全文获取类型
收费全文 | 5809篇 |
免费 | 188篇 |
国内免费 | 101篇 |
专业分类
电工技术 | 27篇 |
综合类 | 158篇 |
化学工业 | 2107篇 |
金属工艺 | 155篇 |
机械仪表 | 232篇 |
建筑科学 | 84篇 |
矿业工程 | 41篇 |
能源动力 | 239篇 |
轻工业 | 607篇 |
水利工程 | 9篇 |
石油天然气 | 137篇 |
武器工业 | 22篇 |
无线电 | 338篇 |
一般工业技术 | 1028篇 |
冶金工业 | 39篇 |
原子能技术 | 141篇 |
自动化技术 | 734篇 |
出版年
2024年 | 30篇 |
2023年 | 94篇 |
2022年 | 276篇 |
2021年 | 318篇 |
2020年 | 163篇 |
2019年 | 137篇 |
2018年 | 120篇 |
2017年 | 219篇 |
2016年 | 209篇 |
2015年 | 167篇 |
2014年 | 306篇 |
2013年 | 364篇 |
2012年 | 290篇 |
2011年 | 417篇 |
2010年 | 272篇 |
2009年 | 342篇 |
2008年 | 331篇 |
2007年 | 294篇 |
2006年 | 270篇 |
2005年 | 193篇 |
2004年 | 216篇 |
2003年 | 152篇 |
2002年 | 154篇 |
2001年 | 96篇 |
2000年 | 108篇 |
1999年 | 100篇 |
1998年 | 102篇 |
1997年 | 69篇 |
1996年 | 57篇 |
1995年 | 42篇 |
1994年 | 44篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有6098条查询结果,搜索用时 15 毫秒
81.
聚乙烯吡咯烷酮(以下简称PVP)作为一种抑制能力较强、应用较成熟的水合物动力学抑制剂(以下简称KHIs),一直是国内外学者关注和研究的焦点,但对于不同分子量PVP对水合物形成的影响情况还存在着争议。为此,在常压、变温条件下进行了四氢呋喃(以下简称THF)水合物形成模拟实验,研究了相同加量条件下、不同分子量的PVP对THF水合物形成及生长的影响,并从宏观现象、介观结构和微观机制3个层面对影响机理进行了分析和探讨。结果表明:(1)对于THF水合物的形成,PVP的抑制能力随分子量的增大逐渐增强;(2)对于THF水合物的生长,PVP分子量介于8 000~58 000时,抑制效果较接近且相对较弱,但抑制作用稳定,PVP分子量介于270 000~1 500 000时,在THF水合物生长初始阶段PVP的抑制效果较好,但整个实验过程THF水合物形成的平均速率相对较快,且PVP分子量越大这一现象越明显;(3)PVP的存在增强了THF水合物聚集体的聚集强度。结论认为,该研究成果对于KHIs的研发和实际应用均具有较重要的参考价值。 相似文献
82.
M. Reddy J. M. Peterson S. M. Johnson T. Vang J. A. Franklin E. A. Patten W. A. Radford J. W. Bangs D. D. Lofgreen 《Journal of Electronic Materials》2009,38(8):1764-1770
This paper presents the progress in the molecular beam epitaxy (MBE) growth of HgCdTe on large-area Si and CdZnTe substrates
at Raytheon Vision Systems. We report a very high-quality HgCdTe growth, for the first time, on an 8 cm × 8 cm CdZnTe substrate.
This paper also describes the excellent HgCdTe growth repeatability on multiple 7 cm × 7 cm CdZnTe substrates. In order to
study the percentage wafer area yield and its consistency from run to run, small lots of dual-band long-wave infrared/long-wave
infrared triple-layer heterojunction (TLHJ) layers on 5 cm × 5 cm CdZnTe substrates and single-color double-layer heterojunction
(DLHJ) layers on 6-inch Si substrates were grown and tested for cutoff wavelength uniformity and micro- and macrovoid defect
density and uniformity. The results show that the entire lot of 12 DLHJ-HgCdTe layers on 6-inch Si wafers meet the testing
criterion of cutoff wavelength within the range 4.76 ± 0.1 μm at 130 K and micro- and macrovoid defect density of ≤50 cm−2 and 5 cm−2, respectively. Likewise, five out of six dual-band TLHJ-HgCdTe layers on 5 cm × 5 cm CdZnTe substrates meet the testing criterion
of cutoff wavelength within the range 6.3 ± 0.1 μm at 300 K and micro- and macrovoid defect density of ≤2000 cm−2 and 500 cm−2, respectively, on the entire wafer area. Overall we have found that scaling our HgCdTe MBE process to a 10-inch MBE system
has provided significant benefits in terms of both wafer uniformity and quality. 相似文献
83.
F. G. Johnson B. L. Olmsted Samuel Chen G. W. Wicks 《Journal of Electronic Materials》1993,22(3):331-334
The composition profile of an (AlAs)1/2(GaAs)1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the
energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift
in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is
used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile
that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal,
varying from Al0.40Ga0.60As to Al0.60Ga0.40As. 相似文献
84.
报道了分子束外延生长80个周期的Al_xGa_(1-x)As/GaAs超晶格,X射线衍射和透射电镜的结果表明超晶格样品有良好的结构特性,光反射光谱观察到阱内的电子跃迁过程,其结果与理论计算相符。 相似文献
85.
The genetic diversity of 5 populations of Jatropha curcas L. (Euphorbiaceae), a species cultivated in tropical countries and used in biodiesel production, was analyzed by amplified fragment length polymorphism (AFLP). Plants from distinct populations found in the State of São Paulo, Brazil, had their genetic diversity characterized by using three primer combinations. The number of polymorphic bands obtained reached 184 and the base pair length of bands ranged from 75 to 350, with average PIC values of 0.418. Accessions from the Aguas de Santa Barbara population presented the highest percentage of polymorphic loci (89.76%), followed by the populations of Catanduva (84.24%), Jales (80.98%), Jurucê (78.80%) and Taquaritinga (70.65%). Plants collected from the populations of Taquaritinga and Jales presented the smallest and highest genetic diversities, respectively, measured by using both Nei's genetic variability index (h = 0.2242 and 0.2973) and Shannon's index (I = 0.3359 and 0.4319). The results obtained indicated that 73.1% of genetic variability corresponds to intrapopulational variation and 26.8% to variation among populations. The clustering dendrogram using Jacquard showed four clusters. Three clusters with low genetic diversity grouped most of individuals collected in distinct regions (63.3% JU, 47.0% JA and 82.5% TA) and the fourth with the higher genetic diversity was composed with basically individuals collected in CA and AS, but it also had samples collected in JU, JA and TA, where it is possible to select individuals to be included in breeding programs. 相似文献
86.
87.
Ga47In53As films have been grown by molecular beam epitaxy (MBE) on InP substrates. The unintentionally doped material has a free
electron concentration of 8 × 1015cm-3 and exhibits sharp (~5 meV linewidth) exciton recombination in the 4K photoluminescence. The films were grown on (100) InP
surfaces which were thermally cleaned in the arsenic beam. The effects of the substrate temperature during growth, the Ga
to In flux ratio and the group V to group III flux ratio on the 4K photoluminescence are reported. 相似文献
88.
本文根据溶液缩聚基本原理及反应过程的基本事实,用随机过程方法,得到缩聚产物分子量分布函数,并对分子量及其分布的控制作了讨论。 相似文献
89.
90.