全文获取类型
收费全文 | 180428篇 |
免费 | 9075篇 |
国内免费 | 4619篇 |
专业分类
电工技术 | 6355篇 |
技术理论 | 6篇 |
综合类 | 8448篇 |
化学工业 | 27248篇 |
金属工艺 | 10764篇 |
机械仪表 | 9965篇 |
建筑科学 | 10186篇 |
矿业工程 | 3903篇 |
能源动力 | 4016篇 |
轻工业 | 9794篇 |
水利工程 | 2915篇 |
石油天然气 | 7675篇 |
武器工业 | 822篇 |
无线电 | 19644篇 |
一般工业技术 | 27311篇 |
冶金工业 | 7354篇 |
原子能技术 | 1271篇 |
自动化技术 | 36445篇 |
出版年
2024年 | 215篇 |
2023年 | 1668篇 |
2022年 | 2581篇 |
2021年 | 4136篇 |
2020年 | 3258篇 |
2019年 | 2636篇 |
2018年 | 16838篇 |
2017年 | 16213篇 |
2016年 | 12650篇 |
2015年 | 4715篇 |
2014年 | 5158篇 |
2013年 | 6043篇 |
2012年 | 9452篇 |
2011年 | 15997篇 |
2010年 | 13954篇 |
2009年 | 10960篇 |
2008年 | 12052篇 |
2007年 | 12780篇 |
2006年 | 5621篇 |
2005年 | 5946篇 |
2004年 | 4125篇 |
2003年 | 4017篇 |
2002年 | 3236篇 |
2001年 | 2542篇 |
2000年 | 2546篇 |
1999年 | 2725篇 |
1998年 | 2145篇 |
1997年 | 1765篇 |
1996年 | 1742篇 |
1995年 | 1422篇 |
1994年 | 1160篇 |
1993年 | 740篇 |
1992年 | 656篇 |
1991年 | 460篇 |
1990年 | 349篇 |
1989年 | 297篇 |
1988年 | 230篇 |
1987年 | 144篇 |
1986年 | 112篇 |
1985年 | 69篇 |
1984年 | 45篇 |
1983年 | 40篇 |
1982年 | 41篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1959年 | 37篇 |
1958年 | 37篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
81.
采用正硅酸乙酯(TEOS)和3-氨丙基三乙氧基硅烷(APTES)通过共缩聚法合成介孔二氧化硅(MCM-41)。首先对其氨基修饰,再通过有机合成接枝—R基团(—R:—CHO、—OH、—CH3、—COOH),制备得到Me-Ph-NH-MCM-41、OHC-Ph-NH-MCM-41、HO-Ph-NH-MCM-41、HOOC-Ph-NH-MCM-41四种不同的药物载体。利用FT-IR、Zeta电位、XRD和SEM对其结构和形貌表征,结果表明NH2-MCM-41改性成功。以罗丹明B(RhB)为模型进行载药性能测试,并考察了此释药系统在模拟不同pH的体液下的敏感释药行为,同时探究了不同—R基团对释药的影响。结果显示,四种载体在中性条件下几乎不发生药物释放,通过改变环境体系pH可以有效控制药物释放,其释药行为可以用Korsmeyer-Peppas动力学模型来描述。实验表明,释药量:RhB@HOOC-Ph-NH-MCM-41>RhB@OHC-Ph-NH-MCM-41>RhB@HO-Ph-NH-MCM-41>RhB@Me-Ph-NH-MCM-41,不同—R基团的药物载体的pH响应性不同,其中RhB@HOOC-Ph-NH-MCM-41释药量在pH=1.2时可达57.87%,在用于药物智能控释材料方面具有一定的应用潜力。 相似文献
82.
