全文获取类型
收费全文 | 19860篇 |
免费 | 3461篇 |
国内免费 | 4374篇 |
专业分类
化学 | 14537篇 |
晶体学 | 569篇 |
力学 | 1230篇 |
综合类 | 388篇 |
数学 | 2860篇 |
物理学 | 8111篇 |
出版年
2024年 | 29篇 |
2023年 | 202篇 |
2022年 | 461篇 |
2021年 | 575篇 |
2020年 | 614篇 |
2019年 | 683篇 |
2018年 | 616篇 |
2017年 | 718篇 |
2016年 | 840篇 |
2015年 | 987篇 |
2014年 | 1246篇 |
2013年 | 1558篇 |
2012年 | 1643篇 |
2011年 | 1804篇 |
2010年 | 1552篇 |
2009年 | 1606篇 |
2008年 | 1803篇 |
2007年 | 1586篇 |
2006年 | 1560篇 |
2005年 | 1344篇 |
2004年 | 1046篇 |
2003年 | 842篇 |
2002年 | 915篇 |
2001年 | 777篇 |
2000年 | 670篇 |
1999年 | 417篇 |
1998年 | 264篇 |
1997年 | 207篇 |
1996年 | 183篇 |
1995年 | 139篇 |
1994年 | 143篇 |
1993年 | 88篇 |
1992年 | 94篇 |
1991年 | 77篇 |
1990年 | 62篇 |
1989年 | 77篇 |
1988年 | 57篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
111.
基于傅立叶变换轮廓术的物面相位提取 总被引:1,自引:0,他引:1
采用傅立叶变换轮廓术,针对基频提取的关键技术采用逐行傅立叶变换,准确提取基频信息的方法恢复相位信息.在此基础上,以未畸变条纹为基准,得出被测物体的真实位相值.该方法只需一幅条纹图,节约了测量时间.实验证明可实现无接触面型的自动传感. 相似文献
112.
养殖池塘沉积物的重金属分布及污染特征 总被引:3,自引:0,他引:3
浙江省淅西北地区淡水养殖池塘沉积物重金属调查研究表明,养殖池塘沉积物中7种重金属元素分布不均衡,差异也较大,除Hg和Cr元素外,其余重金属元素已大大超过土壤本底值.虽然其实测含量都未超出国家规定的标准值范围,但沉积物中重金属元素对养殖水环境、养殖品种存在的潜在污染与危害值得关注.污染指数评价显示,养殖池塘沉积物中主要污染物质为Cu和Cr,而Hg、Pb污染程度相对较轻. 相似文献
113.
114.
TieYong YangGuangjun 《分析论及其应用》2004,20(1):58-68
In this paper, we construct some continuous but non-differentiable functions defined by quinary decimal, that are Kiesswetter-like functions. We discuss their properties, then investigate the Hausdorff dimensions of graphs of these functions and give a detailed proof. 相似文献
115.
A novel measurement method of temperature based on the phenomena that the phase difference between principle polarization states in the optical retarder is function of temperature is described. The polarization state of optical beam is changed as it passes through the optical retarder, which depends on the temperature. The temperature of optical retarder is determined by comparison of the power difference between principal polarization states. We demonstrate successfully the temperature measurement by using a polarization maintaining fiber as the optical retarder. With a 100 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.236 rad/°C and the measurement error was ±0.038°C over the temperature range of −2.6 – +3.4°C. With a 11.5 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.021 rad/°C and the measurement error was ±0.79°C over the temperature range of −8.5 – +86.5°C. 相似文献
116.
酮与稳定膦叶立德在家用微波炉中加热,在无任何溶剂或固体介质条件下,4.5min之内完成反应,得到了良好产率的Wittig反应产物,较之液相苯中回流反应的传统方法,此法具有时间短、操作步骤简单、无毒害等优点,同时使一些在传统方法中与稳定叶立德不反应或难反应的酮得以进行并有较好收率。此外,在得到α,β-不饱和酯的同时,还发现了少量重排产物β,γ-不饱和酯,并对其机理进行了推测与证明。 相似文献
117.
118.
A periodic one-dimensional four-state hopping model is proposed. In the model, the substeps betweenarbitrary adjacent states are unequal, and an explicit solution of the master equation is first obtained for the probabilitydistribution as a function of the time and position for any initial distribution with all the transients included. Next, thetransient behaviors in the initial period of time and the characteristic time to reach the steady state for the molecularmotor are discussed. Finally, we compare the steady state results to experiments and illustrate qualitatively the kineticbehaviors of a molecular motor under external load F. 相似文献
119.
This paper is to investigate the approximate confidence limits of the reliability performances (such as failure rate, reliability function and average life) for a cold standby series system. The Bayesian approximate upper confidence limit of failure rate is obtained firstly, and next Bayesian approximate lower confidence limits for reliability function and average life are presented. The expressions for calculating Bayesian lower confidence limits of the reliability function and average life are also obtained, and an illustrative example is examined numerically by means of the Monte-Carlo simulation. Finally, the accuracy of confidence limits is discussed. 相似文献
120.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献