全文获取类型
收费全文 | 1187篇 |
免费 | 76篇 |
国内免费 | 3篇 |
专业分类
化学 | 1054篇 |
晶体学 | 5篇 |
力学 | 5篇 |
数学 | 91篇 |
物理学 | 111篇 |
出版年
2024年 | 2篇 |
2023年 | 22篇 |
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 44篇 |
2019年 | 34篇 |
2018年 | 29篇 |
2017年 | 23篇 |
2016年 | 35篇 |
2015年 | 50篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 96篇 |
2011年 | 106篇 |
2010年 | 52篇 |
2009年 | 40篇 |
2008年 | 83篇 |
2007年 | 82篇 |
2006年 | 91篇 |
2005年 | 69篇 |
2004年 | 60篇 |
2003年 | 52篇 |
2002年 | 32篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1266条查询结果,搜索用时 13 毫秒
961.
Christopher Braddock D Bhuva R Pérez-Fuertes Y Pouwer R Roberts CA Ruggiero A Stokes ES White AJ 《Chemical communications (Cambridge, England)》2008,(12):1419-1421
Enynes undergo stereoselective syn intramolecular bromoetherification; the stereochemical course of the reaction was elucidated by X-ray crystallographic studies and by stereospecific synthesis of authentic bromoallenes. 相似文献
962.
Bacon CE Eisler DJ Melen RL Rawson JM 《Chemical communications (Cambridge, England)》2008,(40):4924-4926
Treatment of N-lithiopyridylketimide derivatives Li[R(C=N)py] (R=Ph, py) with ECl(2) (E=S, Se) affords the fused thiadiazolium and selenadiazolium salts [RC(6)H(4)N(2)E]Cl [1]Cl and [2]Cl containing a bridgehead N atom through intramolecular coordination. 相似文献
963.
Castriciano MA Romeo A Baratto MC Pogni R Scolaro LM 《Chemical communications (Cambridge, England)》2008,(6):688-690
An acid-base interaction between hemin and PAMAM dendrimers affords supramolecular non-covalent peroxidase systems whose catalytic activity is enhanced after spontaneous electrostatic self-assembling onto a solid surface. 相似文献
964.
965.
966.
Retail B Rose RA Pearce JK Greaves SJ Orr-Ewing AJ 《Physical chemistry chemical physics : PCCP》2008,10(12):1675-1680
Rotational state distributions and state-selected CM-frame angular distributions were measured for HCl (v' = 0, j') products from the reaction of Cl-atoms with tetramethylsilane (TMS) under single collision conditions at a collision energy, E(coll), of 8.2 +/- 2.0 kcal mol(-1). The internal excitation of these products was very low with only 2% of the total energy available partitioned into HCl rotation. A transition state with a quasi-linear C-H-Cl moiety structure was computed and used to explain this finding. A backward peaking differential cross section was also reported together with a product translational energy (T') distribution with a maximum at T' approximately E(coll). This scattering behaviour is accounted for by reactions proceeding through a tight transition state on a highly skewed potential energy surface, which favours collisions at low impact parameters with a strong kinematic constraint on the internal excitation of the products. The large Arrhenius pre-exponential factor previously reported for this reaction is reconciled with the tight differential scattering observed in our study by considering the large size of the TMS molecule. 相似文献
967.
Baldwin GS Brooks NJ Robson RE Wynveen A Goldar A Leikin S Seddon JM Kornyshev AA 《The journal of physical chemistry. B》2008,112(4):1060-1064
The structure and biological function of the DNA double helix are based on interactions recognizing sequence complementarity between two single strands of DNA. A single DNA strand can also recognize the double helix sequence by binding in its groove and forming a triplex. We now find that sequence recognition occurs between intact DNA duplexes without any single-stranded elements as well. We have imaged a mixture of two fluorescently tagged, double helical DNA molecules that have identical nucleotide composition and length (50% GC; 294 base pairs) but different sequences. In electrolytic solution at minor osmotic stress, these DNAs form discrete liquid-crystalline aggregates (spherulites). We have observed spontaneous segregation of the two kinds of DNA within each spherulite, which reveals that nucleotide sequence recognition occurs between double helices separated by water in the absence of proteins, consistent with our earlier theoretical hypothesis. We thus report experimental evidence and discuss possible mechanisms for the recognition of homologous DNAs from a distance. 相似文献
968.
Gies AP Ellison ST Vergne MJ Orndorff RL Hercules DM 《Analytical and bioanalytical chemistry》2008,392(4):627-642
MALDI-TOF/TOF CID experiments are reported for hydroxylated poly(α-methylstyrene) precursor ions (PAMS: m/z 1,445.9 (n = 10), 2,036.3 (n = 15), 2,626.7 (n = 20), 3,217.1 (n = 25), and 3,807.5 (n = 30), where the number of repeat units n corresponds to the oligomer mass numbers). The influences of structure, molecular weight, and kinetic energy on degradation
mechanisms were examined to test the generality of our multi-chain fragmentation model developed for polystyrene. Our results
indicate that poly(α-methylstyrene) free radicals are formed initially through multiple chain breaks and subsequently undergo
a variety of depolymerization reactions to yield predominantly monomer and dimer species; the intensity of each species depends
on the effective kinetic energy selected for the CID process. Each depolymerization mechanism is presented in detail with
experimental and computational data to justify/rationalize the process and its kinetic energy dependence. These processes
show the complex interrelationships between the various pathways along with preferred production of tertiary radicals, which
suppresses the appearance of primary radicals. Additionally, Py-GC/MS experimental data are presented to allow a comparison
of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
969.
George Barmpalias Paul Brodhead Douglas Cenzer Jeffrey B. Remmel Rebecca Weber 《Archive for Mathematical Logic》2008,46(7-8):533-546
We investigate notions of randomness in the space ${{\mathcal C}(2^{\mathbb N})}We investigate notions of randomness in the space of continuous functions on . A probability measure is given and a version of the Martin-L?f test for randomness is defined. Random continuous functions exist, but no computable function can be random and no random function can map a computable real to
a computable real. The image of a random continuous function is always a perfect set and hence uncountable. For any , there exists a random continuous function F with y in the image of F. Thus the image of a random continuous function need not be a random closed set. The set of zeroes of a random continuous
function is always a random closed set.
Research partially supported by the National Science Foundation grants DMS 0532644 and 0554841 and 00652732. Thanks also to
the American Institute of Mathematics for support during 2006 Effective Randomness Workshop; Remmel partially supported by
NSF grant 0400307; Weber partially supported by NSF grant 0652326. Preliminary version published in the Third International
Conference on Computability and Complexity in Analysis, Springer Electronic Notes in Computer Science, 2006. 相似文献
970.
Dr. Ayan Dasgupta Yara van Ingen Michael G. Guerzoni Dr. Kaveh Farshadfar Prof. Jeremy M. Rawson Dr. Emma Richards Prof. Alireza Ariafard Prof. Rebecca L. Melen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(45):e202201422
An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds. 相似文献