全文获取类型
收费全文 | 3424篇 |
免费 | 517篇 |
国内免费 | 131篇 |
专业分类
电工技术 | 20篇 |
综合类 | 105篇 |
化学工业 | 740篇 |
金属工艺 | 138篇 |
机械仪表 | 100篇 |
建筑科学 | 10篇 |
矿业工程 | 4篇 |
能源动力 | 37篇 |
轻工业 | 79篇 |
水利工程 | 2篇 |
石油天然气 | 12篇 |
武器工业 | 10篇 |
无线电 | 953篇 |
一般工业技术 | 1664篇 |
冶金工业 | 57篇 |
原子能技术 | 31篇 |
自动化技术 | 110篇 |
出版年
2024年 | 8篇 |
2023年 | 95篇 |
2022年 | 38篇 |
2021年 | 76篇 |
2020年 | 128篇 |
2019年 | 122篇 |
2018年 | 132篇 |
2017年 | 180篇 |
2016年 | 155篇 |
2015年 | 132篇 |
2014年 | 133篇 |
2013年 | 199篇 |
2012年 | 182篇 |
2011年 | 231篇 |
2010年 | 166篇 |
2009年 | 200篇 |
2008年 | 174篇 |
2007年 | 177篇 |
2006年 | 212篇 |
2005年 | 182篇 |
2004年 | 152篇 |
2003年 | 161篇 |
2002年 | 123篇 |
2001年 | 138篇 |
2000年 | 105篇 |
1999年 | 47篇 |
1998年 | 66篇 |
1997年 | 54篇 |
1996年 | 34篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 28篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有4072条查询结果,搜索用时 15 毫秒
81.
本文对掺铬的GGG(Ca,Mg,Zr),GGG,YGG和YAG四种晶体进行了自旋极化的SCC-DV-X_α计算。首次报道了它们的10Dq计算值,与实验值符合得很好,并讨论了中心离子和配位体之间的距离与该计算值的关系。还计算得到了二重态~2E_3的能量值,从而阐明了YAG_2cr~(3+)只能发射窄带荧光,而GGG(Ca,Mg,Zr):Cr~(3+)能发射强的宽带荧光的机理。 相似文献
82.
合成了亲水性和疏水性的饱和杂环类离子液体N-十六烷基-N-甲基四氢吡咯烷溴化物与四氟合硼酸盐,采用偏光显微镜、变温X射线衍射仪和热化学等方法,研究两类离子液体液晶结构、自组装过程和相转变等特性,研究负离子对饱和杂环类离子液体自组装行为的影响.结果发现,该两种离子液体均可在熔点以上形成层状液晶,负离子结构与大小对离子液体液晶的结构与性质具有非常重要的影响,BF4-比Br-体积大,使吡咯烷环和环上的长碳链以较大的间隔排列,形成分子在近晶平面层内有序分布,结构非常接近固态的近晶型液晶. 相似文献
83.
利用平面波展开法计算空气背景中由圆形、正六边形和正方形介质柱构造的二维三角格子光子晶体的带隙结构,并研究介质折射率、光子晶体直径与晶格常数的比值对光子带隙宽度的影响。通过理论计算表明,Si和Ge这两种材料制成的光子晶体中,只有方柱模型的光子晶体才能产生完全光子禁带。 相似文献
84.
Haiqing Yin Wenbin Cao Y. Miyamoto 《北京科技大学学报(英文版)》2006,13(5):461-464
A novel process, which was based on powder injection molding, was investigated for the fabrication of ceramic photonic bandgap structure with three-dimensional diamond lattice. The SiO2-TiO2 ceramic powder was mixed with a water-soluble agent to produce slurry. The slurry was then injected into an epoxy mold with inverse diamond lattice, fabricated by the stereolitographic rapid prototyping process. To increase the density of the green compact, cold isostatic pressing was applied on the unit. Using thermal debinding, the water-soluble agent and the epoxy were extracted at 360 and 650 K, respectively. Sintering was immediately done at 950 K for 5 h and the desired three-dimensional ceramic structure was obtained. The calculated band diagram for this structure indicated the existence of an absolute photonic bandgap for all wave vectors. At 14.7-18.5 GHz, a complete band gap was located with a maximum attenuation of 30 dB at 17 GHz, when transmission was measured in the 〈100〉 direction between 10 and 20 GHz. 相似文献
85.
Dielectric properties, ac conductivity and thermal behaviour of flux grown cadmium titanate crystals
Vineeta Gupta K.K. Bamzai P.N. Kotru B.M. Wanklyn 《Materials Science and Engineering: B》2006,130(1-3):163-172
The dependence of loss tangent (tan δ) and both real and imaginary parts of the dielectric constant (′ and ″) on temperature in the range 298–923 K and frequency in the range 103–106 Hz for flux grown CdTiO3 single crystals is reported. The ln σac versus T plots suggest the conduction mechanism to be ionic hopping conduction. From ln σac versus frequency curves, it can be seen that the slope decreases with the rise in temperature, suggesting that the ionic hopping conduction diminishes with the rise in temperature. The activation energy at various fixed frequencies is calculated from the slope of the graph between ln σac versus 1/T (×103 K−1). Thermal behaviour of flux grown CdTiO3 crystals using thermoanalytical techniques including TG, DTA and DTG is discussed. Thermal analysis suggests decomposition of CdTiO3 in the temperature interval of 1386–1693 K leading to the formation of TiO2 as the final product. Results obtained on application of TG based models viz. Horowitz–Metzger, Coats–Redfern and Piloyan–Novikova are reported. The results of kinetics of thermal decomposition suggest contracting cylinder model as the one that is relevant to the decomposition of CdTiO3. The kinetic parameters viz. the order of reaction, activation energy, frequency factor, and entropy of activation using the above mentioned models are computed. 相似文献
86.
J.Y. Cheng C.A. Ross H.I. Smith E.L. Thomas 《Advanced materials (Deerfield Beach, Fla.)》2006,18(19):2505-2521
One of the key challenges in nanotechnology is to control a self‐assembling system to create a specific structure. Self‐organizing block copolymers offer a rich variety of periodic nanoscale patterns, and researchers have succeeded in finding conditions that lead to very long range order of the domains. However, the array of microdomains typically still contains some uncontrolled defects and lacks global registration and orientation. Recent efforts in templated self‐assembly of block copolymers have demonstrated a promising route to control bottom‐up self‐organization processes through top‐down lithographic templates. The orientation and placement of block‐copolymer domains can be directed by topographically or chemically patterned templates. This templated self‐assembly method provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales. 相似文献
87.
88.
89.
90.
Junichi Takahashi Masahiko Shimada Kouta Iwasaki Hisanori Yaname 《Journal of Electroceramics》2006,17(1):95-98
Single crystals of Bi and Cu-doped Ca3Co2O6were synthesized in a molten K2CO3flux. Using an obtained single crystal of (Ca0.985(5)Bi0.015(5))3(Co0.990(3)Cu0.010(3))2O6elongated to the c-axis direction of the crystal structure, the electric resistivity (ρ) and Seebeck coefficient (S) were measured from room temperature to over 1000 K in air. The single crystal showed p-type semiconducting behavior with ρ values of 1.8 Ω cm at 303 K and 0.017 Ω cm at 1000 K. The S values were +254 μ VK− 1 at 325 K, +360 μ VK− 1 at 420 K, and +214 μ VK− 1 at 1000 K. The power factor (S
2
ρ
− 1) increased with an increase of temperature and attained 2.70 × 10− 4 Wm− 1K− 2 at 1000 K. 相似文献