全文获取类型
收费全文 | 55277篇 |
免费 | 3060篇 |
国内免费 | 2411篇 |
专业分类
电工技术 | 1751篇 |
技术理论 | 2篇 |
综合类 | 2588篇 |
化学工业 | 16676篇 |
金属工艺 | 5600篇 |
机械仪表 | 1576篇 |
建筑科学 | 1279篇 |
矿业工程 | 610篇 |
能源动力 | 944篇 |
轻工业 | 5681篇 |
水利工程 | 522篇 |
石油天然气 | 2175篇 |
武器工业 | 371篇 |
无线电 | 3991篇 |
一般工业技术 | 8197篇 |
冶金工业 | 1535篇 |
原子能技术 | 631篇 |
自动化技术 | 6619篇 |
出版年
2024年 | 106篇 |
2023年 | 642篇 |
2022年 | 2592篇 |
2021年 | 2665篇 |
2020年 | 1148篇 |
2019年 | 1065篇 |
2018年 | 1058篇 |
2017年 | 1314篇 |
2016年 | 1847篇 |
2015年 | 2622篇 |
2014年 | 3032篇 |
2013年 | 3060篇 |
2012年 | 3249篇 |
2011年 | 4653篇 |
2010年 | 3648篇 |
2009年 | 3738篇 |
2008年 | 3379篇 |
2007年 | 3429篇 |
2006年 | 2794篇 |
2005年 | 2455篇 |
2004年 | 2114篇 |
2003年 | 1933篇 |
2002年 | 1676篇 |
2001年 | 1022篇 |
2000年 | 838篇 |
1999年 | 777篇 |
1998年 | 599篇 |
1997年 | 529篇 |
1996年 | 482篇 |
1995年 | 411篇 |
1994年 | 371篇 |
1993年 | 237篇 |
1992年 | 207篇 |
1991年 | 160篇 |
1990年 | 156篇 |
1989年 | 114篇 |
1988年 | 89篇 |
1987年 | 54篇 |
1986年 | 88篇 |
1985年 | 56篇 |
1984年 | 59篇 |
1983年 | 36篇 |
1982年 | 46篇 |
1981年 | 40篇 |
1980年 | 38篇 |
1979年 | 39篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 12篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
61.
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
62.
The microstructural aspects of compressive inelastic deformation in balsa wood are investigated with emphasis on the failure mode transition and its effects on energy dissipation characteristics. The architectural features as well as the composite character of cell wall ultrastructure are discussed in a framework to understand the complex interrelationship between microstructure and macroscopic behavior in this extremely lightweight cellular biocomposite. Based on this discussion and experimental results, it is concluded that the biomimetic approach may prove to be a viable strategy in designing composite structures with high specific energy absorption capacity. 相似文献
63.
石墨炉原子吸收光谱(GFAAS)法测定石英玻璃中硼的研究 总被引:2,自引:0,他引:2
试样经氢氟酸分解,通过加入化学改进剂和多次注射浓缩样品及低温、长时间灰化的方法,在硝酸介质中用石墨炉原子吸收光谱法(GFAAS)测定石英玻璃中硼的含量。该方法解决了GFAAS法分析石英玻璃中硼灵敏度低和准确度低的问题。 相似文献
64.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
65.
Frank te Beest Ad Peeters Kees van Berkel Hans Kerkhoff 《Journal of Electronic Testing》2003,19(4):397-406
Handshake circuits form a special class of asynchronous circuits that has enabled the industrial exploitation of the asynchronous potential such as low power, low electromagnetic emission, and increased cryptographic security. In this paper we present a test solution for handshake circuits that brings synchronous test-quality to asynchronous circuits. We add a synchronous mode of operation to handshake circuits that allows full controllability and observability during test. This technique is demonstrated on some industrial examples and gives over 99% stuck-at fault coverage, using test-pattern generators developed for synchronous circuits. The paper describes how such a full-scan mode can be achieved, including an approach to minimize the number of dummy latches in case latches are used in the data path of the handshake circuit. 相似文献
66.
67.
数字下变频器GC1012B原理及配置方法 总被引:1,自引:0,他引:1
数字下变频技术是软件无线电的一项核心技术,其性能的好坏直接影响数字接收机的精度。GC1012B是美国TI公司推出的新型数字下变频器。文中从GC1012B的结构特点和内部功能框图出发,分析其工作原理,并介绍GC1012B几个主要寄存器的配置方法,从而实现对频率、滤波模式、增益大小等参数的设置。最后给出了一个具体配置实例作为参考。 相似文献
68.
校园网宿舍网络管理模式的探讨 总被引:10,自引:1,他引:9
讨论了高校学生宿舍区网络的特点,结合天津商学院校园网的实践,讨论了校园网宿舍网络管理的模式。 相似文献
69.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
70.