全文获取类型
收费全文 | 6294篇 |
免费 | 744篇 |
国内免费 | 326篇 |
专业分类
电工技术 | 393篇 |
综合类 | 405篇 |
化学工业 | 1171篇 |
金属工艺 | 357篇 |
机械仪表 | 412篇 |
建筑科学 | 506篇 |
矿业工程 | 173篇 |
能源动力 | 240篇 |
轻工业 | 426篇 |
水利工程 | 122篇 |
石油天然气 | 299篇 |
武器工业 | 79篇 |
无线电 | 743篇 |
一般工业技术 | 725篇 |
冶金工业 | 398篇 |
原子能技术 | 91篇 |
自动化技术 | 824篇 |
出版年
2024年 | 34篇 |
2023年 | 140篇 |
2022年 | 248篇 |
2021年 | 401篇 |
2020年 | 256篇 |
2019年 | 198篇 |
2018年 | 258篇 |
2017年 | 251篇 |
2016年 | 246篇 |
2015年 | 291篇 |
2014年 | 396篇 |
2013年 | 394篇 |
2012年 | 494篇 |
2011年 | 478篇 |
2010年 | 407篇 |
2009年 | 350篇 |
2008年 | 294篇 |
2007年 | 266篇 |
2006年 | 280篇 |
2005年 | 214篇 |
2004年 | 185篇 |
2003年 | 151篇 |
2002年 | 145篇 |
2001年 | 129篇 |
2000年 | 120篇 |
1999年 | 135篇 |
1998年 | 105篇 |
1997年 | 96篇 |
1996年 | 68篇 |
1995年 | 64篇 |
1994年 | 65篇 |
1993年 | 38篇 |
1992年 | 34篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有7364条查询结果,搜索用时 406 毫秒
71.
对MTG区熔生长法,慢冷法,粉末熔融生长法这3种方法制备的熔融织构YBCO块样品进行了交流磁化率和磁阻的测量。根据实验结果计算了样品的钉扎势,并且发现3种方法制备的样品在150 mT外磁场下均显示出基本消除弱连接的特性;粉末融熔生长法所制样品中有较纯净123相和较好织构,质量最好。 相似文献
72.
Gaussian type models have been established according to the real detected voltage of magnetically insulated ion diode and intense pulsed ion beam density near the focus of the diode. The energy deposition of Al target irradiated by intense pulsed ion beam has been simulated by Monte Carlo method based on these models. The results of energy depositions of the irradiation of single energy ions and the Gaussian distribution IPIB have been obtained. Especially cases of ion beam irradiating Al target at different angles on one dimension and two dimensions are discussed. The evolution processes of the energy deposition of ions in target have been simulated during a pulse. In addition, incident angles of H+ ions and C+ ions ranging from 20 to 40° have been researched. We obtained the conclusions that C+ ions of the beam affect the physical properties of near surface region, but H+ ions affect the deeper layer. The energy of intense pulsed ion beam mainly deposits on target surface, so melting and evaporation begin both from target surface. 相似文献
73.
74.
采用人胎盘血为原料,利用Sephadex G-200,DEAE-Sephadex A-50层析,Sepharose 4B反相免疫亲和层析技术,获得妊娠相关血浆蛋白A(PAPP-A)纯品,经8.0%聚丙烯酰胺凝胶电泳、免疫电泳、双向免疫扩散证明,所提取的PAPP-A纯品为单一成分。免疫家兔获得抗血清,其效价在1:16以上。 相似文献
75.
Benzene alkylation with propane has been studied over HZSM-5 loading 3.1–15.4 wt% Mo in continuous-flow microreactor under
350 °C and atmospheric pressure with the highest activity obtained at 6.7 wt% Mo loading. C7–9 aromatics were obtained as main products while the total amount of benzene rings kept unchanged. i-Propylbenzene and n-propylbenzene are formed primarily, while toluene, ethylbenzene, and ethyl-toluene are formed secondly from the propylbenzenes.
Catalytic performance of 6.7 wt% Mo/HZSM-5(38) partially poisoned by NH3 shows that the strong acid sites play a crucial role in the alkylation. Low SiO2/Al2O3 ratio of HZSM-5 in the Mo modified catalysts gives high propane conversion. Two hydrothermal treatment methods were applied
to the 6.7 wt% Mo/HZSM-5(38) catalyst, caused decrease of propane conversion but result in different product distribution.
A possible reaction mechanism concerning bifunctional active centers resulted from combination of loaded Mo species and strong
acid centers on HZSM-5 is proposed. 相似文献
76.
氟磷灰石-氟金云母微晶玻璃的生物活性研究 总被引:3,自引:0,他引:3
通过模拟细胞外液浸泡及动物骨内种植的方法研究了氟磷灰石-氟金云母微晶玻璃的生物活性机理。借助于SEM/EDAX,薄膜XRD,IRRS及原子吸收光谱分析等技术,研究了该微晶玻璃在生理环境中表面羟墓碘灰石层的形成过程。根据微晶玻璃中主晶相种类、显微结构特点及溶液中各离子的浓度等讨沦了羟基碑灰石层的形成机理。认为微晶玻璃中残余玻璃相的Ca~(2+)溶出及溶液相对于羟基磷灰石的过饱和状态,对材料表面羟基碑灰石层的形成具有重要意义。形成的羟基磷灰石层具有较低的结晶度,它是由最初的无定形态含水富CaO,P_2O_5薄层晶化转变而成。 相似文献
77.
78.
79.
对高速运动环境下多普勒效应引起的大载波频偏引起的载波间干扰进行数学分析,建立带频偏的非时变和时变频偏OFDM动态状态空间模型,提出了基于平方根无迹卡尔曼滤波(square-root unscented Kalman filter , SR-UKF)的频偏估计算法。将非线性状态估计思想引入OFDM频偏估计中,实现了对频偏的有效跟踪和估计。仿真结果表明,在大频偏、高阶调制下,SR-UKF频偏估计算法较自消除算法、最大似然估计算法具有更好的误码率性能;在收敛精度、稳定度和对信噪比敏感度方面,性能较扩展卡尔曼滤波算法均有所提升。 相似文献
80.
A series of waterborne poly(urethane‐urea)s, WPUUs, based on using nonpolar hydroxyl‐terminated polybutadiene (HTPB) as the soft segment, were successfully synthesized in this article. The effects of the COOH group content and soft‐segment molecular weight (Mns) on the dispersion, morphology, and physical properties were investigated. Variations of the particle size, viscosity, and zeta potential were first governed by the hydrophilicity of the polymer chain, and then by the swelling derived from water. Fourier transfer infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) indicated that the degree of phase separation decreased as the COOH group content increased or as Mns decreased. However, the hydrogen bonding between the soft and hard segments and the two‐phase mixing could not occur in this nonpolar HTPB‐based WPUU system, indicating that the hard segments tended to form smaller domains and to pack more loosely. It was attributed to the fact that the presence of bulky ionic salt groups destroyed the ordered arrangement of the hard segments. In this case, the increases of the interface area between the soft and hard phases resulted in that the present behaviors were similar to the phase mixing. In tensile properties, HTPB‐based WPUUs exhibited higher tensile stress, elongation at break, and modulus as the COOH group content decreased or as Mns decreased. In thermal degradation, the introduction of HTPB polyol improved the thermal stability of WPUU. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献