全文获取类型
收费全文 | 79154篇 |
免费 | 18132篇 |
国内免费 | 2189篇 |
专业分类
电工技术 | 3231篇 |
技术理论 | 3篇 |
综合类 | 3271篇 |
化学工业 | 23265篇 |
金属工艺 | 2701篇 |
机械仪表 | 3501篇 |
建筑科学 | 4582篇 |
矿业工程 | 1355篇 |
能源动力 | 2216篇 |
轻工业 | 10094篇 |
水利工程 | 1082篇 |
石油天然气 | 1653篇 |
武器工业 | 301篇 |
无线电 | 11996篇 |
一般工业技术 | 16260篇 |
冶金工业 | 2990篇 |
原子能技术 | 557篇 |
自动化技术 | 10417篇 |
出版年
2024年 | 138篇 |
2023年 | 614篇 |
2022年 | 1095篇 |
2021年 | 1779篇 |
2020年 | 2536篇 |
2019年 | 4107篇 |
2018年 | 4140篇 |
2017年 | 4529篇 |
2016年 | 4953篇 |
2015年 | 5396篇 |
2014年 | 5817篇 |
2013年 | 7400篇 |
2012年 | 5380篇 |
2011年 | 5089篇 |
2010年 | 5132篇 |
2009年 | 4871篇 |
2008年 | 4362篇 |
2007年 | 4049篇 |
2006年 | 3787篇 |
2005年 | 3223篇 |
2004年 | 2812篇 |
2003年 | 3061篇 |
2002年 | 3598篇 |
2001年 | 3101篇 |
2000年 | 2300篇 |
1999年 | 1451篇 |
1998年 | 962篇 |
1997年 | 711篇 |
1996年 | 541篇 |
1995年 | 479篇 |
1994年 | 396篇 |
1993年 | 297篇 |
1992年 | 228篇 |
1991年 | 220篇 |
1990年 | 157篇 |
1989年 | 135篇 |
1988年 | 100篇 |
1987年 | 82篇 |
1986年 | 72篇 |
1985年 | 55篇 |
1984年 | 41篇 |
1983年 | 27篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1980年 | 40篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
Water‐insoluble polyaspartyl polymers were synthesized by using water as medium instead of organic medium. Taking Ca2+ as a reference, the binding of several heavy‐metal ions, including Pb2+, Cd2+, Hg2+, Cr3+, Cu2+, and Mn2+, by polyaspartyl polymers was studied. The experimental results revealed that polyaspartate is an excellent binding agent for the investigated heavy‐metal ions. These cation ions were bound to polyaspartate polymer by the same mechanism as Pb2+, which can be explained by ion exchange model. Since polyaspartate has a protein‐resembling structure that is sensitive to trace heavy metal, it was used to remove some trace heavy‐metal elements in Chinese herbal medicines. It was found that polyaspartate material was an effective agent for the removal of Pb2+, Cd2+, and Hg2+ ions from glycyrrhizin, angelica, and gynostemma pentaphyllum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
992.
基于变权灰色关联法的长江荆南三口地区水资源短缺程度分析 总被引:1,自引:0,他引:1
对荆南三口地区水资源短缺程度进行分析研究,为实现区域水资源可持续合理利用提供科学依据。在水资源短缺评价研究中,前期研究成果大多采用常权法确定评价指标,致使评价指标产生状态失衡。将变权理论引入到水资源短缺程度分析中,从而确定评价指标变权重,并结合灰色关联法,构建水资源短缺程度分析的变权灰色关联法模型并加以应用。最终得出荆南三口地区三县的水资源短缺程度均为轻度缺水,其缺水程度排序为:华容县南县安乡县。利用变权灰色关联法计算水资源短缺程度,方法可行,结果合理,满足了评价指标均衡性要求。 相似文献
993.
994.
A new type of modified bismaleimide resin was obtained by copolymerization between tris(allylphenoxy)triazine monomer (TAPT) and an aromatic diamine‐chain‐extension bismaleimide [e.g., 4,4′‐diaminodiphenylmethane (DADPM)‐chain‐extension 4,4′‐bismaleimidodiphenylmethane (BMDPM)]. The new three‐component‐polymer system had good processibility and mechanical properties. Better results were obtained when the weight ratio of TAPT to the DADPM‐chain‐extension BMDPM resin was 30%. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 475–480, 2004 相似文献
995.
