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991.
Philip Crews Xing-Chung Cheng Madeline Adamczeski Jaime Rodríguez Marcel Jaspars Francis J. Schmitz Sarah C. Traeger Evamarie O. Pordesimo 《Tetrahedron》1994,50(48):13567-13574
The isolation and characterization of two new sponge alkaloids, 1,2,3,4-tetrahydro-2-N-methyl-8-hydroxymanzamine A (2) and 1,2,3,4-tetrahydro-8-hydroxymanzamine A (3), is described. These compounds were obtained from Papua New Guinea sponges of the genera Petrosia and Cribochalina, which are in different families of the order Haplosclerida. These new manzamines are close in structure to 8-hydroxymanzamine (4) recently reported from Pachypellina, a Haplosclerid sponge belonging to a different family than that of the two preceding sponges. The cytotoxicity of 2 is described and the biogenetic relationship of 2 or 3 to manzamine A (1) and to nine other related polycyclic diamine and one monoamine type alkaloids is described. 相似文献
992.
David T. Connor Roderick J. Sorenson Francis J. Tinney Wiaczeslaw A. Cetenko Joseph J. Kerbleski 《Journal of heterocyclic chemistry》1982,19(5):1185-1188
A general synthesis of 10-Oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidines and 10-Oxo-10H-pyrido[1,2-a]-thieno[3,2-d]pyrimidines is described. Methyl tetrahydro-4-oxo-3-thiophenecarboxylate ( 13 ) was condensed with 6-aminonicotinic acid ( 18 ) to give 3,10-dihydro-10-oxo-1H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 19 ). Treatment of 19 successively with chlorotrimethylsilane, N-chlorosuccinimide and water gave 10-oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 17 ). Methyl tetrahydro-3-oxo-2-thiophenecarboxylate ( 21 ) was converted to 10-oxo-10H-pyrido[1,2-a]thieno[3,2-d]pyrimidine-7-carboxylic acid ( 25 ) by an analogous route. 相似文献
993.
Laurence Duvieubourg Francis Abraham Stéphane Grandjean 《Journal of solid state chemistry》2005,178(11):3437-3444
Two modifications of the new uranyl oxalate hydroxide dihydrate [UO2)2(C2O4)(OH)2(H2O)2] (1 and 2) and one form of the new uranyl oxalate hydroxide trihydrate [(UO2)2(C2O4)(OH)2(H2O)2]·H2O (3) were synthesized by hydrothermal methods and their structures determined from single-crystal X-ray diffraction data. The crystal structures were refined by full-matrix least-squares methods to agreement indices R(wR)=0.0372(0.0842) and 0.0267(0.0671) calculated for 1096 and 1167 unique observed reflections (I>2σ(I)), for α (1) and β (2) forms, respectively and to R(wR)=0.0301(0.0737) calculated for 2471 unique observed reflections (I>2σ(I)), for 3. The α-form of the dihydrate is triclinic, space group , Z=1, a=6.097(2), b=5.548(2), , α=89.353(5), β=94.387(5), γ=97.646(5)°, , β-form is monoclinic, space group C2/c, Z=4, a=12.180(3), b=8.223(2), , β=95.817(4), . The trihydrate is monoclinic, space group P21/c, Z=4, a=5.5095(12), b=15.195(3), , β=93.927(3), . In the three structures, the coordination of uranium atom is a pentagonal bipyramid composed of dioxo UO22+ cation perpendicular to five equatorial oxygen atoms belonging to one bidentate oxalate ion, one water molecule and two hydroxyl ions in trans configuration in 2 and in cis configuration in 1 and 3. The UO7 polyhedra are linked through hydroxyl oxygen atoms to form different structural building units, dimers [U2O10] obtained by edge-sharing in 1, chains [UO6]∞ and tetramers [U4O26] built by corner-sharing in 2 and 3, respectively. These units are further connected by oxalate entities that act as bis-bidentate to form one-dimensional chains in 1 and bi-dimensional network in 2 and 3. These chains or layers are connected in frameworks by hydrogen-bond arrays. 相似文献
994.
Fathy A. Amer Linda P. Strand George W. Francis 《Journal of mass spectrometry : JMS》1977,12(9):557-561
The mass spectra of the title compounds, having various substituents on the aryl group are presented and discussed. High resolution mass measurements and metastable ions allow the fragmentation to be rationalized. The system is typified by the occurrence of intense molecular ions and of ions due to consecutive decomposition of the nitrogen-containing part of the molecule. Ions attributable to substituted, aniline-like fragments, and their decomposition products, are also abundant and may be used to identify the aryl group present. 相似文献
995.
