全文获取类型
| 收费全文 | 1657篇 |
| 免费 | 52篇 |
| 国内免费 | 15篇 |
专业分类
| 化学 | 1028篇 |
| 晶体学 | 27篇 |
| 力学 | 66篇 |
| 数学 | 243篇 |
| 物理学 | 360篇 |
出版年
| 2024年 | 13篇 |
| 2023年 | 20篇 |
| 2022年 | 51篇 |
| 2021年 | 49篇 |
| 2020年 | 51篇 |
| 2019年 | 56篇 |
| 2018年 | 55篇 |
| 2017年 | 56篇 |
| 2016年 | 78篇 |
| 2015年 | 57篇 |
| 2014年 | 70篇 |
| 2013年 | 161篇 |
| 2012年 | 104篇 |
| 2011年 | 138篇 |
| 2010年 | 82篇 |
| 2009年 | 88篇 |
| 2008年 | 98篇 |
| 2007年 | 100篇 |
| 2006年 | 68篇 |
| 2005年 | 57篇 |
| 2004年 | 47篇 |
| 2003年 | 42篇 |
| 2002年 | 33篇 |
| 2001年 | 11篇 |
| 2000年 | 14篇 |
| 1999年 | 5篇 |
| 1998年 | 10篇 |
| 1997年 | 6篇 |
| 1996年 | 11篇 |
| 1995年 | 3篇 |
| 1994年 | 3篇 |
| 1993年 | 9篇 |
| 1992年 | 10篇 |
| 1990年 | 4篇 |
| 1989年 | 3篇 |
| 1988年 | 3篇 |
| 1987年 | 6篇 |
| 1986年 | 4篇 |
| 1985年 | 5篇 |
| 1984年 | 10篇 |
| 1983年 | 3篇 |
| 1981年 | 4篇 |
| 1980年 | 5篇 |
| 1979年 | 3篇 |
| 1977年 | 2篇 |
| 1975年 | 5篇 |
| 1974年 | 3篇 |
| 1970年 | 1篇 |
| 1967年 | 1篇 |
| 1936年 | 1篇 |
排序方式： 共有1724条查询结果，搜索用时 15 毫秒
941.
H. Dilara Kiliç Seda Deveci Koray B. Dönmez Ebru Çetinkaya Sevinç Karadağ Mustafa Doğu 《International journal of environmental analytical chemistry》2018,98(4):308-322
Determination of copper (Cu), zinc (Zn) and manganese (Mn) micronutrients in soil samples have been studied for an efficient fertiliser application. Plant-available micronutrients of soils were extracted with DTPA extraction procedure, then differential pulse stripping voltammetry (DPSV) and square wave stripping voltammetry (SWSV) methods were performed with inexpensive and disposable pencil graphite electrode for determination of Cu(II), Zn(II) and Mn(II). Parameters such as deposition potential, deposition time, pH and concentration of the supporting electrolyte were optimised for these ions. Under optimised conditions, the limits of detection were found as 0.01 mg L?1 for Cu(II) and 0.02 mg L?1 for Zn(II) and 0.25 mg L?1 for Mn(II). Relative standard deviation (%RSD) was 6.80, 8.86 and 3.29 for Cu(II), Zn(II) and Mn(II), respectively. The experimental study was conducted using a flame atomic absorption spectroscopy. The described stripping voltammetry methods were successfully applied for the determination of Mn(II), Cu(II) and Zn(II) in soil samples. 相似文献
942.
Mustafa Soylak Zeliha Erbas 《International journal of environmental analytical chemistry》2018,98(9):799-810
A novel vortex-assisted magnetic solid phase extraction method followed by flame atomic absorption spectrometry was improved to separate, preconcentrate and determine the lead, copper and cadmium ions by using 1-Nitro-2-naphthol-3, 6-disulfonic acid disodium salt (Nitroso-R salt) impregnated magnetic Ambersorb-563 resin. The adsorbent was characterised by Fourier transform infrared spectra, BET surface analyser and scanning electron microscopy. The influences of various analytical parameters, such as pH value, type and volume of the eluent, sample volume, were optimised and the effects of potentially interfering ions were investigated. The analyte ions were quantitatively recovered at pH 7.0 on magnetic adsorbent and desorbed with a 2.0 M HNO3 in 10% acetone as eluent. The detection limits were 1.4, 5.8 and 1.5 ng mL?1 for Cd(II), Cu(II) and Pb(II), respectively. The method has been validated with analytically by the analysis certified reference materials and standard additions prior to application to determine metal ions in water samples. 相似文献
943.
