全文获取类型
收费全文 | 31152篇 |
免费 | 5253篇 |
国内免费 | 5065篇 |
专业分类
化学 | 23808篇 |
晶体学 | 440篇 |
力学 | 1549篇 |
综合类 | 351篇 |
数学 | 3405篇 |
物理学 | 11917篇 |
出版年
2024年 | 89篇 |
2023年 | 610篇 |
2022年 | 1185篇 |
2021年 | 1264篇 |
2020年 | 1295篇 |
2019年 | 1365篇 |
2018年 | 1128篇 |
2017年 | 1158篇 |
2016年 | 1591篇 |
2015年 | 1699篇 |
2014年 | 2063篇 |
2013年 | 2528篇 |
2012年 | 3034篇 |
2011年 | 3053篇 |
2010年 | 2220篇 |
2009年 | 2131篇 |
2008年 | 2244篇 |
2007年 | 1962篇 |
2006年 | 1792篇 |
2005年 | 1393篇 |
2004年 | 1078篇 |
2003年 | 850篇 |
2002年 | 967篇 |
2001年 | 800篇 |
2000年 | 604篇 |
1999年 | 598篇 |
1998年 | 415篇 |
1997年 | 360篇 |
1996年 | 309篇 |
1995年 | 273篇 |
1994年 | 217篇 |
1993年 | 236篇 |
1992年 | 157篇 |
1991年 | 143篇 |
1990年 | 110篇 |
1989年 | 117篇 |
1988年 | 89篇 |
1987年 | 66篇 |
1986年 | 62篇 |
1985年 | 60篇 |
1984年 | 32篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
本将小波分析方法用于一类奇异积分方程的计算,建立了小波展开的非标准形式与标准形式转换关系,根据Mallat小波快速算法,设计了此类积分的计算算法,并通过实际例子验证了方法的有效性,计算具有速度快,运算量少的特点。 相似文献
62.
The magnetic and electric properties of the Sr2FeMoO6 compound produced under different preparation conditions were studied. Depending on the preparation condition, a strong variation in the nonmagnetic SrMoO4 impurity content was found, which in turn determined the metallic or semiconducting behavior of the resistivity of the Sr2FeMoO6 compound. There was also evidence that SrMoO4 played a crucial role in modifying the low magnetic field intergrain tunneling magnetoresistance in Sr2FeMoO6. In addition, we have established a simple method to prepare the single phase Sr2FeMoO6 polycrystals. 相似文献
63.
64.
65.
H. Postma J. D. Bowman C. D. Bowman J. E. Bush P. P. J. Delheij C. M. Frankle C. R. Gould D. G. Haase J. Knudson G. E. Mitchell S. Penttilä N. R. Roberson S. J. Seestrom J. J. Szymansky S. H. Yoo V. W. Yuan X. Zhu 《Hyperfine Interactions》1992,75(1-4):153-163
Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei238U and232Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon.
Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances
are M=0.58 (+0.50/-0.25) meV for238U, respectively 1.39 (+0.35/-0.38) meV for232Th. 相似文献
66.
X. Y. Yang H. C. Gao X. L. Tan H. Z. Yuan G. Z. Cheng S. Z. Mao S. Zhao L. Zhang J. Y. An J. Y. Yu Y. R. Du 《Colloid and polymer science》2004,282(3):280-286
1H chemical shift changes of sodium 4-decyl naphthalene sulfonate (SDNS) at 313 K show that its critical micellar concentration lies between 0.82 and 0.92 mmol/dm3, which is in the same range as that of the previous study at 298 K. The spin–lattice relaxation time, spin–spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy experiments give information about the structure of the SDNS micelle and the dynamics of the molecules in the micelle. The size of the SDNS micelle remains almost unchanged in the temperature range from 298 to 313 K as deduced by analyzing the self-diffusion coefficient. Special arrangement of the naphthyl rings of SDNS in the micelles affects the packing of these hydrophobic chains. The methylene groups of the alkyl chain nearest the naphthalene groups penetrate into the aromatic region, which results in a more tightly packed hydrophobic micellar core than that of sodium dodecyl sulfonate. 相似文献
67.
68.
69.
Peng Ping Wenshou Wang Xuesi Chen Xiabin Jing 《Journal of Polymer Science.Polymer Physics》2007,45(5):557-570
Poly(ε‐caprolactone)‐based segmented polyurethanes (PCLUs) were prepared from poly(ε‐caprolactone) diol, diisocyanates (DI), and 1,4‐butanediol. The DIs used were 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluenediisocyanate (TDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small‐angle X‐ray scattering, and dynamic mechanical analysis were employed to characterize the two‐phase structures of all PCLUs. It was found that HDI‐ and MDI‐based PCLUs had higher degree of microphase separation than did IPDI‐ and TDI‐based PCLUs, which was primarily due to the crystallization of HDI‐ and MDI‐based hard‐segments. As a result, the HDI‐based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard‐segment domains during the sample deformation was responsible for the incomplete shape‐recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 557–570, 2007 相似文献
70.
A Novel and Efficient Catalytic System for Aerobic Oxidative Coupling of 2-Naphthol Derivatives 总被引:2,自引:0,他引:2
LiCHEN JingBoLAN ZhiHuaMAO XiaoQiYU RuGangXIE 《中国化学快报》2004,15(8):903-906
The paper reported a novel and efficient aerobic oxidative coupling reaction of 2-naphthol derivatives catalyzed by CuCu (Ⅰ or Ⅱ)N-alkylimidazole complexes in excellent yields. The crystal structure of CuCu(Ⅱ)N-methylimidazole complex to be determined by X-Ray. 相似文献