全文获取类型
收费全文 | 919篇 |
免费 | 23篇 |
国内免费 | 57篇 |
专业分类
化学 | 751篇 |
晶体学 | 50篇 |
力学 | 4篇 |
综合类 | 2篇 |
物理学 | 192篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 24篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 64篇 |
2012年 | 27篇 |
2011年 | 46篇 |
2010年 | 51篇 |
2009年 | 53篇 |
2008年 | 48篇 |
2007年 | 55篇 |
2006年 | 68篇 |
2005年 | 48篇 |
2004年 | 53篇 |
2003年 | 46篇 |
2002年 | 32篇 |
2001年 | 41篇 |
2000年 | 44篇 |
1999年 | 43篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有999条查询结果,搜索用时 0 毫秒
51.
在液镓电极上,反丁烯二腈(FDN)的电氢化二聚(EHD)不仅能在含离子型表面活性剂如四乙基对甲苯磺酸铵(TEA-PTS)溶液中发生,同样也能在含低浓度的强表面活性剂如TritonX-100溶液中进行,在不含有机表面活性剂的溶液中,FDN在滴镓电极上产生一个2电子还原波,生成为丁二腈的饱和单体。在水溶液中加入一定浓度的TEA-PTS或低浓度的TritonX-100时,原来的2电子还原波分裂成两个连续 相似文献
52.
Lin Peng Liang-Liang Wang Jian-Fei Bai Li-Na Jia Qing-Chuan Yang Qing-Chun HuangXiao-Ying Xu Li-Xin Wang 《Tetrahedron letters》2011,52(11):1157-1160
Cinchona alkaloids were first successfully reported to promote enantioselective Phospho-Aldol reaction of diphenyl phosphite to a variety of N-alkylated isatin derivatives in good to excellent yields (up to 99%) and moderate to good enantioselectivities (up to 73% ee) almost in no time. 相似文献
53.
One-pot three-component Kabachnik-Fields synthesis of α-aminophosphonates with high yields from the reaction between carbonyl compound, primary amine, and substituted phosphite can be carried out in a short period, using H-beta zeolite as a reusable catalyst. 相似文献
54.
Subvalent Gallium Triflates – Potentially Useful Starting Materials for Gallium Cluster Compounds By reaction of GaCp* with trifluormethanesulfonic acid in hexane a mixture of gallium trifluormethanesulfonates (triflates, OTf) is obtained. This mixture reacts readily with lithiumsilanides [Li(thf)3Si(SiMe3)2R] (R = Me, SiMe3) to afford the cluster compounds [Ga6{Si(SiMe3)Me}6], [Ga2{Si(SiMe3)3}4] and [Ga10{Si(SiMe3)3}6]. By crystallization from various solvents the gallium triflates [Ga(OTf)3(thf)3], [HGa(OTf)(thf)4]+ [Ga(OTf)4(thf)3]−, [Cp*GaGa(OTf)2]2 and [Ga(toluene)2]+ [Ga5(OTf)6(Cp*)2]− were isolated and characterized by single crystal X ray structure analysis. 相似文献
55.
An efficient, economical and easy method for the synthesis of dimethylaminomethylenediphosphonates using bis(trichloromethyl) carbonate and RCONR1R2 has been developed, which proceeded under relatively mild conditions. 相似文献
56.
57.
58.
We study the steady-state three-dimensional flow which occurs in a horizontal crucible of molten metal under the action of a horizontal temperature gradient. The geometry and the boundary conditions are similar to those encountered in the Bridgman growth process of semiconductor crystals. We find that three-dimensional effects can have a dramatic influence upon the flow, which, before the onset of periodic disturbances, differs appreciably from its two-dimensional counterpart. We also investigate the sensitivity of the flow to non-symmetric disturbances. 相似文献
59.
A phosphite ligand modified Rh/SiO2 catalyst has been developed for hydroformylation of internal olefins to linear aldehydes, which showed high activity and regioselectivity and could be separated easily by filtration after reaction in an autoclave. Effects of reaction temperature and syngas pressure on the performances of the catalyst in the reaction were also investigated. 相似文献
60.
Zhimin Jiang Han Yan Sheng Liu Zhi Zhang Zhiyin Gan Haisheng Fang 《Crystal Research and Technology》2016,51(1):30-40
Doped or undoped gallium nitride compounds (GaN/InGaN), usually grown by metal‐organic chemical vapor deposition (MOCVD) method, are at the heart of blue and green light emitting diodes (LEDs). Growth uniformities, such as the excited wavelength, luminous intensity and film thickness, critically influence their application in LED devices. In this paper, growth of GaN compounds in a MOCVD reactor, capable of a one‐time production of 36 × 2” wafers of nitrides, has been investigated. To examine growth uniformity across the wafer and from wafer to wafer, the reactor is divided into Zone A, Zone B and Zone C according to distance to the center of the graphite susceptor. Comparative analysis of each zone offers a straightforward view of the mean excitation wavelength, luminous intensity, film thickness and their standard deviations. Conformity of the growth uniformity in each zone is further checked comprehensively through averaging across‐wafer and wafer‐to‐wafer variables and their standard deviations. Zone B is found to retain excellent wavelength uniformity, since it is located at the middle of the susceptor with weaker effects of the susceptor edge and of the inlet gas flow. Zone A, at the center of the reactor, has the best mean intensity and thickness uniformities due to a well control of the infrared temperature measurement during the growth. And Zone C is worst in all uniformities and should be the main focus when optimizing the reactor. The above experimental analysis reveals the principles common to the MOCVD technique, and provides a basic for further optimization of the process window to improve the cycles with considerable reduction of the costs. 相似文献