全文获取类型
收费全文 | 13689篇 |
免费 | 2084篇 |
国内免费 | 1322篇 |
专业分类
电工技术 | 1057篇 |
综合类 | 1849篇 |
化学工业 | 1244篇 |
金属工艺 | 603篇 |
机械仪表 | 807篇 |
建筑科学 | 1471篇 |
矿业工程 | 265篇 |
能源动力 | 245篇 |
轻工业 | 408篇 |
水利工程 | 367篇 |
石油天然气 | 527篇 |
武器工业 | 237篇 |
无线电 | 2465篇 |
一般工业技术 | 1580篇 |
冶金工业 | 399篇 |
原子能技术 | 83篇 |
自动化技术 | 3488篇 |
出版年
2024年 | 72篇 |
2023年 | 235篇 |
2022年 | 427篇 |
2021年 | 516篇 |
2020年 | 517篇 |
2019年 | 510篇 |
2018年 | 472篇 |
2017年 | 554篇 |
2016年 | 670篇 |
2015年 | 745篇 |
2014年 | 872篇 |
2013年 | 1121篇 |
2012年 | 1051篇 |
2011年 | 1114篇 |
2010年 | 774篇 |
2009年 | 776篇 |
2008年 | 819篇 |
2007年 | 944篇 |
2006年 | 772篇 |
2005年 | 654篇 |
2004年 | 526篇 |
2003年 | 492篇 |
2002年 | 387篇 |
2001年 | 384篇 |
2000年 | 290篇 |
1999年 | 263篇 |
1998年 | 190篇 |
1997年 | 154篇 |
1996年 | 134篇 |
1995年 | 120篇 |
1994年 | 94篇 |
1993年 | 71篇 |
1992年 | 61篇 |
1991年 | 49篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 23篇 |
1987年 | 33篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1976年 | 3篇 |
1963年 | 3篇 |
1961年 | 2篇 |
1959年 | 5篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
71.
文中主要针对多爆炸成型弹丸空爆战斗部,在分析区域识别和占空比识别两种不同扫描准则的基础上,应用蒙特卡洛方法计算了战斗部对目标的毁伤概率.通过仿真计算结果对比分析,获得了不同扫描准则对毁伤概率的影响,结果可为多爆炸成型弹丸空爆战斗部设计和选择使用扫描准则提供参考依据. 相似文献
72.
T. MANN B. W. TVEITEN G. HÄRKEGÅRD 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(2):113-122
The fatigue life of a welded aluminium T‐joint made from beams with rectangular hollow section (RHS) has been predicted using a crack propagation analysis and compared with experimental results from joints with different residual stress levels. To include the effect of the residual stresses, the stress ratio was calculated at the weld toe and, via Walker's equation, introduced into the analysis. How to obtain the Walker exponent has been discussed in detail. The introduction of a stress ratio at the weld toe provides good agreement between the experimentally and analytically found S–N curves. The effect of the residual stress was successfully included in the analysis. 相似文献
73.
74.
震源延迟叠加技术及应用效果 总被引:2,自引:0,他引:2
延迟叠加爆炸是针对高分辨率和深层地震勘探而提出来的一种激发方式。这种激发方式能在保证地震分辨率的前提下有效提高地震波能量 ,在地震波的入射角范围内 ,有效克服非球形炸药激发引起的地震波传播的方向性。应用弹性波动力学对多级延迟爆炸进行理论研究 ,结合实际试验资料 ,研究了延迟爆炸情况下激发参数对地震波能量、主频、频宽等的影响。从几何地震学出发 ,分析了不同时间激发的地震波在地下空间中的干涉情况 ,对其能量传播的方向性进行了研究。理论分析和试验效果表明 ,延迟叠加震源与相同药量的普通震源相比 ,激发地震波的主频高 ,频带宽 ,增强了下传能量 ,降低了次生干扰 ,在高分辨率和深层地震勘探中具有明显的优势。 相似文献
75.
Danny Barash Tamar Schlick Moshe Israeli Ron Kimmel 《Journal of Mathematical Imaging and Vision》2003,19(1):33-48
Operator splitting is a powerful concept used in many diversed fields of applied mathematics for the design of effective numerical schemes. Following the success of the additive operator splitting (AOS) in performing an efficient nonlinear diffusion filtering on digital images, we analyze the possibility of using multiplicative operator splittings to process images from different perspectives.We start by examining the potential of using fractional step methods to design a multiplicative operator splitting as an alternative to AOS schemes. By means of a Strang splitting, we attempt to use numerical schemes that are known to be more accurate in linear diffusion processes and apply them on images. Initially we implement the Crank-Nicolson and DuFort-Frankel schemes to diffuse noisy signals in one dimension and devise a simple extrapolation that enables the Crank-Nicolson to be used with high accuracy on these signals. We then combine the Crank-Nicolson in 1D with various multiplicative operator splittings to process images. Based on these ideas we obtain some interesting results. However, from the practical standpoint, due to the computational expenses associated with these schemes and the questionable benefits in applying them to perform nonlinear diffusion filtering when using long timesteps, we conclude that AOS schemes are simple and efficient compared to these alternatives.We then examine the potential utility of using multiple timestep methods combined with AOS schemes, as means to expedite the diffusion process. These methods were developed for molecular dynamics applications and are used efficiently in biomolecular simulations. The idea is to split the forces exerted on atoms into different classes according to their behavior in time, and assign longer timesteps to nonlocal, slowly-varying forces such as the Coulomb and van der Waals interactions, whereas the local forces like bond and angle are treated with smaller timesteps. Multiple timestep integrators can be derived from the Trotter factorization, a decomposition that bears a strong resemblance to a Strang splitting. Both formulations decompose the time propagator into trilateral products to construct multiplicative operator splittings which are second order in time, with the possibility of extending the factorization to higher order expansions. While a Strang splitting is a decomposition across spatial dimensions, where each dimension is subsequently treated with a fractional step, the multiple timestep method is a decomposition across scales. Thus, multiple timestep methods are a realization of the multiplicative operator splitting idea. For certain nonlinear diffusion coefficients with favorable properties, we show that a simple multiple timestep method can improve the diffusion process. 相似文献
76.
77.
A simple and computationally efficient method of determining the transfer function and other characteristics of systems with multiple inputs and multiple outputs (MIMO systems) described by autoregression equations is proposed. The method is based on the use of the discrete Fourier transformation. The algorithm is highly suitable for computer implementation. The efficiency and simplicity of the method are illustrated using the example of a system with three inputs and three outputs. The proposed concept may be applied to systems described by the autoregression sliding mean. 相似文献
78.
79.
80.
针对MIMO链路ad hoc网络中已有传输调度算法未充分利用MIMO空间复用能力的问题,提出了一种新的传输调度算法.该算法通过考虑MIMO的多流接收能力而有效地减小了调度帧长,通过合理安排节点分配顺序使得节点分配的数据流比较平均,同时,该算法通过允许节点发送多个数据流而高效利用了MIMO的空间复用能力.推导分析了传输调度算法的通过量和时延性能,结果表明,与已有算法相比,采用文中算法可以提高网络的通过量,减小网络的平均时延和最大时延. 相似文献