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991.
Y Li WK Heng BS Lee N Aratani JL Zafra N Bao R Lee YM Sung Z Sun KW Huang RD Webster JT López Navarrete D Kim A Osuka J Casado J Ding J Wu 《Journal of the American Chemical Society》2012,134(36):14913-14922
Polycyclic aromatic hydrocarbons with an open-shell singlet biradical ground state are of fundamental interest and have potential applications in materials science. However, the inherent high reactivity makes their synthesis and characterization very challenging. In this work, a convenient synthetic route was developed to synthesize two kinetically blocked heptazethrene (HZ-TIPS) and octazethrene (OZ-TIPS) compounds with good stability. Their ground-state electronic structures were systematically investigated by a combination of different experimental methods, including steady-state and transient absorption spectroscopy, variable temperature NMR, electron spin resonance (ESR), superconducting quantum interfering device (SQUID), FT Raman, and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functional theory (DFT) calculations. All these demonstrated that the heptazethrene derivative HZ-TIPS has a closed-shell ground state while its octazethrene analogue OZ-TIPS with a smaller energy gap exists as an open-shell singlet biradical with a large measured biradical character (y = 0.56). Large two-photon absorption (TPA) cross sections (σ((2))) were determined for HZ-TIPS (σ((2))(max) = 920 GM at 1250 nm) and OZ-TIPS (σ((2))(max) = 1200 GM at 1250 nm). In addition, HZ-TIPS and OZ-TIPS show a closely stacked 1D polymer chain in single crystals. 相似文献
992.
[2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane framework materials that utilise DB24C8 as the wheel component are well known and structural variations based on changing the axle component are common. Studies in which the DB24C8 wheel is structurally modified are much more limited. Herein, is described the synthesis of symmetrical DB24C8 analogues containing four CH(2)OR (R = CH(2)CH(2)CH(3), CH(2)(C(6)H(5)), C(6)H(5) and C(6)H(4)(4-COOEt)) substituents on the 4 and 5 positions of the aromatic rings. The effect of these molecular appendages on the stability and structures of the interpenetrated and interlocked molecules derived from these new wheels is described. The major effects are an increase in association constants for the formation of [2]pseudorotaxanes relative to DB24C8, the crystal packing of [2]rotaxanes and a change on the internal structure of a 2D MORF (R = C(6)H(5)) compared to DB24C8. 相似文献
993.
A single Cu(II) catalyst without the addition of ligand or base couples a diverse range of nitrogen sources with alkynes and aldehydes bearing alkyl, halogenated, silyl, aryl, and heteroaryl groups. The first example of a copper-catalyzed alkynylation involving p-toluenesulfonamide provides high yields of N-Ts-protected propargylamines. The superior activity of copper(II) triflate also allows this three-component alkynylation to incorporate a ketone. 相似文献
994.
The reaction of chiral N-arylnitrones with carbocyclic alkylarylketenes generates spirocyclic oxindoles in good yields and with excellent levels of enantioselectivity (90-99% ee) via a pericyclic cascade process. 相似文献
995.
996.
Siemeling U Memczak H Bruhn C Vogel F Träger F Baio JE Weidner T 《Dalton transactions (Cambridge, England : 2003)》2012,41(10):2986-2994
The zwitterionic dithiocarboxylates 1(+)-CS(2)(-)-4(+)-CS(2)(-) were prepared by reacting the corresponding N-heterocyclic carbenes 1,3-bis(2,6-diisoproylphenyl)imidazol-2-ylidene (1), 1,3-diisopropylimidazol-2-ylidene (2), 1,3-dibenzylimidazol-2-ylidene (3) and 1,3-diethylbenzimidazol-2-ylidene (4) with CS(2). In the latter two cases, the corresponding N-heterocylic carbene was generated in situ. Compounds 2(+)-CS(2)(-)-4(+)-CS(2)(-) were structurally characterised by single-crystal X-ray diffraction studies. The chemisorption of these zwitterionic dithiocarboxylates on solid gold substrates was investigated in situ and in real time by optical second harmonic generation (SHG). The resulting thin films were exemplarily characterised by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) in the case of 1(+)-CS(2)(-) and 2(+)-CS(2)(-), revealing the formation of almost contamination-free self-assembled monolayers, which exhibit a remarkable degree of orientational order. 相似文献
997.
Russell AD Gilroy JB Lam K Haddow MF Harvey JN Geiger WE Manners I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(26):8000-8003
Feeling the strain: The first example of metal-metal bonding between strained [n]metallocenophanes is reported. A dicarba[2]ruthenocenophanium dimer has been synthesised through the oxidation of a dicarba[2]ruthenocenophane (see figure). The structural and electrochemical characterisation of the dimer is also discussed. 相似文献
998.
Detwiler DA Dobes NC Sims CE Kornegay JN Allbritton NL 《Analytical and bioanalytical chemistry》2012,402(3):1083-1091
Despite identification of a large number of adult stem cell types, current primary cell isolation and identification techniques
yield heterogeneous samples, making detailed biological studies challenging. To identify subsets of isolated cells, technologies
capable of simultaneous cell culture and cloning are necessary. Micropallet arrays, a new cloning platform for adherent cell
types, hold great potential. However, the microstructures composing these arrays are fabricated from an epoxy photoresist
1002F, a growth surface unsuitable for many cell types. Optimization of the microstructures’ surface properties was conducted
for the culture of satellite cells, primary muscle cells for which improved cell isolation techniques are desired. A variety
of surface materials were screened for satellite cell adhesion and proliferation and compared to their optimal substrate,
gelatin-coated Petri dishes. A 1-μm thick, polystyrene copolymer was applied to the microstructures by contact printing. A
negatively charged copolymer of 5% acrylic acid in 95% styrene was found to be equivalent to the control Petri dishes for
cell adhesion and proliferation. Cells cultured on control dishes and optimal copolymer-coated surfaces maintained an undifferentiated
state and showed similar mRNA expression for two genes indicative of cell differentiation during a standard differentiation
protocol. Experiments using additional contact-printed layers of extracellular matrix proteins collagen and gelatin showed
no further improvements. This micropallet coating strategy is readily adaptable to optimize the array surface for other types
of primary cells. 相似文献
999.
Yu J Zvarec O Huang DM Bissett MA Scanlon DB Shapter JG Abell AD 《Chemical communications (Cambridge, England)》2012,48(8):1132-1134
The mechanism of electron transfer in α-aminoisobutyric (Aib) homoligomers is defined by the extent of secondary structure, rather than just chain length. Helical structures (Aib units ≥3) undergo an electron hopping mechanism, while shorter disordered sequences (Aib units <3) undergo an electron superexchange mechanism. 相似文献
1000.
B Bagh NC Breit JB Gilroy G Schatte J Müller 《Chemical communications (Cambridge, England)》2012,48(63):7823-7825
[1.1]Ferrocenophanes with gallium and silicon in bridging positions have been prepared in yields of 29 and 41%, respectively. From the same reactions, polymer-containing fractions were isolated (31% in each case) and shown to be comprised of linear and cyclic species with up to 16 ferrocene units (MALDI-TOF analysis). 相似文献