全文获取类型
收费全文 | 51581篇 |
免费 | 15204篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 922篇 |
综合类 | 29篇 |
化学工业 | 20139篇 |
金属工艺 | 859篇 |
机械仪表 | 1451篇 |
建筑科学 | 1986篇 |
矿业工程 | 7篇 |
能源动力 | 1470篇 |
轻工业 | 8222篇 |
水利工程 | 342篇 |
石油天然气 | 54篇 |
武器工业 | 1篇 |
无线电 | 9050篇 |
一般工业技术 | 14196篇 |
冶金工业 | 1879篇 |
原子能技术 | 195篇 |
自动化技术 | 6031篇 |
出版年
2024年 | 12篇 |
2023年 | 195篇 |
2022年 | 261篇 |
2021年 | 713篇 |
2020年 | 1720篇 |
2019年 | 3395篇 |
2018年 | 3444篇 |
2017年 | 3734篇 |
2016年 | 4312篇 |
2015年 | 4270篇 |
2014年 | 4405篇 |
2013年 | 5867篇 |
2012年 | 3578篇 |
2011年 | 3537篇 |
2010年 | 3480篇 |
2009年 | 3333篇 |
2008年 | 2813篇 |
2007年 | 2532篇 |
2006年 | 2205篇 |
2005年 | 1850篇 |
2004年 | 1770篇 |
2003年 | 1691篇 |
2002年 | 1573篇 |
2001年 | 1386篇 |
2000年 | 1337篇 |
1999年 | 743篇 |
1998年 | 567篇 |
1997年 | 387篇 |
1996年 | 291篇 |
1995年 | 193篇 |
1994年 | 188篇 |
1993年 | 134篇 |
1992年 | 102篇 |
1991年 | 91篇 |
1990年 | 90篇 |
1989年 | 78篇 |
1988年 | 54篇 |
1987年 | 60篇 |
1986年 | 70篇 |
1985年 | 41篇 |
1984年 | 38篇 |
1983年 | 42篇 |
1982年 | 12篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1977年 | 26篇 |
1976年 | 34篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
122.
This paper presents a low‐cost RF parameter estimation technique using a new RF built‐in self‐test (BIST) circuit and efficient DC measurement for 4.5 to 5.5 GHz low noise amplifiers (LNAs). The BIST circuit measures gain, noise figure, input impedance, and input return loss for an LNA. The BIST circuit is designed using 0.18 μm SiGe technology. The test technique utilizes input impedance matching and output DC voltage measurements. The technique is simple and inexpensive. 相似文献
123.
Ho Van Khuong Hyung-Yun Kong 《Communications Letters, IEEE》2006,10(3):159-161
In order to evaluate exactly the performance of some diversity schemes, the probability density function (pdf) of a sum of independent exponential random variables (r.v.'s) must be known. This paper proposes a simple method to find it by using characteristic function., The resultant pdf is successfully applied to formulate the closed-form BER expression of 2 Tx-J Rx transmit diversity as well as the outage probability of repetition coding. 相似文献
124.
125.
Ki Yong Lee Souhwan Jung 《Electronics letters》1998,34(16):1567-1568
The authors investigate the problem of nonlinear adaptive equalisation in the presence of intersymbol interference, additive white Gaussian noise and co-channel interference. An extended radial basis function (RBF) network is proposed, in which regression weights are used in the output layer and the hidden unit is defined to have the Gaussian formula with the Mahalanobis distance. It is shown by simulation that the proposed structure gives reduced computational complexity without performance degradation, compared to that of the conventional RBF equaliser 相似文献
126.
Taesung Kim Sung Ho Wang Beomsup Kim 《Electronics letters》2002,38(17):950-951
A delay-locked loop (DLL) architecture capable of incorporating fast locking and low jitter features simultaneously is reported. A test chip was fabricated in a 0.6 μm CMOS process to prove its functionality. The proposed DLL can align the internal clock to the external reference clock within two cycles and maintain its locking state with the aid of feedback operation 相似文献
127.
To determine whether there is any correlation between sudden decrease in barometric pressure and onset of labor, a non-experimental, retrospective study at a 948-bed tertiary care hospital was done. Pregnant patients of 36 weeks gestation or more who presented with spontaneous onset of labor during the 48 hours surrounding the 12 occurrences of significant drop in barometric pressure in 1992 were included in the study. Significantly more occurrences of onset of labor were identified in the 24 hours after a drop in barometric pressure than were identified in the 24 hours prior to the drop in barometric pressure (P < 0.05). Therefore, the overall number of labor onsets increased in the 24 hours following a significant drop in barometric pressure. 相似文献
128.
Large-scale simulation studies in image pattern recognition 总被引:1,自引:0,他引:1
Tin Kam Ho Baird H.S. 《IEEE transactions on pattern analysis and machine intelligence》1997,19(10):1067-1079
Many obstacles to progress in image pattern recognition result from the fact that per-class distributions are often too irregular to be well-approximated by simple analytical functions. Simulation studies offer one way to circumvent these obstacles. We present three closely related studies of machine-printed character recognition that rely on synthetic data generated pseudo-randomly in accordance with an explicit stochastic model of document image degradations. The unusually large scale of experiments - involving several million samples that makes this methodology possible have allowed us to compute sharp estimates of the intrinsic difficulty (Bayes risk) of concrete image recognition problems, as well as the asymptotic accuracy and domain of competency of classifiers 相似文献
129.
Neural network impedance force control of robot manipulator 总被引:1,自引:0,他引:1
The performance of an impedance controller for robot force tracking is affected by the uncertainties in both the robot dynamic model and environment stiffness. The purpose of this paper is to improve the controller robustness by applying the neural network (NN) technique to compensate for the uncertainties in the robot model. NN control techniques are applied to two impedance control methods: torque-based and position-based impedance control, which are distinguished by the way of the impedance functions being implemented. A novel error signal is proposed for the NN training. In addition, a trajectory modification algorithm is developed to determine the reference trajectory when the environment stiffness is unknown. The robustness analysis of this algorithm to force sensor noise and inaccurate environment position measurement is also presented. The performances of the two NN impedance control schemes are compared by computer simulations. Simulation results based on a three-degrees-of-freedom robot show that highly robust position/force tracking can be achieved in the presence of large uncertainties and force sensor noise 相似文献
130.
D Averill D Blockus B Brabson J Brom C Jung H Ogren DR Rust M Derrick P Kooijman JS Loos B Musgrave LE Price J Repond K Sugano B Cork C Akerlof J Chapman D Errede MT Ken DI Meyer H Neal D Nitz R Thun R Tschirhart S Abachi P Baringer BG Bylsma R DeBonte D Koltick EH Low RL McIlwain DH Miller CR Ng EI Shibata 《Canadian Metallurgical Quarterly》1989,39(1):123-137