全文获取类型
收费全文 | 1508篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 1232篇 |
晶体学 | 18篇 |
力学 | 25篇 |
数学 | 71篇 |
物理学 | 186篇 |
出版年
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 18篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 30篇 |
2013年 | 72篇 |
2012年 | 43篇 |
2011年 | 68篇 |
2010年 | 44篇 |
2009年 | 32篇 |
2008年 | 84篇 |
2007年 | 77篇 |
2006年 | 68篇 |
2005年 | 77篇 |
2004年 | 74篇 |
2003年 | 76篇 |
2002年 | 96篇 |
2001年 | 27篇 |
2000年 | 24篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 25篇 |
1996年 | 23篇 |
1995年 | 12篇 |
1994年 | 20篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1983年 | 14篇 |
1982年 | 28篇 |
1981年 | 32篇 |
1980年 | 27篇 |
1979年 | 28篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 10篇 |
1970年 | 6篇 |
排序方式: 共有1532条查询结果,搜索用时 15 毫秒
41.
The C-12˜C-17 segment
of (+)-aplasmomycin (
) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction. 相似文献
42.
Hidemasa Okamoto Shoichi Adachi Tadashi Iwai 《Journal of polymer science. Part A, Polymer chemistry》1979,17(5):1267-1277
The γ-ray-induced addition reaction of carbon tetrachloride onto syndiotactic 1,2-polybutadiene film and liquid 1,2-polybutadiene was carried out at room temperature. In the film gelation was pronounced and the rate of addition increased as the crystallinity of the polymer decreased. In the liquid gelation, which makes the polymer insoluble in carbon tetrachloride, did not take place, although a definite crosslinking reaction was noticed. In this case the appearance of the product changed from a viscous liquid to a white powder as the reaction proceeded. Its structure was compared with that of chlorinated 1,2-polybutadiene. The addition of carbon tetrachloride to the vinyl group in liquid 1,2-polybutadiene caused an anti-Markownikoff-type reaction and was accompanied by an unexpectedly large vinyl depletion in the polymer. The total decrease in the vinyl group was found to be much larger than that brought about by the addition of carbon tetrachloride. This discrepancy was attributed to a cyclization and crosslinking reaction ascribed to the vinyl group bound by the main chain. Cyclization and crosslinking were less noticeable in the chlorination than in the carbon tetrachloride. 相似文献
43.
The concentrations of microbial cells in suspensions can be measured with a graphite electrode modifed with adsorbed 4,4′-bipyridine, by using cyclic volummetry or differential pulse volummetry. The relationship between the peak current and the cell concentration for Saccharomyces cerevisiae is linear over the range 0.03 × 108—2.0 × 108 cells ml?1. Yeast, gram-positive bacteria and gram-negative bacteria gave different peak potentials, which may be useful for classification purposes. Electron transfer between the microbial cells and the 4,4′-bipyridine-modified electrode is mediated by coenzyme A in the cell wall. 相似文献
44.
Bunai K Ariga M Inoue T Nozaki M Ogane S Kakeshita H Nemoto T Nakanishi H Yamane K 《Electrophoresis》2004,25(1):141-155
We analyzed ABC transporter solute-binding proteins (SBPs) of the Bacillus subtilis membrane using a proteomic approach. We prepared a washed cell membrane fraction that was insoluble in 134 mM nondetergent sulfobetaine and then extracted proteins using mixtures of detergents in a stepwise manner. The membrane proteins were resolved by three two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) or two one-dimensional (1-D) PAGE procedures, electroblotted, and digested in the presence of 5% or 80% acetonitrile. Thereafter, matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF MS) identified 637 proteins corresponding to 15.9% of the total cellular proteins. We predicted that among these, 256 were membrane proteins, 101 were lipoproteins or secretory proteins and 280 were soluble proteins containing peripheral proteins that function in both the cytoplasm and the cell membrane such as SecA and FtsY. Among the 637 proteins, we identified 30 SBPs among 38 importers predicted by a bioinformatic search of the genome. We confirmed expression of the genes for the 30 SBPs using DNA microarray analysis. We compared the 2-D gel separation profiles of submembrane fractions solubilized by 1% n-dodecyl-beta-D-maltoside from cells cultured on Luria Bertani (LB), S7, and S7 medium without glutamate as well as DNA microarray data on LB and S7. The results suggested that YcdH, YtmK and YurO are binding proteins for Mn(++), glutamate and glucose, respectively, and that YqiX and YxeM are binding proteins for amino acids (tryptophan in S7 medium). 相似文献
45.
