全文获取类型
收费全文 | 61191篇 |
免费 | 1139篇 |
国内免费 | 444篇 |
专业分类
化学 | 29192篇 |
晶体学 | 1049篇 |
力学 | 3308篇 |
综合类 | 9篇 |
数学 | 4885篇 |
物理学 | 24331篇 |
出版年
2022年 | 655篇 |
2021年 | 610篇 |
2020年 | 607篇 |
2019年 | 594篇 |
2018年 | 726篇 |
2017年 | 604篇 |
2016年 | 1061篇 |
2015年 | 791篇 |
2014年 | 1167篇 |
2013年 | 2724篇 |
2012年 | 2579篇 |
2011年 | 3246篇 |
2010年 | 2280篇 |
2009年 | 2286篇 |
2008年 | 2873篇 |
2007年 | 2687篇 |
2006年 | 2503篇 |
2005年 | 2207篇 |
2004年 | 1999篇 |
2003年 | 1761篇 |
2002年 | 1662篇 |
2001年 | 3007篇 |
2000年 | 2155篇 |
1999年 | 1555篇 |
1998年 | 1086篇 |
1997年 | 1057篇 |
1996年 | 885篇 |
1995年 | 785篇 |
1994年 | 704篇 |
1993年 | 625篇 |
1992年 | 951篇 |
1991年 | 947篇 |
1990年 | 855篇 |
1989年 | 747篇 |
1988年 | 731篇 |
1987年 | 795篇 |
1986年 | 655篇 |
1985年 | 884篇 |
1984年 | 828篇 |
1983年 | 568篇 |
1982年 | 562篇 |
1981年 | 533篇 |
1980年 | 496篇 |
1979年 | 620篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 575篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
Wing-Sum Cheung Patricia J.Y. Wong 《Journal of Mathematical Analysis and Applications》2007,329(2):851-869
We consider a system of focal boundary value problems where the nonlinearities may be singular in the independent variable and may also be singular in the dependent arguments. Using Schauder fixed point theorem, we establish criteria such that the system of boundary value problems has at least one fixed-sign solution. 相似文献
272.
We study two estimators of the long-range parameter of a covariance stationary linear process. We show that one of the estimators
achieve the optimal semiparametric rate of convergence, whereas the other has a rate of convergence as close as desired to
the optimal rate. Moreover, we show that the estimators are asymptotically normal with a variance, which does not depend on
any unknown parameter, smaller than others suggested in the literature. Finally, a small Monte Carlo study is included to
illustrate the finite sample relative performance of our estimators compared to other suggested semiparametric estimators.
More specifically, the Monte-Carlo experiment shows the superiority of the proposed estimators in terms of the Mean Squared
Error.
The first author research was funded by the Economic and Social Research Council (ESRC) reference number: R000238212. The
second author research was funded by the Ministry of Education, Culture, Sports and Technology of Japan, reference number:
09CE2002 and B(2)10202202. 相似文献
273.
Natural convections in conjugated single and double enclosures 总被引:7,自引:0,他引:7
The natural convection in single and double conjugated enclosures are numerically investigated. The single and double enclosures are formed by low conductance walls with finite thickness. The outside vertical surfaces of the conducting walls are of the third kind of boundary condition while the top and bottom outside surfaces are adiabatic. The problem studied is characterized by a dominant horizontal temperature gradient and the thermal boundary conditions at the cavity surfaces can not be specified in priori. Numerical results reveal the characteristics in such kind of enclosures and show the importance of the thermal boundary conditions on the natural convection in enclosures. It is also found that the natural convections in the conjugated double enclosures are basically the same, with a major difference in their fluid temperature levels. 相似文献
274.
Massively parallel computational paradigms can mitigate many issues associated with the analysis of large and complex remotely sensed data sets. Recently, the Beowulf cluster has emerged as the most attractive, massively parallel architecture due to its low cost and high performance. Whereas most Beowulf designs have emphasized numerical modeling applications, the Parallel Image Processing Environment (PIPE) specifically addresses the unique requirements of remote sensing applications. Automated, parallelization of user-defined analyses is fully supported. A neural network application, applied to Along Track Scanning Radiometer-2 (ATSR-2) data shows the advantages and performance characteristics of PIPE. 相似文献
275.
A.Y. Vorobyev 《Applied Surface Science》2007,253(17):7272-7280
In this study we perform the first femtosecond laser surface treatment of titanium in order to determine the potential of this technology for surface structuring of titanium implants. We find that the femtosecond laser produces a large variety of nanostructures (nanopores, nanoprotrusions) with a size down to 20 nm, multiple parallel grooved surface patterns with a period on the sub-micron level, microroughness in the range of 1-15 μm with various configurations, smooth surface with smooth micro-inhomogeneities, and smooth surface with sphere-like nanostructures down to 10 nm. Also, we have determined the optimal conditions for producing these surface structural modifications. Femtosecond laser treatment can produce a richer variety of surface structures on titanium for implants and other biomedical applications than long-pulse laser treatments. 相似文献
276.
277.
In this article, composite nanofibers of poly(ε-caprolactone) (PCL) with iron–platinum (FePt) nanoparticles were successfully fabricated via coaxial electrospinning. The structure and morphology of FePt/PCL composite nanofibers were observed using transmission electron microscope and scanning electron microscope, respectively. The magnetic behavior of FePt/PCL composite nanofibers was investigated by alternating gradient magnetometer at room temperature. 相似文献
278.
Nickel and cobalt films illustrate alternative Bloch lines with cap switches. The strip magnetic domains become zigzag and bubbling cells for Ni and Co films, respectively, under an external field of 1.5 T. The magnetoresistances (MR) for currents parallel (CIW) to the domain walls is 15% less than those of the perpendicular (CPW) case. We also studied the magneto size effect by applying the magnetic field normal to the surface, from which the Sondheimer oscillation appears attributing to periodic striking of the surface for electrons traveling in circular motion on a plane canting to the surface. The experiments can be expressed by the magneto size effect inherited with very small specularity parameters. 相似文献
279.
280.
Y. Zhang T. M. Benson P. Sewell A. Vukovic D. Zhang W. J. Pan A Loni D. Furniss A. B. Seddon 《Optical and Quantum Electronics》2006,38(1-3):97-110
This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices. 相似文献