全文获取类型
收费全文 | 87648篇 |
免费 | 12710篇 |
国内免费 | 7317篇 |
专业分类
化学 | 56540篇 |
晶体学 | 965篇 |
力学 | 5627篇 |
综合类 | 314篇 |
数学 | 9813篇 |
物理学 | 34416篇 |
出版年
2024年 | 175篇 |
2023年 | 1587篇 |
2022年 | 2258篇 |
2021年 | 2746篇 |
2020年 | 3173篇 |
2019年 | 2972篇 |
2018年 | 2699篇 |
2017年 | 2486篇 |
2016年 | 3764篇 |
2015年 | 3519篇 |
2014年 | 4315篇 |
2013年 | 5829篇 |
2012年 | 7358篇 |
2011年 | 7738篇 |
2010年 | 5223篇 |
2009年 | 4982篇 |
2008年 | 5438篇 |
2007年 | 4996篇 |
2006年 | 4629篇 |
2005年 | 3812篇 |
2004年 | 3056篇 |
2003年 | 2427篇 |
2002年 | 2250篇 |
2001年 | 2322篇 |
2000年 | 1938篇 |
1999年 | 2019篇 |
1998年 | 1621篇 |
1997年 | 1625篇 |
1996年 | 1556篇 |
1995年 | 1276篇 |
1994年 | 1146篇 |
1993年 | 935篇 |
1992年 | 861篇 |
1991年 | 736篇 |
1990年 | 665篇 |
1989年 | 524篇 |
1988年 | 447篇 |
1987年 | 375篇 |
1986年 | 353篇 |
1985年 | 301篇 |
1984年 | 230篇 |
1983年 | 171篇 |
1982年 | 134篇 |
1981年 | 111篇 |
1980年 | 109篇 |
1979年 | 82篇 |
1977年 | 83篇 |
1976年 | 85篇 |
1975年 | 87篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
H. Sh. Bai H. X. Jin H. Q. Fan J. Du F. Wang D. M. Chen Zh. Cheng 《Journal of Radioanalytical and Nuclear Chemistry》1998,236(1-2):87-95
The behavior of153Sm-EDTMP in vitro and vivo is analyzed by the size exclusion HPLC. The experimental results show that EDTMP amounts have an
obvious effect on the stability in vitro and uptake of153Sm-EDTMP in the liver. HPLC analysis of urine sample indicates that153Sm-EDTMP es excreted in the original form. The behavior in vivo of153Sm-EDTMP containing 4 μg is similar to that of153Sm-EDTMP containing 50 μg EDTMP at 1 h post-injection. 相似文献
992.
993.
Determination of impurities in highly pure platinum by inductively coupled plasma-atomic emission spectrometry 总被引:1,自引:0,他引:1
In this work, a cyclone spray chamber system is used in conjunction with an inductively coupled plasma-atomic emission spectrometer instead of the conventional Scott-type chamber system to reduce the lower limit of detection achieved by the instrument, and an internal standard element (Y) is introduced to eliminate the effects caused by the drift in the plasma background level. An ICP-AES method for the determination of 13 impurity elements in a highly pure platinum sample has been developed. In this method, it is not necessary either to add a platinum matrix to the calibration standard or to separate and concentrate the elements to be determined in the samples. The effect of the platinum matrix on the elements to be analyzed is corrected for by a background equivalent concentration subtraction method. The determination ranges of the method are as follows: 0.00010-0.0050% for Mg, Mn, Cu, Ag, Fe and Zn; 0.00030-0.015% for Au, Ir, Ni and Pb; 0.00050-0.025% for Rh and Al; and 0.00080-0.040% for Pd. The method is simple, rapid and accurate, and can be applied to the analysis of 99.9–99.995% pure platinum. 相似文献
994.
995.
A glassy carbon electrode was pretreated electrochemically and was coated with a copolymer of maleic acid anhydride attached with Eastman-AQ55D (MA/AQ). The voltammetric behavior of a series of biologically important compounds, such as dopamine, L-DOPA, DOPAC, ascorbic acid and uric acid were examined at both pretreated and coated electrodes. Electrochemical pretreatment increased peak current of dopamine and L-DOPA while decreased that of ascorbic acid, uric acid and DOPAC. The copolymer coating caused a decrease of peak currents, but effectively hindered the anionic species (ascorbic acid, uric acid and DOPAC) access to the electrode surface. In flow injection and liquid chromatographic analysis. The dopamine and L-DOPA yielded the better selectivity response at MA/AQ electrode than at bare and AQ electrodes. 相似文献
996.
A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds. 相似文献
997.
The hydrosilylation reaction of octa(hydrido)silsesquioxane with ω‐halo‐1‐alkenes and other unsaturated substrates allows attachment of 8 long‐chain functionalized alkyls on the cubic Si8O12 skeleton. Pt/C and H2PtCl6 have been adopted as the catalysts, the yields being 74–98% for compounds 2–9 . For terminal alkenes, the hydrosilylation follows the anti‐Markonikov's rule. The morphological state of 2–9 ranges from viscous liquid to crystalline materials. The pyrolysis results indicate that 7 , a material of hard spherical core and soft flexible shell, may likely act as nanometer‐size ball bearings up to more than 400 °C. The X‐ray structure of 9 reveals that the molecule is required to possess a center of symmetry crystallographically. The linear arms on 9 , except for two of them, are virtually all‐trans in conformation, not counting the ω‐C‐Cl bond. 相似文献
998.
999.
固相萃取-气相色谱-质谱分析肉样中盐酸克伦特罗的残留量 总被引:25,自引:12,他引:25
建立了固相萃取 气相色谱 质谱联机分析肉样中盐酸克伦特罗残留量的方法。对盐酸克伦特罗在C1 8和离子交换固相萃取柱上的保留行为进行了研究 ,发现不同浓度盐酸克伦特罗的固相萃取回收率在 75 %~ 95 %之间 ;肉样中的加标回收率在 70 %~ 83 % ;相对标准偏差在 4 .95 %~ 1 3 .4 % ;最低检出限为 1 μg kg。盐酸克伦特罗的硅烷化产物 ,采用选择离子的模式进行检测 ( 86、2 4 3、2 62、2 77) ,衍生物的峰面积与样品浓度在0 .0 0 2 5 2~ 2 .0 2mg L范围内呈良好的线性关系 ,线性回归系数大于 0 .9999。 相似文献
1000.