全文获取类型
收费全文 | 48906篇 |
免费 | 6570篇 |
国内免费 | 3986篇 |
专业分类
电工技术 | 2082篇 |
技术理论 | 1篇 |
综合类 | 6651篇 |
化学工业 | 5519篇 |
金属工艺 | 4272篇 |
机械仪表 | 4140篇 |
建筑科学 | 6507篇 |
矿业工程 | 3706篇 |
能源动力 | 3619篇 |
轻工业 | 1356篇 |
水利工程 | 3823篇 |
石油天然气 | 3876篇 |
武器工业 | 1596篇 |
无线电 | 2081篇 |
一般工业技术 | 4622篇 |
冶金工业 | 1874篇 |
原子能技术 | 892篇 |
自动化技术 | 2845篇 |
出版年
2024年 | 178篇 |
2023年 | 674篇 |
2022年 | 1477篇 |
2021年 | 1659篇 |
2020年 | 1802篇 |
2019年 | 1424篇 |
2018年 | 1398篇 |
2017年 | 1890篇 |
2016年 | 2222篇 |
2015年 | 2348篇 |
2014年 | 3238篇 |
2013年 | 3066篇 |
2012年 | 4312篇 |
2011年 | 4381篇 |
2010年 | 3237篇 |
2009年 | 3288篇 |
2008年 | 2863篇 |
2007年 | 3675篇 |
2006年 | 3206篇 |
2005年 | 2579篇 |
2004年 | 2098篇 |
2003年 | 1701篇 |
2002年 | 1268篇 |
2001年 | 1133篇 |
2000年 | 896篇 |
1999年 | 667篇 |
1998年 | 534篇 |
1997年 | 449篇 |
1996年 | 378篇 |
1995年 | 285篇 |
1994年 | 272篇 |
1993年 | 177篇 |
1992年 | 164篇 |
1991年 | 105篇 |
1990年 | 99篇 |
1989年 | 63篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 27篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1959年 | 12篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
83.
The theoretical-and-experimental investigation has been performed on the stability of smooth cylindrical shells of steel with a single local dent. All the shells manufactured using the same process were tested with the fulfillment of identical conditions for observations and measurements. Theoretical calculations were carried out by the mesh method with the use of the nonlinear theory of shells. A comparison of the experimental and theoretical values of the critical loads has been made. The theoretical-and-experimental approach proposed enables one to evaluate the quality of shells by studying local dents and other specific imperfections. 相似文献
84.
Nanosized partially yttria stabilized zirconia particles, prepared using a co-precipitation method, were reprocessed into agglomerate powders using two methods for plasma spraying. The first method was to make micrometer-sized agglomerates directly following the grinding of the calcined yttria–zirconia agglomerates. The second method was to reconstitute the nanosized particles into micrometer agglomerates using spray drying. The deposition efficiency, porosity, microhardness and average grain size of the deposits made from these two reprocessed powders were studied. Distinct results related to the process parameters were obtained for the two types of powders. The second type of powder was more suitable for plasma spraying than the first one. Using the second type of powder, some unique results distinguished from those of the conventional partially yttria stabilized zirconia powders were observed and an optimized coating with a porosity of 3.8%, Hv0.3 of 953 and mainly consisting of 1–3 μm columnar grains in the columnar direction and smaller than 100 nm in their cross-sections was achieved. 相似文献
85.
Yen-Cho ChenJ.N. Chung 《Computers & Fluids》2003,32(6):795-822
This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (kx=1, kz=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition. 相似文献
86.
水电站引水发电系统无压隧洞中的水力过渡过程是近年来电站设计中出现的一个新课题,特别是流域梯级电站开发中经常遇到。结合工程实例应用扩散法,给出了无压隧洞水力过渡过程数值模拟的基本方程以及上下游及弃水堰等边界附加方程,模拟了弃水堰布置在不同位置下,无压隧洞内的水位变化过程。研究成果和讨论对实际工程应用具有参考意义。 相似文献
87.
88.
工业废水中金属离子对水环境造成污染,并危及人体健康,应准确进行测定.论述了原子吸收分光光度法测定工业废水中金属元素的原理,重点论述了测定Zn的条件、范围、干扰等因素,总结了测定锌的条件及测定结果;实验证明,用原子吸收分光光度法测定工业废水中的Zn元素,可取得较好的结果. 相似文献
89.
Here, we describe the development of a reacting flow multi-species/combustion methodology, implemented as an extension to the differential reduced ejector analysis (DREA) computer program [Mathematical and computer modeling, vol. 31, 2000, p. 21; Appl. Math. Model. 25 (2001) 427; Comput. Math. Appl. 43(10–11); NASA Contractor Report, 1998]. Use of the single fluid IVP solver framework that was developed for the original DREA model has been directly coupled into the combustion formulation. With these modifications, the analysis has an elementary single step reaction Fuel+Oxidizer→Product combustion capability. Though approximate in nature, the simplicity and efficiency of the DREA formulation make it suitable for its original niche, namely design and preliminary design environments where more complex and expensive models may be inappropriate. 相似文献
90.
梁昔明 《中南工业大学学报(英文版)》2005,12(1):93-96
An active set truncated-Newton algorithm (ASTNA) is proposed to solve the large-scale bound constrained sub-problems. The global convergence of the algorithm is obtained and two groups of numerical experiments are made for the various large-scale problems of varying size. The comparison results between ASTNA and the subspace limited memory quasi-Newton algorithm and between the modified augmented Lagrange multiplier methods combined with ASTNA and the modified barrier function method show the stability and effectiveness of ASTNA for simultaneous optimization of distillation column. 相似文献