全文获取类型
收费全文 | 1775篇 |
免费 | 35篇 |
国内免费 | 5篇 |
专业分类
化学 | 1432篇 |
晶体学 | 15篇 |
力学 | 15篇 |
数学 | 90篇 |
物理学 | 263篇 |
出版年
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 26篇 |
2015年 | 28篇 |
2014年 | 39篇 |
2013年 | 91篇 |
2012年 | 70篇 |
2011年 | 93篇 |
2010年 | 61篇 |
2009年 | 43篇 |
2008年 | 82篇 |
2007年 | 98篇 |
2006年 | 106篇 |
2005年 | 122篇 |
2004年 | 96篇 |
2003年 | 81篇 |
2002年 | 81篇 |
2001年 | 33篇 |
2000年 | 38篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 26篇 |
1996年 | 32篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 21篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 39篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1976年 | 15篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1968年 | 12篇 |
1967年 | 11篇 |
排序方式: 共有1815条查询结果,搜索用时 62 毫秒
991.
Here, we report an iridium(III) coordination system with 2‐aminoethanethiolate (aet), which shows the formation of S?H???S hydrogen and S?S disulfide bonds in a controlled manner. Treatment of fac‐[Ir(aet)3] with aqueous HBF4 under aerobic conditions gave dinuclear [Ir2(aet)4(cysta)]2+ ([ 1 ]2+; cysta=cystamine) with a single S?S disulfide bond, while dimeric [Ir2(aet)3(Haet)3](BF4)3 ([ 2 ](BF4)3) with a triple S?H???S hydrogen bond was formed by similar treatment under anaerobic conditions. Upon exposure to air, [ 2 ]3+ was converted to dinuclear [Ir2(aet)2(Haet)2(cysta)]4+ ([ 3 ]4+), in which two IrIII centers are spanned by a double S?H???S hydrogen bond and a single S?S disulfide bond. Complex [ 3 ]4+ was interconvertible with [ 1 ]2+ via the removal/addition of protons on S donors, accompanied by the intermolecular exchange of the fac‐[Ir(aet)3] units. Complexes [ 1 ]2+, [ 2 ]3+, and [ 3 ]4+, isolated as BF4? salts, were fully characterized by single‐crystal X‐ray crystallography. 相似文献
992.
Misaki Ueda Zi Lang Goo Katsue Minami Nobuto Yoshinari Takumi Konno 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14815-14820
A 60‐nuclear silver sulfide nanocluster with a highly positive charge ( 1 ) has been synthesized by mixing an octahedral RhIII complex with 2‐aminoethanethiolate ligands, silver(I) nitrate, and d ‐penicillamine in water under mild conditions. The spherical surface of 1 is protected by the chiral octahedral RhIII complex, with cleavage of the C?S bond of the d ‐penicillamine supplying the sulfide ions. Although 1 does not contain d ‐penicillamine, it is optically active because of the enantiomeric excess of the RhIII molecules induced by chiral transfer from d ‐penicillamine. 1 can accommodate/release external Ag+ ions and replace inner Ag+ ions by Cu+ ions. The study demonstrates that a thiolato metal complex and sulfur‐containing amino acid can be used as cluster‐surface‐protecting and sulfide‐supplying regents, respectively, for creating chiral, water‐soluble, structurally precise silver sulfide nanoclusters, the properties of which are tunable through the addition/removal/exchange of Ag+ ions. 相似文献
993.
Hayder D. J. Arkawazi Dr. Rob Clowes Prof. Andrew I. Cooper Prof. Takumi Konno Dr. Naoto Kuwamura Dr. Christopher M. Pask Prof. Michaele J. Hardie 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(5):1353-1362
Two new heteroleptic metal-organic framework materials show strong adsorption of H2 and ethanol. [Co2(L1)(bdc)2], where L1=N1,N4-bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co2(L1)(bpdc)2], where bpdc=biphenyl-4,4′-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests. 相似文献
994.
Yu Tokita Kotaro Sugawara Riho Awayama Yoshihiro Ohta Tsutomu Yokozawa 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2498-2504
We investigated the synthesis of polyfluorene with a pinacol boronate (PinB) moiety at one end and with controlled molecular weight by means of Suzuki–Miyaura coupling polymerization of pinacol (7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)boronate ( 1 ) with a palladium(0) precatalyst in the presence of pinacol 4‐trifluoromethylphenylboronate ( 2 ) as a chain terminator and CsF/18‐crown‐6 as a base. When we used AmPhos Pd G2, which has a propensity for intramolecular catalyst transfer on a π‐electron face, polyfluorene with the PinB moiety at one end and PhCF3 (derived from 2 ) at the other end was obtained, and the molecular weight increased in proportion to the feed ratio of [ 1 ]0/[catalyst]0, though the molecular weight distribution was broad. Since the molecular weight also linearly increased with respect to the conversion of 1 until the middle stage of polymerization, the polymerization appears to involve chain‐growth polymerization through intramolecular catalyst transfer from the Pd catalyst inserted into the C? Br bond of 1 . The broad molecular weight distribution might be mainly due to slow initiation and slow termination with 2 , rather than polymer–polymer coupling. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2498–2504 相似文献
995.
