全文获取类型
收费全文 | 174056篇 |
免费 | 18384篇 |
国内免费 | 11470篇 |
专业分类
电工技术 | 15956篇 |
技术理论 | 2篇 |
综合类 | 21528篇 |
化学工业 | 16346篇 |
金属工艺 | 6722篇 |
机械仪表 | 12562篇 |
建筑科学 | 19130篇 |
矿业工程 | 7197篇 |
能源动力 | 5003篇 |
轻工业 | 8477篇 |
水利工程 | 6853篇 |
石油天然气 | 6725篇 |
武器工业 | 2433篇 |
无线电 | 18770篇 |
一般工业技术 | 20244篇 |
冶金工业 | 6049篇 |
原子能技术 | 2517篇 |
自动化技术 | 27396篇 |
出版年
2024年 | 759篇 |
2023年 | 2116篇 |
2022年 | 3911篇 |
2021年 | 4626篇 |
2020年 | 5216篇 |
2019年 | 4376篇 |
2018年 | 4240篇 |
2017年 | 5420篇 |
2016年 | 6055篇 |
2015年 | 6528篇 |
2014年 | 10621篇 |
2013年 | 10052篇 |
2012年 | 13393篇 |
2011年 | 13752篇 |
2010年 | 10718篇 |
2009年 | 11114篇 |
2008年 | 10543篇 |
2007年 | 12914篇 |
2006年 | 11364篇 |
2005年 | 9580篇 |
2004年 | 7733篇 |
2003年 | 6646篇 |
2002年 | 5451篇 |
2001年 | 4563篇 |
2000年 | 3906篇 |
1999年 | 3309篇 |
1998年 | 2572篇 |
1997年 | 2241篇 |
1996年 | 1893篇 |
1995年 | 1716篇 |
1994年 | 1431篇 |
1993年 | 1056篇 |
1992年 | 905篇 |
1991年 | 650篇 |
1990年 | 532篇 |
1989年 | 534篇 |
1988年 | 384篇 |
1987年 | 219篇 |
1986年 | 190篇 |
1985年 | 93篇 |
1984年 | 97篇 |
1983年 | 61篇 |
1982年 | 70篇 |
1981年 | 75篇 |
1980年 | 47篇 |
1979年 | 51篇 |
1978年 | 24篇 |
1977年 | 23篇 |
1975年 | 17篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
B.‐J. Fang Y.‐J. Shan H.‐Q. Xu H.‐S. Luo Z.‐W. Yin 《Advanced functional materials》2004,14(2):169-173
Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg1/3‐Nb2/3)0.69Ti0.31]O3 (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d33, in the range of 1800–2200 pC N–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states. 相似文献
122.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
123.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献
124.
化学-电解氧化法制备高铁酸钾的研究 总被引:2,自引:0,他引:2
本文用化学-电解氧化法制备高铁酸钾,克服了纯化学氧化法产品需要提纯和纯电解氧化法制备周期长的缺点,得到了高纯度的高铁酸钾晶体。 相似文献
125.
126.
新型的芯片间互连用CMOS/BiCMOS驱动器 总被引:5,自引:2,他引:3
从改善不同类型 IC芯片之间的电平匹配和驱动能力出发 ,设计了几例芯片间接口 (互连 )用 CMOS/Bi CMOS驱动电路 ,并提出了采用 0 .5 μm Bi CMOS工艺 ,制备所设计驱动器的技术要点和元器件参数。实验结果表明所设计驱动器既具有双极型电路快速、大电流驱动能力的特点 ,又具备 CMOS电路低压、低功耗的长处 ,因而它们特别适用于低电源电压、低功耗高速数字通信电路和信息处理系统。 相似文献
127.
128.
129.
Zanozina I. I. Shabalina O. E. Zanozin I. Yu. Kamyzina E. A. 《Measurement Techniques》2004,47(3):308-311
A computerized form is given of IR spectral determination for structural group composition in high-boiling oil fractions by Berthold's method (7 structural elements) and Kuklinskii's method (28 structural elements), which reduces the analysis time by factors of 3–4 and improves the accuracy. 相似文献
130.