全文获取类型
收费全文 | 4073篇 |
免费 | 104篇 |
国内免费 | 19篇 |
专业分类
化学 | 2639篇 |
晶体学 | 19篇 |
力学 | 126篇 |
数学 | 733篇 |
物理学 | 679篇 |
出版年
2023年 | 30篇 |
2022年 | 66篇 |
2021年 | 80篇 |
2020年 | 78篇 |
2019年 | 82篇 |
2018年 | 68篇 |
2017年 | 47篇 |
2016年 | 107篇 |
2015年 | 97篇 |
2014年 | 107篇 |
2013年 | 167篇 |
2012年 | 209篇 |
2011年 | 301篇 |
2010年 | 170篇 |
2009年 | 171篇 |
2008年 | 219篇 |
2007年 | 217篇 |
2006年 | 214篇 |
2005年 | 165篇 |
2004年 | 146篇 |
2003年 | 125篇 |
2002年 | 132篇 |
2001年 | 51篇 |
2000年 | 42篇 |
1999年 | 39篇 |
1998年 | 27篇 |
1997年 | 38篇 |
1996年 | 62篇 |
1995年 | 35篇 |
1994年 | 47篇 |
1993年 | 35篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 27篇 |
1985年 | 52篇 |
1984年 | 54篇 |
1983年 | 40篇 |
1982年 | 33篇 |
1981年 | 39篇 |
1980年 | 44篇 |
1979年 | 49篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1974年 | 19篇 |
1970年 | 15篇 |
排序方式: 共有4196条查询结果,搜索用时 15 毫秒
121.
Giuseppe Bruno Francesco Nicol Fausto Puntoriero Gaetano Giuffrida Vittorio Ricevuto Giuseppe Rosace 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(7):o390-o391
The title compound, C21H19N7, is a polypyridine ligand that is suitable for assembling complex metal systems capable of photoinduced electron transfer. The solid‐state structure has been determined at room temperature by single‐crystal X‐ray diffraction. The molecule is not flat and both the bis(pyridyl)triazole and the benzylideneamine fragments show significant distortions from planarity. 相似文献
122.
Zhdankin VV Maydanovych O Herschbach J Bruno J Matveeva ED Zefirov NS 《The Journal of organic chemistry》2003,68(3):1018-1023
The preparation and chemistry of novel phosphoranyl-derived lambda(3)-iodanes is reported. The phosphoranyl-derived phenyliodonium sulfonates were prepared in good yields by the reaction of stabilized phosphonium ylides [1-triphenylphosphoranylidene-2-propanone, methyl(triphenylphosphoranylidene)acetate, (triphenylphosphoranylidene)acetaldehyde, and (triphenylphosphoranylidene)acetonitrile] with the pyridinium complex of iodobenzene ditriflate or with [hydroxy(tosyloxy)iodo]benzene under mild conditions. These compounds represent a potentially useful class of reagents that combine in one molecule synthetic advantages of a phosphonium ylide and an iodonium salt. Specifically, phosphorane-derived phenyliodonium tosylates can react with soft nucleophiles, such as iodide, bromide, benzenesulfinate, and thiophenolate anions, with a selective formation of the respective alpha-functionalized phosphonium ylides, which can be further converted to alkenes by the Wittig reaction with benzaldehyde. The phosphoranyl-derived benziodoxoles can be prepared by the reaction of 1-acetoxybenziodoxole with stabilized phosphonium ylides. An unusual ligand exchange on the iodine(III) center resulting in the substitution of a carbon ligand with an oxygen ligand was observed in the reaction of these compounds with strong acids. 相似文献
123.
Exposure risk assessment of uranium intake of the milk products from the region of Pernambuco,Brazil
dos Santos Amaral Romilton dos Santos Júnior José Araújo da Silva Aquino Fabiana de Albuquerque Amaral Bruno Fernández Zahily Herrero Bezerra Mariana Brayner Cavalcanti Freire da Silva Arykerne Nascimento Casado dos Santos Djalma Cordeiro do Nascimento Santos Josineide Marques da Silva Alberto Antônio de Barros Correia Filipe Lopes 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(3):927-935
Journal of Radioanalytical and Nuclear Chemistry - Haloperidol (HP) is a dopamine blocking agent. HP was radiolabeled with 125I using direct electrophilic substitution. Different HP formulations... 相似文献
124.