Andrew A. Francis William L. Carrier James D. Regan 《Photochemistry and photobiology》1988,48(1):67-71
Abstract— Ultraviolet light causes a type of damage to the DNA of human cells that results in a DNA strand break upon subsequent irradiation with wavelengths around 300 nm. This DNA damage disappears from normal human fibroblasts within 5 h, but not from pyrimidine dimer excision repair deficient xeroderma pigmentosum group A cells or from excision proficient xeroderma pigmentosum variant cells. The apparent lack of repair of the ultraviolet light DNA damage described here may contribute to the cancer prone nature of xeroderma pigmentosum variant individuals. These experiments show that the same amount of damage was produced at 0° C and 37° C indicating a photodynamic effect and not an enzymatic reaction. The disappearance of the photosensitive lesions from the DNA is probably enzymatic since none of the damage was removed at 0° C. Both the formation of the lesion and its photolysis by near ultraviolet light were wavelength dependent. An action spectrum for the formation of photosensitive lesions was similar to that for the formation of pyrimidine dimers and(6–4) photoproducts and included wavelengths found in sunlight. The DNA containing the lesions was sensitive to wavelengths from 304 to 340 nm with a maximum at 313 to 317 nm. This wavelength dependence of photolysis is similar to the absorption and photolysis spectra of the pyrimidine(6–4) photoproducts 相似文献
996.
A new sesquiterpene alcohol, dactylol, having an uncommon bicyclo [6.3.0] undecane skeleton has been isolated from the sea hare Aplysia dactylomela. Chemical degradation and NMR studies using a shift reagent established the structure and relative stereochemistry. The absolute configuration was derived from ORD/CD data of a substituted cyclopentanone degradation product. 相似文献
997.
L. G. Chalmet R. L. Francis J. F. Lawrence 《Journal of Optimization Theory and Applications》1981,35(1):129-141
Define a design to be any planar setD of known areaa, but of unknown shape and location; more generally, a design can be any set inR
d
of measurea. For example, a design might be one floor of a warehouse, or a sports arena of known seating capacity. Suppose that the design has, say,m users, or evaluators, with user/evaluatori having a design disutility functionu
i
, 1im, which can be defined for all points in the plane independently of the designs of interest. Given any designD, denote byG
i
(D) the disutility ofD to user/evaluatori where, by definition,G
i
(D) is the supremum ofu
i
over the setD, 1im. LetG(D) be the vector with entriesG
i
(D), 1im, and define a design to be efficient if it solves the vector minimization problem obtained using the set of vectors {G(D):D a design}. Given mild assumptions about the disutility functions, and a slight refinement of the design definition to rule out certain pathologies, we present necessary and sufficient conditions for a design to be efficient, and study properties of efficient designs. In the final section, we extend the analysis to more generall
p
-measures of design disutility.This research was supported in part by the Interuniversity College for PhD studies in Management Sciences, Brussels, Belgium; by the Army Research Office, Triangle Park, North Carolina; by a National Academy of Sciences-National Research Council Postdoctorate Associateship; and by the Operations Research Division, National Bureau of Standards, Washington, DC. The authors would like to thank Dr. A. J. Goldman for his many constructive suggestions, and Dr. A. Veinott for suggesting the problems considered in Section 3. 相似文献
998.
Amy Lea Schumacher Jonathan P. Hill Katsuhiko Ariga Francis DSouza 《Electrochemistry communications》2007,9(12):2751-2754
The effect of anion binding on the oxidation potential of an anion receptor, N21,N23-dibenzyl-5,10,15,20-(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, 1 in o-dichlorobenzene is reported. The anion binding site of 1, at its inner pyrrolic amine hydrogens, is an integral part of the highly conjugated macrocycle, thus predicting larger potential shifts upon anion binding. Accordingly, cathodic shifts up to 600 mV are observed upon anion binding and such potential shifts correlate well with the anion binding constants. 相似文献
999.
Heterologous expression of a myxobacterial natural products assembly line in pseudomonads via red/ET recombineering 总被引:10,自引:0,他引:10
Natural products of microbial origin are widely used as pharmaceuticals and in agrochemistry. These compounds are often biosynthesized by multifunctional megasynthetases whose genetic engineering and heterologous expression offer considerable promise, especially if the natural hosts are genetically difficult to handle, slow growing, unculturable, or even unknown. We describe a straightforward strategy that combines the power of advanced DNA engineering (recombiogenic cloning) in Escherichia coli with the utility of pseudomonads as the heterologous host for the analysis and mutagenesis of known and unknown secondary metabolite pathways. The myxochromide S biosynthetic gene cluster from Stigmatella aurantiaca was rebuilt and engineered in E. coli to contain the elements required for expression in pseudomonads. The successful production in Pseudomonas putida, at unprecedented levels, demonstrates the feasibility of the new approach to the analysis and mutagenesis of these important pathways. 相似文献
1000.
The internal model principle for linear multivariable regulators 总被引:20,自引:0,他引:20
Necessary structural criteria are obtained for linear multivariable regulators which retain loop stability and output regulation in the presence of small perturbations, of specified types, in system parameters. It is shown that structural stability thus defined requires feedback of the regulated variable, together with a suitably reduplicated model, internal to the feedback loop, of the dynamic structure of the exogenous reference and disturbance signals which the regulator is required to process. Necessity of these structural features constitutes the internal model principle.This research was partially supported by the National Research Council of Canada, Grant No. A-7399. 相似文献