全文获取类型
收费全文 | 1563篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
化学 | 1148篇 |
晶体学 | 19篇 |
力学 | 20篇 |
数学 | 135篇 |
物理学 | 258篇 |
出版年
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 19篇 |
2014年 | 14篇 |
2013年 | 82篇 |
2012年 | 45篇 |
2011年 | 76篇 |
2010年 | 41篇 |
2009年 | 43篇 |
2008年 | 78篇 |
2007年 | 82篇 |
2006年 | 77篇 |
2005年 | 84篇 |
2004年 | 73篇 |
2003年 | 76篇 |
2002年 | 76篇 |
2001年 | 44篇 |
2000年 | 25篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 38篇 |
1983年 | 10篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 22篇 |
1977年 | 11篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 7篇 |
1972年 | 13篇 |
排序方式: 共有1580条查询结果,搜索用时 15 毫秒
61.
Kiyoshi Tanemura 《Tetrahedron letters》2018,59(49):4293-4298
Silica gel-mediated hydrochlorination of unactivated alkenes using 35% hydrochloric acid under organic solvent-free conditions proceeded to give the corresponding chlorides in good yields. Hydrobromination or hydriodination using 47% hydrobromic acid or 55% hydriodic acid afforded the corresponding halides, respectively. Silica gel could be recycled five times without any significant loss of activities. 相似文献
62.
A graph with at least vertices is said to be distance -extendable if, for any matching of with edges in which the edges lie at distance at least pairwise, there exists a perfect matching of containing . In this paper we prove that every 5-connected triangulation on the projective plane of even order is distance 3 7-extendable and distance 4 -extendable for any . 相似文献
63.
Abstract The pulse-echo-overlap method was used to measure the longitudinal and transverse wave velocities in single-crystal (100) and (111) samples of InSb up to 3 GPa at room temperature. The peculiar variations of the elastic constants were observed near the covalent-metallic transition. 相似文献
64.
65.
Polystyrene sulfonic acid resin (Amberlyst 15) was found to initiate the cationic polymerization of 1,3-dioxolane easily in bulk at 0 to 50° C, and polymers with a reduced viscosity of 0.1 were obtained. However, this resin showed only low initiator activity for the polymerizations of 2-methyl-1, 3-dioxolane and trioxane. 相似文献
66.
Kiyoshi Tanaka Yasuhiro Yamamoto Hiroto Obara Satoru Iwata 《Supramolecular chemistry》2013,25(4):347-352
5,15- cis -bis(Ureidophenyl)porphyrins have significant recognizing ability for p -benzoquinones through four-point hydrogen bonding. Although an unusual temperature-dependence of the complexation is observed with bis( N '-phenylureidophenyl) porphyrin, bis( N '-ethylureidophenyl)porphyrin shows a satisfactorily linear van't Hoff plot and recognizes an electron-rich p -benzoquinone such as tetramethyl- p -benzoquinone more effectively, which is ascribed to the large enthalpy change in the complex. 相似文献
67.
To clarify the non-enzymatic radical-scavenging activity of β-carotene-related compounds and other polyenes, we used differential scanning calorimetry to study the kinetics of radical polymerization of methyl methacrylate (MMA) by 2,2′-azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) in the absence or presence of polyenes under nearly anaerobic conditions at 70°C, and analyzed the results with an SAR approach. The polyenes studied were all-trans retinol, retinol palmitate, calciferol, β-carotene and lycopene. Polyenes produced a small induction period. The stoichiometric factor (n) (i.e. the number of radicals trapped by each inhibitor molecule) of polyenes was close to 0. Tetraterpenes (β-carotene, lycopene) suppressed significantly more of the initial rate of polymerization (R inh) than did diterpenes (retinol, retinol palmitate). The inhibition rate constants (k inh) for the reaction of β-carotene with AIBN-or BPO-derived radicals were determined to be 1.2–1.6?×?105 l?/?mol?s, similar to published values. A linear relationship between k inh and the kinetic chain length (KCL) for polyenes was observed; as k inh increased, KCL decreased. KCL also decreased significantly as the number of conjugated double bonds in the polyenes increased. Polyenes, particularly β-carotene and lycopene, acted as interceptors of growing poly-MMA radicals. 相似文献
68.
Hirohito Ikeda Yukiko Sano Tomonori Matsubara Mitsunobu Kawahara Miho Yukawa Masao Fujisawa Eiji Yukawa Hatsumi Aki 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1135-1138
Propericiazine (PCZ) is an antipsychotic agent used for the treatment and the prevention of relapse of schizophrenia. We found that when an oral solution containing PCZ was mixed with a green tea drink, the residual content of PCZ was reduced by forming an insoluble complex between PCZ and tea polyphenol. In this study, the mechanism underlying the incompatibility of PCZ with green tea polyphenol (GTP) in the solution was clarified by isothermal titration microcalorimetry (ITC). Both solutions of 27.4 mM PCZ and 2.2 mM (?)-epigallocatechin gallate (EGCg), which is a main ingredient of GTP, were mixed and then PCZ in the filtrate was reduced to approximately 60 %. According to measurement at 298 K by ITC, PCZ formed an insoluble complex with EGCg at an associate constant (K) of 4.75 × 102 M?1 exothermically, ΔH = ?40.0 kJ mol?1. When (?)-epicatechin gallate (ECg) was used as the GTP, PCZ interacted with ECg with K and ΔH values of 3.74 × 102 M?1 and ?22.1 kJ mol?1, respectively. On the other hand, little heat of the reaction between PCZ and (?)-epigallocatechin or (?)-epicatechin was observed. The results indicated that the main reason for this incompatibility was the formation of an insoluble complex by PCZ and a gallate-type GTP such as EGCg and ECg in the aqueous solution. 相似文献
69.
70.
Dipalmitoylphosphatidylcholine was synthesized in a good yield by the reaction of L-α-glycerophosphorylcholine with 1-palmitoylimidazole in the presence of DBU. Polymer-supported 1-palmitoylimidazole moiety also could be used as the acylating reagent, though the yield of the choline was moderate. 相似文献