全文获取类型
收费全文 | 80124篇 |
免费 | 6757篇 |
国内免费 | 7146篇 |
专业分类
化学 | 30029篇 |
晶体学 | 1436篇 |
力学 | 6884篇 |
综合类 | 1496篇 |
数学 | 28547篇 |
物理学 | 25635篇 |
出版年
2023年 | 657篇 |
2022年 | 1060篇 |
2021年 | 1484篇 |
2020年 | 1604篇 |
2019年 | 1809篇 |
2018年 | 1546篇 |
2017年 | 1912篇 |
2016年 | 2271篇 |
2015年 | 1958篇 |
2014年 | 2980篇 |
2013年 | 5248篇 |
2012年 | 3323篇 |
2011年 | 3888篇 |
2010年 | 3340篇 |
2009年 | 4515篇 |
2008年 | 5039篇 |
2007年 | 5242篇 |
2006年 | 4869篇 |
2005年 | 4126篇 |
2004年 | 3800篇 |
2003年 | 3771篇 |
2002年 | 3373篇 |
2001年 | 2863篇 |
2000年 | 2794篇 |
1999年 | 2342篇 |
1998年 | 2172篇 |
1997年 | 1868篇 |
1996年 | 1638篇 |
1995年 | 1524篇 |
1994年 | 1393篇 |
1993年 | 1185篇 |
1992年 | 1143篇 |
1991年 | 899篇 |
1990年 | 746篇 |
1989年 | 631篇 |
1988年 | 585篇 |
1987年 | 464篇 |
1986年 | 386篇 |
1985年 | 458篇 |
1984年 | 444篇 |
1983年 | 219篇 |
1982年 | 359篇 |
1981年 | 414篇 |
1980年 | 307篇 |
1979年 | 301篇 |
1978年 | 228篇 |
1977年 | 208篇 |
1976年 | 157篇 |
1974年 | 111篇 |
1973年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
Durairaj Gopalakrishnan Santhanam Srinath Baburaj Baskar Nattamai S.P. Bhuvanesh Mani Ganeshpandian 《应用有机金属化学》2019,33(3)
Two organometallic Ru(II)‐p‐cymene complexes of the type [Ru(η6‐p‐cymene)(L)Cl]PF6 1 and 2 , where L is N,N‐bis(4‐isopropylbenzylidene)ethane‐1,2‐diamine (bien, L1 ) or N,N‐bis (pyren‐2‐ylmethylene)ethane‐1,2‐diamine (bpen, L2 ) have been prepared and characterized well. Because of appended pyrenyl groups in coordinated bpen ligand, the complex 2 exhibits higher DNA and protein binding than complex 1 in which isopropylbenzyl groups are incorporated. Interestingly, the luminescent characteristic complex 2 is unique in displaying DNA cleavage after light activation by UVA light at 365 nm through oxygen dependent mechanism. AFM analysis attests the photo‐induced DNA fragmentation ability of complex 2 . Also, the complex 2 cleaves the protein after light exposure in a non‐specific manner suggesting that it can act as a protein photo cleaving agent. In contrast to the trend of DNA and protein interaction of complexes, the complex 1 exhibits cytotoxic activity against human breast carcinoma ( MCF‐7 ) and liver carcinoma ( HepG2 ) with potency higher than that of complex 2 due to enhanced hydrophobicity of isopropyl groups present in p‐cymene and bien ligands. Indeed, complex 2 is inactive against MCF‐7 and HepG2 cancer cell lines even up to 200 μM concentration. The AO/EB staining assay reveals that the complex 1 is able to induce late apoptotic mode of cell death in breast cancer cells, which is further confirmed by inter‐nucleosomal DNA cleavage. Furthermore, the complexes 1 and 2 are evaluated for their catalytic activities and found to be working well for the β‐carboline directed C–H arylation to afford the desired products in good yield (40–47%). 相似文献
63.
The heterostructured Ag nanoparticles decorated Fe3O4 Glutathione (Fe3O4‐Glu‐Ag) nanoparticles (NPs) were synthesized by sonicating glutathione (Glu) with magnetite and further surface immobilization of silver NPs on it. The ensuing magnetic nano catalyst is well characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA). The prepared Fe3O4‐Glu‐Ag nanoparticles have proved to be an efficient and recyclable nanocatalyst with low catalyst loading for the reduction of nitroarenes and heteronitroarenes to respective amines in the presence of NaBH4 using water as a green solvent which could be easily separated at the end of a reaction using an external magnet and can be recycled up to 5 runs without any significant loss in catalytic activity. Gram scale study for the reduction of 4‐NP has also being carried out successfully and it has been observed that this method can serve as an efficient protocol for reduction of nitroarenes on industrial level. 相似文献
64.
65.
Joseph D. Martin 《Annalen der Physik》2019,531(10)
Mildred Dresselhaus is known for her influential research on the physics of carbon. Her wide‐ranging influence as a physics teacher, although well‐known to her students, has been less thoroughly examined. Exploring how Dresselhaus grew into her role teaching solid state physics at MIT reveals much about how that subfield evolved. 相似文献
66.
This study reports the structural and spectroscopic characterization of a novel metal organic compound formulated as [Fe (bpy)3] [Fe (dipic)2]2.7H2O ( 1 ) (dipic = pyridine‐2,6‐dicarboxylate and bpy = 2,2′‐bipyridine). 1 was investigated by elemental analysis, FT‐IR spectroscopy, powder X‐ray diffraction and single crystal X‐ray diffraction (SC‐XRD), which revealed a triclinic structure of expected composition. Thermal degradation of 1 was also investigated. Complex 1 was used as a precursor to prepare superparamagnetic nanoparticles of Fe3O4 by thermal analysis. The obtained Fe3O4 was characterized by Fourier transformed infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Fe3O4 nanoparticles were used as a nano‐adsorbent to remove Cd2+ from water at room temperature. The results showed that this nano‐adsorbent is effective in removing Cd2+ from contaminated water sources, and that the maximal effectivity of adsorption occurs at pH = 6. Magnetic measurements of complex 1 and Fe3O4 nanoparticles at room temperature revealed paramagnetic and superparamagnetic behavior, respectively. 相似文献
67.
A priori bounds and multiplicity for fully nonlinear equations with quadratic growth in the gradient
We consider fully nonlinear uniformly elliptic equations with quadratic growth in the gradient, such asin a bounded domain with a Dirichlet boundary condition; here , , , and the matrix M satisfies . Recently this problem was studied in the “coercive” case , where uniqueness of solutions can be expected; and it was conjectured that the solution set is more complex for noncoercive equations. This conjecture was verified in 2015 by Arcoya, de Coster, Jeanjean and Tanaka for equations in divergence form, by exploiting the integral formulation of the problem. Here we show that similar phenomena occur for general, even fully nonlinear, equations in nondivergence form. We use different techniques based on the maximum principle.We develop a new method to obtain the crucial uniform a priori bounds, which permit to us to use degree theory. This method is based on basic regularity estimates such as half-Harnack inequalities, and on a Vázquez type strong maximum principle for our kind of equations. 相似文献
68.
The nonmetal-to-metal transition in dense fluid helium is discussed, which has been, in analogy to metallization of hydrogen, predicted as first-order plasma phase transition using chemical models for the equation of state and plasma composition. However, recent ab initio simulations performed for dense fluid helium indicate that this transition is continuous in the considered regime, without a density jump and latent heat as characteristic of a first-order phase transition. Implications for some astrophysical plasmas are discussed. 相似文献
69.
70.