全文获取类型
收费全文 | 6541篇 |
免费 | 444篇 |
国内免费 | 3篇 |
出版年
2022年 | 32篇 |
2021年 | 68篇 |
2020年 | 34篇 |
2019年 | 59篇 |
2018年 | 63篇 |
2017年 | 54篇 |
2016年 | 97篇 |
2015年 | 190篇 |
2014年 | 229篇 |
2013年 | 304篇 |
2012年 | 338篇 |
2011年 | 367篇 |
2010年 | 293篇 |
2009年 | 250篇 |
2008年 | 338篇 |
2007年 | 367篇 |
2006年 | 362篇 |
2005年 | 339篇 |
2004年 | 358篇 |
2003年 | 347篇 |
2002年 | 358篇 |
2001年 | 95篇 |
2000年 | 76篇 |
1999年 | 103篇 |
1998年 | 126篇 |
1997年 | 84篇 |
1996年 | 83篇 |
1995年 | 96篇 |
1994年 | 76篇 |
1993年 | 88篇 |
1992年 | 69篇 |
1991年 | 62篇 |
1990年 | 74篇 |
1989年 | 54篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 51篇 |
1985年 | 34篇 |
1984年 | 66篇 |
1983年 | 53篇 |
1982年 | 66篇 |
1981年 | 74篇 |
1980年 | 60篇 |
1979年 | 55篇 |
1978年 | 47篇 |
1977年 | 42篇 |
1976年 | 35篇 |
1975年 | 35篇 |
1974年 | 36篇 |
1973年 | 19篇 |
排序方式: 共有6988条查询结果,搜索用时 15 毫秒
991.
Joseph Diaz Remy Guegan Michel Beaumont Jean Benoit Jacques Clement Christian Fauchard Daniel Galtier Joseph Millan Claude Muneaux Yvette Muneaux Michel Vedel Robert Schwyzer 《Bioorganic chemistry》1979,8(4):429-442
A large-scale synthesis of somatostatin was developed. A stepwise C→N approach in solution was used, employing N(α)-t-butoxycarbonyl amino acid active esters. The scheme of semipermanent protection utilized 2-(methylsulfonyl)-ethoxycarbonyl for the -amino group of lysine; acetamidomethyl for the β-thiol groups of cysteine; the orange-colored 2-[4-(phenylazo)-phenylsulfonyl]-ethoxy group for the C-terminal carboxy group of cysteine. All condensations and N(α)-deprotections were carried out in homogeneous solution, while isolation and purification of peptides carrying the colored group was achieved by precipitation and washing of the solid products. Thus, the “alternating solution/solid-phase peptide synthesis” combines advantages of both the classical solution synthesis and the Merrifield solid-phase technique. The overall yield was 5%, or 16 g of somatostatin from 100 g of the novel amino acid derivative, N(α)-t-butoxycarbonyl-S-acetamidomethyl-
-cysteine 2-[4-(phenylazo)-phenylsulfonyl]-ethyl ester. An improved method for the preparation of S-acetamidomethyl-
-cysteine, free of thiazolidine carboxylic acid, is described. 相似文献
992.
993.
994.
995.
996.
997.
998.
999.
Jacques Loeb 《The Journal of general physiology》1920,3(2):247-269
1. Our results show clearly that the Hofmeister series is not the correct expression of the relative effect of ions on the swelling of gelatin, and that it is not true that chlorides, bromides, and nitrates have "hydrating," and acetates, tartrates, citrates, and phosphates "dehydrating," effects. If the pH of the gelatin is taken into considertion, it is found that for the same pH the effect on swelling is the same for gelatin chloride, nitrate, trichloracetate, tartrate, succinate, oxalate, citrate, and phosphate, while the swelling is considerably less for gelatin sulfate. This is exactly what we should expect on the basis of the combining ratios of the corresponding acids with gelatin since the weak dibasic and tribasic acids combine with gelatin in molecular proportions while the strong dibasic acid H2SO4 combines with gelatin in equivalent proportions. In the case of the weak dibasic acids he anion in combination with gelatin is therefore monovalent and in the case of the strong H2SO4 it is bivalent. Hence it is only the valency and not the nature of the ion in combination with gelatin which affects the degree of swelling.
2. This is corroborated in the experiments with alkalies which show that LiOH, NaOH, KOH, and NH4OH cause the same degree of swelling at the same pH of the gelatin solution and that this swelling is considerably higher than that caused by Ca(OH)2 and Ba(OH)2 for the same pH. This agrees with the results of the titration experiments which prove that Ca(OH)2 and Ba(OH)2 combine with gelatin in equivalent proportions and that hence the cation in combination with the gelatin salt with these two latter bases is bivalent.
3. The fact that proteins combine with acids and alkalies on the basis of the forces of primary valency is therefore not only in full agreement with the influence of ions on the physical properties of proteins but allows us to predict this influence qualitatively and quantitatively.
4. What has been stated in regard to the influence of ions on the swelling of the different gelatin salts is also true in regard to the influence of ions on the relative solubility of gelatin in alcohol-water mixtures.
5. Conductivity measurements of solutions of gelatin salts do not support the theory that the drop in the curves for swelling, osmotic pressure, or viscosity, which occurs at a pH 3.3 or a little less, is due to a drop in the concentration of ionized protein in the solution; nor do they suggest that the difference between the physical properties of gelatin sulfate and gelatin chloride is due to differences in the degree of ionization of these two salts. 相似文献
1000.