全文获取类型
收费全文 | 103786篇 |
免费 | 7904篇 |
国内免费 | 3346篇 |
专业分类
电工技术 | 3994篇 |
技术理论 | 1篇 |
综合类 | 4018篇 |
化学工业 | 18091篇 |
金属工艺 | 4822篇 |
机械仪表 | 6139篇 |
建筑科学 | 4681篇 |
矿业工程 | 1363篇 |
能源动力 | 3222篇 |
轻工业 | 9292篇 |
水利工程 | 1380篇 |
石油天然气 | 2216篇 |
武器工业 | 465篇 |
无线电 | 15418篇 |
一般工业技术 | 16247篇 |
冶金工业 | 7718篇 |
原子能技术 | 1203篇 |
自动化技术 | 14766篇 |
出版年
2024年 | 321篇 |
2023年 | 1290篇 |
2022年 | 2359篇 |
2021年 | 3353篇 |
2020年 | 2464篇 |
2019年 | 2276篇 |
2018年 | 2774篇 |
2017年 | 2880篇 |
2016年 | 3132篇 |
2015年 | 3381篇 |
2014年 | 4610篇 |
2013年 | 6636篇 |
2012年 | 6804篇 |
2011年 | 7920篇 |
2010年 | 6625篇 |
2009年 | 6779篇 |
2008年 | 6386篇 |
2007年 | 5759篇 |
2006年 | 5268篇 |
2005年 | 4433篇 |
2004年 | 3628篇 |
2003年 | 3052篇 |
2002年 | 2938篇 |
2001年 | 2364篇 |
2000年 | 2018篇 |
1999年 | 1798篇 |
1998年 | 2557篇 |
1997年 | 1738篇 |
1996年 | 1459篇 |
1995年 | 1157篇 |
1994年 | 891篇 |
1993年 | 829篇 |
1992年 | 597篇 |
1991年 | 586篇 |
1990年 | 475篇 |
1989年 | 455篇 |
1988年 | 359篇 |
1987年 | 309篇 |
1986年 | 280篇 |
1985年 | 241篇 |
1984年 | 210篇 |
1983年 | 162篇 |
1982年 | 167篇 |
1981年 | 132篇 |
1980年 | 136篇 |
1979年 | 113篇 |
1978年 | 103篇 |
1977年 | 133篇 |
1976年 | 171篇 |
1975年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
岭澳核电重件道路施工中所遇到的38m的观景平台在大亚湾核电站占有重要地位,在工程施工中发现边坡坡体陡峭,无法达到规范规定的稳定要求,故采取了加固措施。采用抗滑稳定计算的分析方法,对边坡加固的必要性及实施加固后的稳定性进行了分析。 相似文献
272.
Eunseok Song Yido Koo Yeon-Jae Jung Deok-Hee Lee Sangyoung Chu Soo-Ik Chae 《Solid-State Circuits, IEEE Journal of》2005,40(5):1094-1106
This paper describes a single-chip CMOS quad-band (850/900/1800/1900 MHz) RF transceiver for GSM/GPRS applications. It is the most important design issue to maximize resource sharing and reuse in designing the multiband transceivers. In particular, reducing the number of voltage-controlled oscillators (VCOs) required for local oscillator (LO) frequency generation is very important because the VCO and phase-locked loop (PLL) circuits occupy a relatively large area. We propose a quad-band GSM transceiver architecture that employs a direct conversion receiver and an offset PLL transmitter, which requires only one VCO/PLL to generate LO signals by using an efficient LO frequency plan. In the receive path, four separate LNAs are used for each band, and two down-conversion mixers are used, one for the low bands (850/900 MHz) and the other for the high bands (1800/1900 MHz). A receiver baseband circuit is shared for all four bands because all of their channel spaces are the same. In the transmit path, most of the building blocks of the offset PLL, including a TX VCO and IF filters, are integrated. The quad-band GSM transceiver that was implemented in 0.25-/spl mu/m CMOS technology has a size of 3.3/spl times/3.2 mm/sup 2/, including its pad area. From the experimental results, we found that the receiver provides a maximum noise figure of 2.9 dB and a minimum IIP3 of -13.2dBm for the EGSM 900 band. The transmitter shows an rms phase error of 1.4/spl deg/ and meets the GSM spectral mask specification. The prototype chip consumes 56 and 58 mA at 2.8 V in the RX and TX modes, respectively. 相似文献
273.
