全文获取类型
收费全文 | 15631篇 |
免费 | 831篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 169篇 |
综合类 | 43篇 |
化学工业 | 3348篇 |
金属工艺 | 312篇 |
机械仪表 | 317篇 |
建筑科学 | 690篇 |
矿业工程 | 47篇 |
能源动力 | 506篇 |
轻工业 | 1241篇 |
水利工程 | 125篇 |
石油天然气 | 51篇 |
无线电 | 1113篇 |
一般工业技术 | 2977篇 |
冶金工业 | 2300篇 |
原子能技术 | 117篇 |
自动化技术 | 3134篇 |
出版年
2023年 | 167篇 |
2022年 | 360篇 |
2021年 | 575篇 |
2020年 | 382篇 |
2019年 | 381篇 |
2018年 | 496篇 |
2017年 | 462篇 |
2016年 | 533篇 |
2015年 | 465篇 |
2014年 | 596篇 |
2013年 | 1069篇 |
2012年 | 975篇 |
2011年 | 1164篇 |
2010年 | 808篇 |
2009年 | 748篇 |
2008年 | 789篇 |
2007年 | 775篇 |
2006年 | 583篇 |
2005年 | 504篇 |
2004年 | 372篇 |
2003年 | 381篇 |
2002年 | 340篇 |
2001年 | 213篇 |
2000年 | 187篇 |
1999年 | 208篇 |
1998年 | 233篇 |
1997年 | 194篇 |
1996年 | 191篇 |
1995年 | 178篇 |
1994年 | 156篇 |
1993年 | 151篇 |
1992年 | 119篇 |
1991年 | 75篇 |
1990年 | 122篇 |
1989年 | 116篇 |
1988年 | 82篇 |
1987年 | 93篇 |
1986年 | 103篇 |
1985年 | 101篇 |
1984年 | 88篇 |
1983年 | 77篇 |
1982年 | 97篇 |
1981年 | 92篇 |
1980年 | 72篇 |
1979年 | 71篇 |
1978年 | 62篇 |
1977年 | 74篇 |
1976年 | 65篇 |
1975年 | 45篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Colloidal Mn (2+)-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to tau exc = 15 mus at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by approximately 10 (3) and are shown to arise from the creation of excitons by back energy transfer from excited Mn (2+) dopant ions. A kinetic model describing thermal equilibrium between Mn (2+ 4)T 1 and CdSe excitonic excited states reproduces the experimental observations and reveals that, for some quantum dots, excitons can emit with near unity probability despite being approximately 100 meV above the Mn (2+ 4)T 1 state. The effect of Mn (2+) doping on CdSe quantum dot luminescence at high temperatures is thus completely opposite from that at low temperatures described previously. 相似文献
72.
Adelina Orellana Pablo García-Gonzlez Sergi Valero Laura Montrreal Itziar de Rojas Isabel Hernndez Maitee Rosende-Roca Liliana Vargas Juan Pablo Tartari Ester Esteban-De Antonio Urszula Bojaryn Leire Narvaiza Emilio Alarcn-Martín Montserrat Alegret Daniel Alcolea Alberto Lle Lluís Trraga Vanesa Pytel Amanda Cano Marta Marqui Merc Boada Agustín Ruiz 《International journal of molecular sciences》2022,23(13)
Background: Clinical diagnosis of Alzheimer’s disease (AD) increasingly incorporates CSF biomarkers. However, due to the intrinsic variability of the immunodetection techniques used to measure these biomarkers, establishing in-house cutoffs defining the positivity/negativity of CSF biomarkers is recommended. However, the cutoffs currently published are usually reported by using cross-sectional datasets, not providing evidence about its intrinsic prognostic value when applied to real-world memory clinic cases. Methods: We quantified CSF Aβ1-42, Aβ1-40, t-Tau, and p181Tau with standard INNOTEST® ELISA and Lumipulse G® chemiluminescence enzyme immunoassay (CLEIA) performed on the automated Lumipulse G600II. Determination of cutoffs included patients clinically diagnosed with probable Alzheimer’s disease (AD, n = 37) and subjective cognitive decline subjects (SCD, n = 45), cognitively stable for 3 years and with no evidence of brain amyloidosis in 18F-Florbetaben-labeled positron emission tomography (FBB-PET). To compare both methods, a subset of samples for Aβ1-42 (n = 519), t-Tau (n = 399), p181Tau (n = 77), and Aβ1-40 (n = 44) was analyzed. Kappa agreement of single biomarkers and Aβ1-42/Aβ1-40 was evaluated in an independent group of mild cognitive impairment (MCI) and dementia patients (n = 68). Next, established cutoffs were applied to a large real-world cohort of MCI subjects with follow-up data available (n = 647). Results: Cutoff values of Aβ1-42 and t-Tau were higher for CLEIA than for ELISA and similar for p181Tau. Spearman coefficients ranged between 0.81 for Aβ1-40 and 0.96 for p181TAU. Passing–Bablok analysis showed a systematic and proportional difference for all biomarkers but only systematic for Aβ1-40. Bland–Altman analysis showed an average difference between methods in favor of CLEIA. Kappa agreement for single biomarkers was good but lower for the Aβ1-42/Aβ1-40 ratio. Using the calculated cutoffs, we were able to stratify MCI subjects into four AT(N) categories. Kaplan–Meier analyses of AT(N) categories demonstrated gradual and differential dementia conversion rates (p = 9.815−27). Multivariate Cox proportional hazard models corroborated these findings, demonstrating that the proposed AT(N) classifier has prognostic value. AT(N) categories are only modestly influenced by other known factors associated with disease progression. Conclusions: We established CLEIA and ELISA internal cutoffs to discriminate AD patients from amyloid-negative SCD individuals. The results obtained by both methods are not interchangeable but show good agreement. CLEIA is a good and faster alternative to manual ELISA for providing AT(N) classification of our patients. AT(N) categories have an impact on disease progression. AT(N) classifiers increase the certainty of the MCI prognosis, which can be instrumental in managing real-world MCI subjects. 相似文献
73.
