全文获取类型
收费全文 | 2683篇 |
免费 | 79篇 |
国内免费 | 5篇 |
专业分类
化学 | 2133篇 |
晶体学 | 16篇 |
力学 | 35篇 |
数学 | 222篇 |
物理学 | 361篇 |
出版年
2023年 | 15篇 |
2022年 | 74篇 |
2021年 | 79篇 |
2020年 | 37篇 |
2019年 | 57篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 80篇 |
2015年 | 76篇 |
2014年 | 86篇 |
2013年 | 126篇 |
2012年 | 165篇 |
2011年 | 161篇 |
2010年 | 120篇 |
2009年 | 97篇 |
2008年 | 173篇 |
2007年 | 163篇 |
2006年 | 136篇 |
2005年 | 180篇 |
2004年 | 128篇 |
2003年 | 115篇 |
2002年 | 98篇 |
2001年 | 46篇 |
2000年 | 33篇 |
1999年 | 38篇 |
1998年 | 22篇 |
1997年 | 38篇 |
1996年 | 29篇 |
1995年 | 20篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有2767条查询结果,搜索用时 0 毫秒
61.
Rodríguez Rivero M De La Rosa JC Carretero JC 《Journal of the American Chemical Society》2003,125(49):14992-14993
The first asymmetric version of intermolecular Pauson-Khand reactions of unstrained alkenes is described. Generally simple acyclic alkenes exhibit low reactivity and regioselectivity in intermolecular Pauson-Khand reactions; however, o-(dimethylamino)phenyl vinyl sulfoxide reacts under very mild conditions with a wide variety of terminal alkynes in a completely regioselective and highly stereoselective manner. The utility of the resulting 5-sulfinyl-2-cyclopentenones in asymmetric synthesis is illustrated by a very short enantioselective synthesis of the antibiotic (-)-pentenomycin I. 相似文献
62.
1,3-Bis[(2-pyridyl)methyleneamino]thiourea (PMAT) and 1,3-bis[(2-pyridyl)methyleneamino]-guanidine (PMAG) have been prepared. They have been examined and characterized by infrared and ultraviolet spectroscopy. A spectrophotometric method has been used for determination of the protonation constants of the reagents. Finally, a spectrophotometric survey has been made of the reactions of various cations with PMAT and PMAG. 相似文献
63.
The use of a rapid and specific (cross-reactivity<4%) enzyme-linked immunosorbent assay (ELISA) for the determination of alachlor residues in water and vegetable samples is addressed. The analytical method consists of a fast extraction procedure followed by an optimised ELISA. The detection limit was 0.44 microg l(-1), with a linear range from 0.89 to 143.2 microg l(-1). For alachlor extraction from water samples, different solid-phase cartridges (C, Ph, C8 and C2) were assayed using MeOH as eluent. Extracts were diluted (1:4) with distilled water before ELISA. This procedure gave recoveries close to 100% with RSDs<14%. For vegetable samples, alachlor was extracted directly with MeOH and the extracts diluted 1:40 (v/v) with saline buffer prior to ELISA. The results obtained by the proposed procedure correlate well with the reference method (multiresidue extraction-GC-MS) for vegetable samples (r>0.85). 相似文献
64.
65.
66.
P.A.J. Rosa I.F. FerreiraA.M. Azevedo M.R. Aires-Barros 《Journal of chromatography. A》2010,1217(16):2296-2305
The number of biotechnology-based pharmaceuticals in the late-stage pipeline has been increasing more than ever. As a result, there is an enhanced demand for more efficient and cost-effective processes. During the last years, the upstream technology for the production of biopharmaceuticals has been considerably improved. Continuous discoveries in molecular biology and genetics, combined with new advances in media and feed development, have significantly increased the production titres. In order to keep up this gain, it is now essential to design new, as well as to improve the existing downstream processes that remain an unresolved bottleneck. This review evaluates several alternatives to the currently established platforms for the downstream processing biopharmaceuticals, with main focus on aqueous two-phase extraction. 相似文献
67.
Margherita De Rosa 《Tetrahedron》2010,66(16):2981-5955
A combination of water and microwave irradiation was used for the first time to perform a catalyst-free nitro-Michael addition of pyrroles and indoles. Under superheated conditions, the water trends to ionize by changing its chemical and physical properties. Therefore, we performed a new green-protocol using the water either as environmentally no harm solvent or as catalyst. The reaction success is independent from the kind of pyrrole, indole or nitroalkenes rapidly affording the corresponding adducts and giving excellent yields. 相似文献
68.
Zhan Yu Lee Chuin Chen Rosa Erra‐Balsells Hiroshi Nonami Kenzo Hiraoka 《Rapid communications in mass spectrometry : RCM》2010,24(11):1507-1513
Probe electrospray ionization (PESI) is a modified version of the electrospray ionization (ESI), where the capillary for sampling and spraying is replaced by a solid needle. High tolerance to salts and direct ambient sampling are major advantages of PESI compared with conventional ESI. In this study, PESI‐MS was used to monitor some biological and chemical reactions in real‐time, such as acid‐induced protein denaturation, hydrogen/deuterium exchange (HDX) of peptides, and Schiff base formation. By using PESI‐MS, time‐resolved mass spectra and ion chromatograms can be obtained reproducibly. Real‐time PESI‐MS monitoring can give direct and detailed information on each chemical species taking part in reactions, and this is valuable for a better understanding of the whole reaction process and for the optimization of reaction parameters. PESI‐MS can be considered as a potential tool for real‐time reaction monitoring due to its simplicity in instrumental setup, direct sampling with minimum sample preparation and low sample consumption. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
69.
70.
Elena Fernández Manuel Ortuño Andrés Márquez Rosa Fuentes Inmaculada Pascual 《Optik》2010,121(2):151-158
Holographic data pages were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) photopolymer. This material is formed of AA photopolymers which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages in the material. During the storage process, some parameters like exposure time, beam ratio and reading beam intensity were controlled to obtain high image quality after the reconstruction process. The bit error rate (BER) was calculated fitting the histograms of the images to determine what parameters improve the quality of the images. 相似文献