全文获取类型
收费全文 | 17035篇 |
免费 | 1366篇 |
国内免费 | 1299篇 |
专业分类
化学 | 17903篇 |
晶体学 | 147篇 |
力学 | 7篇 |
综合类 | 49篇 |
数学 | 152篇 |
物理学 | 650篇 |
综合类 | 792篇 |
出版年
2024年 | 5篇 |
2023年 | 146篇 |
2022年 | 319篇 |
2021年 | 383篇 |
2020年 | 669篇 |
2019年 | 495篇 |
2018年 | 440篇 |
2017年 | 394篇 |
2016年 | 612篇 |
2015年 | 560篇 |
2014年 | 659篇 |
2013年 | 1157篇 |
2012年 | 1649篇 |
2011年 | 823篇 |
2010年 | 698篇 |
2009年 | 828篇 |
2008年 | 946篇 |
2007年 | 1083篇 |
2006年 | 887篇 |
2005年 | 806篇 |
2004年 | 772篇 |
2003年 | 766篇 |
2002年 | 524篇 |
2001年 | 466篇 |
2000年 | 437篇 |
1999年 | 418篇 |
1998年 | 362篇 |
1997年 | 361篇 |
1996年 | 375篇 |
1995年 | 372篇 |
1994年 | 265篇 |
1993年 | 212篇 |
1992年 | 193篇 |
1991年 | 124篇 |
1990年 | 83篇 |
1989年 | 66篇 |
1988年 | 65篇 |
1987年 | 51篇 |
1986年 | 40篇 |
1985年 | 34篇 |
1984年 | 33篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Michael MuehlhoferThomas Strassner Eberhardt HerdtweckWolfgang A Herrmann 《Journal of organometallic chemistry》2002,660(2):121-126
Novel bridged platinum(II) biscarbene complexes are reported: 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) (3) and 1,1′-dimethyl-3,3′-ethylene-4-diimidazolin-2,2′-diylidene platinum(II) complexes 4 are directly accessible in high yields starting from platinum halides. The one-pot synthesis obviates the need for multi-step reactions via metal precursors or free carbenes. An X-ray crystal structure of 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) dibromide (3b) confirmed the structural similarity to the known corresponding palladium complexes. Since free 1,1′-di-R-3,3′-methylene-4-diimidazolin-2,2′-diylidenes are only available in low yields this synthetic route provides an easy access to the corresponding carbene complexes. 相似文献
42.
Céline Jousse-KarinthiFatima Zouhiri Jacqueline MahuteauDidier Desmaële 《Tetrahedron》2003,59(12):2093-2099
The palladium-catalyzed condensation of a variety of active methylene compounds with methyl 6-acetoxymethyl-hepta-2,6-dienoate was investigated. The six-membered adducts resulting from a η3 palladium complex alkylation-Michael addition sequence were obtained with moderate to good yields. In some cases, further evolution of the primary adduct was observed. The process has been expanded to access nitrogen heterocycles by using sodium p-toluenesulfonamide as the nucleophilic partner. 相似文献
43.
Rainer Streubel 《Coordination chemistry reviews》2002,227(2):175-192
In this review, important aspects of λ3-2H-azaphosphirene metal complexes are discussed in relation to synthesis, physical properties and synthetic applications; ab-initio calculations on relative energies of CH2NP isomers and of λ3-2H-azaphosphirene metal complexes (Cr, Mo, W) are also presented. Currently, there are three routes to this unsaturated three-membered ring system, which are discussed in detail: two of them use a rearrangement of metal carbene complexes, whereas the other relies on [2+1] cycloaddition reactions of electrophilic terminal phosphanediyl complexes and carbonitriles. The structural data show characteristics of a very strained heterocyclic ring system, which partially helps to understand the reactivity of this heterocycle complex in solution. The synthetic potential of λ3-2H-azaphosphirene metal complexes is illustrated by selected examples, which demonstrate their ability to serve, under very mild conditions as precursor for various new building blocks, i.e. nitrilium phosphanylide complexes, electrophilic terminal phosphanediyl complexes and phosphavinyl-nitrene complexes. 相似文献
44.
