全文获取类型
收费全文 | 283990篇 |
免费 | 8086篇 |
国内免费 | 3069篇 |
专业分类
电工技术 | 7249篇 |
技术理论 | 1篇 |
综合类 | 2841篇 |
化学工业 | 41556篇 |
金属工艺 | 10119篇 |
机械仪表 | 9758篇 |
建筑科学 | 9400篇 |
矿业工程 | 1746篇 |
能源动力 | 8130篇 |
轻工业 | 31393篇 |
水利工程 | 2903篇 |
石油天然气 | 3123篇 |
武器工业 | 405篇 |
无线电 | 37480篇 |
一般工业技术 | 49420篇 |
冶金工业 | 47574篇 |
原子能技术 | 3769篇 |
自动化技术 | 28278篇 |
出版年
2022年 | 2186篇 |
2021年 | 3462篇 |
2020年 | 2661篇 |
2019年 | 2624篇 |
2018年 | 3715篇 |
2017年 | 3878篇 |
2016年 | 4061篇 |
2015年 | 4078篇 |
2014年 | 5909篇 |
2013年 | 14406篇 |
2012年 | 9538篇 |
2011年 | 12572篇 |
2010年 | 9993篇 |
2009年 | 10635篇 |
2008年 | 11065篇 |
2007年 | 10894篇 |
2006年 | 10067篇 |
2005年 | 8923篇 |
2004年 | 8241篇 |
2003年 | 7761篇 |
2002年 | 7170篇 |
2001年 | 7487篇 |
2000年 | 6728篇 |
1999年 | 7118篇 |
1998年 | 16576篇 |
1997年 | 11523篇 |
1996年 | 8734篇 |
1995年 | 6658篇 |
1994年 | 5787篇 |
1993年 | 5634篇 |
1992年 | 4063篇 |
1991年 | 3815篇 |
1990年 | 3579篇 |
1989年 | 3408篇 |
1988年 | 3293篇 |
1987年 | 2598篇 |
1986年 | 2488篇 |
1985年 | 3160篇 |
1984年 | 2799篇 |
1983年 | 2559篇 |
1982年 | 2348篇 |
1981年 | 2396篇 |
1980年 | 2212篇 |
1979年 | 2051篇 |
1978年 | 1879篇 |
1977年 | 2177篇 |
1976年 | 2724篇 |
1975年 | 1584篇 |
1974年 | 1489篇 |
1973年 | 1558篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
101.
Fei Xu Xiangli Shi Qingzhu Zhang Wenxing Wang 《International journal of molecular sciences》2015,16(8):18714-18731
The chlorothiophenoxy radicals (CTPRs) are key intermediate species in the formation of polychlorinated dibenzothiophenes/thianthrenes (PCDT/TAs). In this work, the formation of CTPRs from the complete series reactions of 19 chlorothiophenol (CTP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method. The profiles of the potential energy surface were constructed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution at 600–1200 K. The present study indicates that the structural parameters, thermal data, and rate constants as well as the formation potential of CTPRs from CTPs are strongly dominated by the chlorine substitution at the ortho-position of CTPs. Comparison with the study of formation of chlorophenoxy radicals (CPRs) from chlorophenols (CPs) clearly shows that the thiophenoxyl-hydrogen abstraction from CTPs by H is more efficient than the phenoxyl-hydrogen abstraction from CPs by H, whereas the thiophenoxyl-hydrogen abstraction from CTPs by OH is less impactful than the phenoxyl-hydrogen abstraction from CPs by OH. Reactions of CTPs with H can occur more readily than that of CTPs with OH, which is opposite to the reactivity comparison of CPs with H and OH. 相似文献
102.
103.
In this study, further analysis of the osmotic drying process was conducted to identify the optimum combination of parameters for drying rectangular alumina-gelatin beams. This study was designed to determine the effect of three variables related to the osmotic drying process (osmotic pressure, molecular weight, and immersion time) on the interaction between the liquid desiccant and the submerged alumina-gelatin samples. The water loss from the alumina-gelatin samples was positively correlated with the molecular weight, osmotic pressure, and immersion time. Up to 40% by weight of the initial water content was removed during the osmotic drying process. The samples also experienced solids gain due to the counterflow of solute from the liquid desiccant. The least amount of solids gain resulted from drying for the shortest immersion time at low osmotic pressure and high molecular weight. Evidence of possible interactions between variables was noted for the sintered density metric. Statistical methods were used to form regression equations for the measured responses (water loss, solids gain, bulk density). A verification experiment was conducted to compare the experimental outcomes to the predicted outcomes. The responses were simultaneously optimized to identify the combination of variable settings required to meet specified goals. In order to maximize water loss, minimize solids gain, and maximize bulk density, the ceramic-gelatin object should be immersed for approximately 60?min in an aqueous solution of 100,000?g/mol poly(ethylene oxide) at an osmotic pressure of 2.50?MPa. These values are valid for the range of parameter settings tested and the sample fabrication and drying methods used. 相似文献
104.
