全文获取类型
收费全文 | 1167篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 749篇 |
晶体学 | 33篇 |
力学 | 38篇 |
数学 | 87篇 |
物理学 | 290篇 |
出版年
2023年 | 7篇 |
2022年 | 29篇 |
2021年 | 28篇 |
2020年 | 21篇 |
2019年 | 38篇 |
2018年 | 31篇 |
2017年 | 34篇 |
2016年 | 31篇 |
2015年 | 29篇 |
2014年 | 48篇 |
2013年 | 64篇 |
2012年 | 65篇 |
2011年 | 64篇 |
2010年 | 54篇 |
2009年 | 51篇 |
2008年 | 44篇 |
2007年 | 41篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1967年 | 5篇 |
排序方式: 共有1197条查询结果,搜索用时 15 毫秒
191.
Zaheer Ahmad Itrat Fatima Sajid Mehmood Rehana Ifzal Abdul Malik Nighat Afza 《Helvetica chimica acta》2008,91(1):73-78
Three new 20,24‐epoxydammarane triterpenes, santolins A–C ( 1 – 3 ), were isolated from the AcOEt‐soluble fraction of the MeOH extract of Salvia santolinifolia (whole plant). Their structures were assigned based on 1H‐NMR, 13C‐NMR (DEPT), and 2D‐NMR analyses, in combination with HR‐MS experiments and comparison with literature data of related compounds. 相似文献
192.
Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ~200 and ~500 Hz in an undoped and a doped sample, respectively. 相似文献
193.
Rathinasamy Sakthivel Kaviarasan Boomipalagan MA Yong‐Ki Malik Muslim 《Complexity》2016,21(Z2):518-529
In this article, based on sampled‐data approach, a new robust state feedback reliable controller design for a class of Takagi–Sugeno fuzzy systems is presented. Different from the existing fault models for reliable controller, a novel generalized actuator fault model is proposed. In particular, the implemented fault model consists of both linear and nonlinear components. Consequently, by employing input‐delay approach, the sampled‐data system is equivalently transformed into a continuous‐time system with a variable time delay. The main objective is to design a suitable reliable sampled‐data state feedback controller guaranteeing the asymptotic stability of the resulting closed‐loop fuzzy system. For this purpose, using Lyapunov stability theory together with Wirtinger‐based double integral inequality, some new delay‐dependent stabilization conditions in terms of linear matrix inequalities are established to determine the underlying system's stability and to achieve the desired control performance. Finally, to show the advantages and effectiveness of the developed control method, numerical simulations are carried out on two practical models. © 2016 Wiley Periodicals, Inc. Complexity 21: 518–529, 2016 相似文献
194.
Basic Ionic Liquid Promoted Domino Knoevenagel–Thia‐Michael Reaction: An Efficient and Multicomponent Strategy for Synthesis of 1,3‐Thiazines 下载免费PDF全文
I. R. Siddiqui Rahila Shayna Shamim Pragati Rai Shireen Malik A. Waseem Arjita Srivastava Anjali Srivastava 《Journal of heterocyclic chemistry》2016,53(4):1284-1291
An efficient, three‐component strategy for synthesis of 1,3‐thiazines with high atom economy in one‐pot mediated by room temperature basic ionic liquid is described here. The strategy involves basic ionic liquid, [bmim]OH‐catalyzed Knoevenagel condensation between ethyl cyanoacetate and aromatic aldehyde and subsequent thia‐Michael addition with substituted thioureas. The reaction sequence is smooth and quantitative under ambient temperature. [bmim]OH was recovered and reused four times without any appreciable decrease in its reactivity and product yield. 相似文献
195.
Low molecular weight gelators have recently been used as a template to construct novel kind of composite materials of different shape or structures such as helix, fibers, tape or tube through the electrostatic interaction between gelators and the intermediate molecules. In this article, we intricately apply the non-electrostatic interaction between gelator and fluorescent molecules to fabricate the gel fibers. To achieve our goal, we have intentionally designed pyridine containing cholesterol-based gelators 1-3 by keeping one thing in our mind that during the formation of the stacking column the pyridine moieties will be arranged like a spiral staircase around the cholesterol column. The gelation properties of these three gelators are tested in different solvents including sublimable solvents like naphthalene and the gelator 1 has emerged as a ‘supergelator’. The morphologies strongly depend on the process of solvent removal from the gel state and the stabilities of gel have been tuned by the added metal ions like Ag(I) by using metal-ligand interaction. Lastly, we have decorated the gel fibers obtained from gelator 1 with fluorescent molecules like tetraphenyl porphyrin Zn(II) [4·H and 4·Zn] having photopolymerizable unit at the end of tether groups and the modified fibers are well characterized by UV-vis absorption spectroscopy, confocal laser scanning microscopy as well as transmission electron microscopy. This is a novel example of decoration of gel fibers with fluorescent molecules and the process will offer an alternate application in photochemical and electrochemical devices. 相似文献
196.
