全文获取类型
收费全文 | 3039篇 |
免费 | 338篇 |
国内免费 | 273篇 |
专业分类
化学 | 1967篇 |
晶体学 | 17篇 |
力学 | 32篇 |
综合类 | 10篇 |
数学 | 238篇 |
物理学 | 1386篇 |
出版年
2024年 | 5篇 |
2023年 | 61篇 |
2022年 | 65篇 |
2021年 | 98篇 |
2020年 | 105篇 |
2019年 | 80篇 |
2018年 | 55篇 |
2017年 | 85篇 |
2016年 | 72篇 |
2015年 | 69篇 |
2014年 | 79篇 |
2013年 | 124篇 |
2012年 | 164篇 |
2011年 | 163篇 |
2010年 | 135篇 |
2009年 | 321篇 |
2008年 | 270篇 |
2007年 | 242篇 |
2006年 | 249篇 |
2005年 | 182篇 |
2004年 | 177篇 |
2003年 | 158篇 |
2002年 | 117篇 |
2001年 | 83篇 |
2000年 | 73篇 |
1999年 | 59篇 |
1998年 | 59篇 |
1997年 | 59篇 |
1996年 | 39篇 |
1995年 | 37篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有3650条查询结果,搜索用时 15 毫秒
1.
文章首先将史瓦西黑洞场中自由下落质点的固有时(诺维科夫坐标时)公式,由自然单位制化成了国际单位制中的形式.然后,根据牛顿第二定律和万有引力定律,推导出了自由下落质点经历的绝对时间公式,进而证明了广义相对论中自由落体经历的固有时,恰好等于牛顿力学给出的绝对时间.最后,对自由下落质点在黑洞内外经历的时间进行了特例计算. 相似文献
2.
《Comptes Rendus Chimie》2015,18(9):993-1000
The electrochemical oxidation of N-acetyl-p-aminophenol (PAR) was investigated at a Pt electrode with the application of cyclic (CV) and differential pulse (DPV) voltammetry methods. An effect of scan rate, substrate concentration and pH on electrode reactions was determined. The parameters of substrate electro-oxidation, i.e. heterogeneous rate constant, charge transfer coefficient, and diffusion coefficient, were calculated. Our investigation's results prove the exchange of two electrons and one proton in the first step, followed by a chemical reaction. PAR electro-oxidation occurs according to an EC mechanism. 相似文献
3.
4.
Juzo Oyamada 《Tetrahedron》2006,62(29):6918-6925
Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl2/AgOTf, K2PtCl4/AgOTf, and K2PtCl4/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields. 相似文献
5.
Eldad Herceg 《Surface science》2006,600(19):4563-4571
The formation of a well-ordered p(2 × 2) overlayer of atomic nitrogen on the Pt(1 1 1) surface and its reaction with hydrogen were characterized with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The p(2 × 2)-N overlayer is formed by exposure of ammonia to a surface at 85 K that is covered with 0.44 monolayer (ML) of molecular oxygen and then heating to 400 K. The reaction between ammonia and oxygen produces water, which desorbs below 400 K. The only desorption product observed above 400 K is molecular nitrogen, which has a peak desorption temperature of 453 K. The absence of oxygen after the 400 K anneal is confirmed with AES. Although atomic nitrogen can also be produced on the surface through the reaction of ammonia with an atomic, rather than molecular, oxygen overlayer at a saturation coverage of 0.25 ML, the yield of surface nitrogen is significantly less, as indicated by the N2 TPD peak area. Atomic nitrogen readily reacts with hydrogen to produce the NH species, which is characterized with RAIRS by an intense and narrow (FWHM ∼ 4 cm−1) peak at 3322 cm−1. The areas of the H2 TPD peak associated with NH dissociation and the XPS N 1s peak associated with the NH species indicate that not all of the surface N atoms can be converted to NH by the methods used here. 相似文献
6.
沈有根 《中国科学A辑(英文版)》2002,45(3):400-408
Using the membrane model which is based on brick wall model, we calculated the free energy and entropy of Garfinkle-Horne dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a coefficient between them. 相似文献
7.
Kayll Lake 《General Relativity and Gravitation》2004,36(5):1159-1169
The norms associated with the gradients of the two non-differential invariants of the Kerr vacuum are examined. Whereas both locally single out the horizons, their global behavior is more interesting. Both reflect the background angular momentum as the volume of space allowing a timelike gradient decreases with increasing angular momentum becoming zero in the degenerate and naked cases. These results extend directly to the Kerr-Newman geometry. 相似文献
8.
Dong‐Guk Yu Jeong Ho An 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5608-5616
Ultrafine black particles, ranging in diameter from 1 to 3 μm, were prepared by dispersion polymerization in a methanol/water mixture with vinyl monomers, nonpolymerizable Sudan black B dyes, and fluorescein isothiocyanate labeled charge control additives. Both the ratio of the methanol to the water dispersion medium and the polymeric stabilizer concentration had significant effects on the particle size. The important role of the stabilizer concentration lay in the particle formation step, during which it determined the particle stability and final particle size. These could affect the extent of the aggregation of nuclei by changing the adsorption rate of the stabilizer and the viscosity of the dispersion medium, resulting in smaller particles. The fluorescent‐labeled charge control additives strongly affected the electrophoretic mobility. A small concentration of fluorescent‐labeled charge control additives increased the electrophoretic mobility. However, a further addition reduced the electrophoretic mobility of the polymer particles. The concentration dependence of the fluorescent‐labeled charge control additives on the deposition behavior in the polymer particles was successfully imaged and thereafter quantified by image analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5608–5616, 2004 相似文献
9.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献
10.
利用量子统计方法 ,直接计算Barriola_Vilenkin黑洞背景下玻色场和费米场的配分函数 ,然后利用砖墙膜模型计算和讨论黑洞背景下玻色场和费米场的熵 相似文献