全文获取类型
收费全文 | 29761篇 |
免费 | 2862篇 |
国内免费 | 5461篇 |
专业分类
化学 | 28429篇 |
晶体学 | 202篇 |
力学 | 1565篇 |
综合类 | 160篇 |
数学 | 806篇 |
物理学 | 4893篇 |
无线电 | 2029篇 |
出版年
2024年 | 92篇 |
2023年 | 516篇 |
2022年 | 802篇 |
2021年 | 1047篇 |
2020年 | 1472篇 |
2019年 | 1204篇 |
2018年 | 1223篇 |
2017年 | 1168篇 |
2016年 | 1316篇 |
2015年 | 1212篇 |
2014年 | 1825篇 |
2013年 | 2626篇 |
2012年 | 1586篇 |
2011年 | 2020篇 |
2010年 | 1544篇 |
2009年 | 1742篇 |
2008年 | 1813篇 |
2007年 | 2003篇 |
2006年 | 1828篇 |
2005年 | 1626篇 |
2004年 | 1635篇 |
2003年 | 1304篇 |
2002年 | 841篇 |
2001年 | 688篇 |
2000年 | 687篇 |
1999年 | 608篇 |
1998年 | 509篇 |
1997年 | 445篇 |
1996年 | 396篇 |
1995年 | 369篇 |
1994年 | 302篇 |
1993年 | 231篇 |
1992年 | 215篇 |
1991年 | 181篇 |
1990年 | 133篇 |
1989年 | 118篇 |
1988年 | 103篇 |
1987年 | 68篇 |
1986年 | 58篇 |
1985年 | 60篇 |
1984年 | 60篇 |
1983年 | 31篇 |
1982年 | 48篇 |
1981年 | 42篇 |
1980年 | 35篇 |
1979年 | 36篇 |
1977年 | 31篇 |
1976年 | 38篇 |
1974年 | 39篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
Ken‐ichi Shinohara Tasuku Suzuki Takeshi Kitami Shingo Yamaguchi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(2):801-809
We fabricated a micrometer‐long supramolecular chain in which π‐conjugated polyrotaxane was coupled. A new experimental setup was designed and constructed, and the simultaneous direct imaging of the structure and fluorescent function was achieved. Furthermore, we identified the formation of a polymer intertwined network and observed novel fluorescence due to a long‐range interaction via this intertwined network over a distance of 5 μm or more without quenching over 15 min in the near field. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 801–809, 2006 相似文献
32.
Toshiyuki Oyama Akira Kitamura Eiichi Sato Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2694-2706
The factors affecting pattern‐forming properties in reaction development patterning were examined with polyarylates with various bisphenol moieties. The developability of the photosensitive polyarylates was dependent on the properties of the subtituent (R) in the bisphenol moieties. The development time decreased in the following order: R?C(CH3)2 > fluorenyl unit ? phenolphthalein unit > C(CF3)2 > SO2. This order agreed with that of the reactivity between the polyarylates and ethanolamine, and these orders can be explained by pKa of the bisphenol used to prepare the polyarylates. The development with NH2? R′? OH resulted in successful positive‐tone pattern formation. However, pattern formation with the developers containing NH2? R′? OCH3 was unsuccessful. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2694–2706, 2006 相似文献
33.
介绍了谐振式力传感器的工作原理,并从理论上和实验上对中科院合肥智能所研制的第一代微型硅谐振梁(3×0.4×0.045mm^3)式测力传感器进行了全面的振动分析,所得结构为其进一步优化设计提供了科学根据,文中使用的实验分析方法,为其它微小物体的动态和识别提供了一条有效途径。 相似文献
34.
Irina P. Beletskaya 《Journal of organometallic chemistry》2004,689(24):4055-4082
The application of palladacycles as catalysts for cross-coupling and similar reactions is reviewed. In the majority of cases palladacycles are likely to serve as a source of highly active but unstable zero-valent palladium species. In this respect the palladacycles resemble the so-called phosphine-free catalysts. The advantages and limitations of palladacycle catalysts are discussed. 相似文献
35.
The solid state reaction of 3-methyl-1-phenyl-5-pyrazolone (MPP) with aromatic aldehydes and ke-tones benzil derivatives and imides,and the solid state Michael addition reaction of MPP with 4-arylidene-3-methyl-1-phenyl-5-pyrnzolone 2 were investigated.Some new solid state reactions between the reactants were found,from which a series of new compounds were obtained The structures of the products were identified by IR,1H NMR,MS,elemental analyses and also by X-ray crystal analysis,and the reaction mechanism of MPP with aromatic aldehydes and ketones was proposed 相似文献
36.
Orlov I. S. Moiseeva A. A. Butin E. P. Egorov M. P. 《Russian Chemical Bulletin》2002,51(10):1961-1962
An unusual reaction of diaminogermylene and diaminostannylene with sterically hindered phenols which leads to the formation of stable phenoxyl radicals in high concentrations was found. The reaction mechanism was proposed. Amides [(Me3Si)2N]2E (E = Ge, Sn) were investigated electrochemically. 相似文献
37.
The first MCM-41-supported bidentate phosphine palladium(0) complex has been prepared. This complex is a highly efficient catalyst for Sonogashira reaction and can be reused at least 10 times without any decrease in activity. 相似文献
38.
A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the “Facilitated Transition” hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older “Reactive Rotamer” hypothesis was eliminated by generating all conformations of the starting materials using the
and
computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of “reactive rotamers”. 相似文献
39.
V. Z. Shirinian M. M. Krayushkin D. M. Nikalin A. A. Shimkin 《Russian Chemical Bulletin》2005,54(3):738-742
The reaction of alkyl 4-(2-acetylhydrazino)-2-methyl-3-thiophenecarboxylates with 3-methylbutan-2-one was carried out under the Fischer reaction conditions. The influence of Lewis acids and solvents on the process was studied. A convenient method for the synthesis of thieno [3.2-b]pyrrolenine derivatives was proposed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 725–729, March, 2005. 相似文献
40.
The intermolecular interaction energy for reacting systems in singlet, triplet and doublet states was partitioned by the perturbation expansion method into the chemically meaningful five interaction terms: the Coulomb, exchange-repulsion, induction, dispersion, and charge-transfer energies. In the local ZDO approximation, these energy terms were evaluated for the dimerization of methylenes (1,3CH2), the additions of carbenes (1,3CH2 and1,3CF2) as well as amino radicals (2NH2 and2NF2) toward ethylene, and the hydrogen abstractions by methylenes (1,3CH2), nitrene (3NH), and hydroxyl radical (2OH) from methane. It has been found that the reaction path is much influenced by the spinmultiplicity, and that the charge-transfer and exchange-repulsion terms play a dominant role in determining the course of reactions. 相似文献