全文获取类型
收费全文 | 1254篇 |
免费 | 40篇 |
国内免费 | 7篇 |
专业分类
化学 | 897篇 |
晶体学 | 13篇 |
力学 | 17篇 |
数学 | 153篇 |
物理学 | 221篇 |
出版年
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 26篇 |
2013年 | 64篇 |
2012年 | 46篇 |
2011年 | 79篇 |
2010年 | 37篇 |
2009年 | 50篇 |
2008年 | 70篇 |
2007年 | 88篇 |
2006年 | 81篇 |
2005年 | 92篇 |
2004年 | 78篇 |
2003年 | 58篇 |
2002年 | 64篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1971年 | 4篇 |
排序方式: 共有1301条查询结果,搜索用时 15 毫秒
101.
Tsuboyama A Takiguchi T Okada S Osawa M Hoshino M Ueno K 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1115-1116
The synthesis, structure, and photophysical properties of a new cyclometalated dinuclear iridium complex, (ppy)2Ir(mu-BPB)Ir(ppy)2 [ppy = 2-phenylpyridine, BPB = 1,4-bis(pyridin-2-yl)benzene], have been investigated. 相似文献
102.
Kobayashi T Kawai H Suzuki T Kawanishi T Hayakawa T 《Rapid communications in mass spectrometry : RCM》2004,18(10):1156-1160
This report describes an enhancement of the signal intensities of proteins and peptides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). When alpha-cyano-4-hydroxycinnamic acid (CHCA) premixed with human transferrin (Tf) was used as a matrix, the signal intensity of insulin was amplified to more than ten times that of the respective control in CHCA without Tf. The detection limit of insulin was 0.39 fmol on-probe in the presence of Tf, while it was 6.3 fmol in the absence of Tf. The signal intensity of insulin was also enhanced when the CHCA matrix was premixed with proteins other than Tf (80 kDa), such as horse ferritin (20 kDa), bovine serum albumin (BSA, 66 kDa), or human immunoglobulin G (150 kDa). The optimum spectrum of insulin was obtained when the added amount of protein was in the range 0.26-0.62 pmol, regardless of the molecular weight of the added protein. Tf and BSA outperformed the other tested proteins, as determined by improvements in the resulting spectra. When the mass spectra of several peptides and proteins were recorded in the presence of Tf or BSA, the signal intensities of large peptides such as glucagon were enhanced, though those of smaller peptides were not enhanced. In addition, the signal enhancement achieved with Tf and BSA was more pronounced for the proteins, including cytochrome C, than for the large peptides. This enhancement effect could be applied to improve the sensitivity of MALDI-TOFMS to large peptides and proteins. 相似文献
103.
The selective N-methylation of bifunctionalized amines with supercritical methanol (scCH(3)OH) promoted by the conventional solid acids (H-mordenite, beta-zeolite, amorphous silica-alumina) and acid-base bifunctional catalysts (Cs-P-Si mixed oxide and gamma-alumina) was investigated in a continuous-flow, fixed-bed reactor. The use of scCH(3)OH in the reaction of 2-aminoethanol with methanol (amine/CH(3)OH = 1/10.8) over the solid catalysts led to a significant improvement in the chemoselectivity of the N-methylation. Among the catalysts examined, the Cs-P-Si mixed oxide provided the most efficient catalyst performance in terms of selectivity and reactivity at 300 degrees C and 8.2 MPa; the N-methylation selectivity in the products reaching up to 94% at 86% conversion. The present selective methylation was successfully applied to the synthesis of N-methylated amino alcohols and diamines as well as O-methylated ethylene glycol. Noticeably, ethoxyethylamine was less reactive, suggesting that the hydroxy group of the amino alcohols is a crucial structural factor in determining high reactivity and selectivity, possibly because of the tethering effect of another terminus, a hydroxo group, to the catalyst surface. The magic-angle-spinning NMR spectroscopy and X-ray diffraction analysis of the Cs-P-Si mixed oxide catalyst revealed that the acidic and basic sites originate from P(2)O(5)/SiO(2) and Cs/SiO(2), respectively, and the weak acid-base paired sites are attributed to three kinds of cesium phosphates on SiO(2). The weak acid-base sites on the catalyst surface might be responsible for the selective dehydrative methylation. 相似文献
104.
Takao Akahori 《Journal of Mathematical Analysis and Applications》2004,300(1):43-53
Let (M,0T″) be a compact strongly pseudo convex CR structure with dimRM=2n−1. Then, in [Michigan Math. J. 50 (2002) 517-549], the construction of the versal family of CR structures is settled. The purpose of this paper is to introduce a canonical Kaehler metric for the parameter space of this versal family if the CR structure admits a normal vector field and a non-vanishing CR n-form with the condition and
105.
Takao Komatsu 《Journal of Number Theory》2004,109(1):27-40
We show some new variations on Tasoev's continued fractions , where the periodic parts include the exponentials in k instead of the polynomials in k. We also mention some relations with other kinds of continued fractions, in particular, with Rogers-Ramanujan continued fractions. 相似文献
106.
Itoh T 《The Journal of chemical physics》2004,121(14):6956-6960
Fluorescence, fluorescence excitation, and absorption spectra have been measured for diphenylpolyenes with the polyene double bond number (n) from three to seven in solvents with different polarizabilities at room temperature. These polyenes exhibit anti-Kasha S(2) (1 (1)B(u)) fluorescence beside conventional S(1) (2 (1)A(g)) fluorescence in room temperature solution. It is shown that there are two different mechanisms for occurrence of the S(2) (1 (1)B(u)) fluorescence of diphenylpolyenes. S(2) fluorescence occurs through the thermal population of the S(1) state for the shorter diphenylpolyenes (n=3 and 4), while it occurs as prompt S(2) fluorescence due to inefficient S(2)-->S(1) internal conversion for the longer diphenylpolyenes (n=6 and 7). With diphenyldecapentaene (n=5), S(2) fluorescence based on both mechanisms is observed depending on the polarizability of the solvent used. The present results provide deeper insight into the mechanism for the occurrence of anti-Kasha S(2) fluorescence of polyenes. 相似文献
107.
Koyama E Ishida T Tokuhisa H Belaissaoui A Nagawa Y Kanesato M 《Chemical communications (Cambridge, England)》2004,(14):1626-1627
The protonation/deprotonation response of a novel bipyridine containing (phenylene-ethynylene) thiol adsorbed to a Au surface was investigated with scanning tunneling microscopy (STM), showing reversible changes in the average heights (approximately 50 spots) and the height distribution arising from protonation/deprotonation. 相似文献
108.
Takao Fukui 《General Relativity and Gravitation》2003,35(1):121-127
An accelerating flat universe with a variable cosmological term is obtained in the Robertson-Walker metric. The variable cosmological term is defined by the correction terms of the metric tensor field. Simple solutions of the scale factor and the cosmological term are shown. In this model of the universe, the magnitude-redshift relation is analytically studied to see if the model reproduces the tendency of the present observational data. The equation of state parameter is touched. 相似文献
109.
Nishizawa M Yadav VK Skwarczynski M Takao H Imagawa H Sugihara T 《Organic letters》2003,5(10):1609-1611
[reaction: see text] Hg(OTf)(2) exhibits remarkable catalytic activity for the hydroxylative cyclization of 1,6-enynes. The present procedure should involve a sequence of mercuration of a terminal alkyne, carbocyclization, hydration, and protodemercuration that regenerates the catalyst. 相似文献
110.
Onyango AN Inoue T Nakajima S Baba N Kaneko T Matsuo M Shimizu S 《Angewandte Chemie (International ed. in English)》2001,40(9):1755-1757