全文获取类型
收费全文 | 14228篇 |
免费 | 1316篇 |
国内免费 | 1030篇 |
专业分类
电工技术 | 633篇 |
技术理论 | 1篇 |
综合类 | 1073篇 |
化学工业 | 2179篇 |
金属工艺 | 2123篇 |
机械仪表 | 775篇 |
建筑科学 | 932篇 |
矿业工程 | 317篇 |
能源动力 | 311篇 |
轻工业 | 630篇 |
水利工程 | 154篇 |
石油天然气 | 822篇 |
武器工业 | 82篇 |
无线电 | 1370篇 |
一般工业技术 | 1965篇 |
冶金工业 | 1381篇 |
原子能技术 | 134篇 |
自动化技术 | 1692篇 |
出版年
2024年 | 42篇 |
2023年 | 176篇 |
2022年 | 323篇 |
2021年 | 370篇 |
2020年 | 406篇 |
2019年 | 349篇 |
2018年 | 309篇 |
2017年 | 418篇 |
2016年 | 523篇 |
2015年 | 571篇 |
2014年 | 728篇 |
2013年 | 985篇 |
2012年 | 1003篇 |
2011年 | 1092篇 |
2010年 | 865篇 |
2009年 | 892篇 |
2008年 | 767篇 |
2007年 | 965篇 |
2006年 | 856篇 |
2005年 | 753篇 |
2004年 | 667篇 |
2003年 | 527篇 |
2002年 | 464篇 |
2001年 | 400篇 |
2000年 | 362篇 |
1999年 | 335篇 |
1998年 | 253篇 |
1997年 | 195篇 |
1996年 | 181篇 |
1995年 | 148篇 |
1994年 | 117篇 |
1993年 | 105篇 |
1992年 | 72篇 |
1991年 | 61篇 |
1990年 | 73篇 |
1989年 | 64篇 |
1988年 | 42篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 19篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1964年 | 5篇 |
1961年 | 3篇 |
1960年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
Dong Liu Xia Ke Zhong-Ce Hu Yu-Guo Zheng 《Journal of Bioscience and Bioengineering》2021,131(5):518-524
2.
Redundancy allocation problem (RAP) is one of the best-developed problems in reliability engineering studies. This problem follows to optimize the reliability of a system containing s sub-systems under different constraints, including cost, weight, and volume restrictions using redundant components for each sub-system. Various solving methodologies have been used to optimize this problem, including exact, heuristic, and meta-heuristic algorithms. In this paper, an efficient multi-objective meta-heuristic algorithm based on simulated annealing (SA) is developed to solve multi-objective RAP (MORAP). This algorithm is knowledge-based archive multi-objective simulated annealing (KBAMOSA). KBAMOSA applies a memory matrix to reinforce the neighborhood structure to achieve better quality solutions. The results analysis and comparisons demonstrate the performance of the proposed algorithm for solving MORAP. 相似文献
3.
4.
《Ceramics International》2022,48(21):31265-31272
Bismuth layer structured Na0.5Bi4.5Ti4O15 (NBT) ferroelectric is one of the most promising materials for potential applications at high temperature. However, it is challenged to achieve a balance between high Curie temperature piezoelectric coefficient and excellent thermal stability for NBT piezoceramics. Here, through chemical modification at the A site of NBT with Ca2+, novel (Na0.5Bi0.5)1-xCaxBi4Ti4O15 piezoceramics with excellent properties fabricated by solid state reaction were studied. After doping of Ca2+, the Curie temperature TC increased from 648 °C to 662 °C while the piezoelectric coefficient d33 increased from 14 pC/N to 22 pC/N which can be attributed to the intrinsic contribution of TiO6 octahedral lattice distortion (tilting and rotation) and the extrinsic contribution of the increased density of domain walls. The composition of (Na0.5Bi0.5)0.95Ca0.05Bi4Ti4O15 ceramics with x = 0.05 has the optimal performance with high TC of 655 °C, large d33 of 22 pC/N, high electrical resistivity ρ close to 107 Ω cm at 500 °C and especially excellent thermal stability of d33 only about 5% reduction after being annealed at 625 °C. The work effectively reveals the great potential of CNBT-5 ceramics for high-temperature piezoelectric applications. 相似文献
5.
Lorena Rodríguez-López Myriam Rincón-Fontán Xanel Vecino Ana B. Moldes Jose M. Cruz 《Journal of surfactants and detergents》2020,23(1):79-90
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions. 相似文献
6.
Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ... 相似文献
7.
Undoped and fluorine doped ZnO thin films were deposited onto glass substrates using successive ionic layer adsorption and reaction (SILAR) technique and then annealed at 350 °C in vacuum ambience. The F doping level was varied from 0 to 15 at% in steps of 5 at%. The XRD analysis showed that all the films are polycrystalline with hexagonal wurtzite structure and preferentially oriented along the (002) plane. Crystallite sizes were found to increase when 5 at% of F is doped and then decreased with further doping. It was seen from the SEM images that the doping causes remarkable changes in the surface morphology and the annealing treatment results in well-defined grains with an improvement in the grain size irrespective of doping level. All the films exhibit good transparency (>70%) after vacuum annealing. Electrical resistivity of the film was found to be minimum (1.32×10−3 Ω cm) when the fluorine doping level was 5 at%. 相似文献
8.
《Ceramics International》2020,46(10):16548-16555
In this article, NiFe2O4 nanoparticles (NPs) were prepared by co-precipitation method with subsequent thermal annealing leading to obtainment NPs with average sizes of 78 nm. Structure and magnetic analysis were performed by X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy and vibrating sample magnetometry techniques. Stability of NiFe2O4 NPs was evaluated in PBS solution during 20 days. The toxicity of prepared NPs was evaluated in vitro using different cancer cell lines: HeLa (cervical cancer cell), PC-3 (prostate cancer cell). Fibroblasts like cells of L929 obtained from subcutaneous adipose tissue of mouse were used as normal cells. Results indicate successful synthesis of NiFe2O4 NPs that exhibit low cytotoxicity in concentration range from 1 to 100 μg/ml. Presented physical and biological results indicate the possibility of application investigated magnetic nanoparticles in hyperthermia, targeted drug delivery, magnetic resonance imaging or cell separation. 相似文献
9.
10.
摘要:为了研究退火温度对镀锌DP980+Z烘烤硬化值的影响,退火温度控制在760~820℃之间,系统分析退火温度对烘烤硬化值的影响。通过准静态拉伸试验机测量烘烤硬化值及抗拉强度,采用lepara试剂对组织中的马氏体进行着色,利用金相显微镜及图像处理软件测量马氏体的体积分数;采用扫描电镜观察DP980+Z的双相组织特点,并且将组织图片通过CAD转化成有限元图进行网格划分,建立代表性体积单元(RVE),通过有限元分析铁素体、马氏体强度对烘烤硬化值的影响。在同样的变形量情况下,DP980+Z的原始屈服强度越高,烘烤硬化值越高。 相似文献