1,2- Or 1,3-asymmetric induction in the iodocarbocyclization reaction of 4-pentenylmalonate derivatives having a stereogenic center at an allylic or a homoallylic position has been investigated. The iodocarbocyclization reactions of 3-oxy-4-pentenylmalonate derivatives proceeded with high cis-selectivity through stereoelectronic control of the oxygenated substituent at an allylic position. In the reaction of (S)-2-siloxy-4-pentenylmalonate, an excellent diastereoselectivity was achieved through the utilization of double stereodifferentiation with a chiral titanium catalyst. Furthermore, as an application of the present reaction, the asymmetric syntheses of cyclosarkomycin and a synthetic intermediate of brefeldin A from optically pure 2- and 3-oxy-4-pentenylmalonate derivatives are also described. 相似文献
46.
Todoroki K Hayama T Ijiri S Kazuta A Yoshida H Nohta H Yamaguchi M 《Journal of chromatography. A》2004,1038(1-2):113-120
6-Rhodamine B amine functions as a highly sensitive fluorescence derivatization reagent for mono- and oligosaccharides; it reacts with the reducing end of saccharides under acidic conditions. The fluorescent derivatives of five monosaccharides can be separated within 25 min by reversed-phase liquid chromatography with isocratic elution. The detection limits (S/N = 3) for mono-, di-, and oligosaccharides are 7-51, 13, and 9-35 fmol/20 microl injection, which correspond to analyte concentrations of 35-255, 65, 45-175 nM, respectively. We have applied this derivatization method successfully to the analysis of the components of oligosaccharides in glycoproteins (ribonuclease B and fetuin) following their acidic or enzymatic hydrolysis. The results from these analyses are in good agreements with the reported values established previously. 相似文献
47.
Yuzo Yamazawa Tadashi Iwai Akihiko Ito Koichiro Hayashi 《Journal of polymer science. Part A, Polymer chemistry》1971,9(2):257-263
The in-source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm2, respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid-state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above-mentioned polymerization characteristic. 相似文献
48.
Du YZ Hiratsuka Y Taira S Eguchi M Uyeda TQ Yumoto N Kodaka M 《Chemical communications (Cambridge, England)》2005,(16):2080-2082
A new nano-biomachine has been created from microtubules (MTs) and hetero-bifunctional polymer particles bearing pyruvate kinase, which is propelled on glass surfaces coated with kinesin by use of self-supplying ATP. 相似文献
49.
Tetsuo Yamasaki Yuji Yoshihara Yoshinari Okamoto Tadashi Okawara Mitsuru Furukawa 《Journal of heterocyclic chemistry》1992,29(5):1313-1316
The reaction of 5-hydrazinopyridazin-3(2H)-ones 1 with α-keto diester 2 in acetic acid afforded the corresponding 4,6-dihydropyridazino[4,5-c]pyridazin-5(1H)-ones 3 and pyrrolo[2,3-d)pyridazin-4(5H)-ones 4 . Compounds 3 were also obtained from 4-bromo-5-hydrazinopyridazin-3(2H)-ones 8 and 2 under milder conditions. 5-Bromo-4-hydrazinopyridazin-3(2H)-one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7-dihydropyridazino[4,5-c]pyridazin-8(1H)-one 10b , the regioisomer of 3b . 相似文献
50.
Masahito Segi Katsuhiko Tanno Masumi Kojima Mitsunori Honda Tadashi Nakajima 《Tetrahedron letters》2007,48(13):2303-2306
1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels-Alder reaction of anthracene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single isomer in good yields, being 1,4,2-oxaselenazoles or 1,3,4-selenadiazoles, respectively. 相似文献