全文获取类型
收费全文 | 21856篇 |
免费 | 2224篇 |
国内免费 | 1623篇 |
专业分类
电工技术 | 1359篇 |
综合类 | 1770篇 |
化学工业 | 2974篇 |
金属工艺 | 2539篇 |
机械仪表 | 1485篇 |
建筑科学 | 1377篇 |
矿业工程 | 303篇 |
能源动力 | 277篇 |
轻工业 | 330篇 |
水利工程 | 338篇 |
石油天然气 | 526篇 |
武器工业 | 277篇 |
无线电 | 3602篇 |
一般工业技术 | 3461篇 |
冶金工业 | 546篇 |
原子能技术 | 194篇 |
自动化技术 | 4345篇 |
出版年
2024年 | 86篇 |
2023年 | 401篇 |
2022年 | 504篇 |
2021年 | 627篇 |
2020年 | 599篇 |
2019年 | 609篇 |
2018年 | 513篇 |
2017年 | 663篇 |
2016年 | 658篇 |
2015年 | 706篇 |
2014年 | 1112篇 |
2013年 | 1313篇 |
2012年 | 1354篇 |
2011年 | 1414篇 |
2010年 | 1151篇 |
2009年 | 1205篇 |
2008年 | 1179篇 |
2007年 | 1546篇 |
2006年 | 1458篇 |
2005年 | 1293篇 |
2004年 | 1143篇 |
2003年 | 984篇 |
2002年 | 813篇 |
2001年 | 721篇 |
2000年 | 645篇 |
1999年 | 510篇 |
1998年 | 438篇 |
1997年 | 367篇 |
1996年 | 320篇 |
1995年 | 287篇 |
1994年 | 223篇 |
1993年 | 213篇 |
1992年 | 154篇 |
1991年 | 112篇 |
1990年 | 89篇 |
1989年 | 79篇 |
1988年 | 60篇 |
1987年 | 27篇 |
1986年 | 28篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
H. Ji J. E. Dolbow 《International journal for numerical methods in engineering》2004,61(14):2508-2535
We consider a problem stemming from recent models of phase transitions in stimulus‐responsive hydrogels, wherein a sharp interface separates swelled and collapsed phases. Extended finite element methods that approximate the local solution with an enriched basis such that the mesh need not explicitly ‘fit’ the interface geometry are emphasized. Attention is focused on the weak enforcement of the normal configurational force balance and various options for evaluating the jump in the normal component of the solute flux at the interface. We show that as the reciprocal interfacial mobility vanishes, it plays the role of a penalty parameter enforcing a pure Dirichlet constraint, eventually triggering oscillations in the interfacial velocity. We also examine alternative formulations employing a Lagrange multiplier to enforce this constraint. It is shown that the most convenient choice of basis for the Lagrange multiplier results in oscillations in the multiplier field and a decrease in accuracy and rate of convergence in local error norms, suggesting a lack of stability in the discrete formulation. Under such conditions, neither the direct evaluation of the gradient of the approximation at the phase interface nor the interpretation of the Lagrange multiplier field provide a robust means to obtain the jump in the normal component of solute flux. Fortunately, the adaptation and use of local, domain‐integral methodologies considerably improves the flux evaluations. Several example problems are presented to compare and contrast the various techniques and methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
43.
P. Zhao J. C. Heinrich D. R. Poirier 《International journal for numerical methods in engineering》2004,61(6):928-948
A direct front‐tracking method using an Eulerian–Lagrangian formulation is developed in two space dimensions. The front‐tracking method is general in that it can track any type of interface once its local velocity is specified or has been determined by calculation. The method uses marker points to describe the interface position and tracks the interface evolution on a fixed finite‐element mesh, including growth, contraction, splitting and merging. Interfacial conditions are applied directly at the interface position. The method is applied to three scenarios that involve different interface conditions and are based on energy and mass diffusion. The three calculations are for the dendritic solidification of a pure substance, the cellular growth of an alloy, and the Ostwald ripening of silica particles in silicon. Numerical results show that very complicated interface morphologies and topological changes can be simulated properly and efficiently. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
44.
通过对国内外大量石油套管螺纹参数的测量和全尺寸的模拟试验,以及对测量和试验数据的理论分析,找出了影响国产套管发生粘扣的原因,并在实际生产中实施验证。采取相应的措施改善了套管的抗粘结性能,同时套管的密封和抗滑脱性能并未下降。 相似文献
45.
储运罐区计算机监测系统的开发与应用 总被引:3,自引:1,他引:2
储运罐区计算机监测系统是石化企业自动控制的薄弱环节。中国石油集团公司抚顺石油一厂使用ZYG-101型电子智能液位仪,以及使用FIX组态软件完成该系统的数据库组态、工艺流程显示、实时和历史趋势显示、报警和报表等处理过程,通过二次表的串行口与计算机进行通信,由计算机实时监测每个罐的各种重要参数。运行证明:该系统测量误差小,数据实时性好.易于存储及远程传送,较理想地达到储运罐区的自动检测功能。 相似文献
46.
介绍了平板显示控制芯片TO944的特点、功能、原理,并给出了基于T0944芯片的新型平板显示接口卡的软硬件实现方案,该方案具有电路简单、高可靠性、高性价比、高显示质量等优点,可用于各种不同类型与不同尺寸的平板显示器的显示。 相似文献
47.
We succeeded in the fabrication of bonded laser crystals composed of a neodymium-doped YVO4 laser crystal (Nd:YVO4) and its host crystals YVO4 by a newly developed dry etching technique using an argon ion beam. The optical distortion caused by the bonded interface of size 5 mm × 6 mm was estimated to be 0.05λ at 633 nm. From the comparison of laser performance pumped by a laser diode, the bonded crystals could increase the laser output power by nearly twice that of the non-bonded crystals with the same degree of polarization of 99.2%. To analyze the mechanism of the enhanced reduction of the thermal load in the bonded crystals, numerical simulations with a finite-element method were also performed. 相似文献
48.
主要研究带钛合金连接头硼/铝复合材料管构件中B-Al-Ti间的界面结构与性质。研究表明,在复合工艺条件下,硼-铝界面附近没有检测到任何铝-硼化合物,而钛-铝间形成TiAl有序金属间化合物相。实验证明,硼/铝复合材料与铝合金端环之间采用的固结方法是有效的,且可按照受载类型随意调整斜面搭接长度,达到承受不同载荷的目的。 相似文献
49.
A new comprehensive framework for narrative understanding has been developed. Its centerpiece is a new situational logic calledEpisodic Logic (EL), a knowledge and semantic representation well-adapted to the interpretive and inferential needs of general NLU. The most distinctive features of EL is its natural language-like expressiveness. It allows for generalized quantifiers, lambda abstraction, sentence and predicate modifiers, sentence and predicate reification, intensional predicates (corresponding to wanting, believing, making, etc.), unreliable generalizations, and perhaps most importantly, explicit situational variables (denoting episodes, events, states of affairs, etc.) linked to arbitrary formulas that describe them. These allow episodes to be explicitly related in terms of part-whole, temporal and causal relations. Episodic logical form is easily computed from surface syntax and lends itself to effective inference. 相似文献
50.
利用挤压铸造制备氧化铝/锌合金复合材料,在扫描电镜(SEM)上观察复合材料的界面。结果表明,在复合材料中纤维与基体间存在致密界面层,合金元素通过适当的化学反应可改善纤维与基体间的结合;在凝固过程中,纤维/基体界面上的硅在共晶体的共生生长过程中起了领先相作用,导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。 相似文献