全文获取类型
收费全文 | 55937篇 |
免费 | 5873篇 |
国内免费 | 3685篇 |
专业分类
电工技术 | 2210篇 |
综合类 | 4697篇 |
化学工业 | 10479篇 |
金属工艺 | 3720篇 |
机械仪表 | 2464篇 |
建筑科学 | 5664篇 |
矿业工程 | 2589篇 |
能源动力 | 2104篇 |
轻工业 | 4526篇 |
水利工程 | 1699篇 |
石油天然气 | 2788篇 |
武器工业 | 602篇 |
无线电 | 5824篇 |
一般工业技术 | 8647篇 |
冶金工业 | 3418篇 |
原子能技术 | 1134篇 |
自动化技术 | 2930篇 |
出版年
2024年 | 104篇 |
2023年 | 905篇 |
2022年 | 1539篇 |
2021年 | 1922篇 |
2020年 | 2002篇 |
2019年 | 1856篇 |
2018年 | 1631篇 |
2017年 | 2131篇 |
2016年 | 2106篇 |
2015年 | 2110篇 |
2014年 | 3178篇 |
2013年 | 3588篇 |
2012年 | 3769篇 |
2011年 | 4137篇 |
2010年 | 3068篇 |
2009年 | 3283篇 |
2008年 | 3004篇 |
2007年 | 3569篇 |
2006年 | 3348篇 |
2005年 | 2784篇 |
2004年 | 2367篇 |
2003年 | 2116篇 |
2002年 | 1839篇 |
2001年 | 1431篇 |
2000年 | 1275篇 |
1999年 | 1085篇 |
1998年 | 829篇 |
1997年 | 770篇 |
1996年 | 618篇 |
1995年 | 543篇 |
1994年 | 493篇 |
1993年 | 400篇 |
1992年 | 312篇 |
1991年 | 268篇 |
1990年 | 238篇 |
1989年 | 197篇 |
1988年 | 146篇 |
1987年 | 94篇 |
1986年 | 67篇 |
1985年 | 54篇 |
1984年 | 51篇 |
1983年 | 37篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 27篇 |
1964年 | 10篇 |
1963年 | 9篇 |
1959年 | 17篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
42.
《International Journal of Hydrogen Energy》2022,47(6):3972-3979
The sodium borohydride, NaBH4, hydrolysis mechanism is studied via the H2O/D2O kinetic isotope effect (KIE). This reaction is of importance as NaBH4 is considered as a hydrogen storage material. Nowadays, hydrogen is thought to be one of the most promising and efficient clean energy carriers. In order to control the rate of the hydrogen evolution reaction (HER), one has to understand the mechanism of its production. The H2O/D2O KIE of the reactions of NaBH4 and NaBD4 with water was studied in solutions containing a ratio of H2O/D2O = 1.00. The separation factor, α, of both reactions is α = 5.0 ± 1.0. The rate of the hydrolysis of BD4? in H2O is faster than that of BH4?. The results point out that the rate-determining step in all hydrolysis stages is the H–OH bond scission. 相似文献
43.
Accurate and timely network traffic measurement is essential for network status monitoring, network fault analysis, network intrusion detection, and network security management. With the rapid development of the network, massive network traffic brings severe challenges to network traffic measurement. However, existing measurement methods suffer from many limitations for effectively recording and accurately analyzing big-volume traffic. Recently, sketches, a family of probabilistic data structures that employ hashing technology for summarizing traffic data, have been widely used to solve these problems. However, current literature still lacks a thorough review on sketch-based traffic measurement methods to offer a comprehensive insight on how to apply sketches for fulfilling various traffic measurement tasks. In this paper, we provide a detailed and comprehensive review on the applications of sketches in network traffic measurement. To this end, we classify the network traffic measurement tasks into four categories based on the target of traffic measurement, namely cardinality estimation, flow size estimation, change anomaly detection, and persistent spreader identification. First, we briefly introduce these four types of traffic measurement tasks and discuss the advantages of applying sketches. Then, we propose a series of requirements with regard to the applications of sketches in network traffic measurement. After that, we perform a fine-grained classification for each sketch-based measurement category according to the technologies applied on sketches. During the review, we evaluate the performance, advantages and disadvantages of current sketch-based traffic measurement methods based on the proposed requirements. Through the thorough review, we gain a number of valuable implications that can guide us to choose and design proper traffic measurement methods based on sketches. We also review a number of general sketches that are highly expected in modern network systems to simultaneously perform multiple traffic measurement tasks and discuss their performance based on the proposed requirements. Finally, through our serious review, we summarize a number of open issues and identify several promising research directions. 相似文献
44.
Ping-Chi Hsu Jia-Ying Jhong Li-Ping Huang Kuo-Hsin Lee Hsin-Pao Chen Yue-Leon Guo 《International journal of molecular sciences》2021,22(8)
Di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in the manufacture of polyvinylchloride plastics and has been associated with concerns regarding male reproductive toxicity. In this study, we hypothesized that maternal exposure to DEHP induces transgenerational inheritance of adult-onset adverse reproductive outcomes through the male germline in the F1, F2, and F3 generations of male offspring. Pregnant rats were treated with 5 or 500 mg of DEHP/kg/day through gavage from gestation day 0 to birth. The offspring body weight, anogenital distance (AGD), anogenital index (AGI), sperm count, motility, and DNA fragmentation index (DFI) were measured for all generations. Methyl-CpG binding domain sequencing was performed to analyze sperm DNA methylation status in the F3. DEHP exposure at 500 mg/kg affected AGD, AGI, sperm count, mean DFI, and %DFI in the F1; AGD, sperm count, and mean DFI in the F2; and AGD, AGI, mean DFI, and %DFI in the F3. DEHP exposure at 5 mg/kg affected AGD, AGI, sperm count, and %DFI in the F1; sperm count in the F2; and AGD and AGI in F3. Compared with the control group, 15 and 45 differentially hypermethylated genes were identified in the groups administered 5 mg/kg and 500 mg/kg DEHP, respectively. Moreover, 130 and 6 differentially hypomethylated genes were observed in the groups administered 5 mg/kg and 500 mg/kg DEHP. Overall, these results demonstrated that prenatal exposure to DEHP caused transgenerational epigenetic effects, which may explain the observed phenotypic changes in the male reproductive system. 相似文献
45.
