全文获取类型
收费全文 | 23623篇 |
免费 | 3806篇 |
国内免费 | 3082篇 |
专业分类
化学 | 17430篇 |
晶体学 | 282篇 |
力学 | 1449篇 |
综合类 | 188篇 |
数学 | 2493篇 |
物理学 | 8669篇 |
出版年
2024年 | 78篇 |
2023年 | 433篇 |
2022年 | 720篇 |
2021年 | 840篇 |
2020年 | 953篇 |
2019年 | 938篇 |
2018年 | 794篇 |
2017年 | 724篇 |
2016年 | 1173篇 |
2015年 | 1065篇 |
2014年 | 1277篇 |
2013年 | 1777篇 |
2012年 | 2071篇 |
2011年 | 2009篇 |
2010年 | 1475篇 |
2009年 | 1386篇 |
2008年 | 1552篇 |
2007年 | 1370篇 |
2006年 | 1262篇 |
2005年 | 1161篇 |
2004年 | 966篇 |
2003年 | 845篇 |
2002年 | 941篇 |
2001年 | 725篇 |
2000年 | 527篇 |
1999年 | 546篇 |
1998年 | 423篇 |
1997年 | 389篇 |
1996年 | 380篇 |
1995年 | 299篇 |
1994年 | 262篇 |
1993年 | 202篇 |
1992年 | 176篇 |
1991年 | 171篇 |
1990年 | 112篇 |
1989年 | 82篇 |
1988年 | 73篇 |
1987年 | 48篇 |
1986年 | 62篇 |
1985年 | 54篇 |
1984年 | 29篇 |
1983年 | 30篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 13篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1957年 | 5篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
In this paper we define the vertex-cover polynomial Ψ(G,τ) for a graph G. The coefficient of τr in this polynomial is the number of vertex covers V′ of G with |V′|=r. We develop a method to calculate Ψ(G,τ). Motivated by a problem in biological systematics, we also consider the mappings f from {1, 2,…,m} into the vertex set V(G) of a graph G, subject to f−1(x)f−1(y)≠ for every edge xy in G. Let F(G,m) be the number of such mappings f. We show that F(G,m) can be determined from Ψ(G,τ). 相似文献
53.
用三维样边界元法分析水闸闸室结构。底板,闸墩和载水墙等为其子结构,交通桥,工作桥和胸墙等处理为内部支撑。地基和边载可以是任意的,只要能给定地表位移面力关系。在各种工况下,不论是设置平板门还是弧形门,是平底板是反拱底板,即使在稀疏剖分下也能给出高精度的位移场,应力场和地基反力场。 相似文献
54.
双包层椭圆光波导解析解 总被引:3,自引:0,他引:3
解析求解了双包层椭圆光纤中的波动方程,得到了模式精确解有模式特征方程。对基模的特征方程进行了数值计算,给出了不同椭圆比下的归一化双折射和模间色散随归一化频率的变化关系曲线,并与高斯近似解的结果进行了比较。 相似文献
55.
Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs. 相似文献
56.
This paper reports the measurement of magnetic properties of the soft magnetic composite material SOMALOYTM 500 in a square sample under different patterns of flux density with 2D magnetic excitations. The test system, principle of measurement, magnetic power loss calculation, and methods of correction for misalignment of H surface sensing coils are presented. The experimental results show that although nominally isotropic, the SOMALOYTM 500 sample exhibits some anisotropy. The results are useful in the design and performance analysis of rotating electrical machines. 相似文献
57.
58.
Ranked-set sampling is useful when measurements are destructive or costly to obtain but ranking of the observations is relatively easy. The Wilcoxon signed rank test statistic based on the ranked-set sample is considered. We compared the asymptotic relative efficiencies of the RSS Wilcoxon signed rank test statistic with respect to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic. Throughout the ARE’s, the proposed test statistic is superior to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic. 相似文献
59.
meso-四(4-乙酰氧基苯)卟啉-铜(Ⅱ)-乳化剂OP体系荧光熄灭法测定微量铜(Ⅱ)的研究 总被引:1,自引:0,他引:1
本文研究了高灵敏的meso-四(4-乙酰氧基苯)卟啉[T(4-AOP)P]-铜(Ⅱ-乳化剂OP体系。在酸度为pH5.0~5.6范围内形成的三元络合物可引起T(4-AOP)P-OP荧光强度的定量熄灭,其Ex=413nm,EM=656.9nm,Cu(Ⅱ)浓度在0~0.150μg/ml范围内有良好的线性关系,回归方程F=25.51-8.45m,试验了14种离子的干扰影响,并用此法测定了小球藻中Cu的含量,回收率达96~104%。 相似文献
60.
Chemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface-enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4-vinyl pyridine). © 1992 John Wiley & Sons, Inc. 相似文献