全文获取类型
收费全文 | 23154篇 |
免费 | 4063篇 |
国内免费 | 2966篇 |
专业分类
化学 | 16211篇 |
晶体学 | 281篇 |
力学 | 1316篇 |
综合类 | 183篇 |
数学 | 3391篇 |
物理学 | 8801篇 |
出版年
2024年 | 68篇 |
2023年 | 483篇 |
2022年 | 521篇 |
2021年 | 749篇 |
2020年 | 1030篇 |
2019年 | 917篇 |
2018年 | 829篇 |
2017年 | 804篇 |
2016年 | 1164篇 |
2015年 | 1093篇 |
2014年 | 1265篇 |
2013年 | 1733篇 |
2012年 | 2060篇 |
2011年 | 2147篇 |
2010年 | 1533篇 |
2009年 | 1411篇 |
2008年 | 1571篇 |
2007年 | 1379篇 |
2006年 | 1220篇 |
2005年 | 1083篇 |
2004年 | 838篇 |
2003年 | 753篇 |
2002年 | 856篇 |
2001年 | 683篇 |
2000年 | 537篇 |
1999年 | 511篇 |
1998年 | 390篇 |
1997年 | 348篇 |
1996年 | 373篇 |
1995年 | 321篇 |
1994年 | 268篇 |
1993年 | 193篇 |
1992年 | 190篇 |
1991年 | 185篇 |
1990年 | 149篇 |
1989年 | 103篇 |
1988年 | 66篇 |
1987年 | 65篇 |
1986年 | 83篇 |
1985年 | 55篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 23篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
992.
In this study, the electronic structures and optical properties of a cyclometalated Pt(II) complex (M1) and a series of derivatives (M1–F, M1–CF3, and M1–CN) with electron-withdrawing substituents (–F, –CF3, and –CN) at the carbazole moiety were theoretically investigated by density functional theory and time-dependent density functional theory. The calculation results reveal that these Pt complexes display deep red phosphorescence emission above Λ = 640 nm. When the 3MLCT/π → π* to triplet metal-centered 3MC/d–d state decay mechanism is taken into consideration, the nonradiative decay rate constant (knr) decreased in the order M1 > M1–CF3 > M1–F > M1–CN. The <T1|HSOC|Sm> and kr values of M1-F are similar with those of M1, however the Knr rate ofM1-F is larger than that of M1. M1–F is expected to have improved quantum yields. Moreover, through the analyses of the HOMO/LUMO level and triplet energy, it is found that the introduction of –F and –CN substituents in M1 results in efficient energy transfer from the host material 4,4′-N,N′-dicarbazole-biphenyl to these complexes. In view of the electroluminescent applications in organic light-emitting diodes, M1–F can serve as efficient deep-red guest materials with improved electron injection and transport ability. 相似文献
993.
Zhenxiong Huang Dr. Xiangjiu Guan Prof. Mingtao Li Prof. Liejin Guo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(31):7118-7123
Akaganeite (β-FeOOH) is a widely investigated candidate for photo(electro)catalysis, such as water splitting. Nevertheless, insights into understanding the surface reaction between water and β-FeOOH, in particular, the hydrogen evolution reaction (HER), are still insufficient. Herein, a set of first-principles calculations on pristine β-FeOOH and halogen-substituted β-FeOOH are applied to evaluate the HER performance through the computational hydrogen electrode model. The results show that the HER on β-FeOOH tends to occur at Fe sites on the (010) surface, and palladium and nickel are found to serve as excellent co-catalysts to boost the HER process, due to the remarkably reduced free energy change of hydrogen adsorption upon loading on the surface of β-FeOOH, demonstrating great potential for efficient water splitting. 相似文献
994.
