全文获取类型
收费全文 | 1504篇 |
免费 | 50篇 |
国内免费 | 16篇 |
专业分类
化学 | 1058篇 |
晶体学 | 11篇 |
力学 | 52篇 |
综合类 | 3篇 |
数学 | 105篇 |
物理学 | 341篇 |
出版年
2024年 | 11篇 |
2023年 | 13篇 |
2022年 | 61篇 |
2021年 | 67篇 |
2020年 | 41篇 |
2019年 | 48篇 |
2018年 | 41篇 |
2017年 | 28篇 |
2016年 | 69篇 |
2015年 | 52篇 |
2014年 | 58篇 |
2013年 | 128篇 |
2012年 | 107篇 |
2011年 | 118篇 |
2010年 | 59篇 |
2009年 | 65篇 |
2008年 | 63篇 |
2007年 | 53篇 |
2006年 | 61篇 |
2005年 | 51篇 |
2004年 | 44篇 |
2003年 | 39篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1962年 | 3篇 |
排序方式: 共有1570条查询结果,搜索用时 15 毫秒
81.
M.Iqbal Choudhary SyedGhulam Musharraf Amtul Sami Atta‐ur‐Rahman 《Helvetica chimica acta》2004,87(10):2685-2694
The microbial transformation of (?)‐Ambrox® ( 1 ), a perfumery sesquiterpene, by a number of fungi, by means of standard two‐stage‐fermentation technique, afforded ambrox‐1α‐ol ( 2 ), ambrox‐1α,11α‐diol ( 3 ), ambrox‐1α,6α‐diol ( 4 ), ambrox‐1α,6α,11α‐triol ( 5 ), ambrox‐3‐one ( 6 ), ambrox‐3β‐ol ( 7 ), ambrox‐3β,6β‐diol ( 8 ), 13,14,15,16‐tetranorlabdane‐3,8,12‐triol ( 9 ), and sclareolide ( 10 ) (Schemes 1 and 2). Further incubation of compound 10 with Cunninghamella elegans afforded 3‐oxosclareolide ( 11 ), 3β‐hydroxysclareolide ( 12 ), 2α‐hydroxysclareolide ( 13 ), 2α,3β‐dihydroxysclareolide ( 14 ), 1α,3β‐dihydroxysclareolide ( 15 ), and 3β‐hydroxy‐8‐episclareolide ( 16 ) (Scheme 3). Metabolites 2 – 5, 12, 13 , and 16 were found to be new compounds. The major transformations include a reaction path involving hydroxylation, ether‐bond cleavage and inversion of configuration. Metabolites 11 – 16 of sclareolide showed significant phytotoxicity (Table 1). The structures of the metabolites were characterized on the basis of spectroscopic techniques. 相似文献
82.
Takehiko Yamato Carol Pérez-Casas Shofiur Rahman Zeng Xi Mark R. J. Elsegood Carl Redshaw 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):193-197
A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene
diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K+ and halides has been examined by 1H NMR titration experiments. 相似文献
83.
N. Siddique S. Waheed M. Daud A. Rahman S. Ahmad 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(1):181-186
Detailed investigations have been carried out on the well-known method of spectrophotometric determination of boron particularly
in uranium compounds as boron-curcumin complex after extraction into 2-ethyl hexane 1,3-diol (EHD) to understand a number
of parameters, which have not been addressed earlier in the literature. These include (i) effect of different acid media on
analytical results of boron which are employed for dissolution of nuclear fuel samples, (ii) effect of diluents namely ethyl
alcohol and N,N-dimethyl formamide on sensitivity of method which are employed for final dilution, and (iii) studies on loss
of boron, if any, during conversion of uranium compounds to U3O8. Based on the present studies, the existing procedure has been suitably modified to improve the sensitivity in the measurements.
In addition, this paper also describes about interference studies with Al, Cr, Mg, Ca, Fe, Mn, Mo, F− and W and amount of EHD on modified method. Absolute detection limit was found to be 10 ng. The precision and accuracy of
the method, is 3% at level 100 ng·g−1 of boron. 相似文献
84.
Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. The electrochemical behavior and electrocatalytic activity of modified electrode towards reduction of iodate and periodate are studied. The reductions of both ions occur at the unusual positive peak potential of 0.7 V vs. reference electrode. The modified electrode is employed successfully for iodate and periodates detection using cyclic voltammetry, hydrodynamic amperometry and flow injection analysis (FIA). In the performed experiments, flow injection amperometric determination of iodate and periodate yielded calibration curves with the following characteristics: linear dynamic range up to 100 and 80 μM, sensitivity of 140.9 and 150.6 nA μM−1 and detection limits of 5 and 36 nM, respectively. The repeatability of the modified electrode for 21 injections of 1.5 μM of iodate solution is 1.5%. The interference effects of NO2−, NO3−, ClO3−, BrO3−, ClO4−, SO42−, Cu2+, Zn2+, Mn2+, Mg2+, Cd2+, Ca2+, Na+, K+, NH4+ and K+, CH3COO− and glucose were negligible at the concentration ratio of more than 1000. The obtained attractive analytical performance together with high selectivity and simplicity of the proposed method provide an effective and e novel modified electrode to develop an iodate and periodate sensor. Sensitivity, selectivity, the liner concentration range and the detection limit of the developed sensor are all much better than all known similar sensors in the literature for iodate and periodate determination. 相似文献
85.
