全文获取类型
收费全文 | 1408篇 |
免费 | 313篇 |
国内免费 | 556篇 |
专业分类
化学 | 1116篇 |
晶体学 | 81篇 |
力学 | 137篇 |
综合类 | 50篇 |
数学 | 199篇 |
物理学 | 694篇 |
出版年
2024年 | 11篇 |
2023年 | 13篇 |
2022年 | 56篇 |
2021年 | 55篇 |
2020年 | 60篇 |
2019年 | 64篇 |
2018年 | 56篇 |
2017年 | 64篇 |
2016年 | 42篇 |
2015年 | 64篇 |
2014年 | 90篇 |
2013年 | 111篇 |
2012年 | 107篇 |
2011年 | 133篇 |
2010年 | 130篇 |
2009年 | 127篇 |
2008年 | 141篇 |
2007年 | 119篇 |
2006年 | 125篇 |
2005年 | 126篇 |
2004年 | 82篇 |
2003年 | 67篇 |
2002年 | 69篇 |
2001年 | 80篇 |
2000年 | 66篇 |
1999年 | 48篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2277条查询结果,搜索用时 15 毫秒
51.
p-tert-Butylcalix[6]-1,4-2,5-biscrown-4 is a typical member of the family of calix[6]crowns. In the literature, the compound was synthesized from calix[6]arene by two steps and the overall yield based on calix[6]arene was 24%.Herein we wish to report a one-pot method to do this work. By this method the yield was up to 48% and the reaction time was greatly reduced. 相似文献
52.
茉莉醛相转移催化合成法的改良 总被引:4,自引:0,他引:4
茉莉醛又称2-戊基肉桂醛,具有优雅的茉莉花香,是一种深受调香师喜爱的合成香料。目前已广泛应用于各种日用化学品中。 相似文献
53.
Three-dimensional quantum mechanical calculations for vibrational predissociation of HeI2(B) van der Waals molecules are presented using the time-dependent wave packet technique within the golden rule approxima tion.The total and partial decay widths,lifetimes,rates and their dependence on initial vibrational states were obtained for HeI2 at low initial vibrational excited levels.Our calculations show that the calculated tota decay widths,lifetimes and rates agree well with those extrapolated from experimental data available The predicted total decay widths as a function of initial vibrational states exhibit highly nonlinear behavior.The very short propagation time (less.than 1 ps) required in the golden rule wave packet calculation is determined by the duration time of the final state inter-action between the fragments on the vibrationally deexcited adiabatic potential surface.The final state interaction between the fragments is shown to play an important role in determining the final rotational distri 相似文献
54.
聚甲基丙烯酸甲酯辐射裂解和消旋的空间立构效应 总被引:1,自引:1,他引:1
本文研究了三种不同空间立构聚甲基丙烯酸甲酯的辐射效应,提出裂解过程是一种裂解与重合的动态平衡过程。分子量降低和消旋作用对温度的依赖性,是由于分子运动和笼罩效应以及重合的空间位阻效应所致。辐照温度愈高,裂解产额愈大。相同条件下辐照,全同立构比无规立构试样的裂解产额更大。 全同立构聚甲基丙烯酸甲酯辐照后,不仅分子链断裂,而且空间立构也发生很大变化。随着辐照剂量的增加,全同立构含量逐渐减少,而无规立构含量和间同立构含量却逐渐增加。 相似文献
55.
56.
Consider a kind of Hermit interpolation for scattered data of 3D by trivariate polynomial natural spline,such that the objective energy functional (with natural boundary conditions) is minimal.By the s... 相似文献
57.
Li Shuaiqi Han Xiaoxu An Hualiang Zhao Xinqiang Wang Yanji 《Kinetics and Catalysis》2021,62(5):632-640
Kinetics and Catalysis - Ethanol Guerbet condensation (EGC) is a green process for preparing n-butanol and the development of highly effective solid catalysts is still the bottleneck of this... 相似文献
58.
L Hui-Yi WANG Tie-Shan HAN Yun-Cheng FANG Kai-Hong MENG Xuan HE Qing-Hua GUAN Xing-Cai LAN Ming-Cong 《中国物理C(英文版)》2011,35(1):26-30
The D(d,p)T reaction in Be metal environments has been measured to investigate the electron screening effect in metals in an energy region of from 5.5 keV to 10 keV in a center of mass system(CMS)at a temperature of 121 K.The depth distribution of deuteron density in Be metals has an impact on the observed reaction yields.A model of deuteron density distribution in metal has been proposed to obtain the original yields.A screening energy of(116±46)eV has been obtained with the assumed deuteron density distribution model. 相似文献
59.
利用同余式、平方剩余、Pell方程的解的性质、递归序列证明了:不定方程x3-1=749y2仅有整数解(x,y)=(1,0). 相似文献
60.
Metabolism studies on prim‐O‐glucosylcimifugin and cimifugin in human liver microsomes by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
Peipei Jia Yuqian Zhang Qiaoyue Zhang Yupeng Sun Haotian Yang He Shi Xiaoxu Zhang Lantong Zhang 《Biomedical chromatography : BMC》2016,30(9):1498-1505
Prim‐O‐glucosylcimifugin (PGCN) and cimifugin (CN) are major constituents of Radix Saposhnikoviae that have antipyretic, analgesic and anti‐inflammatory pharmacological activities. However, there were few reports with respect to the metabolism of PGCN and CN in vitro. In this paper, we describe a strategy using ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry (UPLC‐Q‐TOF‐MS) for fast analysis of the metabolic profile of PGCN and CN in human liver microsomes. In total, five phase I metabolites of PGCN, seven phase I metabolites and two phase II metabolites of CN were identified in the incubation of human liver microsomes. The results revealed that the main phase I metabolic pathways of PGCN were hydroxylation and hydrolysis reactions. The phase I metabolic pathways of CN were found to be hydroxylation, demethylation and dehydrogenation. Meanwhile, the results indicated that O‐glucuronidation was the major metabolic pathway of CN in phase II metabolism. The specific UDP‐glucuronosyltransferase (UGT) enzymes responsible for CN glucuronidation metabolites were identified using recombinant UGT enzymes. The results indicated that UGT1A1, UGT1A9, UGT2B4 and UGT2B7 might play major roles in the glucuronidation of CN. Overall, this study may be useful for the investigation of metabolic mechanism of PGCN and CN, and it can provide reference and evidence for further pharmacodynamic experiments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献