全文获取类型
收费全文 | 19669篇 |
免费 | 5298篇 |
国内免费 | 994篇 |
专业分类
电工技术 | 2027篇 |
综合类 | 2617篇 |
化学工业 | 2604篇 |
金属工艺 | 532篇 |
机械仪表 | 1879篇 |
建筑科学 | 875篇 |
矿业工程 | 129篇 |
能源动力 | 346篇 |
轻工业 | 759篇 |
水利工程 | 383篇 |
石油天然气 | 329篇 |
武器工业 | 201篇 |
无线电 | 2415篇 |
一般工业技术 | 969篇 |
冶金工业 | 502篇 |
原子能技术 | 247篇 |
自动化技术 | 9147篇 |
出版年
2024年 | 1篇 |
2023年 | 119篇 |
2022年 | 396篇 |
2021年 | 371篇 |
2020年 | 379篇 |
2019年 | 431篇 |
2018年 | 573篇 |
2017年 | 432篇 |
2016年 | 519篇 |
2015年 | 361篇 |
2014年 | 3662篇 |
2013年 | 2566篇 |
2012年 | 3399篇 |
2011年 | 3654篇 |
2010年 | 3212篇 |
2009年 | 2867篇 |
2008年 | 1096篇 |
2007年 | 290篇 |
2006年 | 233篇 |
2005年 | 200篇 |
2004年 | 173篇 |
2003年 | 178篇 |
2002年 | 138篇 |
2001年 | 151篇 |
2000年 | 90篇 |
1999年 | 79篇 |
1998年 | 82篇 |
1997年 | 67篇 |
1996年 | 33篇 |
1995年 | 42篇 |
1994年 | 32篇 |
1993年 | 30篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Finite element analysis of problems in structural and geotechnical engineering results in linear systems where the unknowns are displacements and rotations at nodes. Although the solution of these systems can be carried out using either direct or iterative methods, in practice the matrices involved are usually very large and sparse (particularly for 3D problems) so an iterative approach is often advantageous in terms of both computational time and memory requirements. This memory saving can be further enhanced if the method used does not require assembly of the full coefficient matrix during the solution procedure. One disadvantage of iterative methods is the need to apply preconditioning to improve convergence. In this paper, we review a range of established element-based preconditioning methods for linear elastic problems and compare their performance with a new method based on preconditioning with element displacement components. This new method appears to offer a significant improvement in performance. 相似文献
12.
Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性 总被引:5,自引:0,他引:5
Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料,可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同,它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0.8at%,分凝系数为0.8,与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0.78相当;用称重法测定其密度为5.00g/cm^3;用稳态纵向热流法测出其室温热导率为12.5W/mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。 相似文献
13.
IRIS/AP型电感耦合等离子体光谱仪激发光源常见故障分析 总被引:1,自引:0,他引:1
本文介绍IRIS/AP型ICP的激发光源(炬管),并较为全面地阐述和分析其不能正常激发点燃的常见故障及其原因。 相似文献
14.
A. Benhamida I. Djeran-Maigre H. Dumontet S. Smaoui 《International Journal of Rock Mechanics and Mining Sciences》2005,42(7-8):996-1005
The modelling of hydromechanical behavior of clayey sediments by homogenization theory is described. The rheological model of clays buried in depth requires a three-dimensional approach and laboratory experiments to quantify the model parameters. An iterative process which can be coupled to any homogenization method is used to model the porous media behavior. Hydromechanical compaction results from oedometric experiments are simulated with the proposed model. 相似文献
16.
D. Knig S. Carvajal-Gonzalez A. M. Downs J. Vassy P. Rigaut 《Journal of microscopy》1991,161(3):405-433
Within the concept of point processes, a review is presented of quantities which can be used in studies of three-dimensional (3-D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3-D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3-D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitable marks. 相似文献
17.
18.
19.
迭代回归法计算T型电位滴定中试液含量 总被引:1,自引:0,他引:1
本文将迭代回归法计算T型电位滴定中,叙述了其原理及数学推导,并运算了一批实验数据,结果表明,该法准确度较高,且不需空白溶液校正。 相似文献
20.
M. E. O'Neill 《Chemical Engineering Communications》1996,148(1):161-182
Few exact solutions of the Stokes equations are known, even for steady or quasi-steady flows, involving finite sized bodies, and numerical techniques generally have to be resorted to for finding solutions. However, quite effective modelling of flows involving complicated boundary geometries is possible using the three-dimensional Stokeslet and rotlet point singularities. Two problems are studied in detail. In the first example, exact solutions for the three-dimensional Stokeslet and rotlet placed axisymmetrically along the axis of a circular disc are found and combined with Brenner's first order interaction formulae to determine the effect of the presence of the disc on the force and torque acting on a particle whose dimensions are small compared with its distance from the disc. The results are compared with those of a full numerical integration of the Stokes equations for a sphere translating towards a disc. In the second example, Brenner's first order wall correction theory is applied to the motion of a particle in a circular cylinder using the exact solutions for a torus translating or rotating in isolation. The theoretical predictions for the drag on a torus settling symmetrically in a circular cylinder are compared with those determined experimentally. 相似文献