Rocío Fernndez-Serra Emma Martínez-Alonso Alberto Alczar Mourad Chioua Jos Marco-Contelles Ricardo Martínez-Murillo Milagros Ramos Gustavo V. Guinea Daniel Gonzlez-Nieto 《International journal of molecular sciences》2022,23(13)
Brain stroke is a highly prevalent pathology and a main cause of disability among older adults. If not promptly treated with recanalization therapies, primary and secondary mechanisms of injury contribute to an increase in the lesion, enhancing neurological deficits. Targeting excitotoxicity and oxidative stress are very promising approaches, but only a few compounds have reached the clinic with relatively good positive outcomes. The exploration of novel targets might overcome the lack of clinical translation of previous efficient preclinical neuroprotective treatments. In this study, we examined the neuroprotective properties of 2-aminoethoxydiphenyl borate (2-APB), a molecule that interferes with intracellular calcium dynamics by the antagonization of several channels and receptors. In a permanent model of cerebral ischemia, we showed that 2-APB reduces the extent of the damage and preserves the functionality of the cortical territory, as evaluated by somatosensory evoked potentials (SSEPs). While in this permanent ischemia model, the neuroprotective effect exerted by the antioxidant scavenger cholesteronitrone F2 was associated with a reduction in reactive oxygen species (ROS) and better neuronal survival in the penumbra, 2-APB did not modify the inflammatory response or decrease the content of ROS and was mostly associated with a shortening of peri-infarct depolarizations, which translated into better cerebral blood perfusion in the penumbra. Our study highlights the potential of 2-APB to target spreading depolarization events and their associated inverse hemodynamic changes, which mainly contribute to extension of the area of lesion in cerebrovascular pathologies. 相似文献
74.
Lucas Taoro-Gonzlez Daniel Pereda Catalina Valds-Baizabal Miriam Gonzlez-Gmez Jos A. Prez Ftima Mesa-Herrera Ana Canerina-Amaro Herminia Prez-Gonzlez Covadonga Rodríguez Mario Díaz Raquel Marin 《International journal of molecular sciences》2022,23(13)
Long-chain polyunsaturated fatty acids (LCPUFA), essential molecules whose precursors must be dietary supplied, are highly represented in the brain contributing to numerous neuronal processes. Recent findings have demonstrated that LCPUFA are represented in lipid raft microstructures, where they favor molecular interactions of signaling complexes underlying neuronal functionality. During aging, the brain lipid composition changes affecting the lipid rafts’ integrity and protein signaling, which may induce memory detriment. We investigated the effect of a n-3 LCPUFA-enriched diet on the cognitive function of 6- and 15-months-old female mice. Likewise, we explored the impact of dietary n-3 LCPUFAs on hippocampal lipid rafts, and their potential correlation with aging-induced neuroinflammation. Our results demonstrate that n-3 LCPUFA supplementation improves spatial and recognition memory and restores the expression of glutamate and estrogen receptors in the hippocampal lipid rafts of aged mice to similar profiles than young ones. Additionally, the n-3 LCPUFA-enriched diet stabilized the lipid composition of the old mice’s hippocampal lipid rafts to the levels of young ones and reduced the aged-induced neuroinflammatory markers. Hence, we propose that n-3 LCPUFA supplementation leads to beneficial cognitive performance by “rejuvenating” the lipid raft microenvironment that stabilizes the integrity and interactions of memory protein players embedded in these microdomains. 相似文献
75.
