全文获取类型
收费全文 | 40935篇 |
免费 | 5642篇 |
国内免费 | 3110篇 |
专业分类
电工技术 | 5229篇 |
技术理论 | 1篇 |
综合类 | 4334篇 |
化学工业 | 3821篇 |
金属工艺 | 1150篇 |
机械仪表 | 2175篇 |
建筑科学 | 2608篇 |
矿业工程 | 1011篇 |
能源动力 | 1232篇 |
轻工业 | 1904篇 |
水利工程 | 852篇 |
石油天然气 | 1731篇 |
武器工业 | 664篇 |
无线电 | 5543篇 |
一般工业技术 | 3838篇 |
冶金工业 | 1875篇 |
原子能技术 | 603篇 |
自动化技术 | 11116篇 |
出版年
2024年 | 93篇 |
2023年 | 559篇 |
2022年 | 1073篇 |
2021年 | 1240篇 |
2020年 | 1558篇 |
2019年 | 1436篇 |
2018年 | 1265篇 |
2017年 | 1695篇 |
2016年 | 1845篇 |
2015年 | 1938篇 |
2014年 | 2614篇 |
2013年 | 2964篇 |
2012年 | 2985篇 |
2011年 | 3109篇 |
2010年 | 2257篇 |
2009年 | 2401篇 |
2008年 | 2282篇 |
2007年 | 2690篇 |
2006年 | 2533篇 |
2005年 | 2074篇 |
2004年 | 1707篇 |
2003年 | 1596篇 |
2002年 | 1389篇 |
2001年 | 1208篇 |
2000年 | 989篇 |
1999年 | 733篇 |
1998年 | 614篇 |
1997年 | 503篇 |
1996年 | 395篇 |
1995年 | 355篇 |
1994年 | 287篇 |
1993年 | 232篇 |
1992年 | 158篇 |
1991年 | 155篇 |
1990年 | 109篇 |
1989年 | 91篇 |
1988年 | 67篇 |
1987年 | 68篇 |
1986年 | 47篇 |
1985年 | 58篇 |
1984年 | 41篇 |
1983年 | 29篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1964年 | 12篇 |
1956年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Investigation on the miniaturized parallel multichannel-based devices packed with glass beads to improve the mass exchange execution is the critical focal point of the current study. One of the essential parameters to specify the miniaturized devices' flow distribution is the residence time distribution (RTD). In the present context, the RTDs of a liquid tracer were investigated for the air-water multiphase flows (concurrent) across the multichannel-based miniaturized devices (comprising of 11 similar dimensional parallel channels). The devices were variable in height and packed with glass beads. The conductivity estimations generated the RTD curves and were addressed by the axial dispersion model (ADM). The fluid-flow rates differed within the range of 5–23 ml min−1. The axial dispersion coefficients and the rate of the specific energy dispersion were investigated. The effects of pressure difference and geometry on the hydrodynamic attributes and mixing properties were well-illustrated, and the new correlations were suggested. 相似文献
12.
《Ceramics International》2022,48(14):19806-19817
Aluminosilicates are the base precursors that combined with alkali solutions manufacture geopolymers. A wide variability of aluminosilicate precursors can be found in the market worldwide, which may be an issue when proposing single designs. The goal of this study is to compare the use of different precursors in the hardening mechanisms of geopolymers. For this, two types of metakaolin (a low (MKLR) and a high-reactive (MKHR) one), and partial replacements made with fly-ash (FA) and blast furnace slag (BFS) are used in SiO2/Al2O3 = 4.00, Na2O/SiO2 = 0.25, and H2O/Na2O = 11.00 fixed design ratios. Fresh state (viscosity and squeeze flow), transient state (Vicat needle and sonic strength), and hardening measurements (compression tests under room and high temperature conditions), were used, supported by chemical analysis (calorimetry and SAM/HCl extraction) and materials characterization (particle analysis, density, BET and XRD). In general, the reactivity, chemical composition, and morphology of each precursor, as well as solid/liquid portions of each mix were major factors influencing the hardening process. The use of MKLR achieved shorter setting times and enhanced viscosities due to its particles larger surface area, solid/liquid ratios, and unreactive portions, reaching the highest values of strength and diminished thermomechanical performance. Partial substitutions made with FA and BFS increased the amorphous part of the binder, increasing also its flowability, setting time, and its stability to thermal exposure. The geopolymer made with MKHR presented the lowest viscosity and longer setting time due to its almost constant dissolution rate, attributed to its enhanced reactivity from highly amorphous parts and diminished solid-to-liquid ratio mixture. Therefore, the use of varied aluminosilicates significantly modifies the materials properties, leading to different potential applications that should be considered when designing geopolymers. 相似文献
13.
5G系统将移动通信服务从移动电话、移动宽带和大规模机器通信扩展到新的应用领域,即所谓对通信服务有特殊要求的垂直领域。对使能未来工厂的5G能力进行了全面的分析总结,包括弹性网络架构、灵活频谱、超可靠低时延通信、时间敏感网络、安全和定位,而弹性网络架构又包括对网络切片、非公共网络、5G局域网和边缘计算的支持。希望从广度到深度,对相关的理论及技术应用做透彻、全面的梳理,对其挑战做清晰的总结,从而为相关研究和工程技术人员提供借鉴。 相似文献
14.
