全文获取类型
收费全文 | 1031篇 |
免费 | 70篇 |
国内免费 | 40篇 |
专业分类
化学 | 793篇 |
晶体学 | 9篇 |
力学 | 30篇 |
综合类 | 1篇 |
数学 | 104篇 |
物理学 | 204篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 11篇 |
2016年 | 38篇 |
2015年 | 45篇 |
2014年 | 40篇 |
2013年 | 70篇 |
2012年 | 71篇 |
2011年 | 77篇 |
2010年 | 62篇 |
2009年 | 44篇 |
2008年 | 84篇 |
2007年 | 57篇 |
2006年 | 53篇 |
2005年 | 50篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 34篇 |
2001年 | 15篇 |
2000年 | 23篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1985年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1967年 | 4篇 |
1964年 | 2篇 |
1934年 | 2篇 |
排序方式: 共有1141条查询结果,搜索用时 0 毫秒
61.
Reaction of N-tert-butyloxycarbonylasparagine (Boc-Asn) with 2 equiv of benzyl bromide in presence of cesium carbonate led to N-benzyl-3-Boc-amino-pyrrolidin-2,5-dione 1a (N-benzyl-3-Boc-aminosuccinimide). Borane dimethylsulfide reduced 3-Boc-aminopyrrolidine-2,5-dione 1a into 3-Boc-aminopyrrolidin-2-one 2a. The same procedure could also be used to prepare derivatives 1 and 2 substituted on the aromatic ring. 相似文献
62.
Prof. Dr. Minghuey Shieh Chun‐Hsien Yu Yen‐Yi Chu Yu‐Wen Guo Chung‐Yi Huang Kai‐Jieah Hsing Pei‐Chi Chen Chung‐Feng Lee 《化学:亚洲杂志》2013,8(5):963-973
The reactions of E powder (E=S, Se) with a mixture of Cr(CO)6 and Mn2(CO)10 in concentrated solutions of KOH/MeOH produced two new mixed Cr? Mn? carbonyl clusters, [E2CrMn2(CO)9]2? (E=S, 1 ; Se, 2 ). Clusters 1 and 2 were isostructural with one another and each displayed a trigonal‐bipyramidal structure, with the CrMn2 triangle axially capped by two μ3‐E atoms. The analogous telluride cluster, [Te2CrMn2(CO)9]2? ( 3 ), was obtained from the ring‐closure of Te2Mn2 ring complex [Te2Mn2Cr2(CO)18]2? ( 4 ). Upon bubbling with CO, clusters 2 and 3 were readily converted into square‐pyramidal clusters, [E2CrMn2(CO)10]2? (E=Se, 5 ; Te, 6 ), accompanied with the cleavage of one Cr? Mn bond. According to SQUID analysis, cluster 6 was paramagnetic, with S=1 at room temperature; however, the Se analogue ( 5 ) was spectroscopically proposed to be diamagnetic, as verified by TD‐DFT calculations. Cluster 6 could be further carbonylated, with cleavage of the Mn? Mn bond to produce a new arachno‐cluster, [Te2CrMn2(CO)11]2? ( 7 ). The formation and structural isomers, as well as electrochemistry and UV/Vis absorption, of these clusters were also elucidated by DFT calculations. 相似文献
63.
Sharpless KE Lindstrom RM Nelson BC Phinney KW Rimmer CA Sander LC Schantz MM Spatz RO Thomas JB Turk GC Wise SA Wood LJ Yen JH 《Journal of AOAC International》2010,93(4):1262-1274
Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST. 相似文献
64.
