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991.
Brian B. Frank Berta Camafort Blanco Samuel Jakob Fiammetta Ferroni Silvia Pieraccini Dr. Alberta Ferrarini Prof. Dr. Corinne Boudon Prof. Dr. Jean‐Paul Gisselbrecht Dr. Paul Seiler Gian Piero Spada Prof. Dr. François Diederich Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):9005-9016
Axially chiral, N‐arylated 3,5‐dihydro‐4H‐dinaphtho[2,1‐c:1′,2′‐e]azepines have been prepared by short synthetic protocols from enantiopure 1,1′‐bi(2,2′‐naphthol) (BINOL) and anilines. Alkynes substituted with two N‐phenyldinaphthazepine donors readily undergo a formal [2+2] cycloaddition, followed by retro‐electrocyclization, with tetracyanoethene (TCNE) to yield donor‐substituted 1,1,4,4‐tetracyanobuta‐1,3‐dienes (TCBDs) featuring intense intramolecular charge‐transfer (CT) interactions. A dicyanovinyl derivative substituted with one N‐phenyldinaphthazepine donor was obtained by a “one‐pot” oxidation/Knoevenagel condensation from the corresponding propargylic alcohol. Comparative electrochemical, X‐ray crystallographic, and UV/Vis studies show that the electron‐donor qualities of N‐phenyldinaphthazepine are similar to those of N,N‐dimethylanilino residues. The circular dichroism (CD) spectrum of a push–pull chromophore incorporating the chiral donor moiety features Cotton effects of exceptional intensity. With their elongated shape and the rigidity of the chiral N‐aryldinaphthazepine donors, these chromophores are effective inducers of twist distortion in nematic liquid crystals (LCs). Thus, a series of the dinaphthazepine derivatives was used as dopants in the nematic LC E7 (Merck) and high helical twisting powers (β) of the order of hundreds of μm?1 were measured. Theoretical calculations were employed to elucidate the relation between the structure of the dopants and their helical twisting power. For the derivatives with two dinaphthazepine moieties, a strong dependence of the β‐values on the structure and conformation of the linker between them was found. 相似文献
992.
Silvia Anthoine Dietrich Renate Lindauer Claire Stierlin Jürg Gertsch Dr. Ruth Matesanz Dr. Sara Notararigo José Fernando Díaz Dr. Karl‐Heinz Altmann Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10144-10157
A series of epothilone B and D analogues bearing isomeric quinoline or functionalized benzimidazole side chains has been prepared by chemical synthesis in a highly convergent manner. All analogues have been found to interact with the tubulin/microtubule system and to inhibit human cancer cell proliferation in vitro, albeit with different potencies (IC50 values between 1 and 150 nM ). The affinity of quinoline‐based epothilone B and D analogues for stabilized microtubules clearly depends on the position of the N‐atom in the quinoline system, while the induction of tubulin polymerization in vitro appears to be less sensitive to N‐positioning. The potent inhibition of human cancer cell growth by epothilone analogues bearing functionalized benzimidazole side chains suggests that these systems might be conjugated with tumor‐targeting moieties to form tumor‐targeted prodrugs. 相似文献
993.
994.
Release of dormancy and induction of seed germination are complex traits finely regulated by hormonal signals and environmental cues such as temperature and light. The Red (R):Far-Red (FR) phytochrome photoreceptors mediate light regulation of seed germination. We investigated the possible involvement of heterotrimeric G-protein complex in the phytochrome signaling pathways of Arabidopsis thaliana seed germination. Germination rates of null mutants of the alpha (Gα) and beta (Gβ) subunits of the G-protein (At gpa1-4 and agb1-2 , respectively) and the double mutant ( agb1-2/gpa1-4 ) are lower than the wildtype (WT) under continuous or pulsed light. The Gα and Gβ subunits play a role in seed germination under hourly pulses of R lower than 0.1 μmol m−2 s−1 whereas the Gβ subunit plays a role in higher R fluences. The germination of double mutants of G-protein subunits with phyA-211 and phyB-9 suggests that AtGPA1 seems to act as a positive regulator of phyA and probably phyB signaling pathways, while the role of AGB1 is ambiguous. The imbibition of seeds at 4°C and 35°C alters the R and FR light responsiveness of WT and G-protein mutants to a similar magnitude. Thus, Gα and Gβ subunits of the heterotrimeric G-protein complex modulate light induction of seed germination by phytochromes and are dispensable for the control of dormancy by low and high temperatures prior to irradiation. We discuss the possible indirect role of the G-protein complex on the phytochrome-regulated germination through hormonal signaling pathways. 相似文献
995.
996.
