全文获取类型
收费全文 | 7391篇 |
免费 | 1415篇 |
国内免费 | 1709篇 |
专业分类
化学 | 6172篇 |
晶体学 | 123篇 |
力学 | 384篇 |
综合类 | 207篇 |
数学 | 962篇 |
物理学 | 2667篇 |
出版年
2024年 | 21篇 |
2023年 | 78篇 |
2022年 | 174篇 |
2021年 | 189篇 |
2020年 | 220篇 |
2019年 | 305篇 |
2018年 | 220篇 |
2017年 | 228篇 |
2016年 | 318篇 |
2015年 | 371篇 |
2014年 | 380篇 |
2013年 | 552篇 |
2012年 | 579篇 |
2011年 | 551篇 |
2010年 | 539篇 |
2009年 | 466篇 |
2008年 | 575篇 |
2007年 | 490篇 |
2006年 | 502篇 |
2005年 | 475篇 |
2004年 | 397篇 |
2003年 | 427篇 |
2002年 | 548篇 |
2001年 | 536篇 |
2000年 | 376篇 |
1999年 | 223篇 |
1998年 | 133篇 |
1997年 | 79篇 |
1996年 | 82篇 |
1995年 | 64篇 |
1994年 | 56篇 |
1993年 | 37篇 |
1992年 | 53篇 |
1991年 | 57篇 |
1990年 | 32篇 |
1989年 | 30篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1965年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
One‐Pot Regioselective Synthesis of Novel Oximino Ester‐Containing 1‐Aryl‐4‐chloro‐3‐oxypyrazoles as Potential Fungicides 下载免费PDF全文
Yi Li Yuan‐Yuan Liu Nan‐Qing Chen Kun‐Zhi Lü Xiao‐Hui Xiong Jie Li 《Helvetica chimica acta》2014,97(9):1269-1282
A novel, functional‐group‐tolerant, and highly regioselective one‐pot synthesis of six 4‐chloro‐1‐aryl‐3‐oxypyrazoles, 8a – 8f , containing an oximino ester moiety has been developed. Their structures were characterized by 1H‐ and 13C‐NMR, IR, MS, and elemental analyses. The regioselectivity of the reaction was also determined by single‐crystal X‐ray diffraction analysis of product 8d . The reaction pathway, proposed with the aid of DFT calculations, likely proceeds via a DMF‐catalyzed mechanism, which involves an electrophilic attack by SOCl2 and two nucleophilic substitutions by benzyl bromide (BnBr) and Cl?, respectively, as the key steps. A preliminary in vitro bioassay indicated that most compounds exhibited good fungicidal activities against Sclerotinia sclerotiorum and Gibberella zeae. Especially, 8d and 8e displayed higher or similar fungicidal activities compared with pyraclostrobin at the concentration of 10 μg/ml. 相似文献
952.
Yu‐Xiu Liu Zhi‐Peng Cui Hua‐Ping Zhao Yong‐Hong Li Yu‐Cheng Gu Qing‐Min Wang 《Journal of heterocyclic chemistry》2014,51(Z1):E209-E215
A series of tenuazonic acid analogues in which the acetyl group was replaced with electron‐withdrawing substituents have been synthesized with the aim of obtaining molecules with various bioactivities. Substituents such as cyano, sulfonyl, and amido were introduced at the 3‐position of the pyrrolidine‐2,4‐dione nucleus of tenuazonic acid. 3‐Cyano and sulfonyl pyrrolidine‐2,4‐dione compounds ( 2 and 6 ) were prepared via a Dieckmann cyclization as key step. 3‐Amido pyrrolidine‐2,4‐dione compounds ( 9 ) were prepared by a microwave‐assisted amidation reaction from corresponding 3‐carboxylate derivative. The target compounds were evaluated; their herbicidal, fungicidal, and insecticidal activities, and the preliminary bioassay data showed that some 3‐cyanopyrrolidine‐2,4‐diones 2 gave good insecticidal activity, whereas some 3‐amido compounds 9 exhibited moderate to strong fungicidal activity against Pythium dissimile at 20 mg/L. 相似文献
953.
Study of 1,3‐Dipolar Cycloaddition and Ring Contraction of New 1,4‐Phenylene‐bis[1,5]benzothiazepine Derivatives 下载免费PDF全文
Some 1,4‐phenylene‐bis[1,2,4]oxadiazolo‐[5,4‐d][1,5]benzothiazepine derivatives ( 4a , 4b , 4c ) were synthesized by 1,3‐dipolar cycloaddition reaction of benzohydroximinoyl chloride with 1,4‐phenylene‐bis(4‐aryl)‐2,3‐dihydro[1,5]benzothiazepine ( 2a , 2b , 2c ); meanwhile, compounds 2a , 2b , 2c also occurred ring contraction under acylating condition to obtain bis[2‐aryl‐2′‐(β‐1,4‐phenylenevinyl)‐3‐acetyl]‐2,3‐dihydro[1,5]benzothiazoles ( 3a , 3b , 3c ). The structures of some novel compounds were confirmed by IR, 1H‐NMR, elemental, and X‐ray crystallographic analysis. 相似文献
954.
Improved and Efficient Synthesis of Pyrrolo[2,3,4‐kl]acridin‐1‐one Derivatives under Ultrasound Irradiation 下载免费PDF全文
Li‐Li Li Hui‐Yuan Wang Wei Lin Zhi‐Bin Huang Da‐Qing Shi 《Journal of heterocyclic chemistry》2014,51(6):1778-1784
A improved and efficient procedure for the synthesis of pyrrolo[2,3,4‐kl]acridin‐1‐one derivatives via the reaction of isatin and enaminone catalyzed by ceric ammonium nitrate under ultrasonic condition has been developed. Compared with the conventional methods, the remarkable advantages of this method are mild reaction conditions, operational simplicity, higher yield, and shorter reaction times. 相似文献
955.
Synthesis of Novel Tricyclic 1,5‐Benzothiazepine Derivatives Bearing Quinoline Moiety via [2 + 2] Cycloaddition Reaction 下载免费PDF全文
A series of new tricyclic 1,5‐benzothiazepine derivatives were synthesized by the reaction of 1,5‐benzothiazepine containing 2‐phenoxy‐quinoline with chloracetyl chloride and phenoxyacetyl chloride. The structures of the target compounds were confirmed by IR, 1H NMR MS, and elemental analysis. 相似文献
956.
Zhi‐Bin Huang Li‐Li Li Yan‐Wei Zhao Hui‐Yuan Wang Da‐Qing Shi 《Journal of heterocyclic chemistry》2014,51(Z1):E309-E313
A series of 5‐arylisoxazole and 5‐aryl‐1H‐pyrazole derivatives was synthesized by the reaction of 3‐(dimethylamino)‐1‐arylprop‐2‐en‐1‐one with hydroxylamine hydrochloride or hydrazine hydrate under ultrasound irradiation without using any