全文获取类型
收费全文 | 125155篇 |
免费 | 12702篇 |
国内免费 | 8855篇 |
专业分类
电工技术 | 9802篇 |
技术理论 | 4篇 |
综合类 | 11998篇 |
化学工业 | 17101篇 |
金属工艺 | 7913篇 |
机械仪表 | 8134篇 |
建筑科学 | 8199篇 |
矿业工程 | 4080篇 |
能源动力 | 3549篇 |
轻工业 | 12813篇 |
水利工程 | 3287篇 |
石油天然气 | 3809篇 |
武器工业 | 1474篇 |
无线电 | 14741篇 |
一般工业技术 | 12313篇 |
冶金工业 | 6273篇 |
原子能技术 | 2159篇 |
自动化技术 | 19063篇 |
出版年
2024年 | 684篇 |
2023年 | 1891篇 |
2022年 | 4409篇 |
2021年 | 5658篇 |
2020年 | 4147篇 |
2019年 | 2922篇 |
2018年 | 3224篇 |
2017年 | 3680篇 |
2016年 | 3314篇 |
2015年 | 4815篇 |
2014年 | 6290篇 |
2013年 | 8102篇 |
2012年 | 9233篇 |
2011年 | 9910篇 |
2010年 | 9265篇 |
2009年 | 8999篇 |
2008年 | 9727篇 |
2007年 | 9187篇 |
2006年 | 8022篇 |
2005年 | 6605篇 |
2004年 | 4925篇 |
2003年 | 3701篇 |
2002年 | 3753篇 |
2001年 | 3421篇 |
2000年 | 2576篇 |
1999年 | 1338篇 |
1998年 | 1146篇 |
1997年 | 805篇 |
1996年 | 675篇 |
1995年 | 545篇 |
1994年 | 435篇 |
1993年 | 401篇 |
1992年 | 303篇 |
1991年 | 270篇 |
1990年 | 280篇 |
1989年 | 256篇 |
1988年 | 207篇 |
1987年 | 182篇 |
1986年 | 150篇 |
1985年 | 147篇 |
1984年 | 130篇 |
1983年 | 92篇 |
1982年 | 82篇 |
1981年 | 77篇 |
1980年 | 107篇 |
1979年 | 63篇 |
1978年 | 63篇 |
1977年 | 58篇 |
1976年 | 78篇 |
1975年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
42.
Hyeong Soo Chang 《Automatic Control, IEEE Transactions on》2005,50(9):1413-1418
This note considers finite-step approximations for solving an infinite-horizon controlled Markov set-chain problem with finite state and action spaces. We develop a value-iteration type algorithm based on the optimality equation developed by Kurano et al. and analyze an error bound relative to the optimal value that satisfies the optimality equation from the successive approximation. We further analyze an error bound of the approximate control policy defined from a finite-step approximate value by applying the value-iteration type algorithm. 相似文献
43.
采用高频脉冲电铸工艺制备出了镍钴纳米复合块体材料,利用场发射扫描电镜、能谱和X射线衍射的方法,重点研究了复合块体沉积层的表面形貌、相结构和结晶取向。结果表明.高频率和润湿剂的添加对沉积层的细化有重要影响,高频脉冲电铸能够获得微观组织致密、均匀的复合块体材料。 相似文献
44.
45.
Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes. 相似文献
46.
QRS feature extraction using linear prediction 总被引:10,自引:0,他引:10
This communication proposes a method called linear prediction (a high performant technique in digital speech processing) for analyzing digital ECG signals. There are several significant properties indicating that ECG signals have an important feature in the residual error signal obtained after processing by Durbin's linear prediction algorithm. This communication also indicates that the prediction order need not be more than two for fast arrhythmia detection. The ECG signal classification puts an emphasis on the residual error signal. For each ECG's QRS complex, the feature for recognition is obtained from a nonlinear transformation which transforms every residual error signal to a set of three states pulse-code train relative to the original ECG signal. The pulse-code train has the advantage of easy implementation in digital hardware circuits to achieve automated ECG diagnosis. The algorithm performs very well in feature extraction in arrhythmia detection. Using this method, our studies indicate that the PVC (premature ventricular contraction) detection has at least a 92 percent sensitivity for MIT/BIH arrhythmia database. 相似文献
47.
48.
49.
Wei-Jun Liu Wei-Dong He Xue-Wu Ge Hua-Rong Liu Mo-Zheng Wang Zheng-Qi Chang 《Materials Letters》2007,61(13):2818-2821
Interfacial-initiated polymerization of styrene (St) was carried out in inversed emulsion with cumene hydroperoxide (CHPO) and ferrous sulfate (FeSO4)/disodium ethylenediaminetetraacetate (NaEDTA)/sodium formaldehyde sulfoxylate (SFS) as the redox initiation system. The water-soluble Fe2+-NaEDTA-SFS acted as the reducing component and the oil-soluble CHPO as the oxidant component of the redox initiation system. Therefore, the primary radicals were produced mainly at the oil/water interface to initiate the polymerization of St. Thus, sub-micrometer hollow polystyrene (PSt) spheres were obtained by one-stage polymerization, which was supported by the techniques of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). 相似文献
50.
Sanghyun Ju Jianye Li Pimparkar N. Alam M.A. Chang R.P.H. Janes D.B. 《Nanotechnology, IEEE Transactions on》2007,6(3):390-395
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold 相似文献