全文获取类型
收费全文 | 427750篇 |
免费 | 5715篇 |
国内免费 | 1552篇 |
专业分类
化学 | 234664篇 |
晶体学 | 6520篇 |
力学 | 17365篇 |
综合类 | 11篇 |
数学 | 48728篇 |
物理学 | 127729篇 |
出版年
2019年 | 3290篇 |
2018年 | 3936篇 |
2017年 | 3817篇 |
2016年 | 6522篇 |
2015年 | 4643篇 |
2014年 | 6595篇 |
2013年 | 19039篇 |
2012年 | 13695篇 |
2011年 | 16777篇 |
2010年 | 11126篇 |
2009年 | 10901篇 |
2008年 | 15129篇 |
2007年 | 15236篇 |
2006年 | 14196篇 |
2005年 | 13137篇 |
2004年 | 11861篇 |
2003年 | 10493篇 |
2002年 | 10223篇 |
2001年 | 12176篇 |
2000年 | 9277篇 |
1999年 | 7311篇 |
1998年 | 5927篇 |
1997年 | 5981篇 |
1996年 | 5808篇 |
1995年 | 5419篇 |
1994年 | 5233篇 |
1993年 | 5222篇 |
1992年 | 5929篇 |
1991年 | 5627篇 |
1990年 | 5422篇 |
1989年 | 5441篇 |
1988年 | 5422篇 |
1987年 | 5351篇 |
1986年 | 5021篇 |
1985年 | 6913篇 |
1984年 | 7062篇 |
1983年 | 5824篇 |
1982年 | 6296篇 |
1981年 | 6147篇 |
1980年 | 5935篇 |
1979年 | 6116篇 |
1978年 | 6496篇 |
1977年 | 6250篇 |
1976年 | 6330篇 |
1975年 | 5799篇 |
1974年 | 5826篇 |
1973年 | 6103篇 |
1972年 | 3880篇 |
1968年 | 3397篇 |
1967年 | 3394篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Barotropic FRW cosmologies are presented from the standpoint of nonrelativistic supersymmetry. First, we reduce the barotropic FRW system of differential equations to simple harmonic oscillator differential equations. Employing the factorization procedure, the solutions of the latter equations are divided into the two classes of bosonic (nonsingular) and fermionic (singular) cosmological solutions. We next introduce a coupling parameter denoted by K between the two classes of solutions and obtain barotropic cosmologies with dissipative features acting on the scale factors and spatial curvature of the universe. The K-extended FRW equations in comoving time are presented in explicit form in the low coupling regime. The standard barotropic FRW cosmologies correspond to the dissipationless limit K = 0. 相似文献
992.
Y. Qu J.X. Zhang A. Uddin C.Y. Liu S. Yuan M.C.Y. Chan B. Bo G. Liu H. Jiang 《Applied Physics A: Materials Science & Processing》2006,82(2):305-308
Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength. 相似文献
993.
The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased. 相似文献
994.
A. A. Lamberov E. V. Dement’eva Kh. Kh. Gil’manov S. R. Egorova N. V. Romanova 《Russian Journal of Applied Chemistry》2006,79(9):1453-1457
The effect of the paste molding pressure on the physicomechanical and texture characteristics of catalysts was studied. An indirect criterion is suggested to evaluate the molding pressure in industrial extruders, whose optimal value ensures good physicomechanical properties of the catalysts and kinetic control over the catalyzed reaction. The results obtained were verified in paste molding on various industrial extruders, and this enabled the optimal choice of the molding equipment. 相似文献
995.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献
996.
997.
The yet unknown intermetallic phase La5Al3Ni2 was obtained by partially crystallizing amorphous La50Al25Ni25 at 550 K (further heating above 600 K leads to irreversible disappearance of this phase), and its crystal structure was determined from X‐ray powder diffraction data. The crystal structure of the La5Al3Ni2 phase constitutes a new structure type (Cmcm, a = 14.231Å, b = 6.914Å, c = 10.460Å, oC40) and is built from [Al3Ni2] chains surrounded by La atoms. In the ternary system La‐Al‐Ni La5Al3Ni2 is located on the section La50Al50−nNin (0 ≤ n ≤ 50) with the binary compounds LaAl and LaNi as end members. Strikingly, also the crystal structures of the end members can be conceived as chain structures with Al and Ni chains surrounded by La, respectively. 相似文献
998.
999.
1000.