全文获取类型
收费全文 | 36515篇 |
免费 | 5215篇 |
国内免费 | 5098篇 |
专业分类
化学 | 26924篇 |
晶体学 | 587篇 |
力学 | 2014篇 |
综合类 | 517篇 |
数学 | 4671篇 |
物理学 | 12115篇 |
出版年
2024年 | 67篇 |
2023年 | 528篇 |
2022年 | 1012篇 |
2021年 | 1030篇 |
2020年 | 1152篇 |
2019年 | 1167篇 |
2018年 | 1043篇 |
2017年 | 1050篇 |
2016年 | 1450篇 |
2015年 | 1514篇 |
2014年 | 1850篇 |
2013年 | 2517篇 |
2012年 | 2909篇 |
2011年 | 3119篇 |
2010年 | 2349篇 |
2009年 | 2351篇 |
2008年 | 2551篇 |
2007年 | 2324篇 |
2006年 | 2137篇 |
2005年 | 1884篇 |
2004年 | 1522篇 |
2003年 | 1243篇 |
2002年 | 1326篇 |
2001年 | 1189篇 |
2000年 | 944篇 |
1999年 | 799篇 |
1998年 | 662篇 |
1997年 | 533篇 |
1996年 | 554篇 |
1995年 | 464篇 |
1994年 | 449篇 |
1993年 | 408篇 |
1992年 | 383篇 |
1991年 | 331篇 |
1990年 | 278篇 |
1989年 | 229篇 |
1988年 | 203篇 |
1987年 | 156篇 |
1986年 | 163篇 |
1985年 | 176篇 |
1984年 | 122篇 |
1983年 | 75篇 |
1982年 | 80篇 |
1981年 | 61篇 |
1980年 | 60篇 |
1979年 | 70篇 |
1978年 | 42篇 |
1976年 | 37篇 |
1974年 | 41篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
饮食中微量元素砷的分布规律与人体健康关系 总被引:3,自引:1,他引:2
采用催化动力学光度法测定了六大类(共三十种)样品中的总砷含量,探讨了砷在食品中的分布规律,建立了砷在人体中的安全系效和积累系效的效学评价公式,用于评价砷与人体健康的关系,这对人们选择食物有一定的指导意义。 相似文献
222.
In this article, the linear and nonlinear shear rheological behaviors of polylactide (PLA)/clay (organophilic‐montmorillonite) nanocomposites (PLACNs) were investigated by an Advanced Rheology Expanded System rheometer. The nanocomposites were prepared by master batch method using a twin‐screw extruder with poly(ε‐caprolactone) (PCL) as a compatibilizer. The presence of org‐MMT leads to obvious pseudo‐solid‐like behaviors of nanocomposite melts. The behaviors caused by the formation of a “percolating network” derived from the reciprocity among the strong related sheet particles. Therefore, the storage moduli, loss moduli, and dynamic viscosities of PLACNs show a monotonic increase with MMT content. Nonterminal behaviors exists in PLACNs nanocomposites. Besides the PLACNs melts show a greater shear thinning tendency than pure PLA melt because of the preferential orientation of the MMT layers. Therefore, PLACNs have higher moduli but better processibility compared with pure PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3189–3196, 2007 相似文献
223.
224.
C.M.Lin C.T. Chia Y.J. Shu Y.K. Tseng 《光散射学报》2005,17(3):216-218
Weperformedthehigh-pressureRaman measurementofthethreenanosizedZnOcrystals. Wefoundthesmallerthesize,thehigherthe pressuretoinducethephasetransitionfrom w櫣rzitetorock-saltstructure. High-pressureRamanmeasurementsof nona-shapedZnOcrystalswerepreformed.The… 相似文献
225.
Kuan‐Wei Lee Hong‐Cheu Lin 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4564-4572
A series of new liquid crystalline homopolymers, copolymers, and block copolymers were polymerized from styrene‐macroinitiator ( SMi ) and methacrylates with pendent 4,4′‐bis(biphenyl)fluorene ( M1 ) and biphenyl‐4‐ylfluorene ( M2 ) groups through atom transfer radical polymerization (ATRP). The number‐average molecular weights (Mn) of polymers P1 ‐ P4 were 10,007, 14,852, 6,275, and 10,463 g mol?1 with polydispersity indices values of 1.21, 1.15, 1.31, and 1.22, respectively. All polymers exhibit the nematic phase. The thermal, mesogenic, and photoluminescent properties of all polymers were investigated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4564–4572, 2007 相似文献
226.
The present study is concerned with the determination of the optimal shape for a package containing multiple heating elements.
The optimization tool has been developed based on the inverse heat transfer (IHT) approach, incorporating a direct problem
solver, a numerical grid generator, a direct-differentiation sensitivity analyzer, and the conjugate gradient method. Shape
design that leads to a specified outer surface temperature distribution is predicted by the approach. In this study, the effects
of internal heat generation on optimal shapes of the packagings have also been evaluated. Several practical cases with various
imbedded heating elements and thermal conditions are studied. Results show that the approach provides an efficient computer-aided
design scheme for the shape profile determination. 相似文献
227.
颗粒物质的两个典型效应及其研究现状的分析 总被引:6,自引:0,他引:6
概述了颗粒物质领域中粮仓现象和巴西坚果效应两个典型现象及其解释理论,分析其理论的成功和不足之处,并给出了一些看法。 相似文献
228.
229.
This paper presents an operator‐splitting method (OSM) for the solution of the universal Reynolds equation. Jakobsson–Floberg–Olsson (JFO) pressure conditions are used to study cavitation in liquid‐lubricated journal bearings. The shear flow component of the oil film is first solved by a modified upwind finite difference method. The solution of the pressure gradient flow component is computed by the Galerkin finite element method. Present OSM solutions for slider bearings are in good agreement with available analytical and experimental results. OSM is then applied to herringbone grooved journal bearings. The film pressure, cavitation areas, load capacity and attitude angle are obtained with JFO pressure conditions. The calculated load capacities are in agreement with available experimental data. However, a detailed comparison of the present results with those predicted using Reynolds pressure conditions shows some differences. The numerical results showed that the load capacity and the critical mass of the journal (linear stability indicator) are higher and the attitude angle is lower than those predicted by Reynolds pressure conditions for cases of high eccentricities. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
230.
Junsaku Nitta Yiping Lin Takaaki Koga Tatsushi Akazaki 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):429
We report on electron g-factor in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In0.53Ga0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor. 相似文献