全文获取类型
收费全文 | 38434篇 |
免费 | 3503篇 |
国内免费 | 2703篇 |
专业分类
电工技术 | 2567篇 |
技术理论 | 4篇 |
综合类 | 4493篇 |
化学工业 | 2598篇 |
金属工艺 | 1724篇 |
机械仪表 | 2542篇 |
建筑科学 | 4580篇 |
矿业工程 | 1273篇 |
能源动力 | 841篇 |
轻工业 | 1116篇 |
水利工程 | 1235篇 |
石油天然气 | 1049篇 |
武器工业 | 256篇 |
无线电 | 4241篇 |
一般工业技术 | 4384篇 |
冶金工业 | 1387篇 |
原子能技术 | 508篇 |
自动化技术 | 9842篇 |
出版年
2024年 | 118篇 |
2023年 | 443篇 |
2022年 | 727篇 |
2021年 | 865篇 |
2020年 | 1052篇 |
2019年 | 959篇 |
2018年 | 903篇 |
2017年 | 1165篇 |
2016年 | 1312篇 |
2015年 | 1373篇 |
2014年 | 2557篇 |
2013年 | 2437篇 |
2012年 | 2934篇 |
2011年 | 2796篇 |
2010年 | 2185篇 |
2009年 | 2364篇 |
2008年 | 2381篇 |
2007年 | 2664篇 |
2006年 | 2450篇 |
2005年 | 2091篇 |
2004年 | 1698篇 |
2003年 | 1544篇 |
2002年 | 1231篇 |
2001年 | 1218篇 |
2000年 | 973篇 |
1999年 | 708篇 |
1998年 | 587篇 |
1997年 | 479篇 |
1996年 | 401篇 |
1995年 | 353篇 |
1994年 | 312篇 |
1993年 | 240篇 |
1992年 | 200篇 |
1991年 | 162篇 |
1990年 | 143篇 |
1989年 | 145篇 |
1988年 | 103篇 |
1987年 | 57篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1964年 | 10篇 |
1963年 | 9篇 |
1961年 | 10篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Given a scalar, stationary, Markov process, this short communication presents a closed-form solution for the first-passage problem for a fixed threshold b. The derivation is based on binary processes and the general formula of Siegert [Siegert AJF. On the first-passage time probability problem. Physical Review 1951; 81:617–23]. The relation for the probability density function of the first-passage time is identical to the commonly used formula that was derived by VanMarcke [VanMarcke E. On the distribution of the first-passage time for normal stationary random processes. Journal of Applied Mechanics ASME 1975; 42:215–20] for Gaussian processes. The present derivation is based on more general conditions and reveals the criteria for the validity of the approximation. Properties of binary processes are also used to derive a hierarchy of upper bounds for any scalar process. 相似文献
72.
The effect of a prior gist-based versus item-specific retrieval orientation on recognition of objects and words was examined. Prior item-specific retrieval increased item-specific recognition of episodically related but not previously tested objects relative to both conceptual- and perceptual-gist retrieval. An item-specific retrieval advantage also was found when the stimuli were words (synonyms) rather than objects but not when participants overtly named objects during gist-based recognition testing, which suggests that they did not always label objects under general gist-retrieval instructions. Unlike verbal overshadowing, labeling objects during recognition attenuated (but did not eliminate) test- and interference-related forgetting. A full understanding of how retrieval affects subsequent memory, even for events or facts that are not themselves retrieved, must take into account the specificity with which that retrieval occurs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
杨友龙 《数字社区&智能家居》2007,2(6):1400-1400
随着计算机性能的提高,计算机模拟技术日益复杂,在研究使用计算机模拟洪水的演进,以期给出准确的预警,最大限度减少损失和人员伤亡方面也取得一定进步。本文尝试用MATLAB程序模拟溃坝洪水,并在最后给出一个算例。 相似文献
74.
A novel current source inverter system interconnected to the single‐phase grid is proposed. It has the same construction as the conventional three‐phase current source inverter that is interconnected to the single‐phase three‐wire distribution system. Though the proposed circuit has no output transformer, it can be equivalently performed as the single‐phase double cascade inverter by diverting the pole transformer in the utility system. By controlling the appropriate scheme, the output currents can be obtained as the five‐level waveforms and their distortions can be decreased sufficiently. It is applied to the interactive electric energy storage system with batteries and the basic discharging characteristics are discussed experimentally. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10380 相似文献
75.
After a series of earthquakes in 1999, Turkish Red Crescent (TRC) has engaged in a restructuring for all of its activities, including the blood services. Our study on the blood management system had been started as part of this initiative to restructure the blood services and improve both their effectiveness and efficiency. In the current system of TRC, not much consideration has been given to how the locational decisions affect the performance of blood centers, stations and mobile units. In recent years, however, there has been much discussion regarding the regionalization of the blood management system in Turkey. In this study, we develop several mathematical models to solve the location–allocation decision problems in regionalization of blood services. We report our computational results, obtained by using real data, for TRC blood services. 相似文献
76.
秀卢瑟福背散射-沟道技术(RBS-C)和X射线衍射技术(XRD)研究了Pt和注入YSZ(Y2O3稳定的ZrO2)后产生的损伤和退火过程中损伤的恢复及注入Pt的晶化,RBS-C分析表明YSZ室温下的存在较强自退火效应,XRD分析结果示出硫以铂的晶化产生很大影响。 相似文献
77.
Fast parallel Preconditioned Conjugate Gradient algorithms for robot manipulator dynamics simulation
In this paper fast parallel Preconditioned Conjugate Gradient (PCG) algorithms for robot manipulator forward dynamics, or dynamic simulation, problem are presented. By exploiting the inherent structure of the forward dynamics problem, suitable preconditioners are devised to accelerate the iterations. Also, based on the choice of preconditioners, a modified dynamic formulation is used to speedup both serial and parallel computation of each iteration. The implementation of the parallel algorithms on two interconnected processor arrays is discussed and their computation and communication complexities are analyzed. The simulation results for a Puma Arm are presented to illustrate the effectiveness of the proposed preconditioners. With a faster convergence due to preconditioning and a faster computation of iterations due to parallelization, the developed parallel PCG algorithms represent the fastest alternative for parallel computation of the problem withO(n) processors. 相似文献
78.
We consider the problem of finding a shortest watchman route from which the exterior of a polygon is visible (external watchman route). We present an O (n
4 log logn) algorithm to find shortest external watchman routes for simple polygons by transforming the external watchman route problem to a set of internal watchman route problems. Also, we present faster external watchman route algorithms for special cases. These include optimal O (n) algorithms for convex, monotone, star and spiral polygons and an O (n log logn) algorithm for rectilinear polygons.This work was supported in part by a grant from Texas Instruments, Inc. to S. Ntafos 相似文献
79.
层次式级联多网络模型及其性能 总被引:1,自引:1,他引:0
本文提出了一种层次式级联多网络结构,论述了其训练算法,并验证了该结构的收敛性。这种结构在处理高阶非线性分布数据的分类问题方面具有优良的性能,用北京谱仪事例过滤进行性能测试结果表明,其训练和泛化性能都优于单个BP网络。 相似文献
80.