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51.
M. S. Sakr A. A. El-Shazly M. M. Mostafa H. A. El-Sayed A. A. Mohamed 《Czechoslovak Journal of Physics》1988,38(11):1255-1259
Transient creep of Cd-2 wt. % Zn and Cd-17·4 wt. % Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa near the transformation temperature. The results of both compositions showed two transient deformation regions, the low temperature region (below 483 K) and the high temperature region (above 483 K). From the transient creep described by the equation
tr=Bt
n, where
tr andt are the transient creep strain and time. The parametersB andn were calculated. The parameterB was found to change with the applied stress from 0·3×10–4 to 3×10–4 and from 0·6×10–4 to 18×10–4 for Cd-2 wt. % Zn and Cd-17·4 wt. % Zn, respectively. The exponentn was found to change from 0·8 to 0·95 for both alloys. The parameterB was related to the steady state creep rate
through the equation
, the exponent was found to be 0·5 for Cd-2 wt. % Zn and 0·6 for the eutectic composition. The activation energies of transient creep in the vicinity of the transformation regions (above 483 K) were found to be 50·2 kJ/mole for Cd-2 wt. % Zn and 104·7 kJ/mole for the eutectic composition characterizing the mechanisms of grain boundary diffusion and volume diffusion in Cd, respectively. 相似文献
52.
53.
Abdel -Aziz M. Wahbi Mona M. Bedair Shereen M. Galal Mohamed H. Abdel-Hay Azza A. Gazy 《Mikrochimica acta》1993,111(1-3):83-91
A sensitive and rapid Spectrofluorimetric method for the determination of guanethidine sulphate, guanfacine hydrochloride, guanoclor sulphate and guanoxan sulphate in tablets and spiked human serum and urine samples is described. The method is based on the reaction of monosubstituted guanidino compounds in an aqueous potassium hydroxide solution with benzoin, in the presence of -mercaptoethanol and sodium sulphite. Highly fluorescent derivatives were obtained, with excitation and emission maximum wavelengths around 325 and 430 nm, respectively. In optimal reaction conditions, the linearity ranges were 0.04–0.28 g/ml, with relative standard deviations less than 2%. The method has been successfully applied to the determination of these drugs in tablets. The results are highly correlated with the B.P. method. Chloroform (or for guanoxan dichloromethane) was used to extract the drugs from serum and urine at basic pH, followed by the proposed fluorimetric method. The limit of detection is 0.02 g/ml for the selected drugs. 相似文献
54.
55.
56.
Unusual Formation and Structure of a O‐Sulfinato Zinc Complex Whereas the reaction between hydrotris[(N‐xylyl)‐thioimidazolyl]borato‐zinc perchlorate ([ L· Zn‐OClO3]) and ethanethiolate under an inert atmosphere leads to the thiolate complex [ L· Zn‐SC2H5], the same reaction in air produces the sulfinato complex [ L· Zn‐O‐S(O)‐C2H5] ( 1 ). 1 is the first fully characterized sulfinato‐zinc complex. Its structure determination has confirmed the unusual coordination of the sulfinato ligand via one of its oxygen atoms. 相似文献
57.
Loganin ( 1 ), loganic acid ( 2 ), and periclymenoside ( 3 ) have been isolated from Lonicera periclymenum L . The structure of the new compound 3 and the identity of the others have been determined by chemical transformations and interpretation of the spectral data. 相似文献
58.
Hassan Sedaira Kamal A. Idriss Elham Y. Hashem Mohamed M. Seleim Abu-Bakr El-Nady 《Journal of solution chemistry》1996,25(1):95-103
The solvation number and hydration constant of Th4+ in ethanol-water medium were determined at 25°C using UV-spectral and electrochemical measurements. A solvate formation equilibrium is demonstrated and characterized. Three molecules of ethanol (S) can bond to the metal cation with strengths comparable to that for H2O to form ThS3(H2O) 3 4+ Formation of thorium monochelate with lawsone (2-hydroxy-1,4-naphthoquinone) eliminates bonding with alcohol molecules. The dissociation constant of the chelating agentsKa and the formation contant of the monochelated metal ionsK f * that are essentially independent of the solution composition are evaluated. Hydration titrations involving thorium-lawsone monochelate are performed and the data obtained from the changes of pH with solvent composition are analyzed. The solution independent constant,sK f * for thorium-lawsone complex formation in mixed aqueous ethanol is given by $$log_s K_f * = vpK_a + log_s K_h - log[LH] - vpH + 3logv$$ where vpKa is the dissociation constant of the chelating agent LH in the solvent system of ν volume fraction of water andsKh is the solution-independent hydration constant of thorium (IV) in the solvent system. Log-values for the constantssKh,sK f * andsK a * are found to be 7.8±0.02, 11.38±0.04 and ?0.753, respectively. 相似文献
59.
Mohamed M.?KhalilEmail author Mohamed?Taha 《Monatshefte für Chemie / Chemical Monthly》2004,135(4):385-395
Summary. The formation equilibria for the binary complexes of CoII, NiII, CuII, ZnII, CdII, MnII, PbII, ThIV, UO2II, and CeIII with tricine and for the ternary complexes involving some -amino acids (glycine, -alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, -alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1moldm–3 NaNO3). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of log K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system MII-tricine--alanine (MII=CoII, NiII, and CuII) has been studied. The thermodynamic parameters were calculated and discussed. 相似文献
60.
Bahja Mahmoud 《Tetrahedron letters》2007,48(29):5091-5094
Cross-conjugated 1,4-pentadien-3-ones undergo electrocyclization to 2-oxidocyclopentenyl cations upon treatment with BF3·OEt2. When these reactions are carried out in the presence of electron-rich vinyl sulfides, nucleophilic trapping followed by ring-closure furnishes bridged bicyclic products that can be viewed as formal 3+2 cycloadducts. This process results in three new carbon-carbon bonds and establishes up to five new stereocenters. 相似文献