全文获取类型
收费全文 | 3324篇 |
免费 | 82篇 |
国内免费 | 46篇 |
专业分类
化学 | 1970篇 |
晶体学 | 21篇 |
力学 | 63篇 |
综合类 | 1篇 |
数学 | 703篇 |
物理学 | 694篇 |
出版年
2021年 | 35篇 |
2020年 | 37篇 |
2019年 | 30篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 79篇 |
2015年 | 48篇 |
2014年 | 61篇 |
2013年 | 152篇 |
2012年 | 141篇 |
2011年 | 177篇 |
2010年 | 100篇 |
2009年 | 79篇 |
2008年 | 153篇 |
2007年 | 155篇 |
2006年 | 170篇 |
2005年 | 140篇 |
2004年 | 135篇 |
2003年 | 117篇 |
2002年 | 85篇 |
2001年 | 57篇 |
2000年 | 46篇 |
1999年 | 38篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 54篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 43篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 30篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 24篇 |
1982年 | 54篇 |
1981年 | 38篇 |
1980年 | 52篇 |
1979年 | 45篇 |
1978年 | 41篇 |
1977年 | 51篇 |
1976年 | 58篇 |
1975年 | 51篇 |
1974年 | 47篇 |
1973年 | 26篇 |
1971年 | 24篇 |
排序方式: 共有3452条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
The traditional chemical industry has become a largely mature industry with many commodity products based on established technologies. Therefore, new product and market opportunities will more likely come from speciality chemicals, and from new functionalities obtained from new processing technologies as well as new microstructure control methodologies. It is a well-known fact that in addition to its molecular structure, the microstructure of a material is key to determining its properties. Controlling structures at the micro- and nano-levels is therefore essential to new discoveries. For this article, we define nanotechnology as the controlled manipulation of nanomaterials with at least one dimension less than 100nm. Nanotechnology is emerging as one of the principal areas of investigation that is integrating chemistry and materials science, and in some cases integrating these with biology to create new and yet undiscovered properties that can be exploited to gain new market opportunities. In this article market opportunities for nanotechnology will be presented from an industrial perspective covering electronic, biomedical, performance materials, and consumer products. Manufacturing technology challenges will be identified, including operations ranging from particle formation, coating, dispersion, to characterization, modeling, and simulation. Finally, a nanotechnology innovation roadmap is proposed wherein the interplay between the development of nanoscale building blocks, product design, process design, and value chain integration is identified. A suggestion is made for an R&D model combining market pull and technology push as a way to quickly exploit the advantages in nanotechnology and translate these into customer benefits. 相似文献
5.
6.
O. Perru F. Ibrahim O. Bajeat C. Bourgeois F. Clapier E. Cottereau C. Donzaud M. Ducourtieux S. Galès D. Guillemaud-Mueller C. Lau H. Lefort F. Le Blanc A. C. Mueller J. Obert N. Pauwels J. C. Potier F. Pougheon J. Proust B. Roussière J. Sauvage O. Sorlin D. Verney 《Physics of Atomic Nuclei》2003,66(8):1421-1427
The PARRNe facility has been used to produce neutron-rich isotopes 83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in 83Ge and the first excited level in 84Ge have been measured for the first time. 相似文献
7.
Simplicial complexes X provide commutative rings A(X) via the Stanley- Reisner construction. We calculated the cotangent cohomology, i.e., T1 and T2 of A(X) in terms of X. These modules provide information about the deformation theory of the algebro geometric objects assigned to X. 相似文献
8.
Geometric (Clifford) algebra provides an efficient mathematical language for describing physical problems. We formulate general relativity in this language. The resulting formalism combines the efficiency of differential forms with the straightforwardness of coordinate methods. We focus our attention on orthonormal frames and the associated connection bivector, using them to find the Schwarzschild and Kerr solutions, along with a detailed exposition of the Petrov types for the Weyl tensor. 相似文献
9.
Impacts of structural-acoustic coupling on the performance of energy density-based active sound transmission control 总被引:2,自引:0,他引:2
S.K. Lau 《Journal of sound and vibration》2003,266(1):147-170
This paper investigates numerically the performance of the active sound transmission control into a rectangular cavity through a flexible panel under the energy density-based error-sensing algorithm. Full coupling between the sound transmitting panel and the enclosed space is considered. A pure vibration actuator, a pure acoustic source and a combined control source system are used as the secondary control source in the active control and their performances are studied. Formulae for the coupled eigenfrequencies of the cavity and the flexible panel are also derived. The strength of the structural-acoustic coupling, the ratio between the first eigenfrequencies of the cavity and the panel and the difference between the excitation frequency and the coupled eigenfrequencies, especially the latter, are found to have crucial impacts on the performance of the active control regardless the type of control source used. 相似文献
10.
Arthur G. Maki John C. Grecu Brenda Winnewisser Manfred Winnewisser 《Journal of Molecular Spectroscopy》2003,222(2):198-212
High-resolution spectra of 15N12C12C15N and 14N13C13C14N have been measured and analyzed from 200 to 3600 cm−1. All the vibrational levels below 900 cm−1 have been observed and characterized. The Fermi resonance between ν2 and 2ν4 has been studied and the resonance constant has been determined for several cases. Several Σ− states have been directly observed for the first time for each isotopomer, the (0001111)0f, (0011111)0f, and (0002222)0f states. The pattern of the energy levels for clusters of l-type resonance coupled levels, such as 0001131,3, has been determined for cyanogen for the first time. Among other things this involved the determination of the vibrational l-type resonance constant, r45. Many of the power series constants, αi and xij, and higher order constants have been determined. 相似文献