全文获取类型
收费全文 | 117455篇 |
免费 | 3441篇 |
国内免费 | 1388篇 |
专业分类
电工技术 | 2240篇 |
技术理论 | 4篇 |
综合类 | 3851篇 |
化学工业 | 17262篇 |
金属工艺 | 6268篇 |
机械仪表 | 4618篇 |
建筑科学 | 3832篇 |
矿业工程 | 1314篇 |
能源动力 | 2287篇 |
轻工业 | 5766篇 |
水利工程 | 1700篇 |
石油天然气 | 1349篇 |
武器工业 | 146篇 |
无线电 | 14497篇 |
一般工业技术 | 21165篇 |
冶金工业 | 5311篇 |
原子能技术 | 640篇 |
自动化技术 | 30034篇 |
出版年
2024年 | 105篇 |
2023年 | 449篇 |
2022年 | 864篇 |
2021年 | 1195篇 |
2020年 | 929篇 |
2019年 | 802篇 |
2018年 | 15197篇 |
2017年 | 14177篇 |
2016年 | 10727篇 |
2015年 | 1659篇 |
2014年 | 1631篇 |
2013年 | 2295篇 |
2012年 | 5070篇 |
2011年 | 11582篇 |
2010年 | 10003篇 |
2009年 | 7347篇 |
2008年 | 8591篇 |
2007年 | 9418篇 |
2006年 | 1671篇 |
2005年 | 2436篇 |
2004年 | 2215篇 |
2003年 | 2336篇 |
2002年 | 1928篇 |
2001年 | 1270篇 |
2000年 | 989篇 |
1999年 | 764篇 |
1998年 | 1026篇 |
1997年 | 716篇 |
1996年 | 618篇 |
1995年 | 482篇 |
1994年 | 399篇 |
1993年 | 340篇 |
1992年 | 258篇 |
1991年 | 243篇 |
1990年 | 225篇 |
1989年 | 199篇 |
1988年 | 179篇 |
1987年 | 153篇 |
1986年 | 129篇 |
1985年 | 127篇 |
1984年 | 110篇 |
1983年 | 75篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 81篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1955年 | 71篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
71.
Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of
semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons
of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr). 相似文献
72.
73.
74.
This paper investigates the catalytic ignition of the H2/O2/CO2 mixture on platinum in a stagnation flow at atmospheric pressure experimentally and numerically. We measure the ignition temperatures of the gas mixtures flowing towards resistively heated platinum with various composition ratios and various diluent gases of N2, Ar and CO2. Compared with N2 or Ar, the CO2 dilution shows higher ignition temperature by about 50 K, even at the same composition ratio. The ignition temperature increase is proportional to the dilution ratio. Through the numerical simulation, it is illustrated that higher ignition temperature is caused by the adsorption of CO2 and following dissociation on platinum surface, which was to date considered negligible in catalytic combustion. 相似文献
75.
An adaptive p-persistent MAC scheme for multimedia WLAN 总被引:1,自引:0,他引:1
Chih-Ming Yen Chung-Ju Chang Yih-Shen Chen 《Communications Letters, IEEE》2006,10(11):737-739
The letter proposes an adaptive p-persistent-based (APP) medium access control (MAC) scheme for the IEEE 802.11e distributed WLAN supporting multimedia services. The APP MAC scheme adaptively gives differentiated permission probabilities to transmission stations which are in different access category and with various waiting delay. Simulation results show that the APP MAC scheme can improve the performance of multimedia WLAN, such as small voice packet dropping probability, low delay variation, and high system throughput, compared to conventional MAC algorithms 相似文献
76.
Ming-Dou Ker Chyh-Yih Chang Yi-Shu Chang 《Components and Packaging Technologies, IEEE Transactions on》2004,27(3):445-451
This paper reports a real case of electrostatic discharge (ESD) improvement on a complementary metal oxide semiconductor integrated circuit (IC) product with multiple separated power pins. After ESD stresses, the internal damage have been found to locate at the interface circuit connecting between different circuit blocks with different power supplies. Some ESD designs have been implemented to rescue this IC product to meet the required ESD specification. By adding only an extra ESD clamp N-channel metal oxide semiconductor with a channel width of 10 /spl mu/m between the interface node and the ground line, the human-body-model (HBM) ESD level of this IC product can be improved from the original 0.5 to 3 kV. By connecting the separated vertical sync signal (VSS) power lines through the ESD conduction circuit to a common VSS ESD bus realized by the seal ring, the HBM ESD level of the enhanced version IC product with 12 separated power supplies pairs can be significantly improved from original 1 kV up to > 5 kV, without the noise coupling issue. 相似文献
77.
Dong-Soo Yoon Jae Sung Roh Sung-Man Lee Hong Koo Baik 《Journal of Electronic Materials》2003,32(8):890-898
The effect of a thin RuOx layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuOx/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si
contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuOx/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no
formation of a thin RuOx layer at the RuOx surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film
by pre-annealing leads to the formation of a thin RuOx layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity
of diffusion paths. In particular, the RuOx layer in a nonstoichiometric state is changed to the RuO2-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer.
Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the
RuOx/TiN/poly-Si/Si contact system. 相似文献
78.
Ching-Wen Tang Chi-Yang Chang 《Electronics letters》2002,38(15):801-803
A novel chip-type ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A buried capacitor is included in the balun, so that the length of the coupled transmission lines can be reduced and can be designed very easily. A meander or spiral broadside coupled-line is adopted to realise the proposed LTCC multi-layer balun. The measured performances of phase and amplitude balance for this LTCC-MLC balun show a good match with computer simulation 相似文献
79.
80.
Amplification or overexpression of HER-2/neu in human lung cancer has been correlated with poor prognosis and chemoresistance. We have previously reported that the adenovirus type 5 early region 1A (E1A) gene product can suppress HER-2/neu-mediated transformation phenotypes through inhibition of HER-2/neu expression. To find an efficient way to treat HER-2/neu-overexpressing lung cancer with E1A, a replication-deficient adenovirus containing the E1A gene, Ad.E1A(+), was used to transduce E1A into HER-2/neu-overexpressing and low expressing human lung cancer cell lines. Tumour cell growth in vitro and colony formation in soft agarose were greatly inhibited by Ad.E1A(+) transduction in HER-2/neu-overexpressing lung cancer cell lines. In HER-2/neu low expressing cell lines, E1A could not inhibit cell growth in vitro but could reduce the colony formation ability in soft agarose, indicating different effects of E1A in these two types of cancer cells. To test the therapeutic efficacy of E1A to lung cancer by systemic delivery in vivo, tumor-bearing mice were established by intratracheal injection of lung cancer cells and treated by i.v. tail injections of Ad.E1A(+). As a result, Ad.E1A(+) suppressed HER-2/neu overexpression and inhibited intratracheal lung cancer growth. However, no significant tumor suppression effect of Ad.E1A(+) was observed in mice bearing HER-2/neu low expressing cell line when the same therapeutic procedure was followed. Thus, we conclude that systemic delivery of Ad.E1A(+) can efficiently achieve therapeutic effect in HER-2/neu-overexpressing lung cancer in vivo. 相似文献