全文获取类型
收费全文 | 21528篇 |
免费 | 3943篇 |
国内免费 | 4919篇 |
专业分类
化学 | 16656篇 |
晶体学 | 356篇 |
力学 | 1209篇 |
综合类 | 411篇 |
数学 | 2938篇 |
物理学 | 8820篇 |
出版年
2024年 | 38篇 |
2023年 | 331篇 |
2022年 | 633篇 |
2021年 | 740篇 |
2020年 | 813篇 |
2019年 | 877篇 |
2018年 | 712篇 |
2017年 | 757篇 |
2016年 | 898篇 |
2015年 | 1053篇 |
2014年 | 1222篇 |
2013年 | 1611篇 |
2012年 | 1843篇 |
2011年 | 1913篇 |
2010年 | 1482篇 |
2009年 | 1599篇 |
2008年 | 1715篇 |
2007年 | 1469篇 |
2006年 | 1379篇 |
2005年 | 1230篇 |
2004年 | 1006篇 |
2003年 | 800篇 |
2002年 | 879篇 |
2001年 | 797篇 |
2000年 | 821篇 |
1999年 | 574篇 |
1998年 | 417篇 |
1997年 | 362篇 |
1996年 | 302篇 |
1995年 | 286篇 |
1994年 | 236篇 |
1993年 | 249篇 |
1992年 | 189篇 |
1991年 | 158篇 |
1990年 | 157篇 |
1989年 | 137篇 |
1988年 | 131篇 |
1987年 | 103篇 |
1986年 | 83篇 |
1985年 | 62篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 58篇 |
1981年 | 37篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1965年 | 10篇 |
1964年 | 9篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Liangru Yang Yunfei Li Pu Mao Jinwei Yuan Yongmei Xiao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):780-788
AbstractThe catalytic activity of a series of chiral heteroaryl coordinated chelating N-heterocyclic carbene (NHC) palladium complexes towards asymmetric allylic alkylation (AAA) were presented here. The effects of different N-substituents, NHC backbones and chelate rings on the catalytic activity and the enantioselectivity of the alkylation of (E)-1,3-diarylallyl acetates with dialkyl malonate were investigated. The results showed that, under the optimized conditions, complexes 3a, 3b, and 3i carrying the pyridinyl-coordinated five-membered chelate ring showed high catalytic activity and chiral induction efficiency. The corresponding alkylated products were obtained in high yields with moderate ee. Furthermore, it was found that the substituents of (E)-1,3-diarylallyl acetates and the type of the nucleophile affect the results as well. 相似文献
942.
Chengye Yuan Jiachang Yao Shusen Li 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):21-27
Abstract For the evaluation of the structural effect of electrophiles on the regioselectivity of ambident anions, the reaction of phosphoryl allylic carbanion with p-substituted benzaldehydes was investigated. 相似文献
943.
Chengye Yuan Shusen Li Zhiyi Cheng 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):95-102
Abstract The mass spectra of 2-alkyl-2-oxo-1,3,2-dioxa-phosphorinane and-phosphepane showed that the ring opening was in competition with the cleavage of the P[sbnd]C bond. According to the fragmentation pathway, which was dependent on the structure of exocyclic substituents on phosphorus, the 2-alkyl-2-oxo-1,3,2-di-oxa-phosphorinanes can be classified in two categories. The main process in category A was the ring opening and/or C[sbnd]C bond cleavage. While in category B the cleavage of P[sbnd]C bond was predominant. However, for 2-alkyl-2-oxo-1,3,2-dioxa-phosphepane. no matter how the structure of 2-alkyl group was, the ring opening was a dominant process. 相似文献
944.
Yin Wang Yuan Fang Guohua Jiang Qi Lv Xinke Sun Miaojun Ding 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):890-895
Shell crosslinked nanoparticles, prepared from copolymerization of styrene and disulfide crosslinker, using poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as stabilizer and macroinitiator, exhibited a special fission behavior during the mini-emulsion RAFT polymerization process. 相似文献
945.
Atom transfer radical polymerization (ATRP) of MMA was conducted using 2‐(4‐chloromethyl‐phenyl)‐benzoxazole as initiator, CuCl as catalyst, and PMDETA as ligand. The results show that the polymerization is a first order reaction with respect to monomer concentration. The polymerization displayed living character as evidenced by a liner increase of monomer weight with conversation and a relatively narrow distribution (Mn/Mw range from 1.30 to 1.45). The structure of PMMA was analyzed by 1H‐NMR and proved the polymerization could be controlled to some degree. The optical property of the initiator was well preserved in the resulting PMMA, and the end‐functionalized PMMA exhibited fluorescent emission at 360 nm whether in DMF solution or in film state. 相似文献
946.
947.
A novel flame retardant (PSiN), containing silicon and nitrogen, was synthesized using N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602) and diphenylsilanediol through solution polycondesation and it was used together with potassium-4-(phenylsulfonyl)benzenesulfonate (KSS) to prepare a flame-retardant system for polycarbonate (PC). The structure and thermal property of PSiN were characterized by Fourier transform infrared spectroscopy (FTIR), 1HNMR and thermogravimetric analysis (TG) tests. Flammability and thermal behaviors of PC/KSS/PSiN systems were estimated by limited oxygen index (LOI), cone calorimeter, vertical burning test (UL-94), and TG tests. The results showed that the flame retardancy and char residues of PC/KSS system were improved with the addition of PSiN. When 1 mass% PSiN and 0.5 mass% KSS were incorporated, the LOI value of PC was found to be 46, and class V-0 of the UL-94 test. Moreover, both the heat release rate and the total heat release of PC/KSS/1 mass% PSiN decreased compared with those of PC and PC/KSS systems. The microstructures observed by scanning electron microscopy and FTIR indicated that the surface of the char for PC/KSS/PSiN system hold a more cohesive and denser char structure when compared with the pure PC and PC/KSS system. 相似文献
948.
Yuqiao Wang Huijun Zhang Dan Yao Junjie Pu Yuan Zhang Xiaorui Gao Yueming Sun 《Journal of Solid State Electrochemistry》2013,17(3):881-887
Graphene/Fe3O4 nanocomposite was prepared for the immobilization of hemoglobin (Hb) to improve the electron transfer between Hb and glass carbon electrode (GCE). The characterization of nanocomposites was described by transmission electron microscopy, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemistry of Hb on the graphene/Fe3O4-based GCE was investigated by cyclic voltammetry and amperometric measurement. The modified electrode showed a wide linear range from 0.25 μmol/L to 1.7 mmol/L with a correlation coefficient of 0.9967. The detection limit of the H2O2 biosensor was estimated at 6.0?×?10?6?mol/L at a signal-to-noise ratio of 3. 相似文献
949.
Yan Li Dr. Kazuki Fukushima Dr. Daniel J. Coady Dr. Amanda C. Engler Dr. Shaoqiong Liu Yuan Huang Dr. John S. Cho Dr. Yi Guo Dr. Lloyd S. Miller Dr. Jeremy P. K. Tan Dr. Pui Lai Rachel Ee Dr. Weimin Fan Prof. Yi Yan Yang Dr. James L. Hedrick 《Angewandte Chemie (International ed. in English)》2013,52(2):674-678
950.