全文获取类型
收费全文 | 2511篇 |
免费 | 115篇 |
国内免费 | 410篇 |
专业分类
化学 | 2752篇 |
晶体学 | 60篇 |
力学 | 8篇 |
综合类 | 36篇 |
数学 | 2篇 |
物理学 | 178篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 49篇 |
2020年 | 88篇 |
2019年 | 46篇 |
2018年 | 53篇 |
2017年 | 67篇 |
2016年 | 69篇 |
2015年 | 71篇 |
2014年 | 78篇 |
2013年 | 222篇 |
2012年 | 181篇 |
2011年 | 100篇 |
2010年 | 77篇 |
2009年 | 112篇 |
2008年 | 105篇 |
2007年 | 169篇 |
2006年 | 157篇 |
2005年 | 130篇 |
2004年 | 116篇 |
2003年 | 128篇 |
2002年 | 92篇 |
2001年 | 79篇 |
2000年 | 82篇 |
1999年 | 71篇 |
1998年 | 75篇 |
1997年 | 52篇 |
1996年 | 75篇 |
1995年 | 61篇 |
1994年 | 56篇 |
1993年 | 61篇 |
1992年 | 64篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有3036条查询结果,搜索用时 15 毫秒
61.
Christian Neis Thomas Kradolfer Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(6):632-637
Single crystals of (1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)lithium(I) diiodide dihydrate, [Li(C6H16N3O3)(C6H15N3O3)]I2·2H2O or [Li(Htaci)(taci)]I2·2H2O (taci is 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol), (I), bis(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)sodium(I) iodide, [Na(C6H15N3O3)2]I or [Na(taci)2]I, (II), and bis(1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol‐κ3O2,O4,O6)potassium(I) iodide, [K(C6H15N3O3)2]I or [K(taci)2]I, (III), were grown by diffusion of MeOH into aqueous solutions of the complexes. The structures of the Na and K complexes are isotypic. In all three complexes, the taci ligands adopt a chair conformation with axial hydroxy groups, and the metal cations exhibit exclusive O‐atom coordination. The six O atoms of the resulting MO6 unit define a centrosymmetric trigonal antiprism with approximate D3d symmetry. The interligand O...O distances increase significantly in the order Li < Na < K. The structure of (I) exhibits a complex three‐dimensional network of R—NH2—H...NH2—R, R—O—H...NH2—R and R—O—H...O(H)—H...NH2—R hydrogen bonds. The structures of the Na and K complexes consist of a stack of layers, in which each taci ligand is bonded to three neighbours via pairwise O—H...NH2 interactions between vicinal HO—CH—CH—NH2 groups. 相似文献
62.
Isothermal Titration Calorimetry Study of a Bistable Supramolecular System: Reversible Complexation of Cryptand[2.2.2] with Potassium Ions 下载免费PDF全文
Maria G. del Rosso Dr. Artur Ciesielski Dr. Silvia Colella Prof. Jack M. Harrowfield Prof. Paolo Samorì 《Chemphyschem》2014,15(13):2743-2748
Isothermal titration calorimetry (ITC) is used to investigate the thermodynamics of the complexation of potassium ions by 1,10‐diaza‐4,7,13,16,21,24‐hexaoxabicyclo[8.8.8]hexacosane (cryptand[2.2.2]) in aqueous solution. By changing the pH of the solution it was possible to trigger the reversible complexation/decomplexation of the cryptand in consecutive in situ experiments and to assess for the first time the use of ITC to monitor the thermodynamics of a bistable system. 相似文献
63.
Brendan J. Holland Jacqui L. Adcock Pavel N. Nesterenko Anton Peristyy Paul G. Stevenson Neil W. Barnett Xavier A. Conlan Paul S. Francis 《Analytica chimica acta》2014
Sodium polyphosphate is commonly used to enhance chemiluminescence reactions with acidic potassium permanganate through a dual enhancement mechanism, but commercially available polyphosphates vary greatly in composition. We have examined the influence of polyphosphate composition and concentration on both the dual enhancement mechanism of chemiluminescence intensity and the stability of the reagent under analytically useful conditions. The average chain length (n) provides a convenient characterisation, but materials with similar values can exhibit markedly different distributions of phosphate oligomers. There is a minimum polyphosphate chain length (∼6) required for a large enhancement of the emission intensity, but no further advantage was obtained using polyphosphate materials with much longer average chain lengths. Providing there is a sufficient average chain length, the optimum concentration of polyphosphate is dependent on the analyte and in some cases, may be lower than the quantities previously used in routine detection. However, the concentration of polyphosphate should not be lowered in permanganate reagents that have been partially reduced to form high concentrations of the key manganese(III) co-reactant, as this intermediate needs to be stabilised to prevent formation of insoluble manganese(IV). 相似文献
64.
65.
KNa[CoIII(OH)7{Mo6O17}] ·8H2O is obtained by ion‐exchange from a solution of K3 [Co(μ3‐OH)6Mo6O18] ·7H2O at ≈pH 1.4 using Amberlite IR120 ion exchange resin followed by concentrating the solution in a hot water bath. 相似文献
66.
