全文获取类型
收费全文 | 130266篇 |
免费 | 22706篇 |
国内免费 | 4539篇 |
专业分类
电工技术 | 6595篇 |
技术理论 | 6篇 |
综合类 | 6077篇 |
化学工业 | 31815篇 |
金属工艺 | 6028篇 |
机械仪表 | 7195篇 |
建筑科学 | 8710篇 |
矿业工程 | 2969篇 |
能源动力 | 3676篇 |
轻工业 | 13216篇 |
水利工程 | 2061篇 |
石油天然气 | 5200篇 |
武器工业 | 884篇 |
无线电 | 17264篇 |
一般工业技术 | 22388篇 |
冶金工业 | 5400篇 |
原子能技术 | 1274篇 |
自动化技术 | 16753篇 |
出版年
2024年 | 393篇 |
2023年 | 1701篇 |
2022年 | 2931篇 |
2021年 | 4560篇 |
2020年 | 4485篇 |
2019年 | 5709篇 |
2018年 | 5946篇 |
2017年 | 6370篇 |
2016年 | 6624篇 |
2015年 | 7726篇 |
2014年 | 8630篇 |
2013年 | 10607篇 |
2012年 | 9044篇 |
2011年 | 9288篇 |
2010年 | 8428篇 |
2009年 | 8082篇 |
2008年 | 7494篇 |
2007年 | 6903篇 |
2006年 | 6608篇 |
2005年 | 5460篇 |
2004年 | 4349篇 |
2003年 | 4035篇 |
2002年 | 3980篇 |
2001年 | 3495篇 |
2000年 | 3134篇 |
1999年 | 2557篇 |
1998年 | 1649篇 |
1997年 | 1356篇 |
1996年 | 1219篇 |
1995年 | 1038篇 |
1994年 | 779篇 |
1993年 | 594篇 |
1992年 | 477篇 |
1991年 | 382篇 |
1990年 | 307篇 |
1989年 | 241篇 |
1988年 | 203篇 |
1987年 | 133篇 |
1986年 | 119篇 |
1985年 | 78篇 |
1984年 | 61篇 |
1983年 | 54篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 34篇 |
1979年 | 29篇 |
1978年 | 21篇 |
1976年 | 23篇 |
1975年 | 16篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
141.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
142.
143.
Although Mg alloy attracts great attention for engineering applications because of high specific strength and low density, low corrosion resistance limits its extensive use. In this study, Mg–Al–Zn–Mn alloy was treated via a laser cladding process to generate a dense and compact laser cladding layer with solid metallurgical bonding on the substrate for improving corrosion resistance, effectively hindering the corrosion pervasion into Mg alloy. The corrosion current density declined from 103 μA/cm2 for Mg alloy to 13 μA/cm2 for the laser cladding layer in NaCl aqueous solution. Moreover, the laser cladding layer was slightly corroded in comparison with Mg alloy in NaCl aqueous solution. Besides, the microhardness of the cladding layer reached a mean value of 170.5 HV, 3.1 times of Mg alloy (56.8 HV) due to the in situ formation of hardening intermetallic phases. Wear resistance of laser cladding layer was also obviously improved. These results demonstrated that the laser cladding layer obviously enhanced anticorrosion property of Mg alloy for engineering applications. 相似文献
144.
Alfredo M. Gravagnuolo Eden Morales‐Narváez Charlene Regina Santos Matos Sara Longobardi Paola Giardina Arben Merkoçi 《Advanced functional materials》2015,25(38):6084-6092
Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self‐assemble into chemically stable amphiphilic films, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and efficient glass functionalization by spontaneous self‐assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2‐coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fluorophore, anti‐immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self‐assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications. 相似文献
145.
Yingli Li Shaoying Zhang Yu Dong 《International Journal of Food Science & Technology》2021,56(1):115-125
Ethylene continues to be a major factor influencing quality of European pears during storage. Although research has been done on the effect of pre-harvest 1-methylcyclopropene (1-MCP) on physiological characteristics in pears, a full understanding of cultivar response and antioxidant metabolism remains elusive. Spraying 1-MCP on ‘Bartlett’ and ‘d’Anjou’ pears was studied with respect to physiology, storage and eating quality, disorders, and antioxidant properties at two harvest date (H1 and H2) during storage and ripening. Treatment with 1-MCP extended the harvest window of ‘Bartlett’ and ‘d’Anjou’ pears 3 and 4 days, respectively, without reducing storage or eating quality. Treatment with 1-MCP reduced ethylene production (EPR) and respiration rates (RR), maintained fruit firmness and green colour during storage and retarded development of desirable melting texture in both cultivars. Additionally, 1-MCP lowered the incidence of disorders by alleviating membrane lipid peroxidation, retaining high total flavonoids (TF) and antioxidant capacity, and enhancing superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity in both cultivars. Overall, pre-harvest 1-MCP applications could extend storage time of ‘Bartlett’ and ‘d’Anjou’ pears to 5 and 6 months, respectively, at −1.1 ± 0.5 °C, by reducing ethylene synthesis and enhancing antioxidant metabolism. 相似文献
146.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
147.
148.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
149.
Seong‐Hee Kim 《Quality and Reliability Engineering International》2015,31(6):923-934
We present a distribution‐free tabular cumulative sum chart for monitoring the variability of an autocorrelated process. A quantity known as the asymptotic variance parameter is employed as a measure of the variability, and a distribution‐free tabular cumulative sum chart is applied to variance estimates calculated from batches of nonoverlapping samples. The proposed chart is applicable to a stationary process with a general marginal distribution and a general autocorrelation structure. It also determines control limits analytically without trial‐and‐error simulations. The performance of the proposed chart is tested on stationary processes with both normal and nonnormal marginals with various autocorrelation structures. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
150.