全文获取类型
收费全文 | 93920篇 |
免费 | 10084篇 |
国内免费 | 5197篇 |
专业分类
电工技术 | 20551篇 |
技术理论 | 14篇 |
综合类 | 7284篇 |
化学工业 | 10019篇 |
金属工艺 | 3477篇 |
机械仪表 | 4537篇 |
建筑科学 | 10860篇 |
矿业工程 | 2910篇 |
能源动力 | 13579篇 |
轻工业 | 2914篇 |
水利工程 | 1754篇 |
石油天然气 | 2931篇 |
武器工业 | 861篇 |
无线电 | 6615篇 |
一般工业技术 | 8632篇 |
冶金工业 | 4724篇 |
原子能技术 | 1412篇 |
自动化技术 | 6127篇 |
出版年
2024年 | 376篇 |
2023年 | 1871篇 |
2022年 | 3015篇 |
2021年 | 3490篇 |
2020年 | 3719篇 |
2019年 | 3227篇 |
2018年 | 2786篇 |
2017年 | 3368篇 |
2016年 | 3723篇 |
2015年 | 3715篇 |
2014年 | 6488篇 |
2013年 | 5952篇 |
2012年 | 6987篇 |
2011年 | 7540篇 |
2010年 | 5658篇 |
2009年 | 5810篇 |
2008年 | 5368篇 |
2007年 | 6072篇 |
2006年 | 5012篇 |
2005年 | 4035篇 |
2004年 | 3448篇 |
2003年 | 3043篇 |
2002年 | 2535篇 |
2001年 | 2217篇 |
2000年 | 1848篇 |
1999年 | 1498篇 |
1998年 | 1141篇 |
1997年 | 908篇 |
1996年 | 822篇 |
1995年 | 626篇 |
1994年 | 544篇 |
1993年 | 397篇 |
1992年 | 335篇 |
1991年 | 269篇 |
1990年 | 227篇 |
1989年 | 200篇 |
1988年 | 159篇 |
1987年 | 117篇 |
1986年 | 82篇 |
1985年 | 103篇 |
1984年 | 107篇 |
1983年 | 89篇 |
1982年 | 87篇 |
1981年 | 37篇 |
1980年 | 44篇 |
1979年 | 25篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1959年 | 6篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. A. Vasil’ev 《Combustion, Explosion, and Shock Waves》2007,43(6):703-709
Investigated parameters of combustion and detonation of mixtures of the synthesis gas with oxygen and air are presented. The
ratios between carbon oxide and hydrogen and between the fuels and oxidizer are varied within wide ranges. The critical energy
of detonation initiation is determined.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 90–96, November–December, 2007. 相似文献
992.
A novel and simple growth mark method was developed to make marks during the growth process of carbon nanotube arrays. These marks can be read out under scanning electron microscope or optical microscope. Based on this method, the growth rates at different temperatures and under different acetylene partial pressures were measured, from which the activation energy and the order of reaction were determined. Based on our experimental results, the growth of carbon nanotube arrays in our experimental condition could not be diffusion-limited. The measured activation energy could possibly be attributed to the heterogeneous decomposition of acetylene over the catalyst particle. Furthermore the marked array with special segmental structure may be found some applications in the future. 相似文献
993.
海水反渗透淡化系统的能耗 总被引:1,自引:0,他引:1
通过对海水反渗透淡化系统(SWRO)吨水成本的分析,提出降低SWRO能耗的解决措施,采用能量透平装置(TURBO)或压力转换器(PE)回收浓水的能量传递于进水,不仅可以降低吨水电耗,也可减小一次性投资。值得关注的是,压力转换器,回收效率可达94%,在海水淡化系统中对于降低能耗有更重要的意义。 相似文献
994.
Komeiji Yuto; Uebayasi Masami; Someya Jun-ichiro; Yamato Ichiro 《Protein engineering, design & selection : PEDS》1992,5(8):759-767
The Ser88Cys mutant of the trp-repressor showed a lower affinityfor the corepressor than the wild-type repressor [G = 1.7 ±0.3 kcal/mol, Chou and Matthews (1989) J. Biol. Chem., 264,1831418319].A molecular dynamics/free energy cycle perturbation study wasperformed to understand the origin of the decreased affinity.A value (G = 1.58 ± 0.28 kcal/mol) comparable with theexperimental value was obtained by the simulation. Free energycomponent analysis revealed that destabilization of the vander Waals interaction between Ser88 and Trp109 (corepressor)mainly contributed to the decreased affinity of the mutant.The rotational transition of the hydroxyl (sulfhydryl) groupof Ser88 (Cys88) during the simulations affected the contributionsof Arg84 and water to the free energy change in the aporepressorand those of Arg84 and Trp 109 to that in the holorepressor.However, the contributions from different residues compensatedeach other, and the total free energy changes were almost invariablein the various simulations. 相似文献
995.
Ji Hoon Yang Min Hyung Yum Eun Jung Kim Myeung Hoi Kwon Cheol Woong Yang Ha-Jin Song Yong-Wan Jin 《Carbon》2006,44(11):2219-2223
Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C2H2, NH3, and N2 gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules. 相似文献
996.
Dieter Heymann 《Carbon》2005,43(11):2235-2242
The mean lifetimes of polyyne C8H2 in hexane were determined at 50, 60, 80, and 100 °C and in methanol at 60 °C. The reactions are second order at all temperatures: ln k2 = 20.5 ± 1.5-10303 ± 520T−1 and the corresponding activation energy is 85.7 ± 6.3 kJ mol−1 (7164 cm−1). Extrapolation suggests that solutions at 1 mM concentration are significantly unstable at room temperature. Quantum chemical calculations show that polyynes CmH2 + CnH2 (m + n = 16) could be products, but these were not detected. Alternatively, C16H2 isomers could form. IR spectra of the solid residues from hexane and methanol solutions were obtained. 相似文献
997.
Lin C.H.; Chan F.C.H.; Hwang J.K.; Lyu P.C. 《Protein engineering, design & selection : PEDS》1999,12(7):589-595
Conantokin-T (con-T) and conantokin-G (con-G) are two highlyhomologous peptide toxins found in Conus venom. The former isa 21-residue peptide with four -carboxyglutamic acid (Gla) residues(at positions 3, 4, 10 and 14), while the latter is a 17-residuepeptide with five -carboxyglutamic acid residues (at positions3, 4, 7, 10 and 14). Despite the apparent similarity in numberand relative positions of the -carboxyglutamic acid residues,113Cd-NMR studies indicated a distinct metal binding behaviorfor con-G and con-T. There appears to be four binding sitesin con-G in contrast to one metal binding site in con-T. Toelucidate the mode of calcium binding by the -carboxyglutamicacid residues in these conantokins, we designed various analogouspeptides with their -carboxyglutamic acid replaced by otheramino acid residues. 113Cd-NMR experiments on conantokin analoguesreveal that the major difference in the number of metal bindingsites between con-G and con-T is due to the residue at position7. We also performed molecular simulations to calculate therelative binding free energies of several potential bindingsites. Based on our theoretical and experimental results, wepropose a `four-site' binding model for conantokin-G and a `single-site'binding model for conantokin-T. 相似文献
998.
城市污水低位热能回收利用的研究 总被引:23,自引:0,他引:23
利用污水水源热泵,可回收城市污水的低位能源。回收的能源可用于制热或制冷。通过将污水水源热泵与地下水水源热泵系统和燃气+空调供冷相结合的供能方式进行比较得出结论,综合各项费用污水水源热泵最省,地下水水源热泵次之,燃气+空冷空调系统的费用最高。 相似文献
999.
1000.
The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005 相似文献