全文获取类型
收费全文 | 204812篇 |
免费 | 23146篇 |
国内免费 | 14298篇 |
专业分类
电工技术 | 19671篇 |
技术理论 | 5篇 |
综合类 | 23951篇 |
化学工业 | 21190篇 |
金属工艺 | 8540篇 |
机械仪表 | 16119篇 |
建筑科学 | 21560篇 |
矿业工程 | 9222篇 |
能源动力 | 8245篇 |
轻工业 | 11697篇 |
水利工程 | 8156篇 |
石油天然气 | 8786篇 |
武器工业 | 2794篇 |
无线电 | 14478篇 |
一般工业技术 | 23422篇 |
冶金工业 | 7799篇 |
原子能技术 | 2594篇 |
自动化技术 | 34027篇 |
出版年
2024年 | 1195篇 |
2023年 | 3195篇 |
2022年 | 5841篇 |
2021年 | 6584篇 |
2020年 | 7374篇 |
2019年 | 6339篇 |
2018年 | 5906篇 |
2017年 | 7386篇 |
2016年 | 8143篇 |
2015年 | 8702篇 |
2014年 | 13454篇 |
2013年 | 12814篇 |
2012年 | 16233篇 |
2011年 | 16373篇 |
2010年 | 12281篇 |
2009年 | 12802篇 |
2008年 | 11630篇 |
2007年 | 14035篇 |
2006年 | 12137篇 |
2005年 | 10094篇 |
2004年 | 8277篇 |
2003年 | 6938篇 |
2002年 | 5826篇 |
2001年 | 4841篇 |
2000年 | 4232篇 |
1999年 | 3491篇 |
1998年 | 2836篇 |
1997年 | 2447篇 |
1996年 | 2045篇 |
1995年 | 1827篇 |
1994年 | 1544篇 |
1993年 | 1120篇 |
1992年 | 989篇 |
1991年 | 725篇 |
1990年 | 597篇 |
1989年 | 569篇 |
1988年 | 399篇 |
1987年 | 219篇 |
1986年 | 183篇 |
1985年 | 81篇 |
1984年 | 85篇 |
1983年 | 54篇 |
1982年 | 60篇 |
1981年 | 64篇 |
1980年 | 44篇 |
1979年 | 48篇 |
1978年 | 23篇 |
1975年 | 20篇 |
1959年 | 33篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
发酵法生产医药用透明质酸 总被引:2,自引:0,他引:2
山东临朐华元生物工程有限公司通过对菌株的筛选培育、发酵原料配方和工艺的改进、提纯工艺和设备的优化、制粉工艺和设备的改进、生产环境的改造,利用生物工程技术发酵法研制生产出医药用透明质酸,并形成1.5t/a的生产规模。产品应用于眼科手术、滴眼液、手术防粘连等方面,改变了国内医药用透明质酸依赖进口或动物器官提取法微量生产自用的局面,为国内以透明质酸为基质的制剂产品发展打下了基础。 相似文献
992.
993.
介绍原 2 0万t/a装置增容到 2 4万t/a时的工艺参数优化。PTA平均粒径 95~ 110 μm ,n(EG) /n(PTA) =2 .6~ 2 .7,酯化液位 63 %~ 64 % ,温度 2 92~ 2 96℃ ;乙二醇锑催化剂 ,稳定EG、DEG量 ,选择TiO2 消光剂 ,滤除凝聚粒子 ;预缩聚温度 2 87~ 2 89℃ ,压力 2 .4~ 2 .8kPa,液位 42~ 48cm ;终缩聚温度 2 90~ 2 91℃ ,压力 2 .5~ 3 .0hPa,液位 60~ 62cm ,搅拌速度 2 .7r/min。 相似文献
994.
The shock adiabats of pressed carbamide samples with a density of 1.29 g/cm3 and carbamide samples with a bulk density of 0.78 g/cm3 were studied at pressures of 1–14 GPa using an electromagnetic method. In the coordinates D and U, the shock adiabat of pressed carbamide is linear and the shock adiabat of carbamide of bulk density at a pressure of 2.4 GPa is represented as two linear segments: D = 2U at 0.6 < U <1.3 km/sec and D = 0.6 + 1.55U at 1.3 <U < 2.8 km/sec. The possibility of a phase transition in carbamide under shock compression is discussed. 相似文献
995.
介绍了FP—640火焰光度计采用低、高标法钠含量的测定。与标准曲线法钠含量测定相比较,该法具有方便、快速、准确度高的特点。 相似文献
996.