Ruixiang Qu Xiangyu Li Yanan Liu Huajun Zhai Shuaiheng Zhao Lin Feng Yen Wei 《Angewandte Chemie (International ed. in English)》2020,59(32):13437-13443
Superwetting membranes with responsive properties have attracted heightened attention because of their fine‐tunable surface wettability. However, their functional diversity is severely limited by the “black‐or‐white” wettability transition. Herein, we describe a coating strategy to fabricate multifunctional responsive superwetting membranes with SiO2/octadecylamine patterns. The adjustable patterns in the responsive region are the key factor for functional diversity. Specifically, the coated part of the membrane displayed a superhydrophobicity/superhydrophilicity transition at different pH values, whereas the uncoated part exhibited invariant superhydrophilicity. On the basis of this anisotropy/isotropy transition, the membranes can serve as either responsive permeable membranes or signal‐expression membranes, thus enabling the responsive separation and permeation of liquids with satisfactory separation efficiency (>99.90 %) and flux (ca. 60 L m?2 h), as well as real‐time liquid signal expression with alterable signals. 相似文献
65.
Titanium dioxide (TiO2), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N2 atmosphere at a temperature regime of 400-600 °C. First-principle calculations show that the (Fe, N) co-deposited TiO2 films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO2 films were effective in both prohibiting electron-hole recombination and generating additional Fe-O and N-Ti-O impurity levels for the TiO2 band gap. The (Fe, N) co-deposited TiO2 has a narrower band gap of 1.97 eV than Fe-implanted TiO2 (3.14 eV) and N-doped TiO2 (2.16 eV). A significant reduction of TiO2 band gap energy from 3.22 to 1.97 eV was achieved, which resulted in the extension of photocatalytic activity of TiO2 from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO2 under visible light irradiation. 相似文献
66.
A reproducible, large scale and practical synthesis of N-(benzyloxycarbonyl)-L-vinylglycine methyl ester starting from L-methionine methyl ester hydrochloride is described. 相似文献
67.
68.
Using high‐resolution transmission electronic micrograph (HR‐TEM) observation, one can clearly see the pore geometry of the MCM‐41 and SBA‐15 mesoporous silicas to determine that their pore shapes are hexagonal and round, respectively. With the perpendicular orientations of the nanochannels to the electron beam, parallel line images of the (100) and (110) repeating spacings were observed. In the SBA‐15 mesoporous silicas, there are byproducts of the granular silica and disordered mesostructures, attributed to the weak hydrogen interactions between Pluronic 123 blockcopolymer and the silica species. There are also many different and significant +π disclination defects in SBA‐15 and MCM‐41 surfactant‐silica composites. The SBA‐15 with a thicker silica wall is more stable under irradiation by high‐energy electron beams compared to MCM‐41, which has thinner wall thickness. Some carbon nanostructure impurities were found in some carbon films on the metal grids. 相似文献
69.
Yi-Jung Liu Chih-Hung Yen Chia-Hao Hsu Kuo-Hui Yu Li-Yang Chen Tsung-Han Tsai Wen-Chau Liu 《Optical Review》2009,16(6):575-577
An interesting GaN-based light emitting diode (LED) using a 50 nm indium oxide (In2O3)/250 nm indium-tin oxide (ITO) mixed structure to replace the commonly used ITO (250 nm) current spreading layer is fabricated
and studied. Use of the In2O3 layer could reduce the contact resistance of p-GaN in LEDs. In addition, this highly-resistive In2O3 layer, below the ITO layer could improve the current spreading performance. Experimentally, at room temperature, using this
mixed structure, the luminous and EL intensities are enhanced by 17.7 and 17.1%, respectively. 相似文献
70.
Tang F Wang J Liu D Yuan G Liu Y Jin Zhu C Fen Zhao Y 《Rapid communications in mass spectrometry : RCM》2002,16(11):1035-1039
The electrospray ionization tandem mass spectrometric (ESI-MS/MS) characteristics and fragmentation mechanisms of eight distamycin analogues containing N-methylpyrrole and N-methylimidazole were investigated. The members of two isomeric groups of distamycin analogues with the same elemental composition can be distinguished by MS/MS spectra of protonated molecules and of significant fragment ions. 相似文献