全文获取类型
收费全文 | 6334篇 |
免费 | 875篇 |
国内免费 | 639篇 |
专业分类
化学 | 2106篇 |
晶体学 | 85篇 |
力学 | 828篇 |
综合类 | 116篇 |
数学 | 1594篇 |
物理学 | 3119篇 |
出版年
2024年 | 17篇 |
2023年 | 70篇 |
2022年 | 155篇 |
2021年 | 187篇 |
2020年 | 139篇 |
2019年 | 145篇 |
2018年 | 131篇 |
2017年 | 198篇 |
2016年 | 271篇 |
2015年 | 201篇 |
2014年 | 326篇 |
2013年 | 467篇 |
2012年 | 350篇 |
2011年 | 448篇 |
2010年 | 371篇 |
2009年 | 404篇 |
2008年 | 401篇 |
2007年 | 451篇 |
2006年 | 378篇 |
2005年 | 370篇 |
2004年 | 282篇 |
2003年 | 276篇 |
2002年 | 253篇 |
2001年 | 189篇 |
2000年 | 188篇 |
1999年 | 153篇 |
1998年 | 121篇 |
1997年 | 119篇 |
1996年 | 93篇 |
1995年 | 88篇 |
1994年 | 94篇 |
1993年 | 82篇 |
1992年 | 59篇 |
1991年 | 57篇 |
1990年 | 38篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 31篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1974年 | 4篇 |
排序方式: 共有7848条查询结果,搜索用时 15 毫秒
21.
Su Nee Tan Daniel Fornasiero Rossen Sedev John Ralston 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):307-315
The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol−1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability. 相似文献
22.
用改进的离子束增强沉积方法和恰当的退火从V2O5粉末直接制备了VO2多晶薄膜.实验测试表明,薄膜的取向单一、相变特性显著、结构致密、界面结合牢固、工艺性能良好,薄膜的电阻温度系数(TCR)最高可达4.23%/K.从成膜机理出发,较详细地讨论了离子束增强沉积 VO2多晶薄膜的TCR高于VOx薄膜的TCR的原因.分析认为,单一取向的VO2结构使薄膜晶粒具有较高的电导激活能,致密的薄膜结构减少了氧空位和晶界宽度,使离子束增强沉积 VO2多晶薄膜结构比其他方法制备的VOx薄膜更接近于单晶VO2是其具有高TCR的原
关键词:
VO2多晶薄膜
离子束增强沉积
热电阻温度系数 相似文献
23.
24.
A. P. Prishivalko 《Journal of Applied Spectroscopy》1997,64(1):94-100
A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that
provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments
is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and
is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of
mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the
size distribution of the pigment particles.
B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997. 相似文献
25.
证券投资组合的风险与收益 总被引:4,自引:1,他引:3
李淑锦 《数学的实践与认识》2002,32(4):602-604
本文利用概率统计原理对证券的投资组合能减轻所遇的风险作了讨论 ,并介绍了如何选择投资组合可使所遇风险达到最小 相似文献
26.
用实验的方法,研究电流并联负反馈对放大器性能的改善,提出电流型、并联型负反馈放大器性能参数的测量方法。 相似文献
27.
Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d31 = 6.8 pm/V, d32 = 4.7 pm/V, d33 = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction. 相似文献
28.
Hidetoshi Shimodaira 《Annals of the Institute of Statistical Mathematics》1997,49(3):395-410
The asymptotic error probability of Linhart's model selection test isevaluated, and compared with the nominal significance level. We examine thecase where the expected discrepancies of the candidate models from the truemodel are asymptotically equal. The local alternatives method is employed inthe limiting operation of the asymptotic evaluation. Although the errorprobability under the null hypothesis is actually shown to be equal to orless than the level for most situations, intolerable violations of the errorcontrol are observed for nested models: It is often erroneously concludedthat the smaller model is significantly better than the larger model. Toprevent this violation, a modification of Linhart's test statistic isproposed. The effectiveness of the proposed test is confirmed throughtheoretical analysis and numerical simulations. 相似文献
29.
30.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献