全文获取类型
收费全文 | 19924篇 |
免费 | 648篇 |
国内免费 | 113篇 |
专业分类
化学 | 14328篇 |
晶体学 | 193篇 |
力学 | 382篇 |
综合类 | 1篇 |
数学 | 2964篇 |
物理学 | 2817篇 |
出版年
2022年 | 128篇 |
2021年 | 205篇 |
2020年 | 304篇 |
2019年 | 301篇 |
2018年 | 192篇 |
2017年 | 189篇 |
2016年 | 411篇 |
2015年 | 366篇 |
2014年 | 465篇 |
2013年 | 949篇 |
2012年 | 993篇 |
2011年 | 1295篇 |
2010年 | 628篇 |
2009年 | 533篇 |
2008年 | 1025篇 |
2007年 | 1106篇 |
2006年 | 1087篇 |
2005年 | 1049篇 |
2004年 | 895篇 |
2003年 | 749篇 |
2002年 | 743篇 |
2001年 | 257篇 |
2000年 | 258篇 |
1999年 | 234篇 |
1998年 | 225篇 |
1997年 | 260篇 |
1996年 | 286篇 |
1995年 | 227篇 |
1994年 | 215篇 |
1993年 | 247篇 |
1992年 | 205篇 |
1991年 | 186篇 |
1990年 | 166篇 |
1989年 | 145篇 |
1988年 | 141篇 |
1987年 | 160篇 |
1986年 | 137篇 |
1985年 | 209篇 |
1984年 | 250篇 |
1983年 | 183篇 |
1982年 | 224篇 |
1981年 | 241篇 |
1980年 | 180篇 |
1979年 | 182篇 |
1978年 | 214篇 |
1977年 | 160篇 |
1976年 | 159篇 |
1975年 | 150篇 |
1974年 | 166篇 |
1973年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Paul du Bois-Reymond 《Mathematische Annalen》1879,15(3-4):564-576
Ohne Zusammenfassung 相似文献
22.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen相似文献
23.
24.
25.
26.
Vernon Barger Cheng-Wei Chiang Paul Langacker Hye-Sung Lee 《Physics letters. [Part B]》2004,580(3-4):186-196
We study the effects of an extra U(1)′ gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on Bd→φK and Bd→η′K decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z′ contribution can readily account for the anomaly in SφKS but is not sufficient to explain large branching ratio of Bd→η′K with the same parameter value. SφKS and Sη′KS are seen to be the dominant observables that constrain the extra weak phase in the model. 相似文献
27.
28.
29.
Azepane rings have been constructed diastereoselectively upon a carbohydrate derivative utilising reductive amination and RCM. The stereochemistry of the ring junctions was confirmed by X-ray crystallography and NMR. Diastereoselective dihydroxylation has also been employed to afford a tetrahydroxylated azepane carbohydrate derivative with potential biological activity. 相似文献
30.
This paper deals with the unsupervised classification of univariate observations. Given a set of observations originating from a K-component mixture, we focus on the estimation of the component expectations. We propose an algorithm based on the minimization of the “K-product” (KP) criterion we introduced in a previous work. We show that the global minimum of this criterion can be reached by first solving a linear system then calculating the roots of some polynomial of order K. The KP global minimum provides a first raw estimate of the component expectations, then a nearest-neighbour classification enables to refine this estimation. Our method’s relevance is finally illustrated through simulations of various mixtures. When the mixture components do not strongly overlap, the KP algorithm provides better estimates than the Expectation-Maximization algorithm. 相似文献