全文获取类型
收费全文 | 38788篇 |
免费 | 2675篇 |
国内免费 | 2092篇 |
专业分类
电工技术 | 1257篇 |
综合类 | 2128篇 |
化学工业 | 14102篇 |
金属工艺 | 3598篇 |
机械仪表 | 973篇 |
建筑科学 | 2977篇 |
矿业工程 | 494篇 |
能源动力 | 1104篇 |
轻工业 | 1804篇 |
水利工程 | 97篇 |
石油天然气 | 1537篇 |
武器工业 | 294篇 |
无线电 | 3227篇 |
一般工业技术 | 5346篇 |
冶金工业 | 1447篇 |
原子能技术 | 667篇 |
自动化技术 | 2503篇 |
出版年
2024年 | 116篇 |
2023年 | 540篇 |
2022年 | 1207篇 |
2021年 | 1214篇 |
2020年 | 1009篇 |
2019年 | 903篇 |
2018年 | 783篇 |
2017年 | 1069篇 |
2016年 | 1320篇 |
2015年 | 1302篇 |
2014年 | 1789篇 |
2013年 | 2030篇 |
2012年 | 2250篇 |
2011年 | 2884篇 |
2010年 | 2129篇 |
2009年 | 2596篇 |
2008年 | 2042篇 |
2007年 | 2559篇 |
2006年 | 2384篇 |
2005年 | 1909篇 |
2004年 | 1608篇 |
2003年 | 1623篇 |
2002年 | 1322篇 |
2001年 | 1038篇 |
2000年 | 946篇 |
1999年 | 772篇 |
1998年 | 611篇 |
1997年 | 424篇 |
1996年 | 384篇 |
1995年 | 314篇 |
1994年 | 282篇 |
1993年 | 248篇 |
1992年 | 216篇 |
1991年 | 182篇 |
1990年 | 154篇 |
1989年 | 120篇 |
1988年 | 94篇 |
1987年 | 94篇 |
1986年 | 109篇 |
1985年 | 107篇 |
1984年 | 92篇 |
1983年 | 77篇 |
1982年 | 77篇 |
1981年 | 85篇 |
1980年 | 77篇 |
1978年 | 72篇 |
1977年 | 73篇 |
1976年 | 88篇 |
1975年 | 86篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Shizuo Arichi Noriyuki Sakamoto Shozo Himuro Mayumi Miki Masafumi Yoshida 《Polymer》1985,26(8):1175-1180
In order to obtain the additional data concerning the unperturbed dimension of poly-4-substituted styrene, light scattering measurements are performed on the twenty-two fractions with molecular weight of (0.91–352)·104 of poly(4-acetoxystyrene) in dioxan at 25°C, from which the molecular weight obtained was found easily to be evaluated with the gel permeation chromatography using THF. Phase separation experiments for this polymer indicate that the theta state is attained in isopropyl acetate at 19.7°C and butyl acetate at 26.8°C. By making viscosity measurements at that state, the value of KΘ is directly evaluated as 5.4·10?4 dl g?1. The limiting viscosity number is also obtained in good solvents, THF and dioxan, at 25°C and constants of the Mark-Houwink-Sakurada equation in each solvent are determined. Further, approximately the same KΘ as above is obtained from these data with the Stockmayer-Fixman plot. The calculated value of steric factor, 2.37, on this polymer may be plausible, compared with those of polyvinylaromatic derivatives. 相似文献
63.
报导了新型鞣剂 7-羟基全氢化唑并嗪 (以下简称 OX- Z)的合成方法。试验确定合成的最佳条件为 :在氮气保护下 ,将等摩尔量的二乙醇胺在 10℃水浴中缓慢滴入乙二醛中 ,滴加时间 0 .5 h,在 2 0℃水浴中继续反应 1.5 h,产率为 6 2 .9%。 OX- Z对浸酸绵羊皮单独鞣制 ,可使收缩温度升高到 87℃。最佳鞣制条件为 :p H10 .0 ,OX- Z用量 5 % ,鞣制时间 8h。在对 OX- Z与皮胶原的结合类型的研究中证明它们之间是以化学键结合的。 相似文献
64.
Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed. 相似文献
65.
66.
67.
68.
69.
王芬 《武汉理工大学学报(材料科学英文版)》2005,20(Z1)
1Introduction Harmfulbacteriaexistanywhereintheworldsuchas soil,air,water,surfacesofobjectsandourskins,etc.Thenumberofbacteriumisenormous,withmanydiffer entspecies.Theyhavethreatenedthehealthofhuman beingsseriously.Withthedevelopmentofeconomyand environme… 相似文献
70.
The photoluminescence properties of BiTaO4∶Pr3+ and BiTaO4 at room temperature were studied, and the infrared transmission and diffusion reflection spectra of BiTaO4 were measured. The photoluminescence spectrum of BiTaO4 peaks at about 420, 440 and 465 nm. There has an obvious excitation band from 330 to 370 nm. The photoluminescence spectrum of BiTaO4∶Pr3+ consists of the characteristic emission of Pr3+, and its main peak is at 606 nm from 3P0→3H6 transition of Pr3+. Its excitation spectrum consists of the wide band with maximum at 325 nm, the wide band in the range of 375~430 nm, and the characteristic excitation of Pr3+. The bands at 325 nm and 375~430 nm may be from the absorption of the charge transfer transition of the tantalate group and defect energy levels in its forbidden band, respectively. There is energy transfer from host to Pr3+. Because both the host density and photoluminescence peak intensity of BiTaO4∶Pr3+ are superior to PbWO4, BiTaO4∶Pr3+ may be a potential heavy scintillator. 相似文献