全文获取类型
收费全文 | 5568篇 |
免费 | 178篇 |
国内免费 | 18篇 |
专业分类
化学 | 4116篇 |
晶体学 | 28篇 |
力学 | 127篇 |
数学 | 712篇 |
物理学 | 781篇 |
出版年
2023年 | 37篇 |
2022年 | 145篇 |
2021年 | 206篇 |
2020年 | 130篇 |
2019年 | 164篇 |
2018年 | 142篇 |
2017年 | 116篇 |
2016年 | 196篇 |
2015年 | 176篇 |
2014年 | 168篇 |
2013年 | 353篇 |
2012年 | 384篇 |
2011年 | 386篇 |
2010年 | 257篇 |
2009年 | 222篇 |
2008年 | 316篇 |
2007年 | 362篇 |
2006年 | 301篇 |
2005年 | 249篇 |
2004年 | 221篇 |
2003年 | 188篇 |
2002年 | 148篇 |
2001年 | 72篇 |
2000年 | 71篇 |
1999年 | 60篇 |
1998年 | 59篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 28篇 |
1994年 | 25篇 |
1993年 | 26篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1985年 | 20篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1981年 | 21篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 21篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1973年 | 13篇 |
1972年 | 25篇 |
1971年 | 14篇 |
1970年 | 13篇 |
排序方式: 共有5764条查询结果,搜索用时 15 毫秒
41.
Elena B Lesage A Steuernagel S Böckmann A Emsley L 《Journal of the American Chemical Society》2005,127(49):17296-17302
A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid organic solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond (1)H-(13)C INEPT transfer for crystalline organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 x 10.4 kDa). 相似文献
42.
43.
Carla Milanesi Roberta Biolo Elena Reddi Giuuo Jori 《Photochemistry and photobiology》1987,46(5):675-681
Abstract Balb/c mice bearing a transplanted MS-2 fibrosarcoma were injected with 2.5 mg kg 1 of either tetra(4-sulfonatophenyl/porphine (TPPS) in phosphate-buffered saline or 0.5 mg kg−1 of Zn2+ -phthalocyanine (Zn-Pc) incorporated into unilamellar liposomes of dipalmitoyl-phosphatidylcholine. Chromatographic studies showed that TPPS is mainly transported in the serum by globulins and albumin, while Zn-Pc is specifically bound by lipoproteins. Exposure of the injected mice to red light (300 J cm−2 ) caused extensive tumor necrosis. The ultrastructural analysis of tumor specimens taken from mice at 15 h after PDT showed that TPPS photoinduces a preferential necrosis of the neoplastic cells, while Zn-Pc causes severe photodamage to both the vascular system and the neoplastic cells. The different modes of tumor photosensitization by TPPS and Zn-Pc are discussed on the basis of the transport mechanism of the two dyes. 相似文献
44.
Zn and Pd complexes of meso-tetraphenyltetranaphthaloporphyrins (Ph(4)TNP) exhibit strong infrared absorption bands and luminesce in solutions at room temperature. S1 --> S0 fluorescence (lambda(max) = 732 nm, phi = 5.3%) is the predominant emission in the case of ZnPh(4)TNP (1). This emission is in part due to the delayed fluorescence (phi = 1.1%). Phosphorescence (T1 --> S0) of 1 (lambda(max) = 973 nm) is very weak (phi = 0.04%) and occurs with lifetime of about 440 micros in deoxygenated DMF. In the case of PdPh(4)TNP (2), almost no S1 --> S0 fluorescence could be observed, while the main emission detected was T1 --> S0 phosphorescence (lambda(max) = 938 nm). The phosphorescence of 2 occurs with lifetime of about 65 micros and (phi=6.5%) in deoxygenated DMF solution. Metalloporphyrins 1 and 2 are promising near infrared dyes biomedical applications. 相似文献
45.
Conclusions The selective catalytic epoxidation of 1-alkenes by molecular oxygen was accomplished in the presence of C2-C5 alipahtic aldehydes and catalysts, viz., the salts of Cu(II), Ni(II), Fe(III), or Zr(IV).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2269–2272, October, 1985. 相似文献
46.
