全文获取类型
收费全文 | 4352篇 |
免费 | 116篇 |
国内免费 | 32篇 |
专业分类
化学 | 3482篇 |
晶体学 | 58篇 |
力学 | 63篇 |
数学 | 197篇 |
物理学 | 700篇 |
出版年
2022年 | 24篇 |
2021年 | 41篇 |
2020年 | 41篇 |
2019年 | 51篇 |
2018年 | 31篇 |
2017年 | 34篇 |
2016年 | 64篇 |
2015年 | 77篇 |
2014年 | 95篇 |
2013年 | 300篇 |
2012年 | 195篇 |
2011年 | 261篇 |
2010年 | 135篇 |
2009年 | 131篇 |
2008年 | 221篇 |
2007年 | 233篇 |
2006年 | 258篇 |
2005年 | 234篇 |
2004年 | 209篇 |
2003年 | 210篇 |
2002年 | 224篇 |
2001年 | 71篇 |
2000年 | 69篇 |
1999年 | 67篇 |
1998年 | 48篇 |
1997年 | 44篇 |
1996年 | 63篇 |
1995年 | 61篇 |
1994年 | 56篇 |
1993年 | 31篇 |
1992年 | 40篇 |
1991年 | 33篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 60篇 |
1984年 | 60篇 |
1983年 | 30篇 |
1982年 | 58篇 |
1981年 | 48篇 |
1980年 | 62篇 |
1979年 | 65篇 |
1978年 | 51篇 |
1977年 | 39篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1974年 | 26篇 |
1973年 | 24篇 |
排序方式: 共有4500条查询结果,搜索用时 289 毫秒
991.
Hiroyuki Yamamoto Ayako Nishida Tomoyuki Takimoto Akira Nagai 《Journal of polymer science. Part A, Polymer chemistry》1990,28(1):67-74
Poly(L -ornithine) having azo aromatic side chain was synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the azo polypeptide poly[Nδ-p-(phenylazo)benzoyl-L -ornithine] (PPABLO) was investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP). The photochromism of the dichroic bands in the visible and ultraviolet wavelength regions was found to be reversible as a function of irradiation time at different wavelengths due to the photostationary state (about 70% trans)–cis photoisomerization of the azo aromatic moieties. The reversible photoinduced solubility change was also studied. On irradiation PPABLO is soluble under ultraviolet light (cis) and precipitate under visible light (70% trans) in HFIP–water. A discussion was presented that includes results on azo aromatic poly(L -lysine). 相似文献
992.
Itoh S Kawasaki N Harazono A Hashii N Matsuishi Y Kawanishi T Hayakawa T 《Journal of chromatography. A》2005,1094(1-2):105-117
We developed an efficient and convenient strategy for protein identification and glycosylation analysis of a small amount of unknown glycoprotein in a biological sample. The procedure involves isolation of proteins by electrophoresis and mass spectrometric peptide/glycopeptide mapping by LC/ion trap mass spectrometer. For the complete glycosylation analysis, proteins were extracted in intact form from the gel, and proteinase-digested glycoproteins were then subjected to LC/multistage tandem MS (MSn) incorporating a full mass scan, in-source collision-induced dissociation (CID), and data-dependent MSn. The glycopeptides were localized in the peptide/glycopeptide map by using oxonium ions such as HexNAc+ and NeuAc+, generated by in-source CID, and neutral loss by CID-MS/MS. We conducted the search analysis for the glycopeptide identification using search parameters containing a possible glycosylation at the Asn residue with N-acetylglucosamine (203 Da). We were able to identify the glycopeptides resulting from predictable digestion with proteinase. The glycopeptides caused by irregular cleavages were not identified by the database search analysis, but their elution positions were localized using oxonium ions produced by in-source CID, and neutral loss by the data-dependent MSn. Then, all glycopeptides could be identified based on the product ion spectra which were sorted from data-dependent CID-MSn spectra acquired around localized positions. Using this strategy, we successfully elucidated site-specific glycosylation of Thy-1, glycosylphosphatidylinositol (GPI)-anchored proteins glycosylated at Asn23, 74, and 98, and at Cys111. High-mannose-type, complex-type, and hybrid-type oligosaccharides were all found to be attached to Asn23, 74 and 98, and four GPI structures could be characterized. Our method is simple, rapid and useful for the characterization of unknown glycoproteins in a complex mixture of proteins. 相似文献
993.
