全文获取类型
收费全文 | 66382篇 |
免费 | 5736篇 |
国内免费 | 3090篇 |
专业分类
电工技术 | 3994篇 |
技术理论 | 4篇 |
综合类 | 4330篇 |
化学工业 | 11051篇 |
金属工艺 | 3624篇 |
机械仪表 | 4238篇 |
建筑科学 | 4654篇 |
矿业工程 | 1313篇 |
能源动力 | 1984篇 |
轻工业 | 4966篇 |
水利工程 | 1213篇 |
石油天然气 | 2652篇 |
武器工业 | 484篇 |
无线电 | 8993篇 |
一般工业技术 | 9032篇 |
冶金工业 | 2914篇 |
原子能技术 | 841篇 |
自动化技术 | 8921篇 |
出版年
2024年 | 247篇 |
2023年 | 954篇 |
2022年 | 1795篇 |
2021年 | 2535篇 |
2020年 | 1800篇 |
2019年 | 1659篇 |
2018年 | 1775篇 |
2017年 | 1989篇 |
2016年 | 2057篇 |
2015年 | 2644篇 |
2014年 | 3229篇 |
2013年 | 4114篇 |
2012年 | 4305篇 |
2011年 | 4822篇 |
2010年 | 4230篇 |
2009年 | 3936篇 |
2008年 | 3901篇 |
2007年 | 3589篇 |
2006年 | 3508篇 |
2005年 | 3066篇 |
2004年 | 2255篇 |
2003年 | 2173篇 |
2002年 | 2433篇 |
2001年 | 2016篇 |
2000年 | 1644篇 |
1999年 | 1432篇 |
1998年 | 1299篇 |
1997年 | 1016篇 |
1996年 | 931篇 |
1995年 | 815篇 |
1994年 | 671篇 |
1993年 | 534篇 |
1992年 | 385篇 |
1991年 | 314篇 |
1990年 | 235篇 |
1989年 | 194篇 |
1988年 | 160篇 |
1987年 | 105篇 |
1986年 | 81篇 |
1985年 | 62篇 |
1984年 | 54篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 33篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 21篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Improved homogenization of Ni in sintered steels through the use of Cr-containing prealloyed powders
The homogenization of Ni in powder metal (PM) steel compacts is usually difficult even after high-temperature sintering at
1250°C. An earlier study by the authors demonstrated that this problem can be alleviated through the addition of 0.5 wt pct
Cr in the form of stainless steel powders. To further improve the microstructure and mechanical properties of Ni-containing
PM steels and to understand the mechanisms, an attempt was made in this study using the Fe-3Cr-0.5Mo prealloyed powder as
the base material. The results showed that the distribution of the Ni additives was significantly improved. As a result, the
tensile strength of the Fe-3Cr-0.5Mo-4Ni-0.5C compact sintered at 1250°C reached 1323 MPa. The elongation was higher than
1 pct. These sinter-hardened properties, which were attained using a slow furnace cooling rate, were comparable to those of
the sinter-hardened alloys reported in the literature using accelerated cooling and were equivalent to those of the best quenched-and-tempered
alloys registered in the Metal Powder Industries Federation (MPIF) standards. These improvements were attributed to the positive
effect of Cr addition on alloy homogenization due to the reduction of the repelling effect between Ni and C, as was demonstrated
through the thermodynamic analysis using the Thermo-Calc program. 相似文献
3.
4.
Wu-An Kuo TingTing Hwang Wu A.C.-H. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2006,14(1):81-85
This paper presents a novel power-driven multiplication instruction-set design method for application-specific instruction-set processors (ASIPs). Based on a dual-and-configurable-multiplier structure, our proposed method devises a multiplication instruction set for low-power ASIPs. Our method exploits the execution sequences of multiplication instructions and effective bit widths of variables to reduce power consumed by redundant multiplication bits while minimizing the multiplication execution time. Experimental results on a set of DSP programs demonstrate that our proposed method achieves significant power reduction (up to 18.53%) and execution time improvement (up to 10.43%) with 18% area overhead. 相似文献
5.
Effect of modified atmosphere packaging on the shelf-life of coated, whole and sliced mushrooms 总被引:2,自引:0,他引:2
Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms. 相似文献
6.
Jaehoon Lee Seongha Kim Yonghoon Kim Yunje Oh Seongtaek Hwang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):521-527
Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width. 相似文献
7.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献
8.
9.
Jin Tae Kim Keun Byoung Yoon Choon-Gi Choi 《Photonics Technology Letters, IEEE》2004,16(7):1664-1666
A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices. 相似文献
10.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献