全文获取类型
收费全文 | 118795篇 |
免费 | 18358篇 |
国内免费 | 14306篇 |
专业分类
化学 | 83812篇 |
晶体学 | 1393篇 |
力学 | 6543篇 |
综合类 | 917篇 |
数学 | 14388篇 |
物理学 | 44406篇 |
出版年
2024年 | 376篇 |
2023年 | 2184篇 |
2022年 | 3988篇 |
2021年 | 4190篇 |
2020年 | 4526篇 |
2019年 | 4341篇 |
2018年 | 4051篇 |
2017年 | 3657篇 |
2016年 | 5531篇 |
2015年 | 5519篇 |
2014年 | 6773篇 |
2013年 | 8844篇 |
2012年 | 10450篇 |
2011年 | 10699篇 |
2010年 | 7569篇 |
2009年 | 7280篇 |
2008年 | 7813篇 |
2007年 | 7012篇 |
2006年 | 6573篇 |
2005年 | 5495篇 |
2004年 | 4421篇 |
2003年 | 3614篇 |
2002年 | 3481篇 |
2001年 | 2890篇 |
2000年 | 2463篇 |
1999年 | 2436篇 |
1998年 | 1981篇 |
1997年 | 1786篇 |
1996年 | 1745篇 |
1995年 | 1544篇 |
1994年 | 1408篇 |
1993年 | 1162篇 |
1992年 | 1041篇 |
1991年 | 879篇 |
1990年 | 745篇 |
1989年 | 578篇 |
1988年 | 419篇 |
1987年 | 384篇 |
1986年 | 367篇 |
1985年 | 295篇 |
1984年 | 210篇 |
1983年 | 168篇 |
1982年 | 135篇 |
1981年 | 91篇 |
1980年 | 67篇 |
1979年 | 29篇 |
1978年 | 33篇 |
1976年 | 30篇 |
1975年 | 27篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex 下载免费PDF全文
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
34.
35.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
36.
37.
38.
39.
Development of an LC‐MS/MS method for determining the pharmacokinetics of clonidine following oral administration of Zhenju antihypertensive compound 下载免费PDF全文
Jing Qin Limin Wang Lihong Wu Jun Chen Teng Shen Yongji Li Limei Han Jianxin Wang 《Biomedical chromatography : BMC》2015,29(7):1068-1075
Zhenju antihypertensive compound (ZJAHC) is a combined Chinese–Western medicine formula including clonidine (CLO), hydrochlorothiazide (HCT), rutin, Chrysanthemum indicum extract and pearl powder. Compared with CLO preparations, ZJAHC shows improved activities and decreased adverse effects. It is believed that the side effects of CLO are caused by its high peak plasma concentration. Hence, study of the influence of ZJAHC on the pharmacokinetic behaviors of clonidine seems essential. In present study, the plasma concentrations of CLO were determined with a liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method. The MS/MS transitions monitored for clonidine and internal standard were 230.2 → 213.1 and 152.2 → 110.2, respectively. The analyte was quantified in a single run within 3 min. The pharmacokinetic study showed that the area under the plasma concentration–time curve of CLO in ZJAHC (60 µg/kg CLO) was similar to that of CLO‐HCT‐high (120 µg/kg CLO) but the peak concentration was much lower than that in CLO‐HCT‐high. ZJAHC could enhance the bioavailability without greatly increasing peak concentration of clonidine. This comprehensive effect of enhancing the bioavailability and avoiding the high peak plasma concentration for CLO might mainly result from the co‐contribution of Western medicine and traditional Chinese medicine (TCM), while the effect of TCM was stronger than that of Western medicine. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
40.