全文获取类型
收费全文 | 2396篇 |
免费 | 249篇 |
国内免费 | 212篇 |
专业分类
化学 | 1783篇 |
晶体学 | 29篇 |
力学 | 99篇 |
综合类 | 13篇 |
数学 | 235篇 |
物理学 | 698篇 |
出版年
2024年 | 3篇 |
2023年 | 40篇 |
2022年 | 72篇 |
2021年 | 71篇 |
2020年 | 80篇 |
2019年 | 100篇 |
2018年 | 73篇 |
2017年 | 57篇 |
2016年 | 97篇 |
2015年 | 89篇 |
2014年 | 120篇 |
2013年 | 160篇 |
2012年 | 191篇 |
2011年 | 206篇 |
2010年 | 133篇 |
2009年 | 115篇 |
2008年 | 149篇 |
2007年 | 142篇 |
2006年 | 126篇 |
2005年 | 120篇 |
2004年 | 73篇 |
2003年 | 59篇 |
2002年 | 77篇 |
2001年 | 50篇 |
2000年 | 39篇 |
1999年 | 36篇 |
1998年 | 33篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 34篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 32篇 |
1991年 | 14篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1961年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2857条查询结果,搜索用时 15 毫秒
51.
The evaluation and interpretation of the behavior of construction materials under fire conditions have been complicated. Over the last few years, artificial intelligence (AI) has emerged as a reliable method to tackle this engineering problem. This review summarizes existing studies that applied AI to predict the fire performance of different construction materials (e.g., concrete, steel, timber, and composites). The prediction of the flame retardancy of some structural components such as beams, columns, slabs, and connections by utilizing AI-based models is also discussed. The end of this review offers insights on the advantages, existing challenges, and recommendations for the development of AI techniques used to evaluate the fire performance of construction materials and their flame retardancy. This review offers a comprehensive overview to researchers in the fields of fire engineering and material science, and it encourages them to explore and consider the use of AI in future research projects. 相似文献
52.
治疗胆石症蒙药苏斯-12中多种元素的ICP-AES法测定及分析 总被引:3,自引:0,他引:3
通过分析治疗胆囊炎、胆石症的蒙药苏斯—12中微量元素含量,探讨蒙药苏斯—12的药效与微量元素含量的关系。应用高压密封微波消解、电感耦合等离子体原子发射光谱法(ICP-AES)对蒙药苏斯—12进行微量元素含量分析。在蒙药的配制及整体研究工作中发现它们含有多种氨基酸和丰富的微量元素,实验结果表明:苏斯—12中含有丰富的微量元素,尤其Ca,Al,Mg,Fe,Sr,Mn,Zn,Cu等元素的含量比较高,而Pb,Cd,As等元素含量相对低,都低于国家限定值。加标回收率在94.63%~106.40% 之间,相对标准偏差RSD≤3.35 %,检出限在≤0.009 μg·L-1。蒙药苏斯—12有效控制和治疗胆囊炎、胆石症,总有效率达91.2%和100%,蒙药苏斯—12中的微量元素与药效之间有密切的关系。 相似文献
53.
54.
N. N. Kolos V. D. Orlov E. K. Slobodina E. Yu. Yur'eva S. P. Korshunov Zyong van Tué 《Chemistry of Heterocyclic Compounds》1992,28(2):222-227
1,2,4-Triazolo[3,4-b]-1,3,4-thiadiazines, hydrazones, and -thio adducts were obtained by reactions of 4-amino-3-mercapto-1,2,4-triazole with -bromoacetophenones, aldehydes, and ,-unsaturated ketones. Conditions that promote the cyclocondensation of the -thio adducts to the previously undescribed 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines were found. The chemical and spectral properties of the compounds obtained are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 267–272, February, 1992. 相似文献
55.
