全文获取类型
收费全文 | 5064篇 |
免费 | 124篇 |
国内免费 | 9篇 |
专业分类
化学 | 3577篇 |
晶体学 | 11篇 |
力学 | 50篇 |
数学 | 803篇 |
物理学 | 609篇 |
无线电 | 147篇 |
出版年
2021年 | 31篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2016年 | 95篇 |
2015年 | 76篇 |
2014年 | 88篇 |
2013年 | 191篇 |
2012年 | 174篇 |
2011年 | 185篇 |
2010年 | 113篇 |
2009年 | 111篇 |
2008年 | 150篇 |
2007年 | 171篇 |
2006年 | 175篇 |
2005年 | 175篇 |
2004年 | 160篇 |
2003年 | 122篇 |
2002年 | 130篇 |
2001年 | 92篇 |
2000年 | 60篇 |
1999年 | 72篇 |
1998年 | 83篇 |
1997年 | 89篇 |
1996年 | 93篇 |
1995年 | 74篇 |
1994年 | 86篇 |
1993年 | 84篇 |
1992年 | 91篇 |
1991年 | 65篇 |
1990年 | 81篇 |
1989年 | 85篇 |
1988年 | 80篇 |
1987年 | 89篇 |
1986年 | 115篇 |
1985年 | 125篇 |
1984年 | 93篇 |
1983年 | 81篇 |
1982年 | 78篇 |
1981年 | 76篇 |
1980年 | 100篇 |
1979年 | 56篇 |
1978年 | 87篇 |
1977年 | 76篇 |
1976年 | 73篇 |
1975年 | 44篇 |
1974年 | 63篇 |
1973年 | 57篇 |
1972年 | 53篇 |
1971年 | 42篇 |
1970年 | 49篇 |
排序方式: 共有5197条查询结果,搜索用时 31 毫秒
101.
Steffen Wolf Benedikt Sohmen Bjrn Hellenkamp Johann Thurn Gerhard Stock Thorsten Hugel 《Chemical science》2021,12(9):3350
We report on a study that combines advanced fluorescence methods with molecular dynamics (MD) simulations to cover timescales from nanoseconds to milliseconds for a large protein. This allows us to delineate how ATP hydrolysis in a protein causes allosteric changes at a distant protein binding site, using the chaperone Hsp90 as test system. The allosteric process occurs via hierarchical dynamics involving timescales from nano- to milliseconds and length scales from Ångstroms to several nanometers. We find that hydrolysis of one ATP is coupled to a conformational change of Arg380, which in turn passes structural information via the large M-domain α-helix to the whole protein. The resulting structural asymmetry in Hsp90 leads to the collapse of a central folding substrate binding site, causing the formation of a novel collapsed state (closed state B) that we characterise structurally. We presume that similar hierarchical mechanisms are fundamental for information transfer induced by ATP hydrolysis through many other proteins.We report on a study that combines advanced fluorescence methods with molecular dynamics simulations to cover timescales from nanoseconds to milliseconds for a large protein, the chaperone Hsp90. 相似文献
102.
Hill M Erker G Kehr G Fröhlich R Kataeva O 《Journal of the American Chemical Society》2004,126(35):11046-11057
The dimethylsilanediyl-bridged ansa-zirconocene dichloride 1, that contains a pendent allyl substituent at a Cp-ring, adds HB(C(6)F(5))(2) to the vinyl group to yield the bifunctional zirconocene/borane complex 2. Substituted benzimidazoles were added to the strongly electrophilic borane moiety as protective groups, which allowed subsequent chloride versus -CH(2)SiMe(3) exchange at zirconium to take place by treatment with the respective alkyllithium reagent. Alternatively, the introduction of active sigma-ligands at zirconium is carried out first, followed by the hydroboration reaction. This route was followed for the synthesis of the diphenyl-ansa-zirconocene/borane complex 12. Complex 12 reacts slowly in solution by intramolecular electrophilic attack of the borane at its adjacent Cp-ring, followed by deprotonation using a [Zr]-Ph group to yield the zwitterionic complex 14 featuring a borata-tetrahydroindenyl moiety as part of the ansa-metallocene framework. Complex 14 was characterized by X-ray diffraction. It adds PMe(3) at zirconium to yield 15. Thermolysis of 12 with excess PMe(3) leads to the formation of the (aryne)zirconocene complex 18, which is stabilized by PMe(3) coordination to zirconium and PMe(3) addition to boron. N-Methylbenzimidazole adds to the -B(C(6)F(5))(2) unit of 12 to give the 1:1 adduct 19. Thermolysis of 19 at 80 degrees C in benzene solution in the presence of one additional equivalent of N-methylbenzimidazole results in deprotonation of the substrate to yield the sigma-N-methylbenzimidazolyl zirconium complex 20 (as a mixture of two diastereoisomers). An additional N-methylbenzimidazole ligand is bonded to the B(C(6)F(5))(2) unit in this product. 相似文献
103.
