全文获取类型
收费全文 | 17660篇 |
免费 | 2964篇 |
国内免费 | 2086篇 |
专业分类
化学 | 12735篇 |
晶体学 | 213篇 |
力学 | 1025篇 |
综合类 | 219篇 |
数学 | 2052篇 |
物理学 | 6466篇 |
出版年
2024年 | 32篇 |
2023年 | 336篇 |
2022年 | 609篇 |
2021年 | 587篇 |
2020年 | 687篇 |
2019年 | 667篇 |
2018年 | 554篇 |
2017年 | 525篇 |
2016年 | 849篇 |
2015年 | 804篇 |
2014年 | 955篇 |
2013年 | 1265篇 |
2012年 | 1496篇 |
2011年 | 1671篇 |
2010年 | 1177篇 |
2009年 | 1140篇 |
2008年 | 1204篇 |
2007年 | 1114篇 |
2006年 | 1029篇 |
2005年 | 803篇 |
2004年 | 700篇 |
2003年 | 550篇 |
2002年 | 544篇 |
2001年 | 431篇 |
2000年 | 374篇 |
1999年 | 339篇 |
1998年 | 314篇 |
1997年 | 276篇 |
1996年 | 229篇 |
1995年 | 245篇 |
1994年 | 212篇 |
1993年 | 173篇 |
1992年 | 141篇 |
1991年 | 114篇 |
1990年 | 125篇 |
1989年 | 84篇 |
1988年 | 57篇 |
1987年 | 48篇 |
1986年 | 48篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 34篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1978年 | 10篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1969年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
In the present work, a new method was established by applying solid-phase extraction (SPE) to preconcentrate and separate polymeric aluminum (Al) and using ICP-AES to determine the polymeric Al, the total monomeric Al, and the total Al in soil extracts, respectively. A modified resin was prepared with impregnated 8-hydroxyquinoline-5-sulfoxinate (HQS) on the anion-exchange resin. It has good recognition ability for Al fractions, compared to the commonly used cation ion-exchange resin, which has a better ability to adsorb cations and a weak ability to recognize detailed Al species. The optimum conditions for Al fractionation sorption, elution and separation and the interference of foreign ions were studied with the prepared resin by continuous column and batch procedures. Monomeric Al was bound to Pyrocathecol Violet (PCV) at pH 6.2, whereas the polymeric Al species did not react with PCV for at least 15 min. Because a stable complex of Al-PCV was not absorbed on the HQS modified resin, the polymeric Al could be preconcentrated on-line by the HQS-modified resin. The adsorbed polymeric Al was eluted with 3 mL of 3 mol L(-1) of HCl, and then detected by ICP-AES. The method has been applied to directly determine polymeric Al in soil extracts with high selectivity as well as a high preconcentration factor. It gives a limit of detection of 0.6 ng mL(-1) with a relative standard deviation of less than 5.7% (n = 5, 0.24 microg mL(-1) Al). 相似文献
42.
Polypropylene (PP) was modified with elastomer or CaCO3 particles of two different sizes (1 μm and 50 nm) in various volume fractions. The dispersion morphology and mechanical properties of the two systems were investigated as functions of the particle size and volume fraction of the modifier. The brittle‐to‐tough transition occurred when the matrix ligament thickness was less than the critical ligament thickness, which was about 0.1 μm for the PP used here, being independent of the type of modifier. At the same matrix ligament thickness, the improvement of the toughness was obviously higher with the elastomer rather than with CaCO3, but adding CaCO3 increased the modulus of PP. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1656–1662, 2004 相似文献
43.
44.
45.
46.
47.
A New Triterpene from the Orchid Pholidota yunnanensis 总被引:2,自引:0,他引:2
ZhiMingBI ZhengTaoWANG LuoShanXU 《中国化学快报》2004,15(10):1179-1181
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method. 相似文献
48.
WeiMingXU LuLingWU XianHUANG 《中国化学快报》2004,15(11):1279-1280
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported. 相似文献
49.
JiangMinCHEN LuLingWU XianHUANG 《中国化学快报》2004,15(2):143-144
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process. 相似文献
50.
Direct Observation of Non-covalent Complexes for Phosphorylated Flavonoid-protein Interaction by ESI
XiaoLanCHEN TingZHANG HongXiaLIU LingBoQU YouZhuYU YuFenZHAO 《中国化学快报》2004,15(3):343-346
Diethyl flavon-7-yl phosphate was synthesized by modified Atheron-Todd reaction. The result of ESI shows that the phosphated flavonoids possess stronger binding affinities toward proteins such as myoglobin, insulin and lysozyme and are easier to form the non-covalent complexes with them. 相似文献