全文获取类型
收费全文 | 41723篇 |
免费 | 4081篇 |
国内免费 | 2026篇 |
专业分类
电工技术 | 2587篇 |
技术理论 | 3篇 |
综合类 | 2775篇 |
化学工业 | 6920篇 |
金属工艺 | 2306篇 |
机械仪表 | 2495篇 |
建筑科学 | 3088篇 |
矿业工程 | 1156篇 |
能源动力 | 1192篇 |
轻工业 | 2826篇 |
水利工程 | 816篇 |
石油天然气 | 2601篇 |
武器工业 | 389篇 |
无线电 | 5096篇 |
一般工业技术 | 4946篇 |
冶金工业 | 1843篇 |
原子能技术 | 443篇 |
自动化技术 | 6348篇 |
出版年
2024年 | 264篇 |
2023年 | 900篇 |
2022年 | 1683篇 |
2021年 | 2239篇 |
2020年 | 1638篇 |
2019年 | 1245篇 |
2018年 | 1452篇 |
2017年 | 1516篇 |
2016年 | 1264篇 |
2015年 | 1760篇 |
2014年 | 2277篇 |
2013年 | 2528篇 |
2012年 | 2856篇 |
2011年 | 3042篇 |
2010年 | 2691篇 |
2009年 | 2232篇 |
2008年 | 2376篇 |
2007年 | 2131篇 |
2006年 | 2055篇 |
2005年 | 1789篇 |
2004年 | 1162篇 |
2003年 | 981篇 |
2002年 | 944篇 |
2001年 | 816篇 |
2000年 | 816篇 |
1999年 | 992篇 |
1998年 | 772篇 |
1997年 | 601篇 |
1996年 | 573篇 |
1995年 | 479篇 |
1994年 | 394篇 |
1993年 | 266篇 |
1992年 | 240篇 |
1991年 | 180篇 |
1990年 | 131篇 |
1989年 | 99篇 |
1988年 | 86篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 37篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 22篇 |
1980年 | 24篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
51.
52.
利用米曲霉对牛乳进行发酵,通过单因子及正交试验以菌丝体干重为指标对其在牛乳中的生长进行了研究.结果表明:接种量为4%,装液量为30mL,摇床转速为180r/min时菌丝体干重可达到最大.此外测得最大菌丝体干重时的蛋白质分解率可达35.6%. 相似文献
53.
随着Web服务的数量越来越庞大,服务的质量也越来越低.如何有效地对Web服务进行动态组合,满足广大用户的需求是目前急需解决的问题.在阐述了传统语义Web服务描述模型不足的基础上,解释Web服务组合的概念、基本元素以及分类,构建语义动态服务组合模型,并简要说明支持Web服务中的6种QoS需求. 相似文献
54.
透过节能减排政策和制度看中国节能减排 总被引:2,自引:0,他引:2
随着世界人口的增长、现代工业的高速发展,不可再生资源遭到掠夺式开采、能源消耗几何级增长、环境污染程度大大超出了生态系统的承受能力。如何解决能源短缺与污染严重对经济和社会发展的影响已经成为世界性的难题,我国同样如此。因此,加强对节能减排体系的研究,对我国节能减排工作的开展具有非常重要的意义。对我国节能减排的政策和制度进行剖析,指出了我国节能减排政策、制度以及做法中存在的问题,并提出解决的方法。 相似文献
55.
This paper presents a transient axial dispersion model for an isothermal, catalytic fluidized bed reactor, which is frequently employed in synthetic production processes including coal gasification and liquefaction. A non-linear chemical reaction is considered to occur in the reactor. This model of a fluidized bed reactor takes into account the axial dispersion in the three phases, bubble, cloud-wake and emulsion. The physical properties along the axial coordinate are invariant in the model. Transient characteristics of the gas reactant, and the length of the transient period have been examined based on the model. The model compares favorably with experimental data in the steady state condition. 相似文献
56.
Paul S. K. Choi Liang T. Fan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1973,23(7):531-548
Mathematical models are developed for the transient behaviour of encapsulated enzyme reactor systems such as the continuous stirred tank reactor (CSTR) and the packed bed tubular reactor. The rate processes taking place in the encapsulated enzyme bed are approximated by using a combined rate control model of enzyme reaction and membrane diffusion. The change in transient substrate concentration is obtained by using the developed rate expression in the material balance over the substrate as a function of time for the CSTR and as a function of time and position for the packed bed tubular reactor. The effects of various parameters such as the enzymic reaction rate constant, Michaelis constant, diffusional resistance of membranes, and Peclet number on the substrate concentration distribution, which varies with respect to operating time, are investigated. This study affords insight into the transient operating characteristics of the encapsulated enzyme reactor system. The results should be useful in understanding the start-up performance of the reactor systems and to control such reactor systems at desired operating conditions. 相似文献
57.
Temperature control curve is the key to achieving temperature control and crack prevention of high concrete dam during construction,and its rationality depends on the accurate measurement of temperature stress.With the simulation testing machine for the temperature stress,in the present study,we carried out the deformation process tests of concrete under three temperature curves:convex,straight and concave.Besides,we not only measured the early-age elastic modulus,creep parameters and stress process,but also proposed the preferred type.The results show that at early age,higher temperature always leads to greater elastic modulus and smaller creep.However,the traditional indoor experiments have underestimated the elastic modulus and creep development at early age,which makes the calculated value of temperature stress too small,thus increasing the cracking risk.In this study,the stress values of the three curves calculated based on the strain and early-age parameters are in good agreement with the temperature stress measured by the temperature stress testing machine,which verifies the method accuracy.When the temperature changes along the concave curve,the law of stress development is in consistent with that of strength.Under this condition,the stress fluctuation is small and the crack prevention safety of the concave type is higher,so the concave type is better.The test results provide a reliable basis and support for temperature control curve design and optimization of concrete dams. 相似文献
58.
Multibody System Dynamics - A recursive rotational-coordinate-based formulation of a planar Euler–Bernoulli beam is developed, where large displacements, deformations, and rotations are... 相似文献
59.
While the significance of oscillator dynamics and coupling structure to synchronization behaviors has been well addressed in the literature, little attention has been paid to the possible influence of coupling functions. In the present paper, adopting the scheme of dual-channel time-delayed couplings, we investigate how the synchronization behaviors of networked chaotic oscillators are influenced by parameters in the coupling functions. It is found that, with the introduction of the second coupling channel, the synchronization region, as calculated according to the method of master stability function (MSF), can be largely modified. In particular, by a slight change of the time delay, it is found that the synchronization region can be significantly adjusted, or even switched from non-existing to existing. We demonstrate this interesting phenomenon for both situations of processing and propagation induced time delays, as well as for different coupling functions. Our studies shed new light on the mechanism of chaos synchronization, and may potentially be used for the control of complex network dynamics. 相似文献
60.
张帆 《吉林化工学院学报》2015,(7):76-79
采用目标追求的入世、出世量表筛选出入世水平高组(70名)和低组(72)大学生,出世水平高组(68名)和低组(71名)大学生,探讨不同入世、出世水平大学生在奖学金申请、选修课和求职应聘三种决策任务领域上的框架效应及其在性别上的特点。结果发现:(1)不同出入世水平大学生在决策任务上的框架效应特点不同,入世水平高分组和低分组、出世水平高分组和低分组在奖学金申请问题上均出现了经典的框架效应;(2)在奖学金申请问题上,男性被试和女性被试的选择出现了明显的经典的框架效应。 相似文献