全文获取类型
收费全文 | 1644篇 |
免费 | 71篇 |
国内免费 | 8篇 |
专业分类
化学 | 1238篇 |
晶体学 | 34篇 |
力学 | 43篇 |
数学 | 103篇 |
物理学 | 305篇 |
出版年
2024年 | 15篇 |
2023年 | 17篇 |
2022年 | 102篇 |
2021年 | 86篇 |
2020年 | 52篇 |
2019年 | 56篇 |
2018年 | 81篇 |
2017年 | 61篇 |
2016年 | 83篇 |
2015年 | 58篇 |
2014年 | 55篇 |
2013年 | 131篇 |
2012年 | 132篇 |
2011年 | 117篇 |
2010年 | 74篇 |
2009年 | 63篇 |
2008年 | 78篇 |
2007年 | 62篇 |
2006年 | 41篇 |
2005年 | 33篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 51篇 |
2001年 | 34篇 |
2000年 | 39篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有1723条查询结果,搜索用时 15 毫秒
941.
Junichi Matsumoto Abdul A. Khan Sam S. Y. Wang Mutsuto Kawahara 《International Journal of Computational Fluid Dynamics》2013,27(2):129-134
This paper presents a computational simulation method for a river problem. For the actual flow problem, it is necessary to compute flow velocity, water elevation and water region at the same time. For the basic formulation, the unsteady shallow water equations are used. As the numerical approach, implicit FEM is proposed by bubble function. To control numerical stability and accuracy, LSBF (Least-Squares Bubble Function) is used to solve the finite element equations. Also, the fixed boundary technique is combined to deal with wet and dry areas in the moving finite element mesh. Some numerical tests are shown to check this method. 相似文献
942.
Salvadorin, a new dimeric dihydroisocoumarin (1), was isolated from the chloroform fraction of Salvadora oleoides. Its chemical structure was established as 8-benzyl-6-[6-(6-ethyl-7-methyl-5,8-dihydro-2-naphthalenyl)-1-oxo-3,4-dihydro-1H-isochromen-8yl]-3, 4-dihyro-1H-isochromen-1-one, through spectroscopic techniques and chemical analysis. 相似文献
943.
Fengli Bei Fangfang Jian Xujie Yang Lude Lu Xin Wang Ibrahim Abdul Razak S. Shanmuga Sundara Raj Hoong-Kun Fun 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(1):45-46
In the title compound, [ZnCl2(C14H12N2)2], the environment around the Zn atom is distorted tetrahedral formed by two Cl atoms and two tertiary N atoms of the 2-benzyl-1H-benzimidazole ligands. N—H⃛Cl intermolecular hydrogen bonds link the molecules into infinite chains in the [101] direction. 相似文献
944.
Anwar Usman Ibrahim Abdul Razak Suchada Chantrapromma Hoong‐Kun Fun Tarun K. Sarkar Sankar Basak Gur Dayal Nigam 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1116-1117
In the title compound, C16H19ClN2O4, the pyridine ring is nearly planar, the piperidine ring is non‐planar and the cyclohexane ring adopts a screw‐boat conformation. The carboxylate group makes a dihedral angle of 80.9 (2)° with the least‐squares plane through the cyclohexane ring. 相似文献
945.
946.
