全文获取类型
收费全文 | 2470篇 |
免费 | 61篇 |
国内免费 | 19篇 |
专业分类
化学 | 1361篇 |
晶体学 | 13篇 |
力学 | 103篇 |
数学 | 451篇 |
物理学 | 622篇 |
出版年
2023年 | 13篇 |
2022年 | 33篇 |
2021年 | 35篇 |
2020年 | 52篇 |
2019年 | 52篇 |
2018年 | 57篇 |
2017年 | 54篇 |
2016年 | 88篇 |
2015年 | 38篇 |
2014年 | 79篇 |
2013年 | 103篇 |
2012年 | 135篇 |
2011年 | 151篇 |
2010年 | 118篇 |
2009年 | 96篇 |
2008年 | 126篇 |
2007年 | 124篇 |
2006年 | 104篇 |
2005年 | 108篇 |
2004年 | 102篇 |
2003年 | 63篇 |
2002年 | 64篇 |
2001年 | 54篇 |
2000年 | 41篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 31篇 |
1996年 | 36篇 |
1995年 | 21篇 |
1994年 | 33篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 32篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1969年 | 14篇 |
1968年 | 17篇 |
排序方式: 共有2550条查询结果,搜索用时 15 毫秒
41.
N. N. Aleinikov G. K. Vasil'ev S. A. Kashtanov E. F. Makarov Yu. A. Chernyshev 《Russian Chemical Bulletin》1996,45(6):1344-1349
The of photochemical decomposition of XcO4 under the action of UV-radia(ion in the wavelength range of 200–300 nm was investigated. The quantum yield of the formation of oxygen atoms upon XeO4 photodissociation was measured (Ф = 3.6±0.4). The results obtained point to the predominant role of the XeO4 +hv → 4O + Xe photodissociation channel of XeO4. The value of the rate constant of the reaction XeO4 + O → O2 + XeO3 was estimated (<4.5 · 10?16 cm2 s?1). 相似文献
42.
V. A. Petrov V. K. Kunanets K. N. Makarov L. S. German 《Russian Chemical Bulletin》1989,38(3):572-575
Conclusions When perfluorinated tertiary cyclic amines containing a substituent at the nitrogen atom are heated with antimony pentafluoride, they isomerize to the corresponding azomethines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 646–649, March, 1989. 相似文献
43.
D. A. Makarov N. A. Kuznetsova O. L. Kaliya 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(2):268-274
Acridine dyes were found to exhibit a low light fastness in oxygen-containing aqueous solutions because of photooxidation with the participation of molecular oxygen. The values of the quantum yield for the photooxidation of Acridine Yellow, Acridine Orange, and proflavin acetate at their initial concentration 2 × 10?5 mol/l were determined to be 1.8 × 10?3, 1.5 × 10?3, and 0.8 × 10?3, respectively. It was concluded that the photooxidation of these acridine dyes in dilute solutions results in the formation of primary photoproducts of peroxide nature. For proflav in acetate, as an example, it was demonstrated that the increase of the substrate concentration to 6 × 10?4 mol/l results in a fourfold increase in the quantum yield, a behavior indicative of a change in the photodecomposition mechanism. The rate of the interaction between exited and unexcited proflavin molecules, the process responsible for the photodecomposition of this compound, was found to be ~4 × 107 l/(mol s). The quantum yield for the photooxidation of the proflavin base was estimated to exceed that for the photooxidation of the proflavin monocation by more than an order of magnitude. 相似文献
44.
L. I. Makarov 《Journal of Structural Chemistry》2005,46(4):738-743
Some questions emerged from electronic data processing of molecular structures (graphs) and its fragments have been considered in this work. Quantitative estimations of subgraph positions in molecular graphs are presented and some properties of their maximal common subgraphs are described. 相似文献
45.
O. B. Ryabova E. Yu. Khmel’nitskaya V. A. Makarov L. M. Alekseeva N. B. Grigor’ev V. G. Granik 《Russian Chemical Bulletin》2005,54(12):2873-2879
On heating at pH 6.86, 4-(N,N-dialkylthiocarbamoylthio)-5-nitropyrimidines are transformed into dithiolopyrimidines, which are either oxidized to bis(4-dialkylthiocarbamoylpyrimidin-5-yl)
disulfides or converted into 4,6-diamino-5-nitropyrimidine derivatives with carbon disulfide elimination. The direction of
the reaction is determined by the nature of a substituent in position 2 of pyrimidine and the bulk of the thiocarbamate substituent.
Mechanistic schemes for these processes were proposed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2777–2783, December, 2005. 相似文献
46.
