全文获取类型
收费全文 | 3319篇 |
免费 | 66篇 |
国内免费 | 12篇 |
专业分类
化学 | 1814篇 |
晶体学 | 25篇 |
力学 | 66篇 |
数学 | 448篇 |
物理学 | 1044篇 |
出版年
2021年 | 26篇 |
2020年 | 50篇 |
2019年 | 27篇 |
2017年 | 34篇 |
2016年 | 61篇 |
2015年 | 48篇 |
2014年 | 64篇 |
2013年 | 122篇 |
2012年 | 119篇 |
2011年 | 138篇 |
2010年 | 74篇 |
2009年 | 82篇 |
2008年 | 93篇 |
2007年 | 115篇 |
2006年 | 98篇 |
2005年 | 102篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 75篇 |
2001年 | 56篇 |
2000年 | 70篇 |
1999年 | 66篇 |
1998年 | 38篇 |
1997年 | 33篇 |
1996年 | 50篇 |
1995年 | 55篇 |
1994年 | 60篇 |
1993年 | 67篇 |
1992年 | 77篇 |
1991年 | 61篇 |
1990年 | 48篇 |
1989年 | 44篇 |
1988年 | 38篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 65篇 |
1984年 | 51篇 |
1983年 | 58篇 |
1982年 | 55篇 |
1981年 | 48篇 |
1980年 | 52篇 |
1979年 | 53篇 |
1978年 | 44篇 |
1977年 | 49篇 |
1976年 | 41篇 |
1975年 | 32篇 |
1974年 | 48篇 |
1973年 | 51篇 |
1966年 | 25篇 |
1926年 | 22篇 |
排序方式: 共有3397条查询结果,搜索用时 15 毫秒
101.
Maria Weber Hai-Hao Han Bo-Han Li Maria
L. Odyniec Charlotte E. F. Jarman Yi Zang Steven D. Bull Amanda B. Mackenzie Adam C. Sedgwick Jia Li Xiao-Peng He Tony D. James 《Chemical science》2020,11(32):8567
Reaction-based fluorescent-probes have proven successful for the visualisation of biological species in various cellular processes. Unfortunately, in order to tailor the design of a fluorescent probe to a specific application (i.e. organelle targeting, material and theranostic applications) often requires extensive synthetic efforts and the synthetic screening of a range of fluorophores to match the required synthetic needs. In this work, we have identified Pinkment-OH as a unique “plug-and-play” synthetic platform that can be used to develop a range of ONOO− responsive fluorescent probes for a variety of applications. These include theranostic-based applications and potential material-based/bioconjugation applications. The as prepared probes displayed an excellent sensitivity and selectivity for ONOO− over other ROS. In vitro studies using HeLa cells and RAW 264.7 macrophages demonstrated their ability to detect exogenously and endogenously produced ONOO−. Evaluation in an LPS-induced inflammation mouse model illustrated the ability to monitor ONOO− production in acute inflammation. Lastly, theranostic-based probes enabled the simultaneous evaluation of indomethacin-based therapeutic effects combined with the visualisation of an inflammation biomarker in RAW 264.7 cells. Pinkment, a resorufin based ONOO− selective and sensitive ‘plug and play’ fluorescence-based platform for in vitro and in vivo use, enables facile functionalisation for various imaging and theranostic applications. 相似文献
102.
103.
Wolfgang Oppolzer Roland Achini Emil Pfenninger Hans Peter Weber 《Helvetica chimica acta》1976,59(4):1186-1202
The N-allyl-N-cinnamyl amide 10 undergoes thermal cyclization to a 2:1-mixture of the trans- and cis-benz(f)isoindolines 11a and 12a . By comparison, the thermolysis of the corresponding bis-cinnamylamide 14 proceeds in a highly stereoselective manner to give the cis-fused[4+2]-adduct 16a . Similarly, the trans-fused stereoisomeric adducts 30a and 31a were obtained with high stereochemical control on heating the N-allyl-N-diphenylallyl amide 28 . The thermal transformations 4 → 5 + 6a and 17 → 18a + 20a show the competitive formation of [2+2]-adducts. An alternative approach to (substituted) benz[f]isoindolines 16 via the all-cis-isomer 24a has been developed. The described structures have been assigned on the basis of spectral evidence, chemical correlations and by X-ray-diffraction study of the isomer 16b . These results illustrate the utility of substituent interactions in order to direct intramolecular cyclo-additions at will towards either endo- or exo-products. 相似文献
104.
[reaction: see text] Quinodimethanes are highly reactive toward dienophiles since Diels-Alder cycloaddition results in an aromatic product. Density functional-based (13)C, (1)H NMR, NICS, and MO-NICS calculations indicate that the increase of aromatic character of the developing benzenoid ring along the reaction path is especially pronounced after the transition state is reached, even though the number of pi orbitals decreases. The forming aliphatic ring exhibits large ring current effects during the reaction. 相似文献
105.
Jakob Boelsterli Ursula Eggnauer Esteban Pombo-Villar Hans-Peter Weber Malcolm Walkinshaw Robert O. Gould 《Helvetica chimica acta》1992,75(2):507-512
The l-azabicyclo[2.2.1]heptan-3-exo-ol ( 2 ) was resolved by fractional crystallisation of its hydrogen tartrate salts. The enantiomers (+)- and (?)- 2 were oxidised to the ketones (?)- 4 and (+)- 4 , respectively (Scheme). CD spectroscopy suggested that (?)- 4 possesses the (1R,4S)-configuration. This absolute configuration was confirmed by single-crystal X-ray diffraction of the derivative (+)-(1R,4R)-3-(1,3-dithian-2-ylidene)-1-azabicyclo [2.2.1]-heptane ((+)- 5 ). 相似文献
106.
