全文获取类型
收费全文 | 7421篇 |
免费 | 783篇 |
国内免费 | 736篇 |
专业分类
化学 | 2929篇 |
晶体学 | 21篇 |
力学 | 142篇 |
综合类 | 75篇 |
数学 | 5334篇 |
物理学 | 439篇 |
出版年
2024年 | 9篇 |
2023年 | 116篇 |
2022年 | 77篇 |
2021年 | 112篇 |
2020年 | 223篇 |
2019年 | 222篇 |
2018年 | 214篇 |
2017年 | 191篇 |
2016年 | 319篇 |
2015年 | 293篇 |
2014年 | 379篇 |
2013年 | 630篇 |
2012年 | 363篇 |
2011年 | 464篇 |
2010年 | 407篇 |
2009年 | 539篇 |
2008年 | 547篇 |
2007年 | 502篇 |
2006年 | 477篇 |
2005年 | 415篇 |
2004年 | 367篇 |
2003年 | 345篇 |
2002年 | 278篇 |
2001年 | 190篇 |
2000年 | 197篇 |
1999年 | 189篇 |
1998年 | 153篇 |
1997年 | 199篇 |
1996年 | 105篇 |
1995年 | 61篇 |
1994年 | 54篇 |
1993年 | 30篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 25篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有8940条查询结果,搜索用时 11 毫秒
191.
Egle M. Beccalli Prof. Elena Borsini Stefano Brenna Dr. Simona Galli Dr. Micol Rigamonti Gianluigi Broggini Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1670-1678
The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh3)4], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh3 ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions. 相似文献
192.
Anina Wöhl Dr. Wolfgang Müller Dr. Stephan Peitz Normen Peulecke Dr. Bhaskar R. Aluri Dr. Bernd H. Müller Dr. Detlef Heller Dr. Uwe Rosenthal Prof. Dr. Mohammed H. Al‐Hazmi Dr. Fuad M. Mosa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(26):7833-7842
In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl3(thf)3] (thf=tetrahydrofuran), a Ph2P‐N(iPr)‐P(Ph)‐N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt3) as activator. It could be shown that the initial activity shows a first‐order dependency on the ethylene concentration. Also, a first‐order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol?1. At elevated temperatures (ca. 80 °C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt3. After a fast initial phase, a pronounced ‘kink’ in the ethylene‐uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene. 相似文献
193.
以CuSO4和NH3·H2O为原料,采用微乳-均匀沉淀耦合法制备了一维CuO纳米棒。用XRD、SEM、TEM、HRTEM和FTIR对产物的结构和形貌进行了表征。结果表明:产物为单斜晶相结构的CuO纳米棒,内部具有孔洞结构,其直径为40~110nm,长度为800~3000nm。可通过改变水核比(ω)、反应物的浓度、反应时间、反应温度等条件实现对CuO纳米棒形貌和尺寸的调控。探讨了可能的反应机理,并用热分析方法考察了CuO纳米棒对高氯酸铵(AP)分解的催化作用。 相似文献
194.
Synthesis of Multiply Substituted Polycyclic Aromatic Hydrocarbons by Iridium‐Catalyzed Annulation of Ring‐Fused Benzocyclobutenol with Alkyne through C−C Bond Cleavage 下载免费PDF全文
Jiajia Yu Hong Yan Prof. Dr. Chen Zhu 《Angewandte Chemie (International ed. in English)》2016,55(3):1143-1146
The first iridium‐catalyzed intermolecular cyclization between alkynes and ring‐fused benzocyclobutenols (RBCB) through C?C bond cleavage is described. A variety of elusive polycyclic aromatic hydrocarbons (PAHs) with multiple substituents are obtained in good yields under mild conditions. This procedure provides a unique and expeditious tool for the synthesis of PAHs. 相似文献
195.
M. Sc. Isabel T. Alt Prof. Dr. Bernd Plietker 《Angewandte Chemie (International ed. in English)》2016,55(4):1519-1522
The nucleophilic iron complex Bu4N[Fe(CO)3(NO)] (TBA[Fe]) catalyzes the direct intramolecular C?H amination of α‐azidobiaryls and (azidoaryl)alkenes into the corresponding carbazoles and indoles, respectively, under mild conditions and with low catalyst loadings. These features and the broad functional‐group tolerance render this method a particularly attractive alternative to established noble‐metal‐based procedures. 相似文献
196.
