全文获取类型
收费全文 | 47736篇 |
免费 | 3485篇 |
国内免费 | 2571篇 |
专业分类
化学 | 23689篇 |
晶体学 | 433篇 |
力学 | 2496篇 |
综合类 | 130篇 |
数学 | 11598篇 |
物理学 | 15446篇 |
出版年
2024年 | 86篇 |
2023年 | 434篇 |
2022年 | 650篇 |
2021年 | 698篇 |
2020年 | 863篇 |
2019年 | 781篇 |
2018年 | 1871篇 |
2017年 | 2085篇 |
2016年 | 1669篇 |
2015年 | 1494篇 |
2014年 | 1542篇 |
2013年 | 2080篇 |
2012年 | 4765篇 |
2011年 | 4010篇 |
2010年 | 3005篇 |
2009年 | 2609篇 |
2008年 | 1765篇 |
2007年 | 1668篇 |
2006年 | 1543篇 |
2005年 | 5262篇 |
2004年 | 4569篇 |
2003年 | 2868篇 |
2002年 | 1143篇 |
2001年 | 823篇 |
2000年 | 524篇 |
1999年 | 597篇 |
1998年 | 448篇 |
1997年 | 378篇 |
1996年 | 372篇 |
1995年 | 331篇 |
1994年 | 274篇 |
1993年 | 183篇 |
1992年 | 333篇 |
1991年 | 310篇 |
1990年 | 258篇 |
1989年 | 200篇 |
1988年 | 151篇 |
1987年 | 113篇 |
1986年 | 112篇 |
1985年 | 83篇 |
1984年 | 60篇 |
1983年 | 52篇 |
1976年 | 80篇 |
1975年 | 39篇 |
1974年 | 41篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1969年 | 38篇 |
1968年 | 35篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献
102.
Yangyang Jiang Chen Guo Huizhou Liu 《中国颗粒学报》2007,5(1):130-133
A magnetically rotational reactor (MRR) has been developed and used in absorbing benzene emissions. The MRR has a permanent magnet core and uses magnetic ionic liquid [bmim]FeCl4 as absorbent. Benzene emissions were carried by N2 into the MRR and were absorbed by the magnetic ionic liquid. The rotation of the permanent magnet core provided impetus for the agitation of the magnetic ionic liquid, enhancing mass transfer and making benzene better dispersed in the absorbent. 0.68 g benzene emissions could be absorbed by a gram of [bmim]FeCl4, 0.27 and 0.40 g/g higher than that by [bmim]PF6 and [bmim]BF4, respectively. The absorption rate increased with increasing rotation rate of the permanent magnet. 相似文献
103.
We report X-ray absorption near edge structures (XANES) study of CeAl2 thin films of various thicknesses, 40-120 nm, at Al K- and Ce L3-edges. The threshold of the absorption features at the Al K-edge shifts to the higher photon energy side as film thickness decreases, implying a decreased in Al p-orbital charges. On the other hand, from Ce L3-edge spectra, we observed a decrease in the 5d4f occupancy as the surface-to-bulk ratio increases. The valence of Ce in these thin films, as revealed by the Ce L3-edge spectral results, is mainly trivalent. From a more detailed analysis we found a small amount of Ce4+ contribution, which increases with decreasing film thickness. Our results indicate that the surface-to-bulk ratio is the key factor which affects the electronic structure of CeAl2 thin films. The above observations also suggest that charge transfer from Al to Ce is associated with the decrease of the film thickness. 相似文献
104.
Ping-xing Chen Jian-ming Cai Zheng-wei Zhou Guang-can Guo 《量子光学学报》2006,12(B08):72-73
The second law of thermodynamics is one of the most fundamental and for-reaching laws of physics. It teaches us that when a closed system undergoes a thermodynamic process the entropy of the system never decreases; it increases, or at least remains constant. If the entropy increases the thermodynamic process is irreversible, otherwise it is reversible. Only ideal thermal process is reversible. In classical world a great number of facts have proved the second law is true. But in quantum world since the quantum coherence and correlations exist we are not sure the second law is still true, at least in principle. This is because that: 1. on the microscopic level the irreversibility is conflict with the reversibility of all fundamental physical laws ; 2. there are not enough evidences to show it is true in quantum world. 相似文献
105.
M. A. Rizzutto N. Added M. H. Tabacniks F. R. Espinoza-Qui?ones S. M. Palacio R. M. Galante R. M. Galante N. Rossi R. A. Welter A. N. Módenes 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(3):727-731
Summary Kulcsszavak (angolul, ha nem azonos az elozovel) 相似文献
106.
Peptidosulfonamides are an emerging group of peptidomimetics with a variety of applications in medicinal chemistry. We present a novel approach to the synthesis of peptidosulfonamides, and apply it to a series of new potential inhibitors of the bacterial peptidoglycan biosynthesis enzymes MurD and MurE. The synthesis was conducted via N-phthalimido β-aminoethanesulfonyl chlorides, which are new building blocks for the synthesis of peptidosulfonamides. In the most crucial step, sulfonic acids or their sodium salts were converted into the corresponding sulfonyl chlorides using an excess of either SOCl2 or SOCl2/DMF, and then coupled to the C-protected amino acid. None of the compounds significantly inhibited MurD, however, some inhibited MurE; one had an IC50 below 200 μM, which constitutes a promising starting point for further development. Molecular modelling simulations were performed on two analogues to investigate the absence of inhibitory activity of the sulfonamide compounds on MurD. 相似文献
107.
108.
通过对La0.3Ca0.7Mn1-xWxO3(x=0.00,0.04,0.08,0.12,0.15)多晶样品M-T曲线、M-H曲线及ESR谱的测量,研究了Mn位W掺杂对电荷有序体系La0.3Ca0.7MnO3磁结构的影响.结果表明,当掺杂量为0.00≤x≤0.08时,体系存在电荷有序(CO)相,AFM/CO态共存于相变温度以下,电荷有序温度TCO随着W掺杂量的增加而增加;x=0.04时,样品在低温下为FM相与AFM/CO相共存,在CO相建立前、后均有FM从PM中分离出来;当x≥0.12时,CO态融化,在极低温度下存在顺磁-铁磁(PM-FM)相变. 相似文献
109.
Some Results behind Dividend Problems 总被引:1,自引:0,他引:1
Ming Zhou Li Wei Jun-yi Guo 《应用数学学报(英文版)》2006,22(4):681-686
We consider the basic dividend problem of the compound Poisson model with constant barrierstrategy.Some results concealed behind the dividend problem are made explicit in the present work.Differentmethods and some of which are firstly given in this paper.All these results presented certain direct relationshipbetween some important actuary variables in classical risk theory is also revealed. 相似文献
110.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant. 相似文献