Kudoh T Fukuoka M Ichikawa S Murayama T Ogawa Y Hashii M Higashida H Kunerth S Weber K Guse AH Potter BV Matsuda A Shuto S 《Journal of the American Chemical Society》2005,127(24):8846-8855
We previously developed cyclic ADP-carbocyclic ribose (cADPcR, 2) as a stable mimic of cyclic ADP-ribose (cADPR, 1), a Ca(2+)-mobilizing second messenger. A series of the N1-ribose modified cADPcR analogues, designed as novel stable mimics of cADPR, which were the 2"-deoxy analogue 3, the 3"-deoxy analogue 4, the 3"-deoxy-2"-O-(methoxymethyl) analogue 5, the 3"-O-methyl analogue 6, the 2",3"-dideoxy analogue 7, and the 2",3"-dideoxydidehydro analogue 8, were successfully synthesized using the key intramolecular condensation reaction with phenylthiophosphate-type substrates. We investigated the conformations of these analogues and of cADPR and found that steric repulsion between both the adenine and N9-ribose moieties and between the adenine and N1-ribose moieties was a determinant of the conformation. The Ca(2+)-mobilizing effects were evaluated systematically using three different biological systems, i.e., sea urchin eggs, NG108-15 neuronal cells, and Jurkat T-lymphocytes. The relative potency of Ca(2+)-mobilization by these cADPR analogues varies depending on the cell-type used: e.g., 3"-deoxy-cADPcR (4) > cADPcR (2) > cADPR (1) in sea urchin eggs; cADPR (1) > cADPcR (2) approximately 3"-deoxy-cADPcR (4) in T-cells; and cADPcR (2) > cADPR (1) > 3"-deoxy-cADPcR (4) in neuronal cells, respectively. These indicated that the target proteins and/or the mechanism of action of cADPR in sea urchin eggs, T-cells, and neuronal cells are different. Thus, this study represents an entry to cell-type selective cADPR analogues, which can be used as biological tools and/or novel drug leads. 相似文献
107.
Analysis of high-resolution NMR spectra elucidation has been known for many years. Hard-and software development now permits
the implementation of such programs on personal computers. The structural information hidden in complex proton NMR spectra
becomes easily accessible by using graphical user interfaces and direct data exchange between programs. A new mode has been
implemented in 1D WIN-NMR to support the analysis of multiplet patterns with first order rules. Structure display, direct
export mechanisms to the simulation program WIN-DAISY, and an archiving possibility complete the state-of-the-art data analysis.
Some practical examples are given.
Received: 25 October 1996/Revised: 6 March 1997/Accepted: 10 March 1997 相似文献
108.
The rotational motions of 1-naphthylamine in propylene glycol are investigated by means of steady-state flourescence polarization measurements and differential polarized phase flourometry, on excitation at various wavelengths. For excitation at 370 nm the average rotational rate is faster than for excitation at shorter wavelength and the rotations are clearly anisotropic. On excitation from 370nm to the red edge of the spectrum (390 nm) the average rotational rate slows down by a factor of two and the rotations become nearly isotropic. The results reveal the possible existence of an excited state generated preferentially by excitation at the edge of the absorption, in which the transition moments in both absorption and emission are prependicular to the plane of the aromatic rings. 相似文献
109.
A charged parallel plate capacitor contains less electric energy when its plates are oriented parallel to a gravitational field than it contains when its plates are oriented perpendicular to the same field. If this energy difference can be detected by an observer located inside the field, then the capacitor should experience a torque until the electric field is perpendicular to the radial direction. 相似文献
110.
Synthesis and Structure of Highly Functionalized 2, 3‐Dihydro‐1H‐1, 3, 2‐diazaboroles A series of differently substituted 2, 3‐dihydro‐1H‐1, 3, 2‐diazaboroles has been prepared by various methods. 1, 3‐Di‐tert‐butyl‐2‐trimethylsilylmethyl‐1H‐1, 3, 2‐diazaborole ( 7 ), 2‐isobutyl‐1, 3‐bis(1‐cyclohexylethyl)‐1H‐1, 3, 2‐diazaborole ( 8 ), 1, 3‐bis‐(1‐cyclohexylethyl)‐2‐trimethylsilylmethyl‐1H‐1, 3, 2‐diazaborole ( 9 ) 1, 3‐bis(1‐methyl‐1‐phenyl‐propyl)‐2‐trimethylsilylmethyl‐1H‐1, 3, 2diazaborole ( 10 ) and 2‐bromo‐1, 3‐bis(1‐methyl‐1‐phenyl‐propyl)‐1H‐1, 3, 2‐diazaborole ( 11 ) were formed by reaction of the corresponding 1, 4‐diazabutadienes with the boranes Me3SiCH2BBr2, iBuBBr2 and BBr3 followed by reduction of the resulting borolium salts [R1 = tBu, Me(cHex)CH, [Me(Et)Ph]C; R2 = Me3SiCH2, iBu, Br] with sodium amalgam. Treatment of 11 and 12 with silver cyanide afforded the 2‐cyano‐1, 3, 2‐diazaboroles 13 and 14 . An alternative route to compound 8 is based on the alkylation of 2‐bromo‐1, 3, 2‐diazaborole 12 with isobutyllithium. Equimolar amounts of 13 and isobutyllithium give rise to the formation of 15 . The new compounds were characterized by 1H‐, 13C‐, 11B‐NMR, IR and mass spectra. The molecular structures of 7 and meso ‐10 were confirmed by x‐ray structural analysis. 相似文献