Camila Reyes Estefanía Nova-Lamperti Daniel Duran-Sandoval Daniela Rojas Jorge Gajardo Enrique Guzman-Gutierrez Camila Bustos-Ruiz Valeska Ormazbal Felipe A. Zúiga Carlos Escudero Claudio Aguayo 《International journal of molecular sciences》2022,23(13)
Oxidized low-density lipoprotein (ox-LDL) is the most harmful form of cholesterol associated with vascular atherosclerosis and hepatic injury, mainly due to inflammatory cell infiltration and subsequent severe tissue injury. Lox-1 is the central ox-LDL receptor expressed in endothelial and immune cells, its activation regulating inflammatory cytokines and chemotactic factor secretion. Recently, a Lox-1 truncated protein isoform lacking the ox-LDL binding domain named LOXIN has been described. We have previously shown that LOXIN overexpression blocked Lox-1-mediated ox-LDL internalization in human endothelial progenitor cells in vitro. However, the functional role of LOXIN in targeting inflammation or tissue injury in vivo remains unknown. In this study, we investigate whether LOXIN modulated the expression of Lox-1 and reduced the inflammatory response in a high-fat-diet mice model. Results indicate that human LOXIN blocks Lox-1 mediated uptake of ox-LDL in H4-II-E-C3 cells. Furthermore, in vivo experiments showed that overexpression of LOXIN reduced both fatty streak lesions in the aorta and inflammation and fibrosis in the liver. These findings were associated with the down-regulation of Lox-1 in endothelial cells. Then, LOXIN prevents hepatic and aortic tissue damage in vivo associated with reduced Lox-1 expression in endothelial cells. We encourage future research to understand better the underlying molecular mechanisms and potential therapeutic use of LOXIN. 相似文献
76.
Jean-Baptiste Domergue Julie Lalande Daniel Beucher Pascale Satour Cyril Abadie Anis M. Limami Guillaume Tcherkez 《International journal of molecular sciences》2022,23(15)
Seed size is often considered to be an important trait for seed quality, i.e., vigour and germination performance. It is believed that seed size reflects the quantity of reserve material and thus the C and N sources available for post-germinative processes. However, mechanisms linking seed size and quality are poorly documented. In particular, specific metabolic changes when seed size varies are not well-known. To gain insight into this aspect, we examined seed size and composition across different accessions of barrel medic (Medicago truncatula Gaertn.) from the genetic core collection. We conducted multi-elemental analyses and isotope measurements, as well as exact mass GC–MS metabolomics. There was a systematic increase in N content (+0.17% N mg−1) and a decrease in H content (–0.14% H mg−1) with seed size, reflecting lower lipid and higher S-poor protein quantity. There was also a decrease in 2H natural abundance (δ2H), due to the lower prevalence of 2H-enriched lipid hydrogen atoms that underwent isotopic exchange with water during seed development. Metabolomics showed that seed size correlates with free amino acid and hexoses content, and anticorrelates with amino acid degradation products, disaccharides, malic acid and free fatty acids. All accessions followed the same trend, with insignificant differences in metabolic properties between them. Our results show that there is no general, proportional increase in metabolite pools with seed size. Seed size appears to be determined by metabolic balance (between sugar and amino acid degradation vs. utilisation for storage), which is in turn likely determined by phloem source metabolite delivery during seed development. 相似文献
77.
78.
Previously unexplored resonance conditions are shown to exist for the classical hydrogen atomic system, where the electron
is treated as a classical charged point particle following the nonrelativistic Lorentz-Dirac equation of motion about a stationary
nucleus of opposite charge. For circularly polarized (CP) light directed normal to the orbit, very pronounced subharmonic
resonance behavior is shown to occur with a variety of interesting properties. In particular, only if the amplitude of the
CP light exceeds a critical value, will the resonance continue without radius and energy decay. A perturbation analysis is
carried out to illustrate the main features of the behavior. The present phenomena adds to a growing list of other nonlinear
dynamical behaviors of this simple system, that may well be important for more deeply understanding classical and quantum
connections. 相似文献
79.
Sara Garcinuo Francisco Javier Gil-Etayo Esther Mancebo Marta Lpez-Nevado Antonio Lalueza Raquel Díaz-Simn Daniel Enrique Pleguezuelo Manuel Serrano Oscar Cabrera-Marante Luis M. Allende Estela Paz-Artal Antonio Serrano 《International journal of molecular sciences》2022,23(12)
NK degranulation plays an important role in the cytotoxic activity of innate immunity in the clearance of intracellular infections and is an important factor in the outcome of the disease. This work has studied NK degranulation and innate immunological profiles and functionalities in COVID-19 patients and its association with the severity of the disease. A prospective observational study with 99 COVID-19 patients was conducted. Patients were grouped according to hospital requirements and severity. Innate immune cell subpopulations and functionalities were analyzed. The profile and functionality of innate immune cells differ between healthy controls and severe patients; CD56dim NK cells increased and MAIT cells and NK degranulation rates decreased in the COVID-19 subjects. Higher degranulation rates were observed in the non-severe patients and in the healthy controls compared to the severe patients. Benign forms of the disease had a higher granzymeA/granzymeB ratio than complex forms. In a multivariate analysis, the degranulation capacity resulted in a protective factor against severe forms of the disease (OR: 0.86), whereas the permanent expression of NKG2D in NKT cells was an independent risk factor (OR: 3.81; AUC: 0.84). In conclusion, a prompt and efficient degranulation functionality in the early stages of infection could be used as a tool to identify patients who will have a better evolution. 相似文献
80.