全文获取类型
收费全文 | 28247篇 |
免费 | 1238篇 |
国内免费 | 1437篇 |
专业分类
化学 | 19313篇 |
晶体学 | 204篇 |
力学 | 533篇 |
综合类 | 10篇 |
数学 | 4813篇 |
物理学 | 6049篇 |
出版年
2023年 | 177篇 |
2022年 | 145篇 |
2021年 | 523篇 |
2020年 | 414篇 |
2019年 | 427篇 |
2018年 | 506篇 |
2017年 | 508篇 |
2016年 | 1087篇 |
2015年 | 843篇 |
2014年 | 956篇 |
2013年 | 2199篇 |
2012年 | 1895篇 |
2011年 | 2157篇 |
2010年 | 1237篇 |
2009年 | 1402篇 |
2008年 | 1526篇 |
2007年 | 1443篇 |
2006年 | 1248篇 |
2005年 | 1175篇 |
2004年 | 1435篇 |
2003年 | 1043篇 |
2002年 | 975篇 |
2001年 | 552篇 |
2000年 | 454篇 |
1999年 | 370篇 |
1998年 | 335篇 |
1997年 | 314篇 |
1996年 | 306篇 |
1995年 | 275篇 |
1994年 | 212篇 |
1993年 | 245篇 |
1992年 | 224篇 |
1991年 | 170篇 |
1990年 | 171篇 |
1989年 | 164篇 |
1988年 | 169篇 |
1987年 | 157篇 |
1986年 | 164篇 |
1985年 | 224篇 |
1984年 | 224篇 |
1983年 | 190篇 |
1982年 | 179篇 |
1981年 | 162篇 |
1980年 | 169篇 |
1979年 | 138篇 |
1978年 | 168篇 |
1977年 | 148篇 |
1976年 | 133篇 |
1974年 | 136篇 |
1973年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
82.
In this paper a new definition of a lattice valued intuitionistic fuzzy set (LIFS) is introduced, in an attempt to overcome
the disadvantages of earlier definitions. Some properties of this kind of fuzzy sets and their basic operations are given.
The theorem of synthesis is proved: For every two families of subsets of a set satisfying certain conditions, there is an
lattice valued intuitionistic fuzzy set for which these are families of level sets.
The research supported by Serbian Ministry of Science and Technology, Grant No. 1227. 相似文献
83.
L.G. Casado I. García T. Csendes V.G. Ruíz 《Journal of Optimization Theory and Applications》2003,118(1):27-43
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach. 相似文献
84.
85.
86.
The rate-dependent effects in metallic ferromagnetic materials with magnetization processes attributed to domain-walls motion were studied. The experimental method for eddy-current relaxation time determination was proposed. Some discrepancies between the data and theoretical predictions were observed and discussed. The origin of these discrepancies is accounted for by the decrease of viscous-type relaxation process as the rate of change of averaged magnetization is approaching zero. 相似文献
87.
88.
对不同的本底真空条件下,采用甚高频等离子体增强化学气相沉积技术沉积的氢化微晶硅(μc_Si∶H)薄膜中的氧污染问题进行了比较研究.对不同氧污染条件下制备的薄膜样品的x射线光电子能谱与傅里叶变换红外吸收光谱测量结果表明:μc_Si∶H薄膜中,氧以Si—O,O—O和O—H三种不同的键合模式存在,不同的键合模式源自不同的物理机理.μc_Si∶H薄膜的Raman光谱、电导率与激活能的测量结果进一步显示:沉积过程中氧污染程度的不同,对μc_Si∶H薄膜的结构特性与电学特性产生显著影响;而不同氧污染对μc_Si∶H薄膜电学特性的影响不同于氢化非晶硅(a_Si:H)薄膜.
关键词:
氢化微晶硅薄膜
甚高频等离子体增强化学气相沉积
氧污染 相似文献
89.
Maximiliano A. Burgos Paci Gustavo A. Argüello Plcido García Helge Willner 《国际化学动力学杂志》2003,35(1):15-19
Thermal decomposition of bis(trifluoromethyl) peroxydicarbonate has been studied. The mechanism of decomposition is a simple bond fission, homogeneous first‐order process when the reaction is carried out in the presence of inert gases such as N2 or CO. An activation energy of 28.5 kcal mol?1 was determined for the temperature range of 50–90°C. Decomposition is accelerated by nitric oxide because of a chemical attack on the peroxide forming substances different from those formed with N2 or CO. An interpretation on the influence of the substituents in different peroxides on the O? O bond is given. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 15–19, 2003 相似文献
90.