全文获取类型
收费全文 | 474篇 |
免费 | 26篇 |
专业分类
化学 | 397篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 22篇 |
物理学 | 72篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 17篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 28篇 |
2011年 | 31篇 |
2010年 | 15篇 |
2009年 | 10篇 |
2008年 | 18篇 |
2007年 | 9篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 17篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1972年 | 2篇 |
1958年 | 1篇 |
1943年 | 1篇 |
1937年 | 2篇 |
1936年 | 4篇 |
排序方式: 共有500条查询结果,搜索用时 265 毫秒
31.
Constrained‐Geometry Bisphosphazides Derived from 1,8‐Diazidonaphthalene: Synthesis,Spectroscopic Characteristics,Structural Features,and Theoretical Investigations
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Julius F. Kögel Nuri C. Abacılar Felicia Weber Dr. Benjamin Oelkers Dr. Klaus Harms Dr. Borislav Kovačević Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):5994-6009
Investigations on the Staudinger reaction between 1,8‐diazidonaphthalene and phosphorous(III) building blocks, a key step in the synthesis of superbasic bisphosphazene proton sponges, yielded a set of bisphosphazides with a constrained geometry 1,8‐disubstituted naphthalene backbone. This compound class has attracted our interest not only due to their surprisingly high stability, but in particular because of their theoretically predicted basicity in the range of their bisphosphazene analogues that can be referred to the constrained geometry interaction of two highly basic nitrogen atoms. Eleven new bisphosphazides bearing simple P‐amino groups as well as P‐guanidino substituents, azaphosphatrane moieties, P2 building blocks, or chiral P‐amino substituents derived from L ‐proline are presented. They were studied concerning their spectroscopic properties and partly also their chromophoric and structural features. In the case of the pyrrolidino‐substituted TPPN(2N2) (TPPN=1,8‐bis(trispyrrolidinophosphazenyl)naphthalene), the stepwise nitrogen elimination is investigated theoretically and experimentally, which led to the isolation and structural characterization of TPPN(1N2) bearing a phosphazide and a phosphazene functionality in one molecule. Attempts to protonate the obtained bisphosphazides and to prove the computationally predicted pKBH+ values through NMR titration reactions resulted in their decay, which again was rationalized by theoretical calculations. Altogether we present the so far most extensive spectroscopic, structural and theoretical investigation of constrained geometry bisphosphazides and their Brønsted and Lewis basic properties. 相似文献
32.
Origin and Location of Electrons and Protons during the Formation of Intermetalloid Clusters [Sm@Ga3−xH3−2xBi10+x]3− (x=0, 1)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dipl.‐Chem. Bastian Weinert B.Sc. Fabian Müller Dr. Klaus Harms Dr. Rodolphe Clérac Prof. Dr. Stefanie Dehnen 《Angewandte Chemie (International ed. in English)》2014,53(44):11979-11983
Reaction of [GaBi3]2? with [Sm(C5Me4H)3] yielded the first protonated ternary intermetalloid clusters [Sm@Ga3?xH3?2xBi10+x]3? ( 1 ; x=0,1). The presence of the Ga? H bonds and the transfer of electrons and protons during the formation of 1 were elucidated by a combination of experimental and quantum chemical methods, thereby rationalizing the role of the solvent ethane‐1,2‐diamine as a Brønsted acid. As an organic by‐product, we observed the previously unknown octamethylfulvene ( 2 ) upon C? C coupling of (C5Me4H)?. 相似文献
33.
At polymer-solid contacts with thermoplastic polymers, the chain characteristics can deviate from the bulk on a length-scale of several nanometer in the so-called interphase. Such an interphase depends on the interaction between respective macromolecule and substrate, and affects the free volume in the polymer. Here, we review our experiments on the characterization of the free volume by positron lifetime spectroscopy at planar and curved interfaces. For Teflon AF on silicon, we identify a layer of increased density, corresponding to an interphase width of some 10 nm. PEP based nanocomposites with functionalized silica show no interphase, whereas for functionalized POSS an interphase is detected. 相似文献
34.
35.
Photoelectron angular distribution (PAD) in the laboratory frame for randomly oriented molecules is typically described by a single anisotropy parameter, the so-called asymmetry parameter. However, especially from a theoretical perspective, it is more natural to consider molecular photoionization by using a molecular frame. The molecular frame PADs (MFPADs) may be used to extract information about the electronic structure of the system studied. In the last decade, significant experimental efforts have been directed to MFPAD measurements. MFPADs are highly characterizing signatures of the final ionic states. In particular, they are very sensitive to the nature of the final state, which is embodied in the corresponding Dyson orbital. In our previous work on acetylacetone, a prototype system for studying intra-molecular hydrogen bond interactions, we followed the dynamics of the excited states involved in the photoexcitation–deexcitation process of this molecule. It remains to be explored the possibility of discriminating between different excited states through the MFPAD profiles. The calculation of MFPADs to differentiate excited states can pave the way to the possibility of a clear discrimination for all the cases where the recognition of excited states is otherwise intricate. 相似文献
36.
