全文获取类型
收费全文 | 7989篇 |
免费 | 352篇 |
国内免费 | 64篇 |
专业分类
化学 | 5956篇 |
晶体学 | 88篇 |
力学 | 290篇 |
综合类 | 2篇 |
数学 | 982篇 |
物理学 | 1087篇 |
出版年
2024年 | 23篇 |
2023年 | 66篇 |
2022年 | 416篇 |
2021年 | 415篇 |
2020年 | 270篇 |
2019年 | 308篇 |
2018年 | 319篇 |
2017年 | 249篇 |
2016年 | 415篇 |
2015年 | 278篇 |
2014年 | 284篇 |
2013年 | 693篇 |
2012年 | 528篇 |
2011年 | 539篇 |
2010年 | 345篇 |
2009年 | 305篇 |
2008年 | 373篇 |
2007年 | 343篇 |
2006年 | 271篇 |
2005年 | 236篇 |
2004年 | 212篇 |
2003年 | 178篇 |
2002年 | 208篇 |
2001年 | 92篇 |
2000年 | 107篇 |
1999年 | 59篇 |
1998年 | 48篇 |
1997年 | 55篇 |
1996年 | 52篇 |
1995年 | 47篇 |
1994年 | 46篇 |
1993年 | 50篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 57篇 |
1989年 | 33篇 |
1988年 | 31篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 24篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 9篇 |
排序方式: 共有8405条查询结果,搜索用时 15 毫秒
81.
The synthesis of goethite by oxidation of Fe2+in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na2SO4, (NH4)2SO4, NaCl, and NH4Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl−, the SO42−anion decreases the rate of the two reactions. NH4+acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH4+behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts. 相似文献
82.
Adenier A Chehimi MM Gallardo I Pinson J Vilà N 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8243-8253
The electrochemical oxidation of aliphatic amines (primary, secondary, and tertiary) has been investigated by cyclic voltammetry and preparative electrolysis. The oxidation mechanisms have been established, and the lifetimes of the radical cations have been measured for secondary and tertiary amines. These results have been put in parallel with the attachment of amines to glassy carbon, Au, and Pt electrodes by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and infrared reflection-absorption spectroscopy (IRRAS). It is then possible to show that it is not the radical cation but the radical obtained after the deprotonation which reacts with the electrode surface. XPS results also point to the existence of a covalent bond between Au or Pt and the organic moiety. 相似文献
83.
Ion, precipitate and adsorbing colloid flotation of cobalt(II) have been investigated at different pH values, using N-dodecylpyridinium chloride (DPCl), A strong cationic surfactant, and sodium lauryl sulfate (NaLS), a strong anionic surfactant, as collectors. In case of adsorbing colloid flotation, hydrous manganese dioxide was used as an adsorbent. The precipitate flotation curves experimentally obtained with the two tested collectors were compared with the corresponding theoretical one calculated from the data published for Co(II) hydrolysis. The effects of the collector concentration, ageing of the water-MnO2–Co(II) system, bubbling time period, cobalt(II) concentration and foreign salts on the percent removal of Co(II) by adsorbing colloid flotation using DPCl as collector were determined. Removals approaching 100% could be achieved under the optimum conditions. 相似文献
84.
Benoit Bachand Mohamed Atfani Bita Samim Sophie Lévesque Daniel Simard Xianqi Kong 《Tetrahedron letters》2007,48(49):8587-8589
A practical synthetic route to various 2-alkylpropane-1,3-sultones, the key intermediates for the preparation of 2-substituted homotaurines as analogs of tramiprosate, was developed. 相似文献
85.
Mangelings D Tanret I Matthijs N Maftouh M Massart DL Vander Heyden Y 《Electrophoresis》2005,26(4-5):818-832
The effect of five factors on the capillary electrochromatographic enantioseparation of acidic compounds was studied using an experimental design. The studied factors were pH, acetonitrile content in the mobile phase, temperature, buffer concentration, and applied voltage. These experiments allowed defining a generic separation strategy applicable on acidic compounds with chemical and structural diversity. The starting screening conditions consist of a 45 mM ammonium formate electrolyte at pH 2.9 mixed with 65% acetonitrile, an applied voltage of 15 kV, and a temperature of 25 degrees C. The screening phase occasionally can be followed by an optimization procedure. Evaluation of the proposed strategy pointed out that it allows achieving baseline resolution within a relatively short time when a beginning of separation is obtained at the starting conditions. This strategy revealed enantioselectivity for 11 compounds out of 15, of which 10 could be baseline-separated after the proposed optimization steps. 相似文献
86.