根据横梁风电场的气象和地形地质条件等基本资料,风机塔筒与风机基础采用预应力锚栓组合件进行连接,对梁板式预应力锚栓基础与传统的圆形扩展基础进行了技术经济比较。梁板式预应力锚栓基础整体安全性更好,可减少基础的钢筋与混凝土用量,节约工程投资183.5万元,即技术可行,经济合理。 相似文献
996.
根据金平水电站坝址的水文气象和地形地质条件等基本资料,对砾石土心墙堆石坝和沥青混凝土心墙堆石坝进行技术经济比较。沥青混凝土心墙堆石坝防渗土料工程量小,施工环节少,占用土地少,环境影响小,施工技术成熟,工程投资省745万元,故采用了沥青混凝土心墙堆石坝方案,金平水电站已投产发电,运行良好。 相似文献
997.
Jean‐Rémy Falleri Xavier Blanc Reda Bendraou Marcos Aurélio Almeida da Silva Cédric Teyton 《Software》2014,44(5):621-641
Ensuring models’ consistency is a key concern when using a model‐based development approach. Therefore, model inconsistency detection has received significant attention over the last years. To be useful, inconsistency detection has to be sound, efficient, and scalable. Incremental detection is one way to achieve efficiency in the presence of large models. In most of the existing approaches, incrementalization is carried out at the expense of the memory consumption that becomes proportional to the model size and the number of consistency rules. In this paper, we propose a new incremental inconsistency detection approach that only consumes a small and model size‐independent amount of memory. It will therefore scale better to projects using large models and many consistency rules. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
998.
Jeong-Ho Cho In-Kil Park Ho-Gi Kim Hoon-Taek Chung 《Journal of the American Ceramic Society》1997,80(6):1523-1534
Substituting Cd2+ ions into the A and B sites in a Pb(Ni1/3 Nb2/3 )O3 PbZrO3 PbTiO3 (PNNPZPT) ternary perovskite material made it possible to determine the effects of the Cd2+ ion substitution site on sintering behavior. The substitution site of the Cd2+ ion was identified by using X-ray photoelectron spectroscopy spectra. Although Cd2+ ions were substituted into the A and B sites in PNNPZPT, the Cd2+ ions preferred the A site over the B site. When Cd2+ ions replaced Pb2+ ions, a weight gain was observed during sintering. On the other hand, replacing Ni2 ions with Cd2+ ions promoted weight loss. Those weight changes indicated that Cd2+ ions change the bonding strength between the B-site cations and the oxygen of the octahedron in a perovskite structure. Density was influenced by the Cd2+ ion substitution site, and the A-site-doped compositions had higher densities than the B-site-doped compositions. 相似文献
999.
Kim-Choy Chung 《Behaviour & Information Technology》2014,33(7):743-756
This study investigates perceived risk and trust in relationship to the Diffusion of Innovation Theory [Rogers, E.M., 1962. Diffusion of innovations. Glencoe, IL: The Free Press; 1983. Diffusion of innovations. 3rd ed. New York: The Free Press] from a cultural perspective to understand the determinants of behavioural intent to adopt mobile commerce among the Y Generation in Kazakhstan. Surveys from 345 university-level students and subsequent structural equation modelling revealed perceived risk, trustworthiness and Rogers’ five innovation characteristics are important determinants. Perceived risk and trustworthiness are important determinants because of the high uncertainty avoidance characteristics of the Kazakh society. This study advances theory regarding culture- and generation-based characteristics to transition economies by verifying theoretical proposition regarding the behavioural intent towards mobile commerce adoption, resulting in a greater understanding of mobile commerce adoption among the Y Generation in transition economies. Marketing implications are discussed. 相似文献
1000.
Unsaturated polyester (UP)/montmorillonite (MMT) nanocomposite was prepared by using hydroxypropylacrylate (HPA) as a reactive diluent instead of conventional styrene monomer and the effect of polarity of reactive diluent on properties of nanocomposite was investigated. X‐ray and mechanical test data indicated that mixing for an extended period of time is essential to enhance the physical properties of nanocomposites in the UP/Cloisite 6A system. This was attributed to the high polarity of HPA that may disturb the preintercalation of UP resin into the galleries of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 238–242, 2004 相似文献