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排序方式: 共有1077条查询结果,搜索用时 31 毫秒
1.
Dominik Vítek Prof. Aleš Růžička Lise Vermeersch Dr. Libor Dostál Dr. Jan Turek Prof. Roman Jambor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202639
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed. 相似文献
2.
A path-integral molecular dynamics technique for strongly interacting atoms using ab initio potentials derived from density functional theory is implemented. This allows the efficient inclusion of nuclear quantum dispersion in ab initio simulations at finite temperatures. We present an application to the quantum cluster H
5
+
. 相似文献
3.
W. Ryba-Romanowski G. Dominiak-Dzik S. Golab W. A. Pisarski I. Pracka 《Journal of Applied Spectroscopy》1995,62(5):903-909
Conclusions Nonradiative energy transfer between similar and different rare-earth ions in LiNbO3 has been evidenced for the first time. The contribution of nonradiative energy transfer to the decay of the1G4 and3H4 levels of thulium and the4S3/2 and4I13/2 levels of erbium is significant for activator concentrations of the order of several thousand ppm in LiNbO3. The excitation of higher-lying levels of both activators is transferred faster in codoped crystal to the lowest luminescent
levels, from which the luminescence in the 1–2-μm spectral region occurs. This accelerated relaxation is advantageous for
broadband optical pumping since the contribution of radiative transitions competing with the3F4−3H6 laser transition of thulium is reduced. On the other hand, it appears that erbium ions will influence adversely the efficiency
of a laser-diode-pumped LiNbO3∶Er, Tm laser operating near 1.8 μm since the part of the3H4 excitation transferred to erbium ions is emitted from the long-lived4I11/2 level of Er3+. Furthermore, the4I13/2 excitation is not transferred fully to thulium ions and is lost in4I13/2−4I15/2 emission. Lithium niobate singly doped with thulium is more promising since the cross-relaxation process that transfers the
excitation from the3H4 level to the3F4 level appears to be efficient in this host.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 125–133, September–October, 1995. 相似文献
4.
5.
Pisarski RD 《Physical review letters》1989,63(11):1129-1132
6.
Treatment of the phenyl-substituted silane 4 with lithium metal afforded the functionalized lithiosilane rac-2 by selective cleavage of one Si-C bond between silicon and a phenyl group. The resulting lithiosilane rac-2 crystallizes as the dimer (2.THF)2, which represents the first example of a dimeric organyl-substituted lithiosilane in the presence of THF. 相似文献
7.
Dominik Rejman 《Tetrahedron》2007,63(5):1243-1253
The work deals with the synthesis of hydroxypyrrolidine analogs of nucleosides. Starting from the optically pure l- or d-tartaric acid, we improved the synthesis of enantiomeric trans-3,4-dihydroxypyrrolidines and elaborated a procedure for the synthesis of all possible diastereoisomers of 3-hydroxy-4-pyrrolidinyl derivatives of both purine and pyrimidine nucleobases. The prepared compounds were tested for cytostatic and antiviral properties but no significant activity was found. 相似文献
8.
DeClue MS Baldridge KK Künzler DE Kast P Hilvert D 《Journal of the American Chemical Society》2005,127(43):15002-15003
Isochorismate pyruvate lyase (IPL) catalyzes the cleavage of isochorismate to give salicylate and pyruvate, a key step in bacterial siderophore biosynthesis. We investigated the enzyme from Pseudomonas aeruginosa using isochorismate selectively deuterated at C2 as a substrate. Monitoring the reaction by 2H NMR spectroscopy revealed that the label is quantitatively transferred from C2 to C9, producing stoichiometric amounts of [3-2H]pyruvate as product. Moreover, the deuterium kinetic isotope effect of 2.34 +/- 0.08 on kcat indicates that C-H cleavage is significantly rate limiting. Consistent with these data, hybrid density functional theory (HDFT) calculations at the Becke3LYP/DZ+(2d,p) level of theory predict a concerted but highly asynchronous pericyclic transition structure, in which carbon-oxygen bond cleavage is more advanced than hydrogen atom transfer from C2 to C9; the calculated 2H isotope effect of 2.22 at C2 is in excellent accord with the experimental value. Together, these findings indicate that IPL should be added to the small set of proteins that are known to catalyze pericyclic reactions. They also raise the possibility that enzymes, such as chorismate pyruvate lyase, salicylate synthase, 4-amino-4-deoxychorismate lyase, and anthranilate synthase, which accelerate formally similar reaction steps, may also exploit pericyclic mechanisms. 相似文献
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