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61.
The carbon ceramic electrode prepared with sol-gel technique is modified by a thin film of chlorogenic acid (CGA). By immersing the carbon ceramic electrode in aqueous solution of chlorogenic acid at less than 2 s a thin film of chlorogenic acid adsorbed strongly and irreversibly on the surface of electrode. The cyclic voltammetry of the resulting modified CCE prepared at optimum conditions shows a well-defined stable reversible redox couple due to hydroquinone/quinone system in both acidic and basic solutions. The modified electrode showed excellent electrocatalytic activity toward NADH oxidation and it also showed a high analytical performance for amperometric detection of NADH. The catalytic rate constant of the modified carbon ceramic electrode for the oxidation of NADH is determined by cyclic voltammetry measurement. Under the optimised conditions the calibration curve is linear in the concentration range 1-120 μm. The detection limit (S/N = 3) and sensitivity are 0.2 μM and 25 nA μM−1.The results of six successive measurement-regeneration cycles show relative standard deviations of 2.5% for electrolyte solution containing 1 mM NADH, indicating that the electrode renewal gives a good reproducible and antifouling surface. The advantages of this amperometric detector are: high sensitivity, excellent catalytic activity, short response time t < 2 s, remarkable long-term stability, simplicity of preparation at short time and good reproducibility. 相似文献
62.
Anvarhusein A. Isab Abdul R. Al-Arfaj Mohammed Arab Mir M. Hassan 《Transition Metal Chemistry》1994,19(1):87-90
Summary Pd(CN)2 reacts with imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione(Diaz), 1,3-diazipnane-2-thione (Diap) and their derivatives to yield complexes of stoichiometry [PdL2(CN)2] or [PdL(CN)2] (L = Imt, Diaz or Diap and L = Imt having N-Me, Et or Pr substituents), which were characterized by elemental analysis, i.r., 1H and 13C n.m.r. spectroscopy. Both mono- and bis ligand complexes are thought to be square planar with the monoligand binding to metal via sulphur (bridging) and the bis ligand via the monodentate thione group. The 13C enriched Pd(13CN)2 complex was prepared and the 13C n.m.r. recorded. The C-2 resonance of 13C n.m.r. of Imt, Diaz or Diap complexes of the copper(I), silver(I), gold(I) and palladium(II) were compared. 相似文献
63.
5‐Acetyl‐3‐amino‐4‐aryl‐6‐methylthieno[2,3‐b]pyridine‐2‐carboxamides ( 5a,b ) were reacted with triethyl orthoformate or nitrous acid to give the corresponding pyrimidinones 6a,b and triazinones 7a,b . The reaction of 5a,b with acetic anhydride was carried out and its products were identified as a mixture of 8‐acetyl‐9‐aryl‐2,7‐dimethylpyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐4(3H)‐one ( 9a,b ) and related 5‐acetyl‐4‐aryl‐3‐biacetylamino‐6‐methylthieno[2,3‐b]pyridine‐2‐carbonitrile ( 10a,b ). Reaction of 7a with some halocompounds afforded the N‐alkylated triazinones 8a‐c . Chlorination of 6a,b and 9a,b with phosphorus oxychloride produced 4‐chloropyrimidines 11a‐d which were used as precursors for the rest of the target heterocycles. Some of the prepared compounds were tested in vitro for their antimicrobial activities. 相似文献
64.
