全文获取类型
收费全文 | 37306篇 |
免费 | 3792篇 |
国内免费 | 2164篇 |
专业分类
电工技术 | 2406篇 |
技术理论 | 3篇 |
综合类 | 3176篇 |
化学工业 | 6023篇 |
金属工艺 | 2151篇 |
机械仪表 | 2391篇 |
建筑科学 | 2764篇 |
矿业工程 | 1341篇 |
能源动力 | 1127篇 |
轻工业 | 2870篇 |
水利工程 | 743篇 |
石油天然气 | 1605篇 |
武器工业 | 296篇 |
无线电 | 4270篇 |
一般工业技术 | 4516篇 |
冶金工业 | 1802篇 |
原子能技术 | 466篇 |
自动化技术 | 5312篇 |
出版年
2024年 | 161篇 |
2023年 | 599篇 |
2022年 | 1055篇 |
2021年 | 1496篇 |
2020年 | 1149篇 |
2019年 | 1035篇 |
2018年 | 1111篇 |
2017年 | 1221篇 |
2016年 | 1146篇 |
2015年 | 1552篇 |
2014年 | 1904篇 |
2013年 | 2354篇 |
2012年 | 2461篇 |
2011年 | 2472篇 |
2010年 | 2346篇 |
2009年 | 2141篇 |
2008年 | 2104篇 |
2007年 | 1946篇 |
2006年 | 1929篇 |
2005年 | 1669篇 |
2004年 | 1280篇 |
2003年 | 1510篇 |
2002年 | 2002篇 |
2001年 | 1750篇 |
2000年 | 1089篇 |
1999年 | 860篇 |
1998年 | 560篇 |
1997年 | 456篇 |
1996年 | 373篇 |
1995年 | 344篇 |
1994年 | 271篇 |
1993年 | 176篇 |
1992年 | 165篇 |
1991年 | 143篇 |
1990年 | 91篇 |
1989年 | 77篇 |
1988年 | 62篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 22篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 23篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1959年 | 6篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
CeO2 particles confined within the pores of an SBA-15 mesoporous silica host were prepared by incipient wetness impregnation (IMP)
and deposition precipitation (DP) methods. The materials were characterized by XRD, N2-adsorption and temperature programmed reduction (TPR) to evaluate the structure, texture, and redox properties. The preparation
procedure had significant impact on the assembling mode of CeO2 inside the SBA-15 mesopores. A high dispersion of CeO2 particles was achieved via DP, whereas the dispersion of CeO2 prepared by IMP was found to be inhomogeneous and CeO2 partially blocked the pores. The CO conversion in the water-gas-shift reaction was enhanced over 1 wt% Pt supported on CeO2-modified SBA-15 obtained by DP. 相似文献
82.
83.
The glass transition temperatures (Tg's) of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers were measured using thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). The polymers studied had number-average molecular weights from 3000 to 250,000 g/mole. The results indicate that the composition dependence of the Tg's for the copolymers and terpolymers can be satisfactorily described by a general Fox equation. In general, the measured Tg's of the copolymer and terpolymer samples depend more on the steric effects of the constituent pendent groups than on their molecular weights. The chain flexibility rather than the size of the pendent group is the determining factor in the glass transition properties of the styrene polymers. 相似文献
84.
85.
激光等离子体粒子模拟广泛用于探索极端物质状态下的科学问题。将一种基于粒子云网格方法的三维等离子体粒子模拟程序LARED P移植到Intel Xeon Phi协处理器上。在移植的过程中,综合运用了Native和Offload两种编程模式:首先运用Native模式对LARED P程序中热点计算任务进行优化研究,通过采用SIMD扩展指令使该计算任务获得了4.61倍的加速;然后运用Offload模式将程序移植到CPU-Intel Xeon Phi异构系统上,并通过使用异步数据传输和双缓冲技术分别提升了程序性能9.8%和21.8%。 相似文献
86.