Jonathon E. Beves Edwin C. Constable Catherine E. Housecroft Markus Neuburger Silvia Schaffner Jennifer A. Zampese 《Helvetica chimica acta》2009,92(11):2214-2226
The syntheses of the five 2,2′: 6′,2″‐terpyridine (tpy) ligands 5 – 9 functionalized in the 4′‐position with a hydrazone substituent RR′C?N? NH (R=R′=Me; R=H, R′=4‐BrC6H4, 4‐O2NC6H4, 4‐MeOC6H4, or 3,5‐(MeO)2C6H3) are described. Protonation of the tpy domain of the ligands is facile. Solution behaviour has been studied by NMR and electronic spectroscopies. Representative structural data are presented for neutral and monoprotonated ligands, and illustrate that H‐bonding involving the formal amine NH unit is a dominant structural motif in all cases. 相似文献
997.
Ernst Pittenauer Günter Allmaier 《Journal of the American Society for Mass Spectrometry》2009,20(6):1037-1047
Triacylglycerols were analyzed as cationized species (Li+, Na+, K+) by high-energy CID at 20 keV collisions utilizing MALDI-TOF/RTOF mass spectrometry. Precursor ions, based on [M+Li]+-adduct ions exhibited incomplete fragmentation in the high and low m/z region whereas [M+K]+-adducts did not show useful fragmentation. Only sodiated precursor ions yielded product ion spectra with structurally diagnostic
product ions across the whole m/z range. The high m/z region of the CID spectra is dominated by abundant charge-remote fragmentation of the fatty acid substituents. In favorable
cases also positions of double bonds or of hydroxy groups of the fatty acid alkyl chains could be determined. A-type product
ions represent the end products of these charge-remote fragmentations. B- and C-type product ions yield the fatty acid composition
of individual triacylglycerol species based on loss of either one neutral fatty acid or one sodium carboxylate residue, respectively.
Product ions allowing fatty acid substituent positional determination were present in the low m/z range enabling identification of either the sn-1/sn-3 substituents (E-, F-, and G-type ions) or the sn-2 substituent (J-type ion). These findings were demonstrated with synthetic triacylglycerols and plant oils such as cocoa
butter, olive oil, and castor bean oil. Typical features of 20 keV CID spectra of sodiated triacylglycerols obtained by MALDI-TOF/RTOF
MS were an even distribution of product ions over the entire m/z range and a mass accuracy of ±0.1 to 0.2 u. One limitation of the application of this technique is mainly the insufficient
precursor ion gating after MS1 (gating window at 4 u) of species separated by 2 u. 相似文献
998.
Guo X Bruins AP Covey TR Trötzmüller M Lankmayr E 《Journal of the American Society for Mass Spectrometry》2009,20(1):105-111
Reduction of ionic chemical background noise based on selective gas-phase reactions with chosen neutral reagents has been
proven to be a very promising approach in liquid chromatography—mass spectrometry (LC-MS). In this study further investigations
on alternative reagents including the disulfides (dimethyl disulfide, diethyl disulfide, methyl propyl disulfide), dimethyl
trisulfide, ethylene oxide, and butadiene monoxide, for example, have been carried out. Tandem mass spectrometric studies
of ion/molecule reactions indicate that—besides dimethyl disulfide—ethylene oxide and butadiene monoxide also exhibit very
efficient reactions with background ions. Furthermore, it is confirmed that the reactions are very selective according to
the test with some analyte ions. In contrast to its rapid reactions with background ions, ethylene oxide does not react, or
reacts much less, with these analytes. Therefore, it can be used as an alternative reagent for noise reduction. Although reactions
of the other tested neutral reagents with background ions are evaluated, they are generally not suitable as reagents for this
purpose because of lack of reactivity or dramatic ion losses during reactions. 相似文献
999.
Paolo Ranzieri Dr. Alberto Girlando Prof. Silvia Tavazzi Prof. Marcello Campione Prof. Luisa Raimondo Dr. Ivano Bilotti Dr. Aldo Brillante Prof. Raffaele G. Della Valle Prof. Elisabetta Venuti Prof. 《Chemphyschem》2009,10(4):657-663
Two 4T: Low‐frequency micro‐Raman spectroscopy coupled with lattice dynamics calculations is an invaluable tool for investigating polymorphism in organic semiconductors. The Raman spectra of the low‐temperature (LT) and high‐temperature (HT) polymorphs of α‐quaterthiophene (4T) are presented and interpreted (see picture). Raman mapping is applied to investigate the phase purity.
1000.
Heinz Mustroph Dr. Knut Reiner Dr. Jürgen Mistol Dr. Steffen Ernst Dr. Dietmar Keil Lothar Hennig Dr. 《Chemphyschem》2009,10(5):835-840
Vibronic sub‐bands in the electronic absorption spectra of symmetrical cyanine dyes (see picture) are attributed to the symmetric C? C valence vibration of the polymethine chain in the excited state. The 3J(H,H) coupling constants in the polymethine chain can be used to characterize the bond localization within the chain in the ground state and thus to explain the intensity distribution of the sub‐bands.