Nikolaos Dimitratos Jose Antonio Lopez-Sanchez David Morgan Albert Carley Laura Prati Graham J. Hutchings 《Catalysis Today》2007,122(3-4):317-324
Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation. 相似文献
997.
In order to obtain an efficient hybrid inorganic–organic nonlinear optical (NLO) materials, an azo-dye containing three electronic donor groups 2,5-dimethyl-4-(4′-nitrophenylazo)phenol (DMNPAP) was synthesized and reacted with 3-isocyanatopropyl triethoxysilane (ICTES) to give an alkoxysilane dye (ICTES–DMNPAP). Molecular structural characterizations for DMNPAP and ICTES–DMNPAP were investigated by elemental analysis, 1H NMR, FTIR, UV–visible spectra and differential scanning calorimetry (DSC). The alkoxysilane dye could be hydrolyzed and polymerized in the presence of water, and then transparent hybrid films could be fabricated by spin coating on the indium–tin-oxide (ITO) glass substrates. Compared with the dye 4-nitro-4′-hydroxy-azobenzene (NHA) containing only one hydroxyl as donor group, DMNPAP exhibited larger βCTμg value measured by solvatochromic method, and second harmonic generation (SHG) measurement of the hybrid films was in agreement with the result. 相似文献
998.
A versatile electrochemical platform for characterizing the adsorption of neutral and positively charged surfactants on hydrophobic surfaces was established using methylene blue (MB) as the probe. As a rigid, planar and electroactive species, MB can intercalate inside the regular self-assembled monolayers (SAMs) of n-hexanethiol and exhibit well-defined electrochemical responses. The adsorption of surfactants on the hydrophobic SAMs through the intercalation interaction between the hydrophobic tails of surfactants and the SAMs might change the density of the SAMs and influence the electrochemical behaviors of MB, providing a simple but effective approach for characterizing surfactant adsorption on hydrophobic surfaces. As an example, the adsorptive behaviors of cetyltrimethylammonium bromide (CTAB), a positively charged surfactant, and Triton X-100, a neutral surfactant, on hydrophobic surfaces were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that these surfactants generally experienced three different adsorptive behaviors: the monomer adsorption at low concentrations, the loose monolayer adsorption at intermediate concentrations and the dense monolayer adsorption at high concentrations. In the case of CTAB, a new additional submonolayer adsorptive behavior between the monomer and the loose monolayer adsorption was observed for the first time, due to its rather long hydrophobic tail. 相似文献
999.
Manganese ferrite nanoparticles synthesized through a nanocasting route as a highly active Fenton catalyst 总被引:2,自引:0,他引:2
Teresa Valds-Solís Patricia Valle-Vign Sonia lvarez Gregorio Marbn Antonio B. Fuertes 《Catalysis communications》2007,8(12):2037-2042
Spinel ferrite MnFe2O4 nanoparticles were synthesized by means of a nanocasting technique using a low-cost mesoporous silica gel as a hard template. The magnetic nanoparticles, of <10 nm diameter and with a surface area of around 100 m2/g, were tested as a heterogeneous Fenton catalyst for the decomposition of hydrogen peroxide under neutral and basic conditions. This catalyst shows a much higher activity than previous heterogeneous catalysts reported in the literature, which is mainly ascribed to its small particle size. Furthermore, the magnetic catalyst can be easily separated from the reaction medium by means of an external magnetic field. The effects of residual silica and the purity of the catalyst (hematite formation) on catalytic activity have been studied and correlated. The results obtained show this catalyst to be a suitable candidate for the removal of pollutants in wastewaters by means of the Fenton heterogeneous reaction. 相似文献
1000.
Koji Makino 《Electrochimica acta》2005,51(5):961-965
The electrodes prepared by a sputtering method were evaluated as the cathodes for direct methanol fuel cells (DMFCs). Pt loading below 0.25 mg cm−2 achieved higher mass activities than that of 0.5 mg cm−2 prepared by the paste method, which was general conventional method. However, an increase in Pt loading reduced the catalyst activity for the oxygen reduction reaction (ORR). This result may suggest an increase in only electrochemically inactive Pt. Pt utilization efficiency can be found about ten times higher at Pt loading of 0.04 mg cm−2. Moreover, addition of Nafion to sputter-deposited Pt cathodes is found possible to improve the catalyst activity for the ORR, but the excess Nafion over the optimum condition reduces the active sites. 相似文献