全文获取类型
收费全文 | 1521篇 |
免费 | 50篇 |
国内免费 | 4篇 |
专业分类
化学 | 1118篇 |
晶体学 | 21篇 |
力学 | 21篇 |
综合类 | 1篇 |
数学 | 73篇 |
物理学 | 341篇 |
出版年
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 22篇 |
2014年 | 28篇 |
2013年 | 85篇 |
2012年 | 70篇 |
2011年 | 67篇 |
2010年 | 49篇 |
2009年 | 36篇 |
2008年 | 100篇 |
2007年 | 74篇 |
2006年 | 88篇 |
2005年 | 77篇 |
2004年 | 69篇 |
2003年 | 56篇 |
2002年 | 64篇 |
2001年 | 39篇 |
2000年 | 38篇 |
1999年 | 29篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 25篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 24篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 19篇 |
排序方式: 共有1575条查询结果,搜索用时 15 毫秒
31.
Jun-Ichi Kikuchi Yukito Murakami 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(2-3):209-221
Steroid cyclophanes, bearing four bile acid moieties covalently placed on a tetraazaparacyclophane skeleton, were designed and synthesized as artificial cell-surface receptors. Guest-binding behavior of the steroid cyclophanes embedded in a bilayer membrane formed with a synthetic peptide lipid was clarified by means of fluorescence and circular dichroism spectroscopy. We found that the steroid cyclophane effectively bound aromatic guests in both bilayer membranes and aqueous solution. In addition, copper(II) ions acted as a guest species for the steroid cyclophane and a competitive inhibitor toward a NADH-dependent lactate dehydrogenase (LDH). On these grounds, we constituted a supramolecular assembly as an artificial signaling system in combination with the steroid cyclophane, a cationic peptide lipid, and LDH. As a consequence, the steroid cyclophane acted as an effective artificial cell-surface receptor being capable of transmitting an external signal to the enzyme in collaboration with copper(II) ions as a signal transmitter. 相似文献
32.
1. Introduction As an effective utilization of methane, the methane dehydro-aromatization was focused in the last decade [1-28]. Over the Mo/HZSM-5 bi- functional catalyst at high reaction temperature, methane can be converted into light aromatics (ben- zene and naphthalene) and hydrogen. Mo active species can activate the C—H bond of methane; and HZSM-5 supplies the acid sites for the oligomeriza- tion and cyclization of hydrocarbons to form aromat- ics, and suppresses the deeper condens… 相似文献
33.
Shigendo?Enomoto Ken-ichi?Kumagai Taro?Tamura Miki?Hasegawa Kyoko?Nakada Toshihiko?Hoshi Michio?KobayashiEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(5):471-481
Summary. Fluoranthene (FA) forms a 1:1 van der Waals complex with benzene in cyclohexane. The 1H NMR spectrum of this complex shows that the FA moiety in the complex state has five kinds of hydrogen atoms and that the 1H NMR peaks assigned to the protons attached to the naphthalene skeleton are largely shifted to higher magnetic field on complex formation with benzene. These observations indicate that the complex takes the structure of CS symmetry, in which the benzene molecule mainly interacts with the electronic system localized on the naphthalene moiety of FA. The present ab initio calculations reproduce well the 1H NMR spectral shifts mentioned above and the experimentally predicted CS structure of the complex. According to the PPP calculations for the electronic absorption spectral changes on the complex formation, the FA-benzene complex is considered to take a sandwich type structure. 相似文献
34.
A NKT cell repertoire is characterized by the expression of the Valpha19-Jalpha26 invariant TCR alpha chain (Valpha19 NKT cell). This repertoire, as well as a well-established Valpha14-Jalpha281 invariant TCR alpha(+) NKT cell subset (Valpha14 NKT cell), has been suggested to have important roles in the regulation of the immune system and, thus, is a major therapeutic target. Here, we attempted to find specific antigens for Valpha19 NKT cells. Valpha19 as well as Valpha14 NKT cells exhibited reactivity to alpha-galactosyl ceramide (alpha-GalCer). Thus, a series of monoglycosyl ceramides with an axially oriented glycosidic linkage between the sugar and ceramide moiety were synthesized and their antigenicity to Valpha19 NKT cells was determined by measuring their immune responses in culture with glycolipids. Comprehensive examinations revealed substantial antigenic activity for Valpha19 NKT cells by alpha-mannosyl ceramide. 相似文献
35.
