全文获取类型
收费全文 | 859篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
化学 | 571篇 |
晶体学 | 4篇 |
力学 | 23篇 |
数学 | 58篇 |
物理学 | 228篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 6篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 71篇 |
2012年 | 32篇 |
2011年 | 41篇 |
2010年 | 27篇 |
2009年 | 19篇 |
2008年 | 31篇 |
2007年 | 33篇 |
2006年 | 48篇 |
2005年 | 27篇 |
2004年 | 19篇 |
2003年 | 18篇 |
2002年 | 30篇 |
2001年 | 13篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1968年 | 4篇 |
1951年 | 6篇 |
排序方式: 共有884条查询结果,搜索用时 15 毫秒
21.
Marcantonio KM Frey LF Liu Y Chen Y Strine J Phenix B Wallace DJ Chen CY 《Organic letters》2004,6(21):3723-3725
[reaction: see text] The palladium-catalyzed cyanation reaction is known to be sensitive to dissolved cyanide. Investigation into some causes of high levels of dissolved cyanide is presented here, along with a robust solution to this problem. 相似文献
22.
Gerhard Frey 《manuscripta mathematica》1975,16(4):333-362
For k∈?\0 we define the elliptic curve Ak, by the equation: Y2=X3+k. Let C(k) be the class group of \(K_o = Q(\sqrt[6]{k})\) . If k is a square we find a close connection between the elements of order 2 of the Selmer group of Ak and C(k); there is a corresponding connection between the elements of order 3 if k is a cube and satisfies some additional conditions. The main tool to prove the statements is the global and local Galois cohomology of elliptic curves; it seems remarkable that nearly no “explicit” number theory has to be used. 相似文献
23.
Janis V. Musso Jordan De Jesus Silva Mathis J. Benedikter Jonas Groos Wolfgang Frey Christophe Copret Michael R. Buchmeiser 《Chemical science》2022,13(29):8649
Cationic d0 group 6 olefin metathesis catalysts have been recently shown to display in most instances superior activity in comparison to their neutral congeners. Furthermore, their catalytic performance is greatly improved upon immobilization on silica. In this context, we have developed the new family of molecular cationic molybdenum oxo alkylidene complexes stabilized by N-heterocyclic carbenes of the general formula [Mo(O)(CHCMe3)(IMes)(OR)[X−]] (IMes = 1,3-dimesitylimidazol-2-ylidene; R = 1,3-dimesityl-C6H3, C6F5; X− = B(3,5-(CF3)2C6H3)4−, B(ArF)4, tetrakis(perfluoro-t-butoxy)aluminate (PFTA)). Immobilization of [Mo(O)(CHCMe3)(IMes)(O-1,3-dimesityl-C6H3)+B(ArF)4−] on silica via surface organometallic chemistry yields an active alkene metathesis catalyst that shows the highest productivity towards terminal olefins amongst all existing molybdenum oxo alkylidene catalysts.The first cationic molybdenum oxo complexes were synthesized and immobilized on partially dehydroxylated silica. Vastly enhanced catalytic activity for terminal olefins was found compared to their neutral congeners. 相似文献
24.
Liu J Gardel ML Kroy K Frey E Hoffman BD Crocker JC Bausch AR Weitz DA 《Physical review letters》2006,96(11):118104
We exploit the power of microrheology to measure the viscoelasticity of entangled F-actin solutions at different length scales from 1 to 100 microm over a wide frequency range. We compare the behavior of single probe-particle motion to that of the correlated motion of two particles. By varying the average length of the filaments, we identify fluctuations that dissipate diffusively over the filament length. These provide an important relaxation mechanism of the elasticity between 0.1 and 30 rad/sec. 相似文献
25.
Charles E. Carraher JR. 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1293-1356
This review emphasizes the breadth of metallic and metallic-like polymers evaluated as to thermal properties. Techniques usefully applied to particular systems are noted with the aim of suggesting their application to other systems. 相似文献
26.
