全文获取类型
收费全文 | 54777篇 |
免费 | 5177篇 |
国内免费 | 2650篇 |
专业分类
电工技术 | 3489篇 |
技术理论 | 8篇 |
综合类 | 3630篇 |
化学工业 | 9202篇 |
金属工艺 | 2947篇 |
机械仪表 | 3273篇 |
建筑科学 | 3953篇 |
矿业工程 | 1489篇 |
能源动力 | 1746篇 |
轻工业 | 3434篇 |
水利工程 | 1081篇 |
石油天然气 | 2781篇 |
武器工业 | 646篇 |
无线电 | 6870篇 |
一般工业技术 | 6722篇 |
冶金工业 | 2837篇 |
原子能技术 | 702篇 |
自动化技术 | 7794篇 |
出版年
2024年 | 125篇 |
2023年 | 851篇 |
2022年 | 1518篇 |
2021年 | 2384篇 |
2020年 | 1770篇 |
2019年 | 1490篇 |
2018年 | 1674篇 |
2017年 | 1772篇 |
2016年 | 1587篇 |
2015年 | 2253篇 |
2014年 | 2682篇 |
2013年 | 3424篇 |
2012年 | 3583篇 |
2011年 | 3792篇 |
2010年 | 3334篇 |
2009年 | 3236篇 |
2008年 | 3118篇 |
2007年 | 2954篇 |
2006年 | 2990篇 |
2005年 | 2475篇 |
2004年 | 1859篇 |
2003年 | 1623篇 |
2002年 | 1679篇 |
2001年 | 1541篇 |
2000年 | 1325篇 |
1999年 | 1334篇 |
1998年 | 1162篇 |
1997年 | 983篇 |
1996年 | 794篇 |
1995年 | 671篇 |
1994年 | 503篇 |
1993年 | 439篇 |
1992年 | 330篇 |
1991年 | 268篇 |
1990年 | 187篇 |
1989年 | 182篇 |
1988年 | 142篇 |
1987年 | 84篇 |
1986年 | 86篇 |
1985年 | 73篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 41篇 |
1981年 | 36篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
141.
142.
Xiaojun Xie Yonghong Cheng Hong Wang Qian Wang Xiaolin Chen Caixin Sun 《Ceramics International》2008,34(4):689-693
In the ideal A2B2O6O′ pyrochlore structure, the x-value of O atom position is a variable parameter. In Bi1.5ZnNb1.5−xTaxO7 (BZNT) cubic pyrochlores, the x-values alter with the different compositions of Nb/Ta. In this work, a series of initial models for BZNT were established by analyzing X-ray diffraction data. Then three structure modifying methods, including Rietveld refinement, Rietveld refinement with energy and geometry optimization based on quantum mechanics, were employed to obtain the precise models using Materials Studio. Moreover, the reflectivities of BZNT were computed by quantum mechanical simulation based on the refined models. Comparing the simulation results from different modifying models with the experimental results, it is found that Rietveld refinement with energy optimization is the most accurate method for BZNT pyrochlores. According to the simulation results, the different reflectivities correspond well with various x-values of O atom positions in BZNT pyrochlores. 相似文献
143.
冲击响应谱在惯导减振防冲设计中的应用 总被引:3,自引:0,他引:3
根据冲击原理,研究惯导减振系统在半正弦冲击激励下的响应特性,绘制了惯导系统在半正弦冲击激励下的冲击响应谱图。根据冲击响应谱图,可为惯导系统防冲设计提供正确、有效的理论依据,同时,为使减振器同时具备减振、防冲两种性能,冲击响应谱对于减振器关键参数选择、减振系统优化也具有重要应用价值。最后文章依据该研究结论,对某惯导系统进行了实际设计计算。 相似文献
144.
145.
A new torque estimator for switched reluctance motor (SRM) drives based on 2-D rotary regression analysis is presented in this paper. The proposed torque estimator is composed of a bicubic regressive polynomial as a function of rotor position and input current. The regressive coefficients can be computed offline or online from the torque characteristics acquired either experimentally or from numerical computation. Furthermore, a torque estimation method by taking mutual coupling into consideration is proposed. It can be seen that the estimated and experimentally obtained self-coupling and mutual-coupling torque characteristics are in good agreement with each other. In addition, the dynamic torque waveforms with and without the mutual coupling, estimated by the proposed estimator, are found to be virtually the same as those obtained from the bicubic spline interpolation for SRM drives with single-pulse voltage, hysteresis current chopping, as well as with voltage pulse width modulation control. The success of all the case studies being reported is a good validation of the usefulness and accuracy of the proposed real-time torque estimator that, as described in this paper, can be used to quickly estimate the instantaneous output torque of SRM drives. 相似文献
146.
Junwei Fu Zhengbiao Zhang Zhenping Cheng Jian Zhu Wei Zhang Xiulin Zhu 《Polymer Bulletin》2008,61(3):287-297
A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA)
group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used
in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers.
The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE
as the RAFT agent. Number-average molecular weight (Mn,GPC) increased linearly
with monomer conversion, and molecular weight distributions were relatively narrow (PDI<
1.50). The results of chain-extension reaction, 1H NMR spectra and UV/Vis
spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine
(TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated. 相似文献
147.
Jiang Minhong Gu Zhengfei Cheng Gang 《中国稀土学报(英文版)》2005,23(6):723-723
Polymer matrix RE-Fe giant magnetostrictire composite (GMPC) was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC. 相似文献
148.
中央空调系统由制冷主机房、水子系统、风子系统以及楼宇自控(BA)等部分组成。制冷主机房是中央空调系统的心脏部分,它是由若干台制冷主机,一次冷冻水子系统,二次冷冻水子系统、冷却水子系统、冷却塔、控制柜等组成。它的运行状况直接关系到中央空调系统的能耗,本文将叙述新锦江大酒店制冷主机房建设中的几点节能措施。 相似文献
149.
1 3G组网中的主要问题
1.1 机房选址困难 随着我国2G网络的多年扩容和优化,未来3G基站机房无论是与2G共站还是新建,在城市里符合要求的可用机房储备都非常有限。移动网络80%的话务量集中在大中城市的密集城区,而3G网络特征业务——数据业务也主要发生在这些站址资源稀缺的区域。对于原固网运营商,此问题将更加突出。因此如何降低机房要求,减少配套投资将是网络建设中各界关注的焦点。 相似文献
150.
WASP6水质模型在渭河流域水环境容量解析中的应用 总被引:4,自引:0,他引:4
将WASP6水质模型应用于渭河流域陕西片,分析流域水环境的污染现状,并采用模型试错法模拟计算渭河陕西段水环境容量,并对比分析节水增流前后水质变化,根据分析结果提出节水增流减污的水污染控制方案,为渭河的污染治理提供依据。 相似文献