全文获取类型
收费全文 | 9873篇 |
免费 | 899篇 |
国内免费 | 595篇 |
专业分类
化学 | 10858篇 |
晶体学 | 49篇 |
力学 | 5篇 |
综合类 | 47篇 |
数学 | 7篇 |
物理学 | 401篇 |
出版年
2024年 | 7篇 |
2023年 | 93篇 |
2022年 | 219篇 |
2021年 | 263篇 |
2020年 | 318篇 |
2019年 | 263篇 |
2018年 | 261篇 |
2017年 | 246篇 |
2016年 | 377篇 |
2015年 | 373篇 |
2014年 | 424篇 |
2013年 | 835篇 |
2012年 | 552篇 |
2011年 | 516篇 |
2010年 | 456篇 |
2009年 | 514篇 |
2008年 | 527篇 |
2007年 | 591篇 |
2006年 | 549篇 |
2005年 | 535篇 |
2004年 | 534篇 |
2003年 | 448篇 |
2002年 | 586篇 |
2001年 | 248篇 |
2000年 | 216篇 |
1999年 | 162篇 |
1998年 | 170篇 |
1997年 | 142篇 |
1996年 | 128篇 |
1995年 | 126篇 |
1994年 | 83篇 |
1993年 | 84篇 |
1992年 | 77篇 |
1991年 | 63篇 |
1990年 | 49篇 |
1989年 | 49篇 |
1988年 | 48篇 |
1987年 | 33篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 38篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
51.
52.
Guey‐Sheng Liou Sheng‐Huei Hsiao Yi‐Kai Fang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6466-6483
Two new phenyl‐ and naphthyl‐substituted rigid‐rod aromatic dicarboxylic acid monomers, 2,2′‐diphenylbiphenyl‐4,4′‐dicarboxylic acid ( 4 ) and 2,2′‐di(1‐naphthyl)biphenyl‐4,4′‐dicarboxylic acid ( 5 ), were synthesized by the Suzuki coupling reaction of 2,2′‐diiodobiphenyl‐4,4′‐dicarboxylic acid dimethyl ester with benzeneboronic acid and naphthaleneboronic acid, respectively, followed by alkaline hydrolysis of the ester groups. Four new polyhydrazides were prepared from the dicarboxylic acids 4 and 5 with terephthalic dihydrazide (TPH) and isophthalic dihydrazide (IPH), respectively, via the Yamazaki phosphorylation reaction. These polyhydrazides were amorphous and readily soluble in many organic solvents. Differential scanning calorimetry (DSC) indicated that these hydrazide polymers had glass transition temperatures in the range of 187–234 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 300–400 °C. The resulting poly(1,3,4‐oxadiazole)s exhibited Tg's in the range of 252–283 °C, 10% weight‐loss temperature in excess of 470 °C, and char yield at 800 °C in nitrogen higher than 54%. These organo‐soluble polyhydrazides and poly(1,3,4‐oxadiazole)s exhibited UV–Vis absorption maximum at 262–296 and 264–342 nm in NMP solution, and their photoluminescence spectra showed maximum bands around 414–445 and 404–453 nm, respectively, with quantum yield up to 38%. The electron‐transporting properties were examined by electrochemical methods. Cyclic voltammograms of the poly(1,3,4‐oxadiazole) films cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited reversible reduction redox with Eonset at ?1.37 to ?1.57 V versus Ag/AgCl in dry N,N‐dimethylformamide solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6466–6483, 2006 相似文献
53.
Tali Menahem Yitzhak Mastai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):3009-3017
A series of chiral polymers based on poly(N‐acryl) amino acids was synthesized using a convergent synthetic approach. These chiral polymers have been used as chiral additives to induce enantioselective crystallization of racemic or conglomerate amino acids in solutions. These polymeric additives showed strong capabilities to enhance highly enantioselective resolution during the crystallization of amino acids. In addition, these polymers caused unusual modifications of amino acid crystal morphologies. Furthermore, spherical microparticles of those same chiral polymers were also shown active in similar chiral discriminations during amino acid crystallizations occurring on microparticle surfaces. Our study demonstrates the high potential of chiral polymers and microparticles to resolve amino acids throughout crystallization processes. High enantiomeric excesses in one targeted enantiomer of amino acids can also be maximized via time‐dependent kinetic control of crystallizations. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3009–3017, 2006 相似文献
54.
55.
56.
用铜(Ⅱ)—L—精氨酸配体交换薄层色谱拆分氨基酸对映体 总被引:2,自引:0,他引:2
报道了一种新的配体交换薄层色谱拆分氨基酸对映体的方法。以醋酸铜-L-精氨酸的络合物为配体交换剂,用浸渍的方法吸附在硅胶薄层板上,制成配体交换薄层,用PRISMA优化法选择出展开剂的最佳组成为:甲醇/乙腈/四氢呋喃/水=80:8.2:5.8:6,在此色谱条件下,十对氨基酸对映体得到良好的分离,D-和L-氨基酸的相对比移值在1.09-2.40之间。文中对配体交换薄层的制备方法,样品的分子结构及色谱行为 相似文献
57.
本文报道了合成1-氨基环丙烷-1-羧酸的简便而价廉的方法,即乙酰乙酸乙酯法和α-氰乙酸乙酯法;并测定了产品的结构。 相似文献
58.
59.
D. G. Mazhakin V. K. Khlestkin A. Ya. Tikhonov L. B. Volodarsky 《Russian Chemical Bulletin》1996,45(4):880-884
Derivatives of 1,4-dihydroxypiperazine-2,3-dione were obtained by reaction of cis-1,2-bis(hydroxyamino)cycloalkanes with diethyl oxalate. Their alkylation with CH2N2 or Mel afforded 1,4-dimethoxypiperazine-2,3-diones. Hydrolysis of the latter gave 1,2-bis(methoxyamino)cycloalkanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–929, April, 1996. 相似文献
60.