全文获取类型
收费全文 | 1701篇 |
免费 | 118篇 |
国内免费 | 77篇 |
专业分类
化学 | 124篇 |
晶体学 | 2篇 |
力学 | 22篇 |
综合类 | 13篇 |
数学 | 243篇 |
物理学 | 91篇 |
综合类 | 1401篇 |
出版年
2024年 | 9篇 |
2023年 | 17篇 |
2022年 | 47篇 |
2021年 | 60篇 |
2020年 | 71篇 |
2019年 | 25篇 |
2018年 | 32篇 |
2017年 | 33篇 |
2016年 | 42篇 |
2015年 | 42篇 |
2014年 | 61篇 |
2013年 | 63篇 |
2012年 | 55篇 |
2011年 | 67篇 |
2010年 | 54篇 |
2009年 | 79篇 |
2008年 | 82篇 |
2007年 | 110篇 |
2006年 | 96篇 |
2005年 | 86篇 |
2004年 | 87篇 |
2003年 | 88篇 |
2002年 | 102篇 |
2001年 | 76篇 |
2000年 | 75篇 |
1999年 | 65篇 |
1998年 | 55篇 |
1997年 | 35篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 25篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1896条查询结果,搜索用时 156 毫秒
1.
Patrick Imrie Jianyong Jin 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):149-174
4D printing is an exciting branch of additive manufacturing. It relies on established 3D printing techniques to fabricate objects in much the same way. However, structures which fall into the 4D printed category have the ability to change with time, hence the “extra dimension.” The common perception of 4D printed objects is that of macroscopic single-material structures limited to point-to-point shape change only, in response to either heat or water. However, in the area of polymer 4D printing, recent advancements challenge this understanding. A host of new polymeric materials have been designed which display a variety of wonderful effects brought about by unconventional stimuli, and advanced additive manufacturing techniques have been developed to accommodate them. As a result, the horizons of polymer 4D printing have been broadened beyond what was initially thought possible. In this review, we showcase the many studies which evolve the very definition of polymer 4D printing, and reveal emerging areas of research integral to its advancement. 相似文献
2.
3.
4.
多级制造系统是现代制造业的主要加工方式,系统的每一级的加工速度和加工周期是系统设计的主要决策变量,正确确定这两个变量是系统得到优化的主要目标。本文导出了系统优化的基本模型,它包括系统各级的生产时间、等待时间、生产速度、生产成本以及系统的循环时间、总成本、产品利润和利润率等,并给出了一个应用实例。 相似文献
5.
C.P. Paul P. Ganesh S.K. Mishra P. Bhargava J. Negi A.K. Nath 《Optics & Laser Technology》2007,39(4):800-805
This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility. 相似文献
6.
本文针对单件小批量生产系统 ,建立了模糊优化的动态随机投入产出模型 ,同时给出了该模型的递推解法 ,并用此模型对某单件小批企业在生产计划期的商品量进行了规划 相似文献
7.
8.
制造模式变迁的动力机制及其特征分析 总被引:1,自引:1,他引:0
制造模式变迁过程受制于三类因素,即制造模式现有状态、制造模式的四大基本维度(技术与方法、文化、组织结构以及和谐管理)和外部环境中的随机涨落因素。该过程表现出非平衡相变、对称性破缺、分叉等特征。当新的制造模式形成时,其研发投入、文化、组织结构及其管理、知识调配都须有很大的变动和调整。 相似文献
9.
Manufacturing cell formation using similarity coefficients and a parallel genetic TSP algorithm: Formulation and comparison 总被引:2,自引:0,他引:2
J. BalakrishnanP. D. Jog 《Mathematical and Computer Modelling》1995,21(12):61-73
Many algorithms have been proposed to form manufacturing cells from component routings. However, many of these do not have the capability of solving large problems. We propose a procedure using similarity coefficients and a parallel genetic implementation of a TSP algorithm that is capable of solving large problems of up to 1000 parts and 1000 machines. In addition, we also compare our procedure with many existing procedures using nine well-known problems from the literature.
The results show that the proposed procedure compares well with the existing procedures and should be useful to practitioners and researchers. 相似文献
10.
自由曲面光学产品设计、制造与检测的工艺流程,通常采取试凑法逐次逼近。由于加工 检测 再加工,循环往复,既费时,成本又高,产生了瓶颈问题。为了解决此弊端,本文运用虚拟制造技术,提出光学虚拟制造的基本构想,即虚拟制造系统结构模型,给出光学系统虚拟原型的构成和光学系统成像质量虚拟检测系统的构成,讨论光学成像质量的仿真检测以及敏度分析方法。研究结果表明:运用虚拟制造与检测技术,可缩短研发周期,降低成本,优化工艺并提高产品质量。 相似文献