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排序方式: 共有236条查询结果,搜索用时 312 毫秒
181.
Abrams GS Adolphsen CE Averill D Ballam J Barish BC Barklow T Barnett BA Bartelt J Bethke S Blockus D Bonvicini G Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan DE Dorfan JM Drewer DC Elia R Feldman GJ Fernandes D Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Grindhammer G Grosse-Wiesmann P Hanson G Harr R Harral B Harris FA 《Physical review letters》1990,64(12):1334-1337
182.
Coffman D DeJongh F Dubois G Eigen G Hauser J Hitlin DG Matthews CG Mincer A Richman JD Wisniewski WJ Zhu Y Burchell M Dorfan DE Drinkard J Gatto C Hamilton RP Heusch CA Köpke L Lockman WS Partridge R Sadrozinski HF Scarlatella M Schalk TL Seiden A Weinstein AJ Weseler S Xu R Becker JJ Blaylock GT Eisenstein BI Freese T Gladding G Izen JM Plaetzer SA Simopoulos C Spadafora AL Stockdale IE Tripsas B Mallik U Roco M Wang MZ Adler J Bolton T Brient JC Bunnell KO Cassell RE Coward DH Einsweiler KF 《Physical review D: Particles and fields》1990,41(5):1410-1413
183.
Baltrusaitis RM Becker JJ Blaylock GT Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Dado S Del Papa C Dorfan DE Dubois GP Duncan AL Einsweiler KF Eisenstein BI Fabrizio R Gladding G Grancagnolo F Hamilton RP Hauser J Heusch CA Hitlin DG Koepke L Lockman WS Mockett PM Moss L Mozley RF Nappi A Odian A Partridge R Perrier J Plaetzer SA Richman JD Roehrig JR Russell JJ Sadrozinski HF Scarlatella M Schalk TL Schindler RH Seiden A Sleeman JC Spadafora AL Thaler JJ Toki W 《Physical review letters》1985,54(18):1976-1979
184.
Jacobsen RG Koetke DS Adolphsen CE Fujino D Schumm BA Wagner SR Alexander JP Averill D Barish BC Barklow T Barnett BA Blockus D Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan JM Drell PS Drewer DC Durrett D Elia R Feldman GJ Field RC Ford WT Fordham C Frey R Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Hanson G Harr R Harral B Harris FA Hayes K Hearty C Heusch CA 《Physical review letters》1991,67(24):3347-3350
185.
The conditions for the onset of thermal runaway in partiallyinsulated or cooled reactors are investigated. The temperaturein the reactor is taken to satisfy a nonlinear elliptic equationand the reaction is modelled by an Arrhenius heat generationterm with finite activation energy. To determine the onset ofthermal runaway, the method of matched asymptotic expansionsis used to derive expressions for the critical Frank-Kamenetskiiparameter c() for reactors containing either a small coolingrod or having a small cooling patch on their boundary. The theoryused to determine c() is an extension of the results of Wardand Keller (1991). These previous results of Ward and Kellerare also extended to the case of finite activation energiesby using a numerical scheme to evaluate the coefficients inthe asymptotic results for c(). In some special cases, the asymptoticexpansions for c() are compared with numerical results for c(),and clear agreement is found. 相似文献
186.
EDMUND W. PALASZYNSKI FRANCES P. NOONAN EDWARD C. DE FABO 《Photochemistry and photobiology》1992,55(2):165-171
It has been demonstrated that UVB radiation (290-320 nm) suppresses mammalian cell-mediated immunity by effecting the trans to cis isomerization of urocanic acid (UCA) in the stratum corneum, the uppermost layer of the skin. Trans-urocanic acid has been shown to be the photoreceptor for UVB-induced immune suppression and the cis-isomer has been demonstrated to be immunosuppressive. Little is known, however, about how the isomerization of UCA may affect the proximal or distal cells of the skin or the immune system. We report here that trans-UCA is biologically active in vitro in human dermal fibroblasts, inducing adenyl cyclase as measured by cAMP (adenosine 3',5'-cyclic monophosphate) formation in a dose-dependent manner similar to the action of histamine. Trans-UCA and histamine stimulate 50% of maximum activity at concentrations of 3.3 microM and 13.8 microM respectively. Cis-UCA does not increase cAMP in these human fibroblasts but actively down regulates the increase of cAMP induced by either histamine or trans-UCA. Cis-UCA down regulated the histamine response by 75% and the trans-UCA response by 60% at a concentration range of 1 mM to 1 nM. The trans-UCA induction of cAMP can also be downregulated with an H2 histamine receptor antagonist cimetidine. These results support the hypothesis that a cellular target for cis-UCA is the dermal fibroblast and the effects reported here may represent the initial biochemical and cellular event for UVB-induced immune suppression i.e. the immediate step following the isomerization of trans to cis-UCA is the down regulation of cAMP by cis-UCA. Regulation of such an important second messenger such as cAMP could then allow cascading signals to occur, leading to immune suppression. 相似文献
187.