Since its inception five decades ago, imprinted sol-gel materials went practically unnoticed, until in the 1970s the conceptual introduction of molecular imprinting in synthetic polymers triggered a new interest in this field. The recent growth in interest in organic–inorganic hybrid materials prepared by sol-gel chemistry and the development of a variety of new strategies for imprinting polymeric matrices have led to a growing activity in what became known as molecularly imprinted sol-gel materials. This paper intends to give an overview of recent progress in molecular imprinting in sol-gel matrices, the potential analytical applications of these tailor-made materials and their limitations, with the aim of drawing attention to useful information and to enhancing interest in this practically unexplored but promising field. 相似文献
47.
V. M. Vinogradov I. L. Dalinger V. I. Gulevskaya S. A. Shevelev 《Russian Chemical Bulletin》1993,42(8):1369-1371
A preparative method ofN-amination of pyrazoles bearing nitro groups and other electron withdrawing substituents in the pyrazole ring with hydroxylamine-O-sulfonic acid involving control of the pH of the medium has been elaborated. A series of previously unknown pyrazoles has been prepared. Basicities
of 1-aminopyrazole and 1-amino-4-nitropyrazole have been measured and differences between the basicities of theC- andN-amino groups for the pyrazole series have been revealed.For part 3, see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1434–1436, August, 1993. 相似文献
48.
V. A. Tartakovskii A. S. Ermakov Yu. A. Strelenko D. B. Vinogradov E. Yu. Petrov 《Russian Journal of Organic Chemistry》2005,41(1):120-123
A practical procedure has been proposed for the synthesis of functionally substituted 4,5-dihydro-1,2,3-oxadiazole 2-oxides on the basis ofsulfamic acid derivatives.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 121–123.Original Russian Text Copyright © 2005 by Tartakovskii, Ermakov, Strelenko, Vinogradov, Petrov. 相似文献
49.
Remarkably stable mesoionic oxazolones possessing an oxazolo[3,2-a]quinolinium structure (5a–b),8,16, 17) were obtained by the double cyclisation of phenylglycine-o-carboxylic acids (3a–c) in refluxing acetic anhydride or in benzoic anhydride at 140°, The 0-Ac group was eliminated to give the corresponding lactones (6a–b) or replaced by O-Ts (7). IR stretching vibrations of the endo-carbonyl were in the range 1710–1768 cm?1, while v1-CH exhibited unusually high values (3159–3194 cm-1). 1-Acyl derivatives could be obtained only with TFAA (23–24), although easy deuteration of the same position took place in the presence of traces of trifluoroacetic acid. Hydrolysis of 5b led to the α-quinolone-N-acetic acid 27a. In the case of 5a, hydrolysis was accompanied by self-acylation of the nucleophilic site at C-4 with formation of a dimeric acid 28a. The presence of an additional Me group in phenylalanine-o-carboxylic acid (36) activates the corresponding mesoionic oxazolone 37 so that 1-acylation becomes possible with formation of the fused oxazole 38 by the Dakin-West reaction. Temperature dependent magnetic non-equivalence of methylene protons has been observed in acids 3b-d and f and also in the 7-membered anhydride 48b. 相似文献
50.
Irina E. Vasilyeva Elena V. Shabanova 《Fresenius' Journal of Analytical Chemistry》1998,361(3):280-282
A calibration model of multielement methods for simultaneous determination of micro- and macro-concentrations of elements
by computing the arc atomic-emission spectra has been developed. A calibration procedure for the analytical line group of
the elements to be determined is offered. It allows the lower and upper limits of the concentration range for each line of
the determined element to be calculated by means of the least-square method (LSM) and the Weibull distribution law is used
to extend the concentration region. The calibration model was successfully tested for different arc optical emission spectroscopy
(OES) methods.
Received: 17 June 1997 / Revised: 3 November 1997 / Accepted: 7 November 1997 相似文献