全文获取类型
收费全文 | 12614篇 |
免费 | 2148篇 |
国内免费 | 3434篇 |
专业分类
化学 | 8689篇 |
晶体学 | 455篇 |
力学 | 695篇 |
综合类 | 338篇 |
数学 | 2079篇 |
物理学 | 5940篇 |
出版年
2024年 | 28篇 |
2023年 | 115篇 |
2022年 | 417篇 |
2021年 | 401篇 |
2020年 | 429篇 |
2019年 | 392篇 |
2018年 | 457篇 |
2017年 | 550篇 |
2016年 | 492篇 |
2015年 | 600篇 |
2014年 | 755篇 |
2013年 | 1129篇 |
2012年 | 979篇 |
2011年 | 1116篇 |
2010年 | 966篇 |
2009年 | 1018篇 |
2008年 | 1143篇 |
2007年 | 987篇 |
2006年 | 996篇 |
2005年 | 757篇 |
2004年 | 592篇 |
2003年 | 505篇 |
2002年 | 482篇 |
2001年 | 463篇 |
2000年 | 534篇 |
1999年 | 298篇 |
1998年 | 158篇 |
1997年 | 137篇 |
1996年 | 167篇 |
1995年 | 103篇 |
1994年 | 122篇 |
1993年 | 100篇 |
1992年 | 101篇 |
1991年 | 75篇 |
1990年 | 72篇 |
1989年 | 62篇 |
1988年 | 56篇 |
1987年 | 36篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 49篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 32篇 |
1980年 | 25篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1975年 | 10篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
5-甲基吡咯-2-羧酸酯在磺酰氢,溴或四乙酸铅作用下,生成相应的在5-甲基上含取代基的产物,后者不经分离不便可自缩合得标题化合物,核磁共振氢谱研究和分子构象木匠,当3,3位的取代基为甲酸(酯)基或乙酸(酯)基时,可形成3,3位酯基与另一吡咯环上的氮氢之间的分子内氢键,而3,3位是其它取代基,如乙酰基,丙酸(酯)基,丁酸(酯)基时不能形成类似的分子内氢键。 相似文献
62.
63.
M. A. Morón C. Romero F. R. Ruiz del Portal 《Journal of Optimization Theory and Applications》1996,91(3):643-649
The purpose of this paper is to seek utility functions satisfying a weak condition which guarantees that the utility optimum always belongs to the compromise set. This set is a special subset of the attainable or feasible set, which is generated through the application of the well-known operational research approach called compromise programming. It is shown that there are large families of utility functions satisfying this condition, thus reinforcing the value of compromise programming as a good surrogate of the traditional utility optimum.Thanks are due to the reviewers for their helpful suggestions. The English editing by Ms. Christine Méndez is appreciated. The authors have been supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Madrid, Spain. 相似文献
64.
65.
66.
67.
Polyethylene terephthalate(PET)/polycaprolactone(PCL) segmented copolymers with different hard segment contents and a blend of two of them were studied by using DSC, WAXS, TEM and IR techniques and dynamic mechanical, stress-strain and isothermal crystallization measurements. Emphasis was laid on the studies of influence of compositional heterogeneity on the morphology and properties of these segmented copolymers. It was found that the solution cast specimens of the more heterogeneous sample exhibit better segregation of segments, high crystallinity and melting temperature. They have higher thermal stability of mechanical properties at small deformations. However, they are less stable against large deformations and may become softer than the more homogeneous ones. 相似文献
68.
ZHANG Wei-wei CHEN Yu-chun LUO Zhao-feng WANG Ju-ying MA De-yi 《高等学校化学研究》2007,23(4):404-407
In this study, surface plasmon resonance (SPR) for monitoring 17β-eatradiol (E2) was developed. The small molecule E2 was immobilized on a CM5 sensor chip for an indirect competitive immunoassay to detect E2. The SPR response bahed on the antigen-antibody reaction was measured by injecting the sample solution into the flow system. The limitation of detection was 0.445 μg/L. The developed SPE-SPR system was applied to analyze the seawater samples. Recovery of E2 was 91.6%-93. 1%. Relative standard deviations(RSD) for the E2 assay were between 10.9%-15.1% (n = 3). The range of determination of E2 samples from the sewage in the coastal marine environ-ment was between ND(lower than detection limit) and ca. 11.78 ng/L. 相似文献
69.
Synthesis and Characterization of Novel Orange-emitting Iridium(Ⅲ) Complexes with Diphenylquinoline Ligands Containing Fluorinated Substituent 总被引:1,自引:0,他引:1
Xiao Wei ZHANG Chu Luo YANG Zhong An LI Lin Na ZHU Jin Gui QIN Jia GAO Dong Ge MA 《中国化学快报》2006,17(3):411-414
Three new cyclometalated iridium(m) complexes based on ligands of diphenylquinoline with fluorinated subsfituents were prepared, and characterized by elemental analysis (EA), ^1H NMR, and mass spectroscopy (MS). The photophysical and electrophosphorescent properties of the complexes were briefly discussed. 相似文献
70.
几种常见水果的微量元素分析 总被引:1,自引:0,他引:1
运用原子吸收分光光度法测定了几种常见水果中部分微量元素含量。其中榴莲的Mg、Zn、Cu、K含量位于四种水果之首。美国提子中Ca含量最高,芒果中Fe含量最高。以上差别具有统计学意义。六种元素的回收率为90%-106.5%。连续6次测定样品,变异系数(CV)为0.96%。 相似文献