全文获取类型
收费全文 | 32585篇 |
免费 | 3829篇 |
国内免费 | 2715篇 |
专业分类
化学 | 15735篇 |
晶体学 | 534篇 |
力学 | 1137篇 |
综合类 | 237篇 |
数学 | 2446篇 |
物理学 | 10191篇 |
综合类 | 8849篇 |
出版年
2024年 | 58篇 |
2023年 | 208篇 |
2022年 | 537篇 |
2021年 | 584篇 |
2020年 | 745篇 |
2019年 | 759篇 |
2018年 | 769篇 |
2017年 | 944篇 |
2016年 | 1212篇 |
2015年 | 1131篇 |
2014年 | 1374篇 |
2013年 | 2694篇 |
2012年 | 1842篇 |
2011年 | 1857篇 |
2010年 | 1580篇 |
2009年 | 1678篇 |
2008年 | 1701篇 |
2007年 | 1958篇 |
2006年 | 1789篇 |
2005年 | 1679篇 |
2004年 | 1533篇 |
2003年 | 1435篇 |
2002年 | 1474篇 |
2001年 | 1124篇 |
2000年 | 1128篇 |
1999年 | 977篇 |
1998年 | 824篇 |
1997年 | 710篇 |
1996年 | 638篇 |
1995年 | 630篇 |
1994年 | 560篇 |
1993年 | 446篇 |
1992年 | 458篇 |
1991年 | 371篇 |
1990年 | 314篇 |
1989年 | 256篇 |
1988年 | 258篇 |
1987年 | 189篇 |
1986年 | 158篇 |
1985年 | 126篇 |
1984年 | 98篇 |
1983年 | 43篇 |
1982年 | 72篇 |
1981年 | 35篇 |
1980年 | 40篇 |
1979年 | 42篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
51.
Katsuhiro Inomata Chieko Fukuda Kuniyoshi Hori Hideki Sugimoto Eiji Nakanishi 《Journal of Polymer Science.Polymer Physics》2007,45(2):129-137
The phase behavior and crystallization of graft copolymers consisting of poly(n‐hexyl methacrylate) (PHMA) as an amorphous main chain and poly(ethylene glycol) (PEG) as crystallizable side chains (HMAx with 15 ≤ x ≤ 73, where x represents the weight percentage of PEG) were investigated. Small‐angle X‐ray scattering profiles measured above the melting temperature of PEG suggested that a microdomain structure with segregated PHMA and PEG domains was formed in HMA40 and HMA46. This phase behavior was qualitatively described by a calculated phase diagram based on the mean‐field theory. Because of the segregation of PEG into microdomains, the crystallization temperature of the PEG side chains in HMAx was higher than that in poly(methyl acrylate)‐graft‐poly(ethylene glycol) having a similar value of x, which was considered to be in a disordered state above the melting temperature. In HMAx with x ≤ 40, PEG crystallization was strongly restricted, probably because the PEG microdomains were isolated in the PHMA matrix. As a result, the growth of PEG spherulite was not observed because the PEG crystallization occurred after vitrification of the PHMA segregated domains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 129–137, 2007 相似文献
52.
XU Wen-you JI Min 《武汉大学学报:自然科学英文版》2005,10(5):892-896
KF or K2CO3 was added into the 1-butanol-water system and two phases were formed: water-rich phase (water phase) and 1-butanol-rich phase (1-butanol phase). The liquid liquid equilibrium (LLE) data for 1-butanol-water-KF and 1-butanol-water-K2CO3 systems were measured at 25℃ and showed that 1-butanol phase contained negligible salt and water phase contained negligible 1-butanol when the concentrations of KF and K2CO3 in the water phase were equal to or higher than 27.11% and 31.68% , respectively. Thus water could be separated efficiently from 1-butanol-water by adding KF or K2CO3 into the system. A theoretical calculation of LLE data was calculated by using the Pitzer theory to get water activity in the water phase, and by the models, such as the Wilson, NRTL or the UNIQUAC for the 1-butanol phase. For 1-hutanol-water-KF system, the experimental data were found in good agreement with the calculated results by using Pitzer theory and Wilson equa tion, while for 1-butanol-water-K2CO3 system, the experimental data were found in good agreement with the calculated results by using Pitzer theory and UNIQUAC eauation. 相似文献
53.
F. Rampf K. Binder W. Paul 《Journal of polymer science. Part A, Polymer chemistry》2006,44(18):2542-2555
We present simulation results for the phase behavior of a single chain for a flexible lattice polymer model using the Wang-Landau sampling idea. Applying this new algorithm to the problem of the homopolymer collapse allows us to investigate not only the high temperature coil–globule transition but also an ensuing crystallization at lower temperature. Performing a finite size scaling analysis on the two transitions, we show that they coincide for our model in the thermodynamic limit corresponding to a direct collapse of the random coil into the crystal without intermediate coil–globule transition. As a consequence, also the many chain phase diagram of this model can be predicted to consist only of gas and crystal phase in the limit of infinite chain length. This behavior is in agreement with findings on the phase behavior of hard-sphere systems with a relatively short-ranged attractive square well. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2542–2555, 2006 相似文献
54.
Glauber和Kawasaki动力学下正方格子上伊辛模型居里温度的蒙特卡罗计算 总被引:1,自引:1,他引:0
利用蒙特卡罗方法研究正方格子上的伊辛模型的相变问题.讨论了不同翻转方式(随机翻转和顺序翻转)以及不同动力学规则(Glauber动力学和Kawasaki动力学)对正方格子上的伊辛模型的居里温度Tc的影响.结果表明,当Glauber动力学占主要地位时,在两种翻转方式下都可以计算出居里温度Tc的值,当Kawasaki动力学占主要地位时,只能用随机翻转的方法获得居里温度Tc. 相似文献
55.
56.
介绍了针对油藏流体及其注气体系的相态及物性的预测而开发的DGPVT软件包功能、模型及特点。基于实验数据对DGPVT软件包的预测准确性进行了检验,并与石油界知名的商用油气相态及物性计算软件包STATPACK进行了比较。 相似文献
57.
为了消除应用焓法进行含有相变的有限元传热计算结果呈台阶形的现象,本文作者提出“焓计算单元”和“固相分数”的概念,并将几种一维有限元实施方案的计算结果与精确解对比,说明采用所提出的概念,可以使有限元计算得出更为合理的结果。 相似文献
58.
59.
Aspects of the mechanism of the overall reaction between CaCO3/CaO and SO2/SO3 under oxidizing conditions are discussed. The limestone and lime sulphation processes were carried out in a thermobalance
under conditions relevant to atmospheric fluidized bed combustion. Sulphated samples, prepared in the form of cross-section
particles, were examined in a scanning electron microscope by energy-dispersive X-ray and back-scattered electron imaging.
Photomicrographs are presented. The reaction proceeded from the outer surface of the particles and along the pores. Surface
textural changes during the reaction were considered. The layer of products was identified as controlling both the rate and
extent of limestone/lime sulphation. In the products, two sulphur-bearing solids (CaSO4 and CaS) were identified. The presence of CaS, which may cause difficulties in practice, is attributed to CaSO3 disproportionation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT
c < 138 C (Regime III) and preferentially radiating lamellae atT
c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites. 相似文献