全文获取类型
收费全文 | 970篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
化学 | 614篇 |
晶体学 | 7篇 |
力学 | 39篇 |
数学 | 138篇 |
物理学 | 193篇 |
出版年
2022年 | 14篇 |
2021年 | 12篇 |
2019年 | 19篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 27篇 |
2012年 | 59篇 |
2011年 | 43篇 |
2010年 | 31篇 |
2009年 | 20篇 |
2008年 | 44篇 |
2007年 | 31篇 |
2006年 | 49篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 24篇 |
2002年 | 30篇 |
2001年 | 21篇 |
2000年 | 25篇 |
1999年 | 7篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 18篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有991条查询结果,搜索用时 0 毫秒
91.
Jürgen Brem Weston B. Struwe Anna M. Rydzik Hanna Tarhonskaya Inga Pfeffer Emily Flashman Sander S. van Berkel James Spencer Timothy D. W. Claridge Michael A. McDonough Justin L. P. Benesch Christopher J. Schofield 《Chemical science》2015,6(2):956-963
Metallo-β-lactamases (MBLs) catalyse the hydrolysis of almost all β-lactam antibiotics. We report biophysical and kinetic studies on the São Paulo MBL (SPM-1), which reveal its Zn(ii) ion usage and mechanism as characteristic of the clinically important di-Zn(ii) dependent B1 MBL subfamily. Biophysical analyses employing crystallography, dynamic 19F NMR and ion mobility mass spectrometry, however, reveal that SPM-1 possesses loop and mobile element regions characteristic of the B2 MBLs. These include a mobile α3 region which is important in catalysis and determining inhibitor selectivity. SPM-1 thus appears to be a hybrid B1/B2 MBL. The results have implications for MBL evolution and inhibitor design. 相似文献
92.
Lydia A. Panther Dr. Daniel P. Guest Dr. Andrew McGown Hugo Emerit Dr. Raysa Khan Tareque Dr. Arathy Jose Mr. Chris M. Dadswell Dr. Simon J. Coles Dr. Graham J. Tizzard Dr. Ramón González-Méndez Dr. Charles A. I. Goodall Prof. Mark C. Bagley Prof. John Spencer Dr. Barnaby W. Greenland 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(49):e202201444
Solvent-free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic acid (Br2-NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)2) and are tolerant to air and atmospheric moisture. Furthermore, the real-world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs. 相似文献
93.
The distribution of the chromatic number on random graphsG
n, p
is quite sharply concentrated. For fixedp it concentrates almost surely in √n ω(n) consecutive integers where ω(n) approaches infinity arbitrarily slowly. If the average degreepn is less thann
1/6, it concentrates almost surely in five consecutive integers. Large deviation estimates for martingales are used in the proof. 相似文献
94.
Griffith GA Percy JM Pintat S Smith CA Spencer N Uneyama E 《Organic & biomolecular chemistry》2005,3(15):2701-2712
Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT (19)F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers. 相似文献
95.
Steven J. Shirbin Steven C. Zammit Sebastian M. Marcuccio Spencer J. Williams 《Tetrahedron letters》2010,51(22):2971-1759
Aryl imidazylates are effective electrophilic partners in copper-free palladium-catalyzed Hiyama and Sonogashira cross-coupling reactions. The Sonogashira cross-coupling of estron-3-yl imidazylate afforded the corresponding phenylacetylene derivative in excellent yield. 相似文献
96.
Spencer Bloch Hélène Esnault Dirk Kreimer 《Communications in Mathematical Physics》2006,267(1):181-225
The appearance of multiple zeta values in anomalous dimensions and β-functions of renormalizable quantum field theories has given evidence towards a motivic interpretation of these renormalization group functions. In this paper we start to hunt the motive, restricting our attention to a subclass of graphs in four dimensional scalar field theory which give scheme independent contributions to the above functions. 相似文献
97.
Moreland L.D. Schamiloglu E. Lemke W. Korovin S.D. Rostov V.V. Roitman A.M. Hendricks K.J. Spencer T.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(5):554-565
The Sinus-6, a high-power relativistic repetitively-pulsed electron beam accelerator, is used to drive various slow wave structures in a BWO configuration in vacuum. Peak output power of about 550 MW at 9.45 GHz was radiated in an 8-ns pulse. We describe experiments which study the relative efficiencies of microwave generation from a two-stage nonuniform amplitude slow wave structure and its variations without an initial stage. Experimental results are compared with 2.5 D particle-in-cell computer simulations. Our results suggest that prebunching the electron beam in the initial section of the nonuniform BWO results in increased microwave generation efficiency, Furthermore, simulations reveal that, in addition to the backward propagating surface harmonic of the TM01 mode, backward and forward propagating volume harmonics with phase velocity twice that of the surface harmonic play an important role in high-power microwave generation and radiation 相似文献
98.
We find the asymptotic number of connected graphs with k vertices and k−1+l edges when k,l approach infinity, re-proving a result of Bender, Canfield and McKay. We use the probabilistic method, analyzing breadth-first search on the random graph G(k,p) for an appropriate edge probability p. Central is the analysis of a random walk with fixed beginning and end which is tilted to the left. 相似文献
99.
100.
J. N. Spencer Travis F. Ganunis Abrahim I. Zafar Shaym Puppala James L. Ealy Larry J. Fenton Sunita Gupta C. H. Yoder J. E. Mihalick 《Journal of solution chemistry》1992,21(9):1005-1012
Equilibrium constants and enthalpies of hydrogen-bond formation of mcresol to various cyclic (crown) and acyclic polyethers have been determined in benzene solvent. Equilibrium constants indicated no evidence for an operative macrocyclic effect; the relationship between the increasing size of the equilibrium constant and the number of ether oxygens was rationalized with a simple statistical thermodynamic model. Enthalpies of interactions ranged between –19 and –23 kJ-mol–1. In agreement with PCILO calculations, enthalpies of interaction were essentially independent of the number of oxygen atoms in the ether; no significant difference in enthalpies of interaction between cyclic and acyclic ethers was found. 相似文献