全文获取类型
收费全文 | 512篇 |
免费 | 28篇 |
专业分类
化学 | 365篇 |
晶体学 | 8篇 |
力学 | 8篇 |
数学 | 58篇 |
物理学 | 101篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 31篇 |
2012年 | 49篇 |
2011年 | 44篇 |
2010年 | 17篇 |
2009年 | 22篇 |
2008年 | 25篇 |
2007年 | 33篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有540条查询结果,搜索用时 15 毫秒
41.
ABSTRACT We examined the effect as donors of three aryl β-D-galactosides (i.e. p-nitrophenyl β-D-galactopyranoside, o-nitrophenyl β-D-galactopyranoside and phenyl β-D-galacto-pyranoside) on the regioselectivity and the yield of the synthesis of N-acetyllactosamine obtained from the transglycosylation reaction catalyzed by a crude preparation of β-D-galactosidase from Bacillus circulans at 25 °C, 37 °C and 55 °C, respectively. Using p-nitrophenyl β-D-galactopyranoside the reaction results were fully regiospecific at all the temperatures considered: the maximum molar yield (74%) was obtained at an incubation temperature of 55 °C. Using o-nitrophenyl β-D-galactopyranoside as the donor the reaction was still highly regioselective and the maximum molar yield (50%) was achieved at an incubation temperature also of 55 °C. Using phenyl β-D-galactopyranoside transglycolytic products appear only at an incubation temperature of 55 °C but at very low molar yield (about 14%) and lower regioselectivity. 相似文献
42.
43.
Michelina Soccio Nadia Lotti Lara Finelli Massimo Gazzano Andrea Munari 《Journal of Polymer Science.Polymer Physics》2010,48(17):1901-1910
Poly(glycolic acid) (PGA) and a series of novel random copolymers of PGA containing 2‐hydroxyisobutyrric acid (PGAPHIB) (HIB unit content from 1.5 to 7.4 mol %) were synthesized and characterized in terms of chemical structure and molecular weight. Afterward, the polyesters were examined by thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction techniques. The copolymers, which displayed a better thermal stability than PGA, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PGA. Baur's equation described well the Tm‐composition data. X‐ray diffraction measurements allowed the identification of the PGA crystalline structure in all cases. After melt quenching, semicrystalline samples were obtained with the exception of PGAPHIB7.4 copolymer. The introduction of HIB units decreased the crystallization rate compared with pure PGA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1901–1910, 2010 相似文献
44.
The Direction of Time: From the Global Arrow to the Local Arrow 总被引:1,自引:0,他引:1
Mario Castagnino Luis Lara Olimpia Lombardi 《International Journal of Theoretical Physics》2003,42(10):2487-2504
In this paper we discuss the traditional approaches to the problem of the arrow of time. On the basis of this discussion we adopt a global and nonentropic approach, according to which the arrow of time has a global origin and is an intrinsic, geometrical feature of space-time. Finally, we show how the global arrow is translated into local terms as a local time-asymmetric flux of energy. 相似文献
45.
Roberto O. Aquilano Mario A. Castagnino Luis P. Lara 《General Relativity and Gravitation》1994,26(5):525-530
The conclusions of paper [2] are modified: using the shell formalism, relativistic effect could eventually be detected in X-ray bursters. 相似文献
46.
47.
Lara R. Malins Nicholas J. Mitchell Sheena McGowan Richard J. Payne 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(43):12907-12912
Despite the unique chemical properties of selenocysteine (Sec), ligation at Sec is an under‐utilized methodology for protein synthesis. We describe herein an unprecedented protocol for the conversion of Sec to serine (Ser) in a single, high‐yielding step. When coupled with ligation at Sec, this transformation provides a new approach to programmed ligations at Ser residues. This new reaction is compatible with a wide range of functionality, including the presence of unprotected amino acid side chains and appended glycans. The utility of the methodology is demonstrated in the rapid synthesis of complex glycopeptide fragments of the epithelial glycoproteins MUC5AC and MUC4 and through the total synthesis of the structured, cysteine (Cys)‐free protein eglin C. 相似文献
48.
Dr. Tian Qin Dr. Lara R. Malins Jacob T. Edwards Rohan R. Merchant Alexander J. E. Novak Jacob Z. Zhong Riley B. Mills Ming Yan Dr. Changxia Yuan Dr. Martin D. Eastgate Prof. Phil S. Baran 《Angewandte Chemie (International ed. in English)》2017,56(1):260-265
Two named reactions of fundamental importance and paramount utility in organic synthesis have been reinvestigated, the Barton decarboxylation and Giese radical conjugate addition. N ‐hydroxyphthalimide (NHPI) based redox‐active esters were found to be convenient starting materials for simple, thermal, Ni‐catalyzed radical formation and subsequent trapping with either a hydrogen atom source (PhSiH3) or an electron‐deficient olefin. These reactions feature operational simplicity, inexpensive reagents, and enhanced scope as evidenced by examples in the realm of peptide chemistry. 相似文献
49.
F. Lara 《Optimization》2017,66(8):1259-1272
In this paper, we use generalized asymptotic functions and second-order asymptotic cones to develop a general existence result for the nonemptiness of the proper efficient solution set and a sufficient condition for the domination property in nonconvex multiobjective optimization problems. A new necessary condition for a point to be efficient or weakly efficient solution is given without any convexity assumption. We also provide a finer outer estimate for the asymptotic cone of the weakly efficient solution set in the quasiconvex case. Finally, we apply our results to the linear fractional multiobjective optimization problem. 相似文献
50.