全文获取类型
收费全文 | 4581篇 |
免费 | 308篇 |
国内免费 | 177篇 |
专业分类
化学 | 1001篇 |
晶体学 | 18篇 |
力学 | 551篇 |
综合类 | 60篇 |
数学 | 2770篇 |
物理学 | 666篇 |
出版年
2024年 | 12篇 |
2023年 | 57篇 |
2022年 | 67篇 |
2021年 | 85篇 |
2020年 | 126篇 |
2019年 | 126篇 |
2018年 | 117篇 |
2017年 | 120篇 |
2016年 | 130篇 |
2015年 | 121篇 |
2014年 | 179篇 |
2013年 | 450篇 |
2012年 | 220篇 |
2011年 | 222篇 |
2010年 | 177篇 |
2009年 | 270篇 |
2008年 | 281篇 |
2007年 | 282篇 |
2006年 | 227篇 |
2005年 | 198篇 |
2004年 | 195篇 |
2003年 | 138篇 |
2002年 | 138篇 |
2001年 | 113篇 |
2000年 | 117篇 |
1999年 | 99篇 |
1998年 | 100篇 |
1997年 | 99篇 |
1996年 | 72篇 |
1995年 | 49篇 |
1994年 | 58篇 |
1993年 | 39篇 |
1992年 | 48篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 15篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1974年 | 6篇 |
排序方式: 共有5066条查询结果,搜索用时 15 毫秒
981.
This paper discusses electromagnetic boundary conditions on crack faces in magneto- electroelastic materials, where piezoelectric, piezomagnetic and magnetoelectric effects are coupled. A notch of finite thickness in these materials is also addressed. Four idealized electromagnetic boundary conditions assumed for the crack-faces are separately investigated, i.e. (a) electrically and magnetically impermeable (crack-face), (b) electrically impermeable and magnetically permeable, (c) electrically permeable and magnetically impermeable, and (d) electrically and magnetically permeable. The influence of the notch thickness on important parameters, such as the field intensity factors, the energy release rate at the notch tips and the electromagnetic fields inside the notch, are studied and the results are obtained in closed-form. Results under different idealized electromagnetic boundary conditions on the crack-face are compared, and the applicability of these idealized assumptions is discussed.The project supported by the National Natural Science Foundation of China (10102004) The English text was polished by Yunming Chen. 相似文献
982.
983.
Perumal Gobinath Ponnusamy Packialakshmi Ali Daoud Saud Alarifi Akbar Idhayadhulla Surendrakumar Radhakrishnan 《Molecules (Basel, Switzerland)》2020,25(24)
In this study, the synthesis of one-pot 10-phenyl-3,4,6,7-tetrahydro-1H-spiro [acridine-9,2′-indoline]-1,3,8-trione derivatives was achieved via a four-component cyclocondensation reaction, which was carried out in solvent-free conditions, and using p-toluenesulfonic acid (p-TSA) as a catalyst. The product was confirmed by FT-IR, 1H-NMR, 13C-NMR, mass spectra, and elemental analysis. Furthermore, the anticancer activity was screened for all compounds. Among these compounds, compound 1c was more effective (GI50 0.01 µm) against MCF-7 cancer cell lines than standard and other compounds. Therefore, the objective of this study was achieved with a few promising molecules having been demonstrated to be potential anticancer agents. 相似文献
984.
Necessary and sufficient conditions for oscillation of second‐order dynamic equations on time scales
Yong Zhou Bashir Ahmad Ahmed Alsaedi 《Mathematical Methods in the Applied Sciences》2019,42(13):4488-4497
In this paper, we establish necessary and sufficient conditions for oscillation of second‐order strongly superlinear and strongly sublinear dynamic equations. Our results unify and improve many known results in the literature. 相似文献
985.
首先引入了涉及高阶强Pre-invex函数的多目标优化问题m阶严格局部极小元的定义,在此基础上讨论了多目标优化问题的优化条件,最后研究了变分不等式的解与多目标优化问题高阶严格极小元之间的关系,其变分不等式的解正是多目标优化问题的高阶严格极小元,这些研究内容推广了Guneer-Bhatia给出的相关结论. 相似文献
986.
Mohammad Rahman Haining Tian Tomas Edvinsson 《Angewandte Chemie (International ed. in English)》2020,59(38):16278-16293
In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co‐catalyst (e.g. Pt). For pursuing a carbon neutral and cost‐effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench‐top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half‐reaction, and have so far shown limited success in hydrogen production from overall water‐splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water‐splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar‐to‐hydrogen) conversion efficiency. 相似文献
987.
988.
Dr. Mohammad Rahman Assoc. Prof. Haining Tian Prof. Dr. Tomas Edvinsson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16418-16433
In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co-catalyst (e.g. Pt). For pursuing a carbon neutral and cost-effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench-top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half-reaction, and have so far shown limited success in hydrogen production from overall water-splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water-splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar-to-hydrogen) conversion efficiency. 相似文献
989.
Yuan Xue Jinbao Liu Maiying Xie Fengfei Chen Mingan Zhou Hualin Lin Fan Zhang Shizhou Liu Zhiqiao Wu Sheng Han 《中国化学快报》2020,31(2):345-348
In this study,various nonionic surfactants(NS) with different ethylene oxide(EO) numbers and tail lengths and its binary blends with anionic surfactants(AS) were used as emulsifiers for naphthenic oil to form the microemulsion metalworking fluids(MWFs),and the effects of them on the stability of the emulsion system were investigated by formulation triangle method.The results indicated that binary complex surfactants of NS and AS as emulsifiers exhibited better emulsifying effect than that of single NS.NS with different EO numbers and tail lengths presented various emulsifying effects.NS(EO=10)exhibited the greatest number of stable formulations,especially the TX-10,but no linear relationship existed between the number of stable formulations and the tail length of NS.In addition,aromatic primary alcohol ethoxy late(APAE) series surfactants containing benzene groups similar to the cycloalkanes in the naphthenic oil so that presented the best emulsifying affect and the greatest number of stable formulations.The co-surfactant of sodium dodecyl benzene sulfonate(SDBS) binary blends with NS exerted the best synergistic effect,and the stable formulations numbers were ranged from 5 to 7,next sodium stearate(SS) comes last followed by sodium dodecyl sulfate(SDS-1) and sodium dodecyl sulfonate(SDS-2). 相似文献
990.
《Tetrahedron letters》2019,60(43):151164
A collection of 1,2,3-triazole fused benzooxazepine and benzodiazepine analogues was prepared by one pot azide substitution and intramolecular azide-olefin oxidative cycloaddition sequence under metal-free conditions. 相似文献