To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization
of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium
persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration
compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization.
Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was
observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the
end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles.
From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion
radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA.
Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen
abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen
abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical
to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of
hydrogen abstraction is far smaller than that with the sulfate anion radical by 10−4 times.
Received: 26 April 2001 Accepted: 6 September 2001 相似文献
36.
Hitoshi?MatsukiEmail author Michio?Yamanaka Hiroshi?Kamaya Shoji?Kaneshina Issaku?Ueda 《Colloid and polymer science》2005,283(5):512-520
The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH+) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality mt at 0X20.5, where X2 is the mole fraction of LC in the mixture, while they decreased rapidly with increasing mt at 0.5<X21. It was shown from the pH measurements that almost all LC molecules were changed into LCH+ ions by protonation at 0X20.5 and both forms coexisted only at 0.5<X21. The quantities of the respective LC and LCH+ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH+ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH+ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH+ in the region at 0X20.5, (2) preferential partitioning of LC at 0.5<X2<around 0.7, and (3) negative partitioning of LCH+ at around 0.7X21. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones. 相似文献
37.
K. Kaya K. Fuke S. Nonose N. Kikuchi 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):571-573
Aluminum clusters were generated by a laser vaporization method. Ionization potential of Al2 was found to be lower than that of Al. In the reaction with oxygen at high concentration, the mixed cluster Al9O7 survives predominantly as a stable cluster. Ammonia was found to be adsorbed weakly on the Aln surface. 相似文献
38.
Takeshi Kikuchi George Nmethy Harold A. Scheraga 《Journal of computational chemistry》1989,10(3):287-294
The method presented earlier [T. Kikuchi, G. Némethy, and H.A. Scheraga, (1986) J. Comput. Chem. 7 , 67] for the classification of patterns of the three-dimensional folding of a covalently crosslinked polypeptide chain has been extended to nonplanar proteins. The procedure described earlier was applicable only to proteins termed planar, i.e., with a connexity of the crosslinks (e.g., disulfide bonds) that can be represented in a planar diagram. The procedure described in the present work is applicable to any (planar or nonplanar) pattern of crosslinking. The classification is based on a systematic and objective method of enumeration of spatial geometric arrangements of loops (SGAL) using no information other than the location of the disulfide bonds in the amino acid sequence. Various SGAL classes correspond to the presence of different ways of mutual penetration of loops, called thrustings and entanglements. Information on SGAL classes can be of use in structural predictions of folding patterns of proteins. 相似文献
39.
Kikuchi H Saito Y Komiya J Takaya Y Honma S Nakahata N Ito A Oshima Y 《The Journal of organic chemistry》2001,66(21):6982-6987
We investigated the constituents of Dictyostelium discoideum to clarify the diversity of secondary metabolites of Dictyostelium cellular slime molds and to explore biologically active substances that could be useful in the development of novel drugs. From a methanol extract of the multicellular fruit body of D. discoideum, we isolated two novel amino sugar analogues, furanodictine A (1) and B (2). They are the first 3,6-anhydrosugars to be isolated from natural sources. Their relative structures were elucidated by spectral means, and the absolute configurations were confirmed by asymmetric syntheses of 1 and 2. These furanodictines potently induce neuronal differentiation of rat pheochromocytoma (PC-12) cells. 相似文献
40.
Michio Horiike Gu Yuan Chul-Sa Kim Chisato Hirano Katsuhiko Shibuya 《Journal of mass spectrometry : JMS》1992,27(9):944-948
Fourteen isomers of chemically unmodified hexadecenol were analysed by two types of quadrupole mass spectrometer, coupled with a gas chromatograph, for the location of the double-bond position. A series of spectra were interpreted in terms of mass spectral patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were preferred in devising similarity indices. The accuracy of the method in the location of double-bond position was confirmed by testing with other series of spectra. 相似文献