全文获取类型
收费全文 | 67188篇 |
免费 | 7357篇 |
国内免费 | 3700篇 |
专业分类
电工技术 | 5649篇 |
技术理论 | 8篇 |
综合类 | 5121篇 |
化学工业 | 9874篇 |
金属工艺 | 4114篇 |
机械仪表 | 4280篇 |
建筑科学 | 5525篇 |
矿业工程 | 2363篇 |
能源动力 | 2046篇 |
轻工业 | 4272篇 |
水利工程 | 1610篇 |
石油天然气 | 3364篇 |
武器工业 | 799篇 |
无线电 | 7962篇 |
一般工业技术 | 7471篇 |
冶金工业 | 2832篇 |
原子能技术 | 917篇 |
自动化技术 | 10038篇 |
出版年
2024年 | 370篇 |
2023年 | 1323篇 |
2022年 | 2768篇 |
2021年 | 3631篇 |
2020年 | 2735篇 |
2019年 | 2089篇 |
2018年 | 2398篇 |
2017年 | 2601篇 |
2016年 | 2382篇 |
2015年 | 3329篇 |
2014年 | 3984篇 |
2013年 | 4684篇 |
2012年 | 5238篇 |
2011年 | 5529篇 |
2010年 | 4723篇 |
2009年 | 4409篇 |
2008年 | 4258篇 |
2007年 | 3853篇 |
2006年 | 3617篇 |
2005年 | 2973篇 |
2004年 | 2001篇 |
2003年 | 1452篇 |
2002年 | 1317篇 |
2001年 | 1051篇 |
2000年 | 1006篇 |
1999年 | 918篇 |
1998年 | 694篇 |
1997年 | 559篇 |
1996年 | 576篇 |
1995年 | 402篇 |
1994年 | 336篇 |
1993年 | 243篇 |
1992年 | 208篇 |
1991年 | 120篇 |
1990年 | 105篇 |
1989年 | 79篇 |
1988年 | 75篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1959年 | 9篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Group interaction analysis in dynamic context. 总被引:1,自引:0,他引:1
Peng Dai Huijun Di Ligeng Dong Linmi Tao Guangyou Xu 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2008,38(1):275-282
Computer understanding of human actions and interactions is one of the key research issues in human computing. In this regard, context plays an essential role in semantic understanding of human behavioral and social signals from sensor data. This paper put forward an event-based dynamic context model to address the problems of context awareness in the analysis of group interaction scenarios. Event-driven multilevel dynamic Bayesian network is correspondingly proposed to detect multilevel events, which underlies the context awareness mechanism. Online analysis can be achieved, which is superior over previous works. Experiments in our smart meeting room demonstrate the effectiveness of our approach. 相似文献
92.
This paper proposes a probabilistic variant of the SOM-kMER (Self Organising Map-kernel-based Maximum Entropy learning Rule)
model for data classification. The classifier, known as pSOM-kMER (probabilistic SOM-kMER), is able to operate in a probabilistic
environment and to implement the principles of statistical decision theory in undertaking classification problems. A distinctive
feature of pSOM-kMER is its ability in revealing the underlying structure of data. In addition, the Receptive Field (RF) regions
generated can be used for variable kernel and non-parametric density estimation. Empirical evaluation using benchmark datasets
shows that pSOM-kMER is able to achieve good performance as compared with those from a number of machine learning systems.
The applicability of the proposed model as a useful data classifier is also demonstrated with a real-world medical data classification
problem. 相似文献
93.
Chang CW Peng SC Cheng WY Liu SH Cheng HH Huang SY Chang YC 《Proteomics. Clinical applications》2007,1(11):1499-1512
Postsynaptic densities (PSDs), isolated from porcine cerebral cortices, are large disk-shaped aggregates consisting of hundreds of different proteins. To study the protein-protein interactions in such complex supramolecules, we developed a procedure to break up the PSD's overall structure, while preserving some interactions between individual proteins. Using the resulting PSD sample and an indirect immunoabsorption procedure, PSD-95 was isolated along with the α- and β-subunits of calcium calmodulin-dependent protein kinase II (CaMKIIα and CaMKIIβ), α-tubulin, β-tubulin, and Chapsyn110. Similarly, CaMKIIα was isolated along with CaMKIIβ, α-tubulin, β-tubulin, and small amounts of PSD-95. The proteins isolated from PSDs treated with a cleavable bifunctional crosslinking reagent were further subjected to diagonal gel electrophoresis analysis, and the results indicated that CaMKIIα resides next to α-tubulin in the PSD. Overall, the results obtained here suggest that within the PSD, large aggregates of CaMKIIα, CaMKIIβ, α-tubulin, and β-tubulin may occur that indirectly associate with PSD-95 and Chapsyn110. Such a protein organization would allow interactions with F-actin in the cytoplasm and with proteins, such as N-methyl-D-aspartate receptors, which reside on the postsynaptic membrane. Furthermore, it would facilitate binding to proteins such as the various microtubule-associated proteins that reside in the core region of the PSD. 相似文献
94.
95.