We prove the existence of abelian, solvable and nilpotent definable envelopes for groups definable in models of an NTP2 theory. 相似文献
37.
Zakir Murtaza Leah Tolosa Peter Harms Joseph R. Lakowicz 《Journal of fluorescence》2002,12(2):187-192
We describe a new approach to optical sensing of glucose based on the competitive interactions between a ruthenium metal ligand complex, a boronic acid derivative and glucose. The metal-ligand complex [Ru(2,2-bipyridine)2(5,6-dihydroxy-1,10-phenanthroline)](PF6)2 at pH 8 forms a reversible complex with 2-toluylboronic acid or 2-methoxyphenyl boronic acid. Complexation is accompanied by a several-fold increase in the luminescent intensity of the ruthenium complex. Addition of glucose results in decreased luminescent intensity, which appears to be the result of decreased binding between the metal-ligand complex and the boronic acid. Ruthenium metal-ligand complexes are convenient for optical sensing because their long luminescent decay times allow lifetime-based sensing with simple instrumentation. 相似文献
38.
The N-alkoxycarbonyl substituted 2,3-dihydropyrroles 3 and 8 are converted to 2-benzyl-3-pyrrolidinols by the Paternò - Büchi reaction followed by hydrogenolysis. Since the addition of the photoexcited benzaldehyde at the unsaturated heterocycle proceeds in a syn fashion, the benzyl group at C-2 and the hydroxy group at C-3 of the product are cis oriented. The simple and facial diastereoselectivities of the Paternò-Büchi reaction were studied more closely and the relative configuration of the products was elucidated. The thermodynamically less stable endo product is formed as a result of simple diastereoselection. The face differentiation in 2-substituted 2,3-dihydropyrroles is presumably due to the nonplanarity of these heterocycles, which forces attack of the carbonyl group on the face with the existing substituent. All-cis-pyrrolidinols are consequently formed after hydrogenolysis. Following this route, a total synthesis of the pyrrolidinol alkaloid (+)-preussin (1) was conducted, which yielded the target compound in a total yield of 11% over nine steps starting from L-pyroglutaminol (11). 相似文献
39.
Zusammenfassung Spuren der Elemente Bi, Cd, Cu, Co, In, Ni, Pb, Tl und Zn können aus Wasserproben (Seewasser, Mineralwasser, Trinkwasser u.a.) nach Komplexierung mit APDTC durch einen einfachen Filtationsschritt über ein mit Aktivkohle beschichtetes Filter aus 100 ml bis 10l Probevolumen abgetrennt und angereichert werden. Bei der Bestimmung der angereicherten Elementspuren mit der Flammen-AAS oder der ICP/OES werden Nachweisgrenzen < 1 g/l erhalten. Die relativen Standardabweichungen betragen für Elementspuren-Konzentrationen im unteren g/l-Bereich für das Gesamtverfahren mit beiden Bestimmungsmethoden im allgemeinen weniger als 4%.
Herrn Prof. Dr. H. Monien zum 60. Geburtstag gewidmet. 相似文献
Multielement trace preconcentration from water on activated carbon for the sample pretreatment for atomic spectroscopy (flame-AAS, ICP/OES)
Summary It is possible to separate traces of the elements Bi, Cd, Cu, Co, In, Ni, Pb, Tl and Zn from water samples (sea water, mineral water, drinking water) of 100 ml–10 lsample volume, by employing the complexing agent APDTC and a simple filtration step via an activated carbon-lined filter. On determination of the preconcentrated element traces with flame-AAS or ICP/OES techniques, detection limits of <1 g/l are obtained. Generally, relative standard deviations with respect to the entire analysis are for both determination methods 4% when element trace concentrations in the lower 1 g/l range are concerned.
Herrn Prof. Dr. H. Monien zum 60. Geburtstag gewidmet. 相似文献
40.
G. Alexander L. Criegee H.C. Dehne K. Derikum R. Devenish G. Flügge G. Franke Ch. Gerke E. Hackmack P. Harms G. Horlitz Th. Kahl G. Knies E. Lehmann R. Schmitz U. Timm P. Waloschek K. Wacker 《Physics letters. [Part B]》1978,78(1):162-166
The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction. 相似文献