全文获取类型
收费全文 | 5417篇 |
免费 | 652篇 |
国内免费 | 589篇 |
专业分类
电工技术 | 423篇 |
综合类 | 642篇 |
化学工业 | 151篇 |
金属工艺 | 56篇 |
机械仪表 | 227篇 |
建筑科学 | 303篇 |
矿业工程 | 72篇 |
能源动力 | 116篇 |
轻工业 | 40篇 |
水利工程 | 235篇 |
石油天然气 | 147篇 |
武器工业 | 71篇 |
无线电 | 639篇 |
一般工业技术 | 322篇 |
冶金工业 | 124篇 |
原子能技术 | 37篇 |
自动化技术 | 3053篇 |
出版年
2024年 | 19篇 |
2023年 | 69篇 |
2022年 | 75篇 |
2021年 | 97篇 |
2020年 | 114篇 |
2019年 | 141篇 |
2018年 | 102篇 |
2017年 | 145篇 |
2016年 | 154篇 |
2015年 | 180篇 |
2014年 | 246篇 |
2013年 | 292篇 |
2012年 | 311篇 |
2011年 | 362篇 |
2010年 | 309篇 |
2009年 | 356篇 |
2008年 | 384篇 |
2007年 | 479篇 |
2006年 | 369篇 |
2005年 | 358篇 |
2004年 | 285篇 |
2003年 | 262篇 |
2002年 | 220篇 |
2001年 | 160篇 |
2000年 | 150篇 |
1999年 | 136篇 |
1998年 | 118篇 |
1997年 | 130篇 |
1996年 | 110篇 |
1995年 | 84篇 |
1994年 | 96篇 |
1993年 | 75篇 |
1992年 | 47篇 |
1991年 | 50篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有6658条查询结果,搜索用时 15 毫秒
21.
22.
This study examined how 1 symbol is selected to control the allocation of attention when several symbols appear in the visual field. In Experiments 1-3, the critical target feature was color, and it was found that uninformative central arrows that matched the color of the target were selected and produced unintentional shifts of attention (i.e., involuntary, initiated slowly, producing long-lasting facilitatory effects). Experiment 4 tested whether such selection is the result of an attentional filter or of a competition bias due to a match of incoming information against integrated object representations stored in working memory. Here, the critical feature was shape and color was irrelevant, but matching color arrows were still selected. Thus, features of objects in working memory will bias the selection of symbols in the visual field, and such selected symbols are capable of producing unintentional shifts of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
23.
Oded Goldreich 《Distributed Computing》2003,16(2-3):177-199
We survey the paradigms, approaches and techniques used to conceptualize, define and provide solutions to natural cryptographic problems. We start by presenting some of the central tools (e.g., computational difficulty, pseudorandomness, and zero-knowledge proofs), and next turn to the treatment of encryption and signature schemes. We conclude with an extensive treatment of secure cryptographic protocols both when executed in a stand-alone manner and when many sessions of various protocols are concurrently executed and controlled by an adversary. The survey is intended for researchers in distributed computing, and assumes no prior familiarity with cryptography.Received: June 2001, Accepted: July 2002, 相似文献
24.
一种新的基于极大似然估计的系统辨识方法 总被引:1,自引:0,他引:1
进化计算是一种基于自然选择和自然变异机制的并行随机优化算法。由于递推极大似然估计法难以实现性能指标函数的全局寻优,所以本文提出了将改进的进化计算用于系统参数辨识的方法。计算机仿真结果表明,该算法能够实现似然函数的全局寻优。 相似文献
25.
The paper proposes and describes several tools enabling their user to estimate the efficiency of Pascal or C-like programs. The approach consists of generating symbolic formulas expressing the efficiency of the programs being analyzed. The formulas are applicable to a variety of compiler-machine configurations. The actual numeric values of the variables in the symbolic formula are determined using linear programming techniques. The proposed approach reduces considerably the amount of benchmarking needed to analyze programs. Several examples are presented showing the applicability of the tools. The effort necessary to implement them is considerably reduced by the combined usage of Prolog and a symbolic formula manipulation package (Maple). 相似文献
26.
气化炉自动建模系统研究 总被引:1,自引:0,他引:1
为了减轻建模人员在建模公式推导、逻辑关系推导和编制仿真程序的工作量,设计了气化炉自动建模系统。该系统在反应物为多种气体、多种固体(均考虑为单筛分)的条件下,按照小室模型的框架自动列写相应各个物质的质量、能量平衡方程,并自动生成相应的计算机程序,方便仿真计算。由于该系统避开了工程中常用的纯数值建模的思路,采用了新的数学工具-以符号运算特长的计算机代数系统为计算平台,才使得该系统具有强大的逻辑关系推导能力。该系统在某气化炉的建模过程中得到了验证和示范,事实表明:该系统大大减少了气化炉的建模工作量,特别是减少由于化学反应假定的不同带来的建模复杂性,对于建模与仿真研究新方法的突破有所贡献。 相似文献
27.
28.
横流均匀环境中三维线源型正负浮力射流特性研究 总被引:2,自引:2,他引:0
本文利用混合有限分析法及交错网格。对横流均匀环境中三维线源型正负浮力射流及负浮力射流的特性进行研究,分析了不同工况下流速,温度和湍动能在断面上的分布及影响射流轨迹线的因素,讨论了轨迹线上温度的变化及浮力射流的贴壁现象。对三维长线源型负浮力射流,分析了流速比,喷口弗汝德数对负浮力射流的影响。 相似文献
29.
The paper presents a computational approach and numerical data which facilitate the use of the smeared-tip method for cohesive fracture in large enough structures. In the recently developed K-version of the smeared tip method, the large-size asymptotic profile of the stress intensity factor density along a cohesive crack is considered as a material characteristic, which is uniquely related to the softening stress-displacement law of the cohesive crack. After reviewing the K-version, an accurate and efficient numerical algorithm for the computation of this asymptotic profile is presented. The algorithm is based on solving a singular Abel's integral equation. The profiles corresponding to various typical softening stress-displacement laws of the cohesive crack model are computed, tabulated and plotted. The profiles for a certain range of other typical softening laws can be approximately obtained by interpolation from the tables. Knowing the profile, one can obtain with the smeared-tip method an analytical expression for the large-size solution to fracture problems, including the first two asymptotic terms of the size effect law. Consequently, numerical solutions of the integral equations of the cohesive crack model as well as finite element simulations of the cohesive crack are made superfluous. However, when the fracture process zone is attached to a notch or to the body surface and the cohesive zone ends with a stress jump, the solution is expected to be accurate only for large-enough structures. 相似文献
30.
Frank G. Pagan 《Software》1988,18(6):509-527
There is an effective and quite general method of manually deriving compilers from programming-language interpreters without dealing directly with machine language. The method is an implementation of the largely theoretical and under-appreciated concept of partial computation, but can be understood on its own terms. It involves the translation of a source program's intermediate form into the interpreter's implementation language. This paper shows how the method can be used to transform both a sample iterative interpreter and a sample recursive interpreter into compilers. The result can be a large gain in program execution speed. Other advantages of the method, including the ease and practicality of applying it, are discussed. 相似文献