全文获取类型
收费全文 | 89534篇 |
免费 | 8785篇 |
国内免费 | 6320篇 |
专业分类
化学 | 19211篇 |
晶体学 | 615篇 |
力学 | 6041篇 |
综合类 | 681篇 |
数学 | 12504篇 |
物理学 | 21749篇 |
综合类 | 43838篇 |
出版年
2024年 | 360篇 |
2023年 | 904篇 |
2022年 | 1805篇 |
2021年 | 1942篇 |
2020年 | 2211篇 |
2019年 | 2037篇 |
2018年 | 2028篇 |
2017年 | 2586篇 |
2016年 | 3047篇 |
2015年 | 3023篇 |
2014年 | 4293篇 |
2013年 | 6072篇 |
2012年 | 5166篇 |
2011年 | 5480篇 |
2010年 | 4389篇 |
2009年 | 5033篇 |
2008年 | 4864篇 |
2007年 | 5719篇 |
2006年 | 5135篇 |
2005年 | 4663篇 |
2004年 | 4222篇 |
2003年 | 3753篇 |
2002年 | 3617篇 |
2001年 | 2824篇 |
2000年 | 2723篇 |
1999年 | 2395篇 |
1998年 | 2001篇 |
1997年 | 1738篇 |
1996年 | 1497篇 |
1995年 | 1404篇 |
1994年 | 1224篇 |
1993年 | 1031篇 |
1992年 | 958篇 |
1991年 | 806篇 |
1990年 | 736篇 |
1989年 | 559篇 |
1988年 | 525篇 |
1987年 | 408篇 |
1986年 | 295篇 |
1985年 | 248篇 |
1984年 | 215篇 |
1983年 | 110篇 |
1982年 | 145篇 |
1981年 | 90篇 |
1980年 | 62篇 |
1979年 | 74篇 |
1978年 | 48篇 |
1977年 | 36篇 |
1976年 | 25篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
通过实例介绍了系统活动作为一个对象/类的概念,给出了对系统活动进行分析和建模的一般步骤,提出了系统活动描述的形式化方法。 相似文献
52.
钟凡 《中山大学学报(自然科学版)》1996,(2)
把重正化群理论应用于一受外场驱动而发生一级相变的系统中,结果表明,与有序化过程一样,该系统也由零温不动点所决定,并得到磁化强度及结构函数的新的动力学标度关系.由此可获得滞后回约面积与变场速率的标度关系. 相似文献
53.
将快速傅里叶变换技术和数字滤波器设计技术应用于铝电解过程控制信号的滤波与噪声解析模型中,在160kA中间点式下料预焙槽上的试验结果表明了模型的有效性。 相似文献
54.
曹泽星 《四川大学学报(自然科学版)》1993,30(2):221-226
提出了一种适合于研究非理想溶液的溶剂化缔合物模型.借助该模型,对物质的溶解度在定量和半定量的水平上进行了研究,并获得了满意的结果。 相似文献
55.
李扬国 《汕头大学学报(自然科学版)》1992,7(1):9-16
在已获得的中能区反质子与核的中心势的光学势基础上,把光学势扩大到包含自旋轨道耦合势.在反质子能量为179.8,294.8和508MeV各情况下,分别计算和分析与~(12)C靶核的微分截面(dσ)/(dΩ),极化度P(θ)和自旋转动函数Q(θ).在与极化度的实验比较中,得到中能区普遍形式的反质子光学势. 相似文献
56.
57.
Poly (n-butylisocyanate)-benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer-rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase-separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze-thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism. 相似文献
58.
Hiroshi Ito Masaki Okazaki Dolores C. Miller 《Journal of polymer science. Part A, Polymer chemistry》2004,42(6):1478-1505
Radical copolymerizations of electron‐deficient 2‐trifluoromethylacrylic (TFMA) monomers, such as 2‐trifluoromethylacrylic acid and t‐butyl 2‐trifluoromethylacrylate (TBTFMA), with electron‐rich norbornene derivatives and vinyl ethers with 2,2′‐azobisisobutyronitrile as the initiator were investigated in detail through the analysis of the kinetics in situ with 1H NMR and through the determination of the monomer reactivity ratios. The norbornene derivatives used in this study included bicyclo[2.2.1]hept‐2‐ene (norbornene) and 5‐(2‐trifluoromethyl‐1,1,1‐trifluoro‐2‐hydroxylpropyl)‐2‐norbornene. The vinyl ether monomers were ethyl vinyl ether, t‐butyl vinyl ether, and 3,4‐dihydro‐2‐H‐pyran. Vinylene carbonate was found to copolymerize with TBTFMA. Although none of the monomers underwent radical homopolymerization under normal conditions, they copolymerized readily, producing a copolymer containing 60–70 mol % TFMA. The copolymerization of the TFMA monomer with norbornenes and vinyl ethers deviated from the terminal model and could be described by the penultimate model. The copolymers of TFMA reported in this article were evaluated as chemical amplification resist polymers for the emerging field of 157‐nm lithography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1478–1505, 2004 相似文献
59.
Timur Zharnikov Alexander Yakovlev Semion Kuchanov 《Journal of Polymer Science.Polymer Physics》2003,41(9):892-902
The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free‐radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 892–902, 2003 相似文献
60.
Small‐Angle Neutron Scattering has been performed from poly(ethylene oxide) in deuterated water at temperature ranging from 10 to 80 °C. A simple fitting model was used to obtain a correlation length and a Porod exponent. The correlation length L characterizes the average distance between entanglements in the semidilute region and is proportional to the individual coil sizes in the dilute region. L was found to increase with temperature in the semidilute region but it decreases with temperature in the dilute region. This decrease is the precursor to the single‐chain collapse which applies to very dilute polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2196–2200, 2007 相似文献