105.
Shanquan Chen Sicong Wei Fei Jin Shanming Ke Xierong Zeng Lang Chen Chuanwei Huang 《Ceramics International》2018,44(12):13695-13698
From the perspectives of scientific researches and practical applications, it is desirable to explore high operating temperature ferromagnetic films. The effect of biaxial strain on magnetic properties of (110)-oriented La0.7Sr0.3MnO3 films was studied. High quality La0.7Sr0.3MnO3 films were grown on (110)-oriented perovskite single crystal substrates using pulsed laser deposition, varying substrate-induced misfit strains from ??2.27–0.75%. A remarkable enhancement of Curie temperature has been achieved for (110)-oriented La0.7Sr0.3MnO3 films clamped with small misfit strains (i.e., grown on LAST (110)). The enhanced Curie temperature of (110)-oriented La0.7Sr0.3MnO3 films could be attributed to the misfit strain between the films and the underlying substrates and may have technological implication for applications at high temperature environments. 相似文献
106.
Fei Li Xin-Gang Wang Xiao Huang Ji-Xuan Liu Weichao Bao Guo-Jun Zhang Hongzhi Wang 《Journal of the European Ceramic Society》2018,38(14):4806-4813
We present a straightforward method via sol-gel process using polyethylene glycol (PEG) as phase separation inducer to prepare zirconium carbide/silicon carbide (ZrC/SiC) porous monoliths. Organic/inorganic hybrid gels are prepared using zirconium oxychloride, furfuryl alcohol, and tetraethyl orthosilicate as major starting materials. In the presence of PEG, crack-free hybrid monoliths are obtained by drying the wet gels under ambient pressure, whereas in the absence of PEG, the wet gels break into pieces as expected. PEG plays a key role in maintaining the macroscopic shape of the monoliths. After ceramization at 1300–1500?°C, ZrC/SiC porous monoliths are obtained. SEM and mercury intrusion porosimetry data show that PEG also has strong influence on the microstructures of the monoliths. The compressive strengths of the ceramic monoliths are in the range of 0.3 to 0.7?MPa. And their compressive behavior starts to differ due to the changes in their microstructures, especially the pore structure. 相似文献
107.
T. Galvin N.C. Hyatt W.M. Rainforth I.M. Reaney D. Shepherd 《Journal of the European Ceramic Society》2018,38(14):4585-4589
The molten salt method was used to synthesise the MAX phase compounds Ti2AlC and Ti3AlC2 from elemental powders. Between 900–1000?°C, Ti2AlC was formed alongside ancillary phases TiC and TiAl, which decreased in abundance with increasing synthesis temperature. Changing the stoichiometry and increasing the synthesis temperature to 1300?°C resulted in formation of Ti3AlC2 alongside Ti2AlC and TiC. The type of salt flux used had little effect on the product formation. The reaction pathway for Ti2AlC was determined to be the initial formation of TiC1-x templating on the graphite and titanium aluminides. 相似文献
108.
S.K. Vimala Bharathi M. Maria Leena J.A. Moses C. Anandharamakrishnan 《International Journal of Food Science & Technology》2020,55(3):1238-1245
The usage of cling wraps is emerging as an easy and cost-effective approach to protect fresh-cut fruits and vegetables from dust, whilst improving visual appeal on retail counters. This study focused on developing an alternate, protein-based packaging material as a food grade cling wrap for food packaging applications. Zein-based cling wraps were produced, and their physical and mechanical characteristics were evaluated and compared with conventionally used chitosan biopolymer films and commercial synthetic polymer films. Antioxidant potential of the prepared films was studied, and the effectiveness of the developed films as anti-browning cling wraps was evaluated using studies conducted on fresh-cut apple slices at ambient conditions. Anti-browning effects were in par with polymeric counterparts; however, zein cling wraps could better prevent weight loss in apple slices. Zein-based films can be adopted as biodegradable food grade cling wraps as an alternative to chitosan and synthetic polymeric materials. 相似文献
109.
110.
P. Sampath Brijesh Kakarla Raghava Reddy C. Venkata Reddy Nagaraj P. Shetti Raghavendra V. Kulkarni Anjanapura V. Raghu 《化学工程与技术》2020,43(7):1240-1248
Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency. 相似文献