全文获取类型
收费全文 | 189525篇 |
免费 | 17875篇 |
国内免费 | 28357篇 |
专业分类
化学 | 54846篇 |
晶体学 | 2421篇 |
力学 | 4990篇 |
综合类 | 2103篇 |
数学 | 10574篇 |
物理学 | 33136篇 |
综合类 | 127687篇 |
出版年
2024年 | 622篇 |
2023年 | 1806篇 |
2022年 | 4587篇 |
2021年 | 5049篇 |
2020年 | 4851篇 |
2019年 | 4340篇 |
2018年 | 4051篇 |
2017年 | 5235篇 |
2016年 | 5294篇 |
2015年 | 7773篇 |
2014年 | 10459篇 |
2013年 | 12422篇 |
2012年 | 13580篇 |
2011年 | 14859篇 |
2010年 | 14311篇 |
2009年 | 14860篇 |
2008年 | 16522篇 |
2007年 | 15812篇 |
2006年 | 14380篇 |
2005年 | 12258篇 |
2004年 | 9708篇 |
2003年 | 7036篇 |
2002年 | 7555篇 |
2001年 | 7144篇 |
2000年 | 6492篇 |
1999年 | 3584篇 |
1998年 | 1493篇 |
1997年 | 1227篇 |
1996年 | 1104篇 |
1995年 | 1041篇 |
1994年 | 962篇 |
1993年 | 838篇 |
1992年 | 722篇 |
1991年 | 626篇 |
1990年 | 579篇 |
1989年 | 528篇 |
1988年 | 388篇 |
1987年 | 332篇 |
1986年 | 250篇 |
1985年 | 179篇 |
1984年 | 162篇 |
1983年 | 110篇 |
1982年 | 108篇 |
1981年 | 99篇 |
1980年 | 98篇 |
1979年 | 90篇 |
1978年 | 29篇 |
1977年 | 23篇 |
1959年 | 23篇 |
1955年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Organometallic chemistry, biology and medicine: ruthenium arene anticancer complexes 总被引:1,自引:0,他引:1
Yan YK Melchart M Habtemariam A Sadler PJ 《Chemical communications (Cambridge, England)》2005,(38):4764-4776
Our work has shown that certain ruthenium(II) arene complexes exhibit promising anticancer activity in vitro and in vivo. The complexes are stable and water-soluble, and their frameworks provide considerable scope for optimising the design, both in terms of their biological activity and for minimising side-effects by variations in the arene and the other coordinated ligands. Initial studies on amino acids and nucleotides suggest that kinetic and thermodynamic control over a wide spectrum of reactions of Ru(II) arene complexes with biomolecules can be achieved. These Ru(II) arene complexes appear to have an altered profile of biological activity in comparison with metal-based anticancer complexes currently in clinical use or on clinical trial. 相似文献
102.
1INTRODUCTIONRecentlyorganicnonlinearoptical(NLO)materialsarebeingdevelopedforfre-quencyconversionoflaserinopto-electrics-Especiallybluelightisrequiredforopti-calmemoryofhighdensityrecording.Becauseadiodelaserisusedasalightsource,thenonlinearmaterialswhichhaveextremelyhighvalueofNLOcoefficientsandthetransmissionofblueregionarenecessary.Sincethesecond-orderNLOpropertyoforganiccompoundisderivedfromconjugateddelocalizedrrelectrons,thecompoundswhichhavebeenreportedhavefocusedonthenitroanil… 相似文献
103.
The quantum groupsgl
andA
are constructed. The representation theory of these algebras is developed and the universalR-matrix is presented. 相似文献
104.
Jian Ping LI* Ping LIU Yu Lu WANG College of Chemistry & Environmental Science Henan Normal University Xinxiang Key Laboratory of Environmental Science Technology of High Education of Henan Province Xinxiang 《中国化学快报》2003,14(7)
Azo compounds are widely utilized as analytic reagents and dyes1, they can also be used in material of non-linear optics, material of optics information storing in laser disks, and dyes with oil solubility in photochromy in modern technology2. Recently, many noteworthy studies have shown that some azo compounds possess excellent optical memory and photoelectric properties3,4. For example, polymer scaffolds bearing azobenzene-potential are useful for optical information storage, azo-dye doped… 相似文献
105.
