全文获取类型
收费全文 | 169680篇 |
免费 | 13787篇 |
国内免费 | 11259篇 |
专业分类
电工技术 | 10145篇 |
技术理论 | 3篇 |
综合类 | 11408篇 |
化学工业 | 38216篇 |
金属工艺 | 12271篇 |
机械仪表 | 11291篇 |
建筑科学 | 6341篇 |
矿业工程 | 3509篇 |
能源动力 | 5171篇 |
轻工业 | 11334篇 |
水利工程 | 1742篇 |
石油天然气 | 6701篇 |
武器工业 | 1431篇 |
无线电 | 20893篇 |
一般工业技术 | 20608篇 |
冶金工业 | 5453篇 |
原子能技术 | 2058篇 |
自动化技术 | 26151篇 |
出版年
2024年 | 573篇 |
2023年 | 2632篇 |
2022年 | 4568篇 |
2021年 | 5446篇 |
2020年 | 4686篇 |
2019年 | 4426篇 |
2018年 | 4072篇 |
2017年 | 5208篇 |
2016年 | 5643篇 |
2015年 | 5747篇 |
2014年 | 8298篇 |
2013年 | 9383篇 |
2012年 | 10307篇 |
2011年 | 12720篇 |
2010年 | 10034篇 |
2009年 | 11413篇 |
2008年 | 10526篇 |
2007年 | 11789篇 |
2006年 | 11020篇 |
2005年 | 9123篇 |
2004年 | 7574篇 |
2003年 | 7103篇 |
2002年 | 5782篇 |
2001年 | 4515篇 |
2000年 | 4134篇 |
1999年 | 3292篇 |
1998年 | 2472篇 |
1997年 | 1965篇 |
1996年 | 1818篇 |
1995年 | 1684篇 |
1994年 | 1524篇 |
1993年 | 1239篇 |
1992年 | 964篇 |
1991年 | 661篇 |
1990年 | 445篇 |
1989年 | 414篇 |
1988年 | 275篇 |
1987年 | 209篇 |
1986年 | 215篇 |
1985年 | 138篇 |
1984年 | 107篇 |
1983年 | 83篇 |
1982年 | 90篇 |
1981年 | 76篇 |
1980年 | 64篇 |
1979年 | 52篇 |
1978年 | 32篇 |
1977年 | 33篇 |
1976年 | 40篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. 相似文献
52.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
53.
WC/Cu复合材料制备及其高温性能 总被引:11,自引:0,他引:11
用机械合金化法结合冷变形,制备了WC/Cu复合材料,研究了冷变形后复合材料的组织特征和高温退火时韵性能变化。结果表明:烧结后的材料经冷变形,组织呈显著纤维状,WC颗粒弥散分布,密度明显提高,达到理论密度的99.2%;复合材料经600~900℃高温退火,强度和硬度略有下降,塑性则有大幅提高;900℃退火时未发生明显的再结晶,界面结合良好;所制备的WC/Cu复合材料有优良的综合性能。 相似文献
54.
55.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f 相似文献
56.
串行和并行接口模式是A/D转换器诸多分类中的一种,但却是应用中器件选择的一个重要指标.在同样的转换分辨率及转换速度的前提下,不同的接口方式不但影响了电路结构,更重要的是将在高速数据采集的过程中对采样周期产生较大影响.本文通过12位串行ADC ADS7822和并行ADC ADS774与AT89C51的接口电路,给出二者采样时间的差异性. 相似文献
57.
业务支撑系统作为3G运营的重要组成,它的建设情况直接决定了电信运营商今后3G运营的成败,文章简单介绍了如何构建面向3G时代的业务支撑系统,对建设今后的业务支撑系统提供建议。 相似文献
58.
59.
60.
A. I. D’Souza M. G. Stapelbroek P. N. Dolan P. S. Wijewarnasuriya R. E. DeWames D. S. Smith J. C. Ehlert 《Journal of Electronic Materials》2003,32(7):633-638
The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit
sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms
of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of
1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The
1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors
at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density
in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth
in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under
illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias,
with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if
this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps
are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as
a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular
bias. The 1/f noise was not a direct function of the applied bias. 相似文献