全文获取类型
收费全文 | 28165篇 |
免费 | 2629篇 |
国内免费 | 1255篇 |
专业分类
电工技术 | 1721篇 |
技术理论 | 4篇 |
综合类 | 1939篇 |
化学工业 | 4525篇 |
金属工艺 | 1745篇 |
机械仪表 | 1950篇 |
建筑科学 | 2242篇 |
矿业工程 | 853篇 |
能源动力 | 826篇 |
轻工业 | 2166篇 |
水利工程 | 537篇 |
石油天然气 | 1942篇 |
武器工业 | 217篇 |
无线电 | 3095篇 |
一般工业技术 | 3172篇 |
冶金工业 | 1222篇 |
原子能技术 | 307篇 |
自动化技术 | 3586篇 |
出版年
2024年 | 132篇 |
2023年 | 545篇 |
2022年 | 974篇 |
2021年 | 1336篇 |
2020年 | 1086篇 |
2019年 | 802篇 |
2018年 | 914篇 |
2017年 | 995篇 |
2016年 | 859篇 |
2015年 | 1256篇 |
2014年 | 1436篇 |
2013年 | 1682篇 |
2012年 | 1791篇 |
2011年 | 1964篇 |
2010年 | 1662篇 |
2009年 | 1519篇 |
2008年 | 1603篇 |
2007年 | 1495篇 |
2006年 | 1499篇 |
2005年 | 1292篇 |
2004年 | 831篇 |
2003年 | 799篇 |
2002年 | 866篇 |
2001年 | 752篇 |
2000年 | 635篇 |
1999年 | 714篇 |
1998年 | 515篇 |
1997年 | 426篇 |
1996年 | 374篇 |
1995年 | 323篇 |
1994年 | 255篇 |
1993年 | 177篇 |
1992年 | 143篇 |
1991年 | 90篇 |
1990年 | 82篇 |
1989年 | 61篇 |
1988年 | 40篇 |
1987年 | 37篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1959年 | 1篇 |
1953年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Molecular Ordering: Selectivity of Threefold Symmetry in Epitaxial Alignment of Liquid Crystal Molecules on Macroscale Single‐Crystal Graphene (Adv. Mater. 40/2018)
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
992.
The inlet/outlet is an important part of a water conveyance system in a pumped storage power station (PSPS). Its hydraulic characteristics are directly related to the operation and economic benefit of the PSPS. Frequent changes between inflow and outflow operations pose significant challenges in the design of the inlet/outlet diffusion segment shape. In this study, an effective optimization method, including three-dimensional parametric modelling, computational fluid dynamics and a genetic algorithm, is introduced and coupled to the design of the diffusion segment shape. The hydraulic characteristics of bi-directional flow, including the head loss, velocity uneven distribution and uneven discharge distribution, are selected as the objective function in the optimization method. Using this method, the recommended shape of the inlet/outlet is studied and its hydraulic characteristics are discussed. The results indicate that the optimized inlet/outlet has better performance. 相似文献
993.
In situ electrokinetic remediation of toxic metal‐contaminated soil driven by solid phase microbial fuel cells with a wheat straw addition
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
994.
近远场地震中土工格栅加筋土挡墙抗震特性的振动台试验研究 总被引:2,自引:0,他引:2
地震中土工格栅加筋土挡墙的动态行为与抗震机理的认识还尚不清楚。采用叠层剪切型模型土箱开展大型振动台试验,基于量纲理论π定理的Froude常数设计试验模型,考虑近远场地震动影响,采用汶川地震中松潘远场波、什邡近场波和Taft中远场地震波,测试墙体加速度、加筋回填土加速度、墙体侧向变形、加筋区与非加筋区回填土表面震陷、加筋区填土超静孔隙水压力以及土工格栅应变特性,得出远场和中远场地震波对加筋结构产生了强烈的宏观反应特征,而近场波对加筋区填土超静孔隙水压力的微观反应影响显著,加速度和沉降反应特征表明土工格栅为柔性挡土墙提供了较强的抗震能力,格栅应变分布特征揭示了柔性挡土墙上受力分布规律。研究结果将为土工格栅加筋土挡墙抗震安全设计和工程施工提供依据。 相似文献
995.
