全文获取类型
收费全文 | 3658篇 |
免费 | 301篇 |
国内免费 | 964篇 |
专业分类
化学 | 2691篇 |
晶体学 | 49篇 |
力学 | 184篇 |
综合类 | 51篇 |
数学 | 1485篇 |
物理学 | 463篇 |
出版年
2024年 | 3篇 |
2023年 | 55篇 |
2022年 | 49篇 |
2021年 | 100篇 |
2020年 | 167篇 |
2019年 | 162篇 |
2018年 | 114篇 |
2017年 | 193篇 |
2016年 | 179篇 |
2015年 | 134篇 |
2014年 | 229篇 |
2013年 | 348篇 |
2012年 | 310篇 |
2011年 | 241篇 |
2010年 | 182篇 |
2009年 | 254篇 |
2008年 | 256篇 |
2007年 | 236篇 |
2006年 | 190篇 |
2005年 | 187篇 |
2004年 | 202篇 |
2003年 | 158篇 |
2002年 | 118篇 |
2001年 | 92篇 |
2000年 | 93篇 |
1999年 | 95篇 |
1998年 | 69篇 |
1997年 | 86篇 |
1996年 | 81篇 |
1995年 | 66篇 |
1994年 | 42篇 |
1993年 | 38篇 |
1992年 | 44篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1959年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有4923条查询结果,搜索用时 15 毫秒
91.
Ezzat M. Abdel-moety 《光谱学快报》2013,46(5):669-677
A direct derivative, D1 i.e. dA/dλ, spectrophotometric procedure for simultaneous determination of diethylamine salicylate and methyl nicotinate in their binary mixtures and in ointments has been investigated. Good percent mean recoveries, 99.68 ± 0.58 & 99.71 ± 0.27 and 100.85 ± 0.21, could be obtained for diethylamine salicylate at 303 nm & 236 nm and methyl nicotinate at 224 nm, in order, added to ointment. The band overlapping in the first order due to the coexisting parabens, main additive, and the water-washable ointment base occurs sufficient away from those wavelengths chosen for the direct D1-measurement of both drug substances. 相似文献
92.
F. A. El-Yazbi 《光谱学快报》2013,46(2):279-291
Two methods are presented for the analysis of ofloxacin. The first method is based on the application of Amax, ΔA, first and second derivative techniques for its determination in bulk powder, tablet form, and in urine. The use of absorbance and derivative maxima ratios as purity indices has been discussed. The second depends on the fluorescence characteristics of ofloxacin in acidic solutions. The spectrofluorimetric method is 10 times more sensitive than the spectrophotometric one. The accuracy and reproducibility of the methods were shown by the within day and between day coefficient of variation (less than 3%). 相似文献
93.
Synthesis,spectral investigation and development of tetrahedral copper(II) complexes as artificial metallonucleases and antimalarial agents 下载免费PDF全文
Seven new copper(II) complexes of type [Cu(A)(L)]?H2O (A = sparfloxacin, ciprofloxacin, levofloxacin, gatifloxacin, pefloxacin, ofloxacin, norfloxacin; L = 5‐[(3‐chlorophenyl)diazenyl]‐4‐hydroxy‐1,3‐thiazole‐2(3H)‐thione) were synthesized and characterized using elemental and thermogravimetric analyses, and electronic, electron paramagnetic resonance (EPR), Fourier transform infrared and liquid chromatography–mass spectroscopies. Tetrahedral geometry around copper is assigned in all complexes using EPR and electronic spectral analyses. All complexes were investigated for their interaction with herring sperm DNA utilizing absorption titration (Kb = 1.27–3.13 × 105 M?1) and hydrodynamic volume measurement studies. The studies suggest the classical intercalative mode of DNA binding. The cleavage reaction on pUC19 DNA was monitored by agarose gel electrophoresis. The results indicate that the Cu(II) complexes can more effectively promote the cleavage of plasmid DNA. The superoxide dismutase mimic activity of the complexes was evaluated by nitroblue tetrazolium assay, and the complexes catalysed the dismutation of superoxide at pH = 7.8 with IC50 values in the range 0.597–0.900 μM. The complexes were screened for their in vitro antibacterial activity against five pathogenic bacteria. All the complexes are good cytotoxic agents and show LC50 values ranging from 5.559 to 11.912 µg ml?1. All newly synthesized Cu(II) complexes were also evaluated for their in vitro antimalarial activity against Plasmodium falciparum strain (IC50 = 0.62–2.0 µg ml?1). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
94.
