全文获取类型
收费全文 | 50015篇 |
免费 | 8335篇 |
国内免费 | 6569篇 |
专业分类
化学 | 35508篇 |
晶体学 | 740篇 |
力学 | 3101篇 |
综合类 | 488篇 |
数学 | 5906篇 |
物理学 | 19176篇 |
出版年
2024年 | 123篇 |
2023年 | 863篇 |
2022年 | 1633篇 |
2021年 | 1703篇 |
2020年 | 1859篇 |
2019年 | 1893篇 |
2018年 | 1642篇 |
2017年 | 1580篇 |
2016年 | 2377篇 |
2015年 | 2403篇 |
2014年 | 2901篇 |
2013年 | 3715篇 |
2012年 | 4564篇 |
2011年 | 4774篇 |
2010年 | 3368篇 |
2009年 | 3342篇 |
2008年 | 3569篇 |
2007年 | 3245篇 |
2006年 | 3040篇 |
2005年 | 2619篇 |
2004年 | 1979篇 |
2003年 | 1503篇 |
2002年 | 1632篇 |
2001年 | 1214篇 |
2000年 | 1065篇 |
1999年 | 974篇 |
1998年 | 775篇 |
1997年 | 694篇 |
1996年 | 664篇 |
1995年 | 522篇 |
1994年 | 448篇 |
1993年 | 355篇 |
1992年 | 344篇 |
1991年 | 292篇 |
1990年 | 237篇 |
1989年 | 197篇 |
1988年 | 145篇 |
1987年 | 133篇 |
1986年 | 111篇 |
1985年 | 110篇 |
1984年 | 65篇 |
1983年 | 54篇 |
1982年 | 43篇 |
1981年 | 23篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The solid-liquid interface motion of NaBi(WO4)2 (NBWO) melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from fiat interface and cellular to dendrite are visualized. The spacing of the dendrite under smaller temperature gradient turns out to be larger than that under larger temperature gradient, which is found to be sensitive to the temperature distribution. The mechanism of dendrite growth of NBWO is studied based on the model of the growth units of anion coordination polyhedra. The { 001} face has two apex links, so it shows higher stability and has high growth rate and forms the arm of dendrite, whereas the {010} face has only one apex link, and thus shows relative slower growth rate and firstly forms the branches. 相似文献
62.
We discuss the matrix model in a class of 11D time dependent supersymmetric backgrounds as obtained in [B. Chen, Phys. Lett. B 632 (2006) 393, hep-th/0508191]. We construct the matrix model action through the matrix regularization of the membrane action in the background. We show that the action is exact to all orders of fermionic coordinates. Furthermore we discuss the fuzzy sphere solutions in this background. 相似文献
63.
In the present paper, a Lotka–Volterra type mutualism system with several delays is studied. Some new and interesting sufficient conditions are obtained for the global existence of positive periodic solutions of the mutualism system. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions. Our results are different from the existing ones such as those in of Yang et al. [F. Yang, D. Jiang, A. Ying, Existence of positive solution of multidelays facultative mutualism system, J. Eng. Math. 3 (2002) 64–68] and Chen et al. [F. Chen, J. Shi, X. Chen, Periodicity in a Lotka–Volterra facultative mutualism system with several delays, J. Eng. Math. 21 (3) (2004) 403–409]. 相似文献
64.
65.
A simple method of determining ultra-trace Au in natural water was presented by using graphite furnace atomic absorption spectrophotometry (GFAAS) after in situ enrichment with thiol cotton fiber (TCF). The sample solution was adjusted to pH 1.5-2.0 with HCl, then the water sample was passed through a column packed with 0.10-0.20 g TCF and the flow rate was controlled at 20-40 ml min−1. The effects of interferences, such as complexing and oxidizing agents and other elements adsorbed on TCF were overcome by chemical treatments prior to the desorption of Au. The adsorbed Au was adsorbed with 2.0 ml hot acid, then it was extracted with 1.00 ml methyl isobutylketone (MIBK). For a 5 l water sample, the detection limit of Au is 0.02 ng l−1. The relative standard deviation (R.S.D.) for the determination of 1.44 ng l−1 Au was 9.4%.The method was applied to determine ultra-trace Au both in suspended phase and soluble phase in natural water, the concentrations of total Au in natural water samples range from 0.51 to 67.82 ng l−1. The recovery of added 0.50-6.00 ng l−1 Au was 80-95%. The method is useful in prospecting for Au deposits by means of hydrogeochemical methods. The enrichment is carried out in the field, and then the determination of Au is completed later in the laboratory. 相似文献
66.
This paper has demonstrated that the Schwartz alternating process must converge if D-N alternating process has converged. Its technique is that the overlapping regions in Schwartz alternating process are considered as independent domains, then Schwartz alternating process could be transformed into D-N alter-nating process. Finally the convergence estimation of Schwartz alternating process could be obtained. The results show that its convergence rate is same as that of D-N alternating process. 相似文献
67.
TieYong YangGuangjun 《分析论及其应用》2004,20(1):58-68
In this paper, we construct some continuous but non-differentiable functions defined by quinary decimal, that are Kiesswetter-like functions. We discuss their properties, then investigate the Hausdorff dimensions of graphs of these functions and give a detailed proof. 相似文献
68.
A novel measurement method of temperature based on the phenomena that the phase difference between principle polarization states in the optical retarder is function of temperature is described. The polarization state of optical beam is changed as it passes through the optical retarder, which depends on the temperature. The temperature of optical retarder is determined by comparison of the power difference between principal polarization states. We demonstrate successfully the temperature measurement by using a polarization maintaining fiber as the optical retarder. With a 100 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.236 rad/°C and the measurement error was ±0.038°C over the temperature range of −2.6 – +3.4°C. With a 11.5 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.021 rad/°C and the measurement error was ±0.79°C over the temperature range of −8.5 – +86.5°C. 相似文献
69.
70.
This paper uses the method of linear approximation for impulsive systems and gets a theorem which guarantees a fishery modei to be asymptotically stable at its equilibrium point and gives the ecological explanation. 相似文献