全文获取类型
收费全文 | 1151篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
化学 | 936篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 152篇 |
物理学 | 94篇 |
出版年
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 43篇 |
2020年 | 36篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 38篇 |
2015年 | 30篇 |
2014年 | 35篇 |
2013年 | 63篇 |
2012年 | 70篇 |
2011年 | 93篇 |
2010年 | 55篇 |
2009年 | 54篇 |
2008年 | 67篇 |
2007年 | 88篇 |
2006年 | 66篇 |
2005年 | 88篇 |
2004年 | 51篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1194条查询结果,搜索用时 187 毫秒
131.
Ferraz RC Fontana CR Ribeiro AP Trindade FZ Bartoloni FH Baader JW Lins EC Bagnato VS Kurachi C 《Journal of photochemistry and photobiology. B, Biology》2011,103(2):87-92
The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem? concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm2 level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources. 相似文献
132.
Boga C Forlani L Calienni R Hindley T Hochkoeppler A Tozzi S Zanna N 《Natural product research》2011,25(4):417-421
A decoction of Capparis spinosa L. roots, widely used in the traditional folk medicine of southern Italy, was prepared and submitted to antibacterial activity tests, which showed an interesting bacteriostatic activity on the growth of Deinococcus radiophilus. Heterocyclic compounds were also recovered from the chloroformic extract of the roots. 相似文献
133.
Here, we describe a rapid and efficient screening method using surface plasmon resonance (SPR) and saturation transfer difference–nuclear
magnetic resonance (STD-NMR) spectroscopy to yield information regarding the residues involved in nucleotide binding to amino
acid-coated supports. The aim of this work was to explore the use of these spectroscopic techniques to study amino acid–nucleotide
interactions in order to improve the binding specificity of the amino acid ligands used to purify plasmid DNA. For SPR, we
present a strategy that immobilizes arginine and lysine on a surface as model supports, and we analyze binding responses when
synthetic homo-deoxyoligonucleotides are injected over the amino acid surface. The binding responses are detectable and reproducible
despite the small size of the immobilized amino acids. Using STD-NMR, we performed epitope mapping of homo-deoxyoligonucleotides
bound to l-arginine–bisoxyran–Sepharose and l-lysine–Sepharose supports. Polynucleotide binding preferences differed; for example, polyC interacted preferentially through
its backbone with the two supports, whereas polyT bound the supports through its thymine moiety. STD-NMR combined with SPR
measurements was successfully used to screen amino acid–nucleotide interactions and determine the binding affinities of the
complexes. 相似文献
134.
Bechstein K Michels J Vogt J Schwartze GC Vogt C 《Analytical and bioanalytical chemistry》2011,399(1):501-508
Previous studies have revealed silica formation in the teeth of mandibular gnathobases of copepods while significant amounts
of zinc and copper are present, which might improve mechanical stability of the teeth and represent an adaptation to compact
food particles. The present study aimed at analysing the distribution and concentration of trace elements in the mandibular
gnathobases of females of the Antarctic copepod species Calanoides acutus. Because of the low overall masses of few micrograms per specimen the application of a combination of position-resolved micro-beam
techniques was necessary and micro-particle-induced X-ray emission spectrometry and laser ablation inductively coupled plasma
mass spectrometry were used to determine Ba, Br, Ca, Cl, Cu, Fe, K, Mg, Na, Ni, P, S, Si and Zn in the samples with μm to
sub-μm resolution. Calibration strategies were optimised to fit for the carbonate matrix. The analyses revealed a distinct
enrichment of Br, Ca, Fe, K, S, Si and Zn in the teeth of the gnathobases. 相似文献
135.
Staphylococcal enterotoxin A (SEA) is an exotoxin excreted mainly by Staphylococcus aureus and nowadays is the most prevalent compound in staphylococcal food poisoning worldwide. SEA is highly heat-resistant, and usual cooking times and temperatures are unlikely to completely inactivate it. A procedure for extraction of this toxin based on protein precipitation with a mixture of dichloromethane and acidified water was used before SDS-PAGE separation of soluble proteins. Finally, bands of interest were excised from the gel and in-gel enzymatic digestion was done. SEA from pasteurized milk was detected with matrix-assisted laser-desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. Nineteen peptides (range 800-2400 Da) were identified as products of trypsin cleavage of the SEA standard with a score of 204 and 73% coverage of the protein sequence, whereas thirteen peptides were revealed for SEA extracted from milk with a score of 148 and 58% sequence coverage obtained. This procedure has been applied successfully for identification of SEA in milk. 相似文献
136.