Pencil graphite electrode (PGE) modified with MWCNT and Bi3+ (MWCNT/Bi/PGE) was utilized in simultaneous analysis of Pb2+, Cd2+, and Zn2+. Surface and electrochemical characteristics of MWCNT/Bi/PGE were investigated via SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and FTIR measurements. Even though modification with MWCNT did not improve the electroactive surface area, it significantly decreased the charge transfer resistance. Furthermore, modification with Bi3+ significantly increased the sensitivity. Finally, MWCNT/Bi/PGE exhibited the highest sensitivity and reproducibility compared to PGE and PGE modified with only MWCNT. MWCNT/Bi/PGE provided LOD values of 0.27, 0.43, and 1.63 μg L−1, and linear ranges of 1–80, 5–80, and 10–80 μg L−1 for Pb2+, Cd2+, and Zn2+, respectively. Proposed modification method offers effective electroanalytical performance with low time consumption and cost for the analyst. 相似文献
944.
Experimental studies on heat transfer and fluid flow of water in a vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon, have been carried out in this article. The annulus has a radius ratio (outer radius to inner radius) of 1.184 and aspect ratio (length to annular gap) equal to 352. The experiments were conducted for constant heat fluxes of 1, 2.5, 5, 7.5, 10, 12.5, and 15 kW/m2. Transient behavior during the heat-up period of the system until the steady-state condition is attained and discussed. Variation in the heat transfer coefficient and Nusselt number along the annulus height represent the developing boundary layer at the entrance and fully developed flow in the remaining length. A large drop in the differential pressure is experienced when the liquid is circulated through the flow meters, which restrict the flow due to their very small passages. Flow restriction causes mass accumulation and rise of pressure at the exit of the annulus. It also causes a decrease in liquid head in the cooling leg. An increase in the heat flux leads to an increase in the heat transfer coefficient and Nusselt number. As a result of the data analysis correlations for the average Nusselt number, Reynolds number and circulation rate have been developed in terms of the heat flux. 相似文献
945.
Shujaat Ahmad Manzoor Ahmad Mazen Almehmadi Syed Adnan Ali Shah Farman Ali Khan Nasir Mehmood Khan Asifullah Khan Zainab Mustafa Halawi Hanif Ahmad 《Molecules (Basel, Switzerland)》2022,27(14)
This study reports the isolation of three new C20 diterpenoid alkaloids, Chitralinine A–C (1–3) from the aerial parts of Delphinium chitralense. Their structures were established on the basis of latest spectral techniques and single crystal X-rays crystallographic studies of chitralinine A described basic skeleton of these compounds. All the isolated Compounds (1–3) showed strong, competitive type inhibition against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in comparison to standard allanzanthane and galanthamine however, chitralinine-C remained the most potent with IC50 value of 11.64 ± 0.08 μM against AChE, and 24.31 ± 0.33 μM against BChE, respectively. The molecular docking reflected a binding free energy of −16.400 K Cal-mol−1 for chitralinine-C, having strong interactions with active site residues, TYR334, ASP72, SER122, and SER200. The overall findings suggest that these new diterpenoid alkaloids could serve as lead drugs against dementia-related diseases including Alzheimer’s disease. 相似文献
946.
Yu-Ming Chu Muhammad Farooq Khan Saif Ullah Syed Azhar Ali Shah Muhammad Farooq Mustafa bin Mamat 《Mathematical Methods in the Applied Sciences》2023,46(1):232-247
Vector–host diseases outbreak is a major public health concern, and it has greatly affected human health and economy in various regions around the globe. Different approaches have been adopted to investigate the dynamical behavior and possible control of these diseases. In this study, we present a compartmental transmission model in order to explore the dynamics of vector–host infectious diseases. The saturated incidence rate instead of bilinear (or standard) and saturated treatment function is considered in model formulation which enhance the biological suitability of the proposed model. We first formulate the model based on nonlinear classical integer-order differential equations. Then, the proposed integer-order model is reformulated using the fractional-order operator in Caputo–Fabrizio sense with nonsingular kernel. We investigate the model equilibria and evaluate the expression for the most important threshold parameter known as the basic reproduction number. Furthermore, the existence and uniqueness are presented via the fixed point approach. Additionally, using an efficient numerical scheme, the iterative solution of the model is obtained. Finally, we present the model simulations to illustrate the impact of arbitrary fractional order and some of other important parameters involved in the model on the disease dynamics and minimization. 相似文献
947.
In this study, photoionization cross sections of guest hydrogen atom in endohedral fullerene () modeled by the Woods–Saxon confinement potential implanted in the nonideal classical plasma (NICP) under spherical confinement are reported for the first time in the related literature. The relevant wave equation is solved numerically via the tridiagonal matrix method and then the energy levels, bound and continuum wave functions are interpreted. Plasma effect is examined by considering plasma temperature and density and is evaluated in the photoionization process. Since the plasma modifies the discrete and continuum spectra by changing the potential energy of hydrogen atom, it closely affects the overlapping of the wave functions of ground state and continuum state. This effect has a distinct response on photoionization resonances. Using different values of endohedral confinement parameters, which means regarding different types of fullerenes, detailed analysis of energy levels, bound and continuum wave functions, and photoionization cross sections are provided by evaluating confinement width, depth, smoothing effect and distance from the spherical encompassement center. The photoionization process of implanted in the NICP (nonideal classical plasma) is highly sensitive to both plasma and endohedral confinement. At this sensitivity, Cooper resonance character is like an encoder for fullerene structure. 相似文献
948.
