全文获取类型
收费全文 | 4462篇 |
免费 | 156篇 |
国内免费 | 107篇 |
专业分类
化学 | 3190篇 |
晶体学 | 53篇 |
力学 | 62篇 |
综合类 | 6篇 |
数学 | 268篇 |
物理学 | 1146篇 |
出版年
2023年 | 28篇 |
2021年 | 41篇 |
2020年 | 71篇 |
2019年 | 67篇 |
2018年 | 47篇 |
2017年 | 36篇 |
2016年 | 74篇 |
2015年 | 87篇 |
2014年 | 103篇 |
2013年 | 195篇 |
2012年 | 201篇 |
2011年 | 252篇 |
2010年 | 129篇 |
2009年 | 163篇 |
2008年 | 240篇 |
2007年 | 251篇 |
2006年 | 250篇 |
2005年 | 209篇 |
2004年 | 214篇 |
2003年 | 189篇 |
2002年 | 211篇 |
2001年 | 178篇 |
2000年 | 126篇 |
1999年 | 86篇 |
1998年 | 57篇 |
1997年 | 61篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 53篇 |
1993年 | 60篇 |
1992年 | 75篇 |
1991年 | 61篇 |
1990年 | 52篇 |
1989年 | 59篇 |
1988年 | 42篇 |
1987年 | 57篇 |
1986年 | 48篇 |
1985年 | 56篇 |
1984年 | 51篇 |
1983年 | 39篇 |
1982年 | 26篇 |
1981年 | 47篇 |
1980年 | 37篇 |
1979年 | 51篇 |
1978年 | 42篇 |
1977年 | 25篇 |
1976年 | 36篇 |
1975年 | 27篇 |
1974年 | 29篇 |
1973年 | 21篇 |
排序方式: 共有4725条查询结果,搜索用时 609 毫秒
91.
Shu Jun WANG Wen Yuan GAO Jing Lin YU Pei Gen XIAO 《中国化学快报》2006,17(9):1255-1258
Dioscoreae (Chinese name Shanyao), the rhizome of various species of genus Dioscorea opposita Thunb.(Dioscoreaceae), has been used as an important invigorant in traditional Chinese medicine (TCM) for many years1. Starch, the most abundant carbohydrate in … 相似文献
92.
A new method for determination of antithrombotic activity of egg white protein hydrolysate by microplate reader 总被引:3,自引:0,他引:3
Wan Gen Yang Zhang Wang* Shi Ying Xu School of Food Science&Technology Southern Yangtze University Wuxi China 《中国化学快报》2007,18(4):449-451
A new method for the determination of antithrombotic activity of egg white protein hydrolysate(EWPH)was developed using amicroplate reader.Reaction was carried out at 37℃ and pH 7.2 with fibrinogen concentration 0.1%.Microplate reading wasconducted at 405 nm.Inhibition rate of EWPH on thrombin activity showed linearity(R~2=0.9971),when the inhibition rate was inthe range of 10-90%.The lower limit of detection(LLD,at 99.7%probability)and the biological limit of detection(BLD,at 99.7%probability)of the method were 10.643 and 40 mg/mL,respectively.The repeatability standard deviation(R.S.D.)was 1.08%.Thestandard deviation of the method was 0.027 AT-U. 相似文献
93.
Travert A Nakamura H van Santen RA Cristol S Paul JF Payen E 《Journal of the American Chemical Society》2002,124(24):7084-7095
Hydrogen adsorption on Mo[bond]S, Co[bond]Mo[bond]S, and Ni[bond]Mo[bond]S (10 1 macro 0) surfaces has been modeled by means of periodic DFT calculations taking into account the gaseous surrounding of these catalysts in working conditions. On the stable Mo[bond]S surface, only six-fold coordinated Mo cations are present, whereas substitution by Co or Ni leads to the creation of stable coordinatively unsaturated sites. On the stable MoS(2) surface, hydrogen dissociation is always endothermic and presents a high activation barrier. On Co[bond]Mo[bond]S surfaces, the ability to dissociate H(2) depends on the nature of the metal atom and the sulfur coordination environment. As an adsorption center, Co strongly favors molecular hydrogen activation as compared to the Mo atoms. Co also increases the ability of its sulfur atom ligands to bind hydrogen. Investigation of surface acidity using ammonia as a probe molecule confirms the crucial role of sulfur basicity on hydrogen activation on these surfaces. As a result, Co[bond]Mo[bond]S surfaces present Co[bond]S sites for which the dissociation of hydrogen is exothermic and weakly activated. On Ni[bond]Mo[bond]S surfaces, Ni[bond]S pairs are not stable and do not provide for an efficient way for hydrogen activation. These theoretical results are in good agreement with recent experimental studies of H(2)[bond]D(2) exchange reactions. 相似文献
94.
