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191.
192.
Brands KM Payack JF Rosen JD Nelson TD Candelario A Huffman MA Zhao MM Li J Craig B Song ZJ Tschaen DM Hansen K Devine PN Pye PJ Rossen K Dormer PG Reamer RA Welch CJ Mathre DJ Tsou NN McNamara JM Reider PJ 《Journal of the American Chemical Society》2003,125(8):2129-2135
An efficient stereoselective synthesis of the orally active NK(1) receptor antagonist Aprepitant is described. A direct condensation of N-benzyl ethanolamine with glyoxylic acid yielded a 2-hydroxy-1,4-oxazin-3-one which was activated as the corresponding trifluoroacetate. A Lewis acid mediated coupling with enantiopure (R)-1-(3,5-bis(trifluoromethyl)phenyl)ethan-1-ol afforded a 1:1 mixture of acetal diastereomers which was converted into a single isomer via a novel crystallization-induced asymmetric transformation. The resulting 1,4-oxazin-3-one was converted via a unique and highly stereoselective one-pot process to the desired alpha-(fluorophenyl)morpholine derivative. Interesting and unexpected [1,2]-Wittig and [1,3]-sigmatropic rearrangements were identified during the optimization of these key steps. In the final step, a triazolinone side chain was appended to the morpholine core. The targeted clinical candidate was thus obtained in 55% overall yield over the longest linear sequence. 相似文献
193.
Martin L. Meltz Nancy Jo Whittam William H. Thornburg 《Photochemistry and photobiology》1978,27(5):545-550
Abstract— The DNA precursor 3 H-thymidine incorporation rate (dpm/pg DNA) in mouse L-929 cells decreases immediately after exposure to UV light. This decrease is initially dose dependent, but at exposures greater than 22.5 J/m2 appears to be radio-resistant. This was not explained by measurements of uptake of 3 H-thymidine into the acid soluble pool (dpm/pg DNA). The radio-resistant incorporation amounted to approximately 35% of the control rate. DNA reassociation ("C0 T") studies were performed with DNA labeled with 3 H-thymidine immediately after exposure of L-929 cells with a dose of UV resulting in radio-resistant incorporation to determine whether this radio-resistant incorporation was occurring in sequences of a particular repetitious frequency. These studies, performed in the highly repetitive to intermediate range, showed that the radio-resistant incorporation was occurring in DNA of all classes of repetitious frequency. DNA synthesized at different times after UV exposure, during the period when post-replication repair can occur, was similarly labeled for short intervals and isolated. The DNA reassociation studies showed that this DNA synthesis was also of all classes of repetitious frequency. 相似文献
194.
The microwave spectrum of isopropyl fluoroformate is characterized by intense a-type R-branch transitions from one conformational species. The rotational constants of the ground state, A0 = 4967.0(8) MHz, B0 = 1704.69(2) MHz, C0 = 1468.86(1) MHz and κ = −0.8651(2) are consistent with a τ1 (O=COC) = 0°, τ2(COCH) ˜35° structure. This structure can be viewed as a combination of the two conformational species found in ethyl fluoroformate. Two vibrational satellites having rotational constants A0 = 4963(5) MHz, B0 = 1694.11(7) MHz. C0 = 1471.43(4) MHz and A0=4998(6) MHz, B0 = 1705.21(7) MHz, C0 = 1471.10(4) MHz have been assigned. 相似文献
195.
An equation of state (EOS) for the NH3–H2O system has been developed. This EOS incorporates a highly accurate end-member EOS and on an empirical mixing rule. The mixing rule is based on an analogy with high order contributions to the virial expansion for mixtures. Comparison with experimental data indicates that the mixed system EOS can predict both phase equilibria and volumetric properties for this binary system with accuracy close to that of the experimental data from 50°C and 1 bar to critical temperatures and pressures. 相似文献
196.
