全文获取类型
收费全文 | 47933篇 |
免费 | 6964篇 |
国内免费 | 4958篇 |
专业分类
化学 | 33159篇 |
晶体学 | 480篇 |
力学 | 2928篇 |
综合类 | 312篇 |
数学 | 5631篇 |
物理学 | 17345篇 |
出版年
2024年 | 163篇 |
2023年 | 999篇 |
2022年 | 1610篇 |
2021年 | 1759篇 |
2020年 | 1849篇 |
2019年 | 1765篇 |
2018年 | 1519篇 |
2017年 | 1460篇 |
2016年 | 2117篇 |
2015年 | 2130篇 |
2014年 | 2573篇 |
2013年 | 3381篇 |
2012年 | 4151篇 |
2011年 | 4132篇 |
2010年 | 2824篇 |
2009年 | 2637篇 |
2008年 | 2927篇 |
2007年 | 2572篇 |
2006年 | 2420篇 |
2005年 | 1947篇 |
2004年 | 1681篇 |
2003年 | 1265篇 |
2002年 | 1216篇 |
2001年 | 949篇 |
2000年 | 912篇 |
1999年 | 1091篇 |
1998年 | 876篇 |
1997年 | 772篇 |
1996年 | 842篇 |
1995年 | 741篇 |
1994年 | 652篇 |
1993年 | 584篇 |
1992年 | 544篇 |
1991年 | 453篇 |
1990年 | 406篇 |
1989年 | 298篇 |
1988年 | 262篇 |
1987年 | 237篇 |
1986年 | 163篇 |
1985年 | 187篇 |
1984年 | 159篇 |
1983年 | 130篇 |
1982年 | 95篇 |
1981年 | 65篇 |
1980年 | 55篇 |
1979年 | 37篇 |
1978年 | 32篇 |
1976年 | 30篇 |
1975年 | 34篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Shipeng Wu Yinghao Wang Prof. Qiue Cao Prof. Qihua Zhao Dr. Wenhao Fang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(9):3019-3028
High-surface-area mesoporous CeO2 (hsmCeO2) was prepared by a facile organic-template-induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO2 and hsmCeO2 after different thermal treatments were also investigated. XRD, N2 physisorption, UV-Raman, H2 temperature-programmed reduction, O2 temperature-programmed desorption, EPR spectroscopy, and X-ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO2 calcined at 400 °C shows the highest specific surface area (158 m2 g−1), the highest fraction of surface coordinatively unsaturated Ce3+ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4×1015 spins g−1). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO2 catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol h−1 based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram-scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO2 catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated. 相似文献
992.
993.
994.
A novel electrochemical approach has been proposed to measure the interface potential at the electrode/solution interface based on reconstructing the three‐electrode system of a potentiostat. In this work, the method was investigated both theoretically and experimentally. Mathematical expressions, describing current? potential characteristics, were derived. Zero current potential Ezcp was defined as the potential at which the current is zero based on linear sweep voltammetry, and was determined from the I? E curve to measure the interface potential. The experimental results obtained with the couples Fe(CN)63?/Fe(CN)64? and Co(NH3)63+/Co(NH3)62+ as examples agreed well with the theory. The proposed approach exhibits an excellent performance for measuring the interface potential due to the advantages of rapidity, high stability and accuracy. 相似文献
995.
Organobentonite (OBT)/sodium polyacrylate (PAAS) composite material was prepared. The OBT/PAAS humidity-control cement-based mortars were prepared by mixing OBT/PAAS in mortar. Its morphology and structure were characterized by environmental scanning electron microscope (ESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the Brunauer-Emmett-Teller (BET) method. The results showed that the morphology and humidity-control capacity of OBT/PAAS mortar are superior to those of the original mortar. The OBT/PAAS mortar had larger pore specific surface area and larger pore volume, corresponding to the most probable pore diameter, than that of mortar. There was no chemical reaction between mortar and OBT/PAAS and there was no new crystal structure generated. The prepared, solidified OBT-PAAS mortar can maintain humidity in a desiccator at 38~62 RH%. 相似文献
996.
Abstract The chemical modified β-cyclodextrin(CD), which bears a fluorophore group — N,N-dimethylamino-chalcone (DMAC), was synthesized. The self-inclusion behavior of this compound in aqueous solution and in alcohol/water mixed solvents was investigated in detail, and compared with the inclusion system of non-modified CD with free DMAC molecule. The results showed that a deep self-inclusion complex was formed for this compound in aqueous solution and had the ability to recognize different organic molecules by two fully different modes: “in-out” and “co-inclusion” mechanisms. The inclusion behavior of these systems in various ratio of alcohol/water mixture as solvents was investigated. The results indicated that the self-inclusion complex has a higher stability in alcohol/water mixed solvents than that in the case of non-modified CD. The chalcone group appended at β-CD enabled the host as a sensitive probe to study the inclusion behavior of CD. 相似文献
997.
998.
999.
1000.