全文获取类型
收费全文 | 6005篇 |
免费 | 460篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 72篇 |
综合类 | 4篇 |
化学工业 | 1731篇 |
金属工艺 | 74篇 |
机械仪表 | 174篇 |
建筑科学 | 231篇 |
矿业工程 | 15篇 |
能源动力 | 276篇 |
轻工业 | 970篇 |
水利工程 | 77篇 |
石油天然气 | 32篇 |
无线电 | 396篇 |
一般工业技术 | 942篇 |
冶金工业 | 251篇 |
原子能技术 | 29篇 |
自动化技术 | 1201篇 |
出版年
2024年 | 21篇 |
2023年 | 73篇 |
2022年 | 248篇 |
2021年 | 306篇 |
2020年 | 185篇 |
2019年 | 223篇 |
2018年 | 272篇 |
2017年 | 249篇 |
2016年 | 288篇 |
2015年 | 215篇 |
2014年 | 279篇 |
2013年 | 526篇 |
2012年 | 419篇 |
2011年 | 493篇 |
2010年 | 315篇 |
2009年 | 359篇 |
2008年 | 318篇 |
2007年 | 284篇 |
2006年 | 216篇 |
2005年 | 175篇 |
2004年 | 152篇 |
2003年 | 116篇 |
2002年 | 125篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 40篇 |
1998年 | 67篇 |
1997年 | 47篇 |
1996年 | 42篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 4篇 |
排序方式: 共有6475条查询结果,搜索用时 15 毫秒
61.
Felipe Herrera 《JOM Journal of the Minerals, Metals and Materials Society》1963,15(6):443-445
Revolutionary developments in the patterns of world trade have taken place during the past five years, and Latin America is no exception. This article discusses the effects of the Latin American Free Trade Association, the Central American Common Market, and the Inter-American Development Bank on the economic integration of Latin America. 相似文献
62.
Luis O. Soto-Rojas B. Berenice Campa-Crdoba Charles R. Harrington Andrs Salas-Casas Mario Hernandes-Alejandro Ignacio Villanueva-Fierro Marely Bravo-Muoz Linda Garcs-Ramírez Fidel De La Cruz-Lpez Miguel ngel Ontiveros-Torres Goar Gevorkian Mar Pacheco-Herrero Jos Luna-Muoz 《International journal of molecular sciences》2021,22(7)
Alzheimer’s disease (AD) is a neurodegenerative disease, characterized histopathologically by intra-neuronal tau-related lesions and by the accumulation of amyloid β-peptide (Aβ) in the brain parenchyma and around cerebral blood vessels. According to the vascular hypothesis of AD, an alteration in the neurovascular unit (NVU) could lead to Aβ vascular accumulation and promote neuronal dysfunction, accelerating neurodegeneration and dementia. To date, the effects of insoluble vascular Aβ deposits on the NVU and the blood–brain barrier (BBB) are unknown. In this study, we analyze different Aβ species and their association with the cells that make up the NVU. We evaluated post-mortem AD brain tissue. Multiple immunofluorescence assays were performed against different species of Aβ and the main elements that constitute the NVU. Our results showed that there are insoluble vascular deposits of both full-length and truncated Aβ species. Besides, insoluble aggregates are associated with a decrease in the phenotype of the cellular components that constitute the NVU and with BBB disruption. This approach could help identify new therapeutic targets against key molecules and receptors in the NVU that can prevent the accumulation of vascular fibrillar Aβ in AD. 相似文献
63.
64.