Ming Xian LIU Li Hua GAN Gen CHEN Zi Jie XU Zhi Xian HAO Long Wu CHEN 《中国化学快报》2006,17(8):1085-1088
Recently the research on structures with an ordered two-dimensional(2D) pattern has attracted great attention due to its versatile applications in the fields of microelectronic and optoelectronic devices, displays, biochips and sensors, enzymatic immobilization, drug carriers, and photonic band gap materials. Various well-arrayed 2D structures have been made by the modern technique such as laser writing pattern fabrication, photoetching technique, micro-electromechanical systems based on scann… 相似文献
95.
A new strategy using a BINOL derivative as a chiral leaving group and Lewis acid has been developed for enantioselective alkylation of prochiral olefins. (R)-2,2'-Bis[2-(trimethylsilyl)ethoxymethyl]-1,1'-binaphthol is demonstrated to be an effective reagent for enantioselective hydroxymethylation of silyl enol ethers and trisubstituted alkenes. Electrophilic addition to prochiral olefins is accompanied by cleavage of an acetal that is dual activated by SnCl4 and the delta-effect of silicon through the S(N)2 substitution process. Enantioselective synthesis of cyclic terpenes is also described using this strategy. 相似文献
96.
Nakamura T Ikemoto JY Fujitsuka M Araki Y Ito O Takimiya K Aso Y Otsubo T 《The journal of physical chemistry. B》2005,109(30):14365-14374
The dramatic changes of the lifetimes of the charge-separated (CS) states were confirmed in zinc porphyrin (ZnP)-oligothiophene (nT)-fullerene (C(60)) linked triads (ZnP-nT-C(60)) with the solvent polarity. After the selective excitation of the ZnP moiety of ZnP-nT-C(60), an energy transfer took place from the (1)ZnP moiety to the C(60) moiety, generating ZnP-nT-(1)C(60). In polar solvents, the CS process also took place directly via the (1)ZnP moiety, generating ZnP(*+)-nT-C(60)(*-), as well as the energy transfer to the C(60) moiety. After this energy transfer, an indirect CS process took place from the (1)C(60) moiety. In the less polar solvent anisole, the radical cation (hole) of ZnP(*+)-nT-C(60)(*-) shifted to the nT moiety; thus, the nT moiety behaves as a cation trapper, and the rates of the hole shift were evaluated to be in the order of 10(8) s(-1); then, the final CS states ZnP-nT(*+)-C(60)(*-) were lasting for 6-7 mus. In the medium polar solvent o-dichlorobenzene (o-DCB), ZnP-nT(*+)-C(60)(*-) and ZnP(*+)-nT-C(60)(*-) were present as an equilibrium, because both states have almost the same thermodynamic stability. This equilibrium resulted in quite long lifetimes of the CS states (450-910 mus) in o-DCB. In the more polar benzonitrile, the generation of ZnP-nT(*+)-C(60)(*-) was confirmed with apparent short lifetimes (0.6-0.8 mus), which can be explained by the fast hole shift to more stable ZnP(*+)-nT-C(60)(*-) followed by the faster charge recombination. It was revealed that the relation between the energy levels of two CS states, which strongly depend on the solvent polarity, causes dramatic changes of the lifetimes of the CS states in ZnP-nT-C(60); that is, the most appropriate solvents for the long-lived CS state are intermediately polar solvents such as o-DCB. Compared with our previous data for H(2)P-nT-C(60), in which H(2)P is free-base porphyrin, the lifetimes of the CS states of ZnP-nT-C(60) are approximately 30 times longer than those in o-DCB. 相似文献
97.
Isolation and structure determination of six glucocerebrosides from the starfish Luidia maculata 总被引:1,自引:0,他引:1
Two new glucocerebrosides, luidiacerebroside A (2) and B (6), were isolated from the cerebroside molecular species obtained from the less polar fraction of the CHCl3/MeOH extract of the starfish Luidia maculata using HPLC. Four known cerebrosides, CE-2b (1), astrocerebroside B (3), acanthacerebroside B (4), and CE-3-2 (5) have also been isolated and characterized. The structures of these cerebrosides were determined on the basis of chemical and spectroscopic evidence. Mass spectrometry of dimethyl disulfide derivatives was useful for the determination of the double-bond position in the long-chain base. 相似文献
98.
A kinetic study on methanol dehydrogenation over an FeTiZn0.44 alloy at 673 K suggested a mechanism including an adsorbed formaldehyde intermediate. A lower W/F and a higher methanol pressure favored a higher formaldehyde selectivity. 相似文献
99.
100.
Photolysis of perfluoroazooctane with diamond powders led to chemical modification of the surface with the introduction of perfluorooctyl ester and ether functional groups, the presence of which was confirmed by means of FT-IR, XPS and 19F NMR measurements. 相似文献