全文获取类型
收费全文 | 11450篇 |
免费 | 1259篇 |
国内免费 | 1313篇 |
专业分类
化学 | 11986篇 |
晶体学 | 95篇 |
力学 | 140篇 |
综合类 | 64篇 |
数学 | 241篇 |
物理学 | 1496篇 |
出版年
2024年 | 24篇 |
2023年 | 149篇 |
2022年 | 214篇 |
2021年 | 544篇 |
2020年 | 540篇 |
2019年 | 397篇 |
2018年 | 312篇 |
2017年 | 351篇 |
2016年 | 581篇 |
2015年 | 514篇 |
2014年 | 555篇 |
2013年 | 1008篇 |
2012年 | 604篇 |
2011年 | 600篇 |
2010年 | 516篇 |
2009年 | 595篇 |
2008年 | 663篇 |
2007年 | 721篇 |
2006年 | 633篇 |
2005年 | 552篇 |
2004年 | 552篇 |
2003年 | 470篇 |
2002年 | 356篇 |
2001年 | 286篇 |
2000年 | 291篇 |
1999年 | 292篇 |
1998年 | 220篇 |
1997年 | 246篇 |
1996年 | 198篇 |
1995年 | 199篇 |
1994年 | 178篇 |
1993年 | 136篇 |
1992年 | 159篇 |
1991年 | 73篇 |
1990年 | 44篇 |
1989年 | 46篇 |
1988年 | 46篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
由于痕量元素在煤中的含量低微、检测困难,加之其原子量一般较大,可能的反应途径多,使得相关的反应机理研究难度极大。本文结合作者的研究成果,介绍了煤燃烧过程中痕量元素化学反应动力学的国内外研究进展,包括痕量元素化学动力学机理的建立;相关的典型实验、计算模拟及其实验验证、动力学机理模型的简化;痕量元素反应动力学机理的完善和发展,包括采用简单碰撞理论、活化络合物理论(亦称过渡态理论,或绝对反应速率理论)对痕量元素化学反应动力学机理的修正;最后指出煤燃烧过程中痕量元素动力学研究的若干方向是: (1)痕量元素反应动力学模型数据库的建立;(2)煤燃烧过程中,主量元素和次量元素的动力学机理的完善; (3)各痕量元素之间动力学研究的开展; (4)实际燃烧过程中痕量元素动力学行为的研究。 相似文献
72.
本文给出直接求线性规划问题基可行解的一种简易方法,该方法既避免了引入人工变量,减少存储,一般又能较快地得到一个较好的基可行解. 相似文献
73.
S.V. Kini 《Tetrahedron letters》2004,45(21):4171-4173
Hofmann degradation of 1-arylmethyl-1,2,3,4-tetrahydro-2,2-dimethylisoquinolinium iodides with methanolic KOH gave stilbene derivatives, for example, (E)-N-2{2-[2-(phenyl)ethenyl]-4,5-dimethoxyphenyl}ethyl-N,N-dimethylamine. Photochemical electrocyclization of these stilbenes afforded the corresponding phenanthrene alkaloids/phenanthrene derivatives. 相似文献
74.
We develop an effective numerical method of studying large-time properties of reversible reaction-diffusion systems of type
A + B ↔ C with initially separated reactants. Using it we find that there are three types of asymptotic reaction zones. In particular
we show that the reaction rate can be locally negative and concentrations of species A and B can be nonmonotonic functions
of the space coordinate x, locally significantly exceeding their initial values.
Received 6 June 2002 / Received in final form 20 January 2003 Published online 7 May 2003 相似文献
75.
S. Longo G. Comunale C. Gorse M. Capitelli 《Plasma Chemistry and Plasma Processing》1993,13(4):685-700
Two simple kinetic models of a Ne-buffered XeCl laser discharge are presented based on different simplifications of the chemical kinetics of a complex model that recently appeared in the literature. When applied to the study of a small-volume XeCl laser, the results of both simple and complex models are in satisfactory agreement with the experiments. Shifting to a larger-volume laser, both models show problems due to loss of stability of the discharge. A one-dimensional modelling is performed, and it is found that different assumptions on the kinetics of the NeXe+ ion in the discharge lead to completely different results as regards the effect of a preionization-triggered instability. 相似文献
76.
