全文获取类型
收费全文 | 89459篇 |
免费 | 7000篇 |
国内免费 | 3270篇 |
专业分类
电工技术 | 4665篇 |
技术理论 | 9篇 |
综合类 | 4844篇 |
化学工业 | 16003篇 |
金属工艺 | 4647篇 |
机械仪表 | 5473篇 |
建筑科学 | 7330篇 |
矿业工程 | 2073篇 |
能源动力 | 2557篇 |
轻工业 | 5150篇 |
水利工程 | 1532篇 |
石油天然气 | 4698篇 |
武器工业 | 513篇 |
无线电 | 11094篇 |
一般工业技术 | 11647篇 |
冶金工业 | 4805篇 |
原子能技术 | 858篇 |
自动化技术 | 11831篇 |
出版年
2024年 | 400篇 |
2023年 | 1526篇 |
2022年 | 2634篇 |
2021年 | 3502篇 |
2020年 | 2584篇 |
2019年 | 2183篇 |
2018年 | 2393篇 |
2017年 | 2659篇 |
2016年 | 2484篇 |
2015年 | 3084篇 |
2014年 | 4169篇 |
2013年 | 5243篇 |
2012年 | 5411篇 |
2011年 | 5696篇 |
2010年 | 5070篇 |
2009年 | 4882篇 |
2008年 | 4619篇 |
2007年 | 4530篇 |
2006年 | 4773篇 |
2005年 | 4246篇 |
2004年 | 2869篇 |
2003年 | 2557篇 |
2002年 | 2255篇 |
2001年 | 2059篇 |
2000年 | 2341篇 |
1999年 | 2610篇 |
1998年 | 2430篇 |
1997年 | 1912篇 |
1996年 | 1775篇 |
1995年 | 1467篇 |
1994年 | 1225篇 |
1993年 | 886篇 |
1992年 | 659篇 |
1991年 | 549篇 |
1990年 | 416篇 |
1989年 | 367篇 |
1988年 | 320篇 |
1987年 | 175篇 |
1986年 | 166篇 |
1985年 | 112篇 |
1984年 | 98篇 |
1983年 | 63篇 |
1982年 | 62篇 |
1981年 | 55篇 |
1980年 | 38篇 |
1979年 | 32篇 |
1978年 | 13篇 |
1977年 | 33篇 |
1976年 | 16篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Analysis and architecture design of variable block-size motion estimation for H.264/AVC 总被引:1,自引:0,他引:1
Ching-Yeh Chen Shao-Yi Chien Yu-Wen Huang Tung-Chien Chen Tu-Chih Wang Liang-Gee Chen 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(3):578-593
Variable block-size motion estimation (VBSME) has become an important video coding technique, but it increases the difficulty of hardware design. In this paper, we use inter-/intra-level classification and various data flows to analyze the impact of supporting VBSME in different hardware architectures. Furthermore, we propose two hardware architectures that can support traditional fixed block-size motion estimation as well as VBSME with less chip area overhead compared to previous approaches. By broadcasting reference pixel rows and propagating partial sums of absolute differences (SADs), the first design has the fewer reference pixel registers and a shorter critical path. The second design utilizes a two-dimensional distortion array and one adder tree with the reference buffer that can maximize the data reuse between successive searching candidates. The first design is suitable for low resolution or a small search range, and the second design has advantages of supporting a high degree of parallelism and VBSME. Finally, we propose an eight-parallel SAD tree with a shared reference buffer for H.264/AVC integer motion estimation (IME). Its processing ability is eight times of the single SAD tree, but the reference buffer size is only doubled. Moreover, the most critical issue of H.264 IME, which is huge memory bandwidth, is overcome. We are able to save 99.9% off-chip memory bandwidth and 99.22% on-chip memory bandwidth. We demonstrate a 720-p, 30-fps solution at 108 MHz with 330.2k gate count and 208k bits on-chip memory. 相似文献
92.
