全文获取类型
收费全文 | 16969篇 |
免费 | 535篇 |
国内免费 | 703篇 |
专业分类
化学 | 4056篇 |
晶体学 | 857篇 |
力学 | 442篇 |
综合类 | 69篇 |
数学 | 10343篇 |
物理学 | 2440篇 |
出版年
2023年 | 75篇 |
2022年 | 196篇 |
2021年 | 160篇 |
2020年 | 155篇 |
2019年 | 389篇 |
2018年 | 414篇 |
2017年 | 302篇 |
2016年 | 317篇 |
2015年 | 296篇 |
2014年 | 569篇 |
2013年 | 878篇 |
2012年 | 524篇 |
2011年 | 1116篇 |
2010年 | 1171篇 |
2009年 | 1295篇 |
2008年 | 1301篇 |
2007年 | 1286篇 |
2006年 | 1042篇 |
2005年 | 805篇 |
2004年 | 779篇 |
2003年 | 608篇 |
2002年 | 521篇 |
2001年 | 371篇 |
2000年 | 320篇 |
1999年 | 305篇 |
1998年 | 274篇 |
1997年 | 240篇 |
1996年 | 328篇 |
1995年 | 270篇 |
1994年 | 286篇 |
1993年 | 252篇 |
1992年 | 201篇 |
1991年 | 123篇 |
1990年 | 108篇 |
1989年 | 110篇 |
1988年 | 75篇 |
1987年 | 85篇 |
1986年 | 91篇 |
1985年 | 124篇 |
1984年 | 72篇 |
1983年 | 51篇 |
1982年 | 68篇 |
1981年 | 60篇 |
1980年 | 36篇 |
1979年 | 19篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1974年 | 15篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Francis Jordan 《Topology and its Applications》2006,153(14):2386-2412
An abstract scheme using particular types of relations on filters leads to general unifying results on stability under supremum and product of local topological properties. We present applications for Fréchetness, strong Fréchetness, countable tightness and countable fan-tightness, some of which recover or refine classical results, some of which are new. The reader may find other applications as well. 相似文献
2.
Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl2, FeCl2 and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N2 as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase. 相似文献
3.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
4.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
5.
基于校园网的实验管理系统的设计 总被引:2,自引:1,他引:1
主要讨论了应用实验室管理系统的必要性,并从用户需求分析、系统总体设计、功能模块的设计等方面对B/S实验室管理系统的开发进行了详细的阐述。 相似文献
6.
We show that there are close relations between extremal problems in dual Brunn-Minkowski theory and isotropic-type properties for some Borel measures on the sphere. The methods we use allow us to obtain similar results in the context of Firey-Brunn-Minkowski theory. We also study reverse inequalities for dual mixed volumes which are related with classical positions, such as ?-position or isotropic position. 相似文献
7.
Andrei K. Lerner 《Archiv der Mathematik》2005,85(6):538-543
We show that the Hardy-Littlewood maximal operator and a class of Calderón-Zygmund singular integrals satisfy the strong type
modular inequality in variable Lp spaces if and only if the variable exponent p(x) ∼ const.
Received: 15 September 2004 相似文献
8.
Nonlocal vertex algebras generated by formal vertex operators 总被引:2,自引:0,他引:2
Haisheng Li 《Selecta Mathematica, New Series》2005,11(3-4):349-397
This is the first paper in a series to study vertex algebra-like objects arising from infinite-dimensional quantum groups
(quantum affine algebras and Yangians). In this paper we lay the foundations for this study. For any vector space W, we study what we call quasi compatible subsets of Hom (W,W((x))) and we prove that any maximal quasi compatible subspace has a natural nonlocal (namely noncommutative) vertex algebra
structure with W as a natural faithful quasi module in a certain sense, and that any quasi compatible subset generates a nonlocal vertex algebra
with W as a quasi module. In particular, taking W to be a highest weight module for a quantum affine algebra we obtain a nonlocal vertex algebra with W as a quasi module. We also formulate and study a notion of quantum vertex algebra and we give general constructions of nonlocal
vertex algebras, quantum vertex algebras and their modules. 相似文献
9.
10.