全文获取类型
收费全文 | 9301篇 |
免费 | 1319篇 |
国内免费 | 757篇 |
专业分类
化学 | 6841篇 |
晶体学 | 122篇 |
力学 | 429篇 |
综合类 | 57篇 |
数学 | 857篇 |
物理学 | 3071篇 |
出版年
2024年 | 26篇 |
2023年 | 187篇 |
2022年 | 271篇 |
2021年 | 311篇 |
2020年 | 359篇 |
2019年 | 326篇 |
2018年 | 259篇 |
2017年 | 234篇 |
2016年 | 445篇 |
2015年 | 388篇 |
2014年 | 462篇 |
2013年 | 660篇 |
2012年 | 856篇 |
2011年 | 858篇 |
2010年 | 516篇 |
2009年 | 522篇 |
2008年 | 597篇 |
2007年 | 583篇 |
2006年 | 502篇 |
2005年 | 466篇 |
2004年 | 303篇 |
2003年 | 212篇 |
2002年 | 230篇 |
2001年 | 196篇 |
2000年 | 183篇 |
1999年 | 160篇 |
1998年 | 145篇 |
1997年 | 113篇 |
1996年 | 109篇 |
1995年 | 139篇 |
1994年 | 120篇 |
1993年 | 92篇 |
1992年 | 79篇 |
1991年 | 70篇 |
1990年 | 67篇 |
1989年 | 35篇 |
1988年 | 45篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
91.
Based on the investigation of a non-ionic surfactant-salt-H2O liquid-liquid extraction system, general rules concerning salt selection are concluded and the mechanism of phase separation is explained. The extraction behavior of chlorpromazine hydrochloride (CPZ) and procaine hydrochloride (PCN) in such a system is studied. Research shows that the extraction efficiency of CPZ can amount to 96% by twice extraction, which means that quantitative extraction is realized, while that of PCN is 77%. This system produces distribution coefficients (KD) of 12.3 and 2.6, respectively, for CPZ and PCN. Extraction mechanism is deduced according to ultraviolet absorbance; and molecular fluorescence spectra change of the drugs in the system studied. 相似文献
92.
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
93.
94.
95.
以氯化锌、铁氰化钾(含有整合剂)的水溶液为原料,合成了铁锌双金属氰化物(DMC)催化剂。为获得高活性的DMC催化剂,需将叔丁醇 、多元醇螯合剂螯合至其结构中,用XRD、XPS等分析手段,对铁锌DMC催化剂的结构与活性进行分析表征。实验发现,DMC催化剂的晶体结构与螯合剂密切相关,螯合剂能显著降低DMC催化剂的结晶程度,从而提高DMC催化剂的活性。同时,氯化锌过量也有利于DMC催化剂活性的提高。并表征了相关DMC催化剂的活性中心。 相似文献
96.
Three new polyoxygenated briarane-type diterpenoids, briaexcavatolides X-Z (1-3), have been isolated from the gorgonian coral Briareum excavatum. The structures, including the relative configurations of briaranes 1-3, were elucidated by spectroscopic methods, particularly in 1D and 2D NMR experiments. The configuration of briarane 1 was further supported by molecular mechanics calculations. 相似文献
97.
Su Qin HAN Er Bao LIU Hua LI 《中国化学快报》2005,16(8):1067-1070
This paper reported an indirect flow injection chemiluminescence (FI-CL) method for the determination of the drugs tetracycline (TC), chlortetracycline (CTC) and oxytetracycline(OTC) using Cu( Ⅱ ) as a probe ion. The CL reaction was induced on-line and after injection of the sample the negative peaks appeared as a result of complexation. The method was applied to the determination of TCs in pharmaceuticals and human urine with recoveries in the range95-105%. 相似文献
98.
Fukuji Higashi Chong Su Cho Hideo Kakinoki Osao Sumita 《Journal of polymer science. Part A, Polymer chemistry》1977,15(10):2303-2309
Semiconducting organic polymer was obtained by the modification of polyacrylamide (PAAm)–Cu++ chelate with iodine in acetone. Favorable conditions for preparing the chelate effective for the conduction were investigated. Surface resistivities were affected by the amounts of cupric salts and iodine, satisfactory results being given by about 25 wt % of the salts based on PAAm and more than 1 wt % of iodine on the chelate. The conductivity was also varied with the degree of neutralization of the chelate in solution, and optimal values were obtained by addition of about an equimolar amount of potassium hydroxide to cupric salts. Effective structures of the polymer chelate in solution were assumed on the basis of the visible and the NMR spectra and potentiometric titration. 相似文献
99.
100.
Zhen-Qian Zhang Hong Li Juan Xu Su Yao Zheng-He Xu Jin-Gang Liu Liang-Nian Ji 《Transition Metal Chemistry》2007,32(6):776-780
The effects of copper ion on the interaction of [Ru(bpy)2HPIP]2+(bpy = 2,2′-bipyridine, HPIP = 2-(2-hydroxyphenyl) imidazo [4,5-f] [1, 10] phenanthroline) with DNA have been investigated
by electronic absorption spectroscopy and fluorescence spectroscopy. HPIP ligand of the complex with an intramolecular hydrogen
bond can bind Cu2+ in the absence of DNA, as revealed by the absorbance and fluorescence decrease for [Ru(bpy)2HPIP]2+. The resultant heterometallic complex binds to DNA via intercalation of HPIP into the DNA base pairs and its DNA-binding ability is stronger than [Ru(bpy)2HPIP]2+ itself. The DNA bound [Ru(bpy)2HPIP]2+ cannot bind Cu2+ at low Cu2+ concentration and the intramolecular hydrogen bond in HPIP is located inside the DNA helix. While the Cu2+ concentration is relative high, Cu2+ can quench the fluorescence of DNA bound [Ru(bpy)2HPIP]2+. The quenching reason is proposed. 相似文献