全文获取类型
收费全文 | 54959篇 |
免费 | 5880篇 |
国内免费 | 3678篇 |
学科分类
工业技术 | 64517篇 |
出版年
2024年 | 189篇 |
2023年 | 772篇 |
2022年 | 1582篇 |
2021年 | 1906篇 |
2020年 | 1983篇 |
2019年 | 1662篇 |
2018年 | 1595篇 |
2017年 | 2095篇 |
2016年 | 2275篇 |
2015年 | 2284篇 |
2014年 | 3520篇 |
2013年 | 3874篇 |
2012年 | 4147篇 |
2011年 | 4351篇 |
2010年 | 3261篇 |
2009年 | 3201篇 |
2008年 | 2855篇 |
2007年 | 3529篇 |
2006年 | 2983篇 |
2005年 | 2592篇 |
2004年 | 2209篇 |
2003年 | 1871篇 |
2002年 | 1663篇 |
2001年 | 1388篇 |
2000年 | 1178篇 |
1999年 | 952篇 |
1998年 | 776篇 |
1997年 | 685篇 |
1996年 | 628篇 |
1995年 | 521篇 |
1994年 | 416篇 |
1993年 | 311篇 |
1992年 | 270篇 |
1991年 | 215篇 |
1990年 | 173篇 |
1989年 | 141篇 |
1988年 | 99篇 |
1987年 | 60篇 |
1986年 | 60篇 |
1985年 | 50篇 |
1984年 | 42篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1975年 | 9篇 |
1964年 | 4篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
11.
L.J. Espinoza-Pérez S. Esquivel-Medina E. López-Honorato 《Ceramics International》2021,47(11):15527-15532
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC. 相似文献
12.
Tadeusz Zając Agnieszka Klimek-Kopyra Ryszard Mazurek Andrzej Oleksy Jacek Strojny 《Journal of Natural Fibers》2020,17(8):1199-1211
ABSTRACT Nine sowing densities of linseed were compared in a two-year experiment. Self-regulation of the density of a linseed stand resulted in a differentiated branching of the plants. The number of capsules on a linseed shoot, as well as seeds in the capsule, and the number of seeds from the shoot were highly varied from year to year, and there is even a stronger differentiation in the weight of 1000 seeds. Linear relationships were noted between the mass of seeds from the linseed plant and the number of capsules. The yield of linseed was affected by both factors. An increasing sowing rate reduced the seed yield from the shoot and the plant. At lower seeding rates, the lateral shoots contributed in the seeds yield of the plant to a higher degree compared to the main ones. 相似文献
13.
Indoor surfaces may be adsorptive sinks with the potential to change Indoor Air Quality. To estimate this effect, the sorption parameters of formaldehyde and toluene were assessed on five floorings by an experimental method using solid-phase microextraction in an airtight emission cell. Adsorption rate constants ranged from 0.003 to 0.075 m·h−1, desorption rate constants from 0.019 to 0.51 h−1, and the partition coefficient from 0.005 to 3.9 m, and these parameters vary greatly from one volatile organic compound/material couple to another indicating contrasted sorption behaviors. A rubber was identified as a sink of formaldehyde characterized by a very low desorption constant close to 0. For these sorbent floorings identified, the adsorption rates of formaldehyde are from 2 to 4 times higher than those of toluene. Two models were used to evaluate the sink effects of floorings on indoor pollutant concentrations in one room from different realistic conditions. The scenarios tested came to the conclusion that the formaldehyde sorption on one rubber (identified as a sink) has a maximum contribution from 15% to 21% for the conditions of low air exchange rate. For other floorings, the sorption has a minor contribution less than or equal to 5%, regardless of the air exchange rate. 相似文献
14.
《低温学》2015
The development of a high cooling power and high efficiency 4.2 K two stage G-M cryocooler is critically important given its broad applications in low temperature superconductors, MRI, infrared detector and cryogenic electronics. A high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler has recently been designed and developed by ARS. The effect of expansion volume rate and operation conditions on the cooling performance has been experimentally investigated. A typical cooling performance of 1.5 W/4.2 K has been achieved, and the minimum temperature of the second stage is 2.46 K. The steady input power of the compressor at 60 Hz is 6.8 kW, while the operation speed of the rotary valve is 30 rpm. A maximum cooling power of 1.75 W/4.2 K has been obtained in test runs. 相似文献
15.
《Journal of the European Ceramic Society》2020,40(10):3577-3584
In this work, the grain boundaries composition of the polycrystalline CaCu3Ti4O12 (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu2O and the metastable phase Cu3TiO4. 相似文献
16.
17.
Strain rate is not only an important measure to characterize the deformation property, but also an important parameter to analyze the dynamic mechanical properties of rock materials. In this paper, by using the SHPB test system improved with high temperature device, the dynamic compressive tests of sandstone at seven temperatures in the range of room temperature to 1000 °C and five impact velocities in the range of 11.0–15.0 m/s were conducted. Investigations were carried out on the influences of strain rate on dynamic compressive mechanical behaviors of sandstone. The results of the study indicate that the enhancement effects of strain rates on dynamic compressive strength, peak strain, energy absorption ratio of sandstone under high temperatures still exist. However, the increase ratios of dynamic compressive strength, peak strain, and energy absorption ratio of rock under high temperature compared to room temperature have no obvious strain rate effects. The temperatures at which the strain rates affect dynamic compressive strength and peak strain most, are 800, and 1000 °C, respectively. The temperatures at which the strain rates affect dynamic compressive strength and peak strain weakest, are 1000 °C, and room temperature, respectively. At 200 and 800 °C, the strain rate effect on energy absorption ratio are most significant, while at 1000 °C, it is weakest. There are no obvious strain rate effects on elastic modulus and increase ratio of elastic modulus under high temperatures. According to test results, the relationship formula of strain rate with high temperature and impact load was derived by internalizing fitting parameters. Compared with the strain rate effect at room temperature condition, essential differences have occurred in the strain rate effect of rock material under the influence of high temperature. 相似文献
18.
19.
《International Journal of Hydrogen Energy》2021,46(70):34970-34982
Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air. 相似文献
20.