全文获取类型
收费全文 | 3968篇 |
免费 | 118篇 |
国内免费 | 34篇 |
专业分类
化学 | 2951篇 |
晶体学 | 33篇 |
力学 | 85篇 |
综合类 | 1篇 |
数学 | 536篇 |
物理学 | 514篇 |
出版年
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 31篇 |
2020年 | 55篇 |
2019年 | 54篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 89篇 |
2015年 | 90篇 |
2014年 | 99篇 |
2013年 | 212篇 |
2012年 | 206篇 |
2011年 | 321篇 |
2010年 | 120篇 |
2009年 | 126篇 |
2008年 | 256篇 |
2007年 | 259篇 |
2006年 | 257篇 |
2005年 | 251篇 |
2004年 | 224篇 |
2003年 | 162篇 |
2002年 | 158篇 |
2001年 | 41篇 |
2000年 | 48篇 |
1999年 | 40篇 |
1998年 | 37篇 |
1997年 | 42篇 |
1996年 | 60篇 |
1995年 | 35篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 35篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 46篇 |
1984年 | 39篇 |
1983年 | 30篇 |
1982年 | 54篇 |
1981年 | 43篇 |
1980年 | 41篇 |
1979年 | 32篇 |
1978年 | 40篇 |
1977年 | 32篇 |
1976年 | 24篇 |
1975年 | 31篇 |
1974年 | 19篇 |
排序方式: 共有4120条查询结果,搜索用时 0 毫秒
31.
Marcia I. Dawson Rebecca L.-S. Chan Ian S. Cloudsdale Wesley R. Harris 《Tetrahedron letters》1981,22(29):2739-2742
Tris(catecholcarboxamide) ligands were covalently linked to poly(vinyl amine—vinyl sulfonate sodium salt), and the iron binding capacity of the resultant polymers was found to exceed that of transferrin. 相似文献
32.
[structure: see text] By relying on the asymmetric aldol reactions of chiral ketones, a highly stereocontrolled synthesis of each of the C(17)-C(22) and C(23)-C(35) degradation fragments of reidispongiolide A has been achieved. This permits a configurational assignment of the complete C(17)-C(36) region of this antimitotic macrolide, along with providing advanced intermediates for a projected total synthesis. 相似文献
33.
Use of a hard sphere model and the concept of an effective hard sphere diameter of a colloidal particle with its associated double layer is reported. This method allows rapid determination of the order-disorder transition in colloidal dispersions and yields reasonable estimates of the osmotic pressures compared with “exact” Monte Carlo calculations. 相似文献
34.
Alan Shaver Paul J. Fitzpatrick Kosta Steliou Ian S. Butler 《Journal of organometallic chemistry》1979,172(4):C59-C62
μ,μ′-(1,3-Dithiolatocyclohepta-4,6-diene)hexacarbonyldiiron(I) was prepared by the reaction of 2,3,4-trithiabicyclo[4,3,1]deca-6,8-diene with Fe2(CO)9. The carbonyls undergo rapid site exchange within each Fe(CO)3 group but there is no exchange of carbonyls between the two different Fe(CO)3 moieties. The novel bicyclic nature of the bridging ligand results in a short iron—iron bond distance and a long sulfur—sulfur distance as compared to other members of this class. 相似文献
35.
O'Driscoll BM Ruggles JL Gentle IR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6246-6251
Langmuir and Langmuir-Blodgett (LB) films of a cationic amphiphilic porphyrin mixed with n-alkanes octadecane and hexatriacontane were prepared and characterized, to examine the influence of the alkanes on film structure and stability. While the structure present in these films was controlled primarily by the porphyrin, the addition of the alkanes resulted in significant changes to both the phase behavior of the Langmuir films and the molecular arrangement of the LB films. These changes, as well as the observed chain length effects, are explained in terms of the intermolecular interactions present in the films. 相似文献
36.
