全文获取类型
收费全文 | 7722篇 |
免费 | 636篇 |
国内免费 | 314篇 |
专业分类
电工技术 | 184篇 |
技术理论 | 1篇 |
综合类 | 689篇 |
化学工业 | 706篇 |
金属工艺 | 551篇 |
机械仪表 | 370篇 |
建筑科学 | 834篇 |
矿业工程 | 282篇 |
能源动力 | 154篇 |
轻工业 | 933篇 |
水利工程 | 99篇 |
石油天然气 | 126篇 |
武器工业 | 38篇 |
无线电 | 357篇 |
一般工业技术 | 1656篇 |
冶金工业 | 758篇 |
原子能技术 | 226篇 |
自动化技术 | 708篇 |
出版年
2024年 | 18篇 |
2023年 | 93篇 |
2022年 | 199篇 |
2021年 | 232篇 |
2020年 | 245篇 |
2019年 | 220篇 |
2018年 | 186篇 |
2017年 | 237篇 |
2016年 | 240篇 |
2015年 | 208篇 |
2014年 | 420篇 |
2013年 | 518篇 |
2012年 | 483篇 |
2011年 | 530篇 |
2010年 | 451篇 |
2009年 | 461篇 |
2008年 | 424篇 |
2007年 | 447篇 |
2006年 | 391篇 |
2005年 | 364篇 |
2004年 | 368篇 |
2003年 | 293篇 |
2002年 | 270篇 |
2001年 | 199篇 |
2000年 | 172篇 |
1999年 | 147篇 |
1998年 | 111篇 |
1997年 | 106篇 |
1996年 | 114篇 |
1995年 | 116篇 |
1994年 | 74篇 |
1993年 | 73篇 |
1992年 | 45篇 |
1991年 | 53篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有8672条查询结果,搜索用时 17 毫秒
101.
应用电感耦合等离子体发射光谱仪(ICP-AES),不经消解直接测定8种白酒中的Al,As,B,Ba,Be,Ca,Cd,Co,Cr,Cu,Fe,K,Li,Mg,Mn,Mo,Na,Ni,Pb,Pd,S,Sb,Si,Sr,Ti,V,W,Zn元素并对方法的仪器条件进行了优化。与传统的消解方法进行比较,实验结果表明本方法的测定结果与消解的测定结果基本一致。本方法各元素线性相关系数均大于0.9995,加标回收率在94%~105%之间。本方法不需要消解,大大提高了样品的测试速度并且节省人力物力。本实验为白酒品质的鉴定提供实验数据。 相似文献
102.
103.
Time‐domain hybrid formulations for wave simulations in three‐dimensional PML‐truncated heterogeneous media 下载免费PDF全文
Arash Fathi Babak Poursartip Loukas F. Kallivokas 《International journal for numerical methods in engineering》2015,101(3):165-198
We are concerned with the numerical simulation of wave motion in arbitrarily heterogeneous, elastic, perfectly‐matched‐layer‐(PML)‐truncated media. We extend in three dimensions a recently developed two‐dimensional formulation, by treating the PML via an unsplit‐field, but mixed‐field, displacement‐stress formulation, which is then coupled to a standard displacement‐only formulation for the interior domain, thus leading to a computationally cost‐efficient hybrid scheme. The hybrid treatment leads to, at most, third‐order in time semi‐discrete forms. The formulation is flexible enough to accommodate the standard PML, as well as the multi‐axial PML. We discuss several time‐marching schemes, which can be used à la carte, depending on the application: (a) an extended Newmark scheme for third‐order in time, either unsymmetric or fully symmetric semi‐discrete forms; (b) a standard implicit Newmark for the second‐order, unsymmetric semi‐discrete forms; and (c) an explicit Runge–Kutta scheme for a first‐order in time unsymmetric system. The latter is well‐suited for large‐scale problems on parallel architectures, while the second‐order treatment is particularly attractive for ready incorporation in existing codes written originally for finite domains. We compare the schemes and report numerical results demonstrating stability and efficacy of the proposed formulations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
104.
