全文获取类型
收费全文 | 5025篇 |
免费 | 212篇 |
国内免费 | 52篇 |
专业分类
化学 | 3526篇 |
晶体学 | 36篇 |
力学 | 128篇 |
数学 | 921篇 |
物理学 | 678篇 |
出版年
2023年 | 50篇 |
2022年 | 99篇 |
2021年 | 137篇 |
2020年 | 121篇 |
2019年 | 94篇 |
2018年 | 92篇 |
2017年 | 83篇 |
2016年 | 186篇 |
2015年 | 185篇 |
2014年 | 208篇 |
2013年 | 368篇 |
2012年 | 345篇 |
2011年 | 435篇 |
2010年 | 290篇 |
2009年 | 231篇 |
2008年 | 328篇 |
2007年 | 330篇 |
2006年 | 260篇 |
2005年 | 241篇 |
2004年 | 218篇 |
2003年 | 159篇 |
2002年 | 163篇 |
2001年 | 72篇 |
2000年 | 47篇 |
1999年 | 52篇 |
1998年 | 30篇 |
1997年 | 45篇 |
1996年 | 50篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 11篇 |
1972年 | 9篇 |
排序方式: 共有5289条查询结果,搜索用时 0 毫秒
101.
Prof. Pavel Anzenbacher Jr. Dr. Yuanli Liu Dr. Manuel A. Palacios Dr. Tsuyoshi Minami Dr. Zhuo Wang Dr. Ryuhei Nishiyabu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8497-8506
As the demand for probes suitable for sensor development increases, investigation of approaches that utilize known successful receptors gains in general importance. This study describes a two‐prong approach that can be used as a guide to developing sensors from known receptors. First, the conversion of a simple receptor, calix[4]pyrrole, into a fluorescent probe to establish a ratiometric signal is described. Secondly, the sensors that employ an output from a single ratiometric calix[4]pyrrole probe are fabricated by using poly(ether‐urethane) hydrogel copolymers. These hydrogels are designed to absorb, internalize and transport aqueous electrolytes. A sensor array of ten different poly(ether‐urethane) matrices with varying comonomer proportions were doped with a single probe and were exposed to eight different anions: acetate, benzoate, fluoride, chloride, phosphate, pyrophosphate, hydrogen sulfide, and cyanide, eight urine samples and anti‐inflammatory drugs (NSAIDs). The poly(ether‐urethane) matrices comprise different proportions of anion‐binding urethane moieties and different hydrophilicity given by the ratio between ethylene glycol ether and butylene glycol ether. This diversity in the hydration behavior provides different environment polarity, in which the recognition and self‐assembly processes display enough diverse behavior to allow for unique response of the probe to the analytes. Furthermore, a single probe is shown to recognize eight different aqueous anions and eight urine samples when embedded in ten different polyurethanes in an array that displays 100 % classification accuracy. To demonstrate the potential of the concept for quantitative studies, an estimation of non‐steroidal anti‐inflammatory drugs ibuprofen and diclofenac in water and in saliva was performed. A limit of detection of 0.1 ppm and a dynamic range of 0.1–0.6 and 0.05–60 ppm was observed, respectively. Given the general difficulty of chemosensors to recognize aqueous anions, the fact that one probe recognizes eight different analytes attests to an enormous effect of the polymer environment on the recognition process. This method could be used to generate a variety of sensor arrays for various analyses including species that are difficult to recognize, such as small‐molecule‐ and inorganic anions. 相似文献
102.
Crispín Cristóbal Dr. Yohar A. Hernández Dr. Joaquín López‐Serrano Prof. Dr. Margarita Paneque Dr. Ana Petronilho Prof. Dr. Manuel L. Poveda Dr. Verónica Salazar Florencia Vattier Dr. Eleuterio Álvarez Dr. Celia Maya Prof. Dr. Ernesto Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):4003-4020
The reactivity of a series of iridium? pyridylidene complexes with the formula [TpMe2Ir(C6H5)2(C(CH)3C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H2, O2, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e? unsaturated [TpMe2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H2 is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO2, and H2C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH2CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH2)N moiety. C6H5(C?O)H and C6H5C?CH react with formation of Ir? C6H5 and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O2 is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported. 相似文献
103.
Dipl.‐Chem. Christian Pett M. Sc. Manuel Schorlemer Dr. Ulrika Westerlind 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):17001-17010
By displaying different O‐glycans in a multivalent mode, mucin and mucin‐like glycoproteins are involved in a plethora of protein binding events. The understanding of the roles of the glycans and the identification of potential glycan binding proteins are major challenges. To enable future binding studies of mucin glycan and glycopeptide probes, a method that gives flexible and efficient access to all common mucin core‐glycosylated amino acids was developed. Based on a convergent synthesis strategy starting from a shared early stage intermediate by differentiation in the glycoside acceptor reactivity, a common disaccharide building block allows for the creation of extended glycosylated amino acids carrying the mucin type‐2 cores 1–4 saccharides. Formation of a phenyl‐sulfenyl‐N‐Troc (Troc=trichloroethoxycarbonyl) byproduct during N‐iodosuccinimide‐promoted thioglycoside couplings was further characterized and a new methodology for the removal of the Troc group is described. The obtained glycosylated 9‐fluorenylmethoxycarbonyl (Fmoc)‐protected amino acid building blocks are incorporated into peptides for multivalent glycan display. 相似文献
104.
105.
106.
