全文获取类型
收费全文 | 3624篇 |
免费 | 438篇 |
国内免费 | 263篇 |
专业分类
化学 | 2479篇 |
晶体学 | 14篇 |
力学 | 166篇 |
综合类 | 24篇 |
数学 | 517篇 |
物理学 | 1125篇 |
出版年
2024年 | 11篇 |
2023年 | 60篇 |
2022年 | 69篇 |
2021年 | 89篇 |
2020年 | 103篇 |
2019年 | 91篇 |
2018年 | 77篇 |
2017年 | 62篇 |
2016年 | 139篇 |
2015年 | 119篇 |
2014年 | 161篇 |
2013年 | 255篇 |
2012年 | 324篇 |
2011年 | 322篇 |
2010年 | 226篇 |
2009年 | 183篇 |
2008年 | 252篇 |
2007年 | 199篇 |
2006年 | 187篇 |
2005年 | 170篇 |
2004年 | 143篇 |
2003年 | 150篇 |
2002年 | 123篇 |
2001年 | 97篇 |
2000年 | 71篇 |
1999年 | 66篇 |
1998年 | 47篇 |
1997年 | 59篇 |
1996年 | 62篇 |
1995年 | 48篇 |
1994年 | 44篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 5篇 |
排序方式: 共有4325条查询结果,搜索用时 421 毫秒
951.
A novel perfluorinated corrole, 2,3,7,8,12,13,17,18-octafluoro-5,10,15-tris(pentafluorophenyl)corrole, and its manganese(III) and oxomanganese(V) derivatives have been synthesized. The perfluorinated manganese corrolate exhibited excellent reactivity and stability in the catalytic oxidation of alkenes with iodosylbenzene. 相似文献
952.
CH3(2A′)自由基与臭氧反应机理的量子化学研究 总被引:2,自引:0,他引:2
用量子化学UMP2方法,在6-311++G**基组水平上研究了CH3(2A′)自由基与臭氧反应机理,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型,在UQCISD(T)/6-311++G**水平上计算了它们的能量;并对它们进行了振动分析,以确定中间体和过渡态的真实性;同时应用经典过渡态理论计算了反应的速率常数,并与实验值进行了比较, CH3自由基与臭氧反应速率常数的理论计算结果为: 4.73×10-14 cm3•molecule-1•s-1,与实验报导的结果(k=2.52×10-14 cm3•molecule-1•s-1)很接近,同时发现CH3(2A′)自由基与O3的反应是强放热反应. 相似文献
953.
The reduction of cupric ion in ammonia solution by aqueous sulfur dioxide was studied. Each run was carried out at constant initial cupric concentration, stirred rate and total mixed gas flow rate. The effect of temperature, partial pressure of sulfur dioxide in gas phase and cupric ion concentration of the solution was investigated. The reaction of Cu3++SO2(aq.)→Cu++SO42? was carried out by bubbling mixed gas (SO2/N2) through the aqueous ammonia complex of copper (II). The color change for the system was from deep blue, green, yellow to white. The pH values in the system changed from 10 to 4. The product of the reaction was identified by the analyses of IR spectrum and X-ray diffraction, having the formula of 7Cu2SO3· 2CuSO3·3(NH4)2SO3·24H2O. The kinetic model of the reduction was proposed as: –d[Cu2+]/dt = k exp(–E/RT)[Cu2+]α[SO2%] According to the experiments, the parameters were determined as: α=1.64±0.03, þ=1.20, E=13.7 Kcal/mol and k = (1.77±0.20)×1010 (g-equ./?)?0.64min?2. 相似文献
954.
Guo‐Fang Lai Yi‐Fen Wang Chun‐Hua Lu Jian‐Xin Cao Yun‐Long Xu Shi‐De Luo 《Helvetica chimica acta》2003,86(6):2136-2141
Three novel triterpenoids named chinenols A – C ( 1 – 3 ), together with two known compounds, glutin‐5‐en‐3β‐ol ( 4 ) and daucosterol ( 5 ), were isolated from the aerial part of Helwingia chinensis Batal . The structures of 1 – 3 were determined on the basis of their HR‐EI‐MS, IR, 1H‐ and 13C‐NMR (DEPT), and 2D (HMQC, HMBC, NOESY) data. Compounds 1 – 3 and 5 showed inhibition activity in an antibacterial assay. 相似文献
955.
956.
Green DR Fenker HC Lai KW LeBritton J Lin YC Pifer AE Davenport TF Goldman JH Hagopian SL Lannutti JE Canough G Chang CC Davis TC Joyner RW Poirier JA Georgiopoulos CH Napier A Schneps J Marraffino JM Waters JW Webster MS Williams EG Woosley J Ficenec JR Torres S Trower WP 《Physical review letters》1986,56(16):1639-1642
957.
The synthesis and mesomorphic properties of a homologous series of N-(3-hydroxypropyl)-4-alkoxylsalicylaldimine, N-(3-hydroxypropyl)-4-(4′-alkoxybenzoxy)salicylaldimine, and their dicopper(II) and di-oxovanadium(VI) complexes are reported. Copper complexes exhibited monotropic smectic A phases; however, vanadyl complexes showed no mesomorphism. A systematic comparison revealed that the meso-genie behaviors of these bimetallic complexes are induced by the weak intermolecular force and determined mainly by the central metal. The effects on the structural variations near the metal central cores and side chain density are also discussed. 相似文献
958.
偶氮胂酸型荧光试剂测定铝的研究 总被引:10,自引:1,他引:10
比较了5种新试剂及偶氮胂-I的铝铬合物的荧光性能,讨论了试剂结构与性能之间的关系。试验出7-〔(4-甲基-2-胂酸基苯)偶氮〕-8-羟基喹啉-5-磺酸为铝的优良荧光试剂,并用其测定茶叶、含茶叶饲料,以及大白鼠排泄物中的铝和水样中的铝,结果满意。 相似文献
959.
以内型3,3-二甲基-2-降冰片基乙醛(1)与叔丁胺反应制得醛亚胺(2),依次和溴化乙基镁,碘乙烷反应制得内型2-(3,3-二甲基-2-降冰片基)丁醛的亚胺(4),再经水解得内型2-(3,3-二甲基-2-降冰片基)丁醛(5)。后者经与乙二醇缩醛化及氧化分别制得该醛的缩醛(6)及羧酸(7)。这些化合物均为新化合物,经纯化后进行了结构分析,并对其质谱进行了讨论。 相似文献
960.
We study the early stage coagulation kinetics for a charged colloidal dispersion which is here modeled by an effective two-body colloid-colloid potential. The colloidal system was physically prepared by choosing sets of colloidal parameters varying in particular the Hamaker constant and the particle's size. The kinetics of coagulation process was driven by the addition of an indifferent electrolyte and assumed to proceed in two quasi-steady steps. In the first step, colloidal particles are destabilized by the presence of a second potential minimum to diffuse from a bulk-stabilized liquid phase to a flocculated phase. In the second step, we assume that different entities are found in the second potential minimum. The entities comprise secondary dimers, secondary dimers undergoing redispersion, and monomers still in singlet states. If, under favorable condition, this kind of interaction-driven diffusive motion continues, a fraction of the secondary dimers will be induced to undergo primary dimers formation in the first deep minimum. Whether or not the latter process occurs is determined either energetically by the potential barrier falling below a prescribed value, say of 15k(B)T, or/and the second potential minimum becoming negligibly small (with a magnitude coagulation transition and would throw a fresh light on the use of both the energy and the kinetic criteria for understanding the colloidal stability such as those observed in the liquid-liquid coexistence. 相似文献