全文获取类型
收费全文 | 11290篇 |
免费 | 1254篇 |
国内免费 | 2322篇 |
专业分类
化学 | 6761篇 |
晶体学 | 340篇 |
力学 | 2130篇 |
综合类 | 70篇 |
数学 | 344篇 |
物理学 | 5221篇 |
出版年
2024年 | 37篇 |
2023年 | 158篇 |
2022年 | 430篇 |
2021年 | 448篇 |
2020年 | 389篇 |
2019年 | 340篇 |
2018年 | 294篇 |
2017年 | 476篇 |
2016年 | 549篇 |
2015年 | 488篇 |
2014年 | 675篇 |
2013年 | 988篇 |
2012年 | 773篇 |
2011年 | 771篇 |
2010年 | 675篇 |
2009年 | 771篇 |
2008年 | 764篇 |
2007年 | 855篇 |
2006年 | 676篇 |
2005年 | 577篇 |
2004年 | 564篇 |
2003年 | 479篇 |
2002年 | 403篇 |
2001年 | 328篇 |
2000年 | 291篇 |
1999年 | 230篇 |
1998年 | 214篇 |
1997年 | 194篇 |
1996年 | 157篇 |
1995年 | 132篇 |
1994年 | 117篇 |
1993年 | 89篇 |
1992年 | 95篇 |
1991年 | 62篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 96篇 |
1987年 | 41篇 |
1986年 | 33篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Runru Liu Dapeng Xu Shuang Li Zhe Lü Yanfeng Xue Deyong Wang Wenhui Su 《Frontiers of Chemistry in China》2006,1(4):398-401
In this paper, perovskite oxide SmCoO3 was prepared by the solid-state reaction method using Co2O3 and Sm2O3 as raw materials. The structure and properties of the samples were investigated by XRD, Raman spectral techniques, and DC
measurements and so on. The results of XRD and Raman spectra showed that the mixtures of Co2O3 and Sm2O3 can react to produce a single phase perovskite oxide SmCoO3 around 1353 K. The single-phase SmCoO3 changes from an insulator to a semi-conductor and transition occurs around 470 K. The thermal expansion coefficient (2.17
× 10−5 K−1) of the single-phase SmCoO3 is approximately equal to that of doped LaGaO3, but much bigger than that of SDC(Ce0.85Sm0.15O2) above 873 K. 相似文献
122.
123.
本文通过红外光谱(FT-IR)测量数据和预测数据,计算与研究了十九种长链正烷基脂肪酸(简称脂肪酸或碳酸)的碳链骨架振动能量。结果显示出脂肪酸的碳链骨架振动能量随碳数增加呈阶梯状关系,而且脂肪酸的碳链骨架振动能量∑E出现奇偶数更迭规律。此结果可用来解释脂肪酸的熔点或熔化热呈现奇偶数更迭现象。 相似文献
124.
主链含膦酸酯的聚酸酐药物控制释放材料研究 总被引:1,自引:0,他引:1
通过二氯膦甲(乙)酸乙酯与对羟乙氧基苯甲酸反应,制备了二羧苯氧乙氧基膦甲(乙)酸乙酯,并其转化成混合醋酐并通过熔融缩聚,合成了主链含膦甲(乙)酸乙酯的聚酸酐,以二羧苯氧乙氧基膦甲(乙)酸乙酯,分别与1,3-双(4-羧基苯氧基)丙烷(CPP)及癸二酸(SA)共聚,得到相应的共聚酸酐,对所合成的单体和聚合物的结构进行了表征,研究了它们的体外降解,酶促降解及其对抗肿瘤药物5-氟尿嘧啶和氨甲喋蛉的释放性能 相似文献
125.
126.
Aaron Goldman Frank J. Murcray Frank H. Murcray David G. Murcray Curtis P. Rinsland 《Mikrochimica acta》1988,95(1-6):409-415
Simultaneous total column amounts of a number of minor and trace atmospheric gases above the South Pole in December 1980 and December 1986 have been deduced from analysis of high resolution solar absorption spectra recorded (by F. J. M. and F. H. M.) from Amundsen-Scott South Pole Station. These spectra also contain some limited information on the vertical profiles of the observed atmospheric gases.The data sets were recorded with a Bomem Michelson-type interferometer and analyzed with a spectral least-squares fitting procedure, utilizing the best available spectroscopic line parameters and absorption cross sections. Because the same instrument, line parameters, and analysis method have been used in analyzing the December 1980 and December 1986 data sets, the precision in comparing the column amounts from these two dates is rather high, about 10–20% for the stronger absorbing gases. For this reason, it has been possible to quantify or determine upper limits for differences between the December 1980 and December 1986 total column amounts, of a number of atmospheric gases including O3, N2O, HNO3, CO2, CH4, and CF2C1
2 (CFC 12). In addition, vertical column amounts for a number of atmospheric gases covered only in the December 1986 observations have been derived, including HC1, NO, NO2, and C2H6. Some of these results will be discussed here. The HC1 measurements are especially interesting since the observed amounts are higher than expected from observations made at lower latitudes in the northern and southern hemispheres. 相似文献
127.
At room temperature, three of the six polymorphic compounds described are not present in their highest melting-point form, owing to enantiotropy. These three are triphenyltin chloride (3 modifications), 1-(4,4-dimethyl-2-oxo-3-tetrahydrofuryl)thiourea (4 modifications), and 2-aminoethyl diphenylborinate (3 modifications). In the case of 4-amino-1-(2-phenylethyl)-1,2,4-triazoline-5-thione, in addition to the absolutely stable modificationI, a further six unstable crystal forms have been observed. The three modifications of,-dimethyl-[1,1-biphenyl]-4-methanol are also monotropic in character. 2,9-Dimethyl-1,10-phenanthroline, the three polymorphic forms of which are unstable, is a special case, since it absorbs water from the air and changes into a semi-hydrate. 相似文献
128.
A systematic investigation was performed to elucidate the cause of spontaneous ignition of Refuse Derived Fuel (RDF) and Meat Bone Meal (MBM). Heat generation in both RDF and MBM with addition of water liquid and vapor at room temperature was determined by isothermal calorimetry. Compared with water liquid, the heat of wetting by sorption of water vapor at 80% relative humidity and 25 °C was larger, which can raise the temperature of RDF and MBM more than 30 and 56 °C, respectively. Heat generation due to fermentation occurred and the temperature of RDF and MBM reached or exceeded 80 °C after 5 days for RDF and 4 days for MBM at 100% RH. The spontaneous ignition for RDF and MBM results from heat of wetting and fermentation at room temperature and a further exothermic reaction at higher temperature. 相似文献
129.
Zn3V3O8 two-dimensional micro sheets are successfully synthesized by combination of solvothermal method and heat treatment. The Zn3V3O8 has better electrochemical performances after calcinations. 相似文献
130.