Jie Tian Tingting Li Srinivas Janaswamy Nan Wang Shuang Song Hang Qi Chengrong Wen 《Polymer International》2022,71(1):132-138
Polypeptides play a key role in improving food quality, and understanding their interactions with polysaccharides would be beneficial to developing new foods. Herein, κ-carrageenan (KC) and ε-polylysine hydrochloride (PLH) were chosen as the model polysaccharide and polypeptide, respectively, to study polysaccharide/polypeptide complexes. The KC/PLH solutions were characterized for turbidity as a function of mass ratio, pH, salts and stirred conditions at 0.5 and 1 mg mL–1 concentrations. The solutions at a KC/PLH mass ratio of 7:3 have the highest turbidity, and the turbidity is stable in acidic conditions, decreases with increase in pH in alkaline conditions and salt concentration, and increases with increase of stirred time and temperature. The Fourier transform infrared spectra suggest that the amide I band of PLH disappears along with a change in the amide II band upon complexing with KC. These changes further influence the microstructure and reveal a rough, non-uniform and large irregular cavity network structure. Indeed, these observations are intimately associated with the dynamic interactions persistent at the molecular level between the KC and PLH. © 2021 Society of Industrial Chemistry. 相似文献
996.
997.
Xiaobao Li Ruyi Zou Yanyan Niu Wei Sun Xinlong Tian 《International Journal of Hydrogen Energy》2018,43(48):21791-21797
A facile and effective approach was developed for the preparation of mesoporous Fe-NC by pyrolyzing the mixture of FeCl2, urea, (NH4)2MoO7, phthalic anhydride and SBA-15, during which the in-situ formation of iron phthalocyanine is confirmed. The obtained catalyst exhibits high catalytic activity towards ORR, whose half-wave potential can be 53 mV more positive than that of commercial Pt/C catalyst. Besides, the catalyst also exhibits high selectivity of four electron path, along with excellent stability and methanol tolerance in alkaline media. Based on the characterization results, we suggest, the higher surface areas, highly porous structures induced by SBA-15 addition, as well as high graphitic N content should be the proper origins for its outstanding catalytic performance. 相似文献
998.
Zining Cui Xinghai Li Fang Tian Xiaojing Yan 《International journal of molecular sciences》2014,15(5):8941-8958
A series of 5-substituted-2-furoyl diacylhydazide derivatives with aliphatic chain were designed and synthesized. Their structures were characterized by IR, 1H NMR, elemental analysis, and X-ray single crystal diffraction. The anti-tumor bioassay revealed that some title compounds exhibited promising activity against the selected cancer cell lines, especially against the human promyelocytic leukemic cells (HL-60). Their fungicidal tests indicated that most of the title compounds showed significant anti-fungal activity. The preliminary structure-activity relationship showed that the aliphatic chain length and differences in the R2 group had obvious effects on the anti-tumor and anti-fungal activities. The bioassay results demonstrated that the title compounds hold great promise as novel lead compounds for further drug discovery. 相似文献
999.
1000.
A novel wearable sensor system was developed for monitoring respiration and pulse using polyvinylidene fluoride (PVDF) piezoelectric films as sensor materials. Due to the different signal intensity between respiration and pulse, a “double-sided arch” structure and a “thin-shell” structure were designed and fabricated as substrates for the respiratory sensor and pulse sensor, respectively. These sensors installed on belts can be easily tied on the chest, abdomen, or wrist for comfortable fit. In order to obtain clear respiratory and pulse signals from the sensor patch, some high-quality signal processing modules were designed. The digital signals were transmitted to a computer via Bluetooth and displayed by LabVIEW software. The fundamental principle and functional verification of the developed sensor system were described in this study. By comparing the sensor signals from the proposed structure with those of flat structure, it can be concluded that the proposed sensor is more sensitive and stable than its flat counterpart. In addition, the whole sensor system has the features of ease of use and comfortable to wear. All these make the proposed sensor system a promising sensing device for respiration and pulse real time monitoring. 相似文献