A Pitot tube is a popular device used for the measurements of flow fields. To control the accuracy of the Pitot tube coefficient, the international standard organization (ISO), the American Society for Testing and Materials (ASTM), and the Japanese Industrial Standards (JIS) issued guidelines that recommended the shape and working conditions of these devices. However, many Pitot tubes on the market do not follow these guidelines. In the present study, various types of Pitot tubes in the market were tested at the National Metrology Institute of Japan (NMIJ) to determine the effects of the geometry and flow characteristics. The results revealed certain limitations in the existing ISO and JIS standards, specifically with regard to the recommended design parameters of the AMCA Pitot tube, the reference coefficient value for the JIS Pitot tube, and the redefinition and limitation of Reynolds numbers pertaining to Pitot tube working conditions. 相似文献
46.
Xiuli Xie Zhengsong Fang Meijia Yang Fangming Zhu Dingshan Yu 《Advanced functional materials》2021,31(13):2007942
Aqueous rechargeable Zinc (Zn)–polymer batteries are promising alternatives to prevalent Li-ion cells in terms of cost, safety, and rate capability but they suffer from limited specific capacity in addition to poor environmental adaptability. Herein, air and light are successfully utilized from external environments in single near-neutral two-electrode Zn batteries to enable remarkably improved electrochemical performance, fast self-charging, and switchable multimode-operation from Zn–polymer to Zn–air cells. This system is enabled by a well-designed polyaniline-nanorod-array based “all-in-one” cathode combining reversible redox capability, oxygen reduction activity, and photothermal-responsiveness. The initiative design allows perfect integration of multiple energy harvesting from ambient “air” and light, energy conversion, and storage in one single cathode. Thus, it can act as an efficient light-assisted electrically-rechargeable Zn–polymer cell featuring the highest specific capacity of 430.0 mAh g−1 among all existing polymer cathodes. Without external power sources, it can be self-charged to deliver a high discharging capacity of 363.1 mAh g−1 by concurrently harvesting chemical energy from air and light energy for only 20 min. It can also switch to a light-responsive Zn–air battery mode to surmount the output capacity limit of Zn–polymer battery mode for continued electricity supply. 相似文献
47.
Terahertz (THz) imaging is expected to become powerful tools for non-destructive inspections. To ensure the practical use of THz non-destructive monitoring, versatile THz imagers with adjustable designs that can eliminate the complexities and the bulkiness of the device are urgently required. Herein, a self-aligned filtration process for a 2D, free-standing carbon nanotube film array and its application to a THz video camera patch are reported. The presented techniques enable a) to freely design the camera size, sensor array pattern, and suspended shape according to its applications, b) to cut the camera patch into desired shapes, and c) to attach them to the objects that are intended to be measured. Real-time, non-destructive monitoring of various infrastructures is demonstrated. These results indicate that it can function regardless of restrictions, such as the shapes and locations of the measurement samples, thus providing a strong possibility for use in future non-destructive sensor networks. 相似文献
48.
49.
Mingqiang Cheng Erding Zhao Fangjian Jiang Xiaodong Jiang Ze Fang Feng Li Wanneng Ye Yalin Qin Yongcheng Zhang 《Ceramics International》2021,47(13):18417-18423
The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field Ei is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization PD in aged samples can reverse the spontaneous polarization PS back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented PD and resulting Ei in poled-state samples will lead to the asymmetric loops and strain memory effect. 相似文献
50.
Qianqian Liu Yu-Jin Kim Gwang-Bum Im Jintao Zhu Yuzhou Wu Yijing Liu Suk Ho Bhang 《Advanced functional materials》2021,31(12):2008171
Inorganic nanoparticles (NPs) offer significant advantages to the biomedical field owing to their large surface area, controllable structures, diverse surface chemistry, and unique optical and physical properties. Researchers worldwide have shown that inorganic NPs and the released metal ions can act as therapeutic agents in targeted tissues or to cure various diseases without acute toxicity. In this progress report, the recent developments in inorganic NPs with different compositions directly used as therapeutics are discussed. First, the recent convergence of nanotechnology and biotechnology in biomedical applications as well as the unique functions, features, and advantages of inorganic NPs in biomedical applications are summarized. Thereafter, the biological effects of inorganic compositions in NPs which include balancing the intracellular redox environment, regulating the specific cellular signaling and cellular behaviors, and apoptosis are explained. In addition, the emerging therapeutic applications of inorganic NPs in various diseases are exemplified. Finally, the perspectives and challenges for overcoming the weaknesses of inorganic NPs as therapeutics are discussed. By carefully considering and investigating the biological effects of inorganic NPs and metal ions released from NPs, more promising inorganic NPs based therapeutic agents can be developed. 相似文献