全文获取类型
收费全文 | 133856篇 |
免费 | 10134篇 |
国内免费 | 5115篇 |
专业分类
电工技术 | 6973篇 |
技术理论 | 11篇 |
综合类 | 8164篇 |
化学工业 | 23166篇 |
金属工艺 | 6781篇 |
机械仪表 | 7686篇 |
建筑科学 | 9964篇 |
矿业工程 | 3496篇 |
能源动力 | 3646篇 |
轻工业 | 10086篇 |
水利工程 | 2192篇 |
石油天然气 | 6889篇 |
武器工业 | 827篇 |
无线电 | 15850篇 |
一般工业技术 | 16616篇 |
冶金工业 | 6604篇 |
原子能技术 | 1431篇 |
自动化技术 | 18723篇 |
出版年
2024年 | 526篇 |
2023年 | 2061篇 |
2022年 | 3718篇 |
2021年 | 4992篇 |
2020年 | 3830篇 |
2019年 | 3225篇 |
2018年 | 3689篇 |
2017年 | 4151篇 |
2016年 | 3649篇 |
2015年 | 4908篇 |
2014年 | 6282篇 |
2013年 | 7933篇 |
2012年 | 8502篇 |
2011年 | 9247篇 |
2010年 | 8022篇 |
2009年 | 7850篇 |
2008年 | 7724篇 |
2007年 | 7214篇 |
2006年 | 7189篇 |
2005年 | 6255篇 |
2004年 | 4261篇 |
2003年 | 3602篇 |
2002年 | 3184篇 |
2001年 | 2985篇 |
2000年 | 3053篇 |
1999年 | 3515篇 |
1998年 | 3019篇 |
1997年 | 2635篇 |
1996年 | 2356篇 |
1995年 | 1980篇 |
1994年 | 1594篇 |
1993年 | 1258篇 |
1992年 | 997篇 |
1991年 | 762篇 |
1990年 | 625篇 |
1989年 | 519篇 |
1988年 | 405篇 |
1987年 | 315篇 |
1986年 | 222篇 |
1985年 | 194篇 |
1984年 | 117篇 |
1983年 | 90篇 |
1982年 | 92篇 |
1981年 | 68篇 |
1980年 | 52篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 28篇 |
1976年 | 51篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
就5500m^3/min高炉鼓风机动,静叶片损坏事故发生的经过以及有关资料,从几个方面详细分析了事故发生的原因。 相似文献
42.
Abstract: Maintainability problems associated with traditional software systems are exacerbated in rule-based systems. The very nature of that approach — separation of control knowledge and data-driven execution — hampers maintenance. While there are widely accepted techniques for maintaining conventional software, the same is not true for rule-based systems. In most situations, both a knowledge engineer and a domain expert are necessary to update the rules of a rule-based system. This paper presents, first, an overview of the software engineering techniques and object-oriented methods used in maintaining rule-based systems. It then discusses alternate paradigms for expert system development. The benefits of using case-based reasoning (from the maintenance point of view) are illustrated through the implementation of a case-based scheduler. The main value of the scheduler is that its knowledge base can be modified by the expert without the assistance of a knowledge engineer. Since changes in application requirements can be given directly to the system by the expert, the effort of maintaining the knowledge base is greatly reduced. 相似文献
43.
Wu Ting M. Badaye T. Morishita N. Koshizuka S. Tanaka 《Journal of Superconductivity》1996,9(6):637-645
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T
c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films. 相似文献
44.
灾难备份的概念所谓“灾难备份”,是指利用技术、管理手段以及相关资源,确保已有的关键数据和关键业务在灾难发生后,在确定的时间内可以恢复和继续运营的过程。灾难备份建设是一项复杂的系统工程,涉及到灾难备份中心选点、灾难备份中心建设,机房建设、基础设施建设等,同时还涉及到灾难备份系统建设、专业运营队伍建设、灾难备份中心运营管理体制建设和灾难备份中心运营管理等工作。因此,建立灾难备份不仅需要投入大量人力、物力和财力,还需要考虑灾难备份系统实施所面临的技术难度和经验不足所带来的风险,以及长期运营管理方面的资金投入。… 相似文献
45.