随着国内预拌混凝土行业的发展,混凝土企业高层越来越意识到搅拌站信息化管理的必要性,各种混凝土搅拌站ERP软件在国内得到了迅速的发展,通过这种软件的信息化管理,后台数据库每天都会产生大量的生产数据。为了避免搅拌站之间的恶性竞争,混凝土行业协会和政府部门需要对某个区域乃至整个行业的搅拌站的生产运营情况有实时的了解,以便对其进行监管,最终促进行业的公平竞争。本文结合国内混凝土行业自身的特点,阐述了混凝土行业海量数据协同的总体构想和数学模型,之后从多维度论述了基于JCS多级缓存的海量数据协同模块的设计,最后,采用Socket的方式最终实现了Server端与Client端的一对多的数据通信。 相似文献
87.
物联网作为未来的发展趋势之一,将在各个方面决定未来世界和人类社会的发展方向。而自智慧地球、感知中国等战略提出以来,世界各国也纷纷开展物联网领域的规划布局,将物联网建设上升到国家战略。物联网在全世界范围内掀起了继计算机和互联网之后的第三次信息革命浪潮。在这空前火爆的物联网宏观背景下,微观企业也不可避免的受到物联网影响。在这一背景下,通过分析物联网环境对企业内部控制环境的影响。本文认为,物联网环境下企业内部控制环境将更加信息化、虚拟化、智能化。 相似文献
88.
通过DSC曲线研究了不同含量的ZrO2对CaO-SiO2系玻璃析晶的影响,根据JMA方程计算动力学参数(如析晶活化能E、频率因子ν、晶化指数n)。从计算结果可以看出,随着ZrO2含量的增加,析晶活化能E减少,而频率因子ν和晶化指数n增加。当ZrO2含量为7%时,E值最小:235.58kJ/mol;n值最大:4.70。说明ZrO2在CaO-SiO2玻璃体系是有效的晶核剂。 相似文献
89.
Acidic polyelectrolyte copolymers containing 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and methacrylic acid (MAA) were prepared by free radical polymerization to high conversion in solution. Copolymer yields were obtained by gravimetry (all in the 30–50% range), relative molecular weights estimated by intrinsic viscosity measurements (all in the 50–70 cc/g range), tacticity by 13C nuclear magnetic resonance (NMR) spectroscopy (all polymers predominantly syndiotactic with some atactic content), and composition by acid/base titrations in conjunction with 1H-NMR spectroscopy (all close to the monomer charge ratios). Acid strengths or apparent pKa's were examined as a function of extent of ionization. Measurements performed in water indicated that the compact/extended coil transformation in predominantly syndiotactic polymethacrylic acid occurs also in copolymers of similar tacticity containing moderate to high concentrations of MAA. The apparent pKa of such polymers containing only small amounts of MAA did not vary with extent of ionization, indicating a low degree of interaction between the acid groups. In copolymer pairs containing similar amounts of MAA but differing HEMA and MMA contents, the polymer containing more HEMA appeared the stronger acid, presumably due to a better solvation of that polymer which would increase the net spatial charge–charge separation and decrease cooperative effects that lead to suppressed ionization. 相似文献
90.
Magnetic iron oxide (Fe3O4) was prepared by a coprecipitation method. Core–shell composite magnetic polymer microspheres with carboxyl groups were synthesized by the dispersion polymerization of styrene and acrylic acid in the presence of magnetic oxide, and dibenzoyl peroxide was used as an initiator. The synthesized magnetic polymer microspheres were characterized with X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and so forth. The results indicated that the product was single‐phase Fe3O4, and its average size was about 10 nm. The configuration of the microspheres, which contained carboxyl groups, was spherical, and the average size was about 2 μm. The results of vibrating sample magnetometry tests showed that the magnetic powders produced by different surfactants had different saturation magnetizations. When poly(ethylene glycol) with a weight‐average molecular weight of 4000 was used as a surfactant, the saturation magnetization of the samples reached 69.2 emu/g. The factors that affected the shape, magnetism, size, and distribution of the microspheres were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献