全文获取类型
收费全文 | 385224篇 |
免费 | 4566篇 |
国内免费 | 877篇 |
专业分类
电工技术 | 6453篇 |
综合类 | 2606篇 |
化学工业 | 58227篇 |
金属工艺 | 18752篇 |
机械仪表 | 15247篇 |
建筑科学 | 9232篇 |
矿业工程 | 2605篇 |
能源动力 | 7251篇 |
轻工业 | 29958篇 |
水利工程 | 4435篇 |
石油天然气 | 6513篇 |
武器工业 | 32篇 |
无线电 | 39492篇 |
一般工业技术 | 76552篇 |
冶金工业 | 54795篇 |
原子能技术 | 7047篇 |
自动化技术 | 51470篇 |
出版年
2021年 | 2397篇 |
2019年 | 2268篇 |
2018年 | 22578篇 |
2017年 | 22084篇 |
2016年 | 16157篇 |
2015年 | 3444篇 |
2014年 | 4638篇 |
2013年 | 11527篇 |
2012年 | 11439篇 |
2011年 | 23680篇 |
2010年 | 20415篇 |
2009年 | 18076篇 |
2008年 | 19199篇 |
2007年 | 21699篇 |
2006年 | 7733篇 |
2005年 | 10678篇 |
2004年 | 8881篇 |
2003年 | 8428篇 |
2002年 | 7126篇 |
2001年 | 5992篇 |
2000年 | 5916篇 |
1999年 | 5658篇 |
1998年 | 12931篇 |
1997年 | 9190篇 |
1996年 | 7198篇 |
1995年 | 5626篇 |
1994年 | 5035篇 |
1993年 | 4894篇 |
1992年 | 3921篇 |
1991年 | 3580篇 |
1990年 | 3806篇 |
1989年 | 3654篇 |
1988年 | 3466篇 |
1987年 | 3046篇 |
1986年 | 3063篇 |
1985年 | 3540篇 |
1984年 | 3403篇 |
1983年 | 3033篇 |
1982年 | 2884篇 |
1981年 | 2978篇 |
1980年 | 2844篇 |
1979年 | 2767篇 |
1978年 | 2791篇 |
1977年 | 3056篇 |
1976年 | 3951篇 |
1975年 | 2479篇 |
1974年 | 2337篇 |
1973年 | 2472篇 |
1972年 | 2040篇 |
1971年 | 1905篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Ozone measurement based on the optical absorption of visible light at 603 nm using polymer optical fibres is investigated and tested. Comparisons with a commercial UV based sensor demonstrate the ability of the visible based sensor to measure high concentrations over a range 27-127 mg/litre. A resolution of 5 mg/litre is also demonstrated for this sensor. 相似文献
982.
A. V. Solokhin S. L. Nazanskii V. S. Timofeev 《Theoretical Foundations of Chemical Engineering》2005,39(2):105-109
The evolution of the phase portrait for the dynamic system of open evaporation combined with a chemical reaction for a fixed liquid amount was studied as dependent on the rate constants of the reaction. A three-component azeotropic mixture whose vapor-liquid equilibrium diagram is characterized by two distillation regions was considered. The possibility of the open evaporation trajectory to transfer through the separatrix between the distillation regions was shown, as well as the possibility of implementing the principle of redistribution of the concentration fields due to chemical reactions occurring in reactive distillation columns.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 115–119.Original Russian Text Copyright © 2005 by Solokhin, Nazanskii, Timofeev. 相似文献
983.
984.
N. V. Vostokov Yu. N. Drozdov Z. F. Krasil’nik O. A. Kuznetsov A. V. Novikov V. A. Perevoshchikov M. V. Shaleev 《Russian Microelectronics》2005,34(4):203-209
The results are presented of the fabrication of strain-relaxed graded Si1 − x
Gex/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<106 cm−2) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.__________Translated from Mikroelektronika, Vol. 34, No. 4, 2005, pp. 243–250.Original Russian Text Copyright © 2005 by Vostokov, Drozdov, Krasil’nik, Kuznetsov, Novikov, Perevoshchikov, Shaleev. 相似文献
985.
We are concerned with the detection of edges—the location and amplitudes of jump discontinuities of piecewise smooth data realized in terms of its discrete grid values. We discuss the interplay between two approaches. One approach, realized in the physical space, is based on local differences and is typically limited to low-order of accuracy. An alternative approach developed in our previous work [Gelb and Tadmor, Appl. Comp. Harmonic Anal., 7, 101–135 (1999)] and realized in the dual Fourier space, is based on concentration factors; with a proper choice of concentration factors one can achieve higher-orders—in fact in [Gelb and Tadmor, SIAM J. Numer. Anal., 38, 1389–1408 (2001)] we constructed exponentially accurate edge detectors. Since the stencil of these highly-accurate detectors is global, an outside threshold parameter is required to avoid oscillations in the immediate neighborhood of discontinuities. In this paper we introduce an adaptive edge detection procedure based on a cross-breading between the local and global detectors. This is achieved by using the minmod limiter to suppress spurious oscillations near discontinuities while retaining high-order accuracy away from the jumps. The resulting method provides a family of robust, parameter-free edge-detectors for piecewise smooth data. We conclude with a series of one- and two-dimensional simulations.To David Gottlieb, on his 60th birthday, with friendship and appreciation. 相似文献
986.
M. M. Stadnyk 《Materials Science》2007,43(6):764-768
We deduce the theoretical formula taking into account the influence of biaxial loading of a plate weakened by a crack on the
stress intensity factor K
I. This enables us to compute the characteristic of crack resistance K
c according to the known boundary forces.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 14–16, November–December, 2007. 相似文献
987.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
988.
The paper describes an experimental investigation of the diamond-like carbon deposition process from methane precursor with an innovative high-density inductively coupled plasma source. It appears that a high plasma density allows a fast growth of diamond-like carbon coatings exhibiting a high hardness. In contrast to what is usually found in the literature, it seems that the ion species participate significantly to the growth of the carbon film when exposed to a high ion flux. 相似文献
989.
Ya. O. Shablovskii 《Inorganic Materials》2007,43(12):1345-1349
The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion. 相似文献
990.
A new technique for the preparation of CuI nanoparticles from CuSO4 and KI ethanol solutions has been developed. Preparation conditions were optimized through a series of experiments. Under
these conditions, the yield of CuI reached 95.39%. The product was characterized and the reaction kinetics was studied. The
results show that the product takes a roughly spherical shape with an average particle size of less then 50 nm. The activation
energy of the formation of CuI is found to be E
a = 0.58 × 102 kJ/mol, and the preexponential factor in the Arrhenius equation is k
0 = 7.43 × 1016 mol/(l s).
The text was submitted by the authors in English. 相似文献