Six genotypes of sweet potato commercially available in Taiwan, including TNG57, TNG66, TNG68, TYY1, RP and WP, were used as samples in this study of the effects of steaming and kneading with pre-steaming treatments on the antioxidant components and antioxidant properties of methanolic extracts. Steam treatment increased the total phenols contents of all genotypes (2–13 times), flavonoids content of RP (1.3 times) and anthocyanins contents of RP and WP (5–6 times). Steam treatment also increased the reducing power and scavenging DPPH radical effect of sweet potato flours. For the methanolic extracts of steamed and kneaded flours, reducing powers were 0.02–1.70 at 5.0 mg ml−1 and the scavenging effects on DPPH radicals were 19–92% at 2.5 mg ml−1. Both showed the order of RP > WP > TYY1 and TNG66 > TNG57 and TNG68. However, the chelating effect of the six genotypes at 1.0 mg ml−1 ranged from 50% to 73%. Contents of total phenols, flavonoids, and anthocyanins of sweet potato flours were significantly positively correlated with the reducing power and scavenging DPPH radical effects. After steaming and kneading treatments, RP showed the highest increase in the contents of total phenols, flavonoids and anthocyanins among the six genotypes studied. 相似文献
93.
实验室的质量监督(上) 总被引:4,自引:0,他引:4
质量监督是实验室保持人员能力,进行自我完善,日常渐进的重要手段,是持续改进的重要组成部分,也是实验室管理工作的难点,本文给出质量监督的目的、对象、方法、记录等. 相似文献
94.
95.
Szu-Wei Huang Jenn-Gwo Hwu 《Electron Devices, IEEE Transactions on》2003,50(7):1658-1664
A cost-effective technique was introduced to prepare ultrathin aluminum oxide (Al/sub 2/O/sub 3/) gate dielectrics with equivalent oxide thickness (EOT) down to 14 /spl Aring/. Al/sub 2/O/sub 3/ was fabricated by anodic oxidation (anodization) of ultrathin Al films at room temperature in deionized water and then furnace annealed at 650/spl deg/C in N/sub 2/ ambient. Both dc and dac (dc superimposed with ac) anodization techniques were investigated. Effective dielectric constant of k/spl sim/7.5 and leakage current of 2-3 orders of magnitude lower than SiO/sub 2/ are observed. The conduction mechanism in Al/sub 2/O/sub 3/ gate stack is shown to be Fowler-Nordheim (F-N) tunneling. Saturated current behavior in the inversion region of MOS capacitor is observed. It is found that the saturation current is sensitive to interface state capacitance and can be used as an efficient way to evaluate the Al/sub 2/O/sub 3/ gate stack/Si-substrate interfacial property. An optimal process control for preparing Al/sub 2/O/sub 3/ gate dielectrics with minimized interface state capacitance via monitoring the inversion saturation current is demonstrated. 相似文献
96.
97.
分析了设备对PCB电镀过程中孔中镀液更新之影响,为有效地利用设备条件改善孔中镀液的更新提供了一些方法及理论数据。 相似文献
98.
本文将空间结构变化的要求与动态资料确定的储量共同作为约束,建立了包含两个约束条件的目标函数, 应用模拟退火算法对孔隙率的空间分布进行预测。在实现过程中,通过初始控制参数的给定及目标函数修改提高了运算效率。由于目标函数有效地整合了静、动态信息,从而降低了模拟结果的不确定性.提高了模拟的精度。合成数据及实际数据的模拟试验表明,整合区域特性约束不仅提高了孔隙率模拟精度,而且算法收敛快、稳定性高。 相似文献
99.
100.
含氮化合物对NiW体系催化剂芳烃加氢性能的影响 总被引:2,自引:0,他引:2
以γ-Al2O3、B改性的γ-Al2O3、F改性的γ-Al2O3、SiO2-Al2O3为载体制备Ni、W含量相同的四种催化剂,通过程序升温还原表征考察活性金属与不同载体的相互作用。利用氮含量不同、四氢萘含量相同的四种原料考察含氮化合物对同种NiW体系催化剂四氢萘加氢的影响以及对活性金属与载体相互作用不同的催化剂四氢萘加氢的影响。结果表明,以γ-Al2O3或SiO2-Al2O3载体制备的催化剂的金属组分与载体相互作用较强,B或F改性的γ-Al2O3能显著削弱活性金属与载体的相互作用;含氮化合物对四氢萘加氢具有强烈的抑制作用,使四氢萘加氢反应的表观活化能增加;在实验研究的四种催化剂中,金属组分与载体相互作用较弱的催化剂受含氮化合物的抑制较强。 相似文献