An efficient synthesis of tetrasubstituted unsymmetrical pyrazines and their related pyrazine N-oxides has been developed from commercially available 2-chloro-3-methylpyrazine. The procedure and scope of these synthesis routes are described. 相似文献
86.
M. Y. A. Rahman A. A. Umar L. Roza M. M. Salleh 《Russian Journal of Electrochemistry》2014,50(11):1072-1076
This work is concerned with the growth of TiO2 nanostructures as photovoltaic materials of dyesensitized solar cell (DSSC) via phase liquid deposition technique treated with CTAB surfactant. This work investigates the influence of organic dyes, N719, N3 and Z907 as photosensitizer on the photovoltaic parameters of TiO2 nanostructures dye-sensitized solar cells (DSSCs). It also highlights the effect of the concentration of the best dye, N719 on the performance of the cell. The platinum films as counter electrode of the DSSC were prepared by sputtering platinum pellet on ITO substrate. The redox couple of the electrolyte utilized in the DSSC was iodide/triiodide. The cell sensitized with N719 dye demonstrated the best performance compared with the cell sensitized with another two dyes, N3 and Z907. This is due to N719 dye possess the highest optical absorption in visible region. The cell sensitized with 0.8 mM N719 dye performs the highest short-circuit current density, J sc and power conversion efficiency, η since it posses the highest absorption in visible region. The DSSC utilizing 0.8 mM N719 dye demonstrated the highest J sc and η of 6.48 mA cm?2 and 1.69%, respectively. 相似文献
87.
Ridaphun Nongrum George Kupar Kharmawlong Jims World Star Rani Noimur Rahman Arup Dutta Rishanlang Nongkhlaw 《Journal of heterocyclic chemistry》2019,56(10):2873.-2883
The development of a metal‐free protocol for transformations in organic synthesis offers a significant potential environmental benefit. This article reports the exploration of meglumine, a nontoxic and biodegradable amino sugar, as an organocatalyst for the synthesis of biologically active 1H‐dibenzo[b,e][1,4]diazepin‐1‐ones, highly regioselective benzimidazole derivatives and derivatives of quinoxalines. Operational simplicity, mild reaction conditions, shorter reaction times, and use of green solvents are the highlights of this protocol. The advantage of ultrasonic irradiation has been significantly explored for the synthesis of the aforesaid compounds. Furthermore, the multifaceted use of o‐phenylenediamine has also been accentuated in the study. 相似文献
88.
Patterned langmuir-blodgett films of monodisperse nanoparticles of iron oxide using soft lithography 总被引:7,自引:0,他引:7
Langmuir-Blodgett (LB) films of monodisperse iron oxide nanoparticles have been successfully deposited onto patterned poly(dimethylsiloxane) surfaces. These patterned LB films of iron oxide nanoparticles were transferred onto solid substrates using micro contact printing. 相似文献
89.
Norimah Yusof Asnah Hassan M.N. Firdaus Abd Rahman Suzina A. Hamid 《Radiation Physics and Chemistry》2007,76(11-12):1756-1759
Most of the tissue banks in the Asia Pacific region have been using ionising radiation at 25 kGy to sterilise human tissues for save clinical usage. Under tissue banking quality system, any dose employed for sterilisation has to be validated and the validation exercise has to be a part of quality document. Tissue grafts, unlike medical items, are not produced in large number per each processing batch and tissues relatively have a different microbial population. A Code of Practice established by the International Atomic Energy Agency (IAEA) in 2004 offers several validation methods using smaller number of samples compared to ISO 11137 (1995), which is meant for medical products. The methods emphasise on bioburden determination, followed by sterility test on samples after they were exposed to verification dose for attaining of sterility assurance level (SAL) of 10−1. This paper describes our experience in using the IAEA Code of Practice in conducting the validation exercise for substantiating 25 kGy as sterilisation dose for both air-dried amnion and those preserved in 99% glycerol. 相似文献
90.
The temperature‐ and electric field‐dependent dielectric relaxation and polarisation of a new chiral swallow tailed antiferroelectric liquid crystal, i.e. 1‐ethylpropyl (S)‐2‐{6‐[4‐(4′‐decyloxyphenyl)benzoyloxy]‐2‐naphthyl}propionate (abbreviated as EP10PBNP), were investigated. The electric field‐induced dielectric loss spectra of EP10PBNP revealed electroclinic and anomalous dielectric behaviour in the chiral smectic A (SmA*)–chiral antiferroelectric smectic C (SmCA*) pre‐transitional regime. From an analysis of thermal hysteresis of the dielectric constant, electric field‐induced polarisation and dielectric loss spectra, the appearance of a ferrielectric‐like mesophase is observed followed by an unstable SmCA* phase in the SmA*–SmCA* pre‐transitional regime. 相似文献