全文获取类型
收费全文 | 2298篇 |
免费 | 347篇 |
国内免费 | 232篇 |
专业分类
化学 | 1835篇 |
晶体学 | 15篇 |
力学 | 123篇 |
综合类 | 26篇 |
数学 | 159篇 |
物理学 | 719篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 71篇 |
2021年 | 71篇 |
2020年 | 69篇 |
2019年 | 79篇 |
2018年 | 51篇 |
2017年 | 55篇 |
2016年 | 74篇 |
2015年 | 90篇 |
2014年 | 121篇 |
2013年 | 162篇 |
2012年 | 189篇 |
2011年 | 199篇 |
2010年 | 152篇 |
2009年 | 139篇 |
2008年 | 153篇 |
2007年 | 143篇 |
2006年 | 115篇 |
2005年 | 93篇 |
2004年 | 83篇 |
2003年 | 74篇 |
2002年 | 70篇 |
2001年 | 77篇 |
2000年 | 78篇 |
1999年 | 57篇 |
1998年 | 59篇 |
1997年 | 47篇 |
1996年 | 52篇 |
1995年 | 34篇 |
1994年 | 21篇 |
1993年 | 29篇 |
1992年 | 15篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1966年 | 2篇 |
1931年 | 1篇 |
1924年 | 1篇 |
1884年 | 1篇 |
排序方式: 共有2877条查询结果,搜索用时 15 毫秒
91.
苯并菲盘状液晶的合成、亲氟效应及分子对称性对介晶性的影响 总被引:3,自引:0,他引:3
New symmetrical and asymmetrical triphenylene-containing discotic liquid crystals with two different peripheral alkyl chains, known as sym-TP(OC6H13)3(OR)3 and asym-TP(OC6H13)3(OR)3, were synthesized. Their thermotropic liquid crystal properties were investigated through polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The asyrranetdcal discogens are 2,6,11-rialkoxy-3,7,10-trihexyloxytriphenylenes, with the alkyl chain carbon numbers varying from 3-10, 12, and 14, while the symmetrical compounds are 2,6,10-trialkyloxy-3,7,11-trihexyloxytriphenylene. Two fluoroalkoxy substituted triphenylene discogens, 2,6,10-td(4,4,4-trifluorobutoxy)-3,7,11-trihexyloxytriphenylene and its asymmetrical isomer 2,6,11-tri(4,4,4-trifluorobutoxy)-3,7,10-trihexyloxytdphenylene were prepared. These two compounds show higher melting and clearing points than their alkoxy analogs, which implies that fluorophilic effect exists in the formation and stabilization of discotic columnar mesophase. The triphenylene derivatives TP(OC6H13)3(OR)3 with two different peripheral chains, symmetrically or asymmetrically attached on triphenylene cores, have lower melting points and clearing points than those of the higher symmetrical compounds TP(OR)6 with the same total chain carbon numbers. The mixed-chain-triphenylenes with longer alkoxy chains (n=9,10,12,14) show columnarmesophase at room temperature. 相似文献
92.
93.
94.
Yukun Feng Zhenzhen Liu Ying Peng Lunhui Zhang Ping Ju Kaishun Bi Xiaohui Chen 《Biomedical chromatography : BMC》2013,27(11):1503-1510
A simple and efficient liquid chromatography‐mass spectrometry (LC‐MS) method was developed and validated for simultaneous quantitation of catalpol and harpagide in normal and diabetic rat plasma. Protein precipitation extraction with acetonitrile was carried out using salidroside as the internal standard (IS). The LC separation was performed on an Elite C18 column (150 × 4.6 mm, 5 µm) with the mobile phase consisting of acetonitrile and water within a runtime of 12.0 min. The analytes were detected without endogenous interference in the selected ion monitoring mode with positive electrospray ionization. Calibration curves offered satisfactory linearity (r > 0.99) at linear range of 0.05–50.0 µg/mL for catalpol and 0.025–5.0 µg/mL for harpagide with the lower limits of quantitation of 0.05 and 0.025 µg/mL, respectively. Intra‐ and inter‐day precisions (RSD) were <9.4%, and accuracy (RE) was in the ?6.6 to 4.9% range. The extraction efficiencies of catalpol, harpagide and IS were all >76.5% and the matrix effects of the analytes ranged from 86.5 to 106.0%. The method was successfully applied to the pharmacokinetic study of catalpol and harpagide after oral administration of Zeng‐Ye‐Decoction to normal and diabetic rats, respectively. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
95.
96.
97.
98.
99.
100.
Likai Du Jun Gao Fuzhen Bi Lili Wang Chengbu Liu 《Journal of computational chemistry》2013,34(23):2032-2040
The anisotropic effects and short‐range quantum effects are essential characters in the formation of halogen bonds. Since there are an array of applications of halogen bonds and much difficulty in modeling them in classical force fields, the current research reports solely the polarizable ellipsoidal force field (PEff) for halogen bonds. The anisotropic charge distribution was represented with the combination of a negative charged sphere and a positively charged ellipsoid. The polarization energy was incorporated by the induced dipole model. The resulting force field is “physically motivated,” which includes separate, explicit terms to account for the electrostatic, repulsion/dispersion, and polarization interaction. Furthermore, it is largely compatible with existing, standard simulation packages. The fitted parameters are transferable and compatible with the general AMBER force field. This PEff model could correctly reproduces the potential energy surface of halogen bonds at MP2 level. Finally, the prediction of the halogen bond properties of human Cathepsin L (hcatL) has been found to be in excellent qualitative agreement with the cocrystal structures. © 2013 Wiley Periodicals, Inc. 相似文献