全文获取类型
收费全文 | 3153篇 |
免费 | 61篇 |
国内免费 | 12篇 |
专业分类
化学 | 1850篇 |
晶体学 | 17篇 |
力学 | 92篇 |
数学 | 650篇 |
物理学 | 617篇 |
出版年
2021年 | 33篇 |
2020年 | 27篇 |
2019年 | 38篇 |
2016年 | 49篇 |
2015年 | 62篇 |
2014年 | 48篇 |
2013年 | 120篇 |
2012年 | 102篇 |
2011年 | 115篇 |
2010年 | 72篇 |
2009年 | 65篇 |
2008年 | 124篇 |
2007年 | 113篇 |
2006年 | 87篇 |
2005年 | 76篇 |
2004年 | 70篇 |
2003年 | 52篇 |
2002年 | 61篇 |
2001年 | 34篇 |
2000年 | 57篇 |
1999年 | 47篇 |
1998年 | 36篇 |
1997年 | 44篇 |
1996年 | 37篇 |
1995年 | 45篇 |
1994年 | 42篇 |
1993年 | 36篇 |
1992年 | 49篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 33篇 |
1988年 | 40篇 |
1987年 | 42篇 |
1986年 | 38篇 |
1985年 | 51篇 |
1984年 | 40篇 |
1983年 | 27篇 |
1982年 | 34篇 |
1981年 | 41篇 |
1980年 | 51篇 |
1979年 | 46篇 |
1978年 | 34篇 |
1977年 | 53篇 |
1976年 | 36篇 |
1975年 | 31篇 |
1974年 | 26篇 |
1971年 | 26篇 |
1967年 | 22篇 |
1933年 | 22篇 |
1930年 | 21篇 |
排序方式: 共有3226条查询结果,搜索用时 281 毫秒
91.
Ott T Kern A Schuffenhauer A Popov M Acklin P Jacoby E Stoop R 《Journal of chemical information and computer sciences》2004,44(4):1358-1364
For the clustering of chemical structures that are described by the Similog, ISIS count, and ISIS binary fingerprints, we propose a sequential superparamagnetic clustering approach. To appropriately handle nonbinary feature keys, we introduce an extension of the binary Tanimoto similarity measure. In our applications, data sets composed of structures from seven chemically distinct compound classes are evaluated and correctly clustered. The comparison, with results from leading methods, indicates the superiority of our sequential superparamagnetic clustering approach. 相似文献
92.
Westmacott G Zhong F Frank M Friedrich S Labov SE Benner WH 《Rapid communications in mass spectrometry : RCM》2000,14(7):600-607
The performance of an energy sensitive, niobium superconducting tunnel junction (STJ) detector is investigated by measuring the pulse height produced by impacting molecular and atomic ions at different kinetic energies. Ions are produced by laser desorption and matrix-assisted laser desorption in a time-of-flight mass spectrometer. Our results show that the STJ detector pulse height decreases for increasing molecular ion mass, passes through a minimum at around 2000 Da, and then increases with increasing mass of molecular ions above 2000 Da. The detector does not show a decline in sensitivity for high mass ions as is observed with microchannel plate ion detectors. These detector plus height measurements are discussed in terms of several physical mechanisms involved in an ion-surface collision. 相似文献
93.
Uwe K. A. Klein Gertrud Hönes Friedrich W. Hafner 《Photochemistry and photobiology》1984,40(5):569-574
Abstract —The time-dependent rotational relaxation of Rhodamine 6G in fresh and dried human blood serum was investigated using picosecond phasefluorometry. Measurements were also carried out in aqueous solutions of amino acids, glucose, urea, and bovine serum albumin to evaluate our model for the interactions. It is shown that the distribution of Rhodamine 6G between the aqueous and the protein phase of the blood serum strongly depends on protein concentration and temperature. 相似文献
94.
Friedrich Asinger Alfons Saus Magdalena von Wachtendonk 《Monatshefte für Chemie / Chemical Monthly》1980,111(2):385-398
Thiomorpholine as well as alkyl substituted thiomorpholines and their Sdioxides, respectively, are transformed into the corresponding N-Aminothiomorpholines by nitrosation (1–5) followed by the reduction with zinc in acetic acid/acetic acid anhydride under simultaneous formation of the corresponding N-acetyl derivates, and hydrolysis by hydrochloric acid (6–9). Examples of this method are described. 4-Aminothiomorpholines and their Sdioxides react with aldehydes or ketones to give azomethines (10–31). Acylation with mono-and dicarbonic acid chlorides leads to the N-acyl derivatives32–44.Mannich condensation is also possible. By oxidation with yellow mercury oxide tetracenes are formed (46–47).
Teil der DissertationM. Schmitz, Techn. Hochschule Aachen, 1975. 相似文献
95.
Ralf Eiden Ralf Falter Barbara Augustin-Castro Heinz Friedrich Schöler 《Analytical and bioanalytical chemistry》1997,357(4):439-441
Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high
performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for
the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this
method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within
their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition
method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples
were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight.
Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996 相似文献
96.
Jiang He Florian Rauch Dr. Alexandra Friedrich Dr. Daniel Sieh Dr. Tatjana Ribbeck Dr. Ivo Krummenacher Prof. Dr. Holger Braunschweig Prof. Dr. Maik Finze Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13777-13784
N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)–π–A compounds 1 – 3 . In addition, an enamine π-donor analogue ( 4 ) was synthesized for comparison. UV–visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1 – 4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3 , =−0.40 V vs. ferrocene/ferrocenium, Fc/Fc+, in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1 – 3 are much more destabilized than that of the enamine-containing 4 , which confirms the stronger donating ability of NHOs. 相似文献
97.
H. Schnecko W. Lintz W. Kern 《Journal of polymer science. Part A, Polymer chemistry》1967,5(1):205-214
Relative changes in polymerization activity of ethylene, propylene, and butene-1 in Ziegler-Natta polymerization were compared by use of TiCl3 samples contaminated with O2 and H2O to various extents. Catalyst depletion varied for the three monomers which supported the existence of different active centers. In butene-1 polymerizations with the system Al(C2H5)2Cl–TiCl3, the formation of active centers involves an irreversible and a reversible (adsorption) reaction, the former pertaining to the formation of Al(C2H5)Cl2 and dependent upon the purity of the TiCl3. The kinetic treatment of the rate curves suggests a mixed order of catalyst deactivation and again points to the importance of Al(C2H5)Cl2. 相似文献
98.
99.
100.
G. T. Jones R. W. L. Jones B. W. Kennedy D. R. O. Morrison M. M. Mobayyen S. Wainstein M. Aderholz D. Hantke E. Hoffmann U. F. Katz J. Kern N. Schmitz W. Wittek H. P. Borner G. Myatt D. Radojicic S. Burke 《Zeitschrift fur Physik C Particles and Fields》1991,51(2):205-208
Using data obtained with the bubble chamber BEBC at CERN, the inclusivef 2 (1270) meson production invp and \(\bar vp\) charged current reactions is studied. It is found thatf 2 production occurs mainly in events with a hadronic invariant massW?7 GeV. In these events, the averagef 2 multiplicity is about half the average ρO multiplicity, and thex F andp T 2 distributions of thef 2 agree in shape with those of the ρO. The predictions of a semi-empirical model (Wells model) are in accord with the measured multiplicities atW>7 GeV, whereas at lowerW the model predicts too largef 2 multiplicities. 相似文献