全文获取类型
收费全文 | 76590篇 |
免费 | 5946篇 |
国内免费 | 3196篇 |
专业分类
电工技术 | 5279篇 |
技术理论 | 21篇 |
综合类 | 13578篇 |
化学工业 | 5884篇 |
金属工艺 | 3975篇 |
机械仪表 | 4598篇 |
建筑科学 | 12790篇 |
矿业工程 | 3775篇 |
能源动力 | 1877篇 |
轻工业 | 3694篇 |
水利工程 | 4549篇 |
石油天然气 | 2939篇 |
武器工业 | 500篇 |
无线电 | 4978篇 |
一般工业技术 | 4517篇 |
冶金工业 | 4071篇 |
原子能技术 | 499篇 |
自动化技术 | 8208篇 |
出版年
2024年 | 86篇 |
2023年 | 596篇 |
2022年 | 1204篇 |
2021年 | 1430篇 |
2020年 | 1455篇 |
2019年 | 1113篇 |
2018年 | 1130篇 |
2017年 | 1573篇 |
2016年 | 1902篇 |
2015年 | 2410篇 |
2014年 | 5648篇 |
2013年 | 4012篇 |
2012年 | 5399篇 |
2011年 | 5953篇 |
2010年 | 4783篇 |
2009年 | 5197篇 |
2008年 | 4595篇 |
2007年 | 6080篇 |
2006年 | 5644篇 |
2005年 | 4825篇 |
2004年 | 3957篇 |
2003年 | 3279篇 |
2002年 | 2630篇 |
2001年 | 2226篇 |
2000年 | 1903篇 |
1999年 | 1385篇 |
1998年 | 892篇 |
1997年 | 705篇 |
1996年 | 679篇 |
1995年 | 585篇 |
1994年 | 501篇 |
1993年 | 380篇 |
1992年 | 320篇 |
1991年 | 199篇 |
1990年 | 207篇 |
1989年 | 197篇 |
1988年 | 147篇 |
1987年 | 93篇 |
1986年 | 73篇 |
1985年 | 49篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 19篇 |
1981年 | 41篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1975年 | 13篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
2.
《Current Opinion in Solid State & Materials Science》2022,26(6):101024
One of the main challenges in the laser powder bed fusion (LPBF) process is making dense and defect-free components. These porosity defects are dependent upon the melt pool geometry and the processing conditions. Power-velocity (PV) processing maps can aid in visualizing the effects of LPBF processing variables and mapping different defect regimes such as lack-of-fusion, under-melting, balling, and keyholing. This work presents an assessment of existing analytical equations and models that provide an estimate of the melt pool geometry as a function of material properties. The melt pool equations are then combined with defect criteria to provide a quick approximation of the PV processing maps for a variety of materials. Finally, the predictions of these processing maps are compared with experimental data from the literature. The predictive processing maps can be computed quickly and can be coupled with dimensionless numbers and high-throughput (HT) experiments for validation. The present work provides a boundary framework for designing the optimal processing parameters for new metals and alloys based on existing analytical solutions. 相似文献
3.
为应对"三软"煤层综放沿空掘巷围岩稳定性差的问题,通过数值模拟分析、揭示"三软"煤层中锚杆、锚索载荷变化规律及其与围岩变形相互作用关系,为"三软"煤层沿空掘巷锚网支护参数优化提供理论依据,改善了巷道支护状况,降低相邻工作面间保护煤柱压煤率,提高矿井经济效益和社会效益。 相似文献
4.
为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成;细菌群落在不同季节有显著差异;地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用;随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。 相似文献
5.
