全文获取类型
收费全文 | 27777篇 |
免费 | 2286篇 |
国内免费 | 1565篇 |
专业分类
电工技术 | 991篇 |
综合类 | 3143篇 |
化学工业 | 2300篇 |
金属工艺 | 2506篇 |
机械仪表 | 4182篇 |
建筑科学 | 2072篇 |
矿业工程 | 1761篇 |
能源动力 | 1240篇 |
轻工业 | 1952篇 |
水利工程 | 926篇 |
石油天然气 | 1298篇 |
武器工业 | 224篇 |
无线电 | 1249篇 |
一般工业技术 | 3681篇 |
冶金工业 | 1141篇 |
原子能技术 | 266篇 |
自动化技术 | 2696篇 |
出版年
2024年 | 100篇 |
2023年 | 363篇 |
2022年 | 667篇 |
2021年 | 784篇 |
2020年 | 918篇 |
2019年 | 726篇 |
2018年 | 661篇 |
2017年 | 888篇 |
2016年 | 970篇 |
2015年 | 994篇 |
2014年 | 1505篇 |
2013年 | 1658篇 |
2012年 | 1822篇 |
2011年 | 2024篇 |
2010年 | 1438篇 |
2009年 | 1454篇 |
2008年 | 1387篇 |
2007年 | 1645篇 |
2006年 | 1571篇 |
2005年 | 1439篇 |
2004年 | 1170篇 |
2003年 | 1065篇 |
2002年 | 917篇 |
2001年 | 828篇 |
2000年 | 736篇 |
1999年 | 621篇 |
1998年 | 531篇 |
1997年 | 473篇 |
1996年 | 411篇 |
1995年 | 356篇 |
1994年 | 298篇 |
1993年 | 202篇 |
1992年 | 194篇 |
1991年 | 157篇 |
1990年 | 161篇 |
1989年 | 136篇 |
1988年 | 97篇 |
1987年 | 49篇 |
1986年 | 33篇 |
1985年 | 21篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1966年 | 5篇 |
1964年 | 9篇 |
1962年 | 6篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Kruk Menno R.; Halász József; Meelis Wout; Haller József 《Canadian Metallurgical Quarterly》2004,118(5):1062
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
Mohammed Farid 《Chemical engineering science》2003,58(13):2985-2993
A model was developed to predict the change in droplet mass and temperature when it is exposed to hot air, as in spray drying of droplets containing solids. The droplet was assumed first to undergo sensible rapid heating with no mass change. Then the droplet experiences some shrinkage, with no temperature change but rapid mass losses, followed by a period of crust formation with a significant change in droplet mass and temperature and finally a short period of sensible heating of the dried particle. The model, unlike previous models, accounts for shrinkage and for the temperature distribution in the droplet. It provided a good prediction for the change in droplet temperature and mass for some of the experimental measurements available in the literatures. 相似文献
4.
0.89dtex细旦涤纶短纤维工艺优化探讨 总被引:2,自引:1,他引:1
介绍了纺制 0 89dtex× 3 8mm细旦涤纶短纤维的工艺技术特点 ,着重讨论了熔体温度、纺丝速度、冷却条件等工艺对原丝性能及产品质量的影响 相似文献
5.
6.
Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast
(PMC) and semi-solid die cast (SDC) with Al−7%Si−0.35%Mg composition in order to examine the relationship between solidification
structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved
in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance
to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate
tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at
the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries. 相似文献
7.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower. 相似文献
8.
Jaber Almedeij 《Powder Technology》2008,186(3):218-223
An empirical relationship of drag coefficient of flow around a sphere is developed for the entire range of Particle Reynolds numbers reported in the literature from Stokes regime to the condition when turbulent boundary layer prevails. The relationship is obtained using an approach to match asymptotically the wide trend of drag coefficient. The matching approach, which relies on dividing the wide trend into smaller segments that can be combined into an overall relationship, employs regression techniques and thus warrants the best-fit accuracy results. The relationship is calibrated with experimental data available in the literature covering the entire range for Reynolds numbers up to ~ 106. For Reynolds values greater than 106, the relationship renders a drag coefficient of 0.2. The performance of the relationship is tested and compared with other suitable models found in the literature. This relationship is also transformed into an explicit expression for settling velocity calculations. 相似文献
9.
高温和低张应力引起的非平衡晶界偏聚动力学(Ⅱ)--实验结果的动力学模拟 总被引:2,自引:2,他引:0
以文献[1]建立的张应力引起的非平衡晶界偏聚动力学方程模拟了Shinoda T等的磷在钢中的应力时效实验结果和Misra R D K的硫在钢中的应力时效实验结果,模拟结果与实验结果互相吻合。通过模拟发现,张应力使磷-空位复合体以及硫-空位复合体在钢中的扩散系数均增加3个数量级,且磷原子和硫原子的扩散系数分别降低3个和5个数量级。 相似文献
10.
In this paper we present some preliminary results about the coupling of shallow water equations for free surface flows and Darcy equation for groundwater flows. A suitable set of interface conditions is discussed: the Beavers and Joseph formula for the bottom stress is used. An iterative algorithm to solve the coupled problem is proposed and some numerical results are presented. 相似文献