全文获取类型
收费全文 | 4573篇 |
免费 | 130篇 |
国内免费 | 12篇 |
专业分类
化学 | 2504篇 |
晶体学 | 42篇 |
力学 | 140篇 |
数学 | 483篇 |
物理学 | 1546篇 |
出版年
2023年 | 30篇 |
2022年 | 70篇 |
2021年 | 75篇 |
2020年 | 83篇 |
2019年 | 89篇 |
2018年 | 95篇 |
2017年 | 73篇 |
2016年 | 131篇 |
2015年 | 91篇 |
2014年 | 120篇 |
2013年 | 278篇 |
2012年 | 261篇 |
2011年 | 299篇 |
2010年 | 181篇 |
2009年 | 165篇 |
2008年 | 224篇 |
2007年 | 231篇 |
2006年 | 235篇 |
2005年 | 202篇 |
2004年 | 141篇 |
2003年 | 126篇 |
2002年 | 106篇 |
2001年 | 78篇 |
2000年 | 76篇 |
1999年 | 56篇 |
1998年 | 43篇 |
1997年 | 40篇 |
1996年 | 52篇 |
1995年 | 50篇 |
1994年 | 44篇 |
1993年 | 59篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1985年 | 45篇 |
1984年 | 41篇 |
1983年 | 40篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 42篇 |
1979年 | 35篇 |
1978年 | 40篇 |
1977年 | 33篇 |
1976年 | 38篇 |
1975年 | 32篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有4715条查询结果,搜索用时 15 毫秒
41.
J.Michael Birchall Roy Fields Robert N. Haszeldine Reginald J. McLean 《Journal of fluorine chemistry》1980,15(6):487-495
Thermolysis of hexafluorocyclopropane in the presence of ethylene, propene, vinyl chloride, and vinyl bromide gives good yields of the corresponding 1,1-difluorocyclopropanes, formed by addition of difluorocarbene to the olefin. The tetrafluoroethylene formed dimerises to octafluorocyclobutane, co-dimerises with the olefin, or survives, depending on the reaction conditions. With allene, hexafluorocyclopropane gives 1-(difluoromethylene)cyclopropane, 2,2,3,3-tetrafluorospiropentane, and products derived from tetrafluoroethylene and allene. 相似文献
42.
Santosh K. Mondal Parimal Paul Rita Roy Kamalaksha Nag 《Transition Metal Chemistry》1984,9(7):247-250
Summary Complexes of nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) with methyl-2-(-salicylaldiminoethyl)-cyclopent-1-en-dithiocarboxylate (H2L1) and methyl-2-(-salicylaldiminoisopropyl)cyclopent-1-en-dithiocarboxylate (H2L2) have been prepared. They contain the donor sites ONNS. The metal(II) ions from neutral, monomeric square planar chelate complexes. The cobalt(III) complexes [CoL1-(H2O)2]X (X=Cl or ClO4) appear to betrans-diaqua-species. All compounds have been characterized by a number of physico-chemical methods. 相似文献
43.
Abstract —Chloride anions, when added to DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea]-treated spinach chloroplasts, change the rate of decay of the delayed light emission in the seconds region but do not change the shape or the temperature dependence of the decay. Benzoate anions, on the other hand, change both the rate and the shape of the decay of the delayed light emission. These results are consistent with a model in which the membrane potential and the structure of the reaction center affect the decay kinetics of the delayed light emission in the seconds region. 相似文献
44.
Rabindra N. Roy James J. Gibbons Guilio LaCross Jr. Charles W. Krueger 《Journal of solution chemistry》1976,5(5):333-343
The two thermodynamic dissociation constants of glycine at 11 temperatures from 5 to 55°C in 50 mass % methanol-water mixed solvent have been determined from precise emf measurements with hydrogen-silver bromide electrodes in cells without liquid junction. The first acidic dissociation constant (K
1)for the process HG+H++G± is expressed as a function ofT(oK) by the equation pK
1 = 2043.5/T – 9.6504 + 0.019308T. At 25°C, pK
1is 2.961 in the mixed solvent, as compared with 2.350 in water, with H°=1497 cal-mole–1, G°=4038 cal-mole–1, S°=–8.52 cal-°K–1-mole–1, and C
p
o
=–53 cal-°K–1-mole–1. The second acidic dissociation constant (K
2)for the process G±H++G– over the temperature range studied is given by the equation pK
2 = 3627.1/T – 7.2371 + 0.015587T. At 25°C, pK
2is 9.578 in MeOH–H2O as compared with 9.780 in water, whereas H° is 10,257 cal-mole–1, G° is 13,063 cal-mole–1, S° is –9.41 cal-°K–1-mole–1, and C
p
o
is –43 cal-°K–1-mole–1. The protonated glycine becomes weaker in 50 mass % methanol-water, whereas the second dissociation process becomes stronger despite the lower dielectric constant of the mixed solvent (=56.3 at 25°C). 相似文献
45.
Arunagirinathan MA Roy M Dua AK Manohar C Bellare JR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(12):4816-4822
Surfactant outgrowth during dissolution as myelin figures, which happens on contact with water, is of prime importance in emulsification and detergency. Micro-Raman investigation of different lyotropic phases formed during dissolution of aerosol-OT (bis 2-ethylhexyl sulfosuccinate) in water during myelin formation reveals the flexible arrangement of the surfactant bilayers in myelin. The conformation around CC-CS bond and the hydrocarbon chains of aerosol-OT in the different liquid crystalline phases were identified from the fingerprints of CC-CS stretching, C-C stretching, C-H bending, and stretching frequencies. Existence of mixture of trans and gauche conformations around CC-CS bond and that of the hydrocarbon chains in myelin supports the fluid nature of bilayers by which it is made. Similar conformations of hydrocarbon chains in lamellar phase and in myelin support the concept of myelins being rolled up lamella. The observations are in line with the disorderness of the hydrocarbon chains in the bilayers of phospholipids that has been reported earlier. From the C-C stretching frequencies at the root of myelins, the kinked structure of the hydrocarbon chain is identified, and loose packing of molecules which would facilitate water transport across membranes is evident. 相似文献
46.
Ujjal Kanti Roy 《Tetrahedron》2006,62(4):678-683
A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl2 and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields. 相似文献
47.
48.
Roy Mathias 《Numerische Mathematik》1992,63(1):213-226
LetM
n
denote the space ofn×n matrices. GivenX, ZM
n
define
相似文献
49.
50.
|