Antioxidant and Anti-Inflammatory Effects of Peganum harmala Extracts: An In Vitro and In Vivo Study
Malik Waseem Abbas Mazhar Hussain Muhammad Qamar Sajed Ali Zahid Shafiq Polrat Wilairatana Mohammad S. Mubarak 《Molecules (Basel, Switzerland)》2021,26(19)
Peganum harmala (P. harmala) belongs to the family Zygophyllaceae, and is utilized in the traditional medicinal systems of Pakistan, China, Morocco, Algeria, and Spain to treat several chronic health disorders. The aim of the present study was to identify the chemical constituents and to evaluate the antioxidant, anti-inflammatory, and toxicity effects of P. harmala extracts both in vitro and in vivo. Sequential crude extracts including 100% dichloromethane, 100% methanol, and 70% aqueous methanol were obtained and their antioxidant and anti-inflammatory effects evaluated both in vitro and in vivo. The anti-inflammatory effect of the extract was investigated using the carrageenan-induced paw edema method in mice, whereas the toxicity of the most active extract was evaluated using an acute and subacute toxicity rat model. In addition, we have used the bioassay-guided approach to obtain potent fractions, using solvent–solvent partitioning and reversed phase high performance liquid chromatography from active crude extracts; identification and quantification of compounds from the active fractions was achieved using electrospray ionization mass spectrometry and high performance liquid chromatography techniques. Results revealed that the 100% methanol extract of P. harmala exhibits significant in vitro antioxidant activity in DPPH assay with an IC50 of 49 µg/mL as compared to the standard quercetin with an IC50 of 25.4 µg/mL. The same extract exhibited 63.0% inhibition against serum albumin denaturation as compared to 97% inhibition by the standard diclofenac sodium in an in vitro anti-inflammatory assay, and in vivo anti-inflammatory against carrageenan-induced paw edema (75.14% inhibition) as compared to 86.1% inhibition caused by the standard indomethacin. Furthermore, this extract was not toxic during a 14 day trial of acute toxicity when given at a dose of 3 g/kg, indicating that the lethal dose (LD50) of P. harmala methanol extract was greater than 3 g/kg. P. harmala methanolic fraction 2 obtained using bioassay-guided fractionation showed the presence of quinic acid, peganine, harmol, harmaline, and harmine, confirmed by electrospray ionization mass spectrometry and quantified using external standards on high performance liquid chromatography. Taken all together, the current investigation further confirms the antioxidant, anti-inflammatory, and safety aspects of P. harmala, which justifies its use in folk medicine. 相似文献
197.
When examined by fluorescence microscopy, tumor cells loaded with a zinc benzochlorin iminium salt showed a very faint deep-red fluorescence that was rapidly transformed to a substantially brighter red-orange fluorescence. Fourier transfer spectroscopy analysis with a red-sensitive detection system revealed that an initial fluorescence at 770 nm was gradually converted to 640 nm fluorescence during excitation. Image analysis showed that photoproduct formation was accompanied by a change in the site of drug localization from the cytoplasm to the nucleus. These studies illustrate the power of interferometry for the characterization of photoproducts and changes in sensitizer localization during photoproduct formation. 相似文献
198.
Charles M. Marson Jon Campbell Michael B. Hursthouse K. M. Abdul Malik 《Angewandte Chemie (International ed. in English)》1998,37(8):1122-1124
Ring contraction of a 3,4-epoxyalcohol, then lactolization and electrophilic attack are the steps in the domino cyclization protocol for the formation of 8-oxabicyclo[3.2.1]octane systems [Eq. (a)]. 相似文献
199.
Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well. 相似文献
200.
R. P. Malik 《The European Physical Journal C - Particles and Fields》2009,60(3):457-470
We derive the off-shell nilpotent Becchi–Rouet–Stora–Tyutin (BRST) and anti-BRST symmetry transformations for all the fields of a free Abelian 2-form gauge theory by exploiting the geometrical superfield approach to the BRST formalism.
The above four (3+1)-dimensional (4D) theory is considered on a (4, 2)-dimensional supermanifold parameterized by the four
even spacetime variables x
μ
(with μ=0,1,2,3) and a pair of odd Grassmannian variables θ and
(with
). One of the salient features of our present investigation is that the above nilpotent (anti-) BRST symmetry transformations
turn out to be absolutely anticommuting due to the presence of a Curci–Ferrari (CF) type of restriction. The latter condition emerges due to the application
of our present superfield formalism. The actual CF condition, as is well known, is the hallmark of a 4D non-Abelian 1-form
gauge theory. We demonstrate that our present 4D Abelian 2-form gauge theory imbibes some of the key signatures of the 4D
non-Abelian 1-form gauge theory. We briefly comment on the generalization of our superfield approach to the case of Abelian
3-form gauge theory in four, (3+1), dimensions of spacetime. 相似文献