A. Alhadeff W. Celes G. H. Paulino 《International journal for numerical methods in engineering》2015,103(12):859-893
A graphics processor units(GPU)‐based computational framework is presented to deal with dynamic failure events simulated by means of cohesive zone elements. The work is divided into two parts. In the first part, we deal with pre‐processing of the information and verify the effectiveness of dynamic insertion of cohesive elements in large meshes in parallel. To this effect, we employ a novel and simplified topological data structure specialized for meshes with triangles, designed to run efficiently and minimize memory occupancy on the GPU. In the second part, we present a parallel explicit dynamics code that implements an extrinsic cohesive zone formulation where the elements are inserted ‘on‐the‐fly’, when needed and where needed. The main challenge for implementing a GPU‐based computational framework using an extrinsic cohesive zone formulation resides on being able to dynamically adapt the mesh, in a consistent way, by inserting cohesive elements on fractured facets. In order to handle that, we extend the conventional data structure used in the finite element method (based on element incidence) and store, for each element, references to the adjacent elements. This additional information suffices to consistently insert cohesive elements by duplicating nodes when needed. Currently, our data structure is specialized for triangular meshes, but an extension to tetrahedral meshes is feasible. The data structure is effective when used in conjunction with algorithms to traverse nodes and elements. Results from parallel simulations show an increase in performance when adopting strategies such as distributing different jobs among threads for the same element and launching many threads per element. To avoid concurrency on accessing shared entities, we employ graph coloring. In a pre‐processing phase, each node of the dual graph (bulk elements of the mesh as graph nodes) is assigned a color different from the colors assigned to adjacent nodes. In that fashion, elements of the same color can be processed in parallel without concurrency. All the procedures needed for the insertion of cohesive elements along fracture facets and for computing nodal properties are performed by threads assigned to triangles, invoking one kernel per color. Computations on existing cohesive elements are also performed based on adjacent bulk elements. Experiments show that GPU speedup increases with the number of nodes and bulk elements. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
105.
Combined continuum damage‐embedded discontinuity model for explicit dynamic fracture analyses of quasi‐brittle materials 下载免费PDF全文
Timo Saksala Delphine Brancherie Isaac Harari Adnan Ibrahimbegovic 《International journal for numerical methods in engineering》2015,101(3):230-250
In this paper, a novel constitutive model combining continuum damage with embedded discontinuity is developed for explicit dynamic analyses of quasi‐brittle failure phenomena. The model is capable of describing the rate‐dependent behavior in dynamics and the three phases in failure of quasi‐brittle materials. The first phase is always linear elastic, followed by the second phase corresponding to fracture‐process zone creation, represented with rate‐dependent continuum damage with isotropic hardening formulated by utilizing consistency approach. The third and final phase, involving nonlinear softening, is formulated by using an embedded displacement discontinuity model with constant displacement jumps both in normal and tangential directions. The proposed model is capable of describing the rate‐dependent ductile to brittle transition typical of cohesive materials (e.g., rocks and ice). The model is implemented in the finite element setting by using the CST elements. The displacement jump vector is solved for implicitly at the local (finite element) level along with a viscoplastic return mapping algorithm, whereas the global equations of motion are solved with explicit time‐stepping scheme. The model performance is illustrated by several numerical simulations, including both material point and structural tests. The final validation example concerns the dynamic Brazilian disc test on rock material under plane stress assumption. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
106.
107.
108.
对钼精矿加工钼酸铵生产工艺流程进行了钼元素的查定,采用生产统计结合化学分析及物相鉴定方法,弄清各工序钼收率及影响其收率的因素,并根据查定结果对现有流程提出优化改进的建议。 相似文献
109.
在乡村旅游迅速发展的同时,乡村地区开始显现出乡村景观的无序化开发和城市化倾向,根据游客行为特征,合理进行规划和建设,才能引导乡村旅游的可持续健康发展。以汉中市乡村旅游地为例,以马蜂窝UGC数据为数据样本,通过GIS时空分析技术对数据信息进行时间和空间上的处理与表达,继而分析乡村旅游游客行为的时空特征及影响因素。研究表明:1)乡村游客出游呈现春秋旺、夏冬淡的时间特征,其兴趣点分布呈一核多点式的空间分布特征,以及以古村镇、历史遗址与乡村自然风光类景点为导向的空间偏好特征;2)空间分布对于道路的依赖性较强,使得交通不太便利的镇巴等区域游客聚集程度低,而景点距离市区的远近对游客行为影响不大,提升景点吸引力才是关键。基于以上研究基础,为乡村旅游的空间规划及未来的保护利用和建设管理提供建议。 相似文献
110.
新村空间设计语汇模块化是村落景观设计较为普遍的现象,也是地域特征弱化和空间不契合空间行为等问题的主要原因之一。古村落宅间元素是村民日常生活与村落环境在相互影响下长期适应性发展的结果,宅间元素模式研究可促进丰富新村空间设计语汇。以徽州地区古村落为例,从宅间元素的分类、图示、与空间行为的关联3个方面论述了古村落宅间元素模式研究方法论。通过徽州茆田新村景观设计阐述了宅间元素模式的应用,论述了基于古村落宅间元素模式的村落景观设计优化策略,有益于形成并推广地方空间设计语汇,避免过度依赖和使用既有的、来自城市的广场、草坪、树池等元素造成的全国村落的无差别设计。 相似文献