全文获取类型
收费全文 | 681701篇 |
免费 | 7670篇 |
国内免费 | 1603篇 |
专业分类
电工技术 | 12871篇 |
综合类 | 642篇 |
化学工业 | 108406篇 |
金属工艺 | 27764篇 |
机械仪表 | 22194篇 |
建筑科学 | 16075篇 |
矿业工程 | 4630篇 |
能源动力 | 17386篇 |
轻工业 | 58164篇 |
水利工程 | 7782篇 |
石油天然气 | 15476篇 |
武器工业 | 44篇 |
无线电 | 74969篇 |
一般工业技术 | 137491篇 |
冶金工业 | 114831篇 |
原子能技术 | 16288篇 |
自动化技术 | 55961篇 |
出版年
2021年 | 6026篇 |
2019年 | 5879篇 |
2018年 | 9992篇 |
2017年 | 10232篇 |
2016年 | 10808篇 |
2015年 | 6807篇 |
2014年 | 11588篇 |
2013年 | 31229篇 |
2012年 | 18093篇 |
2011年 | 24497篇 |
2010年 | 19614篇 |
2009年 | 21855篇 |
2008年 | 22534篇 |
2007年 | 22424篇 |
2006年 | 19489篇 |
2005年 | 17768篇 |
2004年 | 16980篇 |
2003年 | 16583篇 |
2002年 | 16137篇 |
2001年 | 15757篇 |
2000年 | 15060篇 |
1999年 | 14738篇 |
1998年 | 32664篇 |
1997年 | 24056篇 |
1996年 | 18986篇 |
1995年 | 14787篇 |
1994年 | 13381篇 |
1993年 | 13049篇 |
1992年 | 10402篇 |
1991年 | 10084篇 |
1990年 | 9957篇 |
1989年 | 9714篇 |
1988年 | 9322篇 |
1987年 | 8433篇 |
1986年 | 8141篇 |
1985年 | 9386篇 |
1984年 | 8573篇 |
1983年 | 8074篇 |
1982年 | 7375篇 |
1981年 | 7487篇 |
1980年 | 7127篇 |
1979年 | 7219篇 |
1978年 | 7041篇 |
1977年 | 7857篇 |
1976年 | 9797篇 |
1975年 | 6371篇 |
1974年 | 6039篇 |
1973年 | 6164篇 |
1972年 | 5257篇 |
1971年 | 4920篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A nonstationary model of SO2 absorption from a gas phase to a countercurrent falling film of absorbing slurry was developed. Laminar, wavy and turbulent film structures were considered based on published information. Resistances to the mass transfer on the gas and the liquid sides of the interphase were considered, together with chemical reactions in the liquid phase. Relevant chemical equilibria in the liquid phase were modeled. Original experimental data on the neutralization reagent dissolution rate presented as a polydispersed two‐phase system of solids and on the rate of dissolved sulfite oxidation were used. The model was verified with experimental data from a laboratory‐scale falling‐film absorber using a single vertical tube under various geometrical and operating conditions, and a very good agreement was found with the experiment. Parametric sensitivity analysis showed the critical parts of the model. 相似文献
72.
The microstructure evolution in nonstoichiometric titanium carbide is studied during high-temperature deformation at high strain rates and low strains (shock compression) and at slow strain rates and high strains (superplastic regime). The results demonstrate that high-temperature deformation in a broad range of strain rates offers a means of controlling the microstructure of titanium carbide. By varying deformation conditions, one can obtain materials differing in microstructure and chemical composition, in particular, with equilibrium and nonequilibrium microstructures. Accordingly, the physicochemical properties of such materials also differ. 相似文献
73.
An analysis is made of the characteristic features and problems of the optimal processing of the results of measurements in the case of a random observation function utilizing a nonlinear Kalman filter. A method is proposed for increasing the convergence domain of the filter with additional processing of measurements in the frequency domain. 相似文献
74.
A·Ю·阿列克桑德罗夫斯基 《水利水电快报》2003,24(14):30-31
水电站运行过程中河床变形会使河底高程逐渐降低。从而导致下游流量特性曲线下降以及水电站水头增大。水头增大使水电站气蚀特性发生变化,导致动力设备的正常工作条件受到破坏。并对其运行安全性和效率造成不利影响。以卡马河的沃特金水电站为例,阐述了河床变形对水电站动力设备工作条件的影响。 相似文献
75.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
76.
77.
The prohibitive - exponential in the number of users - computational complexity of the maximum-likelihood multiuser detector for direct-sequence code-division multiple-access communications has fueled an extensive research effort for the development of low-complexity multiuser detection alternatives. We show that we can efficiently and effectively approach the error rate performance of the optimum multiuser detector as follows. We utilize a multiuser zero-forcing or minimum mean-square error (MMSE) linear filter as a preprocessor and we establish that the output magnitudes, when properly scaled, provide a reliability measure for each user bit decision. Then, we prepare an ordered, reliability-based error search sequence of length linear in the number of users; it returns the most likely user bit vector among all visited options. Numerical and simulation studies for moderately loaded systems that permit exact implementation of the optimum detector indicate that the error rate performance of the optimum and the proposed detector are nearly indistinguishable over the whole predetection. signal-to-noise ratio range of practical interest. Similar studies for higher user loads (that prohibit comparisons with the optimum detector) demonstrate error rate performance gains of orders of magnitude in comparison with straight decorrelating or MMSE multiuser detection. 相似文献
78.
This paper extends an analysis developed for tubular permanent-magnet machines to account for the effect of fringing associated with the finite length of the ferromagnetic armature core. The magnetic field distribution, established by using an analytical technique formulated in the cylindrical coordinate system, provides an accurate means of evaluating the effect of the fringing flux on the thrust force and the back-electromotive force. Finite-element calculations confirm the analytically derived results. In Part II of the paper, the analysis is used to predict the cogging force that results from end effects and to facilitate minimization of the force. 相似文献
79.
Hambleton P.J. Ng B.K. Plimmer S.A. David J.P.R. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(2):347-351
The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions. 相似文献
80.
Anaerobic co-digestion of organic wastes from households, slaughterhouses and meat processing industries was optimised in a half technical scale plant. The plant was operated for 130 days using two different substrates under organic loading rates of 10 and 12 kgCOD.m(-3).d(-1). Since the substrates were rich in fat and protein components (TKN: 12 g.kg(-1) the treatment was challenging. The process was monitored on-line and in the laboratory. It was demonstrated that an intensive and stable co-digestion of partly hydrolysed organic waste and protein rich slaughterhouse waste can be achieved in the balance of inconsistent pH and buffering NH4-N. In the first experimental period the reduction of the substrate COD was almost complete in an overall stable process (COD reduction >82%). In the second period methane productivity increased, but certain intermediate products accumulated constantly. Process design options for a second digestion phase for advanced degradation were investigated. Potential causes for slow and reduced propionic and valeric acid degradation were assessed. Recommendations for full-scale process implementation can be made from the experimental results reported. The highly loaded and stable codigestion of these substrates may be a good technical and economic treatment alternative. 相似文献