Abstract –The peroxidative metabolism of TV-methylcarbazole emits light independently of the presence of oxygen. It is likely that two chemiexcited transients are formed by electron transfer to the activated peroxidase, the cation radical by one electron transfer and a cation biradical by two electron transfer consistent with the failure to observe horseradish peroxidase-II in the steady state of the reaction. In the spectral range investigated (390–700 nm) the observed emission (570–700 nm) is ascribed to the biradical, as the latter is equivalent to an excited state of the postulated iminium cation.
While lipoxygenase has no effect upon JV-methylcarbazole, it markedly enhances the emission if peroxidase is present. This effect requires oxygen and is ascribed to an excited product formed by lipoxygenase acting upon an intermediate hydroperoxide of the aerobic process promoted by peroxidase. 相似文献
While lipoxygenase has no effect upon JV-methylcarbazole, it markedly enhances the emission if peroxidase is present. This effect requires oxygen and is ascribed to an excited product formed by lipoxygenase acting upon an intermediate hydroperoxide of the aerobic process promoted by peroxidase. 相似文献
188.
Photocurrent spectra and photoluminescence measurements of the electrode covered by a thin film of chromium tetra-2,3-pyridinoporphyrazine by conventional 3-electrode system method have been performed. The cathodic photocurrent has been measured. The shape of the photocurrent spectrum is similar to that of photoluminescence spectrum. Their intensities change as a function of the applied potential. Two photoluminescence peaks are located at about 470 nm and 520 nm. The results indicate that the thin film behaves like a p-type semiconductor with a band gap width of about 2 eV. 相似文献
189.
MARICILDA P. DE MELLO ANA LUCIA T. O. NASCIMENTO Cornelia Bohne GIUSEPPE CILENTO 《Photochemistry and photobiology》1988,47(3):457-461
Abstract— Challenging Euglena gracilis —a unicellular microorganism that contains chloroplasts—with phenylacetaldehyde induces malondialdehyde formation, sustained red emission and Hill activity. In chloroplasts, phenylacetaldehyde appears to undergo peroxidase catalyzed oxidation to formic acid and triplet benzaldehyde; the latter or, less likely, a precursor thereof promotes lipid peroxidation. Triplet benzaldehyde and/or the excited species formed in lipid peroxidation transfer energy to the chlorophylls. This explanation also applies to spinach chloroplasts preparations, thus accounting for the previous unexplained observation that phenylacetaldehyde induced sustained red emission and Hill activity. A homogeneous picture is now available regarding the intracellular generation of excited states and concomitant excitation of built-in structures. 相似文献
190.
The geometries of acyclic and three-membered ring (nitroxide) H4C2NO radicals in their ground 2Π electronic states have been optimized completely at ab initio UHF and ROHF theoretical levels with the STO-3G and the 6-31G** basis sets. The optimizations favour the cyclic nitroxide
structure energetically. However ΔE(acyclic - cyclic) at the UHF and ROHF/6-31G** levels are only 3.2 and 1.9 kcal mol-1, respectively. Incomplete MP2/6-311G** optimizations support these results. The zero-point energy computed at the ROHF/6-31G**
level for the nitroxide radical is 2.5 kcal mol-1 higher than that for the acyclic structure, thus reversing the relative energies by 0.6 kcal mol-1. The energies of the two radical structures, relative to the sum of those for ethylene and NO, are very close to literature
values of the activation energies for the thermal, NO catalyzed geometrical isomerizations of olefins. Thus cyclic nitroxide
intermediates may play a role not only in the Hg 6(3P1) photosensitized, but also in the thermal, NO-catalyzed geometric isomerizations of olefins.
Paper dedicated to Professor Otto P. Strausz; presented in part at the 75th Canadian Chemical Congress and Exhibition, Edmonton,
May 31 – June 4, 1992. 相似文献