Organometallic polymers containing tricarbonyl(η4-diene)-ruthenium(0) and -iron(0) as pendant groups
Hajime Yasuda Yoshitsugu Morita Ippei Noda Kyoko Sugi Akira Nakamura 《Journal of organometallic chemistry》1981,205(2):C9-C13
Vinyl ethers containing tricarbonyl(14-η4-1,3-pentadiene)-ruthenium(0) and -iron(0) species were prepared utilizing selective dienylation with penta-dienylpotassium and were polymerized with cationic initiators to give high molecular weight polymers. The diene-metal moieties were converted into tricarbonyl(13-η3-allyl)metal species by protonation with dry HCl. Tricarbonyl(3-allyl-14-η4-1,3-pentadiene)iron(0) also undergoes cationic polymerization but the presence of its isomer, tricarbonyl(3-propenyl-14-η4-1,3-pentadiene)iron(0) inhibits the polymerization. 相似文献
994.
We present a new Monte Carlo simulation procedure which is capable of capturing aggregate structures in a suspension where fine particles are dispersed. The algorithm we call the “cluster-moving” Monte Carlo algorithm involves moving aggregates (clusters) as unitary particles at every certain Monte Carlo step. We discuss here the theoretical background of the cluster-moving Monte Carlo algorithm and the availability of the algorithm for simulations of systems where fine particles aggregate. The results of simulations for two model systems, magnetic fluids and colloidal dispersions, have shown that the new algorithm produces much more rapid convergence than the conventional one for unstable dispersion systems and reproduces physically reasonable aggregate structures of fine particles. 相似文献
995.
The facile reactions of CF3 with a variety of non-fluorinated nucleophiles are discussed. CF3 + Nu- → CF3N(Nu)C(O)F + F- Reactions with alcohols, carboxylic acids, mercaptans, amines, KSCN, KCN, NaN3 and NaOCN were carried out. All except NaN3 and NaOCN were reactive and the expected compounds were isolated in most cases. Subsequent reaction of CF3N(Nu)C(O)F with additional nucleophile was observed in many cases forming CF3N(Nu)C(O)Nu. With CH3CO2H, the latter reaction forms CH3C(O)F and the novel amine CF3N(H)OC(O)CH63. Ten new compounds are reported with characterization by IR, NMR and physical properties. 相似文献
996.
Suginome M Iwanami T Ohmori Y Matsumoto A Ito Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):2954-2965
Highly enantioenriched (E)-allylsilanes have been synthesized from optically active allylic alcohols on the basis of Pd-catalyzed intramolecular bis-silylation followed by highly stereospecific Si-O elimination reactions. The method involves three steps: 1) O-disilanylation of the allylic alcohols with chlorodisilanes, 2) intramolecular bis-silylation in the presence of a 1,1,3,3-tetramethylbutyl isocyanide/[Pd(acac)2] (acac = acetylacetonate) catalyst at 110 degrees C, and 3) treatment of the reaction mixture with organolithium reagents. The overall transformation proceeds with nearly complete conservation of the enantiopurity of the starting allyl alcohols by transposition of the C=C bond. For instance, (R)-(E)-3-decen-2-ol (99.6-99.7 % ee) produced (S)-(E)-4-(organosilyl)-2-decene of 98.8-99.4 % ee for a variety of silyl groups, including Me3Si, Me2PhSi, tBuMe2Si, Et3Si, and iPr3Si. In the bis-silylation step, the initially formed trans-1,2-oxasiletanes immediately dimerize to stereoselectively give 1,5-dioxa-2,6-disilacyclooctanes, which are isolated in high yield by carrying out the reaction at 70 degrees C. The eight-membered ring compounds undergo thermal extrusion of (E)-allylsilanes in high yield at 110 degrees C, along with formation of 1,3-dioxa-2,5-disilacyclohexane derivatives. These in turn undergo a Peterson-type elimination by treatment with nucleophiles such as BuLi and PhLi to give the (E)-allylsilanes. All of the steps involved in the sequence proceed with extremely high stereoselectivity and stereospecificity, leading to almost complete 1,3-chirality transfer through the overall transformation. The dimerization step, which forms diastereomeric intermediates, allows the synthesis of a highly enantioenriched allylsilane (99.4 % ee) from an optically active allylic alcohol with lower enantiopurity (79.2 % ee) by enrichment of enantiopurity. A general method for the determination of the enantiomeric excesses of (E)-allylsilanes is also described in detail. 相似文献
997.