Şenol Çelik;Gökhan Dervişoğlu;Ebubekir İzol;Łukasz Sęczyk;Fethi Ahmet Özdemir;Muhammed Enes Yilmaz;Mustafa Abdullah Yilmaz;İlhami Gülçin;Khalid Mashay Al-Anazi;Mohammad Abul Farah;Muhammad Zafar;Trobjon Makhkamov;Mueen Alam Khan; 《Biomedical chromatography : BMC》2024,38(10):e5975
In this research, the study utilized the root, leaf, and petiole parts of in vitro grown Salvia hispanica plants as explants. Following UV-C treatment applied to developing callus, methanol extracts were obtained and analyzed using liquid chromatography–mass spectrometry (LC/MS) to investigate their anticancer properties. First, the seeds of S. hispanica were soaked in commercial bleach for 6 min to ensure surface sterilization. The most effective antimicrobial activity on Gram-negative bacteria, with a zone diameter (11 ± 0.82 mm), was noticed in callus extracts obtained from the petiole explant in the second protocol against Klebsiella pneumoniae EMCS bacteria. Anticancer activities on SH-SY5Y human neuroblastoma cells were investigated by using 1000, 500, 250, 125, 62.5, 31.25, 15.62, and 78.12 μg/mL doses of the extracts, and the most effective cytotoxic activity was determined at the 1000 μg/mL dose of the extracts obtained from both protocols. The extracts were determined to inhibit hCAI, hCAII, AChE, and BChE enzymes. The content of 53 different phytochemical components of the extracts was analyzed by liquid chromatography with tandem mass spectrometry (LC–MS/MS). Rosmarinic acid, quinic acid, and caffeic acid were found in the highest concentration. The comprehensive LC–MS/MS analysis of S. hispanica extracts revealed a diverse array of phytochemical compounds, highlighting its potential for therapeutic applications. 相似文献
949.
Hina Zahir;Javaria Akram;Mustafa Bayram;Mehnaz Shakeel;Rabbia Fatima;Shahram Rezapour;Mustafa Inc; 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2024,104(10):e202300989
This study examines entropy generation in the peristaltic flow of Johnson–Segalman fluid through a curved channel, considering the effects of Hall and ion slip due to an externally applied magnetic field and activation energy. The fluid dynamics are modeled using a highly nonlinear mathematical framework, which is non-dimensionalized and simplified with a lubrication approach. Numerical solutions are obtained using the shooting technique to analyze fluid flow properties. The results, presented graphically, provide a comprehensive understanding of the interactions between the non-Newtonian characteristics of the Johnson–Segalman fluid, entropy generation, and activation energy effects. The study finds that increasing the Hall parameter enhances entropy generation. Higher activation energy increases the rate of chemical reactions and by-products, raising system randomness. Additionally, reducing the channel curvature or increasing the curvature parameter elevates the system's entropy. These insights are valuable for biomedical and industrial applications. 相似文献
950.
A novel silica sorbent, silica gel-immobilized 5-aminoisophthalohydrazide (SiO2-APH), was prepared by the condensation of 3-chloropropyl-functionalized silica gel with 5-aminoisophthalohydrazide (APH) derived from dimethyl 5-aminoisophthalate as a starting material and used for separation and preconcentration of Cu, Zn, and Pb metals in water samples using Flame Atomic Absorption Spectrometry (FAAS). The characterization of the new sorbent was carried out by Elemental Analysis, Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). Important analytical parameters including as pH, amount of sorbent, type and amount of eluting solvent, sample volume, vortex and ultrasonic bath time, matrix ions that effect the developed SiO2-APH-solid phase extraction (SPE) method were investigated and optimum parameters were detected. Recoveries of examined metals were obtained as 98% for Cu and Pb and 101% for Zn. The relative standard deviation (RSD, n = 8) of Cu, Zn and Pb metals were 3.2, 2.8 and 1.6%, respectively. Limit of detections (LODs) (n = 10) were found as 2.7 μg L−1 for Cu, 7.4 μg L−1 for Zn and 3.5 μg L−1 for Pb μg L−1. The accuracy of the new method was assessed by analyzing of TMDA-51.4 and TMDA-70.2 certified reference materials. The results obtained for metals were in a good agreement with certified values. Addition/recovery test was applied to the real well, river, dam and stream water samples to check the accuracy of the method. The results showed that the developed SiO2-APH-SPE method can be effectively used as an alternative method for determination of Cu, Zn, and Pb metals in water samples. 相似文献