全文获取类型
收费全文 | 23995篇 |
免费 | 2724篇 |
国内免费 | 1908篇 |
专业分类
化学 | 14764篇 |
晶体学 | 408篇 |
力学 | 1480篇 |
综合类 | 98篇 |
数学 | 2370篇 |
物理学 | 9507篇 |
出版年
2024年 | 29篇 |
2023年 | 305篇 |
2022年 | 543篇 |
2021年 | 603篇 |
2020年 | 714篇 |
2019年 | 738篇 |
2018年 | 676篇 |
2017年 | 559篇 |
2016年 | 902篇 |
2015年 | 822篇 |
2014年 | 1059篇 |
2013年 | 1570篇 |
2012年 | 1907篇 |
2011年 | 1999篇 |
2010年 | 1445篇 |
2009年 | 1445篇 |
2008年 | 1576篇 |
2007年 | 1416篇 |
2006年 | 1340篇 |
2005年 | 1107篇 |
2004年 | 953篇 |
2003年 | 799篇 |
2002年 | 795篇 |
2001年 | 823篇 |
2000年 | 639篇 |
1999年 | 535篇 |
1998年 | 424篇 |
1997年 | 380篇 |
1996年 | 359篇 |
1995年 | 291篇 |
1994年 | 255篇 |
1993年 | 191篇 |
1992年 | 198篇 |
1991年 | 200篇 |
1990年 | 156篇 |
1989年 | 127篇 |
1988年 | 92篇 |
1987年 | 66篇 |
1986年 | 66篇 |
1985年 | 76篇 |
1984年 | 55篇 |
1983年 | 37篇 |
1982年 | 45篇 |
1981年 | 47篇 |
1980年 | 34篇 |
1979年 | 22篇 |
1978年 | 27篇 |
1976年 | 22篇 |
1975年 | 25篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
141.
In this paper, we find some new explicit examples of Hamiltonian minimal Lagrangian submanifolds among the Lagrangian isometric immersions of a real space form in a complex space form. 相似文献
142.
In this note, the authors resolve an evolutionary Wente's problem associated to heat equation, where the special integrability of det▽u for u ∈ H1(R2,R2) is used. 相似文献
143.
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
144.
Q. Liang 《Applied Surface Science》2006,252(13):4628-4631
We report a pulsed laser deposition (PLD) growth of VMn/CoCrPt bilayer with a magnetic coercivity (Hc) of 2.2 kOe and a grain size of 12 nm. The effects of VMn underlayer on magnetic properties of CoCrPt layer were studied. The coercivity, Hc, and squareness, S, of VMn/CoCrPt bilayer, is dependent on the thickness of VMn. The grain size of the CoCrPt film can also be modified by laser parameters. High laser fluence used for CoCrPt deposition produces a smaller grain size. Enhanced Hc and reduced grain size in VMn/CoCrPt is explained by more pronounced surface phase segregation during deposition at high laser fluence. 相似文献
145.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
146.
利用SHS等离子喷涂技术,将经过机械团聚法制备的Fe2O3-Al复合粉体送入等离子焰流,沉积出厚度约为400 μm的复合涂层.利用XRD,SEM 和TEM等检测手段对涂层的成分和组织进行了分析,测定了涂层的显微硬度、断裂韧性以及耐磨性.结果表明涂层为具有纳米结构的FeAl2O4-Al2O3-Fe纳米复合组织;涂层的显微硬度为HV100g870;断裂韧性是普通Al2O3涂层的2倍;无润滑磨损的耐磨性是普通Al2O3涂层的2.5倍. 相似文献
147.
148.
149.
运用一种新的动力学突变检测方法——排列熵(permutation entropy,PE)算法,计算并分析了中国华北地区52个站点1960年—2000年逐日平均气温资料的排列熵演化情况,发现中国华北地区气温在20世纪70年代中期、80年代初均发生了较大突变;进一步用经验模态分解(empirical mode decomposition,EMD)方法对排列熵序列进行逐级平稳化处理,结果发现这一地区的气温突变与准10年这一年代际时间尺度的周期变率密切相关,其原因与太阳黑子活动有着密切联系.
关键词:
华北
突变
排列熵算法
经验模态分解 相似文献
150.
Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ2 = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ1, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ1 and the intensity I2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth. 相似文献