全文获取类型
收费全文 | 3556篇 |
免费 | 191篇 |
国内免费 | 94篇 |
专业分类
化学 | 2258篇 |
晶体学 | 53篇 |
力学 | 163篇 |
综合类 | 6篇 |
数学 | 721篇 |
物理学 | 640篇 |
出版年
2024年 | 7篇 |
2023年 | 56篇 |
2022年 | 88篇 |
2021年 | 110篇 |
2020年 | 132篇 |
2019年 | 114篇 |
2018年 | 112篇 |
2017年 | 79篇 |
2016年 | 144篇 |
2015年 | 116篇 |
2014年 | 141篇 |
2013年 | 281篇 |
2012年 | 242篇 |
2011年 | 277篇 |
2010年 | 175篇 |
2009年 | 161篇 |
2008年 | 228篇 |
2007年 | 202篇 |
2006年 | 184篇 |
2005年 | 180篇 |
2004年 | 136篇 |
2003年 | 123篇 |
2002年 | 107篇 |
2001年 | 67篇 |
2000年 | 36篇 |
1999年 | 42篇 |
1998年 | 34篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1904年 | 2篇 |
排序方式: 共有3841条查询结果,搜索用时 15 毫秒
991.
Mourad Hidouri Besma Lajmi Mongi Ben Amara 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):i147-i148
Crystals of sodium zinc diiron(III) triphosphate, NaZnFe2(PO4)3, have been synthesized and structurally characterized by single‐crystal X‐ray diffraction. The compound features a new structural type built up from ZnO6 octahedra, FeO6 octahedra and FeO4 tetrahedra, linked together via the corners and edges of PO4 tetrahedra to form a three‐dimensional framework, with tunnels running along [100]. Within these tunnels, Na+ cations occupy a highly distorted cubic site. 相似文献
992.
Ouerghi O Touhami A Jaffrezic-Renault N Martelet C Ouada HB Cosnier S 《Bioelectrochemistry (Amsterdam, Netherlands)》2002,55(1-2):131-133
A newly developed electrochemical method--Elimination Voltammetry with Linear Scan (EVLS)--has been applied to the electrochemical study of nucleic acids (NAs) on a silver electrode. Using the linear combination of the currents measured at different scan rates, the EVLS is capable of eliminating one or two selected particular currents. It was shown that the elimination function conserving the reversible diffusion current and eliminating the charging and kinetic currents provides the significant increase of voltammetric signals of DNA. Due to the high sensitivity and resolution power, the EVLS can contribute to study behaviour of nucleic acids on the charged interface and can be applied to nucleic acid analyses and the development of DNA sensors. 相似文献
993.
994.
A series of normal aliphatic thiols have been used to derivatise the chemical warfare agents Lewisites I and II (LI and LII) in hydrocarbon matrices. Varying the chain length of the thiol allowed adjustment of derivative tR by 5.9 min for Lewisite I and 5.3 min for Lewisite II. Linear regression analysis of the chain length of the thiol derivatives of the Lewisite species, and that of a series of normal alkanes against tR, allowed regression models to be developed for each set of compounds. Application of the models allowed thiol reagents to be chosen to give derivatives of Lewisites I and II that eluted before and after the major hydrocarbon contaminant. Limits of detection were comparable for all thiol derivatives analysed by GC-MS in the selection ion monitoring mode (all below 1 microg ml(-1)). The robustness of this approach was illustrated by successful identification of Lewisite I in samples from the Sixth Proficiency Test (organised by the Organisation for the Prohibition of Chemical Weapons, OPCW) in a matrix of 1 mg ml(-1) diesel oil. 相似文献
995.
Li Z Dong Y Mi B Tang Y Häussler M Tong H Dong Y Lam JW Ren Y Sung HH Wong KS Gao P Williams ID Kwok HS Tang BZ 《The journal of physical chemistry. B》2005,109(20):10061-10066
We synthesized a group of silole regioisomers 1(x,y), whose photoluminescence varied dramatically with its regiostructure. By internally hindering the intramolecular rotation, we succeeded in creating a novel silole (1(3,4)) that is strongly luminescent in solutions and whose fluorescence quantum yield in acetone is as high as 83%. We revealed that 1(3,4) was a sensitive chemosensor capable of optically discriminating nitroaromatic regioisomers of p-, o-, and m-nitroanilines. Against general belief, crystal formation of 1(2,4) blue-shifted its emission color and boosted its emission efficiency. The light-emitting diode based on the crystal of 1(2,4) emitted a strong blue light (464 nm) in a high current efficiency (5.86 cd/A). 相似文献
996.
Yi Xiong Jiajie Zeng Bin Chen Jacky W. Y. Lam Zujin Zhao Shuming Chen Ben Zhong Tang 《中国化学快报》2019,30(3):592-596
New aggregation-induced emission molecules of carbazole-substituted siloles are prepared, based on which efficient non-doped OLEDs are fabricated, offering high external quantum efficiencies of up to 5.63%. 相似文献
997.
Single crystals of Nd5(AsO3)4Cl3 (monoclinic, P2/n, Z = 2, a = 1026.0(1), b = 543.35(3), c = 1400.2(1) pm, β = 93.48(1)°) were obtained from the reaction of Nd2O3, As2O3 and NaCl in a sealed silica ampoule. In the crystal structure the Nd3+ ions are linked by AsO33? groups into layers that alternate with layers of Cl? ions. Two of the three crystallographically different Nd3+ ions are coordinated by eight oxygen atoms, the third one has four oxygen and four chlorine atoms as neighbours. 相似文献
998.
New, short, and flexible procedures have been developed for syntheses of steroid and D-homo steroid skeletons. A Mukaiyama reaction between the silyl enol ether of 6-methoxytetralone and 2-methyl-2-cyclopentenone or carvone, with transfer of the silyl group to the receiving enone, gave a second silyl enol ether. Addition of a carbocation, generated under Lewis acid conditions from 3-methoxy-2-butenol, 3-ethoxy-3-phenyl-2-propenol or 3-methoxy-2-propenol to this second silyl enol ether gave adducts, which could not be cyclized by aldol condensation to (D-homo) steroid skeletons. The Mukaiyama-Michael reaction of the silyl enol ether of 6-methoxy tetralone with 2-methyl-2-cylopentenone gave a second silyl enol ether, which reacted in high yield with a carbocation generated from 3-hydroxy-3-(4-methoxyphenyl)propene. Ozonolysis of the double bond in this adduct gave a tricarbonyl compound (Zieglers triketone), which has been used before in the synthesis of 9,11-dehydroestrone methyl ether. A second synthesis of C17 substituted CD-trans coupled (D-homo) steroid skeletons has been developed via addition of a carbocation, generated with ZnBr2 from a Torgov reagent, to a silyl enol ether containing ring D precursor. The obtained seco steroids have been cyclized under formation of the 8-14 bond by treatment with acid. The double bonds in one of the cyclized products have been reduced to a C17-substituted all trans steroid skeleton. 相似文献
999.
Zeyan Zhuang Jun Dai Maoxing Yu Jianqing Li Pingchuan Shen Rong Hu Xiaoding Lou Zujin Zhao Ben Zhong Tang 《Chemical science》2020,11(13):3405
Photodynamic therapy (PDT) is considered a pioneering and effective modality for cancer treatment, but it is still facing challenges of hypoxic tumors. Recently, Type I PDT, as an effective strategy to address this issue, has drawn considerable attention. Few reports are available on the capability for Type I reactive oxygen species (ROS) generation of purely organic photosensitizers (PSs). Herein, we report two new Type I PSs, α-TPA-PIO and β-TPA-PIO, from phosphindole oxide-based isomers with efficient Type I ROS generation abilities. A detailed study on photophysical and photochemical mechanisms is conducted to shed light on the molecular design of PSs based on the Type I mechanism. The in vitro results demonstrate that these two PSs can selectively accumulate in a neutral lipid region, particularly in the endoplasmic reticulum (ER), of cells and efficiently induce ER-stress mediated apoptosis and autophagy in PDT. In vivo models indicate that β-TPA-PIO successfully achieves remarkable tumor ablation. The ROS-based ER stress triggered by β-TPA-PIO-mediated PDT has high potential as a precursor of the immunostimulatory effect for immunotherapy. This work presents a comprehensive protocol for Type I-based purely organic PSs and highlights the significance of considering the working mechanism in the design of PSs for the optimization of cancer treatment protocols.Phosphindole oxide-based photosensitizers with Type I reactive oxygen species generation ability are developed and used for endoplasmic reticulum stress-mediated photodynamic therapy of tumors. 相似文献
1000.
I. O. Abugassa Y. S. Khrbish S. O. Abugassa N. Ben Faid A. T. Bashir S. Sarmani 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):27-30
The paper focuses on the validation of the k
0-method of instrumental neutron activation analysis (k
0-INAA) in the Tajura Nuclear Research Center (TNRC) via the analysis of several certified reference materials. The selected
reference materials were: SRM 1572 Citrus Leaves, SRM 1575 Pine Needles, IAEA-A11 Milk Powder, IAEA-V-10 Hay Powder, RM IAEA-Soil-7
and RM IAEA-SL-1 Lake Sediment. The method is based on the PC version Kayzero/Solcoi software package issued by DSM. All the
samples, reference materials and monitors were irradiated in various positions of the Tajura reactor with different f and α. The parameters f and α (f — thermal/epithermal neutron flux ratio, α — parameter accounting for the non-ideality of the 1/E epithermal neutron fluence rate distribution) were determined using the bare triple monitor method. The results obtained
for all the reference materials are in good agreement with the certified values. 相似文献