全文获取类型
收费全文 | 90784篇 |
免费 | 7929篇 |
国内免费 | 4081篇 |
专业分类
电工技术 | 5688篇 |
技术理论 | 2篇 |
综合类 | 5778篇 |
化学工业 | 14013篇 |
金属工艺 | 4956篇 |
机械仪表 | 5216篇 |
建筑科学 | 6721篇 |
矿业工程 | 1853篇 |
能源动力 | 2647篇 |
轻工业 | 7088篇 |
水利工程 | 1811篇 |
石油天然气 | 3877篇 |
武器工业 | 675篇 |
无线电 | 12043篇 |
一般工业技术 | 11651篇 |
冶金工业 | 5047篇 |
原子能技术 | 1029篇 |
自动化技术 | 12699篇 |
出版年
2024年 | 370篇 |
2023年 | 1371篇 |
2022年 | 2574篇 |
2021年 | 3563篇 |
2020年 | 2502篇 |
2019年 | 2105篇 |
2018年 | 2358篇 |
2017年 | 2801篇 |
2016年 | 2455篇 |
2015年 | 3396篇 |
2014年 | 4445篇 |
2013年 | 5666篇 |
2012年 | 6040篇 |
2011年 | 6752篇 |
2010年 | 5858篇 |
2009年 | 5649篇 |
2008年 | 5585篇 |
2007年 | 5350篇 |
2006年 | 5122篇 |
2005年 | 4178篇 |
2004年 | 2845篇 |
2003年 | 2350篇 |
2002年 | 2370篇 |
2001年 | 2025篇 |
2000年 | 1913篇 |
1999年 | 1955篇 |
1998年 | 1949篇 |
1997年 | 1650篇 |
1996年 | 1453篇 |
1995年 | 1213篇 |
1994年 | 945篇 |
1993年 | 786篇 |
1992年 | 612篇 |
1991年 | 473篇 |
1990年 | 389篇 |
1989年 | 304篇 |
1988年 | 265篇 |
1987年 | 188篇 |
1986年 | 156篇 |
1985年 | 144篇 |
1984年 | 100篇 |
1983年 | 75篇 |
1982年 | 70篇 |
1981年 | 62篇 |
1980年 | 56篇 |
1979年 | 36篇 |
1978年 | 33篇 |
1977年 | 41篇 |
1976年 | 76篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
Enhancement of islanding-detection of distributed generation systems via wavelet transform-based approaches 总被引:1,自引:1,他引:0
Cheng-Tao Hsieh Jeu-Min Lin Shyh-Jier Huang 《International Journal of Electrical Power & Energy Systems》2008,30(10):575-580
In this paper, a wavelet transform-based approach is proposed to detect the occurrence of islanding events in distributed generation systems. Thanks to time–frequency localization capabilities exhibited by wavelet transform, the approach embedded with this transform technique has grasped the appearance of the islanding event in a highly effective manner. Moreover, for those regions which are in need of a better visualization, the proposed approach would serve as an efficient aid such that the mains power disconnection can be better distinguished. To validate the feasibility of this approach, the method has been validated through several scenarios. Test results supported the effectiveness of the method for the application considered. 相似文献
203.
The Bisphosphonate Clodronate Modifying Hydroxyapatite Bioceramics for Bone Scaffold 总被引:3,自引:0,他引:3
LUO En HU Jing WEI Shicheng HE Gang XIAO Lin ZHAO Qiang 《武汉理工大学学报(材料科学英文版)》2005,20(B12):98-101
To investigate the efficiency of clodronate modifying HA bioceramics,and to evaluate the effect of clodronate modifying HA bioceramics on the cells in vitro,clodronate modified the porous HA bioceramics for bone scaffold by chelation .The outermost layer of the specimens was analyzd by XPS and FI-IR ,The depth profile was investigated by the argon-ion sputtering method.The cell culture test was conducted using MC3T3-E1 osteoblastic cells,The cells were inoculated and cultured on the scaffolds.Morphological observation of the cells,MTT test and ALP activity test evaluated the cell attachment ,proliferation and activity on the scaffolds.The cell culture test in cell quantity and morphology indicated active proliferation of the cells on the scaffolds.The ALP activity of the cells cultured for 3d and 7d on clodronate-HA bioceramics was slightly higher than that on HA bioceramics ,but the difference was not signifcant,This result indicated that clodronate-HA bioeramics had favorable cytocompatibility to be used as bone scaffold with potential ability to improve asteogensis. 相似文献
204.