Ju Han Lee You Min Chang Young-Geun Han Sang-Hyuck Kim Haeyang Chung Sang Bae Lee 《Photonics Technology Letters, IEEE》2005,17(1):34-36
We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range. 相似文献
274.
Fast DCT algorithm with fewer multiplication stages 总被引:1,自引:0,他引:1
Yeonsik Jeong Imgeun Lee Hak Soo Kim Kyu Tae Park 《Electronics letters》1998,34(8):723-724
A novel fast DCT scheme with reduced multiplication stages and fewer additions and multiplications is proposed. The proposed algorithm is structured so that most multiplications tend to be performed at the final stage, which reduces the propagation error that could occur in the fixed-point computation. Minimisation of the multiplication stages can further decrease the error 相似文献
275.
Dongwook Lee Kiseon Kim 《Electronics letters》1998,34(15):1474-1476
The authors suggest a novel virtual circuit connection method based on the reverse traversing technique to minimise the waste of network bandwidth resources, when the Internet protocol multicast is interoperated using the resource reservation protocol over an asynchronous transfer mode network. Simulation results show that, as the number of receivers increases, the bandwidth requirements on all links of the network of the proposed scheme become more advantageous than those of other conventional methods 相似文献
276.
Shih-Kai Lee Mao-Chao Lin 《Communications, IEEE Transactions on》1995,43(5):1917-1925
We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented 相似文献
277.
This paper analyzes the running mechanism of flexible and thin tape above rotating protrusion through a numerical simulation.
The scope of analysis is confined to the phenomena of elastohydrodynamic lubrication between the rotating drum with a protrusion
and the running tape. This model is based on the modified Reynolds equation and the equation of plate considering the effect
of geometric nonlinearity and geometry of protrusion. Finite element method of Bubnov-Galerkin type is adopted as a numerical
simulation technique to solve the above two coupled nonlinear equations. In numerical simulation, the influences of tape tension
and protrusion velocity are evaluated in simple model. In complex models, the reciprocal action of two protrusions is simulated. 相似文献
278.
JW McAninch PR Carroll NA Armenakas P Lee 《Canadian Metallurgical Quarterly》1993,35(2):279-83; discussion 283-4
Over the past 14 years, 2079 patients have been seen at our institution with renal trauma. Of these, 84 sustained gunshot wounds (81 unilateral, 3 bilateral; a total of 87 renal units). We evaluated this group to characterize the nature of their injuries and establish a methodology for renal salvage and reconstruction. Preoperative radiographic staging was performed with excretory urography (IVP) or computed tomographic (CT) scanning. The injuries were classified into five categories: 16 contusions (18.4%), 12 minor lacerations (13.8%), 44 major lacerations (50.5%), six vascular injuries (6.9%), and nine combination laceration and vascular injury (10.3%). Most patients had multiple organ injuries, with 79 requiring associated surgical procedures (94%). The mean injury Severity Score (ISS) was 26.7 (range, 4-59). Based on radiographic and clinical staging criteria, 69 renal injuries were surgically explored (79.3%), and 12 patients underwent nephrectomy (13.8%). Forty-six renal units were reconstructed (66.6%) by various methods, including renorrhaphy, omental pedical flaps, mesh or peritoneal patch grafts, partial nephrectomy, and vascular repair. Overall, 75 renal units were salvaged (86.2%). Early renal vascular control was achieved in all patients who underwent renal exploration. Follow-up functional studies were done in 24 (28.5%): none had delayed nephrectomy or postinjury hypertension. Overall, 79 patients survived (94%); however, mortality was not related to renal injury. These findings suggest that aggressive radiographic staging coupled with early vascular control and careful selection of reconstructive techniques can ensure a high renal salvage rate in patients with renal gunshot injuries. 相似文献
279.
本文提出了一种直接把红外前视传感器的输出作为测量值来跟踪红外目标的扩展型卡尔曼滤波跟踪算法。在滤波处理时,设置可变的测量矩阵,其目的在于提高运算速度和抑制噪声干扰。通过具体的实例,对所提跟踪算法的特点和有效性进行了细致的分析。 相似文献
280.