Kenna L. Salvatore Diana M. Lutz Dr. Haoyue Guo Dr. Shiyu Yue Joceline Gan Dr. Xiao Tong Dr. Ping Liu Dr. Esther S. Takeuchi Dr. Kenneth J. Takeuchi Dr. Amy C. Marschilok Dr. Stanislaus S. Wong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(42):9389-9402
Solution-based, anionic doping represents a convenient strategy with which to improve upon the conductivity of candidate anode materials such as Li4Ti5O12 (LTO). As such, novel synthetic hydrothermally-inspired protocols have primarily been devised herein, aimed at the large-scale production of unique halogen-doped, micron-scale, three-dimensional, hierarchical LTO flower-like motifs. Although fluorine (F) doping has been explored, the use of chlorine (Cl) dopants is the primary focus here. Several experimental variables, such as dopant amount, lithium hydroxide concentration, and titanium butoxide purity, were probed and perfected. Furthermore, the Cl doping process did not damage the intrinsic LTO morphology. The analysis, based on interpreting a compilation of SEM, XRD, XPS, and TEM-EDS results, was used to determine an optimized dopant concentration of Cl. Electrochemical tests demonstrated an increased capacity via cycling of 12 % for a Cl-doped sample as compared with pristine LTO. Moreover, the Cl-doped LTO sample described in this study exhibited the highest discharge capacity yet reported at an observed rate of 2C for this material at 143mAh g−1. Overall, these data suggest that the Cl dopant likely enhances not only the ion transport capabilities, but also the overall electrical conductivity of our as-prepared structures. To help explain these favorable findings, theoretical DFT calculations were used to postulate that the electronic conductivity and Li diffusion were likely improved by the presence of increased Ti3+ ion concentration coupled with widening of the Li migration channel. 相似文献
995.
Jing Guo Mengli Wang Haitao Guo Ruimiao Chang Haixia Yu Guangbin Zhang Anjia Chen 《Biomedical chromatography : BMC》2019,33(11)
A simple, comprehensive and efficient capillary electrophoresis method using a dual cyclodextrin system was developed for the simultaneous determination of seven isoflavones (3′‐methoxypuerarin, puerarin, 3′‐hydroxypuerarin, ononin, daidzin, daidzein and genistin). Baseline separations of the seven isoflavones were achieved within 11 min with the running buffer consisting of 35 mm sodium tetraborate, 9.0 mm sulfobutylether‐β‐cyclodextrin and 30 mm α‐cyclodextrin at pH 9.34, and peaks were detected at 254 nm. Other separation parameters included the separation voltage for 15 kV and the working temperature for 25°C. Under the optimum conditions, good linearities were obtained with linear correlation coefficients of seven isoflavones of 0.9978–0.9992. The limits of detection and the limits of quantification were 0.7–2.9 and 2.5–9.5 μg/mL, respectively. Excellent precision and accuracy were obtained. The intraday and interday precision ranged from 0.7 to 2.0% and from 0.8 to 1.9%, respectively. The recoveries of seven analytes were from 97.7 to 103.1%. This method was successfully applied to determine the seven analytes in Radix Puerariae and its preparations. 相似文献
996.
997.
998.
999.
合成了氯代1-(2-羟乙基)-3-甲基咪唑离子液体[He MIM]Cl、溴代1-乙胺基-3-甲基咪唑离子液体[Ae MIM]Br和氯代1-羧乙基-3-甲基咪唑离子液体[Ce MIM]Cl 3种功能化咪唑离子液体,并分别进行了红外与氢核磁结构表征.然后用3种离子液体液化木粉,液化3 h后向体系直接加入苯酚、甲醛和氢氧化钠,制备酚醛复合材料,并采用FTIR、XRD、DSC和SEM对酚醛复合材料进行结构、性能与形貌测试,研究离子液体种类对木粉液化率及酚醛树脂性能的影响.结果表明,离子液体及其液化木粉产物制备的酚醛复合材料性能得到明显改善.[Ce MIM]Cl液化效果最好,90℃液化率高达24.6%,当[Ce MIM]Cl与木粉质量比为10∶1时,制备的酚醛复合材料的游离醛释放量由原来的3.64%降低到0.92%.离子液体[Ae MIM]Br能将酚醛复合材料的冲击强度由原来的0.93 k J/m2提高到6.96 k J/m2,而[Ae MIM]Br及其液化的木粉产物制备的酚醛复合材料拉伸强度从原来的3.28 MPa提高到9.70 MPa. 相似文献