全文获取类型
收费全文 | 3732篇 |
免费 | 631篇 |
国内免费 | 532篇 |
专业分类
化学 | 2927篇 |
晶体学 | 38篇 |
力学 | 185篇 |
综合类 | 42篇 |
数学 | 450篇 |
物理学 | 1253篇 |
出版年
2024年 | 12篇 |
2023年 | 67篇 |
2022年 | 134篇 |
2021年 | 131篇 |
2020年 | 149篇 |
2019年 | 151篇 |
2018年 | 141篇 |
2017年 | 117篇 |
2016年 | 154篇 |
2015年 | 171篇 |
2014年 | 185篇 |
2013年 | 251篇 |
2012年 | 297篇 |
2011年 | 331篇 |
2010年 | 225篇 |
2009年 | 201篇 |
2008年 | 275篇 |
2007年 | 183篇 |
2006年 | 182篇 |
2005年 | 177篇 |
2004年 | 154篇 |
2003年 | 152篇 |
2002年 | 185篇 |
2001年 | 153篇 |
2000年 | 106篇 |
1999年 | 85篇 |
1998年 | 72篇 |
1997年 | 44篇 |
1996年 | 90篇 |
1995年 | 65篇 |
1994年 | 46篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4895条查询结果,搜索用时 0 毫秒
41.
The Ullmann-type coupling reaction of vinyl bromides and imidazoles in ILs at 90-110 degrees C gave the corresponding N-vinylimidazoles in good to excellent yields by using L-proline as the ligand; the double bond geometry of the vinyl bromides was retained under the reaction conditions. 相似文献
42.
热重分析(TG)和微商热重法(DTG)广泛应用于各个研究领域,用非等温热重法测定固体化合物的热分解动力学参数已有报导.许多作者提出各种不同的数据处理方法.本文用的ρ-CH_3C_6H_4SR 型硫醚对钯的萃取具有选择性好、分配比高、气味较小、易溶于脂肪烃类溶剂、易于合成、是很有发展前途的一类萃取剂.我们合成五种ρ-CH_3C_6H_4SR(R:n-C_4H_9,n-C_6H_(13),n-C_8H_(17),n-C_(10)H_(21),n-C_(12)H_(25))型硫醚与钯(Ⅱ)的配合物,用TG-DTG 法研究它们的热分解过程,用微商法(Freeman-Carroll 方程)及积分法(Coats-Redfern 方程)获得了这些配合物的热分解动力学参数. 相似文献
43.
44.
Kang De Yao Tao Peng Han Bao Feng Yu Ying He 《Journal of polymer science. Part A, Polymer chemistry》1994,32(7):1213-1223
The aqueous swelling kinetics of a series of crosslinked chitosan (cr-CS) with glutaraldehyde (GA) interpenetrating polyether hydrogels have been studied as functions of pH, the N-deacetylation degree of chitosan, the amount of crosslinking agent, the electrolyte composition in solution, temperature, and gel composition. Based on these results, the swelling mechanism of the hydrogels was discussed. The release profiles of chlorhexidini acetas from the semi-IPN were also investigated. © 1994 John Wiley & Sons, Inc. 相似文献
45.
A parallel solution combustion synthesis technique was developed for combinatorial materials studies. The vigorous combustion reactions were successfully limited in the microreactors by using a substrate-net-mask microreactor system and the lowest adoptable furnace temperature. Using this technique, a luminescent materials library of Y3Al5O12/Tb(chi) was synthesized with the aid of an ink-jet delivery system. Structure and luminescence characterizations were implemented using X-ray diffraction and UV/X-ray spectroscopies, respectively. The results show that this technique is reliable and applicable to combinatorial study of powder materials with high synthesis temperature. 相似文献
46.
