全文获取类型
收费全文 | 10496篇 |
免费 | 1740篇 |
国内免费 | 2021篇 |
专业分类
化学 | 8187篇 |
晶体学 | 142篇 |
力学 | 532篇 |
综合类 | 207篇 |
数学 | 1312篇 |
物理学 | 3877篇 |
出版年
2024年 | 14篇 |
2023年 | 101篇 |
2022年 | 212篇 |
2021年 | 243篇 |
2020年 | 287篇 |
2019年 | 368篇 |
2018年 | 275篇 |
2017年 | 278篇 |
2016年 | 431篇 |
2015年 | 494篇 |
2014年 | 580篇 |
2013年 | 782篇 |
2012年 | 887篇 |
2011年 | 957篇 |
2010年 | 843篇 |
2009年 | 815篇 |
2008年 | 918篇 |
2007年 | 883篇 |
2006年 | 838篇 |
2005年 | 658篇 |
2004年 | 567篇 |
2003年 | 520篇 |
2002年 | 491篇 |
2001年 | 386篇 |
2000年 | 282篇 |
1999年 | 211篇 |
1998年 | 161篇 |
1997年 | 111篇 |
1996年 | 108篇 |
1995年 | 89篇 |
1994年 | 80篇 |
1993年 | 69篇 |
1992年 | 62篇 |
1991年 | 53篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 6篇 |
1983年 | 14篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Zhishen Mo Lixiao Wang Hongfang Zhang Ping Han Baotong Huang 《Journal of Polymer Science.Polymer Physics》1987,25(9):1829-1837
Wide-angle X-ray scattering from presumed block copolymers of polypropylene (PP) and ethylene-propylene copolymer (EPR), i.e., PP-EPR and PP-EPR-PP, synthesized by sequential polymerization with δ-TiCl3? Et2AlCl, was examined and compared with WAXS of mechanical blends and chain-transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensities I040/I110 of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in the prepared copolymers. 相似文献
44.
�� Ƽ������ͨ�������������� 《核聚变与等离子体物理》2006,39(3):265-269
By using Fluent software with the Eulerian multiphase model and Non-equilibrium boiling model, the subcooled flow boiling heat transfers was numerically simulated in the plain upward vertical tubes under the condition of one-side heating. The influences of the different mass flux, inlet temperatures and heat flux on the heat transfer coefficient, the void fraction and heat transfer deterioration were investigated. 相似文献
45.
Li‐Ming Tang Yan‐Guo Li Wei‐Ping Ye Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5846-5854
Ethylene–propylene copolymerization, using [(Ph)NC(R2)CHC(R1)O]2TiCl2 (R1 = CF3, Ph, or t‐Bu; R2 = CH3 or CF3) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High‐molecular‐weight ethylene–propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R1 and R2 influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R1 and R2, one complex (R1 = CF3; R2 = CH3) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with 13C NMR to determine the methylene sequence distribution and number‐average sequence lengths of uninterrupted methylene carbons. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5846–5854, 2006 相似文献
46.
Chin‐Ping Yang Yu‐Yang Su Sheng‐Huei Hsiao 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5909-5922
Two series of novel fluorinated poly(ether imide)s (coded IIIA and IIIB ) were prepared from 2,6‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride and 2,7‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride, respectively, with various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal or chemical imidization of the poly(amic acid) precursors. These fluorinated poly(ether imide)s showed good solubility in many organic solvents and could be solution‐cast into transparent, flexible, and tough films. These films were nearly colorless, with an ultraviolet–visible absorption edge of 364–386 nm. They also showed good thermal stability with glass‐transition temperatures of 221–298 °C, 10% weight loss temperatures in excess of 489 °C, and char yields at 800 °C in nitrogen greater than 50%. The 2,7‐substituted IIIB series also showed better solubility and higher transparency than the isomeric 2,6‐substituted IIIA series. In comparison with nonfluorinated poly (ether imide)s, the fluorinated IIIA and IIIB series showed better solubility, higher transparency, and lower dielectric constants and water absorption. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5909–5922, 2006 相似文献
47.
借助于环论的方法研究了具有交换自同构群的有限群,提出了一种新的自同构构作技术,并用之证明了这样的非交换有限群具有非循环的中心子群,以及其每个极大子群的中心子群也都非循环. 相似文献
48.
The influence of interdiffusion on eigenstates in an interdiffusion-induced GaAs/AlxGa1-xAs single-quantum-well structure is analysed numerically by the finite element method. In this approach, the confinement potential profile of the interdiffused quantum well structure is nonlinear and is modelled by an error function and, in particular, the nature of the effective mass of an electron is considered. The results show that the number of eigenstates and energy levels varies with the extent of the interdiffusion. Numerical results for the quasi-bound states in the quantum well structure with an applied electric field are also presented. 相似文献
49.
以典型的轻希土镧和重希土镝及碱土金属锶作为A位离子,以过渡金属锰、铁、钴、镍作为B位离子,合成了K2NiF4型结构的A2-xSrxBO4希土复合氧化物,采用粉末X射线衍射技术考察了反应条件等因素对生成K2NiF4型四方(T)结构上析影响,实现结果表明,四方结构的形成不仅与几何因素有关,而且与各组分的物理化学性质有关。各个不同的组成,生成四方相的温度范围也有所不同。适当地提高反应温度以及延长灼烧时间 相似文献
50.
微波常压法合成水杨酸酯 总被引:15,自引:0,他引:15
在浓硫酸催化下,采用微波常压法由水杨酸分别与正丁醇、异丁醇、正戊醇和异戊醇反应合成相应的水杨酸酯。结果表明:当水杨酸:醇:H2SO4=1:5.5:0.3(摩尔比)时,采用560W微波辐射22min,水杨酸酯的产率可达88.7% ̄96.4%,反应速度至少是常规反应的14倍。 相似文献