Shinichi Yamabe Tsutomu Minato Teruyuki Watanabe Takahisa Machiguchi 《Theoretical chemistry accounts》2011,130(4-6):981-990
The title reactions were investigated experimentally and theoretically. The benzyne--tropone pair has been known to give a Diels?CAlder [4+2] cycloadduct. However, in the present experiment using two sources of benzyne, many unexpected products were obtained. In particular, a zwitterion with a C?CCl bond is strikingly a major product, the structure of which was determined by the X-ray analysis. The bond is formed by quenching the Cl atom from the solvent CH2Cl2, which demonstrates that the reactions proceed via radical processes. DFT calculations revealed the elementary processes of the reactions. The presence of the novel zwitterion in the solid state has been interpreted in terms of the permanent dipole?Cdipole attractions/interactions/stabilization. 相似文献
996.
997.
Takayoshi Tajima Yuhsuke Akagi Takuya Kumamoto Noriyuki Suzuki Tsutomu Ishikawa 《Tetrahedron letters》2012,53(4):383-387
Jadomycin A and related jadomycin M and W aglycons were synthesized. Easy re-construction of 4-(hydroxymethyl)-1,3-oxazolidin-5-one system into an isomeric 1,3-oxazolidine-4-carboxylic acid system during the synthetic trial of jadomycin S aglycon requests us to more precisely re-examine the structures proposed for jadomycins S and T, derived from hydroxyl-containing amino acids of l-serine and l-threonine, respectively. 相似文献
998.
Hideyasu Kudo Tsutomu Inaoka Noriko Kitamura Tomoya Nakatsuka Shusuke Kasuya Rumiko Kasai Mitsuyuki Tozawa Koichi Nakagawa Hitoshi Terada 《Magnetic resonance imaging》2013,31(8):1309-1317
PurposeTo determine the clinical value of routine use of thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique for internal derangements of the knee joint at 3 T.Method and MaterialsThirty-four knees in 34 patients suspected of having internal derangements of the knee joint were included. Following standard 2D MRI protocol including sagittal PDWI, T1WI and T2*WI, coronal fat-suppressed PDWI, and axial fat-suppressed PDWI with 3-4 mm thicknesses, fat-suppressed and water-excitation PDWI using 3D FSE sequences with a variable flip angle technique with 0.6 mm thickness were obtained in coronal plane and the three major planes with 1 mm thickness (3D MRI) was reformatted. The standard 2D MRI protocol and reformatted 3D MRI protocol (three sagittal 2D sequence images plus 3D MRI) were independently analyzed by two radiologists concerning presence or absence of lesions in the menisci, cartilage, and ligament. Interobserver agreements in both the MRI protocols were assessed by weighted-kappa coefficients. Regarding diagnostic accuracy, areas under the receiver operating characteristic curves (Az values) of both the MRI protocols were compared.ResultsThirty-eight meniscal lesions, 39 cartilage lesions, and 20 ligamentous lesions were surgically detected. Excellent interobserver agreements (kappa = 0.91–0.98) were seen in both the MRI protocols, with a slightly better tendency in the reformatted 3D MRI protocol. Average Az values in detection of the meniscal, cartilage, and ligamentous lesions were significantly higher in the reformatted 3D MRI protocol than in the standard 2D MRI protocol (p < 0.01 or p < 0.001).ConclusionRoutine use of reformatted thin-section 3D MRI using 3D FSE sequences with a variable flip angle technique may improve diagnostic accuracy and confidence in detection of internal derangements of the knee joint. 相似文献
999.
Tsutomu Konno Shigeyuki Yamada Akinori Tani Masataka Nishida Tomotsugu Miyabe Takashi Ishihara 《Journal of fluorine chemistry》2009,130(10):913-2831
Treatment of (E)-4,4,4-trifluoro-1-aryl-2-buten-1-one with various aryldiazonium salts in the presence of palladium catalyst gave the corresponding α-arylated Heck adducts with high regio- and stereoselectivity in good to high yields. 相似文献
1000.
A polymer inclusion membrane (PIM) is reported consisting of 45% (m/m) di(2-ethylhexyl)phosphoric acid (D2EHPA) immobilized in poly(vinyl chloride) (PVC) for use as a solid phase absorbent for selectively extracting Zn(II) from aqueous solutions in the presence of Cd(II), Co(II), Cu(II), Ni(II) and Fe(II). Interference from Fe(III) in the sample is eliminated by precipitation with orthophosphate prior to the extraction of Zn(II). Studies using a dual compartment transport cell have shown that the Zn(II) flux (2.58 × 10−6 mol m−2 s−1) is comparable to that observed for supported liquid membranes. The stoichiometry of the extracted complex is shown to be ZnR2·HR, where R is the D2EHPA anion. 相似文献