全文获取类型
收费全文 | 343096篇 |
免费 | 5324篇 |
国内免费 | 1211篇 |
专业分类
化学 | 186355篇 |
晶体学 | 4613篇 |
力学 | 13908篇 |
综合类 | 12篇 |
数学 | 41420篇 |
物理学 | 103323篇 |
出版年
2020年 | 2390篇 |
2019年 | 2253篇 |
2018年 | 2389篇 |
2017年 | 2306篇 |
2016年 | 4709篇 |
2015年 | 3838篇 |
2014年 | 5100篇 |
2013年 | 15448篇 |
2012年 | 12046篇 |
2011年 | 14752篇 |
2010年 | 9214篇 |
2009年 | 9074篇 |
2008年 | 13645篇 |
2007年 | 13784篇 |
2006年 | 13355篇 |
2005年 | 12190篇 |
2004年 | 10938篇 |
2003年 | 9572篇 |
2002年 | 9310篇 |
2001年 | 10636篇 |
2000年 | 8210篇 |
1999年 | 6435篇 |
1998年 | 5187篇 |
1997年 | 5010篇 |
1996年 | 5135篇 |
1995年 | 4703篇 |
1994年 | 4498篇 |
1993年 | 4335篇 |
1992年 | 4871篇 |
1991年 | 4569篇 |
1990年 | 4302篇 |
1989年 | 4101篇 |
1988年 | 4347篇 |
1987年 | 4046篇 |
1986年 | 3894篇 |
1985年 | 5663篇 |
1984年 | 5722篇 |
1983年 | 4673篇 |
1982年 | 5058篇 |
1981年 | 5098篇 |
1980年 | 4840篇 |
1979年 | 4962篇 |
1978年 | 4953篇 |
1977年 | 4927篇 |
1976年 | 4847篇 |
1975年 | 4768篇 |
1974年 | 4611篇 |
1973年 | 4732篇 |
1972年 | 2674篇 |
1971年 | 1999篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Karla J. Moreno Miroslaw Maczka Ulises Amador 《Journal of solid state chemistry》2006,179(12):3805-3813
The structural and microstructural characteristics of metastable Gd2(Ti1−yZry)2O7 powders prepared by mechanical milling have been studied by a combination of XRD and Raman spectroscopy. Irrespective of their Zr content, as-prepared powder phases present an anion-deficient fluorite-type of structure as opposed to the pyrochlore equilibrium configuration obtained for the same solid solution by other synthetic routes. These fluorites are stable versus thermal activation, at least up to temperatures of 800 °C. For the Ti-rich compositions, thermal treatments at higher temperatures facilitate the rearrangement of the cation and anion substructures and the relaxation of mechanochemically induced defects whereas for compositions with high Zr content, the fluorite crystal structure is retained even at temperatures as high as 1200 °C. Interestingly enough, transient pyrochlores showing a very unusual cation distribution were observed during the thermally induced defect-recovery process. 相似文献
994.
Summary Vezetéknév 相似文献
995.
The system design must be started from the concept with low cost and high performance. In this point, the topological shape of the structure is very important in the view of the structural rigidities and light-weight design.In this paper, the optimization methodology is presented in the design stage of the large optical mirror. We obtain the optimal layout through the topology optimization and then design the details through the size or shape optimization for structural rigidity. 相似文献
996.
Statistical Analysis of the Effect of Mineral Admixtures on the Strength of the Interfacial Transition Zone 总被引:1,自引:0,他引:1
Microscopic evidence indicates that the thickness of the interfacial transition zone (ITZ) between the aggregate and the cement paste is modified when mineral admixtures partially replace portland cement. Unfortunately, there is limited information on the significance of these microscopic modifications to the mechanical properties of the ITZ. This research reports experimental results on the shear and tensile strength of the ITZ as affected by the addition of the following mineral admixtures: silica fume, fly ash, and natural pozzolan. Statistical analysis was used to identify the significant parameters affecting the tensile and shear strength of the ITZ. Experimental results indicate that not only does the incorporation of silica fume and fly ash increase the strength of the ITZ, these mineral admixtures have a greater influence on the strength increase of the ITZ than in the strength increase of the cement paste. 相似文献
997.
The state of the art iterative method for solving large linear systems is the conjugate gradient (CG) algorithm. Theoretical convergence analysis suggests that CG converges more rapidly than steepest descent. This paper argues that steepest descent may be an attractive alternative to CG when solving linear systems arising from the discretization of ill-posed problems. Specifically, it is shown that, for ill-posed problems, steepest descent has a more stable convergence behavior than CG, which may be explained by the fact that the filter factors for steepest descent behave much less erratically than those for CG. Moreover, it is shown that, with proper preconditioning, the convergence rate of steepest descent is competitive with that of CG.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
998.
Cordula Grüttner Knut Müller Joachim Teller Fritz Westphal Allan Foreman Robert Ivkov 《Journal of magnetism and magnetic materials》2007
Bionized nanoferrite (BNF) particles with high specific power absorption rates were synthesized in the size range of 20–100 nm by high-pressure homogenization for targeted cancer therapy with alternating magnetic fields. Several strategies were used to conjugate antibodies to the BNF particles. These strategies were compared using an immunoassay to find optimal conditions to reach a high immunoreactivity of the final antibody–particle conjugate. 相似文献
999.
S Watanabe R R Anderson S Brorson G Dalickas J G Fujimoto T J Flotte 《Photochemistry and photobiology》1991,53(6):757-762
Threshold radiant exposures for grossly apparent immediate whitening and ultrastructural alterations of melanosomes in black guinea pig skin were determined for a series of red visible laser pulses ranging from 4 x 10(-4) to 6.5 x 10(-14) s. Threshold exposures for melanosomal injury were found to be independent of pulsewidth when the pulsewidths were below the estimated thermal relaxation time of melanosomes. Threshold radiant exposures for melanosomal injury were found to increase when the pulsewidths were approximately equal to or above the thermal relaxation time of melanosomes. At longer pulse durations, fracturing of melanosomes was not observed despite the longer exposures necessary for injury. Instead, perimelanosomal vacuoles were noted. These findings are consistent with the theory of selective photothermolysis and provide evidence for the thermal initiation of melanosomal disruption. 相似文献
1000.