全文获取类型
收费全文 | 142489篇 |
免费 | 11572篇 |
国内免费 | 6784篇 |
专业分类
电工技术 | 8710篇 |
综合类 | 9266篇 |
化学工业 | 31951篇 |
金属工艺 | 18361篇 |
机械仪表 | 6950篇 |
建筑科学 | 11207篇 |
矿业工程 | 4107篇 |
能源动力 | 7703篇 |
轻工业 | 10724篇 |
水利工程 | 2682篇 |
石油天然气 | 6510篇 |
武器工业 | 1048篇 |
无线电 | 10128篇 |
一般工业技术 | 15300篇 |
冶金工业 | 8349篇 |
原子能技术 | 2148篇 |
自动化技术 | 5701篇 |
出版年
2024年 | 621篇 |
2023年 | 2291篇 |
2022年 | 4066篇 |
2021年 | 4886篇 |
2020年 | 4808篇 |
2019年 | 4003篇 |
2018年 | 3785篇 |
2017年 | 4921篇 |
2016年 | 4977篇 |
2015年 | 5059篇 |
2014年 | 7808篇 |
2013年 | 8305篇 |
2012年 | 9388篇 |
2011年 | 10805篇 |
2010年 | 7571篇 |
2009年 | 8231篇 |
2008年 | 7131篇 |
2007年 | 8876篇 |
2006年 | 8349篇 |
2005年 | 6905篇 |
2004年 | 5918篇 |
2003年 | 5151篇 |
2002年 | 4339篇 |
2001年 | 3827篇 |
2000年 | 3265篇 |
1999年 | 2708篇 |
1998年 | 2227篇 |
1997年 | 1907篇 |
1996年 | 1669篇 |
1995年 | 1339篇 |
1994年 | 1146篇 |
1993年 | 833篇 |
1992年 | 774篇 |
1991年 | 656篇 |
1990年 | 500篇 |
1989年 | 368篇 |
1988年 | 270篇 |
1987年 | 191篇 |
1986年 | 175篇 |
1985年 | 127篇 |
1984年 | 132篇 |
1983年 | 83篇 |
1982年 | 89篇 |
1981年 | 66篇 |
1980年 | 68篇 |
1979年 | 40篇 |
1978年 | 26篇 |
1977年 | 27篇 |
1975年 | 28篇 |
1959年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling
theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon
interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting
transition temperature (T
c) is then evaluated by using these coupling parameters and obtainedT
c = 95(92)K for Y(Yb)Ba2Cu3O7−δ
superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory.
The result deduced on the variation ofT
c withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed. 相似文献
23.
ImprovingWearResistanceoftheNibaseThermalSprayWeldingCoatingUsingRareEarthsZhaiGuangjie(翟光杰)(InstituteofPhysics,AcademicaSi... 相似文献
24.
本文提出并研究了一种新型的强度反射型光纤温度传感器.根据定容气体温度与压力的线性关系,通过简单的测温元调制光纤中的反射光强,从而得知待测温度.这种传感器结构紧凑,造价低廉.在30~50℃范围内,灵敏度可以达到30mV/℃以上. 相似文献
25.
Muralidhar N. Ingale Vijaykumar V. Mahajani 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,64(1):80-86
The effectiveness of the hybrid system sonication followed by wet oxidation (SONIWO) to treat otherwise refractory waste has been demonstrated. In such a hybrid system homogeneous CuSO4 catalyst was found to be very efficient. 相似文献
26.
S. MESCHINI A. MOLINARI A. CALCABRINI G. CITRO G. ARANCIA 《Journal of microscopy》1994,176(3):204-210
The intracellular distribution of the anthracyclinic antibiotic adriamycin in living cultured cells has been investigated by confocal microscopy. In human melanoma cells (M14), adriamycin was localized inside the nuclei. When adriamycin-treated M14 cells were allowed to recover in drug-free medium, a complete efflux of the drug from the nucleus was revealed. In recovered cells, a weakly fluorescent signal was observed in the perinuclear region. When M14 cells were recovered in a medium containing colcemid, a microtubule depolymerizing agent, the drug transport from the nucleus to the cell periphery appeared to be inhibited, suggesting that the microtubule network is strongly involved in drug transport mechanisms. In multidrug-resistant (MDR) cells the intracellular location of adriamycin was shown to be noticeably different from that of the parental wild-type cells. In particular, in resistant human breast carcinoma cells (MCF-7), adriamycin appeared to be exclusively located within the cytoplasm whereas the nuclei were shown to be completely negative. When adriamycin treatment was performed in association with MDR revertants, such as Lonidamine (inhibitor of the energy metabolism) or verapamil (inhibitor of the P-glycoprotein efflux pump), a marked enhancement of the cytoplasmic signal was observed in resistant cells. Under these conditions, adriamycin appeared concentrated in the perinuclear region, but the nuclei were still negative. Confocal microscopy proved to be a very useful method for the study of the intracellular transport of fluorescent substances, such as anthracyclinic antibiotics, and for the investigation of the multidrug resistance phenomenon in tumour cells. 相似文献
27.
Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts 总被引:1,自引:0,他引:1
S. Stegenga R. van Soest F. Kapteijn J. A. Moulijn 《Applied catalysis. B, Environmental》1993,2(4):257-275
Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed. 相似文献
28.
R.N. ARNOLD K.K. SCHELLER S.C. ARP S.N. WILLIAMS D.M. SCHAEFER 《Journal of food science》1993,58(1):28-33
The effect of long-term feeding (252 days) of three supplemental levels of α-tocopheryl acetate (actual 0, 360 and 1290 IU/head/day) on meat quality was evaluated in Holstein and beef breed steers. Tissue vitamin E concentrations were increased by each increment of supplementation. The color display life of fresh beef under simulated retail conditions was extended 2 to 5 days by vitamin E and lipid oxidation was markedly reduced. Microbial population was not affected by level of supplementation. No deterioration in sensory quality occurred for steaks from supplemented steers that were displayed until the time steaks from unsupplemented steers discolored. 相似文献
29.
30.
异丙苯在Cu-HMS分子筛上的催化氧化 总被引:3,自引:2,他引:1
以含Cu的中孔分子筛(Cu-HMS)为催化剂,研究异丙苯的催化氧化。研究发现,Cu-HMS催化剂的加入使异丙苯氧化的诱导期显著缩短。在75℃下,以Cu-HMS为催化剂,O2为氧化剂的纯异丙苯氧化反应,苯乙酮为主要副产物,反应的选择性和转化率都很高。当催化剂用量为1 5×10-4mol/ml时,反应8h后,异丙苯转化率为32 7%,目的产物的累积浓度(质量分数)为37 7%,选择性为99%;反应12h后,异丙苯转化率为42 4%,目的产物的累积浓度为46 3%,选择性为95 6%。 相似文献