全文获取类型
收费全文 | 58356篇 |
免费 | 5185篇 |
国内免费 | 2683篇 |
专业分类
电工技术 | 3418篇 |
技术理论 | 6篇 |
综合类 | 4018篇 |
化学工业 | 9484篇 |
金属工艺 | 3242篇 |
机械仪表 | 3678篇 |
建筑科学 | 4641篇 |
矿业工程 | 1651篇 |
能源动力 | 1604篇 |
轻工业 | 3754篇 |
水利工程 | 1037篇 |
石油天然气 | 3558篇 |
武器工业 | 411篇 |
无线电 | 7197篇 |
一般工业技术 | 7111篇 |
冶金工业 | 3013篇 |
原子能技术 | 612篇 |
自动化技术 | 7789篇 |
出版年
2024年 | 263篇 |
2023年 | 1042篇 |
2022年 | 1691篇 |
2021年 | 2423篇 |
2020年 | 1877篇 |
2019年 | 1517篇 |
2018年 | 1700篇 |
2017年 | 1944篇 |
2016年 | 1761篇 |
2015年 | 2274篇 |
2014年 | 2898篇 |
2013年 | 3522篇 |
2012年 | 3650篇 |
2011年 | 3985篇 |
2010年 | 3610篇 |
2009年 | 3217篇 |
2008年 | 3260篇 |
2007年 | 3060篇 |
2006年 | 3037篇 |
2005年 | 2570篇 |
2004年 | 1844篇 |
2003年 | 1751篇 |
2002年 | 1803篇 |
2001年 | 1557篇 |
2000年 | 1393篇 |
1999年 | 1463篇 |
1998年 | 1214篇 |
1997年 | 1039篇 |
1996年 | 1051篇 |
1995年 | 799篇 |
1994年 | 664篇 |
1993年 | 460篇 |
1992年 | 416篇 |
1991年 | 315篇 |
1990年 | 244篇 |
1989年 | 208篇 |
1988年 | 170篇 |
1987年 | 121篇 |
1986年 | 90篇 |
1985年 | 66篇 |
1984年 | 61篇 |
1983年 | 33篇 |
1982年 | 46篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. 相似文献
53.
54.
Sun Qing-Ping Guo Tian-Fu Li Xue-Jun Zhang Xing 《International Journal of Fracture》1996,78(3-4):315-330
Numerical study by the finite element method (FEM) is performed to investigate the effect of dual-scale microstructure on the toughness of laminar zirconia composite. The computation is based on the micromechanics constitutive model of polycrystal transformation plasticity developed by Sun et al. [10] where both transformation induced shear and softening effects during autocatalytic transformation are taken into account. The numerical simulation presented in this paper successfully reproduced the experimentally observed two effects of the dual-scale microstructure on the toughness of laminar zirconia composite, i.e., the truncation of the elongated transformation frontal zone that forms in single phase Ce-ZrO2 and the propagation of the transformation zone along the layers normal to the crack plane. Quantitative analysis on the role of microstructure in transformation toughening of laminar zirconia composite is first carried out in the present work which will provide a starting point for the microstructural design of this novel advanced composite in the future.Presented at the Far East Fracture Group (FEFG) International Symposium on Fracture and Strength of Solids. 4–7 July 1994 in Xi'an, China. 相似文献
55.
The changes of nitric oxide synthase (NOS) activity and nitrite level in rat brain regions after spatial learning were investigated. NOS activity was assayed by conversion of [3H]L-arginine to [3H]L-citrulline, and a sensitive fluorometric assay for quantification of nitrite was used. Compared with sham-trained rats, NOS activity and nitrite level in hippocampus and cortex, and also the nitrite level in cerebellum, was elevated significantly one day after rats had learnt a water-rewarded spatial alteration task. These results suggest a spatial memory-related changes of endogenous NO in rat brain, and support the idea that NO participates in learning and memory processes. 相似文献
56.
首先揭示出民族风格是与时代风格对立统一、相互依存的一个概念。因而特定的时代需要具有时代精神的民族风格──创新民族风格。在探索此风格的过程中.我们首先要学习日本的战略,然后在学习的基础上实现超越。 相似文献
57.
According to FDA regulations, a combination drug is not efficacious unless each component contributes to the claimed effects. For a univariate endpoint, this implies that the combination at specific doses must be superior to each of its components at the same doses. More demanding is the property of synergy, in which the effect of the combination must be superior to the effect expected based on those of its components. If it is equal to those effects, it is additive, and if it is inferior, it is antagonistic. We give regions in the combination dose plane where these concepts are well defined. If the effect of the combination is greater than the greatest effect achievable by any of its components it is therapeutically synergistic. A combination can be antagonistic, yet its components can still contribute to the claimed effects. If it is additive, synergistic or therapeutically synergistic, its components must contribute to the claimed effects. We relate these concepts and provide designs and sequential procedures for determining whether a combination is therapeutically synergistic, synergistic, additive, antagonistic and contributing or antagonistic and non-contributing. 相似文献
59.
Zinc sulphide thin film electroluminescent devices doped with Mn or Tb have been produced on p-type Si substrates using a process in which doped zinc oxide films are deposited by a sol-gel drain coating method from a solution of zinc acetate containing a manganese or terbium dopant. The films are then converted to ZnS by heating them in an atmosphere containing hydrogen sulphide which replaces the oxygyn with sulphur. The composition, crystalline structure and optical properties of films have shown that complete conversion from the oxide to the sulphide takes place. The luminescent characteristics of the devices so produced have been measured as a function of the doping concentrations, film thickness, insulator thickness and driving voltage and frequency. It has been found that yellow or green luminescence can be obtained using Mn or Tb doping respectively. 相似文献
60.