Kazi A. Azam Rahima Dilshad Shariff E. Kabir Rashid Miah Mohammad Shahiduzzaman Edward Rosenberg Kenneth I. Hardcastle Michael B. Hursthouse K. M. Abdul Malik 《Journal of Cluster Science》1996,7(1):49-70
The reaction of [Os3(CO)12] with tetramethylthiourea in the presence of a methanolic solution of Me3NO·2H2O at 60° yields the compounds [Os3(CO)11{η 1-SC(NMe2)2}] (1) in 56% yield and [Os3(CO)9(μ-OH)(μ-MeOCO){η 1-SC(NMe2)2}] (2) in 10% yield in which the tetramethylthiourea ligand is coordinatedvia the sulfur atom at an equatorial position. Compound2 is a 50 e? cluster with two metal-metal bonds and the hydroxy and methoxycarbonyl ligands bridging the open metal-metal edge. In contrast, the analogous reaction of [Os3(CO)12] with thiourea gives the compounts [(μ-H)Os3(CO)10{μ-NHC(S)NH2}] (3) in 8% yield and [(μ-H)Os3(CO)9{3-NHC(S)NH2}] (4) in 30% yield. In3, the thioureato ligand bridges two osmium atomsvia the sulfur atom, whereas in4 in addition to the sulfur bridge, one of the nitrogen atoms of thioureato moiety bonds to the remaining osmium atom. The decacarbonyl compounds 3 can also be obtained in 50% yield from the reaction of [Os3(CO)10(MeCN)2] with thiourea at ambient temperature. Compound3 converts to4 (65%) photochemically. Compound1 reacts with PPh3 and acetonitrile at ambient temperature to give the simple substitution products [Os3(CO)11(PPh3)] and [Os3(CO)11(MeCN)], respectively, while with pyridine, the oxidative addition product [(μ-H)Os3(CO)10(μ-NC5H4] is formed at 80°C. All the new compounds are characterized by IR,1-H-NMR and elemental analysis together with the X-ray crystal structures of1,2 and4. Compound1 crystallizes in the triclinic space group P $P\bar 1$ with unit cell parametersa = 8.626(3) Å,b = 11.639(3) Å,c = 12.568(3_ Å,α = 84.67(2)°,β = 75.36(2)°,γ = 79.49(3)°,V = 1199(1) Å3, andZ = 2. Least-squares refinement of 4585 reflections gave a final agreement factor ofR = 0.0766 (R w = 0.0823). Compound2 crystallizes in the monoclinic space group P21/n with unit cell parametersa = 9.149(5) Å,b = 17.483(5) Å,c = 15.094(4) Å,β = 91.75(2)°,V = 2413(2) Å3, andZ = 4. Least-squares refinement of 3632 reflections gave a final agreement factor ofR = 0.0603 (R w = 0.0802). Compound4 crystallizes in the monoclinic space group C2/c with unit cell parametersa = 13.915(7) Å,b = 14.718(6) Å,c = 17.109(6) Å,β = 100.44(3)°,V = 3446(5) Å3, andZ = 8. Least-squares refinement of 2910 reflections gave a final agreement factor ofR = 0.0763 (R w = 0.0863). 相似文献
65.
M. S. Rahman M. Parre?o R. Bossi A. B. Payá-Pérez B. Larsen 《Fresenius' Journal of Analytical Chemistry》1998,360(5):556-563
Six extraction methods for the analysis of PCBs (CB-28, CB-52, CB-101, CB-118, CB-138, CB-153 and CB-180) in sewage sludge
were tested. A certified reference material (CRM 392) was used for the evaluation of the performance of the methods. Soxhlet-Dean-Starch
with toluene as solvent, Soxhlet with hexane:acetone (2:3), cold digestion/saponification with 2 mol/L KOH in methanol followed
by partition with hexane, and sonicated liquid-solid extraction with hexane:acetone (1:1) produced accurate results (97%,
93%, 104%, and 88%, respectively) with acceptable precisions (6.2%, 6.8%, 15% and 12%, respectively). Results in close agreement
with the certified value for all congeners were obtained by treatment with BF3-methanol prior to partition with dichloromethane. However, this is a tedious procedure and involves the use of hazardous
compounds. Cyclic steam distillation produced results with an accuracy of around 80% and a good precision (5.2%). The very
low consumption of solvents and other expensive chemicals by this technique and the possibility of analyzing the extract directly
without clean-up make it an interesting alternative to the more sophisticated methods. Column elution with dichloromethane
was found to be less efficient (61%), but it is a rapid, direct method with a low consumption of solvents and it may therefore
serve as screening method.