Triphenylphosphane Nickel(0) Complexes with Isocyanide Ligands — [(RNC)nNi(PPh3)4–n] (n = 1–3) Synthesis and properties of the isocyanide triphenylphosphane nickel(0) complexes [(RNC)Ni(PPh3)3], [(RNC)2Ni(PPh3)2] and [(RNC)3Ni(PPh3)] (R = tBu, Cy, PhCH2, p-TosCH2) are described. I.r. and 31P n.m.r. spectra were recorded and the X-ray crystal structure of [(PhCH2NC)2Ni(PPh3)2] was determined. 相似文献
45.
Fátima Nunes Serralha José Madeira Lopes Francisco Lemos Duarte Prazeres Maria Aires-Barros Joo Rocha Joaquim Cabral Fernando Ramôa Ribeiro 《Reaction Kinetics and Catalysis Letters》2000,69(2):217-222
Novel [CrIII(amp)(bipy)(Cl)] (1) (H2amp = N-(hydroxyphenyl)salicyldimine; bipy = 2,2-bipyridyl) and [CrIII(app)(bipy)(Cl)]+ (2) (H2app = N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy = 2,2-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). The significance of the results with respect to oxo-functionalization of C-H bonds both in unsaturated and saturated hydrocarbons is noted. 相似文献
46.
K L Madhok 《Journal of Chemical Sciences》1982,91(2):165-171
Nicke(II) chloride reacts with N,N′-diarylformamidino-N′-arylcarbamides thiocarbamides and N-benzoylformamidino-N′-arylcarbamides,
thiocarbamides forming complexes of the general formula [Ni (Ar.NH.C (NH) NH.C.X. NH.R)2] Cl2 (R=phenyl, orthotolyl and paratolyl; Ar=benzoyl; X=S,O) and [Ni (R.NH.C.X.NH.C (N.Ph.).NH.Ph.)2] Cl2 (R=phenyl, orthotolyl, paratolyl; Ph=phenyl; X=S, O). The ligands when oxidized with iodine undergo ring closure to related
3,5-diarylamino 1,2,4-thiadiazolidines and 3,5-diarylamino-1,2,4-diazolidines, while the complexes are not susceptible to
oxidation. This confirms the binding in complexes is through sulphur and oxygen of the ligands. 相似文献
47.
48.
Hao Li 《Tetrahedron letters》2007,48(12):2209-2211
2,2′-Disubstituted ferrocenecarboxaldehydes are subjected to zinc-mediated allylation to form homoallylic ferrocenyl alcohols. The effects of ortho-substituted functional groups on facial selectivities of planar chiral aldehydes were studied and it was found that the corresponding homoallylic alcohols were obtained as single diastereomers in excellent yields. 相似文献
49.
Mingzhong Cai Yizheng Huang Rongli Zhang 《Journal of organometallic chemistry》2004,689(15):2436-2440
A silica-supported poly-γ-diphenylarsinopropylsiloxane palladium(0) complex has been prepared from γ-chloropropyltriethoxysilane via immobilization on fumed silica, followed by reacting with potassium diphenylarsenide and palladium chloride, and then the reduction with hydrazine hydrate. The palladium(0) complex has been found to catalyze the allylation of aldehydes via the formation of π-allylpalladium complexes, using allylic chlorides as allylating agent and SnCl2 as reducing agent. This polymeric palladium complex can be recovered and reused. 相似文献
50.
In this paper we study theoretically the molecular structure of [Be(C5Me5)2], with special interest in similarities and differences found in the computed geometric parameters, depending on the treatment of the electron correlation used. Given the low energy differences found between the different configurations studied (less than 4 kcal mol−1), and the high fluxionality found in experimental studies for this compound, we analyzed the dynamics of the system by means of first principles molecular dynamics calculations. A complex dynamics is found and analyzed in terms of two molecular rearrangement processes: 1,2-sigmatropic intraring rearrangement and a ring inversion mechanism that interchanges the roles (with regard to their coordination to the central Be atom) of the two rings.Dedicated to Dr. Jeal Paul Malrieu on occasion of his 65th birthday. 相似文献