全文获取类型
收费全文 | 460590篇 |
免费 | 5494篇 |
国内免费 | 1404篇 |
专业分类
电工技术 | 8874篇 |
综合类 | 394篇 |
化学工业 | 66884篇 |
金属工艺 | 21929篇 |
机械仪表 | 17558篇 |
建筑科学 | 9512篇 |
矿业工程 | 2737篇 |
能源动力 | 12044篇 |
轻工业 | 29420篇 |
水利工程 | 5120篇 |
石油天然气 | 8820篇 |
武器工业 | 17篇 |
无线电 | 54460篇 |
一般工业技术 | 97697篇 |
冶金工业 | 79143篇 |
原子能技术 | 9863篇 |
自动化技术 | 43016篇 |
出版年
2022年 | 2561篇 |
2021年 | 3897篇 |
2020年 | 2955篇 |
2019年 | 3809篇 |
2018年 | 12842篇 |
2017年 | 13244篇 |
2016年 | 10635篇 |
2015年 | 4730篇 |
2014年 | 7227篇 |
2013年 | 20091篇 |
2012年 | 13453篇 |
2011年 | 21760篇 |
2010年 | 18445篇 |
2009年 | 18955篇 |
2008年 | 19295篇 |
2007年 | 20651篇 |
2006年 | 12477篇 |
2005年 | 13894篇 |
2004年 | 12027篇 |
2003年 | 11698篇 |
2002年 | 10373篇 |
2001年 | 9782篇 |
2000年 | 9257篇 |
1999年 | 9534篇 |
1998年 | 24334篇 |
1997年 | 16714篇 |
1996年 | 12816篇 |
1995年 | 9534篇 |
1994年 | 8394篇 |
1993年 | 8404篇 |
1992年 | 6074篇 |
1991年 | 5717篇 |
1990年 | 5681篇 |
1989年 | 5322篇 |
1988年 | 5053篇 |
1987年 | 4423篇 |
1986年 | 4303篇 |
1985年 | 4819篇 |
1984年 | 4425篇 |
1983年 | 3996篇 |
1982年 | 3657篇 |
1981年 | 3732篇 |
1980年 | 3432篇 |
1979年 | 3326篇 |
1978年 | 3336篇 |
1977年 | 3750篇 |
1976年 | 4849篇 |
1975年 | 2853篇 |
1974年 | 2665篇 |
1973年 | 2731篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. Sadananda Chary S. Narender Reddy T. Chiranjivi 《Journal of Materials Science》1989,24(6):2199-2202
Dielectric properties, dielectric constant (k), dielectric loss (tan δ) and a.c. conductivity (σ) in the solution-grown single crystals of RbNO3 are presented from room temperature to about 200°C covering the frequency range 102 to 105 Hz. A broad peak observed in tan δ-frequency data between 103 and 105Hz is thought to be due to impurity-vacancy dipoles. The sudden rise of three parameters near 160°C is attributed to the known
phase transition from trigonal to CsCl structure. 相似文献
992.
993.
994.
A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---Hn-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data. 相似文献
995.
Summary If the roots of the characteristic equation of the governing differential equation for the stress function of an orthotropic plate under generalized plane stress conditions are equal classical solutions of anisotropic elasticity theory do not hold anymore. The general form of the stress function for such orthotropic materials is discussed and the exact solution is given for the plate with an elliptic opening loaded in tension.Comparison of the stress distribution for the material with distinct characteristic roots indicated that in produces much higher stress concentrations than the model with equal roots. For the latter case solution of any boundary value problem may be obtained very easily through an existing solution for the isotropic material.Given also that there are several problems involving stress concentrations in orthotropic plates as yet unsolved, the analysis presented here might be of considerable help in the, designing of the structure of composite laminates.With 8 Figures 相似文献
996.
S. A. Bengelloun 《Acta Informatica》1986,23(2):119-125
Summary A new algorithm is presented for finding all primes between 2 and an incrementally increasing value n. The algorithm executes in linear arithmetic time and space. An outline is given to show how previously developed techniques can be applied to improve the efficiency of the algorithm to O(n/loglogn) time and space. 相似文献
997.
P. K. Yeung S. C. Kot 《International journal for numerical methods in engineering》1985,21(5):929-939
A body-fitted curvilinear co-ordinate system is used to solve the equations of two-dimensional incompressible laminar flow over bluff obstructions by finite differences. Arbitrary conditions at the corner are removed by this method. Results for a backward-facing step are in reasonable agreement with those obtained with conventional mesh systems, and the differences are explained. A treatment of a channel expansion, in comparison with empirical data, is also included. The capability of the present method to handle arbitrary two-dimensional geometries is stressed and demonstrated, using a triangle and a semi-circle as examples. 相似文献
998.
Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<> 相似文献
999.
Y. Nath P. C. Dumir R. S. Bhatiaf 《International journal for numerical methods in engineering》1985,21(3):565-578
The present work investigates the efficacy and applicability of interior global orthogonal point collocation method to the axisymmetric nonlinear analysis of elastic circular plates and shallow spherical shells subjected to uniformly distributed transverse load. Spacewise discretisation has been carried out using a polynomial expansion with the zeros of a Chebyshev polynomial as collocation points. Timewise integration has been carried out with Newmark k-β scheme corresponding to average acceleration method. The static response and snap-through buckling results, as well as, the dynamic response and dynamic buckling results under a uniformly distributed step load have been obtained and found to agree closely with the available results. 相似文献
1000.
C. Y. Liao S. N. Atluri 《International journal for numerical methods in engineering》1991,32(6):1339-1361
An efficient method, based on the Schwarz–Neumann alternating technique, is presented for computing weight functions of a general solid (3-D as well as 2-D), with embedded or surface-flaw configurations. The total rate of change of the crack-opening displacements, due to simple perturbations of crack-dimension characteristics, is conveniently decomposed into the infinite-domain and boundary-correction parts. The former is determined from available analytical solutions of ideal-shaped cracks, whereas the latter is computed numerically by imposing nil boundary-traction requirements for the displacement field corresponding to the weight functions. Numerical examples, with solutions for 3-D weighted-average and local stress intensity factors, indicate that the proposed method is very accurate and efficient. 相似文献