全文获取类型
收费全文 | 1746篇 |
免费 | 85篇 |
专业分类
化学 | 1522篇 |
晶体学 | 3篇 |
力学 | 12篇 |
数学 | 108篇 |
物理学 | 186篇 |
出版年
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 42篇 |
2019年 | 35篇 |
2018年 | 20篇 |
2017年 | 9篇 |
2016年 | 60篇 |
2015年 | 57篇 |
2014年 | 60篇 |
2013年 | 77篇 |
2012年 | 104篇 |
2011年 | 153篇 |
2010年 | 80篇 |
2009年 | 83篇 |
2008年 | 94篇 |
2007年 | 103篇 |
2006年 | 88篇 |
2005年 | 72篇 |
2004年 | 79篇 |
2003年 | 63篇 |
2002年 | 71篇 |
2001年 | 33篇 |
2000年 | 19篇 |
1999年 | 24篇 |
1998年 | 24篇 |
1997年 | 28篇 |
1996年 | 32篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有1831条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
This paper describes the use of dendritic polyglycerol as a new high-loading polymeric support. The soluble polyether skeleton allows the parallel synthesis of small libraries on a large scale (1-5 mmol). Purification of polymer-bound products is easily achieved by a parallel dialysis apparatus, which was developed to separate up to 12 reaction mixtures simultaneously. The terminal 1,2-diol groups of polyglycerol (loading capacity: 4.1 mmol diol/g) can be directly coupled with carbonyl compounds without additional linker groups. At the same time the polyglycerol support acts as a polymeric ketal protecting group. The coupling of the carbonyl compounds occurs in high yields, and effective loading capacities of up to 3.5 mmol of ketone/g can be reached. The obtained polymeric acetals can easily be characterized by standard analytical techniques, such as NMR, IR, UV, and SEC. The versatility of this new polymeric support for solution-phase organic synthesis is demonstrated by two efficient polymer-supported syntheses: nucleophilic substitutions of gamma-chloroketones with amines and Suzuki-coupling on p-bromobenzaldehyde. The acid-catalyzed acetal cleavage with a solid-phase acidic ion-exchange resin in methanol demonstrates the orthogonal use of these soluble polymeric supports with conventional solid-phase reagents. Cleavage of products occurs in high yields, and almost complete recovery (>95%) of the polyglycerol support has been demonstrated after phase separation or ultrafiltration. 相似文献
95.
Ballardini R Balzani V Clemente-León M Credi A Gandolfi MT Ishow E Perkins J Stoddart JF Tseng HR Wenger S 《Journal of the American Chemical Society》2002,124(43):12786-12795
We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 12+, 2-H3+, and 3. Component 12+ consists of two moieties: a [Ru(bpy)3]2+ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H3+ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown-ether socket of 12+ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 12+ superset 2-H3+ and 2-H3+ subset 3 dyads, and of the 12+ superset 2-H3+ subset 3 triad have been investigated in CH2Cl2 solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 12+ superset 2-H3+ subset 3 triad, light excitation of the [Ru(bpy)3]2+ unit of component 12+ is followed by electron transfer (k = 2.8 x 108 s-1) to the bipyridinium unit of component 2-H3+, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed. 相似文献
96.
Bernd Wrackmeyer Gerald Kehr Sabine Willbold Roland Boese 《Chemistry of Heterocyclic Compounds》1999,35(9):1041-1051
Organo-substituted 2,5-dihydro-1,2,5-oxoniastannaboratoles3 were prepared by methanolysis of zwitterionic 2-(alkyn-l-ylborate)alkenyltin compounds1. Analogously, the bis[2-(alkyn-l-yl-borate)alkenyltin derivative2 reacts with an excess of methanol to give a dimeric MeO-bridged 2,5-dihydro-1,2,5-oxoniastannaboratole (10a)2. Various intermediates could be identified by NMR spectroscopy, and the molecular structure of(10a)
2 was determined by X-ray analysis. The structures of several products of the methanolysis indicate that protolysis of an Sn-C=bond occurs first, followed by an MeO/alkenyl exchange reaction.Dedicated to the 100th Anniversary of A. N. Nesmeyanov's birth.Laboratorium für Anorganische Chemie, Universität Bayreuth, D-95440 Bayreuth, Germany Institut für Anorganische Chemie, Universität-GH Essen, Universitätsstr. 5–7, D-45117 Essen, Germany. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1185–1196, September, 1999. 相似文献
97.
The combination of sequential leaching methods for a first assessment of the kind of species in river sediments with multivariate-statistical methods (like factor analysis) for identifying anthropogenic and/or geogenic loading is useful for the differentiated characterization of the pollution state of a river. Electrochemical investigations, planned on the basis of statistical design and following empirical modelling, enables quantitative conclusions on the binding forms of heavy metals in river waters. Deposition-remobilisation effects of heavy metals in the complex system river water-river sediment can be described by PLS modelling. 相似文献
98.
Rudolf Haag Daniel Kastler Ewa B. Trych-Pohlmeyer 《Communications in Mathematical Physics》1974,38(3):173-193
For an infinite dynamical quantum system idealized as aC*-algebra acted upon by time-translations automorphisms in an asymptotically abelian way, we propose to characterize equilibrium states by the three properties of stationarity, stability for local perturbations of the dynamics, and relative purity. We show that a state with these properties either gives rise to a one-sided energy spectrum or is a KMS- (i.e. essentially a limit Gibbs-) state. 相似文献
99.
100.