Ross F. Koby Alicia M. Doerr Nicholas R. Rightmire Nathan D. Schley Brian K. Long Timothy P. Hanusa 《Angewandte Chemie (International ed. in English)》2020,59(24):9542-9548
Milling two equivalents of K[1,3‐(SiMe3)2C3H3] (=K[A′]) with MgX2 (X=Cl, Br) produces the allyl complex [K2MgA′4] ( 1 ). Crystals grown from toluene are of the solvated species [((η6‐tol)K)2MgA′4] ([ 1 ?2(tol)]), a trimetallic monomer with both bridging and terminal (η1) allyl ligands. When recrystallized from hexanes, the unsolvated 1 forms a 2D coordination polymer, in which the Mg is surrounded by three allyl ligands. The C?C bond lengths differ by only 0.028 Å, indicating virtually complete electron delocalization. This is an unprecedented coordination mode for an allyl ligand bound to Mg. DFT calculations indicate that in isolation, an η3‐allyl configuration on Mg is energetically preferred over the η1‐ (σ‐bonded) arrangement, but the Mg must be in a low coordination environment for it to be experimentally realized. Methyl methacrylate is effectively polymerized by 1 , with activities that are comparable to K[A′] and greater than the homometallic magnesium complex [{MgA′2}2]. 相似文献
67.
以电位滴定终点确定新方法探讨研究为例,从5个方面介绍将创新能力培养融入基础课教学的探索。通过该研究提高了学生基础课学习热情与学习质量。首先改进了二次差值微商终点计算方法,通过Excel 计算Δ2E/ΔV-V 二次差值微商法数据表中的最高点与最低点直线线性方程 y=ax+b,令 y=0, x=-b/a即为终点。另外,研究得到了模拟滴定曲线微分法确定电位滴定终点的新方法。用Excel 对滴定曲线进行三次方程模拟即:y=ax3+bx2+cx+d,二次微分后得到: d2y/dx2=6ax+2b, 当d2y/dx2=0,对应的x=-b/3a处即为滴定终点。2 相似文献
68.
高锰酸钾作为常用的氧化剂,其氧化性强弱与体系酸碱性相关。通过手持技术,利用氧化还原电势(ORP)传感器和pH传感器去探究体系酸碱性对高锰酸钾氧化性的影响。实验发现:pH在酸性条件下,高锰酸钾溶液的氧化性明显增强,随着体系pH的减小,氧化性继续增强;在碱性条件下,其氧化性明显减弱,随着体系pH的增大,其氧化性继续减弱。实际实验中需要根据各种综合因素选用适宜酸碱性的高锰酸钾溶液做氧化剂。 相似文献
69.
Xinsheng Liu Lei Zhao Bin Miao Zhiqi Gu Jin Wang Huoxiang Peng Jiande Li Wei Sun Jiadong Li 《Electroanalysis》2020,32(2):422-428
Biosensors based on field‐effect transistor (FET) structures have attracted considerable attention because they offer rapid, inexpensive parallel sensing and ultrasensitive label‐free detection. However, long‐term repeatable detection cannot be performed, and Ag/AgCl reference electrode design is complicated, which has hindered FET biosensors from becoming truly wearable health‐monitoring platforms. In this paper, we propose a novel wearable detection platform based on AlGaN/GaN high‐electron‐mobility transistors (HEMTs). In this platform, a sweatband was used to continuously collect sweat, and a pH detecting unit and a potassium ion detecting unit were formed by modifying different sensitive films to realize the long‐term stable and repeatable detection of pH and potassium ions. Experimental data show that the wearable detection platform based on AlGaN/GaN HEMTs has good sensitivity (pH 3–7 sensitivity is 45.72 μA/pH; pH 7.4–9 sensitivity is 51.073 μA/pH; and K+ sensitivity is 4.94 μA/lgαK+), stability (28 days) and repeatability (the relative standard deviation (RSD) of pH 3–7 sensitivity is 2.6 %, the RSD of pH 7.4–9 sensitivity is 2.1 %, and the RSD of K+ sensitivity is 7.3 %). Our newly proposed wearable platform has excellent potential for predictive analytics and personalized medical treatment. 相似文献
70.
Johannes H. Harenberg Niels Weidmann Paul Knochel 《Angewandte Chemie (International ed. in English)》2020,59(30):12321-12325
We report the preparation of lithium‐salt‐free KDA (potassium diisopropylamide; 0.6 m in hexane) complexed with TMEDA (N,N,N′,N′‐tetramethylethylenediamine) and its use for the flow‐metalation of (hetero)arenes between ?78 °C and 25 °C with reaction times between 0.2 s and 24 s and a combined flow rate of 10 mL min?1 using a commercial flow setup. The resulting potassium organometallics react instantaneously with various electrophiles, such as ketones, aldehydes, alkyl and allylic halides, disulfides, Weinreb amides, and Me3SiCl, affording functionalized (hetero)arenes in high yields. This flow procedure is successfully extended to the lateral metalation of methyl‐substituted arenes and heteroaromatics, resulting in the formation of various benzylic potassium organometallics. A metalation scale‐up was possible without further optimization. 相似文献