全文获取类型
收费全文 | 10066篇 |
免费 | 1924篇 |
国内免费 | 1559篇 |
专业分类
化学 | 7935篇 |
晶体学 | 141篇 |
力学 | 621篇 |
综合类 | 94篇 |
数学 | 1332篇 |
物理学 | 3426篇 |
出版年
2024年 | 19篇 |
2023年 | 154篇 |
2022年 | 273篇 |
2021年 | 330篇 |
2020年 | 370篇 |
2019年 | 432篇 |
2018年 | 354篇 |
2017年 | 311篇 |
2016年 | 526篇 |
2015年 | 594篇 |
2014年 | 609篇 |
2013年 | 761篇 |
2012年 | 895篇 |
2011年 | 900篇 |
2010年 | 724篇 |
2009年 | 684篇 |
2008年 | 723篇 |
2007年 | 588篇 |
2006年 | 524篇 |
2005年 | 491篇 |
2004年 | 445篇 |
2003年 | 401篇 |
2002年 | 511篇 |
2001年 | 423篇 |
2000年 | 266篇 |
1999年 | 221篇 |
1998年 | 188篇 |
1997年 | 132篇 |
1996年 | 118篇 |
1995年 | 107篇 |
1994年 | 87篇 |
1993年 | 68篇 |
1992年 | 57篇 |
1991年 | 59篇 |
1990年 | 37篇 |
1989年 | 28篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
含三唑与噻二唑Schiff碱的合成与植物激素活性研究 总被引:2,自引:0,他引:2
合成了10种三氮唑与噻二唑的新Schiff碱,讨论了它们的物理性质、UV、IR、1HNMR和元素分析.生物活性测试发现了一些化合物具有优良的植物激素活性,其中噻二唑的Schiff碱具有优良的生长素活性,而三唑的Schiff碱具有好的细胞分裂素活性和优异的生根性能. 相似文献
972.
The construction and performance characteristics of an ion-selective electrode for fentanyl-drug cation, based on an ion-pair complex with tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate anion in a PVC matrix were studied. A linear response for 1 x 10(-5) mol dm-3 to 1 x 10(-2) mol dm-3 drug with a slope of 57.9 +/- 0.5 mV/decade was established. The optimum pH range was 2 to 6. The lower detection limit was 6.29 x 10(-6) mol dm-3 fentanyl citrate (2.1165 micrograms cm-3 fentanyl). There were negligible interferences from a number of inorganic cations, structural analogues, and some common drug additives in injections. The electrode proposed has been successfully applied to determine fentanyl citrate in injections. The results correlated well with those obtained by the United States Pharmacopoeia standard procedure. 相似文献
973.
The principle of step-scan Fourier transform infrared (FTIR) spectroscopy is introduced. Double modulation step-scan FTIR technique is used to obtain the quantum cascade laser's stacked emission spectra in the time domain. Optical property and thermal accumulation of devices due to large drive current are analyzed. 相似文献
974.
Wen Li Dalin Wu A. Dieter Schlüter Afang Zhang 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6630-6640
An improved strategy to synthesize oligo(ethylene glycol)‐based secondary generation (G2) dendron is presented. The overall synthesis efficiency increased by 50% when comparing to the previous method, and the product purification by column chromatography becomes much easier. Based on this approach, the synthesis of the third‐generation (G3) dendrons and the corresponding methacrylate‐based G3 macromonomer becomes feasible. Because of the oil characteristics of this macromonomer, its polymerization was able to be conducted in bulk with AIBN as the initiator. The polymerization degree of the third‐generation dendronized polymer ( PG3 ) was found to be around 16 based on GPC measurement. The thermally induced dehydration processes of this polymer were monitored by temperature‐varied proton NMR spectroscopy, and its thermoresponsive behaviors were investigated with turbidity measurements using UV–vis spectroscopy. Similar to the lower generation counterparts, this threefold branched dendronized polymer also shows characteristic fast and sharp phase transitions around its apparent lower critical solution temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6630–6640, 2009 相似文献
975.
