全文获取类型
收费全文 | 309746篇 |
免费 | 3719篇 |
国内免费 | 714篇 |
专业分类
电工技术 | 6193篇 |
综合类 | 560篇 |
化学工业 | 46738篇 |
金属工艺 | 10323篇 |
机械仪表 | 8820篇 |
建筑科学 | 7901篇 |
矿业工程 | 862篇 |
能源动力 | 8568篇 |
轻工业 | 31079篇 |
水利工程 | 2532篇 |
石油天然气 | 3669篇 |
武器工业 | 8篇 |
无线电 | 39694篇 |
一般工业技术 | 58442篇 |
冶金工业 | 56633篇 |
原子能技术 | 5458篇 |
自动化技术 | 26699篇 |
出版年
2021年 | 2276篇 |
2019年 | 2138篇 |
2018年 | 3607篇 |
2017年 | 3448篇 |
2016年 | 3538篇 |
2015年 | 2540篇 |
2014年 | 4439篇 |
2013年 | 14272篇 |
2012年 | 7363篇 |
2011年 | 10113篇 |
2010年 | 7899篇 |
2009年 | 9131篇 |
2008年 | 9599篇 |
2007年 | 9577篇 |
2006年 | 8504篇 |
2005年 | 7887篇 |
2004年 | 7759篇 |
2003年 | 7496篇 |
2002年 | 7333篇 |
2001年 | 7543篇 |
2000年 | 7205篇 |
1999年 | 7545篇 |
1998年 | 17656篇 |
1997年 | 12831篇 |
1996年 | 10097篇 |
1995年 | 7872篇 |
1994年 | 7203篇 |
1993年 | 6903篇 |
1992年 | 5286篇 |
1991年 | 5066篇 |
1990年 | 4933篇 |
1989年 | 4781篇 |
1988年 | 4673篇 |
1987年 | 3886篇 |
1986年 | 4007篇 |
1985年 | 4717篇 |
1984年 | 4276篇 |
1983年 | 4021篇 |
1982年 | 3601篇 |
1981年 | 3761篇 |
1980年 | 3456篇 |
1979年 | 3418篇 |
1978年 | 3225篇 |
1977年 | 3814篇 |
1976年 | 4847篇 |
1975年 | 2780篇 |
1974年 | 2660篇 |
1973年 | 2675篇 |
1972年 | 2215篇 |
1971年 | 1963篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Lumbar and thoracic spinal angles of 25 male and 25 female subjects were measured in four sitting postures, with standing angles used as reference. Subjects sat with either 90 deg or 65 deg of hip flexion on either flat or forward-sloping seats. Lumbar kyphosis was greatest when the flat seat/90-deg posture was adopted and least when the sloping seat/65-deg posture was adopted. The opposite was observed for the thoracic angles, and intermediate results were observed for the other two sitting postures. No statistically significant interactions were observed among seat slope, hip flexion, and subject sex. The findings are discussed with reference to the anatomy of sitting and factors influencing pelvic tilt and the implications for the ergonomic design of chairs. 相似文献
103.
104.
Coarse filters for shape matching 总被引:3,自引:0,他引:3
Corney J. Rea H. Clark D. Pritchard J. Breaks M. Macleod R. 《Computer Graphics and Applications, IEEE》2002,22(3):65-74
This article describes the coarse shape filters that support the 3D, Internet-based search engine ShapeSifter, which aims to locate parts already in production that have a shape similar to a desired new part. The search engine analyzes the target model's shape characteristics and performs a similarity match on the database's contents. Our main challenge is identifying shape metrics that produce effective characterizations of 3D models for similarity comparison. We focus on using three novel convex hull-based indices to carry out a preliminary coarse filtering of candidates prior to more detailed analysis. We also describe the crucial role played by two databases of benchmark objects. Unlike other shape-matching systems, we chose ShapeSifter's architecture (multistep query), 3D representation (triangulated mesh), and implementation (Java3D) to allow deployment online once it matures 相似文献
105.
106.
Nichols M.A. Siegel H.J. Dietz H.G. Quong R.W. Nation W.G. 《Parallel and Distributed Systems, IEEE Transactions on》1991,2(3):290-303
Efficient data layout is an important aspect of the compilation process. A model for the creation of perfect memory maps for large-scale parallel machines capable of user-controlled partitionable single-instruction-multiple data/single-program-multiple data (SIMD/SPMD) operation is developed. The term perfect implies that no memory fragmentation occurs and ensures that the memory map size is kept to a minimum. A major constraint on solving this problem is based on the single program nature of both the SIMD and SPMD modes of parallelism. It is assumed that all processors within the same submachine used identical addresses to access corresponding data items in each of their local memories. Necessary and sufficient conditions are derived for being able to create perfect memory maps, and results are applied to several partitionable interconnection networks 相似文献
107.
108.
The evolution of RFID security 总被引:11,自引:0,他引:11
As RFID technology progresses, security and privacy threats also evolve. By examining RFID's history, we can learn from past mistakes, rediscover successful solutions, and inspire future research. 相似文献
109.
R. Sankarasubramanian C. S. Jog T. A. Abinandanan 《Metallurgical and Materials Transactions A》2002,33(4):1083-1090
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems
under a plane-strain condition with the principal misfit strain components ε*
xx
and ε*
yy
. For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε*
yy
/ε*
xx
. We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For
systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems
with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant
line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness;
moreover, the transition is also forbidden when the particle stiffness is greater than a critical value. 相似文献
110.