全文获取类型
收费全文 | 1809篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 1295篇 |
晶体学 | 3篇 |
力学 | 58篇 |
数学 | 243篇 |
物理学 | 252篇 |
出版年
2023年 | 9篇 |
2021年 | 11篇 |
2020年 | 26篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 35篇 |
2015年 | 27篇 |
2014年 | 30篇 |
2013年 | 50篇 |
2012年 | 89篇 |
2011年 | 86篇 |
2010年 | 47篇 |
2009年 | 50篇 |
2008年 | 65篇 |
2007年 | 67篇 |
2006年 | 60篇 |
2005年 | 64篇 |
2004年 | 65篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 26篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 12篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1982年 | 12篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 22篇 |
1972年 | 11篇 |
1968年 | 290篇 |
1967年 | 89篇 |
排序方式: 共有1851条查询结果,搜索用时 15 毫秒
1.
2.
3.
Herbert Henning 《ZDM》2003,35(4):172-176
The author discusses at some examples exemplarily, how the pedagogy of mathematics education in the GDR from curricular and educational/psychological knowledge from the time before 1945 has developed scientifically. 相似文献
4.
5.
6.
Ehret R Baumann W Brischwein M Lehmann M Henning T Freund I Drechsler S Friedrich U Hubert ML Motrescu E Kob A Palzer H Grothe H Wolf B 《Fresenius' Journal of Analytical Chemistry》2001,369(1):30-35
The identification of drug targets for pharmaceutical screening can be greatly accelerated by gene databases and expression studies. The identification of leading compounds from growing libraries is realized by high throughput screening platforms. Subsequently, for optimization and validation of identified leading compounds studies of their functionality have to be carried out, and just these functionality tests are a limiting factor. A rigorous preselection of identified compounds by in vitro cellular screening is necessary prior to using the drug candidates for the further time consuming and expensive stage, e.g. in animal models. Our efforts are focused to the parallel development, adaptation and integration of different microelectronic sensors into miniaturized biochips for a multiparametric, functional on-line analysis of living cells in physiologically environments. Parallel and on-line acquisition of data related to different cellular targets is required for advanced stages of drug screening and for economizing animal tests. 相似文献
7.
Monwar M Oh SJ Rinaldi PL McCord EF Hutchinson RA Buback MM Latz H 《Analytical and bioanalytical chemistry》2004,378(6):1414-1427
Poly(n-butylacrylate-co-carbon monoxide-co-ethylene) (polyEBC) samples prepared from 13C-labeled monomer, n-butyl acrylate, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex structure of the terpolymer, 2D-1H/13C-heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced resonances in the spectra of two polymer samples, one polymer resulting from synthesis with 1-13C-n-butylacrylate monomer and a second polymer obtained from a synthesis with 2-13C-n-butylacrylate monomer. High-resolution 2D-NMR combined with 13C-labeling of the polymer greatly simplifies the 2D-NMR spectra, selectively enhances the weak peaks from low occurrence B-centered triad structures, and aids in their resonance assignments. In all experiments, the sample temperature was 120 degrees C, to ensure a homogeneous solution and sufficient molecular mobility. Electronic Supplementary Material: Supplementary material (1D 13C NMR spectra of the 13C-labeled and unlabeled polymers) is available in the online version of this article at http://dx.doi.org/100.1007/s00216-003-2402-3. 相似文献
8.
Hans-Rudolf Waespe Heinz Heimgartner Hans Schmid Hans-Jürgen Hansen Henning Paul Hanns Fischer 《Helvetica chimica acta》1978,61(1):401-429
The photochemical reactions of different allyl aryl ethers (Scheme 3) were investigated in hydrocarbons (Chap. 3.1) and in alcoholic solvents (Chap. 3.2). The composition of the photoproducts depended very much on the nature of the solvent. Irradiation (3–95 h) of different methyl substituted allyl aryl ethers ( 1, 3, 5, 7 and 11 ) with a low pressure mercury lamp (λEmiss. = 254 nm; 6 or 15 Watt) under argon (quartz vessel) resulted in the formation of 2-, 3– and 4-substituted phenols, dienones and products of consecutive reactions (Tables 1–4 and 6). The results suggested that all products were formed by homolytic cleavage of the C? O bond in the singlet state of the ethers to intermediate radical-geminates (Scheme 5) followed by radical recombination of the two fragments. No products were formed by concerted processes (Table 5, Schemes 5 and 6). Upon irradiation of allyl aryl ethers lacking alkyl substituents at position 4 ( 1 and 5 ) in protic solvents, mainly 2- and 4-allylated phenols were obtained (Tables 1 and 4); 3-allylated phenols were formed only in small amounts (0.02%). However, in aromatic hydrocarbons or cyclohexane 3-allylated phenols were obtained from 1 , 5 and 11 in significant amounts (3–11%; Tables 1, 4 and 6). E.g., upon irradiation of allyl-2,6-dimethyl-2,4-cyclohexadien-1-one ( 6 ) besides 3- and 4-allyl-2, 6-dimethyl-phenol ( 23 and 24 ). Irradiation of 5 in methanol afforded 23 and 6 only in traces, whereas 24 was the main product. 相似文献
9.
10.