Catalytic Borylative Opening of Propargyl Cyclopropane,Epoxide, Aziridine,and Oxetane Substrates: Ligand Controlled Synthesis of Allenyl Boronates and Alkenyl Diboronates 下载免费PDF全文
Dr. Jian Zhao Prof. Kálmán J. Szabó 《Angewandte Chemie (International ed. in English)》2016,55(4):1502-1506
A new copper‐catalyzed reaction for the stereo‐ and regioselective synthesis of alkenyl diboronates and allenyl boronates is presented. In this process propargyl derivatives of strained three/four‐membered rings were employed as substrates and B2pin2 was used as the boronate source. Selective formation of the alkenyl diboronate versus the allenyl boronate products was controlled by the choice of phosphine ligand. 相似文献
197.
Dr. Toni Moragas Dr. Morgane Gaydou Prof. Ruben Martin 《Angewandte Chemie (International ed. in English)》2016,55(16):5053-5057
A user‐friendly Ni‐catalyzed reductive carboxylation of benzylic C?N bonds with CO2 is described. This procedure outperforms state‐of‐the‐art techniques for the carboxylation of benzyl electrophiles by avoiding commonly observed parasitic pathways, such as homodimerization or β‐hydride elimination, thus leading to new knowledge in cross‐electrophile reactions. 相似文献
198.
Dr. Jie Wang Dr. Tian Qin Dr. Tie‐Gen Chen Dr. Laurin Wimmer Jacob T. Edwards Dr. Josep Cornella Benjamin Vokits Dr. Scott A. Shaw Prof. Phil S. Baran 《Angewandte Chemie (International ed. in English)》2016,55(33):9676-9679
A transformation analogous in simplicity and functional group tolerance to the venerable Suzuki cross‐coupling between alkyl‐carboxylic acids and boronic acids is described. This Ni‐catalyzed reaction relies upon the activation of alkyl carboxylic acids as their redox‐active ester derivatives, specifically N‐hydroxy‐tetrachlorophthalimide (TCNHPI), and proceeds in a practical and scalable fashion. The inexpensive nature of the reaction components (NiCl2?6 H2O—$9.5 mol?1, Et3N) coupled to the virtually unlimited commercial catalog of available starting materials bodes well for its rapid adoption. 相似文献
199.
Estefanía Gioria Dr. Juan del Pozo Dr. Jesús M. Martínez‐Ilarduya Prof. Dr. Pablo Espinet 《Angewandte Chemie (International ed. in English)》2016,55(42):13276-13280
A Pd complex, cis‐[Pd(C6F5)2(THF)2] ( 1 ), is proposed as a useful touchstone for direct and simple experimental measurement of the relative ability of ancillary ligands to induce C?C coupling. Interestingly, 1 is also a good alternative to other precatalysts used to produce Pd0L. Complex 1 ranks the coupling ability of some popular ligands in the order PtBu3>o‐TolPEWO‐F≈tBuXPhos>P(C6F5)3≈PhPEWO‐F>P(o‐Tol)3≈THF≈tBuBrettPhos?Xantphos≈PhPEWO‐H?PPh3 according to their initial coupling rates, whereas their efficiency, depending on competitive hydrolysis, is ranked tBuXPhos≈PtBu3≈o‐TolPEWO‐F>PhPEWO‐F>P(C6F5)3?tBuBrettPhos>THF≈P(o‐Tol)3>Xantphos>PhPEWO‐H?PPh3. This “meter” also detects some other possible virtues or complications of ligands such as tBuXPhos or tBuBrettPhos. 相似文献
200.
Jiale Huang Wenta Wang Liqin Lin Qingbiao Li Wenshuang Lin Mei Li Stephen Mann 《化学:亚洲杂志》2009,4(7):1050-1054
Tea time! Gold nanoparticles (GNPs) could be readily prepared by a general strategy involving the reduction of aqueous HAuCl4 in the presence of traditional Chinese medicines (TCMs). Spheroidal and triangular gold nanoparticles were observed depending on the TCM used. The strategy exemplified the universal application of plant bioresources for the synthesis of GNPs and catalytic purposes.