全文获取类型
收费全文 | 239129篇 |
免费 | 19837篇 |
国内免费 | 10119篇 |
专业分类
电工技术 | 14502篇 |
技术理论 | 16篇 |
综合类 | 13881篇 |
化学工业 | 40278篇 |
金属工艺 | 12456篇 |
机械仪表 | 14461篇 |
建筑科学 | 18902篇 |
矿业工程 | 6290篇 |
能源动力 | 6821篇 |
轻工业 | 15714篇 |
水利工程 | 4224篇 |
石油天然气 | 12458篇 |
武器工业 | 1810篇 |
无线电 | 29528篇 |
一般工业技术 | 30141篇 |
冶金工业 | 12445篇 |
原子能技术 | 2570篇 |
自动化技术 | 32588篇 |
出版年
2024年 | 1124篇 |
2023年 | 3999篇 |
2022年 | 7515篇 |
2021年 | 10099篇 |
2020年 | 7427篇 |
2019年 | 6186篇 |
2018年 | 6764篇 |
2017年 | 7864篇 |
2016年 | 7068篇 |
2015年 | 9288篇 |
2014年 | 11932篇 |
2013年 | 14932篇 |
2012年 | 15238篇 |
2011年 | 16899篇 |
2010年 | 14104篇 |
2009年 | 13571篇 |
2008年 | 12951篇 |
2007年 | 12222篇 |
2006年 | 12227篇 |
2005年 | 10683篇 |
2004年 | 7305篇 |
2003年 | 6365篇 |
2002年 | 5837篇 |
2001年 | 5215篇 |
2000年 | 5202篇 |
1999年 | 5866篇 |
1998年 | 5465篇 |
1997年 | 4522篇 |
1996年 | 4094篇 |
1995年 | 3438篇 |
1994年 | 2880篇 |
1993年 | 2271篇 |
1992年 | 1766篇 |
1991年 | 1318篇 |
1990年 | 1051篇 |
1989年 | 919篇 |
1988年 | 708篇 |
1987年 | 513篇 |
1986年 | 417篇 |
1985年 | 349篇 |
1984年 | 221篇 |
1983年 | 211篇 |
1982年 | 174篇 |
1981年 | 158篇 |
1980年 | 142篇 |
1979年 | 106篇 |
1978年 | 70篇 |
1977年 | 69篇 |
1976年 | 81篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Jenghwa Chang Graber H.L. Ping Chen Koo Aronson R. Barbour S.-L.S. Barbour R.L. 《IEEE transactions on medical imaging》1997,16(1):68-77
Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed 相似文献
42.
43.
44.
Ku T.K. Chen S.H. Yang C.D. She N.J. Wang C.C. Chen C.F. Hsieh I.J. Cheng H.C. 《Electron Device Letters, IEEE》1996,17(5):208-210
Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities 相似文献
45.
Cheng-Hsiung Lid Shou-Chiung Chen Yung-Chi Lee Theodore D. Sokoloski Ming-Thau Sheu 《Drug development and industrial pharmacy》1994,20(11):1911-1922
Polyvinylpyrrolidone (PVP) in aqueous solution was used as a binding agent in a fluidized-bed system to agglomerate acetaminophen powder into directly compressible granules. It was found that a minimal amount of 5% w/w PVP in a concentration of 7.5% w/v or less was needed to produce granules with an acceptable flow and the corresponding tablets having enough hardness without capping. There was a strong correlation between the time for 80% dissolved (T80) and the logarithm of granule volume-surface mean diameter. A directly compressible acetaminophen composition to manufacture tablets having a T80 value less than 30 min can be prepared simply by adding an appropriate amount of disintegrant (crospovidone, sodium starch glycolate, or pregelatinized starch) to the agglomerated granules. 相似文献
46.
Rong-Jie Tu Chern-Lin Chen 《Industrial Electronics, IEEE Transactions on》1998,45(2):256-262
A unidirectional three-phase switch-mode rectifier that delivers sinusoidal input currents in phase with the corresponding input phase voltages is proposed and analyzed in this paper. In the proposed topology, three AC switches are placed before the bridge rectifier and, respectively, across two power lines. A simple control scheme combing space-vector modulation and hysteresis current control is presented. Sinusoidal input line currents are observed in experimental results 相似文献
47.
Hsin-Li Chen Ching-Yuan Wu 《Electron Devices, IEEE Transactions on》1998,45(10):2245-2247
An analytical model for the grain-barrier height of the intrinsic poly-Si thin-film transistors (TFTs) is developed, in which the grain-barrier height for the applied gate voltage smaller than the threshold voltage is obtained by solving the charge neutrality equation and the grain-barrier height for the applied gate voltage larger than the threshold voltage is obtained by using the quasi-two-dimensional (2-D) method. Good agreements between experimental and simulation results are obtained for a wide gate voltage range 相似文献
48.
A technique for SiO2 formation by liquid-phase deposition (LPD) at nearly room temperature for low-temperature processed (LTP) polysilicon thin-film transistor (poly-Si TFT) was developed. LPD SiO2 film with a lower P-etch rate shows a dense structure. LPD SiO2 also exhibits good electrical characteristics. LTP poly-Si thin-film transistors (TFTs) with LPD SiO 2 as the gate insulator have been fabricated and investigated. Their characteristics indicate performance adequate for their use as pixel transistors in liquid crystal displays (LCDs) 相似文献
49.
In order to cumpare the peformance of different supply diffuers of ventilation air, the airflow passern, temperature stratifiation and contaminant dispersion in a furnitured office ventilated by three kinds of air diffuer were numerically investigated. The air diffuers studied in this paper are a quarter-cylinder displacement diffuer on the floor and mixing diffuers (linear and vortex diffuers) on the ceiling. The heat sources in the of-fice are considered to be 50% convective and 50% radiative. The k-? two-equatwn model of turbulence is employed to predict the turbulent diffusion. The results show that the displacement diffuser provides a rather uniform flow field with low velocify in most areas, and the vertical temperature difference from floor to ceiling is as high as 6 K. With the linear diffuser, the air velociry is high, and the temperature is uniform both horizontally and vertically. The air velocity generated by the vortex diffuser is moderate. The distributions of the temperature and the contaminant are rather uniform. 相似文献
50.
The augmented drift-diffusion current equation, which includes velocity overshoot effects through the space derivatives of the electric field, cannot be directly extended beyond one dimension. A new formalism is developed which considers the carrier heating and the distribution relaxation effects to obtain a multidimensional augmented drift diffusion current equation. The equivalent mobility containing the velocity overshoot correction is derived from the perturbation analysis on the carrier temperature using the energy balance equation. The issues related to the numerical implementation of this generalized model and the validity of the assumptions are also discussed 相似文献