Satoka Aoyagi Akira Yano Yasutaka Yanagida Eiji Tanihira Akio Tagawa Mitsuo Iimoto 《Chemical physics》2006
This study investigated the control of dissolved oxygen concentration using magnetic forces from gradient magnetic fields near a Nd–Fe–B permanent magnet. Maximum values of magnetic flux density and the product of the magnetic flux density and its gradient were 0.63 T and 44 T2/m, respectively. The magnet was placed under a Petri dish filled with 15 ml of 10% ammonia water. The Petri dish had a copper sheet in the center. Absorbance of tetraamminecopper(II) complex produced by the reaction in oxygen was measured using a spectrophotometer to observe oxygen concentration. Results showed that the magnetic field quantitatively enhanced tetraamminecopper(II) complex production. Moreover, remarkable enhancement of the copper complex production occurred in the magnetic field at less than 2 mm depth. The calculated magnetic force increase near the magnet surface supports this result. These results show that greater enhancement of the reaction rate occurs when the stronger magnetic force acts on oxygen molecules. 相似文献
998.
Tsuneo Okubo Takehiro Miyamoto Atsushi Otake Mitsuhiro Suda Akira Tsuchida 《Colloid and polymer science》2004,282(12):1341-1346
Kinetic analyses were made of the seed polymerization of tetraethyl ortho-silicate (TEOS) in the presence of rod-like colloidal particles of palygorskite and cationic -FeO(OH) by turbidity and dynamic light-scattering measurements. Transmission electron microscopic measurements supported the formation of core-shell particles. The seed polymerization of TEOS took place exclusively on the surfaces of palygorskite. The main cause of the observation is due to the fact that the main component of palygorskite is SiO2 and the affinity between palygorskite and TEOS is high, though the electrostatic repulsion between them is not favorable for shell formation. The shell formation of silica on a -FeO(OH) particle also proceeded. The electrostatic attraction forces between the anionic polar TEOS monomers and cationic -FeO(OH) particles played an important role in shell formation. These results are consistent with a polymerization mechanism consisting of the formation of small preliminary particles followed by their coalescence on the surfaces of the seeds to give the final large particles coated with silica layers. 相似文献
999.
Akira Matsumoto Masayoshi Oiwa 《Journal of polymer science. Part A, Polymer chemistry》1970,8(3):751-762
Radical polymerization studies on diallyl oxalate (DAO), diallyl malonate (DAM), diallyl succinate (DASu), diallyl adipate (DAA), and diallyl sebacate (DAS) have been conducted kinetically from the standpoint of cyclopolymerization. Benzoyl peroxide was employed as the initiator. The initial overall rate of polymerization, Rp was not proportional to the square root or the first power of the initiator concentration, [I]. But Rp/[I]1/2 and [I]1/2 bore a linear relationship, provided the monomer concentration was kept constant. The residual unsaturation of the polymers decreased with decreasing monomer concentration. The ratio of the rate constant of the unimolecular cyclization reaction to that of the bimolecular propagation reaction of the uncyclized radical, Kc, was evaluated from the above relationship between the residual unsaturation and the monomer concentration at 60°C. The Kc values obtained were 3.6, 3.2, 2.8, 2.5, and 1.2 mole/l. for DAO, DAM, DASu, DAA, and DAS, respectively. The overall activation energies of polymerization were found to be 21.1 (DAO), 24.2 (DAM), 21.7 (DASu), 22.0 (DAA), and 22.2 (DAS) kcal/mole. 相似文献
1000.
Photoreactions of 2-halotropones with the excited 9,10-dicyanoanthracene gave a meta-adduct and substitution products occurred at the C-2 position of troponoids. The mechanism of the meta-adduct was proved by the product analysis of the reaction of 3,7-dideuterio-2-bromo-5-isopropyltropone and 9,10-dicyanoanthracene. In the photoreaction of 2-chloro-5-isopropyltropone and 9,10-dicyanoanthracene in a mixed solvent of benzene and methanol, a benzaldehyde with a dibenzo-2-oxabicyclo[3.2.2]nonane system was obtained to support occurrence of an [8+4] cycloaddition reaction between them. 相似文献