全文获取类型
收费全文 | 113218篇 |
免费 | 9555篇 |
国内免费 | 5234篇 |
专业分类
电工技术 | 4892篇 |
技术理论 | 21篇 |
综合类 | 17941篇 |
化学工业 | 12801篇 |
金属工艺 | 7029篇 |
机械仪表 | 6057篇 |
建筑科学 | 24691篇 |
矿业工程 | 5509篇 |
能源动力 | 2208篇 |
轻工业 | 5654篇 |
水利工程 | 6159篇 |
石油天然气 | 4217篇 |
武器工业 | 753篇 |
无线电 | 5384篇 |
一般工业技术 | 10229篇 |
冶金工业 | 5972篇 |
原子能技术 | 561篇 |
自动化技术 | 7929篇 |
出版年
2024年 | 404篇 |
2023年 | 1091篇 |
2022年 | 2231篇 |
2021年 | 2631篇 |
2020年 | 2663篇 |
2019年 | 2235篇 |
2018年 | 2351篇 |
2017年 | 3168篇 |
2016年 | 3448篇 |
2015年 | 3935篇 |
2014年 | 7800篇 |
2013年 | 6550篇 |
2012年 | 7898篇 |
2011年 | 8489篇 |
2010年 | 6614篇 |
2009年 | 7174篇 |
2008年 | 6549篇 |
2007年 | 8276篇 |
2006年 | 7657篇 |
2005年 | 6515篇 |
2004年 | 5402篇 |
2003年 | 4529篇 |
2002年 | 3755篇 |
2001年 | 3174篇 |
2000年 | 2723篇 |
1999年 | 2179篇 |
1998年 | 1534篇 |
1997年 | 1235篇 |
1996年 | 1089篇 |
1995年 | 920篇 |
1994年 | 783篇 |
1993年 | 629篇 |
1992年 | 542篇 |
1991年 | 337篇 |
1990年 | 315篇 |
1989年 | 312篇 |
1988年 | 197篇 |
1987年 | 150篇 |
1986年 | 92篇 |
1985年 | 70篇 |
1984年 | 61篇 |
1983年 | 42篇 |
1982年 | 34篇 |
1981年 | 46篇 |
1980年 | 49篇 |
1979年 | 46篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1975年 | 13篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
G. Ranzi M. A. Bradford B. Uy 《International journal for numerical methods in engineering》2004,61(5):657-672
The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
53.
通过对黑岱沟露天煤矿运输设备出动率调查,初步分析了目前主要运输设备的现状以及存在问题的原因和影响因素,就加大预防性维修的比重,实行全面的预防性维修制度提出了一些看法。 相似文献
54.
Yu. A. Radin I. A. Grishin T. S. Kontorovich O. B. Panshina A. V. Chugin 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(2):113-119
Problems arising with connecting the second exhaust-heat boiler to the first exhaust-heat boiler under load in the case of
flow circuits of combined-cycle plants of type PGU-450 are considered. Similar problems exist for two-boiler single-turbine
units of type PGU-325 and for two-boiler single-turbine units of traditional steampower plants with an output of 200–300 MW
upon connection of the second furnace of a two-furnace boiler to the operating first furnace. Analysis of the temperature-induced
stressed state and of the cyclic strength of thick-walled elements of the steam-water conduit of PGU-450 and of two-furnace
boilers of two-boiler single-turbine units with an output of 200–300 MW (the check valve, the inlet header of the water economizer)
is used for determining the steam temperature differences in the high-pressure conduits to the steam turbine and the order
of connection of the second exhaust-heat boiler to the operating fist one. Modes of enabling a two-boiler single-turbine unit
of a combined-cycle plant, which are most “rigid” from the standpoint of thermal strength, are determined.
__________
Translated from élektricheskie Stantsii, No. 2, February 2006, pp. 11–17. 相似文献
55.
陈继初 《湖南冶金职业技术学院学报》2003,(4)
会计政策选择类型在理论上大体可分为机会主义型和效率(或有效契约)型。会计政策选择具有效率性,但也为经理人员的机会主义行为打开了大门。在我国,由于企业缺乏一系列有效的激励约束机制,会计政策选择的机会主义仍然严重。为此,必须建立适合我国企业有效的激励约束机制。 相似文献
56.
《Particulate Science and Technology》2007,25(1):77-89
The removal of particulate contamination is a critical issue for many manufacturing processes. It is particularly critical to the electronics industry in which small pieces of microscopic debris remaining after chemical mechanical planarization (cmp) using submicron polishing particles can cause device failure. One way to enhance particle removal following the cmp process is to utilize surfactants. Recent research has shown ways to model the effect of surfactants on enhanced particle removal. However, previous research has not demonstrated the effect of ionic strength on enhanced particle removal associated with surfactant use. Past research has also not shown the combined effects of ionic strength and surfactant concentration on enhanced particle removal using surfactants. This article summarizes the parameters affecting particle removal, and it provides data and analysis on the effect of ionic strength as well as the combined effects of ionic strength and surfactant concentration on particle removal following cmp processing. 相似文献
57.
R. Boroch J. Wiaranowski R. Mueller-Fiedler M. Ebert J. Bagdahn 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(1):2-12
The aim of this work is to characterize the strength properties of polycrystalline silicon (polysilicon) with the use of tensile and bending test specimens. The strength of thin polysilicon films with different geometry, size and stress concentrations has been measured and correlated with the effective size of the specimen and its stress distribution. The test results are evaluated using a probabilistic strength approach based on the weakest link theory with the use of STAU software. The use of statistic methods of strength prediction of polysilicon test structures with a complex geometry and loading based on test values for standard material tests specimen has been evaluated. 相似文献
58.
R. RODRÍGUEZ-MARTÍN I. OCAÑA A. MARTÍN-MEIZOSO 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(7):664-670
High-strength steels are used to increase the load carrying capacity of components. However, to guarantee a safe design, it is also necessary to combine high strength with adequate fracture toughness. In this paper, fracture toughness of three high-strength steels with yield strengths ranging from 460 to 890 MPa has been studied at very low temperatures. Taking into account experimental evidence, a new mechanism of cleavage at very low temperatures is proposed. This mechanism considers the possibility of reaching the ideal strength (the stress at which the lattice of a single crystal losses its stability) in the immediate vicinity of the fatigue crack tip. Moreover, a computational model able to calculate the external load needed to produce a catastrophic failure of these steels has been developed. 相似文献
59.
A. Alt Dr.‐Ing. H. Mertens U. Arz L. Blessing C. Berger 《Materialwissenschaft und Werkstofftechnik》2007,38(5):402-409
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence. 相似文献
60.
No authorship indicated 《Canadian Metallurgical Quarterly》2007,62(5):388
Announces the 2007 recipient of the Gold Medal Award for Life Achievement in the Practice of Psychology: Patricia M. Bricklin. A brief biography, highlighting areas of special focus in Bricklin's work, is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献