全文获取类型
收费全文 | 195933篇 |
免费 | 23946篇 |
国内免费 | 24001篇 |
专业分类
电工技术 | 18539篇 |
技术理论 | 8篇 |
综合类 | 13381篇 |
化学工业 | 40140篇 |
金属工艺 | 7855篇 |
机械仪表 | 12395篇 |
建筑科学 | 9509篇 |
矿业工程 | 2274篇 |
能源动力 | 6148篇 |
轻工业 | 14505篇 |
水利工程 | 2460篇 |
石油天然气 | 4328篇 |
武器工业 | 1974篇 |
无线电 | 30755篇 |
一般工业技术 | 21522篇 |
冶金工业 | 4604篇 |
原子能技术 | 3275篇 |
自动化技术 | 50208篇 |
出版年
2024年 | 1060篇 |
2023年 | 3625篇 |
2022年 | 6436篇 |
2021年 | 7433篇 |
2020年 | 7072篇 |
2019年 | 6410篇 |
2018年 | 5993篇 |
2017年 | 8122篇 |
2016年 | 8764篇 |
2015年 | 9903篇 |
2014年 | 9642篇 |
2013年 | 12883篇 |
2012年 | 14587篇 |
2011年 | 16570篇 |
2010年 | 11889篇 |
2009年 | 11687篇 |
2008年 | 12972篇 |
2007年 | 14346篇 |
2006年 | 13647篇 |
2005年 | 11699篇 |
2004年 | 9935篇 |
2003年 | 7808篇 |
2002年 | 5975篇 |
2001年 | 4483篇 |
2000年 | 3775篇 |
1999年 | 3172篇 |
1998年 | 2641篇 |
1997年 | 2135篇 |
1996年 | 1670篇 |
1995年 | 1389篇 |
1994年 | 1240篇 |
1993年 | 916篇 |
1992年 | 737篇 |
1991年 | 595篇 |
1990年 | 511篇 |
1989年 | 372篇 |
1988年 | 289篇 |
1987年 | 184篇 |
1986年 | 172篇 |
1985年 | 231篇 |
1984年 | 200篇 |
1983年 | 141篇 |
1982年 | 198篇 |
1981年 | 99篇 |
1980年 | 98篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 15篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
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
102.
《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
103.
Lussier Isabelle; Derevensky Jeffrey L.; Gupta Rina; Bergevin Tanya; Ellenbogen Stephen 《Canadian Metallurgical Quarterly》2007,21(2):165
The study of resilient children has overturned many deficit-focused models concerning the ontogenesis of children raised in adversity. This study explored the relationship between risk and protective factors, resilience, and youth gambling behavior. More specifically, this study examined the relative contribution of various risk and protective domains in relation to problem gambling behavior and examined whether youth identified as resilient (high risk exposure- high internalized protection) were as likely as those identified as vulnerable (high risk exposure-low internalized protection) to engage in excessive gambling behavior. The sample consisted of 1,273 students ages 12 to 19. The findings demonstrated that risk and protective factors each provide a unique contribution to the prediction model of gambling problems. Resilient and vulnerable youth differed significantly in their self-reported gambling severity. As well, resilient youth were not statistically distinguishable from low-risk exposure groups in terms of their gambling severity. Findings are interpreted with respect to resilience and prevention research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
Sinéad C. Mac Namara Maria M. Garlock David P. Billington 《Canadian Metallurgical Quarterly》2007,21(2):152-156
Steam generator replacement at nuclear power plants requires large construction openings in nuclear containment structures. This study examines the effects of such openings placed in a 61?cm (2?ft) thick dome of a shield building. The dome is cast in two layers, and the limiting cases of the two layers acting as one and the lower layer carrying the entire load are considered. Without openings, the stresses due to dead load in the structure are very low when compared to the material strength. With openings, the loads are easily redistributed around the opening, and the maximum stresses for the conservative case are between three and four and one-half times larger than in the original structure with no openings. The extent of the affected area around the holes is relatively small. Smooth corners in the openings are necessary to avoid high local stress concentrations. 相似文献
105.
Performance of Storage Tanks in Oil Facilities Damaged by Hurricanes Katrina and Rita 总被引:1,自引:0,他引:1
Luis A. Godoy 《Canadian Metallurgical Quarterly》2007,21(6):441-449
106.
Shuenn-Yih Chang 《Canadian Metallurgical Quarterly》2007,133(5):555-565
It was found that the discontinuity at the end of an impulse will lead to numerical inaccuracy as this discontinuity will result in an extra impulse and thus an extra displacement in the time history analysis. In addition, this extra impulse is proportional to the discontinuity value at the end of the impulse and the size of integration time step. To overcome this difficulty, an effective approach is proposed to reduce the extra impulse and hence the extra displacement. In fact, the novel approach proposed in this paper is to perform a single small time step immediately upon the termination of applied impulse, whereas other time steps can be conducted by using the step size determined from accuracy consideration in period. The feasibility of this approach is analytically explored. Further, analytical results are confirmed by numerical examples. Numerical studies also show that this approach can be applied to other step-by-step integration methods. It seems that to slightly complicate the programming of dynamic analysis codes is the only disadvantage of this approach. 相似文献
107.
已往库存论中的决策模型,它是把现实过程用数学的方法进行分析,得到决策值,但不能看到决策的过程,不能反映出现实生活中的不确定性、动态性。运用Delphi 7.0和SQL server 2000对销售过程进行了动态仿真,利用Newsboy模型的推广(S,s)订购策略来监控库存并做出决策,这样就体现出此过程的不确定性、动态性;且举出了一个仿真商品销售的实例,对其中的一些关键技术,如何仿真、算法的实现等进行了阐述。 相似文献
108.
109.
KS Atia AI El‐Batal 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):805-811
Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry 相似文献
110.
在评价公众成员摄入放射性核素的辐射危害时,需估算每单位摄入量所致的剂量。摄入放射性素后器官或民受到的剂量是受到的剂量是通过生物学模型和剂量学模型来确定的,因此剂量也必须根据模型来确定。文中初步探讨了国际放射防护委员会给出的剂量系数的可靠性问题。文中首先说明了估算剂量系数的概念和方法,然后分析了剂量系数估算中,采用胃肠道模型,呼吸道模型,系统生物动力学模型和剂量学模型所遇到的不确定度的各种主要来源。 相似文献