Heinz Berner Hermann Vyplel Gerhard Schulz Gernot Fischer 《Monatshefte für Chemie / Chemical Monthly》1985,116(10):1165-1176
2-Hydroxy-19,20-dihydropleuromutilin (10) undergoes a stereospecific ketolisomerisation when treated with base under phase/transfer conditions (11, 12). The subsequent reductive elimination of the 3-acetoxygroup afforded mutilin with a 1,2-transposed ketofunction (13). 相似文献
104.
Zusammenfassung Beim Abbau von Paucin wird Brenzcatechin, Kaffeesäure und Putrescin erhalten. Daraus und aus spektroskopischen Befunden ergibt sich für das Paucin die Strukturformel3.
Mit 6 Abbildungen
Meinem Lehrer, Prof. Dr.H. Bretschneider, zum 65. Geburtstag gewidmet. 相似文献
The structure of Paucine
Paucine can be degradated to catechol, caffeic acid and putrescine. This together with spectroscopic data allows us to deduce formula3 for paucine.
Mit 6 Abbildungen
Meinem Lehrer, Prof. Dr.H. Bretschneider, zum 65. Geburtstag gewidmet. 相似文献
105.
106.
Michel Cibils Yvan Cuche Gerhard Müller 《Zeitschrift für Physik B Condensed Matter》1995,97(4):565-572
The peculiar spectral properties of the spinboson model make it suitable for an investigation of quantum nonintegrability effects and level statistics from a new perspective. For fixed spin quantum numbers, its energy spectrum consists of 2s+1 sequences of levels with no upper bound. These sequences are identified and labelled consecutively by means of a quantum invariant calculated from the time average of a non-stationary operator. For integrable cases, level repulsion (on the energy axis) is limited to states within each sequence. From the observed spectral properties, we infer a series ofs-dependent level-spacing distributions. They converge towards a Poisson distribution fors. For nonintegrable cases, level repulsion becomes a universal phenomenon, but the amount of repulsion between two states decreases with increasing separation (in label) of the two sequences to which they belong. For smalls, the quantum nonintegrability effects are compelling but not at all chaotic. Nevertheless, they contain all the ingredients necessary to produce the symptoms commonly described as indicators of quantum chaos. In this model, we can observe quantum chaos in the making under very controllable conditions. 相似文献
107.
Gerhard Keller 《Israel Journal of Mathematics》1994,86(1-3):301-310
We prove exponential weak Bernoulli mixing for invariant measures of certain piecewise monotone interval maps studied in [BK]
and [KN]. In particular we prove this for unimodal maps with negative Schwarzian derivative satisfying lim
, wherec is the unique critical point ofT. 相似文献
108.
Gerhard Grams 《Geometriae Dedicata》1994,50(1):87-105
In 1972 M. O'Nan proved thatL
n (q),h 3; can be characterized as a doubly-transitive groupG on a finite set , whereG
a has an Abelian normal subgroup acting not semi-regularly on -a. In the Main Theorem we show that a similar statement holds if is infinite. Our result implies O'Nan's theorem.This paper is part of the author's Ph.D. thesis written under supervision of Prof. F. G. Timmesfeld. 相似文献
109.
Gerhard Niklasch 《manuscripta mathematica》1994,83(1):443-446
In the preceding paper [2], D. Clark proved—modulo a finite amount of computation—that the ring of integersR of
admits explicit euclidean algorithms, although it is not euclidean for the norm: In fact, every completely multiplicative
function ϕ:R→R
>-0 which sends the prime elements above 23 to a value larger than 25 and which agrees with the absolute norm at all other primes
defines a euclidean algorithm forR.
The referee had felt that an independent verification of the computer-assisted proofs of Lemmas 1 and 2 of [2] was desirable,
and that it should be carried out separately from the refereeing process in the light of the public, conforming to C. Lam's
eloquent suggestions [3]. F. Lemmermeyer and the present author succeeded in confirming Clark's result (independently of each
other). This note gives some details of the methods employed in the verifications. 相似文献
110.
Hendrik Voigt Aaron Rigoni Evgeniy Boltynjuk Mohammed Reda Chellali Bonnie Tyler Harald Rösner Sergiy Divinski Horst Hahn Gerhard Wilde 《Advanced functional materials》2023,33(44):2302386
Comprehensive analyses of the atomic structure using advanced analytical transmission electron microscopy-based methods combined with atom probe tomography confirm the presence of distinct glass–glass interfaces in a columnar Cu-Zr nanoglass synthesized by magnetron sputtering. These analyses provide first-time in-depth characterization of sputtered film nanoglasses and indicate that glass–glass interfaces indeed present an amorphous phase with reduced mass density as compared to the neighboring amorphous regions. Moreover, dedicated analyses of the diffusion kinetics by time-of-flight secondary ion mass spectroscopy (ToF SIMS) prove significantly enhanced diffusivity, suggesting fast transport along the low density glass–glass interfaces. The present results further indicate that sputter deposition is a feasible technique for reliable production of nanoglasses and that some of the concepts proposed for this new class of glassy materials are applicable. 相似文献