Sofía Valla Nourhan Hassan Daiana Lujn Vitale Daniela Madanes Fiorella Mercedes Spinelli Felipe C. O. B. Teixeira Burkhard Greve Nancy Adriana Espinoza-Snchez Carolina Cristina Laura Alaniz Martin Gtte 《International journal of molecular sciences》2021,22(11)
Glycosaminoglycans (GAGs) and proteoglycans (PGs) are major components of the glycocalyx. The secreted GAG and CD44 ligand hyaluronic acid (HA), and the cell surface PG syndecan-1 (Sdc-1) modulate the expression and activity of cytokines, chemokines, growth factors, and adhesion molecules, acting as critical regulators of tumor cell behavior. Here, we studied the effect of Sdc-1 siRNA depletion and HA treatment on hallmark processes of cancer in breast cancer cell lines of different levels of aggressiveness. We analyzed HA synthesis, and parameters relevant to tumor progression, including the stem cell phenotype, Wnt signaling constituents, cell cycle progression and apoptosis, and angiogenic markers in luminal MCF-7 and triple-negative MDA-MB-231 cells. Sdc-1 knockdown enhanced HAS-2 synthesis and HA binding in MCF-7, but not in MDA-MB-231 cells. Sdc-1-depleted MDA-MB-231 cells showed a reduced CD24-/CD44+ population. Furthermore, Sdc-1 depletion was associated with survival signals in both cell lines, affecting cell cycle progression and apoptosis evasion. These changes were linked to the altered expression of KLF4, MSI2, and miR-10b and differential changes in Erk, Akt, and PTEN signaling. We conclude that Sdc-1 knockdown differentially affects HA metabolism in luminal and triple-negative breast cancer model cell lines and impacts the stem phenotype, cell survival, and angiogenic factors. 相似文献
65.
Canan Akay Neslihan Turan Duygu Karakış Luis Alberto Angurel 《International Journal of Applied Ceramic Technology》2021,18(1):51-59
Zirconia is a dental material that shows excellent biocompatibility and high strength in clinical applications. This study aims to evaluate the effects of ultrafast laser applications. The surface nanostructures were classified into three groups. Group 1 was generated using the burst mode, with three different distances between dots: 52 µm (Group 1a), 104 µm (Group 1b), and 156 µm (Group 1c). Group 2 was processed using the scanning mode configuration, with a set of parallel lines. Group 3 was also processed using this scanning configuration creating a set of square-shaped patterning. Group 4 was the control group. After the surface treatments, a pair of zirconia specimens was bonded end to end with resin cement. Flexural bond strength (FBS) test was applied in a universal test machine. Multiple comparisons were performed using a one-way analysis of variance and the Tukey's HSD test. All the samples that were treated with the laser showed higher FBS values than the untreated surface. Using the burst mode, preformed circular-shaped surface on an angle of 900 at 52 µm distance (Group 1a) showed the highest FBS values among all groups (p < .05). Groups 2 and 3 had significantly higher values than 1b and 1c. 相似文献
66.
Luis Fernando Crdoba Wolfgang M.H. Sachtler Consuelo Montes de Correa 《Applied catalysis. B, Environmental》2005,56(4):269-277
A series of sulfated zirconia supported Pd/Co catalysts was synthesized by the sol–gel method and examined for NOx reduction by methane. The NO conversion increased up to a Co/S ratio of 0.43, and then decreased at a higher Co loading (Co/S = 0.95). Sulfate content was also essential for obtaining high selectivity to molecular nitrogen. A catalyst loaded with 0.06 wt.% Pd, 2.1 wt.% Co and 2.1 wt.% S (Pd/Co-SZ-2) exhibited remarkable performance under lean conditions and displayed stability in a long-term durability test using a synthetic reaction mixture containing 10% water vapor. This catalyst exhibited the highest sulfur retention most probably as cobalt sulfide. Besides, the catalytic oxidation of NO to NOy groups was confirmed by FT-IR, in agreement with the general mechanism for the SCR of NO by hydrocarbons. In the absence of oxygen in the feed stream, the catalyst was highly active for NO reduction with methane. IR stretching bands assigned to N2O and adsorbed nitro groups were identified upon adsorbing NO on Pd/Co-SZ-2. This indicates that under rich conditions disproportionation of NO to N2O and NO2 occurs and confirms that the formation of NO2 species is an essential step for NO reduction by CH4. 相似文献
67.
