全文获取类型
收费全文 | 613篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 425篇 |
晶体学 | 4篇 |
力学 | 7篇 |
数学 | 38篇 |
物理学 | 151篇 |
出版年
2024年 | 2篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 49篇 |
2012年 | 34篇 |
2011年 | 64篇 |
2010年 | 30篇 |
2009年 | 27篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 35篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 24篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有625条查询结果,搜索用时 15 毫秒
31.
Maheswari PU Roy S den Dulk H Barends S van Wezel G Kozlevcar B Gamez P Reedijk J 《Journal of the American Chemical Society》2006,128(3):710-711
Chemical nucleases based on the transition-metal ions cleave DNA hydrolytically and/or oxidatively, with or without added reductant. We report here the novel DNA cleavage properties of the highly water-soluble, square-planar [Cu(Hpyrimol)Cl] complex, together with the results of cytotoxicities toward selected cancer cell lines. The copper complex cleaves PhiX174 supercoiled DNA efficiently without any reductant and shows high cytotoxicities toward L1210 murine leukemia and A2780 human ovarian carcinoma cancer cell lines that are sensitive and resistant to cisplatin. The IC50 values obtained for the copper complex in the sensitive cell lines are in the range of cisplatin, and for the cisplatin-resistant leukemia cell line, this value is even better. 相似文献
32.
Ramu Surakanti Sumalatha Sanivarapu Chiranjeevi Thulluri Pravin S. Iyer Raghuram S. Tangirala Rambabu Gundla Dr. Uma Addepally Y. L. N. Murthy Lakshmi Velide Dr. Subhabrata Sen 《化学:亚洲杂志》2013,8(6):1168-1176
An elegant reagent‐controlled strategy has been developed for the generation of a diverse range of biologically active scaffolds from a chiral bicyclic lactam. Reduction of the chiral lactam with LAH or alkylation with LHMDS to trigger different cyclization reactions have been shown to generate privileged scaffolds, such as pyrrolidines, indolines, and cyclotryptamines. Their amenability to substitution allows us to create various compound libraries by using these scaffolds. In silico studies were used to estimate the drug‐like properties of these compounds. Selected compounds were subjected to anticancer screening by using three different cell lines. In addition, all these compounds were subjected to antibacterial screening to gauge the spectrum of biological activity that was conferred by our DOS methodology. Gratifyingly, with no additional iterative cycles, our method directly generated anticancer compounds with potency at low nanomolar concentrations, as represented by spiroindoline 14 . 相似文献
33.
Both hydrophobic and hydrophilic room-temperature ionic liquids can be separated from aqueous solutions with relatively low-pressure gaseous carbon dioxide. 相似文献
34.
In this study, it is demonstrated that silver nanoparticles can be transferred from formamide to chloroform using oleic acid as a phase transfer agent with a transfer efficiency of 90–95%. The silver nanoparticles are initially formed as an organosol by the reduction of silver ions with formamide. On aging the complex, the particles self-assemble to form an ordered close-packed two-dimensional array of silver nanocrystals when dissolved in CHCl3. The size distribution of the colloidal silver particles after transfer in different solvents remains almost the same. On the basis of IR spectroscopy, we discuss the adsorption of oleic acid over the silver particles. 相似文献
35.
Togapur Pavan Kumar Mohammad Abdul Sattar Vanka Uma Maheshwara Sarma 《Tetrahedron: Asymmetry》2013,24(24):1615-1619
An efficient protocol for the enantioselective Michael additions of ketones to chalcones catalyzed by a hydroxyphthalimide linked triazole–pyrrolidine derivative has been developed. The corresponding products, 1,5-dicarbonyl compounds, were obtained in good yields with high levels of stereoselectivities under mild reaction conditions employing benzoic acid as an additive. 相似文献
36.
S. Santhi Sudha Ch. Syama Sundar N. Bakthavatchala Reddy K. Uma Maheswara Rao S. H. Jaya Prakash C. Suresh Reddy 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):1402-1411
Abstract A simple, efficient, and environmentally benign methodology has been accomplished for the synthesis of α-aminophosphonates by one-pot three-component reaction of ethyl-2-amino-α-(methoxy-imino)-4-thiazoleacetate, aldehydes, and diethylphosphite by using Amberlyst-15 as catalyst at room temperature under solvent-free conditions. Their chemical structures were characterized by infrared (IR), NMR (1H, 13C & 31P), mass spectral, and elemental analysis. All the title compounds were screened for radical-scavenging activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitic oxide (NO), and hydrogen peroxide (H2O2) methods. Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text and figures. 相似文献
37.
Ch. Syama Sundar N. Bakthavatchala Reddy S. Siva Prasad K. Uma Maheswara Rao S. H. Jaya Prakash C. Suresh Reddy 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):551-557
Abstract A new series of α-aminophosphonates have been synthesized by a one-pot three-component reaction of 2,3-dihydrobenzo[b][1,4]dioxine-6-carbaldehyde, various amines, and dimethyl phosphite by using nano-TiO2 as a catalyst under solvent-free conditions at 50°C. The major advantages of the present method are high yields, short reaction times, recyclable catalyst, and solvent-free reaction conditions. Among these new structurally diversified set of α-aminophosphonates, dimethyl (2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(3-nitrophenylamino) methylphosphonate and dimethyl (2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(4-fluoro-3-nitro-phenyl-amino) methylphosphonate have shown higher antioxidant activity in diphenyl picryl hydrazyl (DPPH) scavenging, reducing power assay, and lipid peroxidation methods. 相似文献
38.
Chariklia Sotiriou-Leventis Xiaojiang Wang Sudhir Mulik Arumugam Thangavel Nicholas Leventis 《合成通讯》2013,43(14):2285-2298
Immobilization of catalysts on solid supports is a promising approach to combine the advantages of heterogeneous and homogeneous catalysts. Pd(PPh3)2Cl2, known as an extremely active homogeneous catalyst for the Sonogashira coupling reaction, has been immobilized on high-surface-area MCF (mesocellular foams)–type mesoporous silica powder modified with 3-aminopropyltriethoxysilane and subsequently with diphenylphosphine. The functionalized MCF-type silica and supported catalysts have been characterized by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), elemental analysis, nitrogen sorption porosimetry, and scanning electron microscopy (SEM). Such supported Pd catalysts have proven to be useful recyclable reagents for copper- and amine-free Sonogashira coupling reactions of haloaromatic compounds with terminal alkynes. 相似文献
39.
Das Arulsamy A Kregar Z Eleršič K Modic M Subramani US 《Physical chemistry chemical physics : PCCP》2011,13(33):15175-15181
Hydrogen produced from the photocatalytic splitting of water is one of the reliable alternatives to replace the polluting fossil and the radioactive nuclear fuels. Here, we provide unequivocal evidence for the existence of blue- and red-shifting O-H covalent bonds within a single water molecule adsorbed on the MgO surface as a result of asymmetric displacement polarizabilities. The adsorbed H-O-H on MgO gives rise to one weaker H-O bond, while the other O-H covalent bond from the same adsorbed water molecule compensates this effect with a stronger bond. The weaker bond (nearest to the surface), the interlayer tunneling electrons and the silver substrate are shown to be the causes for the smallest dissociative activation energy on the MgO monolayer. The origin that is responsible to initiate the splitting mechanism is proven to be due to the changes in the polarizability of an adsorbed water molecule, which are further supported by the temperature-dependent static dielectric constant measurements for water below the first-order electronic-phase transition temperature. 相似文献
40.
The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques. 相似文献