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991.
Yong Wang Yajun Zhao Shuaishuai Zhu Xingping Zhou Jing Xu Xiaolin Xie Rinaldo Poli 《Angewandte Chemie (International ed. in English)》2020,59(15):5988-5994
A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine] from ring‐opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co?O bond, allowing for in situ transformation of the ROCOP active species (Salen)CoIII‐OR into the OMRP photoinitiator (Salen)CoIII‐CO2R. The proposed mechanism, which involves CO coordination to (Salen)CoIII‐OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on‐demand sequence control can be achieved for the one‐pot synthesis of polyester‐b‐polyacrylate diblock copolymers (?<1.15). 相似文献
992.
David M. Koshy Shucheng Chen Dong Un Lee Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dennis Nordlund Alessandro Gallo Christopher Hahn Drew C. Higgins Zhenan Bao Thomas F. Jaramillo 《Angewandte Chemie (International ed. in English)》2020,59(10):4043-4050
Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
993.
Chen‐Xi Ye Shuming Chen Feng Han Xiulan Xie Sergei Ivlev K. N. Houk Eric Meggers 《Angewandte Chemie (International ed. in English)》2020,59(32):13552-13556
A transformation of fluxional into configurationally stable axially chiral N‐arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral‐at‐metal rhodium Lewis acid. Specifically, N‐arylpyrroles were alkylated with N‐acryloyl‐1H‐pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow‐up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity. 相似文献
994.
Ramesh C. Samanta Julia Struwe Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2020,59(33):14154-14159
Direct alkylations of carboxylic acid derivatives are challenging and particularly nickel catalysis commonly requires high reaction temperatures and strong bases, translating into limited substrate scope. Herein, nickel‐catalyzed C?H alkylations of unactivated 8‐aminoquinoline amides have been realized under exceedingly mild conditions, namely at room temperature, with a mild base and a user‐friendly electrochemical setup. This electrocatalyzed C?H alkylation displays high functional group tolerance and is applicable to both the primary and secondary alkylation. Based on detailed mechanistic studies, a nickel(II/III/I) catalytic manifold has been proposed. 相似文献
995.
Qun‐Liang Zhang Qin Xiong Miao‐Miao Li Wei Xiong Bin Shi Yu Lan Liang‐Qiu Lu Wen‐Jing Xiao 《Angewandte Chemie (International ed. in English)》2020,59(33):14096-14100
Higher‐order cycloadditions, particularly [8+2] cycloadditions, are a straightforward and efficient strategy for constructing significant medium‐sized architectures. Typically, configuration‐restrained conjugated systems are utilized as 8π‐components for higher‐order concerted cycloadditions. However, for this reason, 10‐membered monocyclic skeletons have never been constructed via catalytic asymmetric [8+2] cycloaddition with high peri‐ and stereoselectivity. Here, we accomplished an enantioselective [8+2] dipolar cycloaddition via the merger of visible‐light activation and asymmetric palladium catalysis. This protocol provides a new route to 10‐membered monocyclic architectures bearing chiral quaternary stereocenters with high chemo‐, peri‐, and enantioselectivity. The success of this strategy relied on the facile in situ generation of Pd‐containing 1,8‐dipoles and their enantioselective trapping by ketene dipolarophiles, which were formed in situ via a photo‐Wolff rearrangement. 相似文献
996.
Maximilian J. Werny Yuanqing Wang Frank Girgsdies Robert Schlgl Annette Trunschke 《Angewandte Chemie (International ed. in English)》2020,59(35):14921-14926
Structural dynamics of a Mn‐Na2WO4/SiO2 catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na2WO4 with Mn7SiO12. The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied. 相似文献
997.
Elena Braconi Nicolai Cramer 《Angewandte Chemie (International ed. in English)》2020,59(38):16425-16429
A novel class of chiral naphthyridine diimine ligands (NDI*) readily accessible from C2‐symmetric 2,6‐di‐(1‐arylethyl)anilines is described. The utility of these ligands, particularly one with fluorinated aryl side arms, is demonstrated by a reductive Ni‐catalyzed enantioselective alkylidene transfer reaction from 1,1‐dichloroalkenes to olefins. This transformation provides direct access to a broad range of synthetically valuable alkylidenecyclopropanes in high yields and enantioselectivities. 相似文献
998.
Muhammet Uyanik Naoto Sahara Mayuko Tsukahara Yuhei Hattori Kazuaki Ishihara 《Angewandte Chemie (International ed. in English)》2020,59(39):17110-17117
We report high‐performance I+/H2O2 catalysis for the oxidative or decarboxylative oxidative α‐azidation of carbonyl compounds by using sodium azide under biphasic neutral phase‐transfer conditions. To induce higher reactivity especially for the α‐azidation of 1,3‐dicarbonyl compounds, we designed a structurally compact isoindoline‐derived quaternary ammonium iodide catalyst bearing electron‐withdrawing groups. The nonproductive decomposition pathways of I+/H2O2 catalysis could be suppressed by the use of a catalytic amount of a radical‐trapping agent. This oxidative coupling tolerates a variety of functional groups and could be readily applied to the late‐stage α‐azidation of structurally diverse complex molecules. Moreover, we achieved the enantioselective α‐azidation of 1,3‐dicarbonyl compounds as the first successful example of enantioselective intermolecular oxidative coupling with a chiral hypoiodite catalyst. 相似文献
999.
Zhaohong Lu Stephen L. Buchwald 《Angewandte Chemie (International ed. in English)》2020,59(37):16128-16132
Arenes with β‐stereogenic centers are important substructures in pharmaceuticals and natural products. We have developed an asymmetric anti‐Markovnikov hydroarylation of 1,1‐disubstituted olefins by dual palladium and copper hydride catalysis as a convenient and general approach to access these substructures. This efficient one‐step process addresses several limitations of the traditional stepwise approaches. The use of cesium benzoate as a base and a common phosphine ligand for both the Cu‐ and Pd‐catalyzed processes were important discoveries that allow these challenging olefin substrates to be efficiently transformed. A variety of aryl bromide coupling partners, including numerous heterocycles, were coupled with 1,1‐disubstituted alkenes to generate arenes with β‐stereogenic centers. 相似文献
1000.
Pengjin Qin Li‐An Wang Joseph M. O'Connor Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Arnold L. Rheingold 《Angewandte Chemie (International ed. in English)》2020,59(41):17958-17965
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition‐metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献