Operations with tensors, or multiway arrays, have become increasingly prevalent in recent years. Traditionally, tensors are represented or decomposed as a sum of rank-1 outer products using either the CANDECOMP/PARAFAC (CP) or the Tucker models, or some variation thereof. Such decompositions are motivated by specific applications where the goal is to find an approximate such representation for a given multiway array. The specifics of the approximate representation (such as how many terms to use in the sum, orthogonality constraints, etc.) depend on the application.In this paper, we explore an alternate representation of tensors which shows promise with respect to the tensor approximation problem. Reminiscent of matrix factorizations, we present a new factorization of a tensor as a product of tensors. To derive the new factorization, we define a closed multiplication operation between tensors. A major motivation for considering this new type of tensor multiplication is to devise new types of factorizations for tensors which can then be used in applications.Specifically, this new multiplication allows us to introduce concepts such as tensor transpose, inverse, and identity, which lead to the notion of an orthogonal tensor. The multiplication also gives rise to a linear operator, and the null space of the resulting operator is identified. We extend the concept of outer products of vectors to outer products of matrices. All derivations are presented for third-order tensors. However, they can be easily extended to the order-p(p>3) case. We conclude with an application in image deblurring. 相似文献
137.
The epitope mapping of nucleotides bound to three chromatography supports is accomplished using saturation transfer difference (STD)-NMR spectroscopy. This experiment involves subtracting a spectrum in which the support was selectively saturated from one recorded without support saturation. In the difference spectrum only the signals of the ligands that bind to the support and received saturation transfer remain. The nucleotide protons in closer contact with the support have more intense signals due to a more efficient transfer of saturation. We investigate the effects on the binding to the nucleotides by the introduction of a spacer arm between l-histidine and Sepharose. Our NMR experiments evidence a clear contribution of the spacer to the interaction with all the nucleotides, increasing the mobility of the amino acid and giving different STD responses. This enhanced mobility originates the reinforcement of the interactions with the sugar moiety and phosphate group of 5'-CMP and 5'-TMP or the base of 5'-GMP and 5'-UMP. Hence, with this study we show that by using STD NMR technique on chromatographic systems it is possible to provide a fast, robust and efficient way of screening the atoms involved in the binding to the supports. 相似文献
138.
Adenosine monophosphate isomers are obtained by self-assembling of adenine, D-ribose and trimetaphosphate in aqueous solution in good yields. This generation of a ribonucleotide from its three molecular components occurs in a one-pot reaction at room temperature for about 30-40 days and with high chemio-, regio-, and stereo-selectivity. Similar results are obtained with guanine. A mechanism is also proposed. 相似文献
139.
Mascaros PA Bazzicalupi C Bianchi A Giorgi C Valero MD Garzón RL Salido ML Valtancoli B 《Chemical communications (Cambridge, England)》2011,47(10):2814-2816
The synergistic action of the different binding groups of the polyfunctional HL receptor leads to the recognition of ADP over ATP in water, with a selectivity coefficient of up to 116, a phenomenon which is unprecedented in the context of synthetic receptors in water. The recognition is mostly due to the good matching between H(3)L(2+) and the protonated forms of ADP. 相似文献
140.
R. A. G. Silva A. T. Adorno A. G. Magdalena T. M. Carvalho M. Stipcich A. Cuniberti M. L. Castro 《Journal of Thermal Analysis and Calorimetry》2011,103(2):459-463
In this study the effect of Ag additions on the thermal behavior of the Cu–22.55 at.%Al alloy was studied using electrical
resistivity measurements, in situ X-ray diffractometry, differential scanning calorimetry, and optical microscopy. The results
indicated that Ag additions do not change the phase transformations sequence in the studied alloys, but modify its critical
temperatures due to a change on entropy of system. It was verified that at the cooling rate of 10 K/min the decomposition
of β phase into (α + γ1) is incomplete, but for lower cooling rates than 1.0 K/min this reaction is completed. 相似文献