全文获取类型
收费全文 | 28066篇 |
免费 | 3659篇 |
国内免费 | 1628篇 |
专业分类
电工技术 | 7857篇 |
综合类 | 3232篇 |
化学工业 | 1129篇 |
金属工艺 | 620篇 |
机械仪表 | 2158篇 |
建筑科学 | 6097篇 |
矿业工程 | 948篇 |
能源动力 | 1547篇 |
轻工业 | 304篇 |
水利工程 | 1177篇 |
石油天然气 | 615篇 |
武器工业 | 249篇 |
无线电 | 1230篇 |
一般工业技术 | 2041篇 |
冶金工业 | 784篇 |
原子能技术 | 135篇 |
自动化技术 | 3230篇 |
出版年
2024年 | 66篇 |
2023年 | 401篇 |
2022年 | 784篇 |
2021年 | 869篇 |
2020年 | 973篇 |
2019年 | 806篇 |
2018年 | 793篇 |
2017年 | 1004篇 |
2016年 | 1048篇 |
2015年 | 1194篇 |
2014年 | 1930篇 |
2013年 | 1561篇 |
2012年 | 2154篇 |
2011年 | 2382篇 |
2010年 | 1763篇 |
2009年 | 1837篇 |
2008年 | 1767篇 |
2007年 | 2040篇 |
2006年 | 1818篇 |
2005年 | 1509篇 |
2004年 | 1203篇 |
2003年 | 1042篇 |
2002年 | 835篇 |
2001年 | 707篇 |
2000年 | 553篇 |
1999年 | 504篇 |
1998年 | 295篇 |
1997年 | 289篇 |
1996年 | 265篇 |
1995年 | 211篇 |
1994年 | 176篇 |
1993年 | 104篇 |
1992年 | 81篇 |
1991年 | 63篇 |
1990年 | 71篇 |
1989年 | 67篇 |
1988年 | 63篇 |
1987年 | 30篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1961年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 398 毫秒
61.
以淮河南岸一级阶地某高层建筑采用CFG桩复合地基工程实例,通过利用工程地质参数复核计算、静载荷试验、沉降观测等验证资料,来探讨说明CFG桩复合地基在该区高层建筑使用的安全适用性。 相似文献
62.
With the growing use of renewable energy sources, Distributed Generation (DG) systems are rapidly spreading. Embedding DG to the distribution network may be costly due to the grid reinforcements and control adjustments required in order to maintain the electrical network reliability. Deterministic load flow calculations are usually employed to assess the allowed DG penetration in a distribution network in order to ensure that current or voltage limits are not exceeded. However, these calculations may overlook the risk of limit violations due to uncertainties in the operating conditions of the networks. To overcome this limitation, related to both injection and demand profiles, the present paper addresses the problem of DG penetration with a Monte Carlo technique that accounts for the intrinsic variability of electric power consumption. The power absorbed by each load of a medium voltage network is characterized by a load variation curve; a probabilistic load flow is then used for computing the maximum DG power that can be connected to each bus without determining a violation of electric constraints. A distribution network is studied and a comparison is provided between the results of the deterministic load flow and probabilistic load flow analyses. 相似文献
63.
The paper presents a spatial analysis of points especially suited to estimate a preference map for new consumers, which is then used as an analytical tool in spatial electric load forecasting. This approach is an exploratory spatial data analysis used to discover useful point patterns in the spatial location of distribution transformers to calculate a preference value for each area, rating it with respect to a hypothetical load change that may occur. We consider the locations of distribution transformers occupied land. Random points are generated in the study area where the new loads are expected; these points are referred to as unoccupied land. The method uses a generalized additive model (GAM) to estimate the probability of unoccupied land becoming occupied land. We test the approach with data from a real distribution system in a mid-size city in Brazil; the result is a preference map that shows the areas where new consumers are most likely to be allocated. The main advantage of this method is the ability work with a small-scale resolution, which enables the use of a resolution suitable for spatial load forecasting method chosen. We test the calculated probabilities in a spatial load forecasting simulation, yielding results with lower spatial error when compared with the heuristic technique. 相似文献
64.
65.
The objective of this research was to analyse the differences in the dissipated energy under uniaxial tension and biaxial tension–compression load of fibre reinforced concretes using the Wedge Splitting Test. Under biaxial load the specimens were subjected to compressive stress ratios from 10% to 50% of the concrete compressive strength perpendicular to the direction of the tensile load.Under biaxial tension–compression load the energy dissipation capacity of the specimens decreases compared to the uniaxial tension load case on average 20–30%. It is believed that the decrease is a result of the damage mechanism of the concrete matrix and deterioration of the fibre–matrix and/or aggregate–cement paste interfaces in case the section is additionally loaded with compression stresses. This indicates that dimensioning of concrete elements under biaxial stress states using material parameters obtained from tests conducted on specimens under uniaxial tensile load is unsafe and could potentially lead to a non-conservative design.In the second part of this paper the extent of the fracture process zone under uniaxial tension and biaxial tension–compression load will be examined with the Acoustic Emission technique and the reasons for decrease of the energy dissipation capacity under biaxial load will be further discussed. 相似文献
66.
67.
68.
橡塑往复密封的密封寿命通常是通过膜厚、承载力、泄漏率、磨损率等参数以表征。为获取上述参数,佐治亚大学SALANT提出橡塑往复密封模型建立和数值计算求解流程。为更好地理解与应用该方法,从橡塑往复密封物理结构、数值求解流程、Reynolds方程建立、方程约束边界建立、GW接触模型建立、力载平衡等6个方面系统地分析其特点与不完备之处,并从6个方面探讨数值求解流程和数值模拟的修正方法;提出密封模型修正方法,给出修正后密封数值求解流程,使得计算结果更好地与实际工作性能相吻合,并能较好地揭示密封机制。 相似文献
69.
70.
Automatic load shedding is the ultimate countermeasure against imbalance in a power system and can effectively help preventing large blackouts. Taking into account a high penetration of renewable energy sources (RES) in the distribution grid, a clear distinction between load and generation at the PCC becomes increasingly more difficult. For that reason an adaptation of frequency relay parameters and their locations of installation are necessary. In Europe this is rest on a multi-step plan based on values such as the yearly peak load. In this paper a novel probabilistic method for automatic load shedding is presented that uses the average values instead of peak values for load shedding. Its applicability is verified by a dynamic power system model that was developed to compare the classical and novel probabilistic load shedding principle. The method is verified using data from a German TSO. 相似文献