全文获取类型
收费全文 | 74990篇 |
免费 | 8671篇 |
国内免费 | 5735篇 |
专业分类
电工技术 | 5728篇 |
技术理论 | 6篇 |
综合类 | 6866篇 |
化学工业 | 14408篇 |
金属工艺 | 7901篇 |
机械仪表 | 3143篇 |
建筑科学 | 5469篇 |
矿业工程 | 1915篇 |
能源动力 | 2247篇 |
轻工业 | 3661篇 |
水利工程 | 830篇 |
石油天然气 | 2462篇 |
武器工业 | 662篇 |
无线电 | 8778篇 |
一般工业技术 | 10202篇 |
冶金工业 | 6339篇 |
原子能技术 | 658篇 |
自动化技术 | 8121篇 |
出版年
2024年 | 342篇 |
2023年 | 1393篇 |
2022年 | 2199篇 |
2021年 | 2712篇 |
2020年 | 2853篇 |
2019年 | 2605篇 |
2018年 | 2368篇 |
2017年 | 2824篇 |
2016年 | 2852篇 |
2015年 | 2996篇 |
2014年 | 4306篇 |
2013年 | 4485篇 |
2012年 | 5065篇 |
2011年 | 5416篇 |
2010年 | 3989篇 |
2009年 | 4262篇 |
2008年 | 3922篇 |
2007年 | 4742篇 |
2006年 | 4324篇 |
2005年 | 3693篇 |
2004年 | 3024篇 |
2003年 | 2869篇 |
2002年 | 2467篇 |
2001年 | 2136篇 |
2000年 | 1810篇 |
1999年 | 1469篇 |
1998年 | 1250篇 |
1997年 | 1136篇 |
1996年 | 896篇 |
1995年 | 817篇 |
1994年 | 746篇 |
1993年 | 504篇 |
1992年 | 489篇 |
1991年 | 388篇 |
1990年 | 366篇 |
1989年 | 319篇 |
1988年 | 177篇 |
1987年 | 113篇 |
1986年 | 103篇 |
1985年 | 74篇 |
1984年 | 84篇 |
1983年 | 46篇 |
1982年 | 59篇 |
1981年 | 53篇 |
1980年 | 59篇 |
1979年 | 34篇 |
1964年 | 49篇 |
1963年 | 39篇 |
1959年 | 33篇 |
1955年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
On the basis of new concept using a solid disperse phase we have developed an efficient catalytic solid-phase-system for epoxidations of alkenes using urea–hydrogen peroxide (urea–H2O2) complex and cetylpyridinium dodecatungstate ((CetylPy)10[H2W12O42]) catalyst on fluorapatite (FAp). The recovered solid catalyst phase was reused to keep the catalytic activity after several times. In the conceptual idea it is a key point that in situ solid-phase-activation of the catalyst with urea–H2O2 proceeds to form microcrystals of the active species dispersed on the solid phase. The dispersion of the catalyst on FAp in the case of tungstic acid (H2WO4) was suggested by EPMA analysis. We proposed the peroxo type of species keeping the parent polyoxometalate framework as novel active species from FT-IR spectroscopic studies. FAp phase plays important roles of dispersing the active species on its surface to have high catalytic activity and of stabilizing the active species to lead to high reusability. 相似文献
122.
STUDY ON PHASE PERCEPTION IN SPEECH 总被引:4,自引:0,他引:4
Tong Ming Bian Zhengzhong Li Xiaohui Dai Qijun Chen Yanpu 《电子科学学刊(英文版)》2003,20(5):387-392
The perceptual effect of the phase information in speech has been studied by auditory subjective tests. On the condition that the phase spectrum in speech is changed while amplitude spectrum is unchanged, the tests show that: (1) If the envelop of the reconstructed speech signal is unchanged, there is indistinctive auditory perception between the original speech and the reconstructed speech; (2) The auditory perception effect of the reconstructed speech mainly lies on the amplitude of the derivative of the additive phase; (3) td is the maximum relative time shift between different frequency components of the reconstructed speech signal. The speech quality is excellent while td <10ms; good while 10ms< td <20ms; common while 20ms< td <35ms, and poor while td >35ms. 相似文献
123.
Kenzo Kitayama 《Journal of the American Ceramic Society》1992,75(6):1447-1451
Phase equilibria in the Ta-Co-O and Nb-Co-O systems have been studied at 1200°C at oxygen partial pressures from 10−0.68 to 10−13.50 atm for the former and from 10−0.68 to 10−13.30 atm for the latter. In both systems, M2 CoO6 and M2 Co4 O9 are stable ternary compounds under the experimental conditions, and a new phase, Nb5 Co2 O14 , has been identified. The Ta-Co-O system is simple, whereas the Nb-Co-O system is somewhat more complicated because of the extra phase. The lattice constants of the ternary compounds have been determined and compared with previous values. The standard Gibbs energies of reactions have been determined using oxygen partial pressures in equilibrium with three solid phases. 相似文献
124.
加固改造中的结构承重体系转换 总被引:2,自引:0,他引:2
从加固改造工程的实践出发 ,探讨了混合结构向框架结构体系转换的方法和构造措施 ,为实际工程提供了新的技术思路 相似文献
125.
Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane. 相似文献
126.
空心微珠改性硬质聚氯乙烯复合材料的应用研究 总被引:13,自引:1,他引:12
经过改性的超细空心微珠可以作为填料加入到硬质聚氯乙烯(PVC-U)树脂中,同时改善PVC树脂的流变性、冲击性能和刚性等性能。研究结果表明,超细空心微珠加入到硬质PVC管材中,可以明显改善PVC硬管的加工流动性能,显著缩短塑化时间,降低最大扭矩。而超细空民微珠加入到硬质PVC板材时,可以提高PVC硬板的冲击性能,减小制品的收缩率,赋予PVC硬板优异的耐腐蚀性能,且产品的各项性能均符合PVC板材国家标准GB/T4454-96。 相似文献
127.
Robbins Michael S.; Turner Charles W.; Alexander James F.; Perez Gonzalo A. 《Canadian Metallurgical Quarterly》2003,17(4):534
This study examined the relationship between alliance and retention in family therapy. Alliance was examined at the individual (parent and adolescent) and family levels (within-family differences). Participants were 34 families who received functional family therapy for the treatment of adolescent (aged 12-18 years) behavior problems. Families were classified as treatment dropouts (n=14) or completers (n=20). Videotapes of the first sessions were rated to identify parent and adolescent alliances with the therapist. Results demonstrated that individual parent and adolescent alliances did not predict retention. However, as hypothesized, dropout cases had significantly higher unbalanced alliances (parent minus adolescent) than did completer cases. These findings highlight the importance of alliances in functional family therapy and suggest that how the alliance operates in conjoint family therapy may be a function of systemic rather than of individual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
128.
激光冲击诱发相变的实验研究 总被引:3,自引:0,他引:3
本对激光冲击是否可以诱发相变进行了试验研究。用功率密度为1.06×10^8W/cm^2的激光器冲击T8钢表面。实验结果表明激光冲击处理使T8钢的表面显微硬度有所提高并可以发生马氏体相变。冲击处理后材料表面硬度提高了两倍,认为相变是T8钢表面硬度提高的原因之一。 相似文献
129.
The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given. 相似文献
130.
雾化水流计算模式 总被引:21,自引:1,他引:20
梁在潮 《水动力学研究与进展(A辑)》1992,7(3):247-255
本文描述了雾化水流现象并提出了雾化水流的一个计算模型。得出了雾化水流影响领域的各种不同的计算公式和方法。 相似文献