全文获取类型
收费全文 | 6044篇 |
免费 | 98篇 |
国内免费 | 15篇 |
专业分类
化学 | 4228篇 |
晶体学 | 44篇 |
力学 | 84篇 |
数学 | 1055篇 |
物理学 | 746篇 |
出版年
2019年 | 50篇 |
2016年 | 98篇 |
2015年 | 63篇 |
2014年 | 53篇 |
2013年 | 202篇 |
2012年 | 128篇 |
2011年 | 193篇 |
2010年 | 134篇 |
2009年 | 147篇 |
2008年 | 186篇 |
2007年 | 189篇 |
2006年 | 199篇 |
2005年 | 195篇 |
2004年 | 152篇 |
2003年 | 149篇 |
2002年 | 139篇 |
2001年 | 95篇 |
2000年 | 112篇 |
1999年 | 85篇 |
1998年 | 72篇 |
1997年 | 80篇 |
1996年 | 96篇 |
1995年 | 94篇 |
1994年 | 81篇 |
1993年 | 102篇 |
1992年 | 105篇 |
1991年 | 119篇 |
1990年 | 97篇 |
1989年 | 99篇 |
1988年 | 81篇 |
1987年 | 95篇 |
1986年 | 98篇 |
1985年 | 109篇 |
1984年 | 119篇 |
1983年 | 106篇 |
1982年 | 116篇 |
1981年 | 129篇 |
1980年 | 97篇 |
1979年 | 101篇 |
1978年 | 87篇 |
1977年 | 120篇 |
1976年 | 87篇 |
1975年 | 99篇 |
1974年 | 115篇 |
1973年 | 84篇 |
1972年 | 73篇 |
1971年 | 56篇 |
1970年 | 56篇 |
1967年 | 42篇 |
1966年 | 42篇 |
排序方式: 共有6157条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Stefan Peterli Dieter Hubmann Urs Squin Helmut Mett Peter Traxler 《Helvetica chimica acta》1994,77(1):59-69
β-Nitrostyrene derivatives of adenosine 5′-glutarates are potent and selective bisubstrate-type inhibitors of the epidermal growth factor receptor protein tyrosine kinase (EGF-R PTK). In an attempt to improve the inhibitory activity, this type of compounds was modified with alkyl spacers of varying length between the nitrostyrene and the glutaryl units. The spacers consisted of 1, 3, 4, and 5 atoms to give compounds of the benzyl, oxyethyl, oxypropyl, and oxybutyl series, respectively (Schemes 1 and 2). Adenosine 5′-esters were prepared in the benzyl and oxypropyl series only. Compared to the compounds in the parent series without spacer (IC50 = 0.7–12 μM ), most of the modified compounds inhibited the EGF-R PTK only marginally or were inactive (IC50 ≥ 100 μM ). The only exceptions were the free acids 19 and 20 with IC50 values of ca. 5 μM . It is noteworthy that esterification of these two hydrogen glutarates with either MeOH or adenosine yielded inactive compounds, which is in contrast to the corresponding substances without spacers. 相似文献
6.
Helmut Schmidhammer Eva Scherb-Bukowiecki Thomas A. Mayer Peter Schnholzer 《Helvetica chimica acta》1994,77(6):1590-1594
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 . 相似文献
7.
8.
9.
Rose Vogel Dr. 《ZDM》2005,37(5):445-449
Taking advantage of patterns is typical of our everyday experience as well as our mathematical thinking and learning. For example a working day or a morning at school displays a certain structure, which can be described in terms of patterns. On the one hand regular structures give us the feeling of permanence and enable us to make predictions. On the other hand they also provide a chance to be creative and to vary common procedures. School students usually encounter patterns in math classes either as number patterns or geometric patterns. There are also patterns that teachers can find in analyzing the errors students make during their calculations (error patterns) as well as patterns that are inherent to mathematical problems. One could even go so far as to say that identifying and describing patterns is elementary for mathematics (cf. Devlin 2003). Practising good interacting with patterns supports not only the active learning of mathematics but also a deeper understanding of the world in general. Patterns can be explored, identified, extended, reproduced, compared, varied, represented, described and created. This paper provides some examples of pattern utilization and detailed analyses thereof. These ideas serve as “hooks” to encourage the good use of patterns to facilitate active learning processes in mathematics. 相似文献
10.
N. Vogel 《等离子体物理论文集》1989,29(1):11-24
The stepwise increase of the burning voltage of short break arcs has been found not only in a gas but also in vacuum. It is suggested that the effect is associated with the occurrence of a positive anode fall which enhances ionisation phenomena near the anode. This view is supported by the simultaneous registration of arc current, burning voltage, light emission from the anode region, of spectral lines of ions, atoms and continuum from the near anode plasma. The phenomena occur beyond a critical gap distance which can be related to the characteristic geometry of the discharge. 相似文献