全文获取类型
收费全文 | 266705篇 |
免费 | 3449篇 |
国内免费 | 808篇 |
专业分类
化学 | 136575篇 |
晶体学 | 3887篇 |
力学 | 11499篇 |
综合类 | 1篇 |
数学 | 31698篇 |
物理学 | 87302篇 |
出版年
2020年 | 2244篇 |
2019年 | 2345篇 |
2018年 | 3102篇 |
2017年 | 3033篇 |
2016年 | 4800篇 |
2015年 | 3163篇 |
2014年 | 4834篇 |
2013年 | 11938篇 |
2012年 | 8954篇 |
2011年 | 11121篇 |
2010年 | 7588篇 |
2009年 | 7390篇 |
2008年 | 10362篇 |
2007年 | 10312篇 |
2006年 | 9704篇 |
2005年 | 8741篇 |
2004年 | 7895篇 |
2003年 | 6926篇 |
2002年 | 6835篇 |
2001年 | 7680篇 |
2000年 | 5925篇 |
1999年 | 4638篇 |
1998年 | 3912篇 |
1997年 | 3820篇 |
1996年 | 3755篇 |
1995年 | 3412篇 |
1994年 | 3396篇 |
1993年 | 3569篇 |
1992年 | 3574篇 |
1991年 | 3660篇 |
1990年 | 3434篇 |
1989年 | 3325篇 |
1988年 | 3380篇 |
1987年 | 3255篇 |
1986年 | 3072篇 |
1985年 | 4244篇 |
1984年 | 4433篇 |
1983年 | 3575篇 |
1982年 | 3791篇 |
1981年 | 3679篇 |
1980年 | 3550篇 |
1979年 | 3637篇 |
1978年 | 3753篇 |
1977年 | 3669篇 |
1976年 | 3726篇 |
1975年 | 3406篇 |
1974年 | 3409篇 |
1973年 | 3453篇 |
1972年 | 2353篇 |
1971年 | 1972篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
991.
B. Griepink E. A. Maier P. Quevauviller H. Muntau 《Fresenius' Journal of Analytical Chemistry》1991,339(9):599-603
Summary The Community Bureau of Reference (BCR) has undertaken the production of a wide range of certified reference materials (CRMs) for the improvement of accuracy and measurement harmony in various areas of concern at European Community level. This paper provides an overview of the sectors of the BCR-programme in the field of environment i.e. for water systems (water, sediment, biota), soil analysis (soil, fertiliser, waste), plant analysis (aquatic and terrestrial plants), analysis related to animals (e.g. muscle or liver) or man (e.g. industry and food). 相似文献
992.
P Nürnberg I Barth E Fuhrmann C Lenzner T Losanova C Peters H P?che G Thiel 《Electrophoresis》1991,12(2-3):186-192
Germline and somatic instability of the human genome was studied, using synthetic oligonucleotides specific for simple repeat motifs. The following probes were used: (GTG)5, (GACA)4, (GATA)4, (CT)8, (TTAGGG)3, (GT)8, (GAA)6 and (GGAT)4. Each of them is unique with respect to the target regions recognized in the genome. Thus compilation of the various fingerprint data provides a complex map of the genome (and its deviations). While the fingerprints of differentiated somatic tissues never showed any alterations, in tumor tissues (namely gliomas) many changes could be detected. Most of the latter reflect secondary karyological aberrations. In nearly one third of the gliomas, drastically amplified and apparently monomorphic DNA fragments were identified. This marker should make it possible to deal with causal pathogenetic mechanisms as well as novel diagnostic strategies. 相似文献
993.
P. Y. Zhu 《Il Nuovo Cimento C》1991,14(3):263-283
Summary The effective-medium approximation is applied to investigate scattering from a half-space of randomly and densely distributed
discrete scatterers. Starting from vector wave equations, an approximation, called effective-medium Born approximation, a
particular way, treating Green's functions, and special coordinates, of which the origin is set at the field point, are used
to calculate the bistatic- and back-scatterings. An analytic solution of backscattering with closed form is obtained and it
shows a depolarization effect. The theoretical results are in good agreement with the experimental measurements in the cases
of snow, multi- and first-year sea-ice. The root product ratio of polarization to depolarization in backscattering is equal
to 8; this result constitutes a law about polarized scattering phenomena in the nature. 相似文献
994.
Arthur Greenberg Oleg P. Charkin Ralph H. Bartram István Hargittai Gyula Beke 《Structural chemistry》1992,3(3):221-224
Unsigned book reviews are by the Book Review Editor. 相似文献
995.
996.
997.
Images of the surface ordering of 4-n-octyl-4'-cyanobiphenyl, a room temperature smectic liquid crystal deposited upon graphite, have been obtained by scanning tunnelling microscopy. The microscope was operated in air using the constant-current mode. Under certain tunnelling conditions it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported conformations have been observed: an overlapping bilayer structure with spacing 3.7 nm, and a monolayer structure with spacing 2.4 nm. The latter structure may represent the first visual evidence for a surface polar ordered structure. 相似文献
998.
999.
P. A. J. van den Bogert R. de Borst 《Archive of Applied Mechanics (Ingenieur Archiv)》1994,64(2):136-146
Summary The mechanical behaviour of rubberlike materials is modelled in a phenomenological approach using a strain-energy formulation. Nonhomogeneous shear experiments on solid rubber specimens have been carried out as well as simple elongation tests on the same rubber compound. The elongation tests have been used to determine the model constants. By a comparison between experiment and numerical simulation of the nonhomogeneous shear test the predictive capabilities of the Mooney-Rivlin, the Ogden and the Besseling model have been assessed for compression-shear deformation paths. An analytical study explains the numerically observed behaviour.
Über das Verhalten von Gummimaterialien unter Druck und Schubverformungen
Übersicht Das mechanische Verhalten von Gummimaterialien wird phänomenologisch modelliert unter Anwendung einer Formänderungsenergiefunktion. Es sind nicht-homogene Schubversuche auf dreidimensionale Versuchsproben aus Gummi so wie auch einfache Verlängerungsversuche auf Gummiproben der gleichen Zusammenstellung durchgeführt worden. Die Verlängerungsversuche sind durchgeführt worden um die Stoffkennwerte feststellen zu können. In einer Vergleichung zwischen dem Experiment und der numerischen Simulation von nicht-homogenen Schubversuchen ist die Genauigkeit des Mooney-Rivlinschen Modells, des Ogdenschen Modells und des Besselingschen Modells für kombinierte Druck-Schubverformungen festgestellt worden. In einem analytischen Studium wird das numerisch betrachtete Verhalten auseinandergesetzt.相似文献
1000.
We estimate the possible influence of spectral line profile (Lorentz profile, Van Vleck–Weisskopf profile, and profile obtained by solving kinetic equation) on the rotation part of the dielectric permittivity of water-vapor monomers. Spectral regions corresponding to long-wavelength (static) and high-frequency (optical) limiting cases as well as regions in close proximity to resonances of various intensities are considered. The studied effects are compared with the corresponding effects on water-vapor absorption coefficient, which are related to factors determining the line-shape structure. 相似文献