全文获取类型
收费全文 | 489353篇 |
免费 | 5468篇 |
国内免费 | 1286篇 |
专业分类
电工技术 | 8087篇 |
综合类 | 289篇 |
化学工业 | 76379篇 |
金属工艺 | 22847篇 |
机械仪表 | 16931篇 |
建筑科学 | 10799篇 |
矿业工程 | 4284篇 |
能源动力 | 10693篇 |
轻工业 | 37888篇 |
水利工程 | 6120篇 |
石油天然气 | 14820篇 |
武器工业 | 32篇 |
无线电 | 51559篇 |
一般工业技术 | 106003篇 |
冶金工业 | 76225篇 |
原子能技术 | 14222篇 |
自动化技术 | 38929篇 |
出版年
2021年 | 4702篇 |
2019年 | 4443篇 |
2018年 | 7960篇 |
2017年 | 8207篇 |
2016年 | 8874篇 |
2015年 | 5209篇 |
2014年 | 8874篇 |
2013年 | 21547篇 |
2012年 | 13787篇 |
2011年 | 18201篇 |
2010年 | 14445篇 |
2009年 | 16154篇 |
2008年 | 16624篇 |
2007年 | 16324篇 |
2006年 | 14172篇 |
2005年 | 12681篇 |
2004年 | 12302篇 |
2003年 | 12029篇 |
2002年 | 11365篇 |
2001年 | 11579篇 |
2000年 | 10881篇 |
1999年 | 10655篇 |
1998年 | 22497篇 |
1997年 | 16448篇 |
1996年 | 12503篇 |
1995年 | 9819篇 |
1994年 | 8803篇 |
1993年 | 8882篇 |
1992年 | 7013篇 |
1991年 | 6920篇 |
1990年 | 6853篇 |
1989年 | 6588篇 |
1988年 | 6395篇 |
1987年 | 5716篇 |
1986年 | 5534篇 |
1985年 | 6321篇 |
1984年 | 5916篇 |
1983年 | 5583篇 |
1982年 | 5215篇 |
1981年 | 5318篇 |
1980年 | 5176篇 |
1979年 | 5207篇 |
1978年 | 5288篇 |
1977年 | 5539篇 |
1976年 | 6551篇 |
1975年 | 4725篇 |
1974年 | 4725篇 |
1973年 | 4819篇 |
1972年 | 4093篇 |
1971年 | 3753篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
O. A. Lambri J. I. Prez-Landazbal J. A. Cano V. Recarte 《Materials Science and Engineering: A》2004,370(1-2):459-463
Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes. 相似文献
92.
93.
The selector activated sludge (SAS) systems are known to prevent excessive growth of filamentous microorganisms responsible for bulking sludge, but these systems were hardly ever modelled. This study aimed to develop a model capable of predicting rapid substrate removal in the SAS systems. For this purpose, the Activated Sludge Model No. 3 (ASM3) was extended with three processes (adsorption, direct growth on the adsorbed substrate under aerobic or anoxic conditions). The modified ASM3 was tested against the results of batch experiments with the biomass originating from two full-scale SAS systems in Germany. The endogenous biomass was mixed with various readily biodegradable substrates (acetate, peptone, glucose and wastewater) and the utilisation of substrate (expresses as COD) and oxygen uptake rates (OURs) were measured during the experiments. In general, model predictions fitted to the experimental data, but a considerable number of kinetic (5) and stoichiometric (2) parameters needed to be adjusted during model calibration. The simulation results revealed that storage was generally a dominating process compared to direct growth in terms of the adsorbed substrate utilisation. The contribution of storage ranged from 65-71% (Plant A) and 69-92% (Plant B). 相似文献
94.
95.
Extraction of Cs, Sr, Eu, U, Np, and Am with mixtures of dipicolinic acid diamides with chlorinated cobalt dicarbollide was studied. A synergistic effect was revealed. 相似文献
96.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献
97.
98.
M A Fennir J A Landry H S Ramaswamy V G S Raghavan 《The Journal of microwave power and electromagnetic energy》2003,38(3):189-196
This study investigates the effect of extraction methods on the color of date syrup and the potential use of microwave power for syrup processing. Sugar solutions were extracted from dates by boiling, soaking and blending. Color and sugar content of the extracted solutions were measured, and the percentage of sugar extracted form the total fruit sugar determined. Boiling was found to be the most efficient method of extraction whereby 74% of total samples sugar was extracted. In contrast, only 54.2% of fruit sugar was extracted by blending and 42% by soaking. In addition, solutions extracted by soaking and blending had a foaming problem in the subsequent concentration process. The extraction method had no effect on the product final color. The extracted solution was concentrated using two heating methods: conventional and microwave heating at a 600 W capacity and a frequency of 2450 MHz applied at three power levels: 10, 7, and 6. In the heating process, 180 minutes were needed to achieve a 77% degrees Brix using convective heating, while it took 81, 138, and 166 minutes of microwave heating at power level 10, 7, and 6, respectively to achieve the same concentration. Water activity of the syrup was measured within a sugar content range of 50 to 80% degrees Brix and the sugar concentration at which the product is shelf stable was determined at 76%. 相似文献
99.
100.
It is demonstrated that the density of binary glasses upon variation of the molar content of the modifier in their compositions obeys a parabolic dependence, whose parameters can be used to estimate the extent and type of reactions between the components. The reaction parameters in glasses that are prone to liquation are lower by an order of magnitude and have the negative sign. 相似文献