全文获取类型
收费全文 | 535260篇 |
免费 | 6198篇 |
国内免费 | 1870篇 |
专业分类
电工技术 | 9931篇 |
综合类 | 674篇 |
化学工业 | 79657篇 |
金属工艺 | 19409篇 |
机械仪表 | 15583篇 |
建筑科学 | 13185篇 |
矿业工程 | 2308篇 |
能源动力 | 14099篇 |
轻工业 | 48126篇 |
水利工程 | 4962篇 |
石油天然气 | 8874篇 |
武器工业 | 50篇 |
无线电 | 65404篇 |
一般工业技术 | 103771篇 |
冶金工业 | 99625篇 |
原子能技术 | 11744篇 |
自动化技术 | 45926篇 |
出版年
2021年 | 4026篇 |
2019年 | 3861篇 |
2018年 | 6543篇 |
2017年 | 6479篇 |
2016年 | 6808篇 |
2015年 | 4636篇 |
2014年 | 7945篇 |
2013年 | 23998篇 |
2012年 | 13020篇 |
2011年 | 17899篇 |
2010年 | 14010篇 |
2009年 | 16214篇 |
2008年 | 16917篇 |
2007年 | 16868篇 |
2006年 | 14770篇 |
2005年 | 13672篇 |
2004年 | 13418篇 |
2003年 | 13070篇 |
2002年 | 12630篇 |
2001年 | 12898篇 |
2000年 | 12219篇 |
1999年 | 12758篇 |
1998年 | 30799篇 |
1997年 | 22208篇 |
1996年 | 17294篇 |
1995年 | 13352篇 |
1994年 | 11915篇 |
1993年 | 11754篇 |
1992年 | 8710篇 |
1991年 | 8429篇 |
1990年 | 8145篇 |
1989年 | 8032篇 |
1988年 | 7666篇 |
1987年 | 6659篇 |
1986年 | 6822篇 |
1985年 | 7758篇 |
1984年 | 7116篇 |
1983年 | 6665篇 |
1982年 | 6096篇 |
1981年 | 6273篇 |
1980年 | 5974篇 |
1979年 | 5764篇 |
1978年 | 5615篇 |
1977年 | 6516篇 |
1976年 | 8380篇 |
1975年 | 4809篇 |
1974年 | 4685篇 |
1973年 | 4707篇 |
1972年 | 3943篇 |
1971年 | 3491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
2.
ABSTRACTIn recent times, the applications of multimedia are rising in a greedy mode and hence the amount of video transactions is also increasing exponentially. This has shouted great demands on effective models on video encoding and also for reducing the transmission channel congestion. This research work introduces a managing technique termed weighted encoding for High-Efficiency Video Coding (HEVC). HEVC, also termed as MPEG-H Part 2 and H.265 is a video compression standard that is widely utilized AVC (H.264 or MPEG-4 Part 10). When compared to AVC, HEVC grants double the ratio of data compression at a similar level of quality of the video or considerably enhanced video quality at a similar bit rate. This work intends to optimize the weight that adopted in HEVC for encoding. For this, this paper proposes a new Iterative based propagation update in the water wave Optimization Algorithm (IPU-WWO), which is the improved form of Water wave Optimization (WWO). The performance of proposed IPU-WWO is compared over other conventional methods like Artificial Bee Colony (ABC), Firefly (FF), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) with respect to Peak Signal to Noise Ratio (PSNR). By doing the encoding process, it minimizes the video size with perceptually better quality video or PSNR. 相似文献
3.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
4.
5.
A. A. Salem S. R. Kalidindi R. D. Doherty S. L. Semiatin 《Metallurgical and Materials Transactions A》2006,37(1):259-268
Novel experiments were conducted to elucidate the effect of deformation twinning on the mechanical response of high-purity
α-titanium deformed at room temperature. Orientation-imaging microscopy (OIM), microhardness, and nanohardness evaluations
were employed in conjunction with optical microscopy and quasi-static compression testing to obtain insight into the deformation
mechanisms. Hardness measurements revealed that the newly formed deformation twins were harder than the matrix. This observation
is perhaps the first experimental evidence for the Basinski mechanism for hardening associated with twinning, arising from
the transition of glissile dislocations to a sessile configuration upon the lattice reorientation by twinning shear. This
work also provided direct evidence for two competing effects of deformation twinning on the overall stress-strain response:
(1) hardening via both a reduction of the effective slip length (Hall-Petch effect) and an increase in the hardness of twinned regions (Basinski
mechanism) and (2) softening due to the lattice reorientation of the twinned regions. 相似文献
6.
The main factors that determine the uniformity with which smelting products are tapped from a blast furnace are the rate of accumulation of the products in the hearth and the tapping rate. The first parameter is in turn determined by the stability of the furnace’s operation and can vary significantly even over the course of 24 h. The second parameter is determined mainly by the condition of the iron notch, the maintenance it receives, any changes that occur in the diameter of the channel of the notch, and the quality of the materials used to form the notch. Recommendations are presented to optimize tapping of the smelting products. 相似文献
7.
P. B. Lovyrev A. I. Lavrov V. A. Babkin A. N. Aminov S. M. Melekhin Yu. P. Kazantsev P. M. Korol’kov 《Metallurgist》2006,50(3-4):152-157
Specifications require that all the welds in 12-m-diam. decomposers with a capacity of 3600 m3 be subjected to high-temperature tempering before going into service in order to alleviate the stresses from the welding
operation. Specialists at the organizations VNIIPTkhimnefteapparatury and VNIImontazhspetsstroi have proposed out-of-furnace
volumetric (complete) of the assembled decomposer with the use of special heaters. The use of this heating method has shortened
assembly operations while providing the welds with a highquality heat treatment and reducing the stresses overall (including
welding stresses, stresses from assembly of the decomposer, etc.) The technology ensures uniform heating of the housing of
the decomposer and provides for close control over the process. The experience gained in heat-treating decomposers can also
be used in the construction of other containers that come into contact with corrosive media.
__________
Translated from Metallurg, No. 3, pp. 61–64, March, 2006. 相似文献
8.
Simulation is useful for evaluating protocol performance and operation. However, the lack of rigor with which it's applied threatens the credibility of the published research within the manet research community. Mobile ad hoc networks (manets) allow rapid deployment because they don't depend on a fixed infrastructure. Manet nodes can participate as the source, the destination, or an intermediate router. This flexibility is attractive for military applications, disaster-response situations, and academic environments where fixed net working infrastructures might not be available. 相似文献
9.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献
10.
P. Cofta 《BT Technology Journal》2006,24(2):214-218
Trust is the key element of commerce, both for traditional models and — more recently — for eCommerce. Unlike its traditional
counterpart, eCommerce relies on trust being created and maintained with the help of digital devices and services. Convergence
brings significant changes to the way people interact through digital media by offering ubiquitous and seamless communication.
This has a significant impact on the way trust is established and maintained, with consequent impact upon eCommerce. This
paper identifies a number of the most important challenges to trust in eCommerce as well as trust-related aspects of key enablers
of eCommerce. From this perspective, the paper studies an impact of convergence on trust within eCommerce to identify several
positive relationships. 相似文献