全文获取类型
收费全文 | 28029篇 |
免费 | 4639篇 |
国内免费 | 3773篇 |
专业分类
化学 | 20300篇 |
晶体学 | 412篇 |
力学 | 1888篇 |
综合类 | 283篇 |
数学 | 3070篇 |
物理学 | 10488篇 |
出版年
2024年 | 78篇 |
2023年 | 509篇 |
2022年 | 901篇 |
2021年 | 990篇 |
2020年 | 1055篇 |
2019年 | 1081篇 |
2018年 | 906篇 |
2017年 | 941篇 |
2016年 | 1297篇 |
2015年 | 1336篇 |
2014年 | 1642篇 |
2013年 | 2027篇 |
2012年 | 2614篇 |
2011年 | 2662篇 |
2010年 | 1859篇 |
2009年 | 1748篇 |
2008年 | 1883篇 |
2007年 | 1710篇 |
2006年 | 1679篇 |
2005年 | 1392篇 |
2004年 | 1033篇 |
2003年 | 845篇 |
2002年 | 864篇 |
2001年 | 738篇 |
2000年 | 563篇 |
1999年 | 538篇 |
1998年 | 445篇 |
1997年 | 388篇 |
1996年 | 385篇 |
1995年 | 311篇 |
1994年 | 268篇 |
1993年 | 218篇 |
1992年 | 225篇 |
1991年 | 222篇 |
1990年 | 160篇 |
1989年 | 138篇 |
1988年 | 94篇 |
1987年 | 75篇 |
1986年 | 88篇 |
1985年 | 71篇 |
1984年 | 62篇 |
1983年 | 48篇 |
1982年 | 36篇 |
1981年 | 35篇 |
1980年 | 32篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
The viscosities of aqueous solutions of gelatin at different temperatures were carefully measured in a common glass‐capillary Ubbelohde viscometer at dilute to extremely dilute concentrations. The adsorption effect that occurred in the viscosity measurements was theoretically analyzed and discussed. A theory based on Langmuir isotherms could adequately describe the existing data. Some structural information was obtained by the use of an iterative fitting procedure to treat the reduced viscosity data, which disclosed that individual gelatin chains underwent a coil‐to‐helix transition as the solution cooled from 40 to 15 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1804–1812, 2006 相似文献
72.
Cheng‐Ho Chen Chih‐Chun Teng Ming‐Shyong Tsai Fu‐Su Yen 《Journal of Polymer Science.Polymer Physics》2006,44(15):2145-2154
A Haake torque rheometer equipped with an internal mixer is used to study the influence of the amount of sodium montmorillonite (Na+‐MMT) and organically modified MMT (O‐MMT) on X‐ray diffraction (XRD), morphology, and mechanical characteristics of rigid poly (vinyl chloride) (PVC)/Na+‐MMT and PVC/O‐MMT nanocomposites, respectively. Results of XRD and transmission electron microscopy (TEM) indicate that MMT is partially encapsulated and intercalated in the rigid PVC/Na+‐MMT nanocomposites. However, results of XRD and TEM show MMT is partially intercalated and exfoliated in the rigid PVC/O‐MMT nanocomposites. Tensile strength, yield strength, and elongation at break of the rigid PVC/MMT nanocomposites were improved simultaneously with adding 1–3 wt % Na+‐MMT or O‐MMT with respect to that of pristine PVC. However, the addition of Na+‐MMT or O‐MMT should be kept as not more than 3 wt % to optimize the mechanical properties and the processing stability of the rigid PVC/MMT nanocomposites. SEM micrographs of the fractured surfaces of the rigid PVC/Na+‐MMT and PVC/O‐MMT nanocomposites both before and after tensile tests were also illustrated and compared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2145–2154, 2006 相似文献
73.
A simple and sensitive method was conducted for the determination of trace amounts of proteins with benzeneazo-8-acetylamino-1-naphthol-3,6-disulfonic acid sodium salt (azophloxine, AP) using a Rayleigh light-scattering (RLS) technique. At pH 2.60 and in the presence of an emulsifier OP microemulsion, the RLS of AP can be greatly enhanced by proteins, owing to the interaction between AP and protein. The enhanced intensity is proportional to the concentration of proteins. Four proteins, including bovine serum albumin (BSA), human serum albumin (HSA), lysozyme (Lys) and gamma globulin (gamma-G) have been tested. For example, the linear range of BSA was 0 - 0.06 microg mL(-1) with detection limits of 2.38 ng mL(-1). The method was applied to the analysis of protein in human urine and penicillin samples with satisfactory results. The relative standard deviation was in all instances less than 4.0%, and the recovery was in the range of 97.5 - 104%. 相似文献
74.
高分子阳离子絮凝剂用于炼油废水处理研究 总被引:15,自引:0,他引:15
用聚二甲基二烯丙基氯化铵型高分子阳离子絮凝剂处理炼油废水考察了险油和化学耗氧量的动态变化规律。对产生的浮渣性质及滤饼的成份进行了研究。并且与聚合铝的处理效果进行对照。研究结果表明,HCA除油和化学耗管氧量的性能优于PAC,HCA产生的浮渣是PAC的三分之一,而浮渣中的含油量则是PAC的三倍。 相似文献
75.
76.
Let
l
be the critical exponent associated with the probability thatl independentN-step ordinary random walks, starting at nearby points, are mutually avoiding. Using Monte Carlo methods combined with a maximum-likelihood data analysis, we find that in two dimensions 2=0.6240±0.0005±0.0011 and 3=1.4575±0.0030±0.0052, where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second error bar represents statistical error (classical 95% confidence limits). These results are in good agreement with the conformal-invariance predictions 2=5/8 and 3=35/24. 相似文献
77.
78.
79.
In this paper we discuss the approximation of life distributions by exponential ones. The main results are: (1) F NBUE, where its mean is 1, we have
, 0, where = 1 - 2/2, 2 being the second moment ofF. The inequality is sharp. (2) In the case ofFIFR, the upper bound is
. (3) For the HNBUE class, the upper bound is min
. Furthermore, the improved upper bound is
. In addition, we show
0} |\bar G(t) - e^{ - t} | \leqslant \sqrt {\frac{\rho }{2}} $$
" align="middle" border="0">
, where
(4) For the IMRL class, the upper bound is /(1+) ([1]). Here we give a simple proof.Project supported by the National Natural Science Fund of China. 相似文献
80.