全文获取类型
收费全文 | 42958篇 |
免费 | 16110篇 |
国内免费 | 361篇 |
专业分类
化学 | 54719篇 |
晶体学 | 45篇 |
力学 | 1276篇 |
综合类 | 20篇 |
数学 | 1578篇 |
物理学 | 1791篇 |
出版年
2024年 | 426篇 |
2023年 | 4270篇 |
2022年 | 1507篇 |
2021年 | 2491篇 |
2020年 | 4767篇 |
2019年 | 2296篇 |
2018年 | 2450篇 |
2017年 | 683篇 |
2016年 | 5635篇 |
2015年 | 5598篇 |
2014年 | 5050篇 |
2013年 | 5226篇 |
2012年 | 3312篇 |
2011年 | 1213篇 |
2010年 | 3497篇 |
2009年 | 3412篇 |
2008年 | 1211篇 |
2007年 | 852篇 |
2006年 | 272篇 |
2005年 | 203篇 |
2004年 | 160篇 |
2003年 | 147篇 |
2002年 | 114篇 |
2001年 | 112篇 |
2000年 | 116篇 |
1997年 | 98篇 |
1996年 | 121篇 |
1995年 | 164篇 |
1994年 | 126篇 |
1993年 | 237篇 |
1992年 | 119篇 |
1991年 | 92篇 |
1988年 | 112篇 |
1987年 | 91篇 |
1984年 | 92篇 |
1982年 | 91篇 |
1981年 | 98篇 |
1980年 | 124篇 |
1979年 | 106篇 |
1978年 | 106篇 |
1977年 | 177篇 |
1976年 | 198篇 |
1975年 | 202篇 |
1974年 | 199篇 |
1973年 | 119篇 |
1972年 | 157篇 |
1971年 | 122篇 |
1970年 | 212篇 |
1969年 | 129篇 |
1968年 | 134篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Prof. Dr. Wolfgang Schwarz 《Monatshefte für Mathematik》1979,87(1):65-67
D. Leitmann andD. Wolke [3] proved that multiplicative functions, which are restrictions of continuous, periodic functionsF: with irrational period, are constant equal to 0 or 1. In this note a simpler proof for this result is given. 相似文献
62.
This paper is concerned with the optimal positioning of a new product in an attribute space. A deterministic optimization model that relies on the axiom of choice is compared with the model byShocker/Srinivasan [1974] that incorporates a probabilistic measure of choice. Investigating the assumptions and the construction of both models, it is shown that the probability function byShocker/Srinivasan is based on a controversial assumption and incorporates a parameter that has not been given an economic explanation. Furthermore, both models are applied to complex configurations. It is demonstrated that the optimal positions for the new product resulting from the model byShocker/Srinivasan depend heavily on the parameter just mentioned and may run contrary to plausible consequences of the axiom of choice.
Zusammenfassung Für die optimale Gestaltung neuer Produkte, d.h. ihrer Positionierung in einem Raum von Produkteigenschaften, wird ein Modell angeboten, das auf einer deterministischen Kaufentscheidung beruht, ein anderes, das eine stochastische Kaufentscheidung unterstellt. Es wird gezeigt, daß der zuletzt genannte Modelltyp stark von der Spezifikation eines ökonomisch bisher nicht erklärten Parameters abhängt und z.T. Konsequenzen aufweist, die dem Wahlaxiom zuwider laufen, auf das das erstgenannte Modell aufbaut. Durch einen Vergleich auch komplexer Konfigurationen von Käuferbeurteilungen neuer Produkte wird gezeigt, welche Gestaltungsentscheidungen auf der Grundlage der beiden Modelle zur Optimierung einer Zielfunktion zu treffen sind.相似文献
63.
LetG denote a locally compact abelian topological group. The aim of the present paper is to prove an “intermediate” result between two well-known results ofL. Hörmander andG. I. Gaudry concerning the structure of the spaces ?G?μ?t p,q (G). 相似文献
64.
