全文获取类型
收费全文 | 283202篇 |
免费 | 3367篇 |
国内免费 | 937篇 |
专业分类
化学 | 151731篇 |
晶体学 | 4838篇 |
力学 | 11631篇 |
综合类 | 7篇 |
数学 | 31213篇 |
物理学 | 88086篇 |
出版年
2019年 | 2176篇 |
2018年 | 2591篇 |
2017年 | 2609篇 |
2016年 | 4426篇 |
2015年 | 2887篇 |
2014年 | 4429篇 |
2013年 | 12146篇 |
2012年 | 8965篇 |
2011年 | 11013篇 |
2010年 | 7561篇 |
2009年 | 7333篇 |
2008年 | 10099篇 |
2007年 | 10031篇 |
2006年 | 9690篇 |
2005年 | 9016篇 |
2004年 | 8193篇 |
2003年 | 7395篇 |
2002年 | 7206篇 |
2001年 | 8152篇 |
2000年 | 6179篇 |
1999年 | 4900篇 |
1998年 | 4153篇 |
1997年 | 4048篇 |
1996年 | 3861篇 |
1995年 | 3690篇 |
1994年 | 3487篇 |
1993年 | 3381篇 |
1992年 | 3836篇 |
1991年 | 3747篇 |
1990年 | 3651篇 |
1989年 | 3601篇 |
1988年 | 3584篇 |
1987年 | 3593篇 |
1986年 | 3384篇 |
1985年 | 4502篇 |
1984年 | 4708篇 |
1983年 | 4022篇 |
1982年 | 4422篇 |
1981年 | 4102篇 |
1980年 | 4135篇 |
1979年 | 4263篇 |
1978年 | 4399篇 |
1977年 | 4264篇 |
1976年 | 4318篇 |
1975年 | 4157篇 |
1974年 | 4022篇 |
1973年 | 4375篇 |
1972年 | 2776篇 |
1971年 | 2232篇 |
1968年 | 2202篇 |
排序方式: 共有10000条查询结果,搜索用时 533 毫秒
131.
C. W. LEUNG Department of Mathematics The Chinese Universityof Hong Kong Shatin. N. T. Hong Kong China. 《数学年刊B辑(英文版)》1997,(1)
ASTRASSENLAWOFTHEITERATEDLOGARITHMFORPROCESSESWITHINDEPENDENTINCREMENTWangJiagangAbstractLetX={X(t),t0}beaproceswithindep... 相似文献
132.
133.
Alloys of the systems Fe–Al (mixable over the whole concentration range) and Fe–Mg (insoluble with each other) were produced by implantation of Fe ions into Al and Mg, respectively. The implantation energy was 200 keV and the ion doses ranged from 1 × 1014 to 9 × 1017cm-2The obtained implantation profiles were determined by Auger electron spectroscopy depth profiling. Maximum iron concentrations reached were up to 60 at.% for implantation into Al and 94 at.% for implantation into Mg. Phase analysis of the implanted layers was performed by conversion electron Mössbauer spectroscopy and X‐ray diffraction. For implantation into Mg, two different kinds of Mössbauer spectra were obtained: at low doses paramagnetic doublets indicating at least two different iron sites and at high doses a dominant ferromagnetic six‐line‐pattern with a small paramagnetic fraction. The X‐ray diffraction pattern concluded that in the latter case a dilated αiron lattice is formed. For implantation into Al, the Mössbauer spectra were doublet structures very similar to those obtained at amorphous Fe–Al alloys produced by rapid quenching methods. They also indicated at least two different main iron environments. For the highest implanted sample a ferromagnetic six‐line‐pattern with magnetic field values close to those of Fe3Al appeared. 相似文献
134.
135.
136.
137.
138.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated
ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base
results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated
ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy.
For Part 3, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997. 相似文献
139.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献
140.
F. A. van Goor S. V. Mitko V. N. Ochkin W. J. Witteman 《Journal of Russian Laser Research》1997,18(2):107-120
Experimental and theoretical results are presented on an XeF(C?A) blue-green laser driven by 5-kJ energy. The laser was pumped by a ferrite-induced discharge of 90 cm in length. The output energy of 0.22 J was obtained with a plane-parallel resonator. A program to simulate laser operation has been developed. Numerical results for a wide range of conditions are compared with experiments performed by us and by other authors. It is found that intracavity refractive losses limit laser operation for XeF pressures above 3 torr. The laser efficiency strongly depends on the discharge-to-cavity length ratio. Possible ways to increase the laser power and efficiency are discussed. 相似文献