Wen-Jia Zhou Shu-Juan Bao Yan-Yu Liang Ben-Lin He Hu-Lin Li 《Journal of Solid State Electrochemistry》2006,10(5):277-282
Pure-phase and well-crystallized spinel LiMn2O4 powders were successfully synthesized by a simple rheological phase method. The thermal behavior and structure properties
of the powders prepared by the rheological phase method compared with the solid-state reaction were investigated by thermogravimetry,
powder X-ray diffraction , scanning electron microscopy and transmission electron microscopy. According to the results of
the electrochemical tests, it is obvious that the sample resulting from the rheological phase method shows higher discharge
capacity and better cycling stability than one formed in the solid-state reaction. The cyclic voltammogram and columbic efficiency
curves also confirm that the product by the rheological phase method has a good cycling performance due to its fine cubic
spinel structure and morphology. 相似文献
47.
A bio-mimic bulk acoustic wave (BAW) sensor was fabricated by coating the caffeine (CAF) template molecular imprinting polymer (MIP). This sensor exhibited high selectivity and a sensitive mass response to CAF. The response range of the sensor was between 5.0 x 10(-9) and 1.0 x 10(-4) M with a detection limit of 5.0 x 10(-9) M at pH 8.0. Recoveries were 96.1-105.6%. Influencing factors were investigated in detail and optimized. When employed to detect real samples, the proposed method proved to be a convenient method with the advantages of high sensitivity, good selectivity and ease of handling. 相似文献
48.
A microchip CE-amperometric detection (AD) system has been fabricated by integrating a two-dimensionally adjustable CE microchip and an AD cell containing a one-dimensionally adjustable disk detection electrode in a Plexiglas holder. It facilitates the precise 3-D alignment between the channel outlet and the detection electrode without a complicated 3-D manipulator. The performance of this unique system was demonstrated by separating five aromatic amines (1,4-phenyldiamine, aniline, 2-methylaniline, 4-chloroaniline, and 1-naphthylamine) of environmental concern. Factors influencing their separation and detection processes were examined and optimized. The five analytes have been well separated within 140 s in a 74 cm long separation channel at a separation voltage of +2500 V using a 10 mM phosphate buffer (pH 3.5). Highly linear response is obtained for the five analytes over the range 20-200 microM with the detection limits ranging from 0.46 to 1.44 microM, respectively. The present system demonstrated long-term stability and reproducibility with RSDs of less than 5% for the peak current (n = 9). The new approach for the microchannel-electrode alignment should find a wide range of applications in CE, flowing injection analysis, and other microfluidic analysis systems. 相似文献
49.
Bao J Baker RK Doss GA Kayser F Kotliar A Miao S Parsons WH Rupprecht KM 《Organic letters》2002,4(11):1871-1873
[reaction: see text] Pentacyclic triterpenoid natural product correolide (1) was converted to ketone 2 via ozonolysis. An unusual fragmentation reaction of ketone 2 with LiCl was discovered. This reaction is general among several similar substrates examined and appears to be specific for the correolide-type E-ring structure (ketone). A mechanism involving a retroaldol reaction, a nucleophilic opening of the epoxide, and a subsequent acetoxy elimination reaction was proposed. 相似文献
50.
H. Bao S. Navaratnam B. J. Parsons G. O. Phillips 《Radiation Physics and Chemistry》1993,42(4-6):989-992
One-electron oxidation of the ferrous tris-PQ complex, a model for lipoxygenase, was attempted using oxidants such as •OH, N•3, Br•-2, Tl2+ and TlOH+. •OH was found to react with the complex with a bimolecular rate constant of (3.9±0.6)x109dm3mol-1s-1, a rate which is not very dissimilar to that for the reaction with the ligand PQ. However the product of the reaction was found to be a OH-adduct rather than a cation radical. No reaction was found to occur with N•3 or Br•-2. Both Tl2+ and TlOH+ reacted with the complex to form its oxidised species with rate constants of (7.0±1)x108dm3mol-1s-1 and (4.0±0.8)x108dm3mol-1s-1, respectively. From a comparison of the rate constants and the transient spectra it was concluded that the centre of oxidation is the ligand rather than the metal. 相似文献