全文获取类型
收费全文 | 1535篇 |
免费 | 57篇 |
国内免费 | 5篇 |
专业分类
化学 | 1130篇 |
晶体学 | 9篇 |
力学 | 32篇 |
数学 | 164篇 |
物理学 | 262篇 |
出版年
2023年 | 13篇 |
2022年 | 70篇 |
2021年 | 69篇 |
2020年 | 44篇 |
2019年 | 54篇 |
2018年 | 36篇 |
2017年 | 32篇 |
2016年 | 57篇 |
2015年 | 52篇 |
2014年 | 77篇 |
2013年 | 101篇 |
2012年 | 125篇 |
2011年 | 143篇 |
2010年 | 78篇 |
2009年 | 76篇 |
2008年 | 89篇 |
2007年 | 84篇 |
2006年 | 82篇 |
2005年 | 47篇 |
2004年 | 47篇 |
2003年 | 34篇 |
2002年 | 28篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 16篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有1597条查询结果,搜索用时 15 毫秒
141.
142.
Nattascha Kyaw Rafael Fonseca de Mesquita Etel Kameda João Crisósthomo de Queiroz Neto Marta Antunes Pereira Langone Maria Alice Zarur Coelho 《Applied biochemistry and biotechnology》2010,161(1-8):171-180
Drilling fluid has many functions, such as carry cuttings from the hole permitting their separation at the surface, cool and clean the bit, reduce friction between the drill pipe and wellbore, maintain the stability of the wellbore, and prevent the inflow of fluids from the wellbore and form a thin, low-permeable filter cake. Filter cake removal is an important step concerning both production and injection in wells, mainly concerning horizontal completion. The drilling fluids are typically comprised of starch, the most important component of the filter cake. A common approach to remove this filter cake is the use of acid solutions. However, these are non-specific reactants. A possible alternative is the use of enzymatic preparations, like amylases, that are able to hydrolyze starch. Wells usually operate in drastic conditions for enzymatic preparations, such as high temperature, high salt concentration, and high pressure. Thus, the main objective of this work was to characterize four enzymatic preparations for filter cake removal under open hole conditions. The results showed that high salt concentrations (204,000 ppm NaCl) in completion fluid decreased amylolytic activity. All enzymatic preparations were able to catalyze starch hydrolysis at all temperatures tested (30, 65, 80, and 95 °C). An increase of amylolytic activity was observed with the increase of pressure (100, 500 and 1,000 psi) for one commercial amylase. 相似文献
143.
144.
This note deals with the extension of the bound-improving sequence idea to general discrete programming problems.Corresponding author. 相似文献
145.
Interaction of lectins withYersinia pestis strains 总被引:1,自引:0,他引:1
Maria S. M. Cavalcanti Alzira M. P. Almeida Luana C. B. B. Coelho 《Applied biochemistry and biotechnology》1990,26(2):125-131
The ability of lectins to interact with Yersinia pestis strains isolated from rodent fleas and human biological fluids, obtained from different geographic areas, was examined. Lectins of Canavalia ensiformis, Ulex europaeus, Phaseolus vulgaris, and Triticum vulgaris, as well as a new autochthonous lectin of Swartzia pickellii of undefined specificity, were used. Most of the Y. pestis strains did not agglutinate with U. europaeus or C. ensiformis lectin. However, P. vulgaris lectin agglutinated suspensions of all the bacillus strains used. Fifteen of the 19 strains tested positive for assays using S. pickellii lectin. It is believed this is the first report of Y. pestis strain agglutination by lectins. A similar agglutination pattern was obtained for lectins with specificity for oligosaccharides containing N-acetylglucosamine and S. pickellii lectin, which did bind to the affinity matrix chitin, a polysaccharide of N-acetylglucosamine. The use of bacterial strains and commercial lectins of defined specificity may be an approach to providing evidence about the lectin binding sites of undefined monosaccharide specificity. 相似文献
146.
We consider the Euler equations describing nonlinear waves on the free surface of a two-dimensional inviscid, irrotational
fluid layer of finite depth. For large surface tension, Bond number larger than 1/3, and Froude number close to 1, the system
possesses a one-parameter family of small-amplitude, traveling solitary wave solutions. We show that these solitary waves
are spectrally stable with respect to perturbations of finite wave-number. In particular, we exclude possible unstable eigenvalues
of the linearization at the soliton in the long-wavelength regime, corresponding to small frequency, and unstable eigenvalues
with finite but bounded frequency, arising from non-adiabatic interaction of the infinite-wavelength soliton with finite-wavelength
perturbations.
Received: 7 February 2001 / Accepted: 6 October 2001 相似文献
147.
This paper considers the inversion of experimental field data collected with light receiving systems designed to meet operational requirements. Such operational requirements include system deployment in free drifting configurations and a limited number of acoustic receivers. A well-known consequence of a reduced spatial coverage is a poor sampling of the vertical structure of the acoustic field, leading to a severe ill-conditioning of the inverse problem and data to model cost function with a massive sidelobe structure having many local extrema. This causes difficulties to meta-heuristic global search methods, such as genetic algorithms, to converge to the true model parameters. In order to cope with this difficulty, broadband high-resolution processors are proposed for their ability to significantly attenuate sidelobes, as a contribution for improving convergence. A comparative study on simulated data shows that high-resolution methods did not outperform the conventional Bartlett processor for pinpointing the true environmental parameter when using exhaustive search. However, when a meta-heuristic technique is applied for exploring a large multidimensional search space, high-resolution methods clearly improved convergence, therefore reducing the inherent uncertainty on the final estimate. These findings are supported by the results obtained on experimental field data obtained during the Maritime Rapid Environmental Assessment 2003 sea trial. 相似文献
148.
Mariana Alarcón‐Correa Dr. Tung‐Chun Lee Prof. Dr. Peer Fischer 《Angewandte Chemie (International ed. in English)》2015,54(23):6730-6734
Host–guest inclusion complexes are abundant in molecular systems and of fundamental importance in living organisms. Realizing a colloidal analogue of a molecular dynamic inclusion complex is challenging because inorganic nanoparticles (NPs) with a well‐defined cavity and portal are difficult to synthesize in high yield and with good structural fidelity. Herein, a generic strategy towards the fabrication of dynamic 1:1 inclusion complexes of metal nanoparticles inside oxide nanocups with high yield (>70 %) and regiospecificity (>90 %) by means of a reactive double Janus nanoparticle intermediate is reported. Experimental evidence confirms that the inclusion complexes are formed by a kinetically controlled mechanism involving a delicate interplay between bipolar galvanic corrosion and alloying–dealloying oxidation. Release of the NP guest from the nanocups can be efficiently triggered by an external stimulus. 相似文献
149.
Unraveling the Degradation Mechanism of Purine Nucleotides Photosensitized by Pterins: The Role of Charge‐Transfer Steps
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mariana P. Serrano Dr. Carolina Lorente Dr. Claudio D. Borsarelli Dr. Andrés H. Thomas 《Chemphyschem》2015,16(10):2244-2252
Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen (1O2) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O2 to proceed, therefore the reaction is classified as 1O2‐mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2′‐deoxyguanosine 5′‐monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring 1O2 photosensitizers, takes place through an electron‐transfer‐initiated process (type I mechanism), whereas the contribution of the 1O2‐mediated oxidation is almost negligible. 相似文献
150.