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Treatment of 1,2-di(thien-2-yl)ethanone with aqueous 75% (v/v) sulfuric acid gives a dimer in which the units are linked head-to-head via a thiophene-tetrahydrothiophene bond. 相似文献
187.
Philip Dimitrov Pradeep Iyer Marcel Van Beylen Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2009,47(8):2198-2206
The anionic polymerization of butadiene initiated with 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane (LiTPB) in diethyl ether (DEE) gives polybutadiene (PBD) with high 1,2 content (>70%), narrow polydispersities (1.04 < Mw/Mn < 1.20), and predicted molecular weights. In THF, this polymerization does not work very well. After removal of DEE and addition of THF, the PBD dianion is end capped quantitatively by addition of 1,1‐diphenylethylene (DPE) to give the diphenylalkyl end capped PBD dianion. Subsequent addition of methyl methacrylate at low temperatures results in the formation of well‐defined PMMA‐b‐PBD‐b‐PMMA triblock copolymers. The results are accounted for by taking into account the effects of Li ion solvation on the BD initiation and end capping of the PBD anion by DPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2198–2206, 2009 相似文献
188.
Bernd Eschgfller JürgenG. Schmidt Marcel Knig StevenA. Benner 《Helvetica chimica acta》2003,86(9):2959-2997
A convergent, solution‐phase synthesis was developed for the bis(methylene) sulfone‐bridged oligodeoxynucleotide analogs (SNA) 5′‐d(HOCH2‐Tso 2Tso 2Tso 2Cso 2Tso 2Tso 2Tso 2T‐CH2SO )‐3′ ( 35b ) and 5′‐d(HOCH2‐Tso 2Tso 2Tso 2Tso 2Tso 2Tso 2Tso 2T‐CH2SO )‐3′ ( 34c ) (SO2 corresponds to CH2SO2CH2 instead of OP(?O)(O?)(O). In these, the phosphodiester linkages are replaced by non‐ionic bis(methylene) sulfone linkers. The general strategy involved convergent coupling of 3′,5′‐bishomo‐β‐D ‐deoxyribonucleotide analogs functionalized at the 6′‐end (?CH2? C(5′)) as bromides or mesylates and at the CH2? C(3′) position as thiols, with the resulting thioether being oxidized to the corresponding sulfone. A single charge was introduced at the terminal CH2? C(3′) position of the octamers to increase their solubility in water. During the synthesis, it became apparent that the key intermediates generated secondary structures through either folding or aggregation in a variety of solvents. This generated unusual reactivity and was unique for very similar structures. For example, although the dimeric thiol d(BzOCH2‐Tso 2C‐CH2SH) ( 14b ) was a well‐behaved synthetic intermediate, the tetrameric thiol d(TrOCH2‐Tso 2Tso 2Tso 2toC‐CH2SH) derived from the corresponding thioacetate was rapidly converted to a disulfide by very small amounts of oxidant ( 28 → 29 , Scheme 6), while the analogous tetrameric thiol d(BzOCH2‐Tso 2Ts Tso 2T‐CH2SH) ( 26 ), differing only by a single heterocycle, was oxidized much more slowly (Bz=PhCO, Tr=Ph3C, to=2‐MeC6H4CO (at N4 of dc)). The sequence‐dependent reactivity, well known in many classes of natural products (including polypeptides), is not prominent in natural oligonucleotides. These results are discussed in light of the proposal that the repeating negative charge in nucleic acids is key to their ability to serve as genetic molecules, in particular, their capability to support Darwinian evolution. The ability of 5′‐d(HOCH2‐Tso 2Tso 2Tso 2Cso 2Tso 2Tso 2Tso 2T‐CH2SO )‐3′ ( 35b ) to bind as a third strand to duplex DNA was also examined. No triple‐helix‐forming propensity was detected in this molecule. 相似文献
189.
Marcel Miglierini Július Dekan Danica Staššíková-Štukovská 《Hyperfine Interactions》2005,166(1-4):651-655
An ancient axe from Early Medieval Age which was unearthed on a territory of the archaeological excavation site near the village Borovce (Slovakia) is investigated. The surface of the axe was supposed to be covered with a sort of glassy system. Mössbauer effect measurements performed in backscattering and transmission geometry upon original as well as powdered pieces of the axe confirmed that the surface layers of the axe consist of goethite, lepidocrite, akageneite, and/or magnetite. After temperature treatment at 400°C/100 min hematite and maghemite were found; these are products of thermal decomposition of the above mentioned iron phases. These findings ruled out the hypothesis that the surface covering substance was put on the axe by intention. 相似文献
190.
Werner Seebacher Marcel Kaiser Reto Brun Robert Saf Robert Weis 《Monatshefte für Chemie / Chemical Monthly》2007,138(7):709-714
Summary. We synthesized several 4-aminobicyclo[2.2.2] octan-2-ols and 4-amino-2-azabicyclo[3.2.2]nonanes from epimerized 4-amino-bicyclo[2.2.2]octan-2-ones.
The new compounds were tested for their activity against Trypanosoma b. rhodesiense, the causative organism of East African sleeping sickness, and Plasmodium falciparum K
1, a multiresistant protozoan parasite which causes Malaria tropica. The results are compared to the activities of their formerly
synthesized stereoisomers and structure–activity relationships are discussed. 相似文献