2-(Trifluoromethyl)imidazo[4,5-] and -[4,5-]quinoline have been prepared from 5(6),acetamido-2-(trifluoromethyl)benzimidazole and 7,8-diaminoquinoline respectively. These (trifluoromethyl)- quinolines like 2-(trifluoromethyl)imidazoles but unlike 2-(trifluoromethyl) benzimidazoles, undergo hydrolysis in dilute sodium hydroxide to give ultimately the corresponding imidazo[4,5-] and -[4,5-]- quinoline, respectively. 相似文献
37.
Dale Spangler Ian Henderson Williams Gerald M. Maggiora 《Journal of computational chemistry》1983,4(4):524-541
Quantum mechanical calculations of the geometric, energetic, electronic, and vibrational features of a transition structure for gas-phase water–formaldehyde addition (FW1?) are described, and a new transition-structure search algorithm is presented. Basis-set-dependent effects are assessed by comparisons of computed properties obtained from self-consistent field (SCF) molecular orbital (MO) calculations with STO-3G, 4-31G, and 6-31G** basis sets in the absence of electron correlation. The results obtained suggest that STO-3G-level calculations may be sufficiently reliable for the prediction of the transition structure of FW1? and for the transition structures of related carbonyl addition reactions. Moreover, the calculated activation energy for formation of FW1? from water and formaldehyde (?44 kcal mol?1) is very similar in all three basis sets. However, the energy of formaldehyde hydration predicted by STO-3G (? ?45 kcal mol?1) is about three times larger than that predicted by the other two basis sets, with the activation energy for dihydroxymethane dehydration also being too large in STO-3G. Calculated force constants in all three basis sets are generally too large, leading to vibrational frequencies that are also too large. However, uniformly scaled force constants (in internal coordinates) give much better agreement with experimental frequencies, scaled 4-31G force constants being slightly superior to scaled STO-3G force constants. 相似文献
38.
The heteronuclear metal clusters [H3MRu4(CO)12(PPh3)] and [MFe3(μ-COMe)(CO)10(PPh3)] (M = Cu, Ag or Au) have been prepared; the gold-tetraruthenium cluster has a different metal core geometry to that adopted by the copper and silver analogues, whereas all three iron-Group IB mixed-metal clusters have the same geometry. 相似文献
39.
A series of donor-stabilized N-silylphosphoranimine salts [DMAP.PCl2=NSiMe3]+X- (DMAP = 4-(dimethylamino)pyridine) were prepared by the reaction of Cl3P=NSiMe3 with DMAP in the presence of silver salts AgX (X = OSO2CF3, BF4, and SbF6). Repeating the reaction in the absence of AgX gave the chloride salt [DMAP.PCl2=NSiMe3]Cl which has been shown to be in equilibrium with free DMAP and Cl3P=NSiMe3. Attempts to stabilize a N-silylphosphoranimine cation with phosphine donors led to unexpected imine transfer chemistry. For example, Cl3P=NSiMe3 reacts with phosphines, R3P (R = nBu and Ph), to produce the metathesis products PCl3 and R3P=NSiMe3 which subsequently react together to afford the N-phosphinophosphoranimines R3P=N-PCl2 and ClSiMe3 as a byproduct. 相似文献
40.
Ian Hamerton John R. Jones David C. Povey Gallienus W. Smith John M. Barton 《Journal of chemical crystallography》1992,22(1):101-108
The structure of the title compound (I) was determined by direct methods using MoK diffractometer data, and refined by full-matrix least squares toR=0.066 for 1536 reflections (I3 (I)). The structure shows a central tetrahedral carbon atom surrounded by two methyl and two 3-allyl-4-cyanatophenyl groups. The geometry of the cyanato group in this molecule compares well with those in 2,2-bis(4-cyanatophenyl)isopropylideneII) and 4-chloro-3,5-dimethyl-phenylcyanate (III), the only other examples of organic compounds bearing the cyanato moiety in the Cambridge Crystallographic Database (V.3). 相似文献