全文获取类型
收费全文 | 133069篇 |
免费 | 9753篇 |
国内免费 | 7775篇 |
专业分类
电工技术 | 4609篇 |
技术理论 | 2篇 |
综合类 | 7366篇 |
化学工业 | 39780篇 |
金属工艺 | 14553篇 |
机械仪表 | 3807篇 |
建筑科学 | 3059篇 |
矿业工程 | 1911篇 |
能源动力 | 4788篇 |
轻工业 | 8885篇 |
水利工程 | 933篇 |
石油天然气 | 4775篇 |
武器工业 | 738篇 |
无线电 | 12164篇 |
一般工业技术 | 22911篇 |
冶金工业 | 5285篇 |
原子能技术 | 1594篇 |
自动化技术 | 13437篇 |
出版年
2024年 | 386篇 |
2023年 | 2090篇 |
2022年 | 4154篇 |
2021年 | 4607篇 |
2020年 | 3485篇 |
2019年 | 3255篇 |
2018年 | 3019篇 |
2017年 | 3699篇 |
2016年 | 4359篇 |
2015年 | 4919篇 |
2014年 | 6541篇 |
2013年 | 7461篇 |
2012年 | 8190篇 |
2011年 | 11360篇 |
2010年 | 8828篇 |
2009年 | 9876篇 |
2008年 | 8371篇 |
2007年 | 9310篇 |
2006年 | 8040篇 |
2005年 | 6660篇 |
2004年 | 5739篇 |
2003年 | 5129篇 |
2002年 | 4243篇 |
2001年 | 2880篇 |
2000年 | 2543篇 |
1999年 | 2081篇 |
1998年 | 1625篇 |
1997年 | 1287篇 |
1996年 | 1174篇 |
1995年 | 984篇 |
1994年 | 907篇 |
1993年 | 681篇 |
1992年 | 535篇 |
1991年 | 420篇 |
1990年 | 361篇 |
1989年 | 279篇 |
1988年 | 186篇 |
1987年 | 127篇 |
1986年 | 123篇 |
1985年 | 103篇 |
1984年 | 80篇 |
1983年 | 51篇 |
1982年 | 77篇 |
1981年 | 86篇 |
1980年 | 110篇 |
1979年 | 38篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1975年 | 20篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Y.H. Sun 《Materials Research Bulletin》2004,39(9):1247-1255
Effects of Ca and Zr substitution upon the dielectric properties of Ba5LaTi3Ta7O30 ceramics were investigated together with the structural characterization. All the samples of Ba5La(ZrxTi1−x)3Ta7O30 formed a filled tungsten-bronze structures, whereas the solid solution limit was determined as x=0.25 in (CaxBa1−x)5LaTi3Ta7O30. Beyond this limit secondary phase of CaTa2O6 was detected and it would become the major phase for the Ca-rich compositions. The temperature coefficient of dielectric constant was improved with increasing Zr content while the dielectric constant decreased and the low dielectric loss varied little (in the order of 10−4). In the case of (CaxBa1−x)5LaTi3Ta7O30, small temperature coefficient of dielectric constant could be obtained with increasing Ca content while the dielectric constant decreased significantly, and a small amount substitution of Ca for Ba induced decrease in dielectric loss. 相似文献
52.
K Madhusudan Reddy Sunkara V Manorama R.D.K Misra 《Materials Research Bulletin》2004,39(10):1491-1498
A comparative study of gas sensing behavior of nanocrystalline nickel ferrite synthesized by micro-emulsion and hydrothermal method to liquefied petroleum gas (LPG) is presented. Nanocrystalline nickel ferrite synthesized by hydrothermal method indicated higher electrical conductivity and gas sensitivity at low operating temperature compared to nanocrystalline nickel ferrite synthesized by reverse micelle technique. This difference in the gas sensing behavior can be attributed to the presence of more oxygen vacancies (i.e. non-stoichiometry) in the hydrothermally synthesized nickel ferrite. Incorporation of palladium had a catalytic effect and the operating temperature was significantly reduced in both the samples. The higher operating temperature of the reverse micelle nickel ferrite material makes the sensor response speed faster (∼10 s) compared to the hydrothermally synthesized material (∼1 min). 相似文献
53.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
54.
The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga2O3 in CeO2.Sintered density increased with increasing Ga2O3 content up to 5 mol.% and then it decreased with further addition of Ga2O3. Grain size also increased with increasing Ga2O3 content up to 5 mol.% and then decreased with further addition of Ga2O3. Decrease in grain size was caused by a pinning effect of Ga2O3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga2O3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga2O3 in Ce0.8Gd0.2O1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2. 相似文献
55.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
56.
O. Khamman 《Materials Letters》2007,61(3):639-643
The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb2O6) powders. The formation of the NiNb2O6 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb2O5 precursors and the Ni4Nb2O9 phase tend to form together with the columbite NiNb2O6 phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb2O6 in an orthorhombic phase. 相似文献
57.
2-环戊基环戊酮香料的制备与应用 总被引:2,自引:0,他引:2
以尼龙酸副产物2-亚环戊基环戊酮为原料,液体镍为催化剂,催化加氢制得了2-环戊基环戊酮。经元素分析、GCMS、IR、^1HNMR、^13C NMR检测,认为结构正确,色谱纯度大于99.9%。大鼠口服LD50雄性5381.5mg/kg,雌性5087.5mg/kg。具有留兰香样的香气,可用作食用和日用香料。 相似文献
58.
以C9油与甲基丙烯酰氧乙基三甲基氯化胺的共聚物P(C9-DMC)为乳化剂制备苯/丙阳离子乳胶粒,并以其为模板,利用直接包覆法制备了由17 nm左右微晶体堆成的ZrO2空心微球。所制得的样品采用FT-IR、XRD、TEM和SEM等进行了表征。 相似文献
59.
Natalia Andronova 《Polymer》2005,46(18):6746-6755
The synthesis and characterization of degradable polymeric networks for biomedical applications was performed. Cross-linked films of poly(ε-caprolactone) (PCL) and poly(1,5-dioxepan-2-one) (PDXO) having various mole fractions of monomers and different cross-link densities were successfully prepared using 2,2′-bis-(ε-caprolactone-4-yl) propane (BCP) as cross-linking agent. Reaction parameters were carefully examined to optimise the film-forming conditions. Networks obtained were elastomeric materials, easy to cast and remove from the mould. Effect of CL content and cross-link density on the final properties of the polymer network was evaluated. High CL content or degree of cross-linking led to increase in Young's modulus and decrease in elongation at break. An increase in crystalline domains in films having a higher CL content was observed by optical microscopy. A greater thermal stability was observed in films having a high CL content. The hydrophilicity of the materials could be tailored by changing the CL content. The surface of the films became rougher with higher CL content. 相似文献
60.
The switchable optical properties of Pd-protected RCo2-type Ho0.6Mm0.4Co2 alloy thin films have been investigated in a KOH electrolyte. The reversible optical switching has been carried out simultaneously by measuring transmitted light through the thin film during electrochemical charging–discharging of hydrogen. The dependence of switching speed and cyclic durability of the film on the charging and discharging current density as well as concentration of KOH electrolyte has been studied. In addition, cyclic voltammetric measurements have been performed to examine the hydride formation and decomposition reactions. 相似文献