全文获取类型
收费全文 | 45965篇 |
免费 | 7757篇 |
国内免费 | 4985篇 |
专业分类
化学 | 32391篇 |
晶体学 | 525篇 |
力学 | 2796篇 |
综合类 | 358篇 |
数学 | 5261篇 |
物理学 | 17376篇 |
出版年
2024年 | 158篇 |
2023年 | 1009篇 |
2022年 | 1659篇 |
2021年 | 1855篇 |
2020年 | 1960篇 |
2019年 | 1819篇 |
2018年 | 1562篇 |
2017年 | 1448篇 |
2016年 | 2102篇 |
2015年 | 2229篇 |
2014年 | 2668篇 |
2013年 | 3349篇 |
2012年 | 4157篇 |
2011年 | 4092篇 |
2010年 | 2788篇 |
2009年 | 2697篇 |
2008年 | 2881篇 |
2007年 | 2504篇 |
2006年 | 2351篇 |
2005年 | 1930篇 |
2004年 | 1581篇 |
2003年 | 1192篇 |
2002年 | 1100篇 |
2001年 | 887篇 |
2000年 | 828篇 |
1999年 | 936篇 |
1998年 | 788篇 |
1997年 | 703篇 |
1996年 | 761篇 |
1995年 | 648篇 |
1994年 | 589篇 |
1993年 | 509篇 |
1992年 | 482篇 |
1991年 | 382篇 |
1990年 | 343篇 |
1989年 | 254篇 |
1988年 | 230篇 |
1987年 | 214篇 |
1986年 | 160篇 |
1985年 | 171篇 |
1984年 | 143篇 |
1983年 | 119篇 |
1982年 | 82篇 |
1981年 | 61篇 |
1980年 | 51篇 |
1979年 | 36篇 |
1978年 | 27篇 |
1976年 | 29篇 |
1975年 | 31篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
光泽精化学发光体系的研究与应用 总被引:5,自引:0,他引:5
对光泽精化学发光体系的动力学性质、荧光光谱、化学发光光谱及化学发光机理进行研究和探讨。详细研究了光泽精 - H2 O2 - Co( )流动注射化学发光体系的最佳分析条件。结果表明 ,当光泽精 (L c)为 2 .5×10 - 5mol/L、H2 O2 为 0 .5 mol/L、Na OH为 0 .4 mol/L、CTMAB为 2 .0× 10 - 5mol/L时 ,测定 Co( )的校准曲线线性范围为 0 .0 5— 2 0 0μg/m L ,检出限为 0 .0 1μg/m L。对 10μg/m L Co( )连续测定 7次 ,相对标准偏差为 1.7%。 相似文献
143.
Investigation of remelting and cladding processing with laminar plasma jets on several metals has been conducted looking for possible development of a new surface modification technique. The remelting tests illustrated that the new method could evidently improve the material microstructure and properties of cast iron. The cladding was done with Al2O3 ceramic powder on stainless steel. The energy dispersive spectra (EDS) analysis was used to determine the distribution of the major cladding element in the plasma-processed layers, for which the microstructure observations and hardness measurements were also performed. 相似文献
144.
LI Cun YANG Bai-Feng CAI Hao HUANG Nian-Ning 《理论物理通讯》2006,46(2):244-248
One of the basic problems about the inverse scattering transform for solving a completely integrable nonlinear evolutions equation is to demonstrate that the Jost solutions obtained from the inverse scattering equations of Cauchy integral satisfy the Lax equations. Such a basic problem still exists in the procedure of deriving the dark soliton solutions of the NLS equation in normal dispersion with non-vanishing boundary conditions through the inverse scattering transform. In this paper, a pair of Jost solutions with same analytic properties are composed to be a 2 × 2 matrix and then another pair are introduced to be its right inverse confirmed by the Liouville theorem. As they are both 2 × 2 matrices, the right inverse should be the left inverse too, based upon which it is not difficult to show that these Jost solutions satisfy both the first and second Lax equations. As a result of compatibility condition, the dark soliton solutions definitely satisfy the NLS equation in normal dispersion with non-vanishing boundary conditions. 相似文献
145.
Chen Hao 《中国科学A辑(英文版)》2006,49(5):715-720
In this paper, for the the primes p such that 3 is a divisor of p − 1, we prove a result which reduces the computation of the linear complexity of a sequence over GF(p
m) (any positive integer m) with the period 3n (n and p
m − 1 are coprime) to the computation of the linear complexities of three sequences with the period n. Combined with some known algorithms such as generalized Games-Chan algorithm, Berlekamp-Massey algorithm and Xiao-Wei-Lam-Imamura
algorithm, we can determine the linear complexity of any sequence over GF(p
m) with the period 3n (n and p
m
− 1 are coprime) more efficiently. 相似文献
146.
147.
The influence of the electron-LO-phonon coupling on energy spectrum of the low-lying states ofan exciton inparabolic quantum dots is investigated as a function of dot size. Calculations are made by using the method of few-bodyphysics within the effective-mass approximation. A considerable decrease of the energy in the stronger confinement rangeis found for the low-lying states of an exciton in quantum dots, which results from the confinement of electron-phononcoupling. 相似文献
148.
将等离子焊接(PAW)电弧和钨极氩弧焊(TIG)电弧串接,相对作用于工件的正反面形成双面电弧焊接(DSAW)系统,可以引导焊接电流沿工件厚度方向流过小孔,补偿等离子电弧穿透工件时消耗的能量,以有效地提高等离子弧的穿透能力.综合考虑影响双面电弧焊接正反面熔池几何形状的力学因素,建立了熔池表面变形的控制方程,以此为基础并采用帖体曲线坐标系建立了DSAW焊接传热的数学模型,分析了DSAW,PAW焊接传热的差异,从传热的角度解释了DSAW焊接熔深增加的原因.焊接工艺实验表明,计算结果与实测结果吻合良好.
关键词:
双面电弧焊接(DSAW)
传热模型
熔池表面变形模型 相似文献
149.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
150.
An improvement has been made to couple isoelectric focusing (IEF) sample injection and capillary zone electrophoresis in an untreated fused silica capillary. Electroosmotic flow is efficiently prevented by simply using a rubber block at the outlet end of the capillary during IEF sample injection. The experimental conditions that affect the concentration effect are discussed. A concentration enhancement factor of over 100-fold can be easily obtained for two model proteins: lysozyme and ribonuclease A. 相似文献