全文获取类型
收费全文 | 1554篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 869篇 |
晶体学 | 34篇 |
力学 | 43篇 |
数学 | 190篇 |
物理学 | 442篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 20篇 |
2020年 | 23篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2016年 | 20篇 |
2015年 | 15篇 |
2014年 | 26篇 |
2013年 | 75篇 |
2012年 | 66篇 |
2011年 | 71篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 57篇 |
2007年 | 74篇 |
2006年 | 60篇 |
2005年 | 62篇 |
2004年 | 51篇 |
2003年 | 50篇 |
2002年 | 45篇 |
2001年 | 44篇 |
2000年 | 34篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 45篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 34篇 |
1983年 | 15篇 |
1982年 | 28篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 10篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1973年 | 18篇 |
排序方式: 共有1578条查询结果,搜索用时 15 毫秒
61.
62.
Dr. Luke D. Elliott Dr. Jonathan P. Knowles Dr. Paul J. Koovits Katie G. Maskill Michael J. Ralph Dr. Guillaume Lejeune Lee J. Edwards Richard I. Robinson Ian R. Clemens Brian Cox David D. Pascoe Guido Koch Martin Eberle Malcolm B. Berry Prof. Kevin I. Booker‐Milburn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):15226-15232
The use of flow photochemistry and its apparent superiority over batch has been reported by a number of groups in recent years. To rigorously determine whether flow does indeed have an advantage over batch, a broad range of synthetic photochemical transformations were optimized in both reactor modes and their yields and productivities compared. Surprisingly, yields were essentially identical in all comparative cases. Even more revealing was the observation that the productivity of flow reactors varied very little to that of their batch counterparts when the key reaction parameters were matched. Those with a single layer of fluorinated ethylene propylene (FEP) had an average productivity 20 % lower than that of batch, whereas three‐layer reactors were 20 % more productive. Finally, the utility of flow chemistry was demonstrated in the scale‐up of the ring‐opening reaction of a potentially explosive [1.1.1] propellane with butane‐2,3‐dione. 相似文献
63.
Chongqing Wang Christopher Lambert Maurice Hauser Adrian Deuschmann Dr. Carsten Zeilinger Prof. Dr. Klemens Rottner Prof. Dr. Theresia E. B. Stradal Prof. Dr. Marc Stadler Dr. Elizabeth J. Skellam Prof. Dr. Russell J. Cox 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13578-13583
Mutasynthesis of pyrichalasin H from Magnaporthe grisea NI980 yielded a series of unprecedented 4′-substituted cytochalasin analogues in titres as high as the wild-type system (≈60 mg L−1). Halogenated, O-alkyl, O-allyl and O-propargyl examples were formed, as well as a 4′-azido analogue. 4′-O-Propargyl and 4′-azido analogues reacted smoothly in Huisgen cycloaddition reactions, whereas p-Br and p-I compounds reacted in Pd-catalysed cross-coupling reactions. A series of examples of biotin-linked, dye-linked and dimeric cytochalasins was rapidly created. In vitro and in vivo bioassays of these compounds showed that the 4′-halogenated and azido derivatives retained their cytotoxicity and antifungal activities; but a unique 4′-amino analogue was inactive. Attachment of larger substituents attenuated the bioactivities. In vivo actin-binding studies with adherent mammalian cells showed that actin remains the likely intracellular target. Dye-linked compounds revealed visualisation of intracellular actin structures even in the absence of phalloidin, thus constituting a potential new class of actin-visualisation tools with filament-barbed end-binding specificity. 相似文献
64.
Giorgio Olivo Giorgio Capocasa Barbara Ticconi Osvaldo Lanzalunga Stefano Di Stefano Miquel Costas 《Angewandte Chemie (International ed. in English)》2020,59(31):12703-12708
Predictability is a key requirement to encompass late‐stage C?H functionalization in synthetic routes. However, prediction (and control) of reaction selectivity is usually challenging, especially for complex substrate structures and elusive transformations such as remote C(sp3)?H oxidation, as it requires distinguishing a specific C?H bond from many others with similar reactivity. Developed here is a strategy for predictable, remote C?H oxidation that entails substrate binding to a supramolecular Mn or Fe catalyst followed by elucidation of the conformation of the host‐guest adduct by NMR analysis. These analyses indicate which remote C?H bonds are suitably oriented for the oxidation before carrying out the reaction, enabling prediction of site selectivity. This strategy was applied to late‐stage C(sp3)?H oxidation of amino‐steroids at C15 (or C16) positions, with a selectivity tunable by modification of catalyst chirality and metal. 相似文献
65.
