全文获取类型
收费全文 | 33524篇 |
免费 | 4519篇 |
国内免费 | 2593篇 |
专业分类
电工技术 | 3819篇 |
技术理论 | 5篇 |
综合类 | 4048篇 |
化学工业 | 1798篇 |
金属工艺 | 220篇 |
机械仪表 | 1228篇 |
建筑科学 | 3321篇 |
矿业工程 | 862篇 |
能源动力 | 797篇 |
轻工业 | 1609篇 |
水利工程 | 1504篇 |
石油天然气 | 835篇 |
武器工业 | 516篇 |
无线电 | 6157篇 |
一般工业技术 | 2517篇 |
冶金工业 | 1282篇 |
原子能技术 | 252篇 |
自动化技术 | 9866篇 |
出版年
2024年 | 264篇 |
2023年 | 604篇 |
2022年 | 1073篇 |
2021年 | 1258篇 |
2020年 | 1360篇 |
2019年 | 1189篇 |
2018年 | 1181篇 |
2017年 | 1371篇 |
2016年 | 1594篇 |
2015年 | 1520篇 |
2014年 | 2377篇 |
2013年 | 2650篇 |
2012年 | 2521篇 |
2011年 | 2688篇 |
2010年 | 2033篇 |
2009年 | 2072篇 |
2008年 | 2127篇 |
2007年 | 2310篇 |
2006年 | 1927篇 |
2005年 | 1547篇 |
2004年 | 1216篇 |
2003年 | 1033篇 |
2002年 | 809篇 |
2001年 | 636篇 |
2000年 | 489篇 |
1999年 | 438篇 |
1998年 | 344篇 |
1997年 | 316篇 |
1996年 | 245篇 |
1995年 | 236篇 |
1994年 | 198篇 |
1993年 | 137篇 |
1992年 | 153篇 |
1991年 | 106篇 |
1990年 | 106篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 40篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 57篇 |
1983年 | 27篇 |
1982年 | 45篇 |
1981年 | 39篇 |
1980年 | 24篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1964年 | 4篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
22.
Software plays an increasingly important role in modern safety-critical systems. Although, research has been done to integrate software into the classical probabilistic risk assessment (PRA) framework, current PRA practice overwhelmingly neglects the contribution of software to system risk. Dynamic probabilistic risk assessment (DPRA) is considered to be the next generation of PRA techniques. DPRA is a set of methods and techniques in which simulation models that represent the behavior of the elements of a system are exercised in order to identify risks and vulnerabilities of the system. The fact remains, however, that modeling software for use in the DPRA framework is also quite complex and very little has been done to address the question directly and comprehensively. This paper develops a methodology to integrate software contributions in the DPRA environment. The framework includes a software representation, and an approach to incorporate the software representation into the DPRA environment SimPRA. The software representation is based on multi-level objects and the paper also proposes a framework to simulate the multi-level objects in the simulation-based DPRA environment. This is a new methodology to address the state explosion problem in the DPRA environment. This study is the first systematic effort to integrate software risk contributions into DPRA environments. 相似文献
23.
Rudolf Habison 《International Journal of Project Management》1985,3(3):178-181
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs. 相似文献
24.
25.
Er-Wei Bai Author Vitae 《Automatica》2003,39(9):1521-1530
This paper proposes a frequency domain algorithm for Wiener model identifications based on exploring the fundamental frequency and harmonics generated by the unknown nonlinearity. The convergence of the algorithm is established in the presence of white noise. No a priori knowledge of the structure of the nonlinearity is required and the linear part can be nonparametric. 相似文献
26.
Common sense sometimes predicts events to be likely or unlikely rather than merely possible. We extend methods of qualitative reasoning to predict the relative likelihoods of possible qualitative behaviors by viewing the dynamics of a system as a Markov chain over its transition graph. This involves adding qualitative or quantitative estimates of transition probabilities to each of the transitions and applying the standard theory of Markov chains to distinguish persistent states from transient states and to calculate recurrence times, settling times, and probabilities for ending up in each state. Much of the analysis depends solely on qualitative estimates of transition probabilities, which follow directly from theoretical considerations and which lead to qualitative predictions about entire classes of systems. Quantitative estimates for specific systems are derived empirically and lead to qualitative and quantitative conclusions, most of which are insensitive to small perturbations in the estimated transition probabilities. The algorithms are straightforward and efficient. 相似文献
27.
B. P. PEHRSON J. D. LANDES 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):73-86
The purpose of this study is to examine the current standard fracture toughness test procedure to determine if there could be an easier method to get a JIc value from the test record. The current method for determining JIc involves a detailed computational and construction procedure. The objective in this study is to simplify the analysis for the determination of JIc. The results of this study show that the load and displacement record for a fracture toughness test can be used to directly estimate a JQ value, a provisional value for fracture toughness, JIc. The J value taken at the maximum load point can be used along with an adjustment factor to estimate a JQ value. This JQ estimate is close to the one obtained from the construction procedure of ASTM Standard E 1820. When a unit‐sized specimen is tested, that is, a specimen with a width of 50 mm and a thickness of 25 mm the maximum load point provides a direct estimate of JQ. Other sizes require a size adjustment factor, which is simply a square root relationship between the width of the test specimen and a unit width. The proposed new method of estimating JQ is simple in concept and requires a minimum number of calculations. It appears to produce values of JQ which are comparable to those obtained from the ASTM E1820 construction procedure and may produce less scatter. 相似文献
28.
Lussier Isabelle; Derevensky Jeffrey L.; Gupta Rina; Bergevin Tanya; Ellenbogen Stephen 《Canadian Metallurgical Quarterly》2007,21(2):165
The study of resilient children has overturned many deficit-focused models concerning the ontogenesis of children raised in adversity. This study explored the relationship between risk and protective factors, resilience, and youth gambling behavior. More specifically, this study examined the relative contribution of various risk and protective domains in relation to problem gambling behavior and examined whether youth identified as resilient (high risk exposure- high internalized protection) were as likely as those identified as vulnerable (high risk exposure-low internalized protection) to engage in excessive gambling behavior. The sample consisted of 1,273 students ages 12 to 19. The findings demonstrated that risk and protective factors each provide a unique contribution to the prediction model of gambling problems. Resilient and vulnerable youth differed significantly in their self-reported gambling severity. As well, resilient youth were not statistically distinguishable from low-risk exposure groups in terms of their gambling severity. Findings are interpreted with respect to resilience and prevention research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
利用多普勒信息的波达方向最大似然估计方法 总被引:11,自引:3,他引:8
为了充分利用信号的时域特性来改善信号波达方向(DOA)的估计性能,本文从最大似然估计出发,推导出了有限快拍,低信噪比情况下多普勒信号波达方向的迭代估计计算法,为进一步减小运算量,本文还推导了一种简化算法,本文提出的两种算法对低信噪比,少快拍数下多普勒信号的DOA估计性能比不利用时域特性的ML方法有明显改善,Monte-Carlo实验验证了本文方法的有效性。 相似文献
30.
本文提出生种新的带限信号的外推方法,该方法能够很好地抑制噪声干扰,且计算复杂性较低,本文给出算法,证明了收敛性,最后给出了误差计算机实验结果。 相似文献