全文获取类型
收费全文 | 174754篇 |
免费 | 9221篇 |
国内免费 | 10616篇 |
专业分类
化学 | 27115篇 |
晶体学 | 339篇 |
力学 | 7015篇 |
综合类 | 1401篇 |
数学 | 29005篇 |
物理学 | 26465篇 |
综合类 | 103251篇 |
出版年
2024年 | 288篇 |
2023年 | 1098篇 |
2022年 | 2014篇 |
2021年 | 2292篇 |
2020年 | 2406篇 |
2019年 | 2615篇 |
2018年 | 2222篇 |
2017年 | 2714篇 |
2016年 | 3043篇 |
2015年 | 3693篇 |
2014年 | 6651篇 |
2013年 | 7982篇 |
2012年 | 8238篇 |
2011年 | 9349篇 |
2010年 | 7849篇 |
2009年 | 9321篇 |
2008年 | 10142篇 |
2007年 | 12182篇 |
2006年 | 11469篇 |
2005年 | 10782篇 |
2004年 | 9201篇 |
2003年 | 8828篇 |
2002年 | 7660篇 |
2001年 | 6541篇 |
2000年 | 5929篇 |
1999年 | 5025篇 |
1998年 | 4251篇 |
1997年 | 3812篇 |
1996年 | 3486篇 |
1995年 | 3117篇 |
1994年 | 2939篇 |
1993年 | 2553篇 |
1992年 | 2378篇 |
1991年 | 2085篇 |
1990年 | 1859篇 |
1989年 | 1764篇 |
1988年 | 1514篇 |
1987年 | 972篇 |
1986年 | 667篇 |
1985年 | 542篇 |
1984年 | 459篇 |
1983年 | 215篇 |
1982年 | 365篇 |
1981年 | 418篇 |
1980年 | 316篇 |
1979年 | 298篇 |
1978年 | 230篇 |
1977年 | 210篇 |
1976年 | 163篇 |
1974年 | 115篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
32.
针对“剥岩高峰”对矿山生产带来的不利影响,研究了设备配置更新策略与露天开采外委剥离的优化问题.基于铲运设备的运营成本与生产能力随设备役龄变化的关系,建立了决策单台设备退役时间的动态经济寿命计算模型,并根据此模型给出了具体的设备配置算法步骤.设置一系列不同的矿山自剥离量与外委剥离量的分界水平,计算各分界水平条件下的外委单价可行区间,然后在区间内确定外委商谈价格并分析得出与之对应的总成本净现值最低的外委方案.实例计算证明,采用该方法减少设备投资的成本要高于外委岩石剥离成本. 相似文献
33.
34.
Synthesis of diisocyanides with phenolic groups and their polymerization to helically chiral poly(quinoxaline‐2,3‐diyl)s 下载免费PDF全文
Johannes Scholz Michael Reggelin 《Journal of polymer science. Part A, Polymer chemistry》2015,53(11):1320-1329
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329 相似文献
35.
36.
Inflation of balloons provides a straightforward way of achieving large biaxial deformations. Previous studies have shown that when a balloon bursts, crack propagation occurs at very high speed – much higher than would be expected from the low strain modulus and elastic wave velocity of the rubber. The present paper is concerned with studies of the deformation and fracture of cylindrical balloons. On inflation, the deformations of such a balloon pass through an unstable region but subsequently increase monotonically with pressure. In this relatively high pressure region, the ratio of the longitudinal and circumferential extension ratios is broadly in accord with expectations from high-strain elasticity theory when the ratio of the corresponding stresses is taken into account. On bursting, crack speeds up to around 300 m/s in this region. It is shown that these speeds are in accord with large increase in incremental moduli for the highly-strained rubber. Marked changes in crack tip profile observed at very high crack speeds are consistent with control of the rate of growth by inertia rather than by the viscoelastic properties of the rubber (as is believed to be the case at lower speeds). Consistent with this, various elastomers having different glass transition temperatures show similar crack growth behaviour in the very high speed region. 相似文献
37.
Accuracy arguments are the en vogue route in epistemic justifications of probabilism and further norms governing rational belief. These arguments often depend on the fact that the employed inaccuracy measure is strictly proper. I argue controversially that it is ill-advised to assume that the employed inaccuracy measures are strictly proper and that strictly proper statistical scoring rules are a more natural class of measures of inaccuracy. Building on work in belief elicitation I show how strictly proper statistical scoring rules can be used to give an epistemic justification of probabilism.An agent's evidence does not play any role in these justifications of probabilism. Principles demanding the maximisation of a generalised entropy depend on the agent's evidence. In the second part of the paper I show how to simultaneously justify probabilism and such a principle. I also investigate scoring rules which have traditionally been linked with entropies. 相似文献
38.
张军亮 《科技情报开发与经济》2015,25(8)
目的:分析《中华实用儿科临床杂志》近5年发展情况,为提高该刊质量提供参考依据. 方法:通过"中国生物医学文献数据库"收集该刊2008—2012年的文献题录,采用文献计量学方法,对文献的时间分布、单位分布、作者分布、作者合作情况、单位合作情况、高频关键词、高频主题词等指标进行统计分析. 结果:2008—2012年《中华实用儿科临床杂志》共载文3 459篇,单篇论文的长度在逐年增长;涉及作者13 870位,每篇论文作者平均数量大于4,每篇论文的平均合作单位数量多于1.45,关键词和主题词符合本刊的主题.2008—2010年被引的文献为1 131条,占期间总文献量的62%.结论:2008—2012年发表的论文选择更具有针对性,向着更为合理性的方向发展,研究方法也多采用定量分析方法,并且论文形式多样,文献被引次数越来越多. 相似文献
39.
Bobby Wilson 《偏微分方程通讯》2015,40(8):1521-1542
This article explores the questions of long time orbital stability in high order Sobolev norms of plane wave solutions to the NLSE in the defocusing case. 相似文献
40.
Mourad Kainane Mezadek Mohamed Kainane Mezadek Michael Reissig 《Mathematical Methods in the Applied Sciences》2020,43(6):3117-3147
In this paper, we study the global (in time) existence of small data solutions to the Cauchy problem for the semilinear wave equation with friction, viscoelastic damping, and a power nonlinearity. We are interested in the connection between regularity assumptions for the data and the admissible range of exponents p in the power nonlinearity. 相似文献