Wen‐Neng Wu Man‐Ni Gao Hong Tu Gui‐Ping Ouyang 《Journal of heterocyclic chemistry》2016,53(6):2042-2048
A series of novel N‐substituted‐2‐(6‐morpholino‐9H‐purin‐9‐yl)acetamide and 4‐(9‐((5‐substituted‐1,3,4‐oxadiazole/thiadiazole‐2‐yl)methyl)‐9H‐purin‐6‐yl)‐morpholine derivatives were synthesized and evaluated their antibacterial activities against rice bacterial leaf blight and tobacco bacterial wilt caused by Xanthomonas oryzae pv. oryzae (Xoo) and Ralstonia solanacearum (R. solanacearum) via the turbidimeter test in vitro. Antibacterial bioassay indicated that most compounds demonstrated good inhibitory effect against Xoo and R. solanacearum. Especially, compound 6a demonstrated the best inhibitory effect against Xoo with half‐maximal effective concentration (EC50) value of 8.39 μg/mL, which was even better than those of commercial agents Bismerthiazol and Thiodiazole copper. The synthesized purine derivatives containing amide and 1,3,4‐oxadiazole/thiadiazole moieties exhibited excellent antibacterial activities against Xanthomonas oryzae pv. oryzae and R. solanacearum in vitro. 相似文献
56.
Direct writing technique is usually used in femtosecond-laser two-photon micromachining. The size of the scanning step has important influence on the surface quality and machining efficiency of microdevices. According to the mechanism of two-photon polymerization combining the distribution function of the light intensity and the free-radical-concentration theory, we establish the mathematical model of coverage of solidification unit and analyze the effect of coverage on the machining quality and efficiency of microdevices. Using the principle of exposure equivalence, we also obtain the analytic expression of the relationship between the surface-quality characteristic parameters of microdevices and the scanning step and carry out the numerical simulation and experiment. The results show that the scanning step has little influence on the surface quality of the line when it is much smaller than the size of the solidification unit. However, when the scanning step is gradually increasing, the smoothness of the line surface is reduced rapidly, and the surface quality becomes worse drastically. For stereo-device processing with different slopes, we propose a kind three-dimensional continuous-variable scanning method and provide the calculation expression of the scanning step. From the experimental example of fabricating a spherical structure, we show that, compared with the fixed-step scanning method, the continuous-variable scanning-step method should be used to improve the surface quality of microdevices. 相似文献
57.
58.
Meng-Che Tu Deepa Rajwar Gopal Ammanath Palaniappan Alagappan Umit Hakan Yildiz Bo Liedberg 《Analytica chimica acta》2016
A colorimetric Al3+ sensor based on fluorescence recovery of a conjugated copolymer-ATP complex is proposed. An optimized ratio of two polythiophene (PT) monomers is utilized to synthesize copolymer (CP) that yielded maximized colorimetric response for Al3+ in deionized (DI) and tap water. The electrostatic disassembly of CP-ATP upon addition of Al3+ led to an evident visual color change. The lowest concentration of Al3+ for naked eye observation is around 4 μM, which is below the threshold levels in drinking water according to European Economic Community (EEC) standard. Besides, the proposed assay showed a similar response to Al3+ in tap water. The proposed methodology showed selective and sensitive detection for Al3+ in analytically relevant concentration ranges without involving sophisticated instrumentation, illustrating the applicability for on-site drinking water monitoring. 相似文献
59.
Dr. Massimiliano Magro Dr. Stefania Domeneghetti Davide Baratella Dr. Petr Jakubec Prof. Dr. Gabriella Salviulo Dr. Emanuela Bonaiuto Dr. Paola Venier Ondřej Malina Dr. Jiří Tuček Dr. Václav Ranc Dr. Giorgio Zoppellaro Prof.Dr. Radek Zbořil Prof. Dr. Fabio Vianello 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14219-14226
The present study is aimed at the exploration of achievable improvements for CrVI ex situ and in situ water remediation by using novel naked colloidal maghemite (γ‐Fe2O3) nanoparticles (surface active maghemite nanoparticles, SAMNs). The reliability of SAMNs for CrVI binding and removal was demonstrated, and SAMN@CrVI complex was characterized, as well as the covalent nature of the absorption was unequivocally proved. SAMNs were structurally and magnetically well conserved after CrVI binding. Thus, in consideration of their affinity for CrVI, SAMNs were exploited in a biological model system, mimicking a real in situ application. The assay evidenced a progressive reduction of revertant colonies of Salmonella typhimurium TA100 strain, as maghemite nanoparticles concentration increased, till the complete suppression of CrVI mutagen effect. Finally, an automatic modular pilot system for continuous magnetic removal and recovery of CrVI from water is proposed. SAMNs, thanks to their colloidal, binding, and catalytic properties, represent a promising tool as a reliable nanomaterial for water remediation by CrVI. 相似文献
60.