全文获取类型
收费全文 | 18022篇 |
免费 | 2726篇 |
国内免费 | 2421篇 |
专业分类
化学 | 13146篇 |
晶体学 | 210篇 |
力学 | 1165篇 |
综合类 | 171篇 |
数学 | 2261篇 |
物理学 | 6216篇 |
出版年
2024年 | 56篇 |
2023年 | 394篇 |
2022年 | 485篇 |
2021年 | 621篇 |
2020年 | 759篇 |
2019年 | 746篇 |
2018年 | 656篇 |
2017年 | 619篇 |
2016年 | 871篇 |
2015年 | 842篇 |
2014年 | 998篇 |
2013年 | 1352篇 |
2012年 | 1537篇 |
2011年 | 1669篇 |
2010年 | 1142篇 |
2009年 | 1075篇 |
2008年 | 1298篇 |
2007年 | 1085篇 |
2006年 | 951篇 |
2005年 | 786篇 |
2004年 | 642篇 |
2003年 | 516篇 |
2002年 | 534篇 |
2001年 | 411篇 |
2000年 | 364篇 |
1999年 | 412篇 |
1998年 | 314篇 |
1997年 | 259篇 |
1996年 | 269篇 |
1995年 | 253篇 |
1994年 | 203篇 |
1993年 | 190篇 |
1992年 | 165篇 |
1991年 | 149篇 |
1990年 | 124篇 |
1989年 | 94篇 |
1988年 | 69篇 |
1987年 | 64篇 |
1986年 | 33篇 |
1985年 | 53篇 |
1984年 | 28篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
Summary Vezetéknév 相似文献
82.
83.
84.
秦俊法 《广东微量元素科学》1995,(7)
用能量色散X射线荧光分析法测定了某厂生产的44种彩色油墨纸中的铅含量.结果发现,除5种油墨外,其它39种彩色油墨纸中的铅含量均比对照纸中高9倍以上,其中桔黄色、桔红色树脂胶版油墨高500倍以上,棕色树脂胶版油墨高379倍,深黄色和柠檬黄色树脂铅印油墨分别高170和113倍.这表明,彩色油墨印刷品可能是儿童慢性铅中毒的重要污染源. 相似文献
85.
设H为复的可分无限维Hilbert空间,称有界线性算子T为强不可约的,如果与T可交换的幂等算子只有0和I.王宗尧、蒋春澜、纪有清等人证明了在任何一个套的套代数中都存在大量的强不可约算子,并且找到了它们的酉轨道闭包.本文考虑有限个套的张量积的代数中强不可约算子的存在性问题。证明了:对复平面上任何一个连通完备集σ、总存在一个对角算子N和它的一个范数可以任意小的紧摄动T=X+K,使得T是一个强不可约算子、T在有限个良序套的张量积的代数中,并且σ(T)=σlre(T)=σ(N)=σlre(N)=σ进一步,文章还对具有单点谱的算子和良序套与正交补为良序套的张量积的代数进行了讨论,得到了一些结果. 相似文献
86.
Chongyu Mei Junqiao Ding Bing Yao Yanxiang Cheng Zhiyuan Xie Yanhou Geng Lixiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1746-1757
Two orange phosphorescent iridium complex monomers, 9‐hexyl‐9‐(iridium (III)bis(2‐(4′‐fluorophenyl)‐4‐phenylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐PIr) and 9‐hexyl‐9‐(iridium(III)bis(2‐(4′‐fluorophenyl)‐4‐methylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐MIr), were successfully synthesized. The Suzuki polycondensation of 2,7‐bis(trimethylene boronate)‐9,9‐dioctylfluorene with 2,7‐dibromo‐9,9‐dioctylfluorene and Br‐PIr or Br‐MIr afforded two series of copolymers, PIrPFs and MIrPFs, in good yields, in which the concentrations of the phosphorescent moieties were kept small (0.5–3 mol % feed ratio) to realize incomplete energy transfer. The photoluminescence (PL) of the copolymers showed blue‐ and orange‐emission peaks. A white‐light‐emitting diode with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/PIr05PF (0.5 mol % feed ratio of Br‐PIr)/Ca/Al exhibited a luminous efficiency of 4.49 cd/A and a power efficiency of 2.35 lm/W at 6.0 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.46, 0.33). The CIE coordinates were improved to (0.34, 0.33) when copolymer MIr10PF (1.0 mol % feed ratio of Br‐MIr) was employed as the white‐emissive layer. The strong orange emission in the electroluminescence spectra in comparison with PL for these kinds of polymers was attributed to the additional contribution of charge trapping in the phosphorescent dopants. © 2007 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 45: 1746–1757, 2007 相似文献
87.
88.
The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with FeA vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic
properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than
other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models
exhibit metallic properties. At the same time, the AB, AB-FeA vac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.
相似文献
89.
Fang Yao 《Journal of multivariate analysis》2007,98(1):40-56
The estimation of a regression function by kernel method for longitudinal or functional data is considered. In the context of longitudinal data analysis, a random function typically represents a subject that is often observed at a small number of time points, while in the studies of functional data the random realization is usually measured on a dense grid. However, essentially the same methods can be applied to both sampling plans, as well as in a number of settings lying between them. In this paper general results are derived for the asymptotic distributions of real-valued functions with arguments which are functionals formed by weighted averages of longitudinal or functional data. Asymptotic distributions for the estimators of the mean and covariance functions obtained from noisy observations with the presence of within-subject correlation are studied. These asymptotic normality results are comparable to those standard rates obtained from independent data, which is illustrated in a simulation study. Besides, this paper discusses the conditions associated with sampling plans, which are required for the validity of local properties of kernel-based estimators for longitudinal or functional data. 相似文献
90.