We first note that Gentzen's proof-reduction for his consistency proof of PA can be directly interpreted as moves of Kirby-Paris' Hydra Game, which implies a direct independence proof of the game (Section 1 and Appendix). Buchholz's Hydra Game for labeled hydras is known to be much stronger than PA. However, we show that the one-dimensional version of Buchholz's Game can be exactly identified to Kirby-Paris' Game (which is two-dimensional but without labels), by a simple and natural interpretation (Section 2). Jervell proposed another type of a combinatorial game, by abstracting Gentzen's proof-reductions and showed that his game is independent of PA. We show (Section 3) that this Jervell's game is actually much stronger than PA, by showing that the critical ordinal of Jervell's game is φω (0) (while that of PA or of Kirby-Paris' Game is φ1 (0) = ?0) in the Veblen hierarchy of ordinals. 相似文献
77.
We present two methods for the creation of two-particle entangled states of excitons in a coupled quantum dot system. The system contains two identical quantum dots that are coupled by an inter-dot hopping process. The manipulation of the system is succeeded by proper application of an external laser field. 相似文献
78.
Stephen W. Burgess Jogin R. Wu Kerry Swift Barry R. Lentz 《Journal of fluorescence》1991,1(2):105-112
Rate constants were determined for the transfer of the fluorescent lipid probe 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] oxy]carbonyl]-3-sn-phosphatidylcholine (DPHpPC) between large, unilamellar extrusion vesicles composed either of dipalmitoyl phosphatidylcholine (DPPC) or of DPPC mixed with a small amount (0.5 mol%) of lyso phosphatidylcholine (Lyso PC). Transfer of the lipid probe in the presence of varying concentrations of poly(ethylene glycol) (PEG) was monitored using the SLM 48000-MHF Multi-Harmonic Fourier Transform phase and modulation spectrofluorometer to collect multifrequency phase and modulation fluorescence data sets on a subsecond time scale. The unique ability of this instrument to yield accurate fluorescence lifetime data on this time scale allowed transfer to be detected in terms of a time-dependent change in the fluorescent lifetime distribution associated with the lipid-like DPHpPC probe. This probe demonstrates two short fluoresence decay times (ca. 1.1–1.4 and 4.3–4.8 ns) in a probe-rich environment but a single long lifetime (ca. 7 ns) in a probe-poor environment. A simple two-state model for initial lipid transfer was used to analyze the multifrequency data sets collected over a 4-s time frame to obtain the time rate of change of the concentrations of donor and acceptor probe populations following rapid mixing of vesicles with PEG. The ability to measure fluorescence lifetimes on this time scale has allowed us to show that the of rate of lipid transfer increased dramatically at 35% PEG in both fusing and nonfusing vesicle systems. These results are interpreted in terms of a distinct interbilayer structure associated with intimate bilayer contact induced by high and potentially fusogenic concentrations of PEG. 相似文献
79.
We study a generalization of the analytic theory of first-order phase transitions to the cases of arbitrary droplet growth, of nonisothermal processes, and of heterogeneous centers in the system. We show that in all these cases, the spectra of droplet dimensions are similar. The same forms of the spectra are also obtained for the stationary condensation process in a spatially inhomogeneous system. 相似文献
80.
本文用对数正态分布对物理显影中常用的Au、Ag及Ag_2s胶体催化剂的颗粒大小的实验分布进行了拟合。理论分布与实验分布的比较表明:本实验条件下制备的十二组胶体溶液其颗粒大小都服从了对数正态分布,并且不依赖于胶体的组成、大小及制备方法。因此,它们很可能遵从了同样的成核成长规律。 相似文献