全文获取类型
收费全文 | 150699篇 |
免费 | 22801篇 |
国内免费 | 15096篇 |
学科分类
工业技术 | 188596篇 |
出版年
2024年 | 1113篇 |
2023年 | 3010篇 |
2022年 | 5075篇 |
2021年 | 5649篇 |
2020年 | 6298篇 |
2019年 | 5353篇 |
2018年 | 5205篇 |
2017年 | 6117篇 |
2016年 | 6841篇 |
2015年 | 7710篇 |
2014年 | 10714篇 |
2013年 | 10794篇 |
2012年 | 12156篇 |
2011年 | 12767篇 |
2010年 | 9714篇 |
2009年 | 10101篇 |
2008年 | 10004篇 |
2007年 | 10880篇 |
2006年 | 9037篇 |
2005年 | 7490篇 |
2004年 | 6050篇 |
2003年 | 4875篇 |
2002年 | 3898篇 |
2001年 | 3107篇 |
2000年 | 2649篇 |
1999年 | 2066篇 |
1998年 | 1727篇 |
1997年 | 1457篇 |
1996年 | 1175篇 |
1995年 | 982篇 |
1994年 | 821篇 |
1993年 | 641篇 |
1992年 | 579篇 |
1991年 | 407篇 |
1990年 | 377篇 |
1989年 | 338篇 |
1988年 | 238篇 |
1987年 | 109篇 |
1986年 | 143篇 |
1985年 | 109篇 |
1984年 | 103篇 |
1983年 | 84篇 |
1982年 | 89篇 |
1981年 | 59篇 |
1980年 | 62篇 |
1979年 | 50篇 |
1978年 | 42篇 |
1977年 | 37篇 |
1959年 | 26篇 |
1955年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Dmitri E. Nikonov George I. Bourianoff Paolo A. Gargini 《Journal of Superconductivity and Novel Magnetism》2006,19(6):497-513
Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron
in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots are
described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to
a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ∼kT per bit,
if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic
device are provided. 相似文献
72.
E. GLASER 《Journal of microscopy》2005,218(1):1-5
It is well known that the estimation of an object's volume by means of serial cross-sections, the so-called Cavalieri method, yields an unbiased estimate. But by itself it provides no means by which to estimate how precise this estimate is unless the shape of the volume is fully known beforehand. This knowledge can only be partially determined from the serial section information that is collected. Methods have been developed that claim to surmount this difficulty by using the serial section data to create a mathematical model of the volume's shape properties. The model then is used to estimate (predict) the precision of the volume estimate (its CE) from the single set of data available. Unfortunately, the theory underlying the model is flawed and so the model itself amounts to no more than an unsubstantiated guess about the shape of the volume. Therefore, the precision of the volume estimates that one obtains from the method is only as good as the model and this cannot be ascertained from the single set of acquired data. In this letter I explain the inadequacies of the modelling method. I suggest that it be used only with caution, if at all. Instead I suggest two alternative ways to predict the CE, one that is based upon a rule-of-thumb approach to the object's shape, and another that is based upon spectral analysis of the measurement function and that is easy to implement with available computer software. 相似文献
73.
74.
This paper attempts to shed light on the determinants of energy demand in Turkey. Energy demand model is first proposed using the ant colony optimization (ACO) approach. It is multi-agent systems in which the behavior of each ant is inspired by the foraging behavior of real ants to solve optimization problem. ACO energy demand estimation (ACOEDE) model is developed using population, gross domestic product (GDP), import and export. All equations proposed here are linear and quadratic. Quadratic_ACOEDE provided better-fit solution due to fluctuations of the economic indicators. The ACOEDE model plans the energy demand of Turkey until 2025 according to three scenarios. The relative estimation errors of the ACOEDE model are the lowest when they are compared with the Ministry of Energy and Natural Resources (MENR) projection. 相似文献
75.
郑文新 《水科学与工程技术》2007,(4):25-27
黑河水利枢纽右岸溢洪洞为缩短引渠左导墙的长度,减少施工开挖量,降低施工难度,减少工程投资,进行优化试验.通过对7种不同的方案对比分析,选择了合适的体型,满足了工程要求. 相似文献
76.
模糊规划在炼油厂生产计划优化中的应用 总被引:7,自引:1,他引:6
生产计划的编制是炼油化工企业生产经营管理中的一个关键环节,然而由于市场变化的不确定性,使得企业的长远规划制定受到限制,笔者将模糊数学应用于炼厂生产计划的编制,通过模糊规划对炼油企业生产计划进行优化,使编得的生产计划在一定程度上反映市场的变化并使企业的生产效益最优,为企业管理决策者进行长期规划给予指导,给出了实例来说明该方法的可行性。 相似文献
77.
78.
79.
Many real-world problems are multi-objective optimization problems and evolutionary algorithms are quite successful on such problems. Since the task is to compute or approximate the Pareto front, multi-objective optimization problems are considered as more difficult than single-objective problems. One should not forget that the fitness vector with respect to more than one objective contains more information that in principle can direct the search of evolutionary algorithms. Therefore, it is possible that a single-objective problem can be solved more efficiently via a generalized multi-objective model of the problem. That this is indeed the case is proved by investigating the computation of minimum spanning trees.This work was supported by the Deutsche Forschungsgemeinschaft (DFG) as part of the Collaborative Research Center Computational Intelligence (SFB 531) and by the German-Israeli Foundation (GIF) in the project Robustness Aspects of Algorithms. 相似文献
80.
测井岩性识别是石油勘探中十分重要的基础工作,准确的岩性识别结果可以为勘探和开发提供可靠的依据。人工神经网络方法可对复杂的高维数据进行非线性映射,在模式识别领域得到越来越广泛的应用。针对传统的BP神经网络算法存在收敛速度慢、隐层数以及隐层节点数难以确定等缺点,研究了一种构造性神经网络学习算法---级联算法(Cascade Correlation Algorithm,简称CC算法)及其在石油工程中的应用。采用该算法对甘肃镇原-泾川地区进行岩性识别研究,通过与BP神经网络的识别结果进行比较,体现出构造性神经网络的优越性。 相似文献