全文获取类型
收费全文 | 610535篇 |
免费 | 4642篇 |
国内免费 | 1479篇 |
专业分类
化学 | 307138篇 |
晶体学 | 8731篇 |
力学 | 31529篇 |
综合类 | 24篇 |
数学 | 81703篇 |
物理学 | 187531篇 |
出版年
2021年 | 5644篇 |
2020年 | 6102篇 |
2019年 | 6969篇 |
2018年 | 9450篇 |
2017年 | 9603篇 |
2016年 | 13049篇 |
2015年 | 6945篇 |
2014年 | 11783篇 |
2013年 | 26607篇 |
2012年 | 20658篇 |
2011年 | 24662篇 |
2010年 | 18655篇 |
2009年 | 18655篇 |
2008年 | 23401篇 |
2007年 | 23185篇 |
2006年 | 21059篇 |
2005年 | 18802篇 |
2004年 | 17629篇 |
2003年 | 15899篇 |
2002年 | 15886篇 |
2001年 | 17105篇 |
2000年 | 13141篇 |
1999年 | 10150篇 |
1998年 | 8844篇 |
1997年 | 8664篇 |
1996年 | 8057篇 |
1995年 | 7291篇 |
1994年 | 7249篇 |
1993年 | 7056篇 |
1992年 | 7433篇 |
1991年 | 8031篇 |
1990年 | 7659篇 |
1989年 | 7626篇 |
1988年 | 7392篇 |
1987年 | 7205篇 |
1986年 | 6887篇 |
1985年 | 8798篇 |
1984年 | 9109篇 |
1983年 | 7716篇 |
1982年 | 8001篇 |
1981年 | 7511篇 |
1980年 | 7073篇 |
1979年 | 7733篇 |
1978年 | 8044篇 |
1977年 | 7970篇 |
1976年 | 7958篇 |
1975年 | 7636篇 |
1974年 | 7429篇 |
1973年 | 7785篇 |
1972年 | 5805篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
52.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
53.
54.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献
55.
I. N. Sergeev 《Journal of Mathematical Sciences》2006,135(1):2764-2793
The definition of the characteristic frequencies of zeroes and changes of sign for solutions is given. It is equal to the
upper medium (with respect to the time half-axis) of their number on the half-interval of length π. We also define the main frequencies for a linear homogeneous equation of order n. These main frequencies for an equation with constant coefficients coincide with the absolute values of the imaginary parts
of the roots of the corresponding characteristic polynomial. It is proved that for the second-order equation the main frequencies
are the same for all solutions and that they are stable with respect to uniformly small and infinitely small perturbations
of the coefficients. For the third-order equation they can be different, and for any of the main frequencies an example of
nonstability is given.
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 249–294, 2005. 相似文献
56.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
57.
In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed. 相似文献
58.
Dean A. Carlson 《Journal of Mathematical Analysis and Applications》2002,276(2):561-588
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate feedback Nash equilibria for a class of n-person differential games. Both the finite-horizon and infinite-horizon cases are considered. Examples are given to illustrate the presented results. 相似文献
59.
A.-S. F. Obada M. Darwish H. H. Salah 《International Journal of Theoretical Physics》2002,41(9):1755-1768
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined. 相似文献
60.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991. 相似文献