Yasri A Berthelot D Gijsen H Thielemans T Marichal P Engels M Hoflack J 《Journal of chemical information and computer sciences》2004,44(6):2199-2206
REALISIS is a software system for reagent selection, library design, and profiling, developed to fit the workflow of bench chemists and medicinal chemists. Designed to be portable, the software offers a comprehensive graphical user interface and rapid, integrated functionalities required for reagent retrieval and filtering, product enumeration, and library profiling. REALISIS is component-based, consisting of four main modules: reagent searching; reagent filtering; library enumeration; and library profiling. Each module allows the chemist to access specific functionalities and diverse filtering and profiling mechanisms. By implementing the entire process of reagent selection, library design, and profiling and by integrating all the necessary functionalities for this process, REALISIS cuts the time required to design combinatorial and noncombinatorial libraries from several days to a few hours. 相似文献
87.
Sandrine LangleFranck David-Quillot Mohamed AbarbriAlain Duchêne 《Tetrahedron letters》2003,44(8):1647-1649
Using double Stille cross-coupling reaction bromo (or chloro)benzylbromide is easily transformed into substituted styrene monomers bearing a wide range of substituents in para position 相似文献
88.
Samath S. Abdul Raman Mani Raman Natarajan Jeyasubramanian Kadarkarai Thangam Ramalingam Suthamalli K. 《Transition Metal Chemistry》1992,17(1):13-15
Transition Metal Chemistry - The synthesis and structural characterization of new metal(II) chelates (M = CoII, NiII, CuII and ZnII) of neutral conjugated bidentate β-diketone ligands, having... 相似文献
89.
Ibrahim Abdul Razak Anwar Usman Hoong‐Kun Fun Bohari M. Yamin Nor Azilah Kasim 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m162-m164
In the title compound, [Fe(C17H14P)2]2[Sb4Cl16]·C2H6O, the Fe atoms lie on inversion centres and the pairs of cyclopentadienyl rings are consequently in a fully staggered conformation. The centrosymmetric anionic clusters formed by [Sb4Cl16]4? are surrounded by the cations and are held together by weak C—H?Cl interactions. These formations stack along the a axis to form columns, and the columns are interconnected by another weak C—H?Cl interaction along the b axis. 相似文献
90.
Smain Bousalem Claire Mangeney Mohamed M. Chehimi Teresa Basinska Beata Miksa Stanislaw Slomkowski 《Colloid and polymer science》2004,282(12):1301-1307
N-Succinimidyl ester functionalized polypyrrole-coated polystyrene latex particles (PSE-PPyNSE) were prepared by the in situ copolymerization of pyrrole and the active ester-functionalized pyrrole (pyrrole-NSE) in the presence of polystyrene latex particles. Polystyrene microspheres were prepared by emulsion polymerization (PSE) leading to particles having a diameter of 450 nm. These PSE particles were precoated with poly(N-vinylpyrrolidone) prior to the in situ copolymerization of pyrrole and pyrrole-NSE. The initial comonomer concentration fractions were 25/75, 50/50 and 75/25 for pyrrole and pyrrole-NSE, respectively. The PPy-coated PSE particles were characterized in terms of morphology, particle size, electrophoretic mobility and chemical composition. The study of morphology by means of scanning electron microscopy showed roughening of the underlying PSE particles owing to the addition of PPyNSE, the overlayer thickness of which was estimated to be around 7 nm. Moreover, loading PPyNSE overlayers resulted in a shift of the electrophoretic mobility from –5.31 m cm/V s to a very small but positive value (0.082–0.112 m cm/V s). X-ray photoelectron spectroscopy and IR spectroscopy permitted the detection of pyrrole-NSE repeat units at the surface indicating that pyrrole and pyrrole-NSE did indeed copolymerize. The PSE-PPyNSE particles were further evaluated as bioadsorbents of human serum albumin used as a test protein. For this study, PSE-PPyNSE50 particles, synthesized from a comonomer feed ratio of 50/50 in pyrrole/pyrrole-NSE, were used and were shown to attach efficiently human serum albumin macromolecules with a maximum amount of 0.2 mg m–2.
相似文献
Mohamed M. ChehimiEmail: |