全文获取类型
收费全文 | 89476篇 |
免费 | 19201篇 |
国内免费 | 2618篇 |
专业分类
电工技术 | 4141篇 |
技术理论 | 8篇 |
综合类 | 3616篇 |
化学工业 | 25353篇 |
金属工艺 | 3210篇 |
机械仪表 | 3937篇 |
建筑科学 | 5548篇 |
矿业工程 | 1483篇 |
能源动力 | 2520篇 |
轻工业 | 10229篇 |
水利工程 | 1356篇 |
石油天然气 | 2813篇 |
武器工业 | 645篇 |
无线电 | 13240篇 |
一般工业技术 | 17318篇 |
冶金工业 | 3337篇 |
原子能技术 | 691篇 |
自动化技术 | 11850篇 |
出版年
2024年 | 179篇 |
2023年 | 848篇 |
2022年 | 1553篇 |
2021年 | 2571篇 |
2020年 | 3109篇 |
2019年 | 4467篇 |
2018年 | 4587篇 |
2017年 | 4995篇 |
2016年 | 5273篇 |
2015年 | 5993篇 |
2014年 | 6324篇 |
2013年 | 8064篇 |
2012年 | 6104篇 |
2011年 | 5956篇 |
2010年 | 5811篇 |
2009年 | 5588篇 |
2008年 | 5037篇 |
2007年 | 4727篇 |
2006年 | 4526篇 |
2005年 | 3754篇 |
2004年 | 3121篇 |
2003年 | 2860篇 |
2002年 | 2873篇 |
2001年 | 2589篇 |
2000年 | 2346篇 |
1999年 | 1745篇 |
1998年 | 1182篇 |
1997年 | 1010篇 |
1996年 | 805篇 |
1995年 | 669篇 |
1994年 | 502篇 |
1993年 | 437篇 |
1992年 | 331篇 |
1991年 | 273篇 |
1990年 | 188篇 |
1989年 | 179篇 |
1988年 | 143篇 |
1987年 | 87篇 |
1986年 | 91篇 |
1985年 | 74篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 36篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
981.
982.
Hai‐Xia Yang Yan‐Feng Li Jin‐Gang Liu Shi‐Yong Yang Da‐Xue Yin Lincheng Zhou Lin Fan 《应用聚合物科学杂志》2004,91(6):3981-3990
A series of new polymerized monomer reactants (PMR) matrix resins of poly(pyrrolone‐benzimidazole)s containing a pyridine unit (PPBP) were synthesized by polycondensation of monoethyl ester of cis‐5‐norbornene‐endo‐2,3‐dicarboxylic acid, 2,6‐diphenyl ester pyridinedicarboxylic acid or 3,5‐diphenyl ester pyridinedicarboxylic acid, and diethyl ester of 4,4′‐oxydiphthalic acid with 3,3′‐diaminobenzidine in a mixing solution of anhydrous ethyl alcohol and N‐methylpyrrolidone under given temperature and pressure conditions. The resulting resin solutions showed good solubility in polar organic solvents and stability at room temperature. The corresponding PPBP matrix resin, molded powder, and molded plate were prepared by undergoing amidation, imidization, cyclization, and crosslinking reactions when the reaction temperature was increased from 80 to 350°C, successively; the crosslinking structure was formed by the reverse Diels–Alder reaction at 270–290°C under 50 MPa pressure (2.5–3.5 MPa displayed by the pressure meter). The chemical reactions and properties of the resulting PPBP were studied by means of FTIR, TGA, and DMA methods, and the results indicated that the kinds of PPBP materials retain excellent thermal stability and processability; when the initial decomposition temperature was above 620°C the Tg was at 413.5°C for 3,5‐PPBP‐20 molded plate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3981–3990, 2004 相似文献
983.
984.
The curing behavior of two kinds of commercial powdered resol phenolic resins was studied by differential scanning calorimetry. Liquid‐state 13C‐NMR spectroscopy was used to aid in understanding the curing behavior by detecting the structure of powdered resins. The reaction mechanism was interpreted with the dependency of activation energy on the degree of conversion. The results indicate that there are differences in the curing mechanism between core and face phenolic resins. The curing process of core resin was faster than that of face resin at the same reaction temperature. The water added in the curing system played an important role of plasticizer or diluent according to different curing stages and water content. In the initial curing stage, water mainly diluted the system and retarded the curing reactions. However, at the higher degrees of conversion, water played the role of plasticizer to decrease the effect of diffusion on the curing reactions to make the curing reactions more complete. The excess water added in the curing system played the role of diluent at almost all stages during the curing process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1371–1378, 2003 相似文献
985.
Ping Shen Lifeng Zhang Jianxun Fu Hao Zhou Yi Wang Limei Cheng 《Ceramics International》2019,45(9):11287-11295
In the present study, the wettability between liquid iron with two different Al contents and MgOAl2O3 binary substrates was studied in reducing atmosphere. The contact angles between liquid iron with 18?ppm Al and MgO, MgO·Al2O3, Al2O3 were 133.5°, 113.7°, 126.9° respectively. With the variation of the substrate composition, the contact angles for the intermediate binary phases of the three components (MgO, MgO·Al2O3, Al2O3) obeyed the Cassie theory. In the experiment using iron with 370?ppm Al, all the contact angles were higher than that using low Al-containing iron. The surface of the iron drop was covered with an oxide layer, which mainly consisted of many small particles. With the variation of the substrate gradually from MgO to Al2O3, the composition of the oxide layer changed from MgO·Al2O3 to CaOAl2O3. The formation of the oxide layer prevented the spreading of liquid iron, leading to the increase of the contact angle. 相似文献
986.
987.
Poly(vinyl pyrrolidone‐co‐isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP–POSS) were synthesized by one‐step polymerization and characterized using FTIR, high‐resolution 1H‐NMR, solid‐state 13C‐NMR, 29Si‐NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The Tg of the PVP–POSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self‐association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low POSS content, the role as diluent dominates, resulting in a decrease in Tg. At a relatively high POSS content, the last two factors dominate and result in Tg increase of the PVP–POSS hybrid. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2208–2215, 2004 相似文献
988.
Jui‐Ming Yeh Chi‐Lun Chen Tai‐Hung Kuo Wen‐Fen Su Hsi‐Ya Huang Der‐Jang Liaw Hsin‐Yi Lu Chi‐Fong Liu Yuan‐Hsiang Yu 《应用聚合物科学杂志》2004,92(2):1072-1079
A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004 相似文献
989.
本文从压力容器设计、制造及标准三方面分析了压力容器环焊缝事故率高的原因,提出了相应的对策。希压力容器有关工程技术人员要充分重视压力容器环焊缝的质量问题,以确保压力容器的安全使用。 相似文献
990.
We discuss the notion of \(H\) -centered surface area of a graph \(G\) , where \(H\) is a subgraph of \(G\) , i.e., the number of vertices in \(G\) at a certain distance from \(H\) , and focus on the special case when \(H\) is a length two path to derive an explicit formula for the length two path centered surface area of the general and scalable arrangement graph, following a generating function approach. 相似文献