Kyle M. Lambert Joshua B. Cox Lin Liu Amy C. Jackson Sam Yruegas Kenneth B. Wiberg John L. Wood 《Angewandte Chemie (International ed. in English)》2020,59(24):9757-9766
The development of a concise total synthesis of (±)‐phyllantidine ( 1 ), a member of the securinega family of alkaloids containing an unusual oxazabicyclo[3.3.1]nonane core, is described. The synthesis employs a unique synthetic strategy featuring the ring expansion of a substituted cyclopentanone to a cyclic hydroxamic acid as a key step that allows facile installation of the embedded nitrogen‐oxygen (N?O) bond. The optimization of this sequence to effect the desired regiochemical outcome and its mechanistic underpinnings were assessed both computationally and experimentally. This synthetic approach also features an early‐stage diastereoselective aldol reaction to assemble the substituted cyclopentanone, a mild reduction of an amide intermediate without N?O bond cleavage, and the rapid assembly of the butenolide found in ( 1 ) via use of the Bestmann ylide. 相似文献
66.
67.
Reactions of copper(I) halides with racemic 2,2′-bis(diphenylphosphano)-1,1′-binaphthyl (rac-binap) in 1:1 molar ratio afforded mononuclear complexes of the type [CuX(rac-binap)] (X = Cl, Br, I) which, on further treatment with 1 equiv. of pyridine-2-thione (py2SH), pyrimidine-2-thione (pymtH) or 4,6-dimethyl-pyrimidine-2-thione (dmpymtH) gave rise to the formation of mixed-ligand complexes of the formula [CuX(rac-binap)(thione)]. The molecular structures of [CuBr(rac-binap)(py2SH)] · 2CH2Cl2, [CuBr(rac-binap)(py2SH)] · CH2Cl2 and [CuBr(rac-binap)(dmpymtH)] · CH2Cl2 have been established by single-crystal X-ray diffraction. Each of the complexes features a distorted tetrahedral copper(I) center with the phosphane acting in a chelating fashion. The complexes are strongly luminescent in the solid state at ambient temperature. Unusually, the [CuBr(rac-binap)(py2SH)] · 2CH2Cl2 molecules crystallise in a chiral space group with independent S- and R-enantiomers in the asymmetric unit. 相似文献
68.
Iannucci NB Navarro del Cañizo AA Cascone O 《Applied biochemistry and biotechnology》2003,104(3):173-183
Twenty triazinic dyes were assayed as ligands for the chromatographic affinity purification of a neutral protease from Flavourzyme™, a commercial preparation. Screening at pH 4.0 allowed the selection of eight dyes on the basis of their high protease adsorption.
When the pH was set to 5.0 in order to increase selectivity, only Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A maintained
protease adsorption at high values. Neither maximum capacities nor dissociation constants calculated from isotherms measured
at 8 and 25°C showed great differences. By contrast, a strong temperature effect was evidenced in the elution step: elution
at 8°C allowed 70, 81, and 98% recovery of adsorbed protease with Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A, respectively,
whereas only 20% recovery was attained at 25°C. Based on the results obtained, a purification process for the neutral protease
contained in Flavourzyme with Cibacron Blue F3G-A as the affinity ligand was developed, yielding 96% of electrophoretically
pure enzyme in a single step, the specific activity rising from 850 to 3650 U/mg. 相似文献
69.
70.
Raufaste C Dollet B Cox S Jiang Y Graner F 《The European physical journal. E, Soft matter》2007,23(2):217-228
We study the two-dimensional flow of foams around a
circular obstacle within a long channel. In experiments, we
confine the foam between liquid and glass surfaces. In
simulations, we use a deterministic software, the Surface
Evolver, for bubble details and a stochastic one, the extended
Potts model, for statistics. We adopt a coherent definition of
liquid fraction for all studied systems. We vary it in both
experiments and simulations, and determine the yield drag of the
foam, that is, the force exerted on the obstacle by the foam
flowing at very low velocity. We find that the yield drag is
linear over a large range of the ratio of obstacle to bubble
size, and is independent of the channel width over a large range.
Decreasing the liquid fraction, however, strongly increases the
yield drag; we discuss and interpret this dependence. 相似文献