Received: 29 April 1997 / Revised: 30 July 1997 / Accepted: 6 August 1997 相似文献
66.
A. M. Yusof M. M. Rahman A. K. H. Wood 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):191-197
A simple and sensitive method for the determination of some metalloids and heavy metals in water samples is presented. The
method is based on the preconcentration of the attachment of chelating functionalities with metalloids and toxic metals irreversibly
and targeted towards toxic metals adsorbed on modified activated carbon, activated carbon and red soil particles at pH 3.0–9.0±0.2,
followed by quantitative determination using instrumental neutron activation analysis (INAA), on the absorbers. Attachment
results from attraction that may be physical, chemical, electrical, or a combination of all three. The efficient removal of
metalloids and toxic metals, especially arsenic, chromium and mercury is anticipated. The adsorption capacity of the chemically
modified activated carbon materials was evaluated for the above mentioned metalloid and toxic metal ions in the presence of
iron ions and simulated water samples. Red soil particles containing iron was utilized in the control of oxidation-reduction
reaction with metalloids and toxic metals. The preconcentration of the elements of interest on red soil particles, activated
carbon and modified activated carbon at different depths, pH and oxidation states was investigated. The results obtained showed
good agreement with certified values giving relative errors of less than 10%. 相似文献
67.
A. Jeyabharathi M. N. Ponnuswamy S. Nanjundan Hoong‐Kun Fun Suchada Chantrapromma Anwar Usman Ibrahim Abdul Razak 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):o26-o28
Chalcones (α,β‐unsaturated ketones) are effective antitumour agents. It has been proved that having halogen or methoxy groups substituted in various positions of the phenyl ring enhances the activity of chalcones many times. The title compounds, C21H20O5 and C19H15BrO3, respectively, were chosen for crystallographic study in order to determine their structures and conformations. In both compounds, the keto group is in the s‐cis conformation and is almost planar. There are weak intramolecular interactions in both structures. 相似文献
68.
Regio- and stereoselectivities in cycloadditions of nitrones to dipolarophiles bearing an allylic oxygen, which furnishes substituted-isoxazolidine analogs of the furanose ring of nucleosides, have been investigated. Although the obtained regioselectivities are anticipated, a rationalization of the preferred formation of endo-cycloadducts necessitates the involvement of an allylic oxygen in secondary interaction. The obtained isoxazolidines display cytotoxic activities against a number of human cancer cell lines. 相似文献
69.
M.T. Rahman 《Journal of organometallic chemistry》1982,225(1):25-30
The reaction of pentachlorobenzene with metallic magnesium in THF at 10–15°C gives after hydrolysis 1, 2, 4, 5-tetrachlorobenzene (76%) and pentachlorobenzene (8%); after trimethylsilylation, 1, 2, 4, 5-tetrachloro-3-(trimethylsilyl)benzene (74%), pentachloro(trimethylsilyl)benzene (8%) and 1, 2, 4, 5-tetrachlorobenzene (6%); after iodination, 1, 2, 4, 5-tetrachloroiodobenzene (44%), pentachloroiodobenzene (12%) and 1, 2, 4, 5-tetrachlorobenzene (9%); and finally after carbonation, 2, 3, 5, 6-tetrachlorobenzoic acid (58%). These products indicate that in the Grignard reaction a mixture of largely 2, 3, 5, 6-tetrachlorophenylmagnesium chloride and some pentachlorophenylmagnesium chloride is formed. The formation pentachlorophenylmagnesium chloride is explained on the basis of metal—hydrogen exchange reaction between 2, 3, 5, 6-tetrachlorophenylmagnesium chloride and the unreacted pentachlorobenzene. 相似文献
70.