Luis A. Pérez-Maqueda José Manuel Criado Concepción Real 《Journal of the American Ceramic Society》2002,85(4):763-768
A new method for the kinetic analysis of the initial stage of sintering for constant-heating-rate data has been proposed. Unlike all of the methods previously reported in the literature, this new method proposed here allows the simultaneous determination of the activation energy and the kinetic model from a single dilatometric curve recorded under a linear-heating-rate program. The proposed method has been tested with simulated sintering curves and experimental results have been obtained for the sintering of a rutile sample. 相似文献
68.
Raúl Quijada Juan Luis Guevara Mehrdad Yazdani-Pedram Griselda B. Galland Daniel Ribeiro 《Polymer Bulletin》2002,49(4):273-280
Summary
1-Octadecene (C18) was polymerized by using different metallocene catalysts. The rac-Et(Ind)2ZrC12/MAO (I) and rac-Me2Si(Ind)2ZrC12/MAO (III) presented the highest activity as compared with ra-Et(2-Me-Ind)2ZrCl2/MAO (II) and Ph2C(Flu)(Cp)ZrC12/MAO (IV) catalysts. Catalyst IV produced polymers with highest molecular weights. The microstructure of the polymers was
determined by 13C-NMR spectroscopy. Catalyst systems I, II and III produced isotactic polymers while catalyst IV produced polymers with mainly
syndiotactic structures but with large amount of stereoregular error.
Received: 21 June 2002/Revised version: 4 November 2002/ Accepted: 4 November 2002 相似文献
69.
Juan José Jiménez José Luis Bernal María Jesús del Nozal Laura Toribio José Bernal 《European Journal of Lipid Science and Technology》2007,109(7):682-690
The concentrations of 102 chemical compounds (saturated and unsaturated hydrocarbons, palmitates, total and free acids, total hydroxyacids, total and free alcohols, acidic monoesters and monoesterified 1,2,3‐propanetriols) have been determined by GC/FID on white and yellow comb beeswax of Apis mellifera from different regions of Spain. Guide‐value ranges are proposed for its characterization and to discriminate adulterated foundation beeswax sheets. The concentrations of many compounds resulted to be statistically different for white and yellow beeswaxes, while the observation of concentrations out of normal in some marketed foundation beeswax sheets suggested their adulteration. However, the measurement of anomalous concentrations in foundation beeswax sheets did not imply necessarily their rejection by the bees. 相似文献
70.
Sergio Alonso-Romero Luis Medina-Torres Roberto Zitzumbo Diola Marina Nuñez-Ramirez 《Chemical Engineering Communications》2020,207(7):933-945
AbstractThe synthesis and the corresponding characterization of styrene-butadiene (SB), branched, star-shaped copolymers was investigated as part of a research project on asphalt modification using polymers with precise molecular structures. The method of anionic polymerization was followed to prepare samples of block copolymers of SB, a synthesis method that controls chain-architecture, molecular weight distribution, monomer distribution, and the average molecular weight. The research studies are the synthesis of block copolymers including linear, three- and four-arms constructs, depending on the coupling agent used. The techniques of nuclear magnetic resonance (1NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology were carried out to characterize the copolymers. From the results of the 1NMR, DSC, and GPC analyses, all star-shaped copolymers investigated showed a similar block copolymer composition. Furthermore, the rheological behavior of one of the synthesized star-shaped copolymers was nearly the same as a four-branched commercial copolymer. Rheologically, the four-arm block copolymer sample had the largest storage modulus (G′) among the branched copolymers synthetized, indicating that such architecture produces a highly structured material. In regard to polymer-modified asphalt formulations, the three-branched copolymer architecture yielded better elastic behavior than the four-branch version. In summary, the findings of this investigation provide new insight about a polymer system that may offer advantages in industrial asphalt paving applications. 相似文献