单苯环氯取代指数法预测二噁类化合物PCDDs的正辛醇/水分配系数 总被引:1,自引:0,他引:1
采用单苯环氯取代指数作为氯代二苯并二口恶口英类化合物 (PCDDs)的分子结构描述符 ,通过正向逐步线性回归方法建立了PCDDs的logKow与分子结构描述符之间的定量关系模型。与文献报道的MOD模型相比 ,该模型不仅具有显著的相关性 (n =43,Radj=0 898,SE =0 195 ,在α =0 0 5时 ,F =2 0 45 5 ,p =0 0 0 0 0 ) ,而且对于分子结构具有更好的区分能力。利用建立的模型 ,对没有logKow文献值的其他 33种PCDDs化合物给出了预测值 相似文献
96.
Huimin Shen Shaou Chen Zhen Yu Yening Wang Zhongxian Zhao Peng Liu 《Journal of Low Temperature Physics》1993,92(3-4):181-187
Tensile tests show that ferroelastic loops always occur at 100–150 K, 200–250 K and room temperature in the Y1–xPrxBa2Cu3Oy samples withx=0 and 0.1 for whichT
c is 92 K and 82.5 K respectively, and the shape memory effect is always observed in the compact sample near 130 K, just similar to that of thermal elastic martensitic alloys. The loss fraction (W/W) which is proportional to the area of ferroelastic loop as a function of temperature shows that there always exist static hysteresis (W/W) peaks at 130 K and 110 K which are attributed to the phaselike transition (PLT) characterized by the jump of lattice parameters. No ferroelastic loops and shape memory effect are observed in the range of 100 K to 150 K for the lowerT
c samples withx=0.3, 0.4 and 0.6. 相似文献
97.
Due to overvoltage produced by inverter output,inverter-fed motor insulation systems often experience fast electrical aging process,especially when partial discharge(PD) is incepted.Before putting into use,the PD detection should be performed on inverter-fed motors at repetitive square voltages to avoid the PD caused insulation deterioration when the motors are collected to inverters having specific characteristics.However,unlike PD tests at AC/DC voltages proposed in IEC 60270,the PD detection at repetitive square voltages is much more complex because of serious interference generated by impulse generator.To solve the problem,ultra-high frequency(UHF) method seems recommendable for its preferable signal-to-noise ratio(SNR).The chief aim of this study is to investigate PD pulse and statistical characteristics of turn-to-turn insulation for inverter-fed traction motors.A square-shaped Archimedes antenna,specially designed for the PD detection at repetitive square voltages of fast rise times,was used to perform PD tests on turn-to-turn insulation models.Time and frequency analysis results indicate that energy component of generator disturbance and PD pulses are mainly distributed in the 0-0.5 GHz and 0.6-1.5 GHz range,respectively.Based on the results,suitable filter was designed for power disturbance suppression.Additionally,resorting to the sensor unit(i.e.antenna and filter) and the PD test system,the PD statistical features at square voltages of different frequencies were obtained.Experimental results show that higher frequency will give rise,statistically,to PD of lower magnitudes distributing at smaller phases.A reasonable interpretation of this phenomenon was presented.Lastly,according to the PD statistical features,some suggestions for the PD detection system design,generator parameter optimization and the PD pulse extracting were given.The results of this work would be beneficial to the increase of the sensitivity when performing the PD detection on insulation systems for inverter-fed motors at repetitive square voltages and thus,improving the reliability of inverter-fed motors. 相似文献
98.
提出一个新的方法求解一维Burgers方程,组合使用有限差分法和隐式龙格库塔法求解Burgers方程。首先使用二阶有限差分法进行空间离散,得到一个常微分方程组,然后使用高阶A稳定的隐式龙格库塔法求解常微分方程组,最后比较数值解和精确解,数值结果证实该方法有很高的精度和稳定性。 相似文献
99.
Jun-Qiu Jiang Kun Wang Xue-Xuan Peng Qing-Liang Zhao Yun-Shu Zhang Xiu-Dong Zhou 《哈尔滨工业大学学报(英文版)》2013,20(4):1-6
This paper compared the degradation efficiency of sludge organic matters and electric-production by two typical microbial fuel cells——dual-chamber microbial fuel cell(DMFC)and single chamber air cathode microbial fuel cell(SAMFC),and the variations of sludge protein,polysaccharide and ammonia nitrogen within the systems were also investigated.The results showed that the concentration of sludge soluble chemical oxygen demand,protein and carbohydrate of DMFC are higher than these of SAMFC during the systems operation,while DMFC can achieve a better ammonia nitrogen removal than SAMFC.Under the same operation condition,the stable voltage output of DMFC and SAMFC is 0.61 V and 0.37 V;the maximum power density of DMFC and SAMFC is 2.79 W/m3and 1.25 W/m3;TCOD removal efficiency of DMFC and SAMFC is 34.14%and 28.63%for 12 d,respectively.Meanwhile,DMFC has a higher coulomb efficiency than SAMFC,but both are less than5%.The results showed that DMFC present a better performance on sludge degradation and electric-production. 相似文献
100.
An accurate closed form solution is proposed to estimate camera pose by several mirrored reference object images acquired via a planar mirror under different unknown poses. Compared with state-of-the-art methods, our method is more accurate when there are more than three images and has explicit geometric meanings. This method also properly handles cases in which some of the mirror poses are parallel. The central idea is to minimize an error metric based on all reflections of rotation, which enables the camera rotation to be estimated directly by SVD of sum of mirrored camera rotations. After that, the camera translation is computed by solving a large system of linear equations to minimize object space collinearity error. Both synthesized data and real data experiments show the advantages of our approach. 相似文献