全文获取类型
收费全文 | 15145篇 |
免费 | 1142篇 |
国内免费 | 724篇 |
专业分类
化学 | 10229篇 |
晶体学 | 136篇 |
力学 | 577篇 |
综合类 | 54篇 |
数学 | 1774篇 |
物理学 | 4241篇 |
出版年
2023年 | 169篇 |
2022年 | 349篇 |
2021年 | 363篇 |
2020年 | 355篇 |
2019年 | 400篇 |
2018年 | 310篇 |
2017年 | 311篇 |
2016年 | 491篇 |
2015年 | 496篇 |
2014年 | 594篇 |
2013年 | 896篇 |
2012年 | 1132篇 |
2011年 | 1260篇 |
2010年 | 786篇 |
2009年 | 785篇 |
2008年 | 922篇 |
2007年 | 857篇 |
2006年 | 777篇 |
2005年 | 686篇 |
2004年 | 622篇 |
2003年 | 527篇 |
2002年 | 485篇 |
2001年 | 359篇 |
2000年 | 309篇 |
1999年 | 239篇 |
1998年 | 190篇 |
1997年 | 163篇 |
1996年 | 196篇 |
1995年 | 148篇 |
1994年 | 169篇 |
1993年 | 136篇 |
1992年 | 132篇 |
1991年 | 97篇 |
1990年 | 116篇 |
1989年 | 91篇 |
1988年 | 98篇 |
1987年 | 67篇 |
1986年 | 77篇 |
1985年 | 112篇 |
1984年 | 76篇 |
1983年 | 75篇 |
1982年 | 55篇 |
1981年 | 51篇 |
1980年 | 55篇 |
1979年 | 39篇 |
1977年 | 43篇 |
1976年 | 42篇 |
1975年 | 37篇 |
1974年 | 54篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Cyclodimerization of norbornadiene (NBD) yielding pentacyclic products of exo-trans(cis)endo-structure in the presence of the model catalytically active complex Ni(H)(η4-NBD) has been studied using the DFT/PBE method. The rate-limiting reaction step is the reductive elimination of the metallacycle, the decomposition of the latter yields the norbornadiene dimer. 相似文献
92.
Sou-Jen Chang 《合成通讯》2013,43(9):673-680
In the course of our investigation of the chemistry of diazoacenaphthene, we needed 2-benzylidene-1-diazoacenaphthene (2). As a possible precursor to 2, benzylideneacenaphthenone (1) was treated with one equivalent of tosylhydrazine with the expectation that 2 would be formed following basic decomposition. Surprisingly, acenaphthenequinone bistosylhydrazone (3) was produced instead (Eq. 1). 相似文献
93.
An efficient one-step synthetic route toward multifunctionalized quaterphenyls 3 or cyclopropanes 4 is developed from substituted chalcones 1 and sulfones 2 in good yields via a regioselective [3C+3C] or [1C+2C] annulation. The reaction features mild conditions, multisubstitution, and functional groups tolerance and is transition metal catalyst-free. The protocol provides a novel alternative to the conventional methodologies for the synthesis of quaterphenyls or cyclopropanes. 相似文献
94.
Wei Chang Lijuan Liu Jin Zhang Qiwei Pan 《Journal of Dispersion Science and Technology》2013,34(5):639-642
A kind of emulsifier-free latex (FL) was successfully synthesized from styrene (St) and butyl acrylate (BA) with 2-acrylamido-2-methyl propane sulfonic acid (AMPS) as a reactive emulsifier. The particle size of latex particles, stability against electrolytes, minimum film forming temperature (MFT) and water contact angle (CA) were evaluated and compared with a conventional latex (CL). Test results show that FL has larger particle size, better stability against electrolytes and lower MFT value compared with CL; higher AMPS content leads to smaller particle size and smaller water CA. 相似文献
95.
