全文获取类型
收费全文 | 3948篇 |
免费 | 117篇 |
国内免费 | 17篇 |
专业分类
化学 | 2645篇 |
晶体学 | 30篇 |
力学 | 149篇 |
数学 | 619篇 |
物理学 | 639篇 |
出版年
2023年 | 15篇 |
2022年 | 21篇 |
2021年 | 42篇 |
2020年 | 43篇 |
2019年 | 58篇 |
2018年 | 46篇 |
2017年 | 45篇 |
2016年 | 91篇 |
2015年 | 64篇 |
2014年 | 106篇 |
2013年 | 239篇 |
2012年 | 185篇 |
2011年 | 244篇 |
2010年 | 151篇 |
2009年 | 150篇 |
2008年 | 226篇 |
2007年 | 218篇 |
2006年 | 202篇 |
2005年 | 225篇 |
2004年 | 205篇 |
2003年 | 176篇 |
2002年 | 177篇 |
2001年 | 74篇 |
2000年 | 90篇 |
1999年 | 57篇 |
1998年 | 55篇 |
1997年 | 55篇 |
1996年 | 46篇 |
1995年 | 32篇 |
1994年 | 49篇 |
1993年 | 42篇 |
1992年 | 28篇 |
1991年 | 31篇 |
1990年 | 15篇 |
1989年 | 28篇 |
1988年 | 16篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 39篇 |
1984年 | 44篇 |
1983年 | 26篇 |
1982年 | 34篇 |
1981年 | 45篇 |
1980年 | 42篇 |
1979年 | 36篇 |
1978年 | 31篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 38篇 |
1974年 | 30篇 |
排序方式: 共有4082条查询结果,搜索用时 15 毫秒
171.
Dessapt R Simonnet-Jégat C Mallard A Lavanant H Marrot J Sécheresse F 《Inorganic chemistry》2003,42(20):6425-6431
Three new Mo(V) dithiolene compounds have been synthesized by addition of alkynes ((Me(3)Si)(2)C(2) (TMSA), (Me(3)Si)(2)C(4), and (Ph)(2)C(4) to MoO(2)S(2)(2-) in a MeOH/NH(3) mixture: [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(2))](2)(-) 1, [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(C(2)Ph))](2-) 2 (X = O or S), and [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(C(2)H))](2-) 3. The structure of 1 as determined by single-crystal X-ray diffraction study (space group Pbca, a = 13.3148(1) A, b = 15.7467(4) A, c = 28.4108(7) A, V = 5956.7(2) A(3)) is discussed. 2 and 3 have been identified by ESMS (electrospray mass spectrometry), (1)H NMR, (13)C NMR, and infrared spectroscopies. This investigation completes our previous study devoted to the addition of DPA (C(2)Ph(2)) to MoO(2)S(2)(2-) which led to [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(2))](2-) 4 (X = O or S). A reaction scheme is proposed to explain the formation of the different species present in solution. The reactivity of the remaining nucleophilic site of these complexes (eta(2)-S(2)) toward dicarbomethoxyacetylene (DMA) is also discussed. 相似文献
172.
Mathieu Gaudin Maï Panchal Sophie Ayciriex Erwan Werner Alain Brunelle David Touboul Claire Boursier‐Neyret Nicolas Auzeil Bernard Walther Charles Duyckaerts Olivier Laprévote 《Journal of mass spectrometry : JMS》2014,49(10):1035-1042
The development of ‘omics’ sciences offers new opportunities for the study of neurodegenerative diseases but increases at the same time the sample demand on brain banks that collect and store valuable human post‐mortem tissue. Our study aims to evaluate in lipidomics the potential of formalin‐fixed tissue compared with the cryopreservation method, considered as the gold standard for biochemical research. Two complementary liquid chromatography/mass spectrometry analytical platforms were used on the basis of hybrid quadrupole time‐of‐flight and triple quadrupole mass spectrometers. Untargeted fingerprinting, semitargeted profiling of specific lipid classes and targeted monitoring of lipid species were performed in formalin‐fixed and cryopreserved samples to provide detailed information at the molecular level on the formalin‐induced alterations of the brain tissue. In vitro incubations of lipid standards were also performed to further describe the degradation processes induced by formaldehyde. Phospholipid compounds were found to be extensively hydrolysed, whilst the sphingolipid ones were preserved. N‐methylation and N‐formylation of amine‐containing phospholipids have also been evidenced. These findings show that the potential detrimental effect of formalin on the analytes of interest must be taken into account when analysing formalin‐fixed samples. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
173.
