全文获取类型
收费全文 | 18494篇 |
免费 | 3674篇 |
国内免费 | 4813篇 |
专业分类
化学 | 13872篇 |
晶体学 | 566篇 |
力学 | 1254篇 |
综合类 | 540篇 |
数学 | 2419篇 |
物理学 | 8330篇 |
出版年
2024年 | 44篇 |
2023年 | 307篇 |
2022年 | 627篇 |
2021年 | 649篇 |
2020年 | 790篇 |
2019年 | 710篇 |
2018年 | 629篇 |
2017年 | 740篇 |
2016年 | 757篇 |
2015年 | 919篇 |
2014年 | 1139篇 |
2013年 | 1410篇 |
2012年 | 1561篇 |
2011年 | 1739篇 |
2010年 | 1398篇 |
2009年 | 1415篇 |
2008年 | 1543篇 |
2007年 | 1364篇 |
2006年 | 1365篇 |
2005年 | 1150篇 |
2004年 | 879篇 |
2003年 | 697篇 |
2002年 | 803篇 |
2001年 | 632篇 |
2000年 | 747篇 |
1999年 | 498篇 |
1998年 | 285篇 |
1997年 | 243篇 |
1996年 | 259篇 |
1995年 | 227篇 |
1994年 | 212篇 |
1993年 | 182篇 |
1992年 | 187篇 |
1991年 | 120篇 |
1990年 | 141篇 |
1989年 | 124篇 |
1988年 | 114篇 |
1987年 | 78篇 |
1986年 | 65篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 11篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 16篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
Gang Tian 《Inventiones Mathematicae》1997,130(1):1-37
In this paper, we prove that the existence of K?hler-Einstein metrics implies the stability of the underlying K?hler manifold
in a suitable sense. In particular, this disproves a long-standing conjecture that a compact K?hler manifold admits K?hler-Einstein
metrics if it has positive first Chern class and no nontrivial holomorphic vector fields. We will also establish an analytic
criterion for the existence of K?hler-Einstein metrics. Our arguments also yield that the analytic criterion is satisfied
on stable K?hler manifolds, provided that the partial C
0-estimate posed in [T6] is true.
Oblatum 12-IV-1996 & 8-XI-1996 相似文献
52.
同步荧光法测定食品中维生素B1 总被引:7,自引:0,他引:7
本文研究了食品中维生素B1的同步荧光法测定条件,采用氯化钾-乙醇作柱层析洗脱液,碱性介质中氧化后立即调为中性,并加入表面活性剂OP对体系增稳增敏,取代丁醇萃取,经济方便,用于几种粮食样品的测定,结果满意。 相似文献
53.
54.
55.
56.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
57.
58.
利用低压MOCVD工艺分别在(001)取向的LaAlO3,SrTiO3和重掺杂硅单晶衬底上制备PbTiO3铁电薄膜,并通过X射线衍射谱对薄膜的微结构进行分析.X射线θ-2θ扫描显示硅衬底上得到了PbTiO3多晶薄膜,另两种衬底上得到了择优取向的PbTiO3薄膜.LaAlO3衬底上的PbTiO3薄膜有a和c两个取向,也就是薄膜中存在着90°畴结构,而生长在SrTiO3衬底上的PbTiO3薄膜中只存在c方向的择优取向.由于薄膜的尺度效应,发现c轴晶格常数与块材相比均缩短.X射线的φ扫描验证了后两类薄膜的外延特性,利用同步辐射的高强度和高能量分辨率用摇摆曲线方法研究了这两种外延薄膜的品质,进一步证明了SrTiO3衬底上的PbTiO3薄膜的单畴特性.利用重掺杂的硅衬底作底电极,测量显示直接生长于硅衬底上的PbTiO3多晶薄膜具有良好的铁电性能
关键词: 相似文献
59.
Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found. 相似文献
60.
Cobalt antidot arrays with different thicknesses are fabricated by rf magnetron sputtering onto porous alumina substrates. Scanning electron microscopy and grazing incidence x-ray diffraction are employed to characterize the morphology and crystal structure of the antidot array, respectively. The temperature dependence of magnetic properties shows that in the temperature range 5K--300K, coercivity and squareness increase firstly, reach their maximum values, then decrease. The anomalous temperature dependences of coercivity and squareness are discussed by considering the pinning effect of the antidot and the magnetocrystalline anisotropy. 相似文献