Molecular Recognition of Bridged Bis(β-cyclodextrin)s Linked by Phenylenediseleno Tether on the Primary or Secondary Side with Fluorescent Dyes 总被引:1,自引:0,他引:1
A Novel β-cyclodextrin dimer,2,2′-o-phenylenediseleno-bridgedbis(β-cyclodextrin)(2),has been synthesized by reaction ofmono-[2-O-(p-tolylsulfonyl)]-β-cyclodextrin and poly(o-phenylenediselenide).The complexation stability constants(K_s)and Gibbs free energy changes(-ΔG°)of dimer 2 with fourfluorescence dyes,that is,ammonium 8-anilino-1-naphthalene-sulfonate(ANS),sodium 6-(p-toluidino)-2-naphthalenesul-fonate(TNS),Acridine Red(AR)and Rhodamine B(RhB)have been determined in aqueous phosphate buffer solution(pH=7.2,0.1 mol·L~(-1)at 25℃ by means of fluorescence spec- 相似文献
106.
This study relates to nanoparticle (NP) platforms that attach to tumor cells externally and only deliver singlet oxygen for photodynamic therapy (PDT) while conserving the embedded photosensitizers (PS). As a model, we demonstrate the successful embedding of the PS meta‐tetra(hydroxyphenyl)‐chlorin (m‐THPC) in NP that are based on a sol–gel silica matrix and also show its positive effect on the singlet oxygen production. The embedding of m‐THPC inside silica NP is accomplished by a modified Stöber sol–gel process, in which (3‐aminopropyl)‐triethoxysilane is introduced during the reaction. Singlet oxygen delivery by the targetable photodynamic NP exceeds that from free PS molecules. In the physiological pH range, there is no significant pH‐induced decrease in the fluorescence of m‐THPC embedded in silica NP, which might otherwise affect the efficiency of PDT. 相似文献
107.
The Gemini surfactant 9B-4-9B containing sodium sulfonate as hydrophilic head group was synthesized based on nonylphenol and characterized by FTIR, 1H NMR spectroscopy and the surface tension measurement. The CMC and C20 of the 9B-4-9B were smaller than that of sodium dodecylbenzene sulfonate and sodium dodecylsulfate, respectively, indicating excellent efficiency of micelle formation and reduced surface tension. Conducting polyaniline salts were synthesized by chemical oxidative micellar polymerization of aniline in water firstly using Gemini surfactant 9B-4-9B as the micelle stabilizer and ammonium peroxydisulfate as the oxidant at 0 °C. The stable polyaniline dispersions have been obtained when the molar ratio of the 9B-4-9B to aniline was equal to or above 0.5 used in the polymerization system. The obtained granular polyaniline particles with the size of 1-2 μm were characterized by FTIR, UV-Vis, SEM, WAXD and conductivity measurement. 相似文献
108.
A photometric method for hydrogencarbonate determination in various natural waters is presented, based on measurements with methyl red. Accuracy of the results is demonstrated by comparison with titrimetric and ion-chromatographic methods. The photometric method is suitable for contents in the range of 1–2000 mg l?1. The linear range of the continous flow method varies form 6–60 mg l?1 to 12–90 mg l?1 depending on conditions. 相似文献
109.
Membrane fusion is very important for the formation of many complex organs in metazoans throughout evolution, such as muscles, bones, and placentae. Lipid vesicles (liposomes) are frequently used as model membranes to study the fusion process. This work demonstrates for the first time the real-time membrane fusion of giant polymer vesicles by directly displaying a series of high-resolution and real-time transformation images of individual vesicles. The fusion process includes the sequential steps of membrane contact, forming the center wall, symmetric expansion of fusion pore and complete fusion, undergoing the intermediates of "8" shape with a protruding rim at the contact site, peanut (pear) shape, and oblate sphere. The vesicle swells during fusion, and the fusing vesicle only deforms in the neck domain around the fusion pore in the lateral direction, which verifies the importance of the lateral tension on the fusion pore at the vesicle deformation level. The successful fusion of the synthetic and protein-free polymer vesicles reported here also supports that vesicle proximity combined with membrane perturbation suffices to induce membrane fusion, and that the protein is not necessary for the fusion process. 相似文献
110.
Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction 总被引:1,自引:0,他引:1
Zhang M Yan Y Gong K Mao L Guo Z Chen Y 《Langmuir : the ACS journal of surfaces and colloids》2004,20(20):8781-8785
Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions. 相似文献