全文获取类型
收费全文 | 3418篇 |
免费 | 65篇 |
国内免费 | 10篇 |
专业分类
化学 | 2381篇 |
晶体学 | 15篇 |
力学 | 61篇 |
数学 | 609篇 |
物理学 | 427篇 |
出版年
2020年 | 29篇 |
2019年 | 30篇 |
2016年 | 52篇 |
2015年 | 47篇 |
2014年 | 49篇 |
2013年 | 137篇 |
2012年 | 88篇 |
2011年 | 116篇 |
2010年 | 67篇 |
2009年 | 89篇 |
2008年 | 116篇 |
2007年 | 96篇 |
2006年 | 121篇 |
2005年 | 109篇 |
2004年 | 98篇 |
2003年 | 84篇 |
2002年 | 96篇 |
2001年 | 74篇 |
2000年 | 71篇 |
1999年 | 46篇 |
1998年 | 49篇 |
1997年 | 62篇 |
1996年 | 61篇 |
1995年 | 56篇 |
1994年 | 57篇 |
1993年 | 50篇 |
1992年 | 59篇 |
1991年 | 45篇 |
1990年 | 58篇 |
1989年 | 71篇 |
1988年 | 76篇 |
1987年 | 71篇 |
1986年 | 37篇 |
1985年 | 51篇 |
1984年 | 54篇 |
1983年 | 29篇 |
1982年 | 55篇 |
1981年 | 50篇 |
1980年 | 69篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 33篇 |
1975年 | 53篇 |
1974年 | 42篇 |
1973年 | 48篇 |
1972年 | 37篇 |
1971年 | 37篇 |
1970年 | 36篇 |
1967年 | 29篇 |
排序方式: 共有3493条查询结果,搜索用时 62 毫秒
91.
Johann-Peter Melder Klaus Weber Andreas Weiler Emmerich Sackers Hans Fritz Dieter Hunkler Horst Prinzbach 《Research on Chemical Intermediates》1996,22(7):667-702
Methodological alternatives for the preparation of highly strained, highly pyramidalized dodecahedrene 2 (Estr=87.3 kcal mol?1; ?=43.5°, MM2) and 1,16-dodecahedradiene 3 (Estr=105.3 kcal mol?1; ?=42.9°, MM2) have been explored, protection/deprotection strategies have been tested—with the eye on their utilization for the generation of higher unsaturated dodecahedranes (e.g. 1,4, 16-triene 4, 1,4,10 (14),16-tetraene 5). For the acquisition of preparative quantities of monoene 2 the “P2F” catalyzed cis-β-elimination in bromododecahedrane, of diene 3 the FVP fragmentation of a “twofold protected” precursor (bis-furan adduct) have become the protocols of choice, which both profit from the recent synthetic advances along the pagodane → dodecahedrane scheme. Because of unusually effective steric protection the highly tilted C=C double bonds of 2 (λmax (CH3CN) = 254 nm, ν C=C = 1658 cm?1, δC=C = 164.4) and 3 (δC=C = 170.5) enter into thermal stabilization pathways (dimerization, oligomerization) only at higher temperatures (for 2 ca. 50% consumption after 5 h at 100°C in a 3·10?3 molar toluene solution); extreme sensitivity to oxygen is primarily attributed to kinetically and thermodynamically promoted allylic hydrogen abstraction. 相似文献
92.
Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH3)3SnOCOCF3 and (CH3)3Pb(OCOCF3) with perfluoroorgano cadmium complexes. (CH3)3SiOCOCF3 reacts with (CF3)2Cd complexes — probably via the intermediate (CH3)3SiCF3 and CF2 elimination — to form (CH3)3SiF and CF3CdOCOCF3 complexes. While the reaction of (CF3)2Cd·D with (CH3)3SnONO2 yields CF3NO as the only volatile product, (Rf)2Cd·D (Rf C2F5, iC3F7) forms RfCdONO2·D and (CH3)3SnRf. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described. 相似文献
93.
A special kind of partiality of heterogeneous algebraic structures is introduced. Every operator of a heterogeneous operator domain is associated with a set of term equations as necessary and sufficient domain condition.It is shown that some kind of hierarchy condition for the system of domain equations is equivalent to the condition that every injective weak homomorphism is a strong homomorphism which is equivalent to the statement that every bijective weak homomorphism is an isomorphism.On the base of this result the notions of a quasi-variety and of a variety of equationally partial heterogeneous algebras are suggested. The class of all small categories becomes a standard example of a variety of equational partial heterogeneous algebras.Presented by V. Trnková. 相似文献
94.