Ayman Ben Mabrouk Hamid Kaddami Sami Boufi Fouad Erchiqui Alain Dufresne 《Cellulose (London, England)》2012,19(3):843-853
The microstructure and chemical composition of alfa (Stipa tenacissima) were investigated. The polysaccharide and lignin contents were around 70 and 20 wt%, respectively. From the bleached and
delignified fibers, two types of nanosized cellulosic particles were extracted, namely cellulose nanocrystals and microfibrillated
cellulose (MFC). The former correspond typically to the elementary crystallite units of the cellulose fibers, with a rod-like
morphology and an aspect ratio of about 20. The latter, mechanically disintegrated from oxidized bleached fibres, presents
an entangled fibrillar structure with widths in the range 5-20 nm. The reinforcing potential of the ensuing nanoparticles
was investigated by casting a mixture of acrylic latex and aqueous dispersion of cellulose nanoparticles. Thermo-mechanical
analysis revealed a huge enhancement of the stiffness above the glass transition of the matrix. Significant differences in
the mechanical reinforcing capability of the nanoparticles were reported. 相似文献
174.
Dr. Paolo Destito Dr. Cristian Vidal Dr. Fernando López Prof. José L. Mascareñas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(15):4789-4816
During the last decade, there has been a tremendous interest for developing non-natural biocompatible transformations in biologically relevant media. Among the different encountered strategies, the use of transition metal complexes offers unique possibilities due to their high transformative power. However, translating the potential of metal catalysts to biological settings, including living cells or small-animal models such as mice or zebrafish, poses numerous challenges associated to their biocompatibility, and their stability and reactivity in crowded aqueous environments. Herein, we describe the most relevant advances in this direction, with a particular emphasis on the systems’ structure, their mode of action and the mechanistic bases of each transformation. Thus, the key challenges from an organometallic perspective might be more easily identified. 相似文献
175.
Abstract The chemical dehydrochlorination of polyvinyl chloride was studied in solution in tetrahydrofuran. The dehydrochlorinated products were characterized by their chlorine contents and by UV/visible spectroscopy. The absorption spectra of dehydrochlorinated PVC consist of a series of absorption maxima between 200 and 600 nm due to the formation of conjugated polyenic sequences. In this article we describe a new method for polyenic sequences evaluation based on deconvolution of the experimental spectrum. A comparison with the former technique usually employed is presented. 相似文献
176.
177.
Alain Comtet Jean-Marc Luck Christophe Texier Yves Tourigny 《Journal of statistical physics》2013,150(1):13-65
We study products of arbitrary random real 2×2 matrices that are close to the identity matrix. Using the Iwasawa decomposition of SL(2,?), we identify a continuum regime where the mean values and the covariances of the three Iwasawa parameters are simultaneously small. In this regime, the Lyapunov exponent of the product is shown to assume a scaling form. In the general case, the corresponding scaling function is expressed in terms of Gauss’ hypergeometric function. A number of particular cases are also considered, where the scaling function of the Lyapunov exponent involves other special functions (Airy, Bessel, Whittaker, elliptic). The general solution thus obtained allows us, among other things, to recover in a unified framework many results known previously from exactly solvable models of one-dimensional disordered systems. 相似文献
178.
Alain Michel 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(3):361-371
4-Chloro-2-hexene can be considered a model compound for the chlorinated allylic structure appearing in PVC chains after dehydrochlorination. This model compound was used to elucidate the mechanism of reaction of primary or secondary stabilizers. 相似文献
179.
For some spatial branching processes with interaction considered as measure–valued processes, convergence to solutions of non–linear macroscopic equation and local equilibrium are proved, without scaling but providing each particle with a small mass ε and assuming convergence of the initial distribution when ε goes to 0 相似文献
180.