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111.
Abhik Ghosh 《Theoretical chemistry accounts》2000,104(2):157-159
The concept of local symmetry has been applied to faces of planar sites such as carbon–carbon double bonds and aromatic rings
with the principal results being as follows. The two faces of a planar site must have the same local symmetry group. This
local symmetry group is limited to the polar point groups. For cyclic compounds, directed cycles must have chirotopic faces
although the reverse is not necessarily true: chirotopic faces are possible for both directed and undirected cycles. A number
of examples are provided to illustrate these results.
Received: 30 June 1999 / Accepted: 4 October 1999 / Published online: 19 April 2000 相似文献
112.
Māris Turks 《Tetrahedron letters》2006,47(16):2783-2786
A new one-pot synthesis of sulfoxides is presented. It involves the bora-ene reaction of sulfur dioxide and prop-2-ene-1-boronic esters, giving mixed anhydrides of sulfinic and boric acids. The latter react chemoselectively at the sulfur center with Grignard reagents in displacement reactions giving the corresponding prop-2-en-1-ylsulfoxides. Preliminary studies on the chirality transfer of enantiomerically enriched boronates to the sulfoxides are also presented. 相似文献
113.
The regulation on cross-border exchanges of electricity in the European Union is meant to enhance the trade of electricity between Member States, by facilitating access to the network and improving the management of congestion at the interconnections. This paper presents a computational model that embeds these two features. The problem is cast in the form of a two-stage equilibrium between regional Regulators. In the first stage, they decide on the allocation of their regional network costs between generators and customers. Either they maximise their regional welfare non-cooperatively (Nash equilibrium), or they centralise the decision as a super-regulator (leading to a cooperative equilibrium). In the second-stage equilibrium, the consequences of first-stage’s decisions are assessed by modelling the energy market as the result of imperfect competition equilibrium on competitive market, coupled with regulated pricing on the domestic less competitive markets. The “rules” that come out of the first-stage game largely influence the final equilibrium. We illustrate this on an extensive numerical example, showing that the model behaves properly and identifying policy issues worth of further investigations. 相似文献
114.
By direct synthesis route, chiral metal-organic frameworks are synthetized with enantiopure ligands or spontaneous resolution; by indirect method, post-synthetic method and chiral inductionare introduced to construct chiral metal-organic frameworks. 相似文献
115.
Helicenes with unique π-conjugated helical structure and excellent chiroptical properties have received more and more attention. In this review, the idea of multidimensional construction of helicenes and their derivatives was proposed, and the related recent progress was summarized comprehensively. 相似文献
116.
Gerardo M. Ramos Tombo Daniel Bellu 《Angewandte Chemie (International ed. in English)》1991,30(10):1193-1215
The modern agrochemical industry is searching, more intensively than ever, for new substances to combat pests (weeds, deleterious insects, plant pathogens, etc.). In the complex and costly selection and optimization process, state-of-the-art scientific methods are always needed. The aims of the interdisciplinary optimization are mainly the reduction of the rate of application of the new substance, an increase in the selectivity against the target organism, and the optimal ecological profile. If a promising crop protection compound is a racemate or a diastereoisomeric mixture, the chemist has a unique opportunity to contribute to this optimization process through the synthesis of enantiomerically pure isomers for testing purposes. If the single isomer proves to be biologically superior to the racemate, the development of an economical and ecologically sound process for the production of the single isomer presents an even greater challenge. The average price of a crop protection compound is much lower than that for a pharmaceutical product, and this fact imposes a severe limitation upon the flexibility of the chemist who is concerned with the synthesis and production of a stereochemically pure agrochemical. This forces the crop protection chemist to make full use of both his scientific and creative capabilities. Fortunately, parallel to the development of the above optimization aims of a modern and ecologically sound crop protection research, there has been a continuous and worldwide advance in the area of asymmetric synthesis. Due to the interplay of these two parallel efforts there has been a great accumulation of chemical, biological, and agronomical knowledge in recent years, which should have implications beyond merely the synthesis of enantiomerically pure agrochemicals. 相似文献
117.
118.
Satu Silver 《Tetrahedron letters》2004,45(2):249-252
A simple procedure for the preparation of new 1-, 2- and 1,3-chirally substituted indenes is described in which indenyllithium or 2-indenylmagnesium bromide is reacted with a β-pinenyl derived chlorosilane. Synthesis of the ethylene bridged bis(indene) analogues of two of the new compounds is also described. 相似文献
119.
Oliver Seewald Ulrich Flrke Hans Egold Hans‐Jürgen Haupt Meinhard Schwefer 《无机化学与普通化学杂志》2006,632(2):204-210
Syntheses and Structure of Chiral Metallatetrahedron Complexes of the Type [Re2(M1PPh3)(M2PPh3)(μ‐PCy2)(CO)7C≡CPh] (M1 = Ag, Au; M2 = Cu, Ag, Au) From the reaction of Li[Re2(μ‐H)(μ‐PCy2)(CO)7(C(Ph)O)] ( 1 ) with Ph3AuC≡CPh both benzaldehyde and the trinuclear complex Li[Re2(AuPPh3)(μ‐PCy2)(CO)7C≡CPh] ( 2a ) were obtained in high yield. The complex anion was isolated as its PPh4‐salt 2b . The latter reacts with coinage metal complexes PPh3M2Cl [M2 = Cu, Ag, Au] to give chiral heterometallatetrahedranes of the general formula [Re2(AuPPh3)(M2PPh3)(μ‐PCy2)(CO)7C≡CPh] (M2 = Cu 3a , Ag 3b , Au 3c ). The corresponding complex [Re2(AgPPh3)2(μ‐PCy2)(CO)7C≡CPh] ( 3d ) is obtained from the reaction of [Re2(AgPPh3)2(μ‐PCy2)(CO)7Cl] ( 4 ) with LiC≡CPh. 3d undergoes a metathesis reaction in the presence of PPh3CuCl giving [Re2(AgPPh3)(CuPPh3)(μ‐PCy2)(CO)7C≡CPh] ( 3e ) and PPh3AgCl. Analogous metathesis reactions are observed when 3c is reacted with PPh3AgCl or PPh3CuCl giving 3a or 3b , respectively. The reaction of 1 with PPh3AuCl gives benzaldehyde and Li[Re2(AuPPh3)(μ‐PCy2)(CO)7Cl] ( 5a ) which upon reaction with PhLi forms the trinuclear complex Li[Re2(AuPPh3)(μ‐PCy2)(CO)7Ph] ( 6a ). Again this complex was isolated as its PPh4‐salt 6b . In contrast to 2b , 6b reacts with one equivalent of Ph3PAuCl by transmetalation to give Ph3PAuPh and PPh4[Re2(AuPPh3)(μ‐PCy2)(CO)7Cl] ( 5b ). The X‐ray structures of the compounds 3a , 3b , 3e and 4 are reported. 相似文献
120.
János Wölfling Ágota Szájli László Vörös Mónika Gáspár Gyula Schneider 《Monatshefte für Chemie / Chemical Monthly》2006,137(8):1099-1107
Summary. 3β-Hydroxy-16,17-seco-13α-androsta-5,16-dien-17-al was obtained from 3β-acetoxyandrost-5-en-17-one in six steps with a Grob fragmentation as the key step. This seco-steroid, containing a formyl group and an unsaturated side-chain in a sterically favourable cis position, is a useful synthon
for the synthesis of novel heterocycles condensed to the 3β-hydroxy-13α-androst-5-en-17-one skeleton. 相似文献