全文获取类型
收费全文 | 5809篇 |
免费 | 443篇 |
国内免费 | 348篇 |
专业分类
电工技术 | 364篇 |
综合类 | 482篇 |
化学工业 | 850篇 |
金属工艺 | 448篇 |
机械仪表 | 291篇 |
建筑科学 | 481篇 |
矿业工程 | 160篇 |
能源动力 | 286篇 |
轻工业 | 233篇 |
水利工程 | 114篇 |
石油天然气 | 184篇 |
武器工业 | 23篇 |
无线电 | 534篇 |
一般工业技术 | 660篇 |
冶金工业 | 277篇 |
原子能技术 | 221篇 |
自动化技术 | 992篇 |
出版年
2024年 | 12篇 |
2023年 | 47篇 |
2022年 | 81篇 |
2021年 | 104篇 |
2020年 | 110篇 |
2019年 | 119篇 |
2018年 | 110篇 |
2017年 | 123篇 |
2016年 | 167篇 |
2015年 | 179篇 |
2014年 | 325篇 |
2013年 | 338篇 |
2012年 | 350篇 |
2011年 | 476篇 |
2010年 | 303篇 |
2009年 | 333篇 |
2008年 | 344篇 |
2007年 | 362篇 |
2006年 | 263篇 |
2005年 | 295篇 |
2004年 | 241篇 |
2003年 | 241篇 |
2002年 | 236篇 |
2001年 | 247篇 |
2000年 | 201篇 |
1999年 | 234篇 |
1998年 | 91篇 |
1997年 | 91篇 |
1996年 | 84篇 |
1995年 | 67篇 |
1994年 | 63篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 29篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 29篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1963年 | 2篇 |
1957年 | 1篇 |
1956年 | 3篇 |
排序方式: 共有6600条查询结果,搜索用时 15 毫秒
11.
参数三次B样条曲线的一种整体光顺方法 总被引:7,自引:0,他引:7
本文在能量法的基础上,提出了一种新的目标函数,给出了参数三次B样条曲线的一种新的整体光顺方法。利用这种方法得到的曲线不仅具有较小的应变能,而且曲率变化比较均匀,具有很好的光顺效果。该方法能推广到对曲面的光顺。 相似文献
12.
The search for dielectric materials with a high dielectric constant and ′r = ƒ(T) curves with a flat profile fitting the X7R specification is still ongoing. Promising results were obtained by mixing compounds with closely related structures, such as the tetragonal tungsten bronze (TTB) niobate K2Sr4Nb10O30 and the perovskite Pb(Mg1/3Nb2/3)O3 (PMN). The present study, based on three methods of synthesis, explores the origin of the spreading out of the dielectric curves ′r = ƒ(T). For the composition 10x K0.2Sr0.4NbO3 (KSN) + (1 − x)Pb(Mg1/3Nb2/3)O3 (PMN) with x = 0.3–0.6, the three synthesis methods provided similar characteristics and for the highest perovskite ratio (x = 0.3), the ′r = ƒ(T) curve exhibits a flat profile. When lithium is used as a sintering agent, ′r = ƒ(T) curves present a linear dependency with the temperature. These materials are also characterized by a structural and a microstructural inhomogeneity. Two phases TTB and perovskite type, different from KSN and PMN, are present after calcination and sintering, but not evenly distributed. The PbO loss during sintering also contributes to the evolution of the properties of the material. 相似文献
13.
14.
Methyl groups from chain scission and H-crosslinks have been identified by solid-state nuclear magnetic resonance in amorphous ethylene-propylene copolymers containing 23 and 36 mole % propylene after γ-irradiation to 10 MGy at 30°C. G (scission) and G (crosslink) values determined from the n.m.r. spectra and by extraction are in agreement, which suggests that the crosslinks are not clustered. This may differ from the situation in polyethylene where there is a substantial crystalline content. G(S). G(X) and the ratio G(S)/G(X) increase with increasing propylene content of the copolymers. 相似文献
15.
根据生产实践 ,结合PLC的技术特点和 385m2 凯利式叶滤机的电气联锁特性 ,阐述了应用PLC技术 ,可进一步提高 385m2 凯利式叶滤机的运转率和自动化水平。 相似文献
16.
A. G. ATKINS Z. CHEN B. COTTERELL 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(1):67-77
In this paper, energy dissipation rate D vs. Δa curves in ductile fracture are predicted using a ‘conversion’ between loads, load‐point displacements and crack lengths predicted by NLEFM and those found in real ELPL propagation. The NLEFM/ELPL link was recently discovered for the DCB testpiece, and we believe it applies to other cracked geometries. The predictions for D agree with experimental results. The model permits a crack tip toughness R(Δa) which rises from Jc and saturates out when (if) steady state propagation is reached after a transient stage in which all tunnelling, crack tip necking and shear lip formation is established. JR is always greater than the crack tip R(Δa) and continues to rise even after R(Δa) levels off. The analysis is capable of predicting the usual D vs. Δa curves in the literature which have high initial values and fall monotonically to a plateau at large Δa. It also predicts that D curves for CCT testpieces should be higher than those for SENB/CT, as found in practice. The possibility that D curves at some intermediate Δa may dip to a minimum below the levelled‐off value at large Δa is predicted and confirmed by experiment. Recently reported D curves that have smaller initial D than the D‐values after extensive propagation can also be predicted. The testpiece geometry and crack tip R(Δa) conditions required to produce these different‐shaped D vs. Δa curves are established and confirmed by comparison with experiment. The energy dissipation rate D vs. Δa is not a transferable property as it depends on geometry. The material characteristic R(Δa) may be the ‘transferable property’ for scaling problems in ELPL fracture. How it can be deduced from D vs. Δa curves (and by implication, JR vs. Δa curves) is established. 相似文献
17.
2003年11月龙滩工程将实现大江截流,随着工程建设的全面推进,越发显出实施龙滩水电站正常蓄水位400m一次建成方案的重要性和紧迫性。相对分期建设而言,400m水位一次建成,工程效益大、增加投资少、无后期加高过程中的各种技术难题,基本不影响电站的初期发电效益,水轮机设计与运行问题少、机组运行条件好,电站规模效益与社会综合效益巨大,有利于移民安置和库区经济的发展,对国家、地方、企业均十分有利,因此应尽快决策实施400m一次建成方案。 相似文献
18.
19.
20.
L. Calmels J.E. Inglesfield S. Crampin Th. Rasing 《Computer Physics Communications》2003,151(3):251-264
We describe a complex frequency technique for evaluating the linear and quadratic dielectric responses of metal surfaces, illustrated by application to the surface of jellium. The electric susceptibilities are shorter-range functions of the spatial coordinates at complex frequency, whereas their general behaviour is complicated, long-range and highly oscillatory at real frequency. As a result the linear and the second harmonic electric charges induced by an optical perturbation are then numerically easier to calculate at complex frequency. As the functions which characterize the optical behaviour of the metal surface are analytic in the upper complex frequency half-plane, the dielectric response at real frequency can be deduced by analytic continuation from the results at complex frequency. We illustrate and discuss this approach, which should be useful for studying more realistic models of a surface in which the crystal potential is included, and where a direct calculation of the dielectric response is difficult to obtain at real frequency. 相似文献