全文获取类型
收费全文 | 48305篇 |
免费 | 4547篇 |
国内免费 | 2350篇 |
专业分类
电工技术 | 3142篇 |
技术理论 | 3篇 |
综合类 | 3455篇 |
化学工业 | 8262篇 |
金属工艺 | 2592篇 |
机械仪表 | 2906篇 |
建筑科学 | 3752篇 |
矿业工程 | 1471篇 |
能源动力 | 1241篇 |
轻工业 | 4337篇 |
水利工程 | 897篇 |
石油天然气 | 2413篇 |
武器工业 | 402篇 |
无线电 | 5480篇 |
一般工业技术 | 5862篇 |
冶金工业 | 2107篇 |
原子能技术 | 662篇 |
自动化技术 | 6218篇 |
出版年
2024年 | 251篇 |
2023年 | 879篇 |
2022年 | 1739篇 |
2021年 | 2052篇 |
2020年 | 1616篇 |
2019年 | 1350篇 |
2018年 | 1479篇 |
2017年 | 1700篇 |
2016年 | 1430篇 |
2015年 | 1989篇 |
2014年 | 2575篇 |
2013年 | 2955篇 |
2012年 | 3166篇 |
2011年 | 3375篇 |
2010年 | 2959篇 |
2009年 | 2920篇 |
2008年 | 2904篇 |
2007年 | 2608篇 |
2006年 | 2611篇 |
2005年 | 2152篇 |
2004年 | 1514篇 |
2003年 | 1428篇 |
2002年 | 1407篇 |
2001年 | 1209篇 |
2000年 | 1119篇 |
1999年 | 1104篇 |
1998年 | 825篇 |
1997年 | 707篇 |
1996年 | 628篇 |
1995年 | 562篇 |
1994年 | 429篇 |
1993年 | 312篇 |
1992年 | 292篇 |
1991年 | 187篇 |
1990年 | 159篇 |
1989年 | 143篇 |
1988年 | 108篇 |
1987年 | 67篇 |
1986年 | 44篇 |
1985年 | 54篇 |
1984年 | 28篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
BaTiO3 multilayer capacitors with a nominal capacitance of 3.5nF have been carefully measured using the thermally stimulated current (TSC) technique. When a 300V polarization voltage is applied at room temperature, a new TSC peak appeared in defective sample A after it has been immersed in water. No new peak was found in good-quality sample B after a similar treatment. The accelerated life test shows that sample A hasa much shorter life than sample B in terms of insulation resistance. 相似文献
92.
本文选用 ICR 雄性小鼠,经腹腔分别注射不同剂量的~(125)I 及~(131)I,观察并比较它们对小鼠精子畸形发生率的影响及染毒后睾丸中放射性活度的变化。实验结果表明:(1)~(125)I 染毒后4—5周,0、185、370和555 kBq 各组精子畸形发生率分别为9.00‰、9.57‰、11.6‰及13.9‰;~(131)I 染毒后4—5周,上述各组精子畸形发生率分别为8.50‰、12.5‰、14.7‰和15.5‰;在相同注入量下,~(125)I 与~(131)I 诱发小鼠精子畸形发生率的差异各组均不显著(X~2检验,p>0.05)。(2)~(125)I、~(131)I 染毒后2h 至7天内,两者在睾丸中的放射性活度及变化规律相似,即在染毒后2h 达最高值,每克睾丸中~(125)I 和~(131)I 的放射性活度分别占初始注入量(370 kBq)的0.72%和0.50%,然后迅速下降,至一周时,仅分别占初始注入量的0.035%和0.011%。 相似文献
93.
With the aid of a double-tilt holder in a transmission electron microscope, a new method for a rapid and precise determination of the misorientations of a large number of subgrain or grain boundaries is given in this article. By use of the method, the continuous recrystallization can be rapidly and precisely evaluated when compared to the other conventional methods. 相似文献
94.
NCFW系统是适合于花岗岩与变质岩地区的勘探地下水专家系统,系统的人机交互既可用菜单(亦称项目单)方式,亦可用汉语对话方式。这两种方式既可混合使用亦能灵活切换。本文着重描述了汉语接口的设计思想、实现中采用关键技术以及系统运行实例。 相似文献
95.
It is shown that a superconductor cannot be simply treated as a low-loss conductor; rather, it should be treated as a negative dielectric material (with a negative dielectric constant). This approach is good only for vanishingly small field application with frequency significantly smaller than gap frequency and temperature not too close to the critical temperature of the superconductor. The electromagnetics of negative dielectric materials are discussed in terms of causality, perturbation technique, surface impedance, time-domain interpretation of current components, and computational electrodynamics 相似文献
96.
A modification to the time-domain finite-difference method (TDFDM) that uses a variable step size is investigated. The entire computational volume is divided into a coarse grid with a large step size. A fine grid with a small step size is introduced only around discontinuities. The corresponding time increments are related to the spatial increments with the same ratio in order to minimize the numerical dispersion. The fields within the coarse and fine grids are found using the TDFDM, while an interpolation in space and time is utilized to calculate the tangential electric field on the coarse-fine grid boundary. This subgridding decreases the required computer memory and therefore expands the capability of the TDFDM. The technique is shown to be numerically stable and does not entail any extra numerical error. The method is applied to the calculation of waveguides and microstrips 相似文献
97.
98.
99.
100.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry 相似文献