Zhdankin VV Maydanovych O Herschbach J Bruno J Matveeva ED Zefirov NS 《The Journal of organic chemistry》2003,68(3):1018-1023
The preparation and chemistry of novel phosphoranyl-derived lambda(3)-iodanes is reported. The phosphoranyl-derived phenyliodonium sulfonates were prepared in good yields by the reaction of stabilized phosphonium ylides [1-triphenylphosphoranylidene-2-propanone, methyl(triphenylphosphoranylidene)acetate, (triphenylphosphoranylidene)acetaldehyde, and (triphenylphosphoranylidene)acetonitrile] with the pyridinium complex of iodobenzene ditriflate or with [hydroxy(tosyloxy)iodo]benzene under mild conditions. These compounds represent a potentially useful class of reagents that combine in one molecule synthetic advantages of a phosphonium ylide and an iodonium salt. Specifically, phosphorane-derived phenyliodonium tosylates can react with soft nucleophiles, such as iodide, bromide, benzenesulfinate, and thiophenolate anions, with a selective formation of the respective alpha-functionalized phosphonium ylides, which can be further converted to alkenes by the Wittig reaction with benzaldehyde. The phosphoranyl-derived benziodoxoles can be prepared by the reaction of 1-acetoxybenziodoxole with stabilized phosphonium ylides. An unusual ligand exchange on the iodine(III) center resulting in the substitution of a carbon ligand with an oxygen ligand was observed in the reaction of these compounds with strong acids. 相似文献
47.
R. M. Kamalov G. M. Makarov D. Kh. Yarmukhametova M. A. Pudovik R. A. Cherkasov A. N. Pudovik 《Russian Chemical Bulletin》1989,38(11):2382-2388
Condensation of phenothiazine with phenyl isocyanide dichloride has given 10(N-phenylchloroformimidoyl)phenothiazine, exchange reactions of which with salts of diakylthio- and dithiophosphoric acids result in rearrangement of the initially formed 10-[N-phenyldialkoxy(thio)phosphorylthioformimidoyl]phenothiazines to 10-{N-phenyl-N-[dialkoxy(thio)phosphoryl]thiocarbamoyl}phenothiazines, while reaction with diisopropyl dithiophosphoric acid affords diisopropyl chlorothiophosphate, phenyl isothiocyanate, and phenothiazine. 10-(N-Phenylethoxyformimidoyl)phenothiazine alkylates dithiophosphoric acid to give 10-(N-phenylcarbamoyl)phenothiazine, while N2-phenyl-N1,N1-diethyl-(10-phenothiazinyl)formamidine reacts with diisopropyl dithiophosphoric acid, affording the salt N2-phenyl-N1,N1-diethyl-(10-phenothiazinyl)formamidinium O,O-diisopropyl dithiophosphate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2596–2601, November, 1989. 相似文献
48.
Multiphoton IR dissociation of SF6 (in a mixture with CH4) under nonequilibrium conditions of a compression shock formed by an intense, gas dynamically cooled, pulsed molecular beam impacting a solid surface was studied using the HF* luminescence detection ( 2.5 m) technique. The dependences of the HF* luminescence intensity on the distance x between the region in which molecules were excited and the surface and on the laser radiation frequency at different values of x were obtained. It was shown that, as the distance x decreased from 4 to 1.5 mm, the HF* luminescence intensity increased by more than an order of magnitude as compared to the case of excitation of molecules in an undisturbed flow, whereas the frequency dependences of luminescence intensity (SF6 dissociation yield) were broadened only insignificantly. 相似文献
49.
Single-molecule experiments in which proteins are unfolded by applying mechanical stretching forces generally force unfolding to proceed along a reaction coordinate that is different from that in chemical or thermal denaturation. Here we simulate the mechanical unfolding and refolding of a minimalist off-lattice model of the protein ubiquitin to explore in detail the slice of the multidimensional free-energy landscape that is accessible via mechanical pulling experiments. We find that while the free-energy profile along typical "chemical" reaction coordinates may exhibit two minima, corresponding to the native and denatured states, the free energy G(z) is typically a monotonic function of the mechanical coordinate z equal to the protein extension. Application of a stretching force along z tilts the free-energy landscape resulting in a bistable (or multistable) free energy G(z)-fz probed in mechanical unfolding experiments. We construct a two-dimensional free-energy surface as a function of both chemical and mechanical reaction coordinates and examine the coupling between the two. We further study the refolding trajectories after the protein has been prestretched by a large force, as well as the mechanical unfolding trajectories in the presence of a large stretching force. We demonstrate that the stretching forces required to destabilize the native state thermodynamically are larger than those expected on the basis of previous experimental estimates of G(z). This finding is consistent with the recent experimental studies, indicating that proteins may refold even in the presence of a substantial stretching force. Finally, we show that for certain temperatures the free energy of a polyprotein chain consisting of multiple domains is a linear function of the chain extension. We propose that the recently observed "slow phase" in the refolding of proteins under mechanical tension may be viewed as downhill diffusion in such a linear potential. 相似文献
50.
Mikhail H. Klin Serge S. Tratch Nikolai S. Zefirov 《Journal of mathematical chemistry》1991,7(1):135-151
We give a necessary and sufficient condition for a reaction graph of a degenerate rearrangement to be connected. This condition is formulated in terms of vertex stabilizers of the automorphism group of a molecular graph. The condition is illustrated on several examples, including the reaction graph of bullvalene. We consider different mathematical models for the construction of reaction graphs and state the problem: which of the models is more adequate? 相似文献