全文获取类型
收费全文 | 13590篇 |
免费 | 1819篇 |
国内免费 | 2096篇 |
专业分类
化学 | 8859篇 |
晶体学 | 580篇 |
力学 | 445篇 |
综合类 | 139篇 |
数学 | 1047篇 |
物理学 | 2954篇 |
无线电 | 3481篇 |
出版年
2024年 | 52篇 |
2023年 | 275篇 |
2022年 | 288篇 |
2021年 | 365篇 |
2020年 | 486篇 |
2019年 | 454篇 |
2018年 | 387篇 |
2017年 | 580篇 |
2016年 | 606篇 |
2015年 | 589篇 |
2014年 | 692篇 |
2013年 | 986篇 |
2012年 | 1022篇 |
2011年 | 1023篇 |
2010年 | 703篇 |
2009年 | 814篇 |
2008年 | 826篇 |
2007年 | 893篇 |
2006年 | 799篇 |
2005年 | 713篇 |
2004年 | 725篇 |
2003年 | 651篇 |
2002年 | 631篇 |
2001年 | 447篇 |
2000年 | 342篇 |
1999年 | 330篇 |
1998年 | 271篇 |
1997年 | 233篇 |
1996年 | 190篇 |
1995年 | 172篇 |
1994年 | 138篇 |
1993年 | 140篇 |
1992年 | 123篇 |
1991年 | 75篇 |
1990年 | 56篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 30篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1975年 | 18篇 |
1974年 | 21篇 |
1971年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
《Journal of Coordination Chemistry》2012,65(6):539-544
Silver(I) complexes of selenones, [LAgNO3] and [AgL2]NO3 (where L is imidazolidine-2-selenone or diazinane-2-selenone and their derivatives) have been prepared and characterized by elemental analysis, IR and NMR (1H, 13C and 107Ag) spectroscopy. An upfield shift in the C=Se resonance of selenones in 13C NMR and a downfield shift in N-H resonance in 1H NMR are consistent with selenium coordination to silver(I). In 107Ag NMR, the AgNO3signal is deshielded by 450-650 ppm on coordination to selenones. Greater upfield shifts in 13C NMR were observed for [LAgNO3] compared to [AgL2]NO3complexes, whereas the opposite trend was observed for 1H and107Ag NMR chemical shifts. 相似文献
52.
53.
54.
S. K. Srivastava Shailja Tomar Rupali Rastogi Richa Saxena 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):634-640
Six new substituted diphenyltin(IV) O,O′-alkylene dithiophosphates, (C6H5)2Sn(X)S(S) POGO [G = —CH2C(CH3)2CH2—, X = Cl (1), SCN (3), ClO4 (5); G = —CH2C (C4H9)(C2H5)CH2—, X = Cl (2), SCN (4), ClO4 (6)], were synthesized by the reaction of the corresponding ammonium salts of the O,O’-alkylene dithiophosphates with an appropriate organotin(IV) chloride. The compounds were characterized on the basis of elemental and spectral analyses (ESI mass spectrometry, IR, 1H, 13C, 31P, and 119Sn NMR). The presence of a four-coordinated Sn atom and monodentate O,O’-alkylene dithiophosphate moiety in compounds 1–4 as well as bidentate O,O’-alkylene dithiophosphate unit in compounds 5,6 is established. 相似文献
55.
Ying Zhang Wei Shen Zhongping Ou Weihua Zhu Yuangyuan Fang Karl M. Kadish 《Electroanalysis》2013,25(6):1513-1518
Two iron(I) porphyrins were electrogenerated and then utilized as catalysts for the reductive dechlorination of 1,1‐bis(4‐chlorophenyl)‐2,2,2‐trichloroethane (DDT) in N,N′‐dimethylformamide. No reaction is observed between DDT and the Fe(III) or Fe(II) forms of the porphyrin, but the electrogenerated Fe(I) porphyrin efficiently catalyzes the electroreduction of DDT to give (1,1‐bis(4‐chlorophenyl)‐2,2‐dichloroethane) DDD, (1,1‐bis(4‐chlorophenyl)‐2,2‐dichloroethylene) DDE and (1,1‐bis(4‐chlorophenyl)‐2‐dichloroethane) DDMU as determined by GC‐MS analysis. The reductive dechlorination was monitored by electrochemistry, controlled potential electrolysis and spectroelectrochemistry and a mechanism for the reaction involving the reduced porphyrins and DDT is proposed. Comparisons are also made between the catalytic properties of metalloporphyrins containing iron, cobalt and manganese central metal ions under the same solution conditions. 相似文献
56.
The ripeness of grapes at the harvest time is one of the most important parameters for obtaining high quality red wines. Traditionally the decision of harvesting is to be taken only after analysing sugar concentration, titratable acidity and pH of the grape juice (technological maturity). However, these parameters only provide information about the pulp ripeness and overlook the real degree of skins and seeds maturities (phenolic maturity). Both maturities, technological and phenolic, are not simultaneously reached, on the contrary they tend to separate depending on several factors: grape variety, cultivar, adverse weather conditions, soil, water availability and cultural practices. Besides, this divergence is increasing as a consequence of the climate change (larger quantities of CO2, less rain, and higher temperatures). 相似文献
57.
N-Arylation of imidazoles with arylboronic acids was efficiently carried out in the presence of a catalytic amount of SiO2-NHC-CuI in methanol at room temperature under base-free reaction conditions. The reactions of a variety of arylboronic acids with imidazoles generated the corresponding products N-arylimidazoles in good to excellent yields. In addition, SiO2-NHC-CuI could be recovered and recycled for six consecutive trials without significant loss of its reactivity. 相似文献
58.
A convenient one-pot method has been developed for the synthesis of substituted acetylchromans involving the condensation of polyhydroxyacetophenone with isoprene and long chain allylic alcohol (phytol) in the presence of borontrifluoride etherate (BF3-Et2O). 相似文献
59.
Thomas A. Manz 《Journal of computational chemistry》2013,34(5):418-421
In recent years, several methods have been developed that partition the electron density among atoms using spherically symmetric atomic weights. D. E. P. Vanpoucke, P. Bultinck, and I. Van Driessche (J. Comput. Chem. 2012, doi: 10.1002/jcc.23088) recently reported a periodic implementation of the Hirshfeld‐I method that uses a combination of Becke‐style and uniform integration grids and modified atomic reference densities to compute net atomic charges in periodic materials. Herein, this method is discussed in the context of earlier periodic implementations of the Hirshfeld‐I method, the Iterated Stockholder Atoms method, and the density derived electrostatic and chemical method. 相似文献
60.
Hisham J. Y. El-Aila 《Journal of Dispersion Science and Technology》2013,34(9):1208-1211
In this article, a mononuclear Mn(Niten)2H2O complex was prepared to catalyze hydrolysis of p-nitrophenyl acetate (PNPA) in presence of Cetyltrimethylammonium bromide (CTAB) micellar system in different pH range from 6.5–10 at 25°C. These results obtained indicate that the complex exhibits good catalytic function. It also appears the complex accelerates the hydrolytic cleavage of PNPA in cationic CTAB micellar solution which may be due to coordinating ability of substrate to complex, electrostatic interaction between micelles and complex and due to electrostatic interaction between micelles with reactant. 相似文献