Juan Carlos Benítez Carlos A. Giúdice Vicente J. D. Rascio 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(8):387-394
This paper discusses the bioactivity of antifouling paints based on organotin toxicants, such as tributyltin fluoride (TBTF) and triphenyltin fluoride (TPTF). These compounds were used alone or mixed as the main toxicant in formulations. The use of TPTF or mixtures of TPTF and TBTF, with vinyl binders, led to paints with satisfactory bioactivity during a 24 months immersion period. With the same binders, TBTF alone provided only 12 months of antifouling protection. The correlation coefficients calculated from the fouling attachment values and the rosin content in the binder showed that the bioactivity of the tested formulations depended on the solubility of the toxicant in sea water and on the composition and solubility of the binders. 相似文献
46.
The famous Antosik-Mikusinski convergent theorem on the Abel topological groups has very extensive applications in measure theory, summation theory and other analysis fields. In this paper, we establish the theorem on a class of effect algebras equipped with the ideal topology. This paper shows also that the ideal topology of effect algebras is a useful topology in studying the quantum logic the- ory. 相似文献
47.
Transport problems typically involve at least two types of constraints, on income and on time. Therefore, the indirect utility
function depends either on the income available after having subtracted the cost of the discrete alternative and on the free
time left after having worked and travelled by each competing option. In the typical linear-in-the-attributes and in-the-parameters
specification, that represents the first grade approximation of the indirect utility function, the effect of income and time
constraints cancel out and only the cost and time of the alternatives matter in the comparison between them. From a microeconomic
point of view this is equivalent to assume that income and time effects could be disregarded; which is not always the case.
To account for these effects the utility function should include second order attributes; however, in non-linear utility functions
it may not be easy to distinguish among several effects that could be relevant: direct preferences for good and leisure, and
simple interactions between attributes other than income and time effects. This paper analyses these effects from a theoretical
point of view focusing on the possible confounding problem in detecting income and time effects. We use a dataset collected
for a modal choice context and containing both revealed and stated preference data, and estimate several NL models examining
the effect of the different second-order terms on detecting income and time effects. We compared specifications including
square cost and time attributes, interactions between time and cost, cost divided by the income available to be spent on free
time, and time multiplied by free time. Our results confirm the strong effect of direct preferences for goods and leisure
time on choice, and the potential confounding effect between quadratic attributes and other non-linear omitted terms. Finally,
we also found that care should be taken in highlighting income and time effects using mixed data sources, since confounding
effects can occur when non-linearities are accounted for in both data sets. 相似文献
48.
Eva M. Valero Juan L. Nieves Sérgio M. C. Nascimento Kinjiro Amano David H. Foster 《Color research and application》2007,32(5):352-360
Many spectral‐recovery methods using RGB digital cameras assume the underlying smoothness of illuminant and reflectance spectra, and apply low‐dimensional linear models. The aim of the present work was to test whether a direct‐mapping method could be used instead of a linear‐models approach to recover spectral radiances and reflectances from natural scenes with an RGB digital camera and colored filters. In computer simulations, a conventional RGB digital camera with up to three colored filters was used to image scenes drawn from a hyperspectral image database. Three measures were used to evaluate recovery with the direct‐mapping method: goodness‐of‐fit, root‐mean‐square error, and a color‐difference metric. It was found that with two and three filters both spectral radiances and reflectances could be recovered sufficiently accurately for many practical applications. With little increase in computational complexity, an RGB camera and a few colored filters can provide significantly better recovery of natural scenes than an RGB camera alone. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 352–360, 2007 相似文献
49.
50.
Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry 相似文献