The reaction of N, N-diethyl 4-(N', N'-dimethylamino)-2-phenylselenobenzamide (7a), N, N-diethyl 4-methoxy-2-phenylselenobenzamide (7b), N, N-diethyl 4-(N', N'-dimethylamino)-2-[(3-(N, N-dimethylamino)phenylseleno]benzamide (7c), and N, N-diethyl 4-methoxy-2-(3-methoxyphenylseleno)-benzamide (7d) with excess lithium diisopropylamide (LDA) gave 2-N, N-(dimethylamino)-9H-selenoxanthone (9a), 2-methoxy-9H-selenoxanthone (9b), 2,7-bis-N, N-(dimethylamino)-9H-selenoxanthone (9c), and 2,5-dimethoxy-9H-selenoxanthone (9d) in 70%, 59%, 23%, and 90% isolated yields, respectively. N, N-Diethyl 2-phenylselenobenzamide (2-Se) gave no reaction with LDA, t-BuLi, MeLi, or lithium 2,2,6,6-tetramethylpiperidide as base. Electron donation from the 4-substituent of benzamide derivatives 7a-7d may increase the directing ability of the carbonyl oxygen to metalate the 2-position of the arylseleno group. 相似文献
197.
A highly efficient, stereospecific synthesis of the epimeric pentenomycins is reported utilizing the stereospecific addition of OsO4 to substituted cyclopentenes. 相似文献
198.
Araujo E Rodríguez-Malave AJ González AM Rojas OJ Peñaloza N Bullón J Lara MA Dmitrieva N 《Applied biochemistry and biotechnology》2002,97(2):91-103
In this work, the effect of Fento’s reagent on the degradation of residual Kraft black liquor was investigated. The effect
of Fenton’s reagent on the black liquor degradation was dependent on the concentration of H2O2. At low concentrations (5 and 15 mM) of H2O2, Fenton’s reagent caused the degradation of phenolic groups (6.8 and 44.8%, respectively), the reduction of reaction medium
pH (18.2%), and the polymerization of black liquor lignin. At a high concentration (60 mM) of H2O2, Fenton’s reagent induced an extensive degradation of lignin (95–100%) and discoloration of the black liquor. In the presence
of traces of iron, the addition of H2O2 alone induced mainly lignin fragmentation. In conclusion, Fenton’s reagent and H2O2 alone can degrade residual Kraft black liquor under acidic conditions at room temperature. 相似文献
199.
Nancy Ghosh S Singh N Kaur Nanda G Venugopalan P Bharatam PV Trehan S 《Chemical communications (Cambridge, England)》2003,(12):1420-1421
The origin of diastereoselectivity in the addition of alkyl lithium to chiral Schiff bases has been investigated experimentally and theoretically and the formation of the major diastereomer can be explained from the energy minimized structure of the Schiff base in which the phenyl group has been found to orient in such a manner that it posed lesser steric hindrance to the incoming nucleophile as compared to the alkyl group. 相似文献
200.
Marc Van den Bulcke Antoon Lievens Elodie Barbau-Piednoir Guillaume MbongoloMbella Nancy Roosens Myriam Sneyers Amaya Leunda Casi 《Analytical and bioanalytical chemistry》2010,396(6):2113-2123
The detection of genetically modified (GM) materials in food and feed products is a complex multi-step analytical process invoking screening, identification, and often quantification of the genetically modified organisms (GMO) present in a sample. “Combinatory qPCR SYBR®Green screening” (CoSYPS) is a matrix-based approach for determining the presence of GM plant materials in products. The CoSYPS decision-support system (DSS) interprets the analytical results of SYBR®GREEN qPCR analysis based on four values: the C t- and T m values and the LOD and LOQ for each method. A theoretical explanation of the different concepts applied in CoSYPS analysis is given (GMO Universe, “Prime number tracing”, matrix/combinatory approach) and documented using the RoundUp Ready soy GTS40-3-2 as an example. By applying a limited set of SYBR®GREEN qPCR methods and through application of a newly developed “prime number”-based algorithm, the nature of subsets of corresponding GMO in a sample can be determined. Together, these analyses provide guidance for semi-quantitative estimation of GMO presence in a food and feed product. 相似文献