全文获取类型
收费全文 | 1135篇 |
免费 | 85篇 |
国内免费 | 6篇 |
专业分类
化学 | 883篇 |
晶体学 | 16篇 |
力学 | 18篇 |
数学 | 134篇 |
物理学 | 175篇 |
出版年
2023年 | 29篇 |
2022年 | 32篇 |
2021年 | 47篇 |
2020年 | 63篇 |
2019年 | 54篇 |
2018年 | 22篇 |
2017年 | 30篇 |
2016年 | 52篇 |
2015年 | 63篇 |
2014年 | 46篇 |
2013年 | 56篇 |
2012年 | 78篇 |
2011年 | 88篇 |
2010年 | 38篇 |
2009年 | 42篇 |
2008年 | 48篇 |
2007年 | 40篇 |
2006年 | 47篇 |
2005年 | 23篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1937年 | 5篇 |
排序方式: 共有1226条查询结果,搜索用时 15 毫秒
61.
Separation theorems for an arbitrary set and a not necessarily convex set in a linear topological space are proved and applied to vector optimization. Scalarization results for weakly efficient points and properly efficient points are deduced. 相似文献
62.
Monte Carlo methods have extensively been used and studied in the area of stochastic programming. Their convergence properties
typically consider global minimizers or first-order critical points of the sample average approximation (SAA) problems and
minimizers of the true problem, and show that the former converge to the latter for increasing sample size. However, the assumption
of global minimization essentially restricts the scope of these results to convex problems. We review and extend these results
in two directions: we allow for local SAA minimizers of possibly nonconvex problems and prove, under suitable conditions,
almost sure convergence of local second-order solutions of the SAA problem to second-order critical points of the true problem.
We also apply this new theory to the estimation of mixed logit models for discrete choice analysis. New useful convergence
properties are derived in this context, both for the constrained and unconstrained cases, and associated estimates of the
simulation bias and variance are proposed.
Research Fellow of the Belgian National Fund for Scientific Research 相似文献
63.
Dipl.‐Chem. Fabian Schax Dr. Eckhard Bill Dr. Christian Herwig Prof. Dr. Christian Limberg 《Angewandte Chemie (International ed. in English)》2014,53(47):12741-12745
The reaction of a tripodal trisilanol with n‐butyllithium and CrCl2 results in a dinuclear CrII complex ( 1 ), which is capable of cleaving O2 to yield in a unique complex ( 2 ) with an asymmetric diamond core composed of two CrIV?O units. Magnetic susceptibility data reveal significant exchange coupling of CrII (S=2) in 1 and large zero‐field splitting for CrIV (S=1) in 2 owing to strong spin–orbit coupling of the ground state. The CrIV?O compound can also be generated using PhIO, and evidence was gathered that although it is the stable product isolated after excessive O2 treatment, it further activates O2 to yield an intermediate species that oxidizes THF or Me‐THF. By extensive 18O labeling studies we were able to show, that in the course of this process 18O2 exchanges its label with siloxide O atoms of the ligand via terminal oxido ligands. 相似文献
64.
Frontispiece: Reactivity Study of Pyridyl‐Substituted 1‐Metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes of Group 4 Metallocenes 下载免费PDF全文
65.
A Biocatalytic Cascade for Versatile One‐Pot Modification of mRNA Starting from Methionine Analogues 下载免费PDF全文
Fabian Muttach Prof. Dr. Andrea Rentmeister 《Angewandte Chemie (International ed. in English)》2016,55(5):1917-1920
Methyltransferases have proven useful to install functional groups site‐specifically in different classes of biomolecules when analogues of their cosubstrate S‐adenosyl‐l ‐methionine (AdoMet) are available. Methyltransferases have been used to address different classes of RNA molecules selectively and site‐specifically, which is indispensable for biophysical and mechanistic studies as well as labeling in the complex cellular environment. However, the AdoMet analogues are not cell‐permeable, thus preventing implementation of this strategy in cells. We present a two‐step enzymatic cascade for site‐specific mRNA modification starting from stable methionine analogues. Our approach combines the enzymatic synthesis of AdoMet with modification of the 5′ cap by a specific RNA methyltransferase in one pot. We demonstrate that a substrate panel including alkene, alkyne, and azido functionalities can be used and further derivatized in different types of click reactions. 相似文献
66.