Fundamental and experimental differences between X-ray and neutron scattering methods are outlined and the advantages of either radiation for the study of disorder in crystals are described. Special emphasis is laid on their complementarity, e.g. to identify the atomic species involved in the disorder or to decide between the elastic or inelastic nature of the diffuse scattering (static or dynamic disorder). This is illustrated by three examples: LiNbO3 (dynamic nature of chain-like disorder), doped Zr02 (identification of cationic and anionic disorder components) and decagonal quasicrystals (distinction between quasi-isoelectronic elements). 相似文献
27.
Multireference configuration interaction (MRCI) and complete active space second-order perturbation theory (CASPT2) calculations are performed on Fe2 and Fe? 2. Although it is not possible to definitively identify the ground states of Fe2 and Fe? 2, the calculations suggest that the ground state of Fe? 2 in 8Σ? u derived from 3d134σ2 g4σ2 u and that the states observed in photodetachment are the 9Σ? g and 7Σ? g states with a 3d134σ2 g4σ1 u occupation, but that the ground state of Fe2 is 7Δu(3d144σ2 g) and is not observed in the photo-detachment spectra. 相似文献
28.
Standardized electronic formats for data are needed to efficiently and transparently communicate the results of scientific studies. A format for the unique identification of chemical species is a requirement in the field of chemistry, and the IUPAC International Chemical Identifier (InChI) has been widely adopted for this purpose. The InChI identifier has proved to be very useful. The InChI identifier, however, is currently insufficient to uniquely specify some types of molecular entities at a detailed molecular level needed to fully characterize their chemical nature, to differentiate between chemically distinct conformers, to uniquely identify structures used in quantum chemical calculations, and to completely describe elementary chemical reactions. To address this limitation, we propose an augmented form of InChI, denoted as InChI–ER, which contains additional optional layers that allow the unique and unambiguous identification of molecules at a detailed molecular level. The new layers proposed herein are optional extensions of the existing InChI formalism and, like all other InChI layers, would not interfere with InChI identifiers currently in use. The focus of the present work is the better specification of required molecular entities such as rotational conformations, ring conformations, and electronic states. In companion articles, we propose additional reaction layers using an extended InChI format that will enable the unique identification of elementary chemical reactions, including specification of associated transition states, specification of the changes in bonds that occur during reaction, and classification of reaction types. 相似文献
29.
Brian L. Frey Daniel T. Ladror Samuel B. Sondalle Casey J. Krusemark April L. Jue Joshua J. Coon Lloyd M. Smith 《Journal of the American Society for Mass Spectrometry》2013,24(11):1710-1721
The carboxyl groups of tryptic peptides were derivatized with a tertiary or quaternary amine labeling reagent to generate more highly charged peptide ions that fragment efficiently by electron transfer dissociation (ETD). All peptide carboxyl groups—aspartic and glutamic acid side-chains as well as C-termini—were derivatized with an average reaction efficiency of 99 %. This nearly complete labeling avoids making complex peptide mixtures even more complex because of partially-labeled products, and it allows the use of static modifications during database searching. Alkyl tertiary amines were found to be the optimal labeling reagent among the four types tested. Charge states are substantially higher for derivatized peptides: a modified tryptic digest of bovine serum albumin (BSA) generates ~90% of its precursor ions with z? > ?2, compared with less than 40 % for the unmodified sample. The increased charge density of modified peptide ions yields highly efficient ETD fragmentation, leading to many additional peptide identifications and higher sequence coverage (e.g., 70 % for modified versus only 43 % for unmodified BSA). The utility of this labeling strategy was demonstrated on a tryptic digest of ribosomal proteins isolated from yeast cells. Peptide derivatization of this sample produced an increase in the number of identified proteins, a >50 % increase in the sequence coverage of these proteins, and a doubling of the number of peptide spectral matches. This carboxyl derivatization strategy greatly improves proteome coverage obtained from ETD-MS/MS of tryptic digests, and we anticipate that it will also enhance identification and localization of post-translational modifications. Figure
? 相似文献
30.