全文获取类型
收费全文 | 14349篇 |
免费 | 1881篇 |
国内免费 | 916篇 |
专业分类
电工技术 | 212篇 |
综合类 | 1233篇 |
化学工业 | 3788篇 |
金属工艺 | 603篇 |
机械仪表 | 328篇 |
建筑科学 | 740篇 |
矿业工程 | 318篇 |
能源动力 | 1067篇 |
轻工业 | 563篇 |
水利工程 | 220篇 |
石油天然气 | 766篇 |
武器工业 | 62篇 |
无线电 | 1903篇 |
一般工业技术 | 2695篇 |
冶金工业 | 492篇 |
原子能技术 | 93篇 |
自动化技术 | 2063篇 |
出版年
2024年 | 68篇 |
2023年 | 389篇 |
2022年 | 433篇 |
2021年 | 670篇 |
2020年 | 672篇 |
2019年 | 558篇 |
2018年 | 539篇 |
2017年 | 629篇 |
2016年 | 663篇 |
2015年 | 605篇 |
2014年 | 800篇 |
2013年 | 981篇 |
2012年 | 906篇 |
2011年 | 983篇 |
2010年 | 725篇 |
2009年 | 888篇 |
2008年 | 716篇 |
2007年 | 900篇 |
2006年 | 854篇 |
2005年 | 739篇 |
2004年 | 580篇 |
2003年 | 561篇 |
2002年 | 413篇 |
2001年 | 360篇 |
2000年 | 356篇 |
1999年 | 233篇 |
1998年 | 186篇 |
1997年 | 130篇 |
1996年 | 119篇 |
1995年 | 104篇 |
1994年 | 76篇 |
1993年 | 54篇 |
1992年 | 55篇 |
1991年 | 28篇 |
1990年 | 28篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Summary In flow through porous media, solutions of poly(ethylene oxide) (PEO) exhibit extension thickening, whereas hydroxypropyl
guar (HPG) solutions are shear-thinning at high concentrations. The results show that the extension-thickening exhibited by
PEO solutions becomes less critical with increasing flow rate as the concentration of HPG in the solution is increased. At
high concentrations of HPG, the presence of PEO inhibits the shear-thinning behaviour, without increasing the apparent viscosity
of the solution. The presence of HPG reduces the rate and extent of degradation of PEO in the flowing solution. 相似文献
92.
Thermal Shock Behavior of Porous Silicon Carbide Ceramics 总被引:1,自引:0,他引:1
Using the water-quenching technique, the thermal shock behavior of porous silicon carbide (SiC) ceramics was evaluated as a function of quenching temperature, quenching cycles, and specimen thickness. It is shown that the residual strength of the quenched specimens decreases gradually with increases in the quenching temperature and specimen thickness. Moreover, it was found that the fracture strength of the quenched specimens was not affected by the increase of quenching cycles. This suggests a potential advantage of porous SiC ceramics for cyclic thermal-shock applications. 相似文献
93.
A new functional perturbation method (FPM) for calculating the probabilistic response of stochastically heterogeneous, linear elastic structures is developed. The method is based on treating the governing differential operator as well as the unknown displacement function as a functional of material modulus field. By executing a functional perturbation around the homogeneous case, a set of successive differential equations is obtained and solved, from which the average and variance of any local parameter (displacements, stresses, strains) can be found. For a linear problem, the equations to be solved in each approximation order differ from the one for the homogeneous case by a pseudo external loading (right hand side) part only. Thus, only the Green function for the homogeneous case is needed for an analytical solution of the corresponding heterogeneous problem. A one dimensional stochastically heterogeneous rod embedded in a uniform shear resistant elastic medium is solved as an example. The statistical variance of displacements and stresses are found analytically, including the edge regions. Morphological (grain size) and material (modulus) effects on the stochastic response are demonstrated. The above results are essential for estimating the stochastic features of local stress concentrations, which are the source for many strength-related macro properties of materials. Extensive usage of generalized functions (Dirac operator and its derivatives) is needed for the analysis. 相似文献
94.
The research was conducted to evaluate the effects of cellulose and polyester fibers on the properties of porous asphalt mixes, using the tests of draindown, abrasion, volumetric properties, rutting, and moisture damage. Images of scanning electron microscopy and X-ray computerized tomography were adopted to identify the microstructure of the fiber and inner stone skeleton of porous asphalt. The influence of rutting parameter (G*/sin δ) of asphalt modified by different fibers on the rutting resistance of the mixes was investigated. Based upon MOHR-COULOMB theory, the cohesion and the angle of internal friction of the mixes were derived from both indirect tension and unconfined compression strength. The experimental results indicate that fibers mainly stabilize asphalt binder and thicken asphalt film around aggregates. Furthermore, they result in the improved mechanical strength of porous asphalt mixes at high temperature slightly. From comparison analysis, cellulose fibers appear to perform better than polyester fibers in porous asphalt mixes. 相似文献
95.
超临界流体中的酶催化 总被引:3,自引:0,他引:3
与其他非水相酶催化介质相比 ,超临界流体有其独特的优越性。阐述了超临界流体的概念、对超临界流体的选择原则以及在超临界流体中酶催化的各种影响因素 ,还讨论了在此类流体中酶催化的应用和发展前景 相似文献
96.
97.
通过对多孔粒状铵油炸药质量影响因素的分析,结合乌海矿业公司爆破的特点,提出了保证炸药加工质量的合理参数。 相似文献
98.
This article reviews research on the implementation of media-rating systems, parents' use and evaluation of them, and the impact of ratings on children. Although half or more of parents report using media-rating systems, understanding of various components of the systems is low, particularly for television ratings. A meta-analysis of national polls shows that parents overwhelmingly prefer that ratings specify content, rather than giving age recommendations. A second meta-analysis, of experiments testing the effects of ratings on children's interest in programs, shows that ratings indicating restricted or controversial content have a deterrent effect for children under age 8 but that, by age 11 and especially for boys, the ratings show a small enticement effect. This effect occurs for both age-based and content-based ratings. Implications for policymakers and parents are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
100.
固体吸附式制冷系统中吸附剂一般是多孔介质结构,吸附剂的内部结构特征对传热特性和吸附质的传质特性有直接影响,进而影响吸附解吸时间。本文探讨利用分形理论来分析固体吸附剂的结构特点,为目前通过对吸附剂的固化处理来提高吸附剂的传热速率的处理方法提供理论上的分析,并指出最佳分形维数的分形结构。 相似文献