95.
We develop the exact WKB analysis of an M2P1T (merging two simple poles and one simple turning point) Schrödinger equation. In Part II, using a WKB-theoretic transformation to the algebraic Mathieu equation constructed in Part I, we calculate the alien derivative of its Borel transformed WKB solutions at each fixed singular point relevant to the simple poles through the analysis of Borel transformed WKB solutions of the Legendre equations. In the course of the calculation of the alien derivative we make full use of microdifferential operators whose symbols are given by the infinite series that appear in the coefficients of the algebraic Mathieu equation and the Legendre equation. 相似文献
96.
Yanfeng Chu Huan Yu Yunti Zhang Guangyan Zhang Yingying Ma Renxi Zhuo Xulin Jiang 《Journal of polymer science. Part A, Polymer chemistry》2014,52(23):3346-3355
Biodegradable amphiphilic ABC Y‐shaped triblock copolymer (MPBC) containing PEG, PBLA, and PCL segments was synthesized via the combination of enzymatic ring‐opening polymerization (ROP) of epsilon‐caprolactone, ROP of BLA‐N‐carboxyanhydride and click chemistry, where PEG, PBLA, and PCL are poly(ethylene glycol), poly(benzyl‐l ‐aspartate), and polycaprolactone, respectively. Propynylamine was employed as ROP initiator for the preparation of alkynyl‐terminated PBLA and methyloxy‐PEG with hydroxyl and azide groups at the chain‐end was used as enzymatic ROP initiator for synthesis of monoazido‐midfunctionalized block copolymer mPEG‐b‐PCL. The subsequent click reaction led to the formation of Y‐shaped asymmetric heteroarm terpolymer MPBC. The polymer structures were characterized by different analyses. The MPBC terpolymer self‐assembled into micelles and physically encapsulated drug doxorubicin (DOX) to form DOX‐loaded micelles, which showed good stability and slow drug release. In vitro cytotoxicity study indicated that the MPBC micelles were nontoxic and the DOX‐loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3346–3355 相似文献
97.
A mixed CuI/CuIIcatalyst based on magnetic cysteine functionalized graphene oxide (CuI/II@Cys-MGO) was prepared and used for the azidonation reaction of aryl boronic acids and one-pot synthesis of 1,4-diaryl −1,2,3-triazoles. Aryl azides were obtained in good yields and short reaction times via cross-coupling of aryl boronic acids with sodium azide in the presence of CuII catalytic species in this catalytic system. The azide-alkyne cycloaddition reaction was catalyzed by CuI catalytic species in CuI/II@Cys-MGO nanocomposite. 相似文献
98.
Poojali P. Warekar Priyanka T. Patil Kirti T. Patil Dattatraya K. Jamale Govind B. Kolekar 《合成通讯》2016,46(24):2022-2030
An ecofriendly route has been investigated for the synthesis of 4-(4-nitro-phenyl)-2-phenyl-1,4-dihydro-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylic acid ethyl ester derivatives by one-pot, three-component condensation of ethyl benzoylacetate, aromatic aldehydes, and 2-amino benzimidazole using 260?mol% of citric acid as reaction mediator. Citric acid is an inexpensive, nontoxic, and green medium with smoothly activates the rate of reaction. The synthesized compounds were assessed for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37RV strain using the microplate alamar blue assay (MABA). The results indicate that among all the synthesized compound series, P-4 and P-9 compounds illustrate effective activity with a minimum inhibitory concentration of 25?µg/ml. 相似文献
99.
Hai-Hua Li 《中国化学快报》2015,26(3):320-322
A reaction of benzylic alcohols with alkenes has been developed in the presence of bis(trifluoromethane)sulfonimide for the synthesis of trisubstituted alkenes and indane derivatives with high stereoselectivity.In general,benzylic alcohols react with 1,1-diaryl alkenes to afford trisubstituted alkenes,and the reaction with 1,2-disubstituted and trisubstituted alkenes affords indane derivatives through a [3 + 2] annulation reaction. 相似文献
100.
In this work, a Lyapunov-type inequality is obtained for the case when one is dealing with a fractional differential boundary value problem. We then use that result to obtain an interval where a certain Mittag–Leffler function has no real zeros. 相似文献