Dr. Antoine Nitelet Dr. Damien Thevenet Dr. Bruno Schiavi Dr. Christophe Hardouin Dr. Jean Fournier Dr. Rodolphe Tamion Prof. Dr. Xavier Pannecoucke Prof. Dr. Philippe Jubault Prof. Dr. Thomas Poisson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3262-3266
The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (CuI/CuI*/Cu0) was suggested. 相似文献
125.
de Santana Felipe Silva Gracioso Louise Hase Karolski Bruno dos Passos Galluzzi Baltazar Marcela Mendes Maria Anita do Nascimento Claudio Augusto Oller Perpetuo Elen Aquino 《Applied biochemistry and biotechnology》2019,189(1):103-115
Applied Biochemistry and Biotechnology - The human exposure to bisphenol A (BPA) occurs frequently. Once, this compound was one of the highest volume chemicals produced worldwide and used as a... 相似文献
126.
On singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano-epoxydienes (E)- 6 and (E)- 7 undergo interconversion and yield the products 8 – 11 . The main process is the cleavage of the oxirane ring to the vinyl carbene intermediate e which undergoes addition to the adjacent double bond furnishing the cyclopropene 8 . The alternative carbene intermediate f is evidenced by the formation of the cyclobutene 10 . For the fragmentation leading to 11 , the carbene f as well as the dipolar species h are considered as possible intermediates. On triplet sensitization (acetone, λ > 280 nm), (E)- 7 shows behavior typical of epoxydienes, undergoing fission of the C? O bond of the oxirane ring and isomerization to the compounds 13 , 14 and (E/Z)- 15 . 相似文献
127.
Sylviane Sabo Bruno Chaudret Danièle Gervais 《Journal of organometallic chemistry》1985,292(3):411-418
The possibility of making metal—metal bonded heterobimetallic species by metathesis of ruthenium dichlorides with anionic carbonylates is demonstrated by the isolation of MoRu(μ-Cl)(μ-CO)(CO)2(PPh3)2(η-C5H5) (1) and MnRuCl(μ-CO)2(CO)3(μ-dppm)2 (2), obtained by action of [Mo(CO)3(η-C5H5]? on RuCl2(PPh3)3 and of Mn(CO)5? on RuCl2(dppm)2, respectively. In contrast, reaction of Mn(CO)5? with RuCl2(PMe3)4 yielded an ionic species 3 containing the diruthenium cation Ru2Cl3(PMe3)6+. More interestingly, the action of Mn(CO)5? on RuCl2(PPh3)3 resulted in the formation of the unexpected complex MnRu(μ-PPh2)(CO)6(PPh3)2 (4) in which the phosphido group PPh2 bridges the two metals; this process is shown to involve a hydride intermediate, and elimination of a molecule of benzene, both identified in the reaction mixture. 相似文献
128.
129.
N-(β-Hydroxy)amides can be cyclised by reaction with diisopropylcarbodiimide (DIC) to give the corresponding 2-oxazolines in high yields. The reaction requires only very mild Lewis-acid catalysis (5 mol % Cu(OTf)2) and can be accomplished with simple heating, or in very short reaction times under microwave irradiation. 相似文献
130.
Maynadié J Delavaux-Nicot B Lavabre D Donnadieu B Daran JC Sournia-Saquet A 《Inorganic chemistry》2004,43(6):2064-2077
[(C(5)H(5))Fe(C(5)H(4)COCH=CHC(6)H(4)NEt(2))] (1) has been electrochemically evaluated toward different cations in solution. Calcium sensing by this compound and its two new derivatives [(C(5)H(5))Fe(C(5)H(4)CO(CH=CH)(2)C(6)H(4)NMe(2))] (2) and [(C(5)H(5))Fe(C(5)H(4)CH=CHCOCH=CHC(6)H(4)NEt(2))] (3) that exhibit a conjugated link between the ferrocene unit and the nitrogen atom has been thoroughly examined. Compounds 2 and 3 have been structurally characterized by single-crystal X-ray diffraction studies. The three related protonated species [1H][BF(4)] (4), [2H][BF(4)] (5), and [3H][BF(4)] (6) have been isolated in a good yield. NMR experiments clearly established that calcium interaction occurs in the vicinity of the carbonyl group, and mass spectrometry studies confirmed that this interaction, which involves several ligand-Ca(2+) adducts, is complex. A combination of electrochemical and NMR experiments highlighted an original salt influence on the electrochemical calcium sensing result. 相似文献