Robert Lassfolk Manuel Pedrón Prof. Tomás Tejero Prof. Pedro Merino Johan Wärnå Prof. Reko Leino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(34):e202200499
Acyl group migration affects the synthesis, isolation, manipulation and purification of all acylated organic compounds containing free hydroxyl groups, in particular carbohydrates. While several isolated studies on the migration phenomenon in different buffers have been reported, comprehensive insights into the overall migration process in different monosaccharides under similar conditions have been lacking. Here, we have studied the acyl migration in different monosaccharides using five different acyl groups by a combination of experimental, kinetic and theoretical tools. The results show that the anomeric configuration in the monosaccharide has a major influence on the migration rate, together with the relative configurations of the other hydroxyl groups and the nature of the migrating acyl group. Full mechanistic model, based on computations, demonstrates that the acyl migration proceeds through an anionic stepwise mechanism with linear dependence on the [OH−] and the pKa of the hydroxyl group toward which the acyl group is migrating. 相似文献
107.
An analysis of the effects induced by F, Cl, and Br-substituents at the α-position of both, the hydroxyl or the amino group for a series of amino-alcohols, HOCH2(CH2)nCH2NH2 (n = 0–5) on the strength and characteristics of their OH···N or NH···O intramolecular hydrogen bonds (IMHBs) was carried out through the use of high-level G4 ab initio calculations. For the parent unsubstituted amino-alcohols, it is found that the strength of the OH···N IMHB goes through a maximum for n = 2, as revealed by the use of appropriate isodesmic reactions, natural bond orbital (NBO) analysis and atoms in molecules (AIM), and non-covalent interaction (NCI) procedures. The corresponding infrared (IR) spectra also reflect the same trends. When the α-position to the hydroxyl group is substituted by halogen atoms, the OH···N IMHB significantly reinforces following the trend H < F < Cl < Br. Conversely, when the substitution takes place at the α-position with respect to the amino group, the result is a weakening of the OH···N IMHB. A totally different scenario is found when the amino-alcohols HOCH2(CH2)nCH2NH2 (n = 0–3) interact with BeF2. Although the presence of the beryllium derivative dramatically increases the strength of the IMHBs, the possibility for the beryllium atom to interact simultaneously with the O and the N atoms of the amino-alcohol leads to the global minimum of the potential energy surface, with the result that the IMHBs are replaced by two beryllium bonds. 相似文献
108.
Tsai I-Ting M. Merced Montero-Campillo Ibon Alkorta Jos Elguero Manuel Yez 《Molecules (Basel, Switzerland)》2021,26(11)
Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In ortho-substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ·mol−1 are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene. Conformers stabilized by a beryllium bond exhibit the typical features of this non-covalent interaction, such as the presence of a bond critical point according to the topology of the electron density, positive Laplacian values, significant geometrical distortions and strong interaction energies between the donor and acceptor quantified by using the Natural Bond Orbital approach. An isodesmic reaction scheme is used as a tool to measure the strength of the beryllium bond in these systems in terms of isodesmic energies (analogous to binding energies), interaction energies and deformation energies. This approach shows that a huge amount of energy is spent on deforming the donor–acceptor pairs to form the new rings. 相似文献
109.
Manuel Jesús Chan-Bacab María Manuela Reyes-Estebanez Juan Carlos Camacho-Chab Benjamín Otto Ortega-Morales 《Molecules (Basel, Switzerland)》2021,26(5)
Trypanosomatids are the causative agents of leishmaniasis and trypanosomiasis, which affect about 20 million people in the world’s poorest countries, leading to 95,000 deaths per year. They are often associated with malnutrition, weak immune systems, low quality housing, and population migration. They are generally recognized as neglected tropical diseases. New drugs against these parasitic protozoa are urgently needed to counteract drug resistance, toxicity, and the high cost of commercially available drugs. Microbial bioprospecting for new molecules may play a crucial role in developing a new generation of antiparasitic drugs. This article reviews the current state of the available literature on chemically defined metabolites of microbial origin that have demonstrated antitrypanosomatid activity. In this review, bacterial and fungal metabolites are presented; they originate from a range of microorganisms, including cyanobacteria, heterotrophic bacteria, and filamentous fungi. We hope to provide a useful overview for future research to identify hits that may become the lead compounds needed to accelerate the discovery of new drugs against trypanosomatids. 相似文献
110.
Manuel Chacn-Fuentes Leonardo Bardehle Ivette Seguel Fernanda Rubilar Daniel Martínez-Cisterna Andrs Quiroz 《Molecules (Basel, Switzerland)》2021,26(7)
In terms of the domestication process in murtilla, studies have found changes in the concentration of phenolic compounds, with reduction of chemical defense of plants, depending on the change in the feeding behavior of insects. Thus, we hypothesized that the domestication of Ugni molinae decreases the content of phenolic compounds and modifies the feeding preference of Chilesia rudis larvae. Leaves of three parental ecotypes and four cultivated ecotypes were used in preference experiments to evaluate the mass gain and leaves consumption of larvae. Phenolic extracts from leaves of U. molinae were analyzed by HPLC. Identified compounds were incorporated in an artificial diet to assess their effect on mass gain, consumption, and survival of the larvae. The presence of phenolic compounds in bodies and feces was also evaluated. In terms of choice assays, larvae preferred parental ecotypes. Regarding compounds, vanillin was the most varied between the ecotypes in leaves. However, plant domestication did not show a reduction in phenolic compound concentration of the ecotypes studied. Furthermore, there was no clear relation between phenolic compounds and the performance of C. rudis larvae. Whether this was because of sequestration of some compounds by larvae is unknown. Finally, results of this study could also suggest that studied phenolic compounds have no role in the C. rudis larvae resistance in this stage of murtilla domestication process. 相似文献