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251.
Faggi E Sebastián RM Pleixats R Vallribera A Shafir A Rodríguez-Gimeno A Ramírez de Arellano C 《Journal of the American Chemical Society》2010,132(51):17980-17982
Direct oxidative Kita-type coupling between naphthalene and substituted benzenes was found to proceed via four-component coupling, leading to a linear tetraarene with a binaphthalene core. The methodology was extendable to the coupling of unfunctionalized 1,1'-binaphthalene with mesitylene to give a linear hexaarene product in a remarkably chemoselective manner in 87% yield. The method represents an attractive alternative to the traditional syntheses of related oligonaphthalene products via a sequence of metal-catalyzed cross-coupling steps. 相似文献
252.
Identification and specificity profiling of protein prenyltransferase inhibitors using new fluorescent phosphoisoprenoids 总被引:4,自引:0,他引:4
Dursina B Reents R Delon C Wu Y Kulharia M Thutewohl M Veligodsky A Kalinin A Evstifeev V Ciobanu D Szedlacsek SE Waldmann H Goody RS Alexandrov K 《Journal of the American Chemical Society》2006,128(9):2822-2835
Posttranslational modification of proteins with farnesyl and geranylgeranyl isoprenoids is a widespread phenomenon in eukaryotic organisms. Isoprenylation is conferred by three protein prenyltransferases: farnesyl transferase (FTase), geranylgeranyl transferase type-I (GGTase-I), and Rab geranylgeranyltransferase (RabGGTase). Inhibitors of these enzymes have emerged as promising therapeutic compounds for treatment of cancer, viral and parasite originated diseases, as well as osteoporosis. However, no generic nonradioactive protein prenyltransferase assay has been reported to date, complicating identification of enzyme-specific inhibitors. We have addressed this issue by developing two fluorescent analogues of farnesyl and geranylgeranyl pyrophosphates {3,7-dimethyl-8-(7-nitro-benzo[1,2,5]oxadiazol-4-ylamino)-octa-2,6-diene-1}pyrophosphate (NBD-GPP) and {3,7,11-trimethyl-12-(7-nitro-benzo[1,2,5]oxadiazo-4-ylamino)-dodeca-2,6,10-trien-1} pyrophosphate (NBD-FPP), respectively. We demonstrate that these compounds can serve as efficient lipid donors for prenyltransferases. Using these fluorescent lipids, we have developed two simple (SDS-PAGE and bead-based) in vitro prenylation assays applicable to all prenyltransferases. Using the SDS-PAGE assay, we found that, in contrast to previous reports, the tyrosine phosphatase PRL-3 may possibly be a dual substrate for both FTase and GGTase-I. The on-bead prenylation assay was used to identify prenyltransferase inhibitors that displayed nanomolar affinity for RabGGTase and FTase. Detailed analysis of the two inhibitors revealed a complex inhibition mechanism in which their association with the peptide binding site of the enzyme reduces the enzyme's affinity for lipid and peptide substrates without competing directly with their binding. Finally, we demonstrate that the developed fluorescent isoprenoids can directly and efficiently penetrate into mammalian cells and be incorporated in vivo into small GTPases. 相似文献
253.
Through the use of cyclic beta-diketones as supporting ligands, the copper-catalyzed coupling of aryl iodides with aliphatic amines occurs at room temperature in as little as 1 h. These high reaction rates allow for the coupling of a wide range of aryl and heteroaryl iodides at room temperature. This method is highly tolerant of a number of reactive functional groups, including -Br and aromatic -NH2 as well as phenolic and aliphatic -OH. The high selectivity of the CuI-beta-diketone catalyst for aliphatic amines represents a useful complement to the palladium-based methods. 相似文献
254.
255.
For a graph G, let ${\sigma_2(G)=\min\{d(u)+d(v):uv\notin E(G)\}}$ . We prove that every n-vertex graph G with σ 2(G)?≥ 4n/3 ? 1 contains each 2-regular n-vertex graph. This extends a theorem due to Aigner and Brandt and to Alon and Fisher. 相似文献
256.
Henry A. Kierstead Alexandr V. Kostochka Marcelo Mydlarz Endre Szemerédi 《Combinatorica》2010,30(2):217-224
A proper vertex coloring of a graph is equitable if the sizes of color classes differ by at most one. The celebrated Hajnal-Szemerédi Theorem states: For every positive integer
r, every graph with maximum degree at most r has an equitable coloring with r+1 colors. We show that this coloring can be obtained in O(rn
2) time, where n is the number of vertices. 相似文献
257.
Talyzin AV Tsybin YO Purcell JM Schaub TM Shulga YM Noréus D Sato T Dzwilewski A Sundqvist B Marshall AG 《The journal of physical chemistry. A》2006,110(27):8528-8534
Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C(60)H(x) (x > 36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation pathways are discussed. 相似文献
258.
Ivana Víov Barbora Smolkov Mariia Uzhytchak Markta Vrabcov Yulia Zhigunova Milan Houska Frantiek Surman Andres de los Santos Pereira Oleg Lunov Alexandr Dejneka Hana Vaisocherov‐Lísalov 《Macromolecular bioscience》2020,20(3)
Ultra‐low fouling and functionalizable coatings represent emerging surface platforms for various analytical and biomedical applications such as those involving examination of cellular interactions in their native environments. Ultra‐low fouling surface platforms as advanced interfaces enabling modulation of behavior of living cells via tuning surface physicochemical properties are presented and studied. The state‐of‐art ultra‐low fouling surface‐grafted polymer brushes of zwitterionic poly(carboxybetaine acrylamide), nonionic poly(N‐(2‐hydroxypropyl)methacrylamide), and random copolymers of carboxybetaine methacrylamide (CBMAA) and HPMAA [p(CBMAA‐co‐HPMAA)] with tunable molar contents of CBMAA and HPMAA are employed. Using a model Huh7 cell line, a systematic study of surface wettability, swelling, and charge effects on the cell growth, shape, and cytoskeleton distribution is performed. This study reveals that ultra‐low fouling interfaces with a high content of zwitterionic moieties (>65 mol%) modulate cell behavior in a distinctly different way compared to coatings with a high content of nonionic HPMAA. These differences are attributed mostly to the surface hydration capabilities. The results demonstrate a high potential of carboxybetaine‐rich ultra‐low fouling surfaces with high hydration capabilities and minimum background signal interferences to create next‐generation bioresponsive interfaces for advanced studies of living objects. 相似文献
259.
Leonid Mochalov Aleksey Nezhdanov Mikhail Kudryashov Alexandr Logunov Askold Strikovskiy Mikhail Gushchin Giuseppe Chidichimo Giovanni De Filpo Aleksandr Mashin 《Plasma Chemistry and Plasma Processing》2017,37(5):1417-1429
First time the method of plasma-enhanced chemical vapor deposition was used for preparation of As–Te chalcogenide films of different chemical and phase composition. The samples were synthesized via direct interaction of arsenic and tellurium vapors into low-temperature non-equilibrium RF (40 MHz) plasma discharge at reduced pressure (0.1 Torr). The plasma parameters such as temperature and concentration of electrons were measured by moving double probe diagnostic system. The dependence of solid phase radial distribution on plasma characteristics was established. Besides, the phase and structural evolution of As–Te films based on equilibrium coexistence of two phases (AsTe and As2Te3) and implemented by changing of the ratio of the initial substances in gas phase has been studied and discussed. 相似文献
260.