全文获取类型
收费全文 | 95260篇 |
免费 | 10293篇 |
国内免费 | 6806篇 |
专业分类
电工技术 | 8703篇 |
技术理论 | 5篇 |
综合类 | 8601篇 |
化学工业 | 12576篇 |
金属工艺 | 5930篇 |
机械仪表 | 6646篇 |
建筑科学 | 8511篇 |
矿业工程 | 2852篇 |
能源动力 | 2931篇 |
轻工业 | 7817篇 |
水利工程 | 2400篇 |
石油天然气 | 4051篇 |
武器工业 | 1198篇 |
无线电 | 11255篇 |
一般工业技术 | 9186篇 |
冶金工业 | 3593篇 |
原子能技术 | 1171篇 |
自动化技术 | 14933篇 |
出版年
2024年 | 491篇 |
2023年 | 1588篇 |
2022年 | 3053篇 |
2021年 | 4182篇 |
2020年 | 3151篇 |
2019年 | 2413篇 |
2018年 | 2764篇 |
2017年 | 3082篇 |
2016年 | 2810篇 |
2015年 | 3995篇 |
2014年 | 5162篇 |
2013年 | 5890篇 |
2012年 | 6984篇 |
2011年 | 7217篇 |
2010年 | 6746篇 |
2009年 | 6506篇 |
2008年 | 6608篇 |
2007年 | 6125篇 |
2006年 | 5830篇 |
2005年 | 4708篇 |
2004年 | 3753篇 |
2003年 | 3512篇 |
2002年 | 4307篇 |
2001年 | 3654篇 |
2000年 | 2225篇 |
1999年 | 1486篇 |
1998年 | 783篇 |
1997年 | 686篇 |
1996年 | 570篇 |
1995年 | 482篇 |
1994年 | 390篇 |
1993年 | 263篇 |
1992年 | 217篇 |
1991年 | 170篇 |
1990年 | 128篇 |
1989年 | 95篇 |
1988年 | 63篇 |
1987年 | 50篇 |
1986年 | 49篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1959年 | 18篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials
Jui‐Ming Yeh Kuan‐Yeh Huang Chung‐Feng Dai B. G. Chand Chang‐Jian Weng 《应用聚合物科学杂志》2008,110(4):2108-2114
In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO2) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO2 nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO2 loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO2 nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
23.
Sodium sulfonate‐terminated dendritic poly(ester‐amine) (SPEA) was synthesized by sulfonation of acrylic double bond‐terminated dendritic poly(ester‐amine) (APEA) with sodium hydrogen sulfite (NaHSO3) in mixture of diglycol and 2‐butanone under normal pressure. The structure of SPEA was characterized by IR, 1H‐NMR, and elemental analysis. SPEA was water‐soluble. 1.0–40.0% (mass) SPEA aqueous solutions appeared as dilatant fluid. When pH value varied from 1.5 to 12.0, the viscosity of 1–5% (mass) SPEA aqueous solutions changed very small, and the electric conductivity almost kept stable within pH 3.0–10.0. The relationship between the viscosity and the concentration of SPEA water solutions was similar to that of NaCl water solutions. The surface tension of SPEA water solutions was lower than that of polyethylene glycol 2000 water solutions with the same concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
24.
Polyoxymethylene (POM) composites filled with low-density polyethylene (LDPE) and rice husk flour (RHF) were prepared by injection molding. The POM/5 wt % LDPE/7.5 wt % RHF composite exhibited the lowest wear rate, whereas the coefficient of friction remained low, and the POM/5 wt % LDPE/5 wt % RHF composite had the best mechanical properties. X-ray diffraction analysis was carried out, and the worn surfaces were examined with scanning electron microscopy. The results showed that the addition of the filler reduced the crystallinity degree of the POM composites. The main wear mechanism for unfilled POM was adhesion, whereas for the POM composites, wear seemed to occur mainly by fatigue and abrasion. It was experimentally confirmed that the POM composite filled with LDPE and RHF, which is well-performing, low-cost, and environmentally friendly, could be a potential material for tribological applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
25.
A novel monomer containing pyridylazo-2-naphthoxyl group, 1-(1-(4-vinylbenzyloxy)naphthalen-2-yl)-2-(pyridin-2-yl)diazene (VBNPA), was successfully synthesized and copolymerized with styrene (St) in N,N-dimethyl formamide (DMF) via reversible addition–fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as RAFT agent. The polymerization behavior exhibited “living”/controlled characters. The obtained copolymer, poly(St-co-VBNPA), with pre-determinable molecular weight and narrow molecular weight distribution can be used as a carrier in metal ion detection and analysis via pre-concentration technique. The copolymer–metal ion (copper (Cu) and europium (Eu)) complexes were prepared and characterized. 相似文献
26.
27.
28.
29.
设计一条钢筋网自动化焊接生产线,包括经料送料平台、纬料自动分料及上料机构、多点电阻点焊机、接料平台、卸料机械手。从上料到出料依靠电机、汽缸之间的协调工作来实现。并由单片机和PLC实现控制功能,上位机用MCGS组态软件在整个过程监视现场,采集工作状态及参数,起到监控作用。 相似文献
30.
An analytical method is presented for calculating the resonant frequency andQ-factor of a superconducting dielectric disk resonator operating in millimeter-wave regime with whispering-gallery mode. Resonant frequency shift due to the optical generation of quasi-particles in superconducting film is investigated as a function of photon flux. An optically tunable resonant frequency of about 500 MHz is estimated, and good agreement is found between numerical results and experimental ones. 相似文献