全文获取类型
收费全文 | 103357篇 |
免费 | 17186篇 |
国内免费 | 11823篇 |
专业分类
化学 | 72474篇 |
晶体学 | 1136篇 |
力学 | 5884篇 |
综合类 | 666篇 |
数学 | 12628篇 |
物理学 | 39578篇 |
出版年
2024年 | 351篇 |
2023年 | 2068篇 |
2022年 | 3669篇 |
2021年 | 3776篇 |
2020年 | 4180篇 |
2019年 | 3962篇 |
2018年 | 3718篇 |
2017年 | 3334篇 |
2016年 | 5019篇 |
2015年 | 4927篇 |
2014年 | 6057篇 |
2013年 | 7782篇 |
2012年 | 9279篇 |
2011年 | 9474篇 |
2010年 | 6624篇 |
2009年 | 6358篇 |
2008年 | 6679篇 |
2007年 | 5967篇 |
2006年 | 5579篇 |
2005年 | 4659篇 |
2004年 | 3647篇 |
2003年 | 2928篇 |
2002年 | 2663篇 |
2001年 | 2231篇 |
2000年 | 1947篇 |
1999年 | 2051篇 |
1998年 | 1738篇 |
1997年 | 1560篇 |
1996年 | 1555篇 |
1995年 | 1366篇 |
1994年 | 1240篇 |
1993年 | 1006篇 |
1992年 | 902篇 |
1991年 | 777篇 |
1990年 | 652篇 |
1989年 | 503篇 |
1988年 | 378篇 |
1987年 | 338篇 |
1986年 | 335篇 |
1985年 | 262篇 |
1984年 | 188篇 |
1983年 | 153篇 |
1982年 | 125篇 |
1981年 | 78篇 |
1980年 | 59篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
ToF-SIMS analysis of the organometallic cluster Os3(μ-H)(CO)10(μ-SCH2CH2SH) chemically attached onto a silver or gold surface, and of the cluster fragment Os3(μ-H)(CO)10(μ-OSi) on a silica surface, allows for identification of the surface organometallic species, and also gives information on its reactivity. 相似文献
972.
用停止-流动分光光度法研究了Eu~(2+)与二甲酚橙(XO)间快速电子转移反应的动力学规律。求得了速控步骤的动力学参数。如反应级数(n=2)、几个不同温度下的速率常数(k_(278 K)=5.7×10~8 L·mol~-·s~(-1), k_(s38 K)=1.01×10~9 L·mol~(-1)·s~(-1))、活化能(E=7.6×10~3 J·mol~(-1)), 以及指前因子(A=1.5×10~(10) L·mol~(-1)·s~(-1)), 并判断出其为溶液中扩散控制型反应。根据实验现象与测试结果, 提出了Eu~(2+)与XO的反应分别在Eu~(2+)相对过量和在XO过量时的反应机理, 并判断了各反应步骤速率常数之间的相对关系。 相似文献
973.
974.
The repression of glucose oxidase (GOD) biosynthesis by catabolites during fermentation can be alleviated through membrane dialysis fermentation (MDF). The results show that the volumetric enzyme productivity of MDF was two times higher than that of the control (fermentation without dialysis), and its total enzyme activity was increased by 30–50%. The operation conditions of MDF, such as pore size of the membrane, initiating time for membrane dialysis, and volume of dialysate used, were optimized. The content of amino acids and organic acids in the fermentation broth and the dialysate in the reservoir were assessed by amino acid analyzer and ionic chromatography, respectively. The relationship among the contents of pyruvic acid, gluconic acid, and enzyme activity during fermentation was analyzed quantitatively. Furthermore, the effect of membrane dialysis technology applied to the low-yield strain was found to be more effective than that applied to the high-yield strain. 相似文献
975.
976.
Yu Liu Yong Chen Shi-Zhao Kang Li Li Chun-Hua Diao Heng-Yi Zhang 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(1-2):91-95
Two novel benzo-15-crown-5 tethered β-cyclodextrins 1 and 2have been synthesized by coupling substituted benzo-15-crown-5 with correspondingβ-cyclodextrin derivatives. Their inclusion complexation behavior withrepresentative guests, such as cyclohexanol, cyclohexane carboxylic acid, cyclohexaneacetic acid, sodium cyclohexane carboxylate, and potassium cyclohexane carboxylate,was investigated in aqueous solution by means of fluorescence spectrometry. As compared with parent β-cyclodextrin, benzo-15-crown-5 tethered β-cyclodextrins 1–2 display significantly enhanced molecular binding abilities and selectivities towards model substrates, especially towards substrates containing alkali-metal cations. These results indicate that, bearing two recognition sites in a single molecule, these supramolecular architectures can strongly enhance the molecular binding ability of parent β-cyclodextrin by the cooperative binding of the β-cyclodextrin cavity and the crown ether moiety. Possessing a shorter linker, crown ether-β-cyclodextrin 2 shows much higher binding affinity with guest molecules than crown ether-β-cyclodextrin 1, which may be attributed to the binding size and molecular multiple recognition behavior between host and guest. 相似文献
977.
A procedure for the simultaneous time-resolved fluoroimmunoassay for phenobarbital and phenytoin, based on the use of europium- and samarium-labeled haptens, has been investigated. These lanthanide ions are bound to the haptens by means of the anhydride of diethylenetriaminepentaacetic acid. The antibody is immobilized onto immunoplate in which samples are assayed in competitive immunoassay. After the immunoreactions and dissociation with a fluorescence enhancement solution, the fluorescence intensity is measured. The detection limits of the assay are, respectively, 20 ng/ml for phenobarbital and 50 ng/ml for phenytoin. Results obtained with the proposed methods correlate well (CV <10%). The inter-reactions between phenobarbital, phenytoin, and their antibodies are studied. 相似文献
978.
紫荆花红色素开发利用的研究 总被引:9,自引:0,他引:9
首次报道紫荆花红色素的提取纯化方法及红色素的理化性质,并与玫瑰茄红色素作对比研究,证实同属于花青甙类化合物,又经急性毒性试验证明其毒性极低,故紫荆花天然红色素具有开发利用的价值。 相似文献
979.
980.