N-Boc-12-aza-epothilone analog (azathilone) 1 is a potent inhibitor of human cancer cell growth and represents a structurally new class of natural product-derived microtubule-stabilizing agents. Compound 1 has been prepared employing a convergent strategy that is based on the consecutive assembly of building blocks 3, 4, and 19 into diene 20 and subsequent RCM-mediated macrocycle formation. The aldol reaction between aldehyde 3 and ketone 4 delivered the required 6R,7S diastereoisomer 5 with good selectivity and provided a reliable entry into the stereoselective synthesis of carboxylic acid 12. RCM with diene 20 was highly E-selective, thus giving efficient access to (E)-9,10-dehydro-1 (2). The latter is a key analog in SAR studies with 1. 相似文献
67.
In the present paper, we describe the first structural characterization of cymantrenyl(dihalo)borane and report on its use for the synthesis of novel cymantrenylboryl complexes. 相似文献
68.
Dr. Kathrin I. Mohr Dr. Carsten Volz Dr. Rolf Jansen Dr. Victor Wray Dr. Judith Hoffmann Dipl.‐Ing. Steffen Bernecker Priv.‐Doz. Dr. Joachim Wink Dr. Klaus Gerth Prof. Dr. Marc Stadler Prof. Dr. Rolf Müller 《Angewandte Chemie (International ed. in English)》2015,54(38):11254-11258
Lantibiotics (lanthionine‐containing antibiotics) from Gram‐positive bacteria typically exhibit activity against Gram‐positive bacteria. The activity and structure of pinensin A ( 1 ) and B ( 2 ), lantibiotics isolated from a native Gram‐negative producer Chitinophaga pinensis are described. Surprisingly, the pinensins were found to be highly active against many filamentous fungi and yeasts but show only weak antibacterial activity. To the best of our knowledge, lantibiotic fungicides have not been described before. An in‐depth bioinformatic analysis of the biosynthetic gene cluster established the ribosomal origin of these compounds and identified candidate genes encoding all of the enzymes required for post‐translational modification. Additional encoded functions enabled us to build up a hypothesis for the biosynthesis, export, sensing, and import of this intriguing lantibiotic. 相似文献
69.
A Visible Light Photocatalytic Cross‐Dehydrogenative Coupling/Dehydrogenation/6π‐Cyclization/Oxidation Cascade: Synthesis of 12‐Nitroindoloisoquinolines from 2‐Aryltetrahydroisoquinolines 下载免费PDF全文
Fabian Rusch Lisa‐Natascha Unkel Dirk Alpers Dr. Frank Hoffmann Prof. Dr. Malte Brasholz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8336-8340
A visible light‐induced photocatalytic dehydrogenation/6π‐cyclization/oxidation cascade converts 1‐(nitromethyl)‐2‐aryl‐1,2,3,4‐tetrahydroisoquinolines into novel 12‐nitro‐substituted tetracyclic indolo[2,1‐a]isoquinoline derivatives. Various photocatalysts promote the reaction in the presence of air and a base, the most efficient being 1‐aminoanthraquinone in combination with K3PO4. Further, the 12‐nitroindoloisoquinoline products can be accessed directly from C1‐unfunctionalized 2‐aryl‐1,2,3,4‐tetrahydroisoquinolines by extending the one‐pot protocol with a foregoing photocatalytic cross‐dehydrogenative coupling reaction, resulting in a quadruple cascade transformation. 相似文献
70.
A detailed reaction mechanism for n-heptane oxidation has been compiled and subsequently simplified. The model is based on a kinetic model for C1-C4 fuel oxidation of Hoyermann et al. [Phys. Chem. Chem. Phys., 2004, 6, 3824] and a detailed mechanism for n-heptane oxidation developed by Curran et al. [Combust. Flame, 1998, 114, 149]. The generated mechanism is kept compact by limiting the application of the low temperature oxidation pathways to the fuel molecule. The first reaction steps and the complex low temperature paths in the oxidation process have been simplified and reorganized by linear chemical lumping. The reported procedure allows a decrease in number of species and reactions with only a minor loss of model accuracy. The simplified model is of very compact size and gives an advantageous starting point for further model reduction. By this chemically lumped general mechanism without further adjustments the large set of experimental data for the high and low temperature oxidation (ignition delay times, species concentration profiles, heat release and engine pressure profiles, flame speeds and flame structure data) for conditions ranging from very low to high temperatures (550-2300 K), very lean to extremely fuel rich (0.22 < phi < 3) mixtures and pressures between 1 and 42 bar is consistently described providing a basis for reliable predictions for future applications, (i) building reaction mechanisms for similar but chemically more complex fuels (e.g. iso-octane, n-decane,...) and (ii) calculating complex flow fields ("fluid dynamics") after further simplification with advanced reduction tools. 相似文献