全文获取类型
收费全文 | 167983篇 |
免费 | 18671篇 |
国内免费 | 11239篇 |
专业分类
化学 | 111041篇 |
晶体学 | 1415篇 |
力学 | 9222篇 |
综合类 | 1423篇 |
数学 | 33582篇 |
物理学 | 41210篇 |
出版年
2024年 | 176篇 |
2023年 | 1044篇 |
2022年 | 2458篇 |
2021年 | 2698篇 |
2020年 | 3359篇 |
2019年 | 5206篇 |
2018年 | 4628篇 |
2017年 | 5501篇 |
2016年 | 6529篇 |
2015年 | 8377篇 |
2014年 | 8940篇 |
2013年 | 14130篇 |
2012年 | 10334篇 |
2011年 | 10522篇 |
2010年 | 8745篇 |
2009年 | 10117篇 |
2008年 | 10744篇 |
2007年 | 10422篇 |
2006年 | 9670篇 |
2005年 | 8472篇 |
2004年 | 7436篇 |
2003年 | 6963篇 |
2002年 | 7016篇 |
2001年 | 4940篇 |
2000年 | 4627篇 |
1999年 | 3553篇 |
1998年 | 2732篇 |
1997年 | 2319篇 |
1996年 | 2034篇 |
1995年 | 1832篇 |
1994年 | 1621篇 |
1993年 | 1374篇 |
1992年 | 1303篇 |
1991年 | 1019篇 |
1990年 | 817篇 |
1989年 | 719篇 |
1988年 | 696篇 |
1987年 | 524篇 |
1986年 | 437篇 |
1985年 | 512篇 |
1984年 | 496篇 |
1983年 | 242篇 |
1982年 | 401篇 |
1981年 | 446篇 |
1980年 | 331篇 |
1979年 | 314篇 |
1978年 | 249篇 |
1977年 | 215篇 |
1976年 | 176篇 |
1973年 | 120篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Influence of the Type of a Ligand on the Intensity of Luminescence of Ln3+ Ions in Aqueous Solutions
I. V. Barsukov E. N. Kabaeva V. V. Syt'ko S. D. Umreiko 《Journal of Applied Spectroscopy》2003,70(3):470-473
The luminescence characteristics of hydrated Ln3+ ions and their complexes with some acidic ligands have been investigated. The possibility of determining the stability of the complexes of lanthanides in solutions from the intensity of luminescence bands is shown. The influence of the characteristic features of the f-electron shell of Ln3+ on the formation of the spectrochemical series is discussed. 相似文献
93.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
94.
MC模式下顾客需求与厂商供应的纳什均衡 总被引:3,自引:0,他引:3
在大规模定制(MC,Mass Customization)模式下,基于市场需求的复杂化,厂商对个性化的顾客需求很难做出及时准确的反应,而且由于其自身生产能力的限制,不可能对所有的个性化用户进行一一地满足,只可能对已经存在的个性化需求,根据自身的生产能力和规模,以利润最大化及顾客对产品的满意度为目标,对个性化需求进行较准确地预测,从而正确指导生产。本通过博弈论的方法,提出了一个基于顾客对产品的满意度及企业的利润的一个非合作博弈模型,并给出求解纳什均衡的方法。 相似文献
95.
96.
恩格尔系数衡量城镇居民生活水平适用性 总被引:2,自引:0,他引:2
根据我固1980年和2000年恩格尔系数所反映的各省(市)居民生活水平资料,发现两个不同时期其真实性有很大差异,分析了造成这种差别的原因:(1)职工非现金福利收入的增加;(2)少数职工的非法收入的大量增加;(3)居民饮食结构的改变;(4)物价上涨的影响;(5)恩格尔系数本身存在技术问题;(6)抽样调查本身存在问题,提出用一种“新系数”来衡量城镇居民生活水平,其优点是:(1)不受各地区实际支出,即人为控制调节的影响;(2)不需用其他指标作解释,直观性强;(3)因可以扣除物价因素,它不受物价波动的影响;(4)调查户填报和计算简易方便。可扩大样本调查量,提高反映住户总量可靠性。 相似文献
97.
Chin‐Ping Yang Ruei‐Shin Chen Kuei‐Hung Chen 《Journal of polymer science. Part A, Polymer chemistry》2003,41(7):922-938
To investigate the position and amount of the CF3 group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane ( 2 ) with four CF3 groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs ( 5 ) were synthesized from 2 and various aromatic dianhydrides ( 3a – 3f ). 5a – 5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6 – 8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF3 group close to the imide group was more effective in lowering the color; this means that CF3 of 5 , 7 , and 8f was more effective than that of 6c . The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8 . The PI 5f , synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF3 groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003 相似文献
98.
一类含有P-Laplacian算子的奇异边值问题解的确切个数 总被引:2,自引:0,他引:2
讨论了一类p-L ap lac ian算子型的奇异边值问题正解的确切个数以及解的性质. 相似文献
99.
Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
100.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献