Moghaddam SS Jaafar HB Aziz MA Ibrahim R Rahmat AB Philip E 《Molecules (Basel, Switzerland)》2011,16(11):8981-8991
The present study investigates the effects of different concentrations, as well as type of plant growth regulators (PGRs) and medium (MS, Duchefa) on the growth and development of Centella asiatica in semi-solid culture. In addition, a protocol for successful sterilization of C.asiatica explants prepared from field-grown plants highly exposed to fungal and bacterial contamination was determined. Results for sterilization treatments revealed that applying HgCl? and Plant Preservative Mixture (PPM) with cetrimide, bavistin and trimethoprim which were included after washing with tap water, followed by the addition of PPM in the medium, produced a very satisfactory result (clean culture 90 ± 1.33%) and TS5 (decon + cetrimide 1% + bavistin 150 mg/L + trimethoprim 50 mg/L + HgCl?0.1% + PPM 2% soak and 2 mL/L in medium) was hence chosen as the best method of sterilization for C.asiatica. The synergistic combination of 6 benzylaminopurine (BAP) and 1-naphthaleneacetic acid (NAA) in concentrations of 2 mg/L and 0.1 mg/L, respectively, in Duchefa medium compared with MS induced the most optimal percentage of sprouted shoots (93 ± 0.667), number of shoots (5.2 ± 0.079) and nodes (4 ± 0.067) per explant, leaf per explant (14 ± 0.107) and shoot length (4.1 ± 0.67 cm). Furthermore, optimum rooting frequency (95.2 ± 0.81%), the number of roots/shoot (7.5 ± 0.107) and the mean root length (4.5 ± 0.133 cm) occurred for shoots that were cultured on full-strength MS medium containing 0.5 mg/L indole-3-butyric acid (IBA). In this study, the acclimatized plantlets were successfully established with almost 85% survival. The findings of this study have proven an efficient medium and PGR concentration for the mass propagation of C.asiatica. These findings would be useful in micropropagation and ex situ conservation of this plant. 相似文献
947.
S. Waheed Sabiha-Javied N. Siddique R. Shakoor M. Tufail 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(2):521-528
Sensitive nondestructive instrumental neutron activation analysis (INAA) technique has been applied for the determination
of rare earth elements (REEs) (Ce, Eu, La, Lu, Sm, Tb and Yb) in phosphate rocks (PR) and granulated single super-phosphate
(GSSP) fertilizer samples from Hazara district of Pakistan. The comparison of the PR with product fertilizers shows that most
of the quantified REEs were found to be in lower contents in the fertilizers. Six fertilizer samples with different N, P and
K ratio for distinctive application to plants were also characterized. The REEs in these showed irregular patterns that can
be attributed to difference in their manufacturing and chemical processes. The REEs contents of local phosphate fertilizer
were found to be lower in comparison to the values cited in the literature; however Ce is relatively high. For quality assurance
fair agreement was found between the results obtained for reference materials IAEA SL-1 (Lake Sediment) and GSJ-JR-1 (Rhyolite). 相似文献
948.
The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM−1, respectively. The oxidation of tryptophan occurred in a pH dependent, 2e− and 2H+ process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability. 相似文献
949.
Kiki A. Kurnia M. I. Abdul Mutalib T. Murugesan B. Ariwahjoedi 《Journal of solution chemistry》2011,40(5):818-831
Densities and viscosities were determined for binary mixtures containing the protic ionic liquid bis(2-hydroxyethyl)methylammonium
formate [BHEMF] with methanol, ethanol, and 1-propanol at four different temperatures (293.15, 303.15, 313.15, and 323.15 K)
and atmospheric pressure. Excess molar volume and viscosity deviations for the binary system were calculated. The calculated
results were fitted to a Redlich-Kister equation to obtain the coefficients and estimate the standard deviations between the
experimental and calculated quantities. The negative values of excess volume molar for these mixtures indicate that ion-dipole
interactions and packing between ionic liquids and alcohols are present. The values of viscosity deviation are also negative
over the whole composition range, and their values become less negative as the temperature increases. 相似文献
950.
Dissolution and Delignification of Bamboo Biomass Using Amino Acid-Based Ionic Liquid 总被引:1,自引:0,他引:1
Muhammad N Man Z Bustam MA Mutalib MI Wilfred CD Rafiq S 《Applied biochemistry and biotechnology》2011,165(3-4):998-1009
In the present work, the dissolution of bamboo biomass was tested using a number of ionic liquids synthesized in laboratory. It was observed that one of the synthesized amino acid-based ionic liquids, namely 1-ethyl-3-methylimidazolium glycinate, was capable of dissolving the biomass completely. The dissolved biomass was then regenerated using a reconstitute solvent (acetone/water) and was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The results were compared to preconditioned bamboo biomass. The regenerated biomass was found to have a more homogenous macrostructure, which indicates that the crystalline form and structure of its cellulose has changed from type Ι to type ΙΙ during the dissolution and regeneration process. 相似文献