全文获取类型
收费全文 | 503989篇 |
免费 | 44765篇 |
国内免费 | 25162篇 |
专业分类
电工技术 | 33895篇 |
技术理论 | 49篇 |
综合类 | 38427篇 |
化学工业 | 79144篇 |
金属工艺 | 29749篇 |
机械仪表 | 32713篇 |
建筑科学 | 40651篇 |
矿业工程 | 16726篇 |
能源动力 | 14079篇 |
轻工业 | 35566篇 |
水利工程 | 10700篇 |
石油天然气 | 30276篇 |
武器工业 | 4655篇 |
无线电 | 56579篇 |
一般工业技术 | 53198篇 |
冶金工业 | 24361篇 |
原子能技术 | 5289篇 |
自动化技术 | 67859篇 |
出版年
2024年 | 2184篇 |
2023年 | 7721篇 |
2022年 | 14643篇 |
2021年 | 20163篇 |
2020年 | 15262篇 |
2019年 | 12145篇 |
2018年 | 13894篇 |
2017年 | 15972篇 |
2016年 | 14387篇 |
2015年 | 20431篇 |
2014年 | 25800篇 |
2013年 | 30860篇 |
2012年 | 34446篇 |
2011年 | 37349篇 |
2010年 | 33722篇 |
2009年 | 31840篇 |
2008年 | 31396篇 |
2007年 | 29809篇 |
2006年 | 29225篇 |
2005年 | 24818篇 |
2004年 | 16991篇 |
2003年 | 14896篇 |
2002年 | 13977篇 |
2001年 | 12428篇 |
2000年 | 11599篇 |
1999年 | 11566篇 |
1998年 | 8517篇 |
1997年 | 7247篇 |
1996年 | 6834篇 |
1995年 | 5673篇 |
1994年 | 4609篇 |
1993年 | 3078篇 |
1992年 | 2447篇 |
1991年 | 1832篇 |
1990年 | 1452篇 |
1989年 | 1181篇 |
1988年 | 956篇 |
1987年 | 615篇 |
1986年 | 486篇 |
1985年 | 294篇 |
1984年 | 239篇 |
1983年 | 185篇 |
1982年 | 155篇 |
1981年 | 116篇 |
1980年 | 135篇 |
1979年 | 67篇 |
1978年 | 26篇 |
1977年 | 32篇 |
1976年 | 38篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
�غ���ܿ���ǿ�ȼ��㼰�ֳ�Ӧ�� 总被引:6,自引:1,他引:5
对于套管挤毁问题较为严重的油气水井,采用非API标准的特厚壁套管来提高其抗挤强度,是今后预防套管挤毁的重要发展方向。目前,特厚壁套管的抗挤强度计算和尺寸系列尚未形成工业标准,文章提出特厚壁套管的抗挤强度计算方法和尺寸系列,供设计者和厂家参考。API/ISO套管挤毁工作组曾对本文公式进行了测评,结果曼示具有较高的计算精度。大量计算表明,特厚壁套管的抗挤强度大大提高,约为加厚前原套管抗挤强度的1.5~4倍,甚至6倍。最后还介绍了特厚壁套管在中原油田的现场应用情况。 相似文献
992.
文章介绍了期货交易所由于其特殊的机制,而对其注册上市产品的质量提高有显著的促进作用,同时介绍了“铜冠”牌阴极铜在LME注册成功,取得进入国际市场通行证中的一些情况。 相似文献
993.
Y.X. Li 《Materials Letters》2007,61(22):4366-4369
TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al3Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al3Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized. 相似文献
994.
Sanghyun Ju Jianye Li Pimparkar N. Alam M.A. Chang R.P.H. Janes D.B. 《Nanotechnology, IEEE Transactions on》2007,6(3):390-395
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold 相似文献
995.
催化技术在降低汽油机排放方面的应用 总被引:3,自引:2,他引:1
本文介绍了当前催化技术在改善和降低汽油机排放方面的应用情况,指出:催化技术是改善汽油机排放的一种有效措施和重要手段。 相似文献
996.
997.
Binoy Ravindran Peng Li Tamir Hegazy 《Journal of Parallel and Distributed Computing》2003,63(12):1219-1242
We present two proactive resource allocation algorithms, RBA*-FT and OBA-FT, for fault-tolerant asynchronous real-time distributed systems. The algorithms consider an application model where task timeliness is specified by Jensen's benefit functions and the anticipated application workload during future time intervals is described by adaptation functions. In addition, we assume that reliability functions of processors are available a priori. Given these models, our objective is to maximize aggregate task benefit and minimize aggregate missed deadline ratio in the presence of processor failures. Since determining the optimal solution is computationally intractable, the algorithms heuristically compute sub-optimal resource allocations, but in polynomial time. Experimental results reveal that RBA*-FT and OBA-FT outperform their non-fault-tolerant counterparts in the presence of processor failures. Furthermore, RBA*-FT performs better than OBA-FT, although OBA-FT incurs better worst-case and amortized computational costs. Finally, we observe that both algorithms robustly withstand errors in the estimation of anticipated failures. 相似文献
998.
999.
近年来,为了更好地应对新的市场挑战,钢铁企业都在积极推进信息化建设,以实现管理提升、效益提升的目标。本文结合安钢集团的实际情况,对信息化实施策略进行初步的探讨,希望能对企业信息化建设有所借鉴。 相似文献
1000.
Preparation of Compound Ultrafine CeO2 by Wet-Solid-Phase Mechanochemical Modification 总被引:1,自引:0,他引:1
To satisfy practical requirements from industrial applications, an alternate route for synthesis compound ultrafine CeO2 powders by wet-solid-phase mechanochemical modification using industrial grade hydrated cerium carbonate as raw material was proposed.The effect of modifier reaction percentage, reaction time, calcining temperature and modifier amount on particle size, density, suspensibility, and hardness of compound CeO2 powder was investigated.The phase evolutions of preparation process were characterized by XRD.SEM micrograph of the final product shows that compound CeO2 powders obtained are well-dispersed, spherically-shaped, uniformly-sized and submicron-sized particles.The method is readily available in raw material, low in cost, simple in process, and has great potential for industrialization.The compound CeO2 powders of different physical properties can be synthesized by controlling the above-mentioned influence factors in preparation process. 相似文献