Marc Neumann Patrick Gehre Rapuruchukwu Ifeyinwa Nwokoye Hans Jelitto Gerold A. Schneider Christos G. Aneziris 《Ceramics International》2021,47(13):18656-18661
Main objective of the presented research is the life time prediction of self-supporting flame-sprayed Al2O3- and Al2O3 -ZrO2 -TiO2-materials under constant load. The characteristic life time and its scatter were derived from stable crack growth tests and Weibull-statistics including the four-point-bending and ball-on-three-balls method. The potential life time was estimated in order to assess room-temperature handling and long term storage of self-supporting flame-sprayed alumina components. In terms of flexural strength, energy release, and subcritical crack growth parameters, distinct differences between both materials were shown. In turn, the characteristic life times only barely deviated from each other. From that the conclusion was drawn that life time performance under constant load application is governed by the characteristic flame-spray microstructure. However, advantages in the flame-spray processing of Al2O3 - ZrO2 -TiO2 are still given, attributed to its lower melting temperature. 相似文献
15.
16.
目的 建立超高效液相色谱-飞行时间质谱检测山药中7种常见杀菌剂的分析方法。方法 样品经乙腈提取,水浴氮吹至近干,丙酮定容,经超高效液相色谱-飞行时间质谱检测。结果 在正离子模式下,7种杀菌剂在水-甲醇(均含有0.01%甲酸和5 mmol/L甲酸铵)流动相中都具有较好的响应;0.01~0.40 mg/L范围内线性良好,相关系数R均大于0.999。不同温度(50℃、70℃)水浴实验结果表明70℃水浴温度符合实验要求。三个浓度水平的加标回收实验的回收率为70.75%~108.07%,相对标准偏差为 0.02%~5.01%。结论 该方法操作简单、分析准确,满足山药中常见杀菌剂的检测要求。 相似文献
17.
Due to the severe outdoor PM2.5 pollution in China, many people have installed air-cleaning systems in homes. To make the systems run automatically and intelligently, we developed a recurrent neural network (RNN) that uses historical data to predict the future indoor PM2.5 concentration. The RNN architecture includes an autoencoder and a recurrent part. We used data measured in an apartment over the course of an entire year to train and test the RNN. The data include indoor/outdoor PM2.5 concentration, environmental parameters and time of day. By comparing three different input strategies, we found that a strategy employing historical PM2.5 and time of day as inputs performed best. With this strategy, the model can be applied to predict the relatively stable trend of indoor PM2.5 concentration in advance. When the input length is 2 h and the prediction horizon is 30 min, the median prediction error is 8.3 µg/m3 for the whole test set. For times with indoor PM2.5 concentrations between (20,50] µg/m3 and (50,100] µg/m3, the median prediction error is 8.3 and 9.2 µg/m3, respectively. The low prediction error between the ground-truth and predicted values shows that the RNN can predict indoor PM2.5 concentrations with satisfactory performance. 相似文献
18.
马尔可夫跳变线性系统(MJLS)是一种具有多个模态的随机系统,系统在各个模态之间的跳变转移由一组马尔可夫链来决定。MJLS模型因其在表示过程中可以产生突变而更能精确的描述实际工程应用中的系统。近年来,MJLS的最优控制问题成为了研究的热点,动态规划、极大值原理以及线性矩阵不等式等成为了解决此类问题的主流方法。本文对MJLS最优控制领域的研究现状进行了综述。分别对一般情况下、带有噪声的情况下、带有时滞的情况下以及某些特定情况下的MLJS最优控制问题的国内外研究现状进行论述。最后进行了总结并提出MJLS最优控制领域未来值得关注的研究方向。 相似文献
19.
现有的时态网络可视化方法大多采用等量时间片来可视化网络的演变,不利于时态模式的快速挖掘和发现。为此,根据时态网络固有的特征提出自适应时间片划分方法(Adaptive Time Slice Partition method,ATSP)。在时态网络的两种表示方式(基于事件的表示方式和基于快照的表示方式)的基础上,构建了ATSP的基础模型,同时提出了一种改进模型用来描述事件间隔时间服从长尾分布的时态网络。为了实现时间片的不等量划分,针对探索任务的不同提出了基于时态模式的ATSP规则和基于中心节点的ATSP规则,并提出了实现算法--层次划分算法(Hierarchical Partition algorithm,HP)和增量划分算法(Incremental Partition algorithm,IP)。实验结果表明,ATSP方法比传统的时间片划分方法更能准确地表示网络的时态特征,且该方法应用于可视化时,能有效归纳并展示网络的特征,明显提高了视觉分析的效率。 相似文献
20.
Ignacio Brevis Ángel Rodríguez-Rozas Jaime H. Ortega David Pardo 《Computers & Mathematics with Applications》2019,77(5):1358-1375
We study the problem of source reconstruction for a linear elasticity problem applied to seismicity induced by mining. We assume the source is written as a variable separable function . We first present a simple proof a local decay result for elasticity in the case of homogeneous media. We then extend the source time reversal method, originally developed for acoustic waves, to an elastic system of waves. Additionally, we present a fast reconstruction implementation for large data sets. This is especially useful in the elastic case, in which the numerical cost is higher than in fluid acoustics. We complement this work with several 2D and 3D numerical experiments and an analysis of the results. 相似文献