全文获取类型
收费全文 | 36241篇 |
免费 | 334篇 |
国内免费 | 331篇 |
专业分类
化学 | 15402篇 |
晶体学 | 300篇 |
力学 | 1643篇 |
综合类 | 12篇 |
数学 | 10454篇 |
物理学 | 9095篇 |
出版年
2023年 | 50篇 |
2022年 | 170篇 |
2021年 | 207篇 |
2020年 | 170篇 |
2019年 | 171篇 |
2018年 | 1309篇 |
2017年 | 1550篇 |
2016年 | 967篇 |
2015年 | 770篇 |
2014年 | 688篇 |
2013年 | 1060篇 |
2012年 | 3605篇 |
2011年 | 2847篇 |
2010年 | 2130篇 |
2009年 | 1867篇 |
2008年 | 1040篇 |
2007年 | 1058篇 |
2006年 | 1052篇 |
2005年 | 4800篇 |
2004年 | 4215篇 |
2003年 | 2537篇 |
2002年 | 756篇 |
2001年 | 377篇 |
2000年 | 158篇 |
1999年 | 234篇 |
1998年 | 184篇 |
1997年 | 152篇 |
1996年 | 141篇 |
1995年 | 97篇 |
1994年 | 120篇 |
1993年 | 76篇 |
1992年 | 224篇 |
1991年 | 195篇 |
1990年 | 188篇 |
1989年 | 155篇 |
1988年 | 138篇 |
1987年 | 100篇 |
1986年 | 71篇 |
1985年 | 80篇 |
1984年 | 91篇 |
1983年 | 66篇 |
1982年 | 63篇 |
1981年 | 50篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 54篇 |
1976年 | 94篇 |
1975年 | 50篇 |
1974年 | 55篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
This paper focuses on a new property for bankruptcy rules, calledsustainability, which requires that the agents with small enough claims be fully reimbursed. We show that the constrained equal-awards rule is the only rule that satisfies path independence and sustainability. Exploiting duality relations, we also provide a characterization of the constrained equal-losses rule, as the only one that satisfies composition and independence of residual claims (the dual property of sustainability). 相似文献
102.
Scopo del lavoro è di studiare la stabilità asintotica per le soluzioni di problemi di evoluzione astratti. Si considerano
operatori differenziali quali ilp-Laplaciano, e il poliarmonico, termini smorzanti e fortemente smorzanti, potenziali di richiamo o di sorgente.
相似文献
103.
104.
Juan F García-Reyes Pilar Ortega-Barrales Antonio Molina-Díaz 《Analytical sciences》2007,23(4):423-428
A combined approach based on solid-phase optosensing and multicommutation principles has been applied to develop a method for the simultaneous analysis of two pharmaceuticals (naproxen and salicylic acid) in biological fluids. The multicommuted flow-through optosensor was based on direct native fluorescence measurements of both analgesics using a non-polar sorbent (C18 silica gel) as a solid sensing zone. The flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for an independent automated manipulation of sample and carrier solutions. Using an optimized sampling time, the method was calibrated in the range of 1 - 25 and 5 - 200 ng mL(-1). The obtained detection limits were 0.3 and 1.3 ng mL(-1) for naproxen and salicylic acid, respectively, with RSD (%) values of better than 2% for both analytes. The proposed methodology was successfully applied to urine, serum and pharmaceutical preparations. Recovery percentages ranging from 96.1 to 104% were obtained for both analytes. 相似文献
105.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
106.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
107.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
108.
Adducts of the conjugate addition of benzylamine to enantiopure amides of aroylacrylic acid possess high enantiomeric and diastereomeric purity. A high degree of stereoselectivity has been achieved by means of crystallization-induced asymmetric transformation. A practical synthesis leading to dipeptides containing homophenylalanine is depicted. 相似文献
109.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献
110.
Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. 相似文献