全文获取类型
收费全文 | 18197篇 |
免费 | 2171篇 |
国内免费 | 1486篇 |
专业分类
化学 | 13206篇 |
晶体学 | 194篇 |
力学 | 772篇 |
综合类 | 102篇 |
数学 | 2661篇 |
物理学 | 4919篇 |
出版年
2024年 | 19篇 |
2023年 | 260篇 |
2022年 | 424篇 |
2021年 | 555篇 |
2020年 | 682篇 |
2019年 | 590篇 |
2018年 | 516篇 |
2017年 | 492篇 |
2016年 | 873篇 |
2015年 | 826篇 |
2014年 | 933篇 |
2013年 | 1273篇 |
2012年 | 1655篇 |
2011年 | 1715篇 |
2010年 | 1205篇 |
2009年 | 1077篇 |
2008年 | 1277篇 |
2007年 | 1137篇 |
2006年 | 1096篇 |
2005年 | 867篇 |
2004年 | 732篇 |
2003年 | 517篇 |
2002年 | 424篇 |
2001年 | 266篇 |
2000年 | 253篇 |
1999年 | 290篇 |
1998年 | 221篇 |
1997年 | 194篇 |
1996年 | 197篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 120篇 |
1992年 | 115篇 |
1991年 | 105篇 |
1990年 | 78篇 |
1989年 | 60篇 |
1988年 | 57篇 |
1987年 | 59篇 |
1986年 | 43篇 |
1985年 | 48篇 |
1984年 | 40篇 |
1983年 | 33篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Juan A. Barceló Jonathan Bennett Alberto Ruiz 《Journal of Fourier Analysis and Applications》2003,9(6):541-562
We study the continuity properties of a projection derived from a recent characterization of Herglotz Wave Functions in the plane. Herglotz Wave Functions are the entire solutions of the Helmholtz equation which have L2-Far-Field-Pattern. The behavior of this projection is reminiscent of the Disc Multiplier Operator on both Lp and mixed Lp-normed spaces. In particular a Kakeya type set plays a central role in our analysis. As a consequence we answer a question posed by Alvarez, Folch-Gabayet and Pérez-Esteva. 相似文献
62.
Toluene adsorption reactions on the (1 1 0) surface of VSbO4 have been analyzed following the changes in the electronic structure of the hydrocarbon molecule and metal cation sites of the oxide using the Just Another Extended Hückel Molecular Orbital Program (JAEHMOP) code. The bonding character of these interactions has also been studied in the same theoretical framework. The calculations indicate that the exothermic hydrocarbon parallel interaction on Sb-V sites results in the weakening of one of the C-H bonds of the methyl fragment. This leads to a H-abstraction that involves the participation of a Sb-cation. Both methyl and phenyl fragments decrease their electronic population and so does the V-cation site. Most of these electrons are transferred to other V atoms in the bulk solid. As a result the LUMO of the toluene-oxide system fully populates. The analysis reveals that methyl-Sb bonding interactions mainly involve C2px and H1s orbitals with Sb5s orbital, while non-bonding phenyl-V interactions involve C2px orbitals with V3dx2−y2 orbital. This last interaction facilitates the desorption of the benzyl species after H-abstraction. 相似文献
63.
We prove that a locally compact ANR-space X is a Q-manifold if and only if it has the Disjoint Disk Property (DDP), all points of X are homological Z
∞-points and X has the countable-dimensional approximation property (cd-AP), which means that each map f: K → X of a compact polyhedron can be approximated by a map with the countable-dimensional image. As an application we prove that
a space X with DDP and cd-AP is a Q-manifold if some finite power of X is a Q-manifold. If some finite power of a space X with cd-AP is a Q-manifold, then X
2 and X × [0, 1] are Q-manifolds as well. We construct a countable family χ of spaces with DDP and cd-AP such that no space X ∈ χ is homeomorphic to the Hilbert cube Q whereas the product X × Y of any different spaces X, Y ∈ χ is homeomorphic to Q. We also show that no uncountable family χ with such properties exists.
This work was supported by the Slovenian-Ukrainian (Grant No. SLO-UKR 04-06/07) 相似文献
64.
The determination of the enantiomeric purity of 2 or 3-substituted cyclanones, particularly cyclohexanones, is conveniently achieved by derivatisation into cyclic aminals with commercially available (R, R)-1,2-diphenylethylenediamine. The derivatisation procedure is directly done into the NMR tube, instantaneously, and 13C NMR allows an accurate measure of the ee. 相似文献
65.
Ga1-xInxAs(x>0.53)材料是未来长距离低损耗光纤通信的理想光源材料和探测器材料之一.我们采用水平常压MOCVD系统,在InP衬底上成功地生长了Ga1-xInxAs(x>0.53)/InAsyP1-y/Inp异质结材料.其中InAs1-yPy为组份阶梯变化的多层结构.由样品的(400)面X光衍射结果测定了各层组份.由二次离子质谱(SIMS)得到了样品剖面组份变化结果,证明InAs1-yPy层组份为阶梯状变化的.通过对光致发光结果和X光衍射结果比较,可以看到,InAsyP1-y层通过位错和弹性畸变二种方式来释放或积累Ga1-xInxAs与InP间的失配应力,从而减少了Ga1-xInxAs中的失配位错.有效地改善了Ga1-xInxAs的质量.已获得了x高达0.94表面光亮的Ga1-xInxAs/InAs1-yPy/InP异质结材料. 相似文献
66.
67.
Xiangdong Liu Hongwei Liu Kexu Yuan Huiping Du 《International Journal of Infrared and Millimeter Waves》1991,12(9):1023-1034
According to the angular-spectrum method, a radiation beam of an antenna horn in the Fresnal region is decomposed into the plane waves with the fast Fourier transform algorithm and the waves diffracted from a reflection grating are superposed as a diffracted beam. Compared with the reflected beam from the same size mirror, the radiation half width of the diffracted beam from a grating is narrower and its lateral shape is shift. These performances have been experimentally verified at Ka-band by: (1). The relative diffraction efficiencies in the first order with two triangular gratings which is put along propagating direction of a beam produced by a conical lens-horn. (2). H-plane lateral width with power—3dB lapsed of the focus beam from a grating and a mirror in a grating spectrometer for millimeter waves (25–100 GHz). 相似文献
68.
测定了室温下烃类(乙炔、乙烷)烟粒的红外复折射率,并讨论了所获数据在测量烟浓度与烟粒大小分类、计算光谱吸收系数及在特定浓度与温度下评估烟雾辐射率方面的应用。 相似文献
69.
We give several equivalent characterisations of left (and hence, by duality, also of right) supported algebras. These characterisations are in terms of properties of the left and the right parts of the module category, or in terms of the classes L0 and R0 which consist respectively of the predecessors of the projective modules, and of the successors of the injective modules. 相似文献
70.