全文获取类型
收费全文 | 347449篇 |
免费 | 3340篇 |
国内免费 | 966篇 |
专业分类
化学 | 185685篇 |
晶体学 | 6089篇 |
力学 | 14398篇 |
综合类 | 12篇 |
数学 | 37415篇 |
物理学 | 108156篇 |
出版年
2020年 | 2931篇 |
2019年 | 3244篇 |
2018年 | 3922篇 |
2017年 | 4112篇 |
2016年 | 6229篇 |
2015年 | 3802篇 |
2014年 | 6143篇 |
2013年 | 15661篇 |
2012年 | 11377篇 |
2011年 | 13734篇 |
2010年 | 9903篇 |
2009年 | 9924篇 |
2008年 | 12684篇 |
2007年 | 12495篇 |
2006年 | 11805篇 |
2005年 | 10658篇 |
2004年 | 9767篇 |
2003年 | 8920篇 |
2002年 | 8611篇 |
2001年 | 10398篇 |
2000年 | 7829篇 |
1999年 | 6022篇 |
1998年 | 4887篇 |
1997年 | 4719篇 |
1996年 | 4536篇 |
1995年 | 4226篇 |
1994年 | 4111篇 |
1993年 | 3917篇 |
1992年 | 4773篇 |
1991年 | 4622篇 |
1990年 | 4509篇 |
1989年 | 4504篇 |
1988年 | 4492篇 |
1987年 | 4514篇 |
1986年 | 4282篇 |
1985年 | 5541篇 |
1984年 | 5617篇 |
1983年 | 4624篇 |
1982年 | 4815篇 |
1981年 | 4698篇 |
1980年 | 4457篇 |
1979年 | 4923篇 |
1978年 | 4969篇 |
1977年 | 5029篇 |
1976年 | 4906篇 |
1975年 | 4577篇 |
1974年 | 4519篇 |
1973年 | 4650篇 |
1972年 | 3122篇 |
1968年 | 2787篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
211.
The use of multigrid methods in complex fluid flow problems is still under development. In this paper a full multigrid procedure has been incorporated in a finite volume solution for predicting fully developed fluid flow in a streamwise periodic geometry. Steady computations in two-dimensional body fitted co-ordinates have shown considerable savings in computation time by this multigrid method. 相似文献
212.
Investigations of coated carbon fibres are reported using Raman spectroscopy. Relationships between different process parameters (for example precursor concentration, reactor temperature and various precursors) and the resulting types of carbon fibres are discussed. 相似文献
213.
214.
Since the early demonstrations of our concept of pulsed microwave catalysis in chemistry, we have witnessed the coming of age of the technique as an enabling technology in the industrial world, despite the inadequate understanding of the basic mechanisms of how microwaves interact with metallic surface sites and the subsequent energy transfer. We shall present here some very recent developments of the microwave-induced acoustic technique and its applications to a better understanding of the basic surface heating and energy transfer phenomena in pulsed microwave catalytic systems. 相似文献
215.
M. M. Eisl B. M. Reichl S. D. Böhmig H. Störi 《Fresenius' Journal of Analytical Chemistry》1994,349(1-3):194-196
Using a discrete model for the segregation kinetics based on the Darken theory of diffusion and on the regular solution model (RSM), one and two dimensional simulations of interface segregation in binary and ternary systems have been performed. The aim of the calculations was to investigate the kinetics of segregation sequences in ternary systems, the segregation kinetics in discrete systems during the initial phase and finally the kinetics of surface segregation in the region of a grain boundary intersected by the surface. 相似文献
216.
H.-J. Kluge B. A. Bushaw G. Passler K. Wendt N. Trautmann 《Fresenius' Journal of Analytical Chemistry》1994,350(4-5):323-329
Resonance ionization spectroscopy (RIS) and its combination with mass spectrometry (RIMS) have grown to become powerful techniques, which offer high sensitivity as well as elemental and isotopic selectivity. The principles of RIS and RIMS are introduced; they primarily concern the analysis of the optical spectra for the choice of efficient excitation schemes and the suitable design of the experimental apparatus. Recent applications span from studies of short-lived isotopes at on-line mass separators to a wide variety of trace analysis applications for radioactive isotopes, which can range from measurements of solar neutrino flux to environmental assessment.On leave from Pacific Northwest Laboratory, Richland, USA 相似文献
217.
B. Hornetz H.-J. Michel J. Halbritter 《Fresenius' Journal of Analytical Chemistry》1994,349(1-3):233-235
ARXPS (angle resolved X-ray photoelectron spectroscopy) measurements are used to obtain informations about surfaces and grain boundaries. Data acquired from nanocrystalline carbidic hard coatings have been employed to establish structural models. Magnetron-sputtered coatings of TiC, SiC and TiC/SiC were examined. In such coatings, partly defective TiC nanocrystallites are surrounded by interfacial carbide. This excess carbon shows a binding state similar to that of doped graphite or fullerenes. X-ray amorphous SiC is found in the residue. On top of sputtered SiC coatings, less oxide and graphite is found as compared to TiC/SiC or TiC coatings. 相似文献
218.
The soft mode dielectric response of three ferroelectric chiral smectic C* substances is studied in the vicinity of the smectic C*-smectic A* phase transition. For some substances the soft mode dielectric strength exhibits a pronounced anomaly in the C* phase just below the phase transition. We show how this anomaly can be systematically correlated with a corresponding anomaly in the experimentally determined ratio of spontaneous polarization over tilt. By comparing the experimental results with the theoretical predictions of an extended Landau model, we demonstrate how the crossover behaviour of the system can be interpreted as being the consequence of the presence of a biquadratic coupling between tilt and polarization in the Landau free-energy of the system. 相似文献
219.
K. B. Aleinikova E. N. Zinchenko A. V. Arakcheeva V. V. Grinevich 《Crystallography Reports》2002,47(4):555-558
An amorphous sediment was prepared by the decomposition of potassium oxofluoroniobate K2 ? x Nb4O3(O, F)3F in water. For this sediment, the atomic radial distribution function was analyzed with the use of a fragment model, which allows one to interpret expanded coordination spheres as being formed by first several strongest diffusion maxima. These spheres carry the most reliable information on the structure. It is shown that the amorphous sediment consists of the randomly packed Nb(O,F)6-octahedra with interatomic distances close to those observed in the ordered region in the N-Nb2O5 structure. During decomposition in water, the initial K2 ? x Nb4O3(O, F)3F phase loses KF-layers, whereas Nb6 clusters with metal bonds are destroyed. 相似文献
220.