全文获取类型
收费全文 | 1867篇 |
免费 | 206篇 |
国内免费 | 183篇 |
专业分类
化学 | 1462篇 |
晶体学 | 20篇 |
力学 | 98篇 |
综合类 | 14篇 |
数学 | 172篇 |
物理学 | 490篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 62篇 |
2021年 | 63篇 |
2020年 | 65篇 |
2019年 | 80篇 |
2018年 | 73篇 |
2017年 | 61篇 |
2016年 | 83篇 |
2015年 | 89篇 |
2014年 | 90篇 |
2013年 | 138篇 |
2012年 | 143篇 |
2011年 | 174篇 |
2010年 | 94篇 |
2009年 | 101篇 |
2008年 | 104篇 |
2007年 | 80篇 |
2006年 | 84篇 |
2005年 | 72篇 |
2004年 | 73篇 |
2003年 | 61篇 |
2002年 | 99篇 |
2001年 | 79篇 |
2000年 | 52篇 |
1999年 | 58篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2256条查询结果,搜索用时 0 毫秒
51.
High‐performance liquid chromatography coupled with photodiode array detection has been extensively applied in many fields and the peaks among the analyzed samples can be shifted due to the variations of instrumental and experimental conditions. In multivariate analysis, retention time alignment is an important pretreatment step. Hence, the shifted peaks in high‐performance liquid chromatography coupled with photodiode array detection three‐dimensional spectra should be aligned for further analysis. Being motivated by this purpose, the interval correlated shifting method combined with the proposed data arrangement methods are recommended and employed on high‐performance liquid chromatography coupled with photodiode array detection data as a demonstration. We validate the alignment performance of the proposed method through comparison the consistency of the retention time before and after alignment. The obtained results demonstrated that the proposed method is capable of successful aligning the employed data. Additionally, the interval correlated shifting method combined with the data arrangement modes is implemented in an easy‐to‐use graphical user interface environment and so can be operated easily by users not familiar with programming languages. 相似文献
52.
Nonlinear Dynamics - This paper proposes a novel stability condition for delayed fractional-order composite systems. First, we extend the vector Lyapunov function to the fractional-order systems to... 相似文献
53.
A new hydroxo‐bridged dimeric Cr(III) complex [Cr(saltn)OH]2·4H2O [H2saltn=N,N′‐bis(salicylidene)trimethylenediamine] has been synthesized and its structural and magnetic properties have been investigated. The complex crystallizes in the triclinic space group P‐1 with one dimeric formula unit in a cell of dimensions a=0.95828(19) nm, b=0.95926(19) nm, c=1.0437(2) nm, α=86.77(3)°, β=82.48(3)°, and γ=64.93(3)°. The geometry around each chromium(III) center is six‐coordinate, distorted‐octahedral. The bridging Cr2O2 unit is strictly planar, as required by the crystallographic symmetry. The Cr? O? Cr′ bridging angle is 99.94(16)°, and the distance between Cr…Cr′ is 0.3019 nm. The magnetic susceptibility of the complex has been examined in the range of 2‐300 K. By using the spin‐spin coupled model for an S1=S2=3/2 dimeric system , the magnetic data were fitted to give the parameters of g=2.01(1), J=‐0.85(2) cm‐1, and zJ' =0.18(3)cm‐1, indicating the presence of a weak antiferromagnetic spin‐exchange interaction between the Cr(III) ions in the binuclear complex. 相似文献
54.
催化反应在极谱分析中的应用及反应速率常数的测定已有报道。通常根据Koutecky公式计算催化反应速率常数,而反应活化能则由不同温度下测定的速率常数,按照Arrhenius公式计算。我们根据前文提出的可逆、不可逆、准可逆、动力和催化过程各种极谱电流——温度关系的普遍方程式,测定了Ti(Ⅳ)-H_2SO_4H_2C_2O_4-KClO_3、Mo(Ⅳ)-H_2SO_4-NaNO_3、Mo(Ⅵ)-H_2SO_4-NH_4NO_3体系催化反应速率常数和反应活化能(或表观活化能),结果令人满意。 相似文献
55.
Meso-四(对-磺基苯基)卟啉光度法测定螺旋藻中的痕量锌 总被引:6,自引:0,他引:6
在pH=4.5的乙酸-乙酸钠缓冲介质中,锌和meso-四-(对磺基苯基)卟啉生成1:l的黄色配合物,λmax=421nm,ε=4.34×105L·mol-1·cm-1。该法可不经分离直接测定螺旋藻中的锌,结果满意。 相似文献
56.
Four 3D lanthanide organic frameworks from potassium pyrazine‐2, 3, 5, 6‐tetracarboxylate (K4pztc) or potassium pyridine‐2, 3, 5, 6‐tetracarboxylate (K4pdtc), namely, {[KEu(pztc)(H2O)2] · H2O}n ( 1 ), {[KTb(pztc)(H2O)2] · 1.25H2O}n ( 2 ), {[KLn(pdtc)(H2O)] · H2O}n [Ln = Gd ( 3 ), Ho ( 4 )], were synthesized by reaction of the corresponding lanthanide oxides with K4pztc or K4pdtc in presence of HCl under hydrothermal conditions, and characterized by elemental analysis, TGA, IR and fluorescence spectroscopy as well as X‐ray diffraction. In complexes 1 and 2 , the dodecadentate chelator pztc4– links four LnIII ions and four KI ions. The coordination mode of the pztc4– ligand is reported for the first time herein. Complexes 3 and 4 are isostructural with earlier reported Nd, Dy, Er complexes. Moreover, the EuIII and TbIII complexes exhibit the characteristic luminescence. 相似文献
57.
The phenomenon that metalloporphyrins are coordinated to axial ligands is very common especially in green-plant and photosynthetic bacteria, where such coordination impacts a signifi-cant effect on both the primary charge separation in the reaction center and energy transfer in an-tenna systems[1]. In addition, it plays a key role in photodynamic therapy and medicine synthesis in a sense that some metalloporphyrins have been assembled by coordination bonds to anti-cancer drugs, enhancing the se… 相似文献
58.
59.
60.