全文获取类型
收费全文 | 1083篇 |
免费 | 54篇 |
国内免费 | 2篇 |
专业分类
化学 | 773篇 |
晶体学 | 23篇 |
力学 | 12篇 |
数学 | 45篇 |
物理学 | 286篇 |
出版年
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 25篇 |
2017年 | 14篇 |
2016年 | 20篇 |
2015年 | 29篇 |
2014年 | 22篇 |
2013年 | 58篇 |
2012年 | 33篇 |
2011年 | 58篇 |
2010年 | 33篇 |
2009年 | 33篇 |
2008年 | 72篇 |
2007年 | 53篇 |
2006年 | 69篇 |
2005年 | 51篇 |
2004年 | 53篇 |
2003年 | 49篇 |
2002年 | 48篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 5篇 |
排序方式: 共有1139条查询结果,搜索用时 15 毫秒
21.
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
22.
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
23.
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
24.
Mantani T Shiomi K Konno T Ishihara T Yamanaka H 《The Journal of organic chemistry》2001,66(10):3442-3448
N,N-Dialkyl(3,3,3-trifluoro-1-propynyl)amines were readily prepared by a three-step procedure starting from commercially available 2,2,3,3,3-pentafluoropropanol. These fluorinated alkynylamines reacted smoothly with a variety of aldehydes or ketones in the presence of a catalytic amount of Lewis acid and molecular sieves 4A at ambient temperature to produce the corresponding alpha-(trifluoromethyl)-alpha,beta-unsaturated amides in good to excellent yields with high Z-stereoselectivity. 相似文献
25.
Paramagnetic centers of NH 3 + , Al, and HO2 · have been observed in alkali feldspars from Aichi prefecture, Japan. The quartet signal has been tentatively ascribed to NH 3 + rather than to ·CH3, although the hyperfine splitting by14N (I=1) was not observed. The averageg- andA-valuesg av=2.0033 andA av H =2.45 mT, respectively, were attributed to hydrogen. The powder spectra of Al centers stable up to 400 K were simulated by the anisotropicg factors ofg zz =2.060,g xx =2.0014,g yy=2.0021 andA=0.9 mT. Newly discovered HO2 · is stable up to 570 K. The intensities of the spectra from NH 3 + and Al centers were enhanced by gamma-ray irradiation, while that of HO2 · was not enhanced. Production efficiency,G-value (radical/100 eV) of NH 3 + has been obtained to beG=0.01. These results suggest that ESR dating of feldspars is possible. 相似文献
26.
Weaver M Arisaka K Roberts D Slater W Briere RA Cheu E Harris DA Roodman A Schwingenheuer B Wah YW Winstein B Winston R Barker AR Swallow EC Bock GJ Coleman R Crisler M Enagonia J Ford R Hsiung YB Jensen DA McFarland KS Ramberg E Tschirhart R Collins EM Gollin GD Nakaya T Yamanaka T Gu P Haas P Hogan WP Kim SK Matthews JN Myung SS Schnetzer S Somalwar SV Thomson GB Zou Y 《Physical review letters》1994,72(24):3758-3761
27.
Gu P Haas P Hogan WP Kim SK Matthews JN Myung SS Schnetzer S Thomson GB Zou Y Arisaka K Roberts D Slater W Spencer MB Weaver M Briere RA Cheu E Harris DA Krolak P McFarland KS Roodman A Schwingenheuer B Somalwar SV Wah YW Winstein B Winston R Barker AR Swallow EC Bock GJ Coleman R Crisler M Enagonio J Ford R Hsiung YB Jensen DA O'Dell VR Ramberg E Tschirhart R Collins EM Gollin GD Nakaya T Yamanaka T 《Physical review letters》1996,76(23):4312-4315
28.
Chemical conversion of some natural oxindoles (pteropodine, isopteropodine and isorhynchophylline) into the corresponding indole alkaloids has been made by way of a sequence of reactions which include formation of iminoethers of the natural oxindoles with Meerwein's reagent, reduction of the iminoethers to 2,3-seco-indoles and cyclization of 2,3-seco-indoles to the desired natural indole alkaloids. Sodium borohydride in acetic acid was found to be a specific reagent for the reduction of oxindole-iminoethers to 2,3-seco-indoles which were the key intermediates in these transformations. Yohimbine-oxindole iminoether was similarly converted to yohimbine and pseudoyohimbine. A number of by-products were obtained and their structures were elucidated. 相似文献
29.
New ring-opening reaction of thiazoline-azetidinones 1 to dithioazetidinones 2 was achieved with 2-benzothiazolyl disulfide in aqueous acidic media and its potentiality for the preparation of a variety of cephalosporins 3 from various thiazoline-azetidinones 1 is demonstrated. 相似文献
30.
Shouhong Xu Yuan Song Shizuko Sato Isamu Miyata Junpei Yamanaka Masakatsu Yonese 《Colloid and polymer science》2005,283(4):383-392
Two-dimensional structures and characteristics of the complexes between sodium hyaluronate (NaHA) and bovine serum albumin (BSA) were studied by using a quartz crystal microbalance method and an atomic force microscope (AFM). NaHA did not adsorb on poly(-methyl-l-glutamate) (PMLG) film. On the other hand, the complexes adsorbed on it and the adsorption behaviors were found to be Langmuir types. With increasing weight ratio of BSA to NaHA, W
BSA, the adsorption constants K decreased and the saturated adsorption masses increased. The adsorbed complexes were spherical particles and at saturated adsorption states they covered compactly on the PMLG film. The mean diameters d
AFM estimated from the topographic images decreased from 70 to 54 nm with increasing W
BSA. The adhesion force F
ad and the frictional force F
f between the complex layers and the AFM tip were obtained by using the contact mode of the AFM. With increasing W
BSA, the values of F
ad decreased and the values of F
f increased. Compared with the frictional coefficient of the NaHA adsorption layer on the BSA monolayer, the values for the NaHA–BSA complex layer were found to be much higher. 相似文献