Ding-Bing Lin Ping-Hung Chiang Hsueh-Jyh Li 《Vehicular Technology, IEEE Transactions on》2005,54(1):136-148
Based on Alamouti code, Lee and Williams proposed two-branch transmit diversity block-coded orthogonal frequency-division multiplexing (TDBC-OFDM) systems, namely, space-time block-coded OFDM (STBC-OFDM) and space-frequency block-coded OFDM (SFBC-OFDM). However, they employed the simple maximum-likelihood (SML) detector, which was designed under the assumption that the channel is static over the duration of a space-time/frequency codeword. Therefore, STBC-OFDM/SFBC-OFDM suffers from the high time/frequency selectivity of the wireless mobile fading channel. In this paper, besides the original SML detector, three detectors proposed by Vielmon et al. are applied to improve the two-branch TDBC-OFDM systems. Additionally, assuming sufficient cyclic prefix, the performances of all systems in spatially uncorrelated time-varying multipath Rayleigh-fading channels are evaluated by theoretical derivation and computer simulation, as well. According to the derived bit-error rate (BER), we further derive the bit-error outage (BEO) to provide a more object judgment on the transmission quality within a fading environment. Numerical results have revealed that significant performance improvement can be achieved even when the systems are operated in highly selective channels. 相似文献
205.
Haijun Fang Zongli Lin 《Automatic Control, IEEE Transactions on》2006,51(1):121-128
This note revisits the problem of globally stabilizing an oscillator with a bounded delayed input. It establishes that an oscillator with input saturation can be globally asymptotically stabilized by a linear state feedback even in the presence of an arbitrarily large delay in the input. This result strengthens a recent result in the literature, which shows that such an oscillator can be globally asymptotically stabilized with a sufficiently small control input and the magnitude of the control input goes to zero as the delay increases to infinity. The controller constructed in this note thus improves the efficiency of the closed-loop system by fully utilizing the actuator capacity. 相似文献
206.
Silver and copper nanowires have been synthesized using a scalable method of AC electrodeposition into porous aluminum oxide templates, which produces gram quantities of metal nanowires ca. 25 nm in diameter and up to 5 and 10 μm in length for Ag and Cu, respectively. The nanowires have been used to prepare polystyrene nanocomposites by solution processing. Electrical resistivity measurements performed on polymer nanocomposites containing different volume fractions of metal indicate that low percolation thresholds of nanowires are attained between compositions of 0.25 and 0.75 vol %. 相似文献
207.
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
208.
Hong Lin H. Nayeb-Hashemi R. M. Pelloux 《Fatigue & Fracture of Engineering Materials & Structures》1993,16(7):723-742
A new multiaxial fatigue damage model for orthotropic materials is proposed based on the strain vector. Six material constants are included in the model. These material constants represent the dependence of fatigue resistance on material orientation, and they can be obtained by conducting strain-controlled uniaxial fatigue tests along the three principal orthotropic directions of an orthotropic material. The model can also be transformed in new coordinate systems to predict the fatigue lives of new material orientations. Biaxial low-cycle fatigue tests are conducted to verify the model. The prediction of the model agrees with the experimental results reasonably well. 相似文献
209.
正则化长波方程的三次样条差分模拟 总被引:2,自引:0,他引:2
本文对正则化长波方程(RLW方程)的时间、空间项分别采用三次样条公式进行离散,所得到的差分方程为三点、三层隐格式,对时间的精度为四阶,对空间的精度为二阶,每个时间步只需求解一个三对角方程组,而三次样条配置法在每个时间步中需要求解三个三对角方程组。本文对单个孤立波的演化进行了计算,参数与文[8]相同,其结果与解析解的最大绝对误差均保持在10~(-3)的量级以内,与文[8]给出的数值方法精度相当。对两、三个孤立波的相互碰撞,本文结果显示出在忽略10~(-3)量级的误差后,碰撞前后的孤立波形状保持不变,无论是一个孤立波的演化,还是两、三个孤立波相互碰撞,当将波形放大100倍后均可以发现有振荡的尾波,这说明这类振荡尾波的产生并非真实的物理现象,而是由数值误差产生的。本文认为仅从工程应用的意义上说,RLW方程具有孤立子性质的结论是可以接受的。 相似文献
210.