Abdellatif GHEDIRA 《粮油食品科技》2022,30(1):79-82
The International Olive Council(IOC) is an international intergovernmental organization dedicated to olive oil and table olives, aiming at modernizing olive production, coordinating olive policies, improving the regulation of international trade, defending the quality of the olive sector and promoting olive oil and table olives to increase their consumption. The IOC grants recognition of laboratories and tasting panels in annual trials when they meet the conditions given in the decisions adopting the IOC certificate for laboratories for the physico–chemical testing of olive oil and laboratories for the sensory analysis of virgin olive oils. The IOC establishes analysis methods applying to olive oils and olive pomace oils for purity, quality and organoleptic assessment. The IOC elaborates guides of storage conditions for olive oils and olive pomace oils, of managing virgin olive oil tasting panels and of sensory testing laboratories. In future works, the IOC includes activities to identify analytical criteria for detecting fraud and guaranteeing the quality of olive oils and olive pomace oils. 相似文献
6.
针对大尺寸光学平面的直线度的纳米级测量精度需求,提出了倾斜入射下单截面平面度绝对检验方法,实现了对超过相移干涉仪口径的长平晶绝对检验。利用棱镜转向实现倾斜入射角度的精密预标定,棱镜标定角度的精度高于圆光栅和图像分析等方法,可提高测量不确定度到0.0042 μm。对比了常规三面互检绝对检验结果与本方法的差异,在相同尺寸下,直线度误差仅为1.2 nm。在确认标定反射镜位置后,整个倾斜入射的干涉图调整过程将被完全集中到待测长平晶的工作面上,不需要再对反射平晶进行操作。调整长平晶时各个维度的操作互不干涉,可快速简便地得到测量结果。 相似文献
7.
8.
Prof. Tsung-Shing Andrew Wang Ruo-Yu Wu Yu Hong Dr. Zhe-Chong Wang Dr. Tsung-Lin Li Dr. Jiun-Jie Shie Prof. Cheng-Chih Hsu 《Chembiochem : a European journal of chemical biology》2021,22(14):2415-2419
Secondary metabolites are structurally diverse natural products (NPs) and have been widely used for medical applications. Developing new tools to enrich NPs can be a promising solution to isolate novel NPs from the native and complex samples. Here, we developed native and deuterated chemoselective labeling probes to target phenol-containing glycopeptides by the ene-type labeling used in proteomic research. The clickable azido-linker was included for further biotin functionalization to facilitate the enrichment of labeled substrates. Afterward, our chemoselective method, in conjunction with LC-MS and MSn analysis, was demonstrated in bacterial cultures. A vancomycin-related phenol-containing glycopeptide was labeled and characterized by our labeling strategy, showing its potential in glycopeptide discovery in complex environments. 相似文献
9.
10.
《Ceramics International》2022,48(2):1451-1483
Metal/ceramic composites are in high demand in several industries because of their superior thermo-mechanical properties. Among various composite types, the interpenetrating phase composites (IPCs) with percolating metallic and ceramic phases offer manifold benefits, such as a good combination of strength, toughness, and stiffness, very good thermal properties, excellent wear resistance, as well as the flexibility of microstructure and processing route selection, etc. The fabrication of metal/ceramic IPCs typically involves two steps - i) processing of an open porous ceramic body, and ii) infiltration of metallic melt in the pores to fabricate the IPC. Although significant progress has been made in recent years for developing both porous ceramics and melt infiltration methods, to the best of the knowledge of the authors, no review article summarizing all the aspects of processing and properties of IPCs has been published till date. This review article is aimed at filling this gap. Starting with a brief introduction about the current status and applications of IPCs, the various processing routes for fabricating open porous ceramic preforms and melt infiltration techniques have been discussed. Subsequently, the data available for various important physical, mechanical, and thermal properties for IPCs have been critically analyzed to thoroughly understand their dependence on various structural and processing parameters. To compare the properties of IPCs with other relevant materials, seven different Ashby material property maps have been used, and the domains for IPCs have been created in them. For each map, the concept of material indices has been employed to critically discuss how IPCs perform in relation to other material classes for various optimum design conditions. Finally, a detailed future outlook for further research on IPCs has been provided. 相似文献