全文获取类型
收费全文 | 1618篇 |
免费 | 84篇 |
国内免费 | 10篇 |
专业分类
化学 | 956篇 |
晶体学 | 5篇 |
力学 | 84篇 |
综合类 | 1篇 |
数学 | 372篇 |
物理学 | 294篇 |
出版年
2023年 | 8篇 |
2022年 | 6篇 |
2021年 | 19篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 28篇 |
2017年 | 21篇 |
2016年 | 56篇 |
2015年 | 54篇 |
2014年 | 51篇 |
2013年 | 100篇 |
2012年 | 98篇 |
2011年 | 112篇 |
2010年 | 78篇 |
2009年 | 77篇 |
2008年 | 93篇 |
2007年 | 108篇 |
2006年 | 94篇 |
2005年 | 89篇 |
2004年 | 86篇 |
2003年 | 81篇 |
2002年 | 49篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 16篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 12篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有1712条查询结果,搜索用时 15 毫秒
21.
To allow for a reliable examination of the interaction between velocity fluctuations, acoustics and combustion, a novel numerical procedure is discussed in which a spectral solution of the Navier–Stokes equations is directly associated to a high-order finite difference fully compressible DNS solver (sixth order PADE). Using this combination of high-order solvers with accurate boundary conditions, simulations have been performed where a turbulent premixed V-shape flame develops in grid turbulence. In the light of the DNS results, a sub-model for premixed turbulent combustion is analyzed. To cite this article: R. Hauguel et al., C. R. Mecanique 333 (2005). 相似文献
22.
David Torréns-Martín Lucía Fernández-Carrasco María Teresa Blanco-Varela 《Journal of Thermal Analysis and Calorimetry》2013,114(2):799-807
Different binders of Portland cement, calcium aluminate cement and calcium sulphate (PC/CAC/C $ {\bar{\text{S}}} $ ) have been investigated to determinate the influence the CAC and C $ {\bar{\text{S}}} $ amount in the reactions mechanism. Several mixtures were studied, ratios of 100, 85/15 and 75/25 of PC/CAC with 0, 3 and 5 % of C $ {\bar{\text{S}}} $ . Conduction calorimetric technique was used to follow the hydration during 100 h. The XRD and FTIR techniques were used as support in the analysis of the hydration products. The results have shown that the studied ternary systems form an extra amount of ettringite, and changes in the reactions mechanism with respect to a PC. The reactions mechanism depends on the CAC and C $ {\bar{\text{S}}} $ amount present in the different binders. 相似文献
23.
Dr. Sylvain Achelle Dr. Jean‐Pierre Malval Dr. Stéphane Aloïse Dr. Alberto Barsella Dr. Arnaud Spangenberg Dr. Loic Mager Dr. Huriye Akdas‐Kilig Dr. Jean‐Luc Fillaut Prof. Bertrand Caro Prof. Françoise Robin‐le Guen 《Chemphyschem》2013,14(12):2725-2736
The nonlinear properties and the photophysical behavior of two π‐conjugated chromophores that incorporate an electron‐deficient pyrimidine core (A) and γ‐methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes’ scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end‐groups. This latter structural parameter also has a strong influence on the excited‐state dynamics, which leads to a very efficient fluorescence quenching. 相似文献
24.
Yannick Vercammen Jaymes Van Luppen Christiaan Van Roost Roel De Mondt Frank Vangaever Luc Van Vaeck 《Analytical and bioanalytical chemistry》2013,405(6):2053-2064
Molecular depth profiling is needed to develop high-tech materials optimised to the μm or even up to the nm scale. Recent progress in time-of-flight static secondary ion mass spectrometry (ToF-S-SIMS) offers perspectives to molecular depth profiling. However, at this moment, the methodology is not yet capable to deal with a range of materials science applications because of the limited depth range, the loss of intensity in the subsurface and the loss of depth resolution at large distances from the original surface. Therefore, the purpose of this paper is to develop a complementary approach for the molecular 3D analysis at large depth, using a combination of ultra-low angle microtomy (ULAM) and surface analysis of the sectioned material with ToF-S-SIMS. Single inkjet dots with a diameter of 100 μm and height of 22 μm on a PET substrate have been used as a test system for the methodology. It is demonstrated that the use of a diamond knife allows the molecular composition and distribution of components within the microscopic feature to be probed with a lateral resolution of 300 nm. Hence the methodology approaches the physical limit for ion imaging of organic components with local concentrations in the % range. In practice, the achievable depth resolution with ULAM-S-SIMS is ultimately limited by the surface roughness of the section. Careful optimisation of the ULAM step has resulted in a surface roughness within 6 nm (R a value) at a depth of 21 μm. This offers perspective to achieve 3D analysis with a depth resolution as good as 18 nm at such a large distance from the surface. Furthermore, the ULAM-S-SIMS approach is applicable to materials unamenable to ion beam erosion. However, the method is limited to dealing with, for instance, Si or glass substrates that cannot be sectioned with a microtomy knife. Furthermore, sufficient adhesion between stacked layers or between the coating and substrate is required. However, it is found that the approach is applicable to a wide variety of industrially important (multi)layers of polymers on a polymer substrate. 相似文献
25.
Marcela S. O. Wanderley Carla Oliveira Danyelly Bruneska Lucília Domingues José L. Lima Filho José A. Teixeira Solange I. Mussatto 《Chemical Papers》2013,67(7):682-687
Frutalin, a galactose-specific lectin used to detect specific tumour markers, is a protein with low expression level in breadfruit. In the present study, fed-batch fermentation in a stirred tank bioreactor was used as a strategy to enhance protein production by a recombinant Pichia pastoris KM71H. By using this process, the production of recombinant frutalin was 4-fold higher than the value obtained in shaker flasks batch assays. Supplementation of the fermentation medium with trace elements (Pichia trace minerals, PTM) was also evaluated in order to stimulate production of the recombinant protein. The addition of PTM to the minimum medium afforded a recombinant protein production of 13.4 mg L?1, which was 2.5-fold higher than that achieved from the culture medium without PTM supplementation. These results are significant as the development of strategies to improve the production of recombinant frutalin may broaden its application in cancer diagnosis. 相似文献
26.
Dr. Rebeca Arevalo Dr. Ramón López Prof. Larry R. Falvello Dr. Lucía Riera Dr. Julio Perez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):379-389
The reactions of [Re(N-N)(CO)3(PMe3)]OTf (N-N=2,2′-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt3 have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt3 reacted with [Re(bipy)(CO)3(PMe3)]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral ReI products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to ReI complexes containing bipy- and phen-derived chelates with several C(sp3) centers. 相似文献
27.
28.
29.
Dr. György Szalóki Prof. Jean‐Luc Pozzo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11124-11132
Diarylethenes possess unique structural properties, which enabled them to find widespread applications in the field of photochromism. Nowadays, bisthienylcyclopentenes (BTCs) present the most popular subfamily of these compounds, which are widely used as P‐type chromophores. This minireview summarises the main strategies for the synthesis of symmetrical and nonsymmetrical BTCs. In addition, attention is drawn to desymmetrisations achieved by monosubstitutions, which is not frequently utilised, although it can be highly advantageous. This is supported with some of the authors’ latest results. 相似文献
30.