95.
Comprehensive two-dimensional liquid chromatography-size-exclusion chromatography (LC x SEC) was investigated as a tool for the characterization of functional poly(methyl methacrylate) (PMMA) polymers. Ultraviolet-absorbance and evaporative light-scattering detection (ELSD) were used. A simple method to quantify ELSD data is presented. Each data point from the ELSD chromatogram can be converted into a mass concentration using experimental calibration curves. The qualitative and quantitative information obtained on two representative samples is used to demonstrate the applicability of LC x SEC for determining the mutually dependent molar-mass distributions (MMD) and functionality-type distributions (FTD) of functional polymers. The influence of the molar mass on the retention behavior in LC was investigated using LC x SEC for hydroxyl-functional PMMA polymers. The critical conditions, at which retention is--by definition--independent of molar mass, were not exactly the same for PMMA series with different end-groups. Our observations are in close agreement with theoretical curves reported in the literature. However, for practical applications of LC x SEC it is not strictly necessary to work at the exact critical solvent composition. Near-critical conditions are often sufficient to determine the mutually dependent distributions (MMD and FTD) of functional polymers. 相似文献
96.
The oligonucleotide building blocks 4b–d derived from 7-bromo-, 7-chloro-, and 7-methyl-substituted 7-deaza-2′-deoxyadenosines 3b–d were prepared. They were employed in the solid-phase synthesis of the oligonucleotides 7–25 . The dA residues of the homomer d(A12), the alternating d[(A-T)6], and the palindromic d(G-T-A-G-A-A-T-T-C-T-A-C) were replaced by 3b–d as well as by the parent 7-deaza-2′-deoxyadenosine ( 3a ). The melting profiles and CD spectra of oligonucleotide duplexes, showing this major groove modification, were measured, and the Tm values as well as the thermodynamic data were determined. It was found that small substituents such as Br, Cl, or Me introduced in the 7-position of a 7-deazaadenine residue increase the duplex stability compared to oligonucleotides containing adenine. 相似文献
97.
Horst Pommer 《Angewandte Chemie (International ed. in English)》1977,16(7):423-429
The effects of a scientific discovery on industrial practice are illustrated with reference to the Wittig reaction. The aim of utilizing the Wittig reaction of linking terpenoid building blocks to give vitamin A and carotenoids on an industrial scale prompted extensive research and development work of a synthetic and chemical engineering nature. The importance of the Wittig reaction and its variants in the synthesis of active compounds and fine chemicals in industrial research is demonstrated in the present article. 相似文献
98.
George N Pick H Vogel H Johnsson N Johnsson K 《Journal of the American Chemical Society》2004,126(29):8896-8897
The specific and covalent labeling of fusion proteins with synthetic molecules opens up new ways to study protein function in the living cell. Here we present a novel method that allows for the specific and exclusive extracellular labeling of proteins on the surfaces of live cells with a large variety of synthetic molecules including fluorophores, protein ligands, or quantum dots. The approach is based on the specific labeling of fusion proteins of acyl carrier protein with synthetic molecules through post-translational modification catalyzed by phosphopantetheine transferase. The specificity and versatility of the labeling should allow it to become an important tool for studying and manipulating cell surface proteins and for complementing existing approaches in cell surface engineering. 相似文献
99.
We are dealing with a numerical method for solving the problem of minimizing a difference of two convex functions (a d.c. function) over a closed convex set in
n
. This algorithm combines a new prismatic branch and bound technique with polyhedral outer approximation in such a way that only linear programming problems have to be solved.Parts of this research were accomplished while the third author was visiting the University of Trier, Germany, as a fellow of the Alexander von Humboldt foundation. 相似文献
100.
Schumm BA Koetke DS Adolphsen CE Alexander JP Averill D Barish BC Barklow T Barnett BA Blockus D Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan JM Drell PS Drewer DC Durrett D Elia R Feldman GJ Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Hanson G Harr R Harral B Harris FA Hayes K Hearty C Heusch CA Hildreth MD Himel T Hinshaw DA 《Physical review D: Particles and fields》1992,46(1):453-456