Jialin Sun Jun Zhao Xiuying Ni Feng Gong Zuoli Li 《Journal of the European Ceramic Society》2018,38(9):3096-3103
This work investigates the critical roles of two-step sintering (TSS) and laminated structure on the sintering behavior and mechanical properties of functionally graded WC-TiC-Al2O3 nanostructured composite materials doped with Cr3C2/VC. Results show that excellent mechanical properties are achieved for tailored TSS conditions with a hardness of 27.91?±?2.3?GPa and a flexural strength of 1423.3?±?23.5?MPa. The desirable mechanical properties are attributed to the suppressed grain growth without densification deterioration. TSS is more effective in facilitating the favorable dispersion of secondary phase toughening nano-particulates in a WC matrix than conventional sintering (CS). Cr3C2/VC dopant plays an important role in maximizing and shifting the temperature range of the kinetic window for WC-Al2O3 composites. Al2O3 crack deflection, transgranular Al2O3, microcracking, WC crack bridging and plate-like WC crack deflection are the major toughening mechanisms. Residual surface compressive stress induced by the graded structure is also an appreciated contribution to the improvement of mechanical properties. 相似文献
83.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
84.
85.
86.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
87.
Stream ciphers based on linear feedback shift register (LFSR) are suitable for constrained environments, such as satellite communications, radio frequency identification devices tag, sensor networks and Internet of Things, due to its simple hardware structures, high speed encryption and lower power consumption. LFSR, as a cryptographic primitive, has been used to generate a maximum period sequence. Because the switching of the status bits is regular, the power consumption of the LFSR is correlated in a linear way. As a result, the power consumption characteristics of stream cipher based on LFSR are vulnerable to leaking initialization vectors under the power attacks. In this paper, a new design of LFSR against power attacks is proposed. The power consumption characteristics of LFSR can be masked by using an additional LFSR and confused by adding a new filter Boolean function and a flip-flop. The design method has been implemented easily by circuits in this new design in comparison with the others. 相似文献
88.
Mingzhi Zhao Jianwei Cao Zhi Wang Guohua Li 《Journal of the European Ceramic Society》2019,39(7):2427-2435
The crystallization phenomena of spinel in CaO-MgO-Al2O3-SiO2-Fe2O3 glass have received much attention due to the particular role in preparation of glass-ceramic materials, which represent an effective option to manage hazardous waste. In this study, both preliminary spinel and secondary spinel were precipitated in the precursor glass. The formation of these spinel was meticulously assessed by a combination of X-ray diffractometry and scanning electron microscopy. The structure of the microenvironment in the precursor glass was characterized by Raman spectrums. These advanced techniques highlight the potential for one-step crystallization of the glass. The investigation, which focused on one-step crystallization, demonstrated the growth of pyroxene on spinel accompanying a migration of chromium. The results also show the microstructure of the obtained glass-ceramic was very dependent on the heat-treat temperature. This study not only unambiguously reveals the precipitation mechanisms of spinel but also provides more documentation for one-step crystallization in the glass-ceramics field. 相似文献
89.
90.
The increased concentration of CO2 due to continuous breathing and no discharge of human beings in the manned closed space, like spacecraft and submarines, can be a threat to health and safety. Effective removal of low concentration CO2 from the manned closed space is essential to meet the requirements of long-term space or deep-sea exploration, which is an international frontier and trend. Ionic liquids (ILs), as a widespread and green solvent, already showed its excellent performance on CO2 capture and absorption, indicating its potential application in low concentration CO2 capture. In this review, we first summarized the current methods and strategies for direct capture from low concentration CO2 in both the atmosphere and manned closed spaces. Then, the multi-scale simulation methods of CO2 capture by ionic liquids are described in detail, including screening ionic liquids by COSMO-RS methods, capture mechanism by density functional theory and molecular dynamics simulation, and absorption process by computational fluid dynamics simulation. Lastly, some typical IL-based green technologies for low concentration CO2 capture, such as functionalized ILs, co-solvent systems with ILs, and supported materials based on ILs, are introduced, and analyzed the subtle possibility in manned closed spaces. Finally, we look forward to the technology and development of low concentration CO2 capture, which can meet the needs of human survival in closed space and proposed that supported materials with ionic liquids have great advantages and infinite possibilities in the vital area. 相似文献