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991.
Guan HP Ksebati MB Cheng YC Drach JC Kern ER Zemlicka J 《The Journal of organic chemistry》2000,65(5):1280-1290
Synthesis of spirocyclic analogues of 2'-deoxyadenosine and 2'-deoxyguanosine (12a-15a and 12b-15b) is described. Rhodium-catalyzed reaction of ethyl diazoacetate with methylenecyclopropane 19, obtained from 2-bromo-2-bromomethylcyclopropane 17 via debromination (16), reduction (18), and acetylation (19), gave a mixture of all four isomeric spiropentanes 20a-20d. Hydrolysis afforded hydroxy carboxylic acids 21a-21d. Acetylation of separated proximal + medial-syn isomers 21a + 21b and medial anti + distal isomers 21c + 21d furnished acetates 22a + 22b and 22c + 22d. Curtius rearrangement effected by diphenylphosphoryl azide in tert-butyl alcohol performed separately with mixtures 22a + 22b and 22c + 22d led to BOC-amino spiropentanes 23a + 23b and 23c + 23d. After deacetylation all isomers 24a-24d were separated and deprotected to give aminospiropentane hydrochlorides 25a-25d. Free bases were of limited stability. The heterocyclic moieties were introduced into individual isomers 25a-25d via 6-chloropurine derivatives 26a-26d or 30a-30d. Ammonolysis of 26a-26d furnished the adenine isomeric series 12a-15a, whereas guanine derivatives 12b-15b were obtained by hydrolysis of 30a-30d with formic acid. The isomeric assignments followed from IR spectra of BOC-aminospiropentanes 24a-24d and NMR spectra of 12a-15a including NOE and (H,H) COSY. The proximal and medial-syn isomers 12a and 12b were modest inhibitors of human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) in culture, whereas the medial-anti isomer 12c was a substrate for adenosine deaminase. The distal isomer 15b was an anti-EBV agent. The medial-syn phosphoralaninate 34 was an effective inhibitor of HCMV replication in vitro. It was also active against herpes simplex virus type 1 (HSV-1), varicella zoster virus (VZV), human immunodeficiency virus (HIV-1), hepatitis B virus (HBV), and EBV with a varying degree of cytotoxicity. 相似文献
992.
We report a systematic study for metal-on-metal surface migration in the weak corrugation regime, i.e., with migration barriers falling below approximately 100 meV. The migration characteristics are elucidated by variable-temperature scanning tunneling microscopy observations in the 50-200 K temperature range, which are analyzed by means of nucleation theory. The results demonstrate that, upon entering the weak corrugation regime, the dynamics of the systems are characterized by increasingly reduced effective preexponential factors, while Arrhenius behavior prevails. 相似文献
993.
João de Deus Marques 《Czechoslovak Mathematical Journal》2000,50(3):539-550
Let E be a real linear space. A vectorial inner product is a mapping from E×E into a real ordered vector space Y with the properties of a usual inner product. Here we consider Y to be a
-regular Yosida space, that is a Dedekind complete Yosida space such that
, where
is the set of all hypermaximal bands in Y. In Theorem 2.1.1 we assert that any
-regular Yosida space is Riesz isomorphic to the space B(A) of all bounded real-valued mappings on a certain set A. Next we prove Bessel Inequality and Parseval Identity for a vectorial inner product with range in the
-regular and norm complete Yosida algebra
. 相似文献
994.
F. Glatz J. Siefert P. Betz E. Bitterwolf A. Burkard F. Heidinger Th. Kern R. Lehmann S. Norbert H. Röpke 《Zeitschrift für Physik A Hadrons and Nuclei》1981,303(3):239-251
A search for high-spin states in28Si has been performed byn?y coincidence measurements in the25Mg(α,nγy) reaction atE α=14 and 15.5 MeV. Spin-parity assignments of the observed levels were obtained fromn?γ angular correlation and lifetime measurements atE α=14.5 MeV. Theγ-decay of the 9,164 keV level was investigated separately with the27Al(p, γ) reaction at theE p=2,160 and 2,312 keV resonances. Rotational bands withK π=3? (comprising levels atE x=6,879, 8,413, 10,188 and 12,204 keV),K π =5? (comprising levels atE x=9,702, 11,577 and 13,741 keV) andK π=0+ (comprising levels atE x=6,691, 7,381, 9,164 and 11,509 keV) were observed. The finding of the latter band supports the idea of coexisting oblate and prolate shapes in28Si. A level at 14,643 keV excitation energy has the properties of theI π=8+ member of the ground state band. There are additional positive-parity high-spin states which do not fit into rotational bands. All types of positive-parity states are well accounted for by shell model calculations. 相似文献
995.
Substituted glyoxals with protected ketogroup were obtained by reaction of α-chloro-α-(aryl- or alkyl-thio)ketones with sodium methylate in methanol. 相似文献
996.
Graham Hungerford Mário Rui Pereira João A. Ferreira Teresa M. R. Viseu Anabela F. Coelho M. Isabel C. Ferreira Klaus Suhling 《Journal of fluorescence》2002,12(3-4):397-417
The photophysical behavior of several probes incorporated in sol-gel–derived matrices (both monoliths and thin films) has been studied using steady-state and time-resolved fluorescence, along with fluorescence anisotropy to study the matrix structure and to elucidate probe-matrix interactions. The probes studied include laser and solvatochromic dyes along with porphyrins and phthalocyanines. It was found that spectral shifts, time-resolved decays, and quantum yields depend on the type of matrix and its preparation conditions combined with the drying time and the nature of retained solvent, which can be added to act as an anticracking agent. The differences between the results in the TiO2 matrix, where electron transfer is most probably present, and SiO2 are shown. 相似文献
997.
998.
João-Paulo Dias 《Annali di Matematica Pura ed Applicata》1972,92(1):263-322
Summary In this paper we study existence and regularity properties for a class of degenerate elliptic and parabolic nonlinear variational
problems.
Entrata in Redazione il 22 aprile 1971.
Boursier de la Fondation Calouste Gulbenkian (Portugal). 相似文献
Entrata in Redazione il 22 aprile 1971.
Boursier de la Fondation Calouste Gulbenkian (Portugal). 相似文献
999.
1000.
α-Ketoaldehydes with protected ketogroup 2 or protected aldehydrogroup 3 are obtained by reaction of thiophenol or methanol with α-chloro-α-(phenylthio)aldehydes 7. 相似文献