全文获取类型
收费全文 | 366694篇 |
免费 | 7738篇 |
国内免费 | 3628篇 |
专业分类
电工技术 | 8024篇 |
技术理论 | 2篇 |
综合类 | 5000篇 |
化学工业 | 53742篇 |
金属工艺 | 17867篇 |
机械仪表 | 12827篇 |
建筑科学 | 11312篇 |
矿业工程 | 2318篇 |
能源动力 | 8590篇 |
轻工业 | 30353篇 |
水利工程 | 3690篇 |
石油天然气 | 4137篇 |
武器工业 | 340篇 |
无线电 | 45155篇 |
一般工业技术 | 65998篇 |
冶金工业 | 54967篇 |
原子能技术 | 4567篇 |
自动化技术 | 49171篇 |
出版年
2022年 | 2340篇 |
2021年 | 3725篇 |
2020年 | 2629篇 |
2019年 | 2864篇 |
2018年 | 17714篇 |
2017年 | 16670篇 |
2016年 | 13498篇 |
2015年 | 4363篇 |
2014年 | 5601篇 |
2013年 | 13604篇 |
2012年 | 11153篇 |
2011年 | 19870篇 |
2010年 | 16595篇 |
2009年 | 14630篇 |
2008年 | 16419篇 |
2007年 | 17224篇 |
2006年 | 9362篇 |
2005年 | 9445篇 |
2004年 | 8589篇 |
2003年 | 8520篇 |
2002年 | 7833篇 |
2001年 | 7402篇 |
2000年 | 6881篇 |
1999年 | 7436篇 |
1998年 | 17396篇 |
1997年 | 12306篇 |
1996年 | 9599篇 |
1995年 | 7209篇 |
1994年 | 6307篇 |
1993年 | 5999篇 |
1992年 | 4281篇 |
1991年 | 4205篇 |
1990年 | 3741篇 |
1989年 | 3652篇 |
1988年 | 3546篇 |
1987年 | 2995篇 |
1986年 | 2895篇 |
1985年 | 3460篇 |
1984年 | 3086篇 |
1983年 | 2777篇 |
1982年 | 2575篇 |
1981年 | 2590篇 |
1980年 | 2453篇 |
1979年 | 2287篇 |
1978年 | 2249篇 |
1977年 | 2816篇 |
1976年 | 4185篇 |
1975年 | 1908篇 |
1974年 | 1801篇 |
1973年 | 1792篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Youngmo Han 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》2007,37(6):854-863
This paper is about gaze control in active vision. The problem to tackle is, given a camera imaging a particular 3-D point, to place the 3-D point at the center of the image by rotating the camera about its own optical center. For separating this procedure from structure estimation, we use a normalized camera coordinate system, which leads to formulation defined on the unit sphere. In designing the algorithm, we try to avoid the disadvantages of local coordinates or approximation. For this purpose, we design the algorithm by considering the intrinsic geometric properties of the underlying space, not using any kinds of parameterization or approximation. The proposed algorithm is simple and of a closed form, and that makes it suitable for real-time application. 相似文献
102.
Junwei Fu Zhengbiao Zhang Zhenping Cheng Jian Zhu Wei Zhang Xiulin Zhu 《Polymer Bulletin》2008,61(3):287-297
A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA)
group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used
in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers.
The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE
as the RAFT agent. Number-average molecular weight (Mn,GPC) increased linearly
with monomer conversion, and molecular weight distributions were relatively narrow (PDI<
1.50). The results of chain-extension reaction, 1H NMR spectra and UV/Vis
spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine
(TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated. 相似文献
103.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was
successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer
with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98
were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF
was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce
sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples
were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible
polymer degradation during synthesis and purification of the samples. 相似文献
104.
Vanesa Rodríguez-Amor Juan P. Fernández-Blázquez Antonio Bello Ernesto Pérez María L. Cerrada 《Polymer Bulletin》2008,60(1):89-96
Summary The effect of molecular weight on the uniaxial orientation process has been analyzed in two samples of thermotropic poly(diethylene
glycol p,p′-bibenzoate), evaluating the influence of that parameter on the type of orientation obtained. Several strain rates and deformation
temperatures have been tested in order to map out the conditions for obtaining the two different kinds of orientation. The
results show that in the lower molecular weight PDEB sample (Mw=31200) it is rather easy to get exclusively perpendicular “anomalous” orientation, with the molecular axes aligned transversely
to the stretching direction. However, it is extremely difficult to obtain 100% parallel “normal” orientation. On the contrary,
either type of orientation or a mixture of them can be easily developed for the higher molecular weight PDEB sample (Mw=102900). 相似文献
105.
106.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
107.
This paper presents results of a research project, in which a process-dependent real-time control (RTC) strategy for a sequencing batch reactor plant was realised in full-scale. The cycle controller is based on NH4 analysers, NO3 probes, TSS probes and sludge level probes. With this new RTC strategy it was possible to increase the treatment capacity by 50%. By implementation of the new controller the TN, TP and NH4-N treatment efficiency could be improved significantly, too. The treatment efficiency concerning COD is comparable. 相似文献
108.
We present closed-form expressions for the average bit error probability (ABEP) of BPSK, QPSK and M-QAM of an amplify-and-forward average power scaling dual-hop relay transmission, over non-identical Nakagami-m fading channels, with integer values of m. Additionally, we evaluate in closed-form the ABEP under sufficiently large signal-to-noise ratio for the source-relay link, valid for arbitrary rn. Numerical and simulation results show the validity of the proposed mathematical analysis and point out the effect of the two hops unbalanced fading conditions on the error performance. 相似文献
109.
Effect of process parameters on impact strength of Al-7% Si alloy castings produced by VAEPC process 总被引:2,自引:2,他引:0
Sudhir Kumar Pradeep Kumar H. S. Shan 《The International Journal of Advanced Manufacturing Technology》2008,38(5-6):586-593
The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm2) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration. 相似文献
110.
S. K. Chen A. Serquis G. Serrano K. A. Yates M. G. Blamire D. Guthrie J. Cooper H. Wang S. Margadonna J. L. MacManus‐Driscoll 《Advanced functional materials》2008,18(1):113-120
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples. 相似文献