitive toward the Ac‐AN EO (MIC 125 μg/ml) than toward the Ac‐BAU EO. This is the first report on the composition of A. cryptantha EO and its anti‐insect and antimicrobial properties. 相似文献
148.
Jeffery R. Hughey Juan C. Braga Julio Aguirre William J. Woelkerling Jody M. Webster 《Journal of phycology》2008,44(2):374-383
The field of molecular paleontology has recently made significant contributions to anthropology and biology. Hundreds of ancient DNA studies have been published, but none has targeted fossil coralline algae. Using regions of the SSU gene, we analyzed rDNA from fossil coralline algae of varying ages and states of preservation from Spain, Papua New Guinea (PNG), and the Great Barrier Reef (GBR). Specimens from PNG, GBR, and some localities from Spain did not contain endogenous ancient DNA. Reproducible sequence data were obtained from specimens ~550 years old from near Cadiz, Spain, and from rocky‐shore deposits in Carboneras, Almeria Province of Spain (~78,000 years before present [YBP]). Based on BLAST searches and a phylogenetic analysis of sequences, an undescribed coralline alga belonging to the Melobesioideae was discovered in the Carboneras material as well as the following coralline genera: Jania, Lithophyllum, Lithothamnion, Mesophyllum, and Phymatolithon. DNA from fleshy brown and red macroalgae was also discovered in the specimens from Carboneras. The coralline algae identified using molecular techniques were in agreement with those based on morphological methods. The identified taxa are common in the present‐day southeastern Spain littoral zone. Amino acid racemization, concentration ratios, and specific concentrations failed to show a correlation between biomolecular preservation and PCR amplification success. Results suggest that molecular investigations on fossil algae, although limited by technical difficulties, are feasible. Validity of our results was established using authentication criteria and a self‐critical approach to compliance. 相似文献
149.
Garrido N Pérez-Martos A Faro M Lou-Bonafonte JM Fernández-Silva P López-Pérez MJ Montoya J Enríquez JA 《The Biochemical journal》2008,414(1):93-102
Cisplatin accumulates in mitochondria, which are a major target for this drug in cancer cells. Thus alterations in mitochondrial function have been implicated in cancer cell resistance to chemotherapeutic agents. Moreover, cisplatin toxic side effects seem to be associated with mitochondrial injury in vivo and in vitro. In order to clarify the potential effect of cisplatin in mtDNA (mitochondrial DNA) maintenance and expression, we have analysed rat liver mtDNA and mtRNA (mitochondrial RNA) synthesis as well as their stability under the influence of in vivo treatment or in vitro exposure to cisplatin. We show that cisplatin causes a direct and significant impairment of mtDNA and mtRNA synthesis and decreases steady-state levels of mtRNAs in isolated mitochondria. Furthermore, in vivo treatment of the animals with cisplatin exerts a protective effect from the impairment of mtRNA metabolism caused by in vitro exposure to the drug, by means of increased mitochondrial GSH levels after in vivo cisplatin treatment. 相似文献
150.