Tianfa Wen Jianping Gao Jiuming Zhang Beiya Bian Juyun Shen 《Infrared Physics & Technology》2001,42(6):241-508
A metallic (Ag)–dielectric (AgI) hollow glass waveguide is a promising and flexible fiber for the delivery of high-power CO2 laser radiation. The thickness of metallic (Ag) films and dielectric (AgI) films is a critical factor which greatly influences the attenuation of the waveguides. In this paper, metallic (Ag)–dielectric (AgI) films were successfully prepared in the capillary whose inner diameter is 0.53 mm, and firstly investigated with theoretical analysis and measured by means of AES and SEM. There is good agreement between theoretical thickness and experimental results, which confirms the validity of the theoretical analysis, which makes the estimate of the thickness of both the metallic and dielectric films possible with high accuracy prior to the preparation of hollow glass waveguides. The attenuation spectra of Ag/AgI hollow waveguides shows the loss increases with the thickness of Ag, AgI films and indicates that the Ag/AgI hollow waveguide is suitable for the transmission of IR radiation. 相似文献
976.
Liu Wen N. I. Sorokina V. I. Voronkova V. K. Yanovskii I. A. Verin A. G. Vigdorchik V. I. Simonov 《Crystallography Reports》2000,45(3):386-388
To reveal correlations between the atomic structure and properties of the KTi1-x SnxOPO4 solid solutions, single crystals of the KTi0.93Sn0.07OPO4 composition were synthesized and their structure was determined. The crystals belong to the KTiOPO4 family; orthorhombic, sp. gr. Pna21. The unit-cell parameters are a = 12.831, b = 6.410, and c = 10.584 Å. The partial substitution of Sn atoms for Ti atoms results in the formation of more symmetric coordination polyhedra in the structure framework and the change of the physical properties of the crystals. 相似文献
977.
令t(G)为有限阿贝尔群G的单因子个数.本文得到了∑|G|≤xt(G)带有更好余项的渐近公式. 相似文献
978.
Weiwei Zuo Shu Zhang Shaofeng Liu Xijie Liu Wen‐Hua Sun 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3396-3410
6‐Benzimidazolylpyridyl‐2‐carboximidic half‐titanocene complexes, Cp′TiLCl (Cp′ = C5H5, MeC5H4, C5Me5, L = 6‐benzimidazolylpyridine‐2‐carboxylimidic, C1–C13 ), were synthesized and characterized along with single‐crystal X‐ray diffraction. The half‐titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo‐bridged complexes, (CpTiL)2O ( C14 and C15 ). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half‐titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14 . With C1 /MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14 /MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008 相似文献
979.
Jing Sun Jian‐Gong Cheng Wen‐Qing Zhu Shi‐Jie Ren Hong‐Liang Zhong Dan‐Li Zeng Jun‐Ping Du Er‐Jian Xu Ying‐Chun Liu Qiang Fang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(16):5616-5625
A new X‐shaped π‐conjugated monomer comprising of fluorene units and anthracene units was synthesized, and it was used to fabricate the new X‐shaped π‐conjugated polymers and investigate the properties of the new polymers. Using different molar ratios between such monomer and a fluorene monomer gave three polymers that showed higher absolute PL quantum yields than the linear polyfluorene (PF) in the solid state. After thermal annealing at 200 °C for 4 h, the linear PF showed an additional bathochromic emission at about 550 nm, whereas such red‐shifted emission was fully eliminated for the X‐shaped polymers. The electroluminescent devices based on the X‐shaped polymers with a configuration of ITO/PEDOT:PSS/polymer/LiF/Ca/Al displayed blue emission with low turn‐on voltage and high brightness. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5616–5625, 2008 相似文献
980.
Guo Dong LIU Wen Peng ZHANG 《数学学报(英文版)》2008,24(2):343-352
The authors establish an explicit formula for the generalized Euler NumbersE2n^(x), and obtain some identities and congruences involving the higher'order Euler numbers, Stirling numbers, the central factorial numbers and the values of the Riemann zeta-function. 相似文献