Zhen-Lin Qiu Dandan Chen Zeying Deng Ke-Shan Chu Yuan-Zhi Tan Jun Zhu 《中国科学:化学(英文版)》2021,(6):1004-1008
Carbon nanohoop,a class of constrained molecular architecture consisting of linked arene units,has attracted considerable interest from both experimental and th... 相似文献
65.
Chih-Hsin Yeh Chia-Yi Chou Chin-Sheng Wu Lee-Ping Chu Wei-Juan Huang Hsin-Chun Chen 《Molecules (Basel, Switzerland)》2022,27(14)
To establish the analytic conditions for examining the aroma quality of vanilla pods, we compared different extraction methods and identified a suitable option. We utilized headspace solid-phase microextraction (HS-SPME), steam distillation (SD), simultaneous steam distillation (SDE) and alcoholic extraction combined with gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) to identify volatile components of vanilla pods. A total of 84 volatile compounds were identified in this experiment, of which SDE could identify the most volatile compounds, with a total of 51 species, followed by HS-SPME, with a total of 28 species. Ten volatile compounds were identified by extraction with a minimum of 35% alcohol. HS-SPME extraction provided the highest total aroma peak areas, and the peak areas of aldehydes, furans, alcohols, monoterpenes and phenols compounds were several times higher than those of the other extraction methods. The results showed that the two technologies, SDE and HS-SPME, could be used together to facilitate analysis of vanilla pod aroma. 相似文献
66.
67.
A solid state metathesis (SSM) reaction was investigated with respect to the formation of rare‐earth carbodiimides, the role of the co‐produced salt (LiCl), and the eutectic flux medium (LiCl/KCl). A SSM reaction is characterized by an exothermic reaction in which a salt (often LiCl) is coproduced. When the salt melts, it can serve as a useful medium for the crystallization of a desired product. An improved crystal growth can be observed by using an eutectic flux. However, the composition of an eutectic LiCl/KCl flux is altered when LiCl is produced during the reaction. The thermal effects concerning the endothermic melting of the flux and the exothermic ingnition of the SSM reaction may compensate each other, which is not necessarily a drawback for the reaction to proceed. 相似文献
68.
Maurits Kuiper Manfred Speldrich Helmut Schilder Prof. Dr. Heiko Lueken 《无机化学与普通化学杂志》2012,638(10):1432-1436
Abstract. The magnetic behavior of the mononuclear nd1 systems MCp2Cl2 (M = V4+[3d1], Nb4+[4d1], Ta4+[5d1], space group P21/c, pseudosymmetry of the molecules C2v) deviates from pure single ion spin magnetism on account of ligand field effect (Hlf), spin‐orbit coupling (Hso), and intermolecular spin‐spin exchange interactions (Hex). For both VCp2Cl2 and NbCp2Cl2 excellent adaptations to the measured susceptibility data were obtained (2 K ≤ T ≤ 300 K) on the basis of spectroscopic data (lf, so) and cooperative metal–metal interactions (ex) of antiferromagnetic nature [molecular field model (mf)]. For TaCp2Cl2 experimental term structure data are not available. Therefore, Jørgensen's spectroscopical series (g‐factor of the central ion) was applied to extrapolate the data set for TaCp2Cl2. Hlf, Hso, and Hex (antiferromagnetic) increase in the order 3d1 → 4d1 → 5d1 leading, with rising atomic number of the metals, to a distinct enhancement of the magnetic anisotropy. At 4 K the μeff components μeff,y (oriented perpendicular to the cg–M–cg plane; “cg” = center of gravity of the Cp ring), μeff,z (oriented along the twofold pseudoaxis), and μeff,x are 1.73, 1.69, 1.68 (V), 1.73, 1.62, 1.59 (Nb), and 1.71, 1.59, 1.49 (Ta). While μeff,y is independent of T, both μeff,z and μeff,x decrease with decreasing T. 相似文献
69.
70.