Chang Jun Zou Quan Wu Tang Gui Hong Lan Qiang Tian Tai Yu Wang 《Journal of inclusion phenomena and macrocyclic chemistry》2013,76(1-2):61-68
For the first time, hydroxypropyl-β-cyclodextrin (HP-β-CD) has been brought in to include 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) in order to enhance inhibition efficiency of PBTCA, which leads a new approach to study oil–gas field corrosion inhibition in the process of acid treatment. Based on the host–guest inclusion reaction, the inclusion complex of PBTCA with HP-β-CD has been prepared in the laboratory. UV–Vis absorption spectrum was applied to study the inclusion behavior of PBTCA with HP-β-CD. The results revealed that PBTCA with HP-β-CD can form a 1:1 stoichiometry inclusion complex. The 1:1 inclusion complex synthesized by using lyophilization was further characterized by Fourier transform infrared spectroscopy. Besides, inhibition effect of the inclusion complex on the corrosion inhibition of Q235 carbon steel has been investigated in 0.1 M sulfuric acid (H2SO4) solution using potentiodynamic polarization, electrochemical impedance spectroscopy techniques and scanning electron microscopy (SEM). It was found that the presence of the inclusion complex better achieved the anti-corrosion property in aggressive medium than was the case with alone PBTCA and the highest inhibition efficiency of the inclusion complex over 90 % was obtained, which are suggestive of the active effect of the inclusion complex for improving inhibition efficiency of PBTCA. Meanwhile, the results obtained from SEM further showed that the inclusion complex acts as a more efficient corrosion inhibitor for Q235 carbon steel in H2SO4 medium. 相似文献
96.
A palladium-mediated high-yielding synthesis of oxygenated 2-methylindolines 4 from 2-allylnitrobenzene 1 and hydrazine is developed. The one-pot route combines the reduction of 2-allylnitrobenzene 1 and the sequential intramolecular hydroamination. The protocol provides a novel alternative for the synthesis of substituted 2-methylindoline 4. 相似文献
97.
A novel metal-free oxidative arylphosphination of activated N-substituted-N-arylacrylamide derivatives by phosphorylation and C–H functionalization cascade process has been developed. This methodology provides an efficient way to construct a variety of phosphorus-containing oxindole moieties. 相似文献
98.
A novel reaction-based probe for the dual signaling of hydrogen sulfide (H2S) was investigated. The selective H2S-induced cleavage of the ether linkage of the 7-nitro-2,1,3-benzoxadiazole (NBD) and 7-hydroxycoumarin conjugate resulted in a dual signaling behavior. The colorimetric and fluorogenic signaling behaviors were attributed to the H2S-induced generation of 7-nitrobenzo-2,1,3-oxadiazole-4-thiol (NBD-SH) and 7-hydroxycoumarin, respectively. The signaling behavior was analyzed by ratiometry. The selective signaling of H2S over other common metal ions and anions was possible with a detection limit of 1.6 × 10−6 M in an aqueous DMSO solution. 相似文献
99.
Y. J. Chang C. H. Chen B. T. Hsieh 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):765-780
In this study, the detailed characteristics, including spatial uniformity, dose distributions, inter-batch variability, reproducibility, and long-term temporal stability, of N-isopropylacrylamide (NIPAM) polymer gel dosimeter were investigated. A commercial 10x fast optical computed tomography scanner (OCTOPUSTM-10×, MGS Research, Inc., Madison, CT, USA) was used to measure NIPAM polymer gel dosimeter. A cylindrical NIPAM gel phantom that measured 10 cm × 10 cm was irradiated via a single-field treatment plan with a field size of 4 cm × 4 cm. The maximum standard deviation of spatial uniformity for NIPAM gel was less than 0.29 %. The average standard deviation among the three batches of gel dosimeters was less than 1 %. The gamma pass rate could reach as high as 96.76 % when a 3 % dose difference and a 3 mm dose-to-agreement criteria were used. The long-term measurement of irradiated NIPAM gel dosimeter indicated that the dose maps attained a gradually stable value 15 h post-irradiation and remained stable until 72 h post-irradiation. The gamma pass rate could achieve a maximum value between 24 and 72 h post-irradiation. The edge enhancement effect that occurred around the irradiated region was observed 72 h post-irradiation. Thus, the results from this study suggest that NIPAM gel dosimeter should be measured approximately 24 h post-irradiation to reduce the occurrence of the edge enhancement effect. 相似文献
100.
Chang Chi-I Chen Cheng-Chi Ko Horng-Huey Chen Jih-Jung Cheng Ming-Jen Chao Che-Yi Kuo Yueh-Hsiung 《Chemistry of Natural Compounds》2022,58(3):478-481
Chemistry of Natural Compounds - A new seco-abietanoid, 12-methoxy-7-oxo-6,7-secoabieta-8,11,13-trien-6-oic acid (1), and a known seco-abietanoid,12-hydroxy-6,7-secoabieta-8,11,13-triene-6,7-dial... 相似文献