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41.
42.
Mang C Jakupovic S Schunk S Ambrosi HD Schwarz O Jakupovic J 《Journal of combinatorial chemistry》2006,8(2):268-274
The generation of a natural-product-based library starting from andrographolide is described. Utilizing andrographolide itself in parallel solution-phase synthesis leads to a 360-membered library. The initial transformation of the starting material via ozonolysis is followed by the conversion into a suitable template by introduction of a thiazole moiety. Subsequent decoration at two points of diversity yields the desired natural product derivatives. The selection of actually synthesized compounds is based on a virtually generated library and the assessment of its members with respect to physicochemical parameters, thus ensuring pharmacological relevance of the compounds. 相似文献
43.
We explore the spin-boson model in a special case, i.e., with zero local field. In contrast to previous studies, we find no possibility for quantum phase transition (QPT) happening between the localized and delocalized phases, and the behavior of the model can be fully characterized by the even or odd parity as well as the parity breaking, instead of the QPT, owned by the ground state of the system. The parity breaking mentioned in our case is completely different from the spontaneously broken symmetry relevant to the conventionally defined QPT in previous studies. Our analytical treatment about the eigensolution of the ground state of the model presents for the first time a rigorous proof of no- degeneracy for the ground state of the model, which is independent of the bath type, the degrees of freedom of the bath and the calculation precision. We argue that the QPT mentioned previously appears due to incorrect employment of the ground state of the model and/or unreasonable treatment of the infrared divergence existing in the spectral functions for Ohmic and sub-Ohmic dissipations. 相似文献
44.
The present article describes a capillary zone electrophoresis method which relies on a multilayered water-alkali solvent stacking with online ionization to enhance detection of mannose, arabinose, and their oligosaccharides, which are used as the migration profile standards but are also the distinctive structural components of lipoarabinomannan. Lipoarabinomannan is detected in patients having tuberculosis. The capillary electrophoresis method with ionization of the whole saccharides without degradation in alkaline solution inside the capillary is based on the structural deprotonation of the molecules under ultrahigh pH conditions. The validation of the capillary electrophoresis parameters revealed that the 15-fold electrolyte–water-injection plug allowed detection of one-third lower concentrations than detected without online concentration. For the first time, the better detectability was seen especially for highly polymerized, but otherwise poorly ionized, arabinooctaose. The applicability of the method for detecting whole large biological saccharide complexes was confirmed by the glycolipid lipoarabinomannan. For the first time also, the migration of the indestructible lipoarabinomannan was detected together with oligosaccharides used representing the capping units, namely mannose, mannobiose, and mannotriose. The myo-inositol-phosphate-lipid unit was seen to migrate separately from the arabinomannan, since it was hydrolyzed from one lipoarabinomannan product under alkaline conditions in capillary electrophoresis. 相似文献
45.
46.
In this study, 2,7-bi-(N-penothiazinyl)fluorenone was employed as photocatalyst (PC), ethyl α-bromophenylacetate (EBP) as atom transfer radical polymerization (ATRP) initiator, and photo-induced metal-free ATRP of methyl methacrylate (MMA) was performed at 25°C under blue light irradiation. PMMAs with well-defined architectures and precisely controlled chain lengths were synthsized. The kinetics results confirmed that molecular weights increased linearly with monomer consumption. The molecular weight distributions (Mw/Mn) of the resultant PMMA were narrow. The polymerization was activated and deactivated by periodic light control process. 1H nuclear magnetic resonance spectrometer (NMR) and gel permeation chromatography (GPC) were used to characterize the obtained PMMAs. The living characters of the polymerization system were further confirmed by chain extension of from the PMMA-Br macroinitiator. 相似文献
47.
A divergent synthesis of functionalized unsaturated delta-lactones 2, 3, 4, and 5 has been developed starting from the readily available alpha-alkenoyl-alpha-carboxyl ketene dithioacetals 1 in high to excellent yields under mild reaction conditions. Thus, 6-substituted 3-(1,3-dithiolan/dithian-2-ylidene)-3H-pyran-2(6H)-ones 2, obtained from a consecutive reduction with NaBH4 and acidic workup of 1 via a novel vinylogous Pummerer cyclization, can be further transformed into alpha-pyranones 3, 4, and 5 upon a sequential isomerization catalyzed by triethylamine (to give 3), followed by dethioacetalization (to give 4) or a formylation with Vilsmeier reagent (to give 5). 相似文献
48.
49.
F. Laue I. Böttcher M. Debowski A. Förster E. Grosse P. Koczoń B. Kohlmeyer M. Mang M. Menzel L. Naumann H. Oeschler F. Pühlhofer E. Schwab P. Senger Y. Shin J. Speer H. Ströbele C. Sturm G. Surówka F. Uhlig A. Wagner W. Waluś 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):397-410
Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies
of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann
distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating
nucleon M(π+)/<A
part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the
Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/ <A
part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/ <A
part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the
absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected.
Received: 10 December 1999 / Accepted: 14 November 2000 相似文献
50.
Based on the former studies, the time-dependent characteristics of the wave packets of a Paul-trapped ion are investigated explicitly in cylindrical coordinates by the method of function series expansion (HE). It is shown that the present work relates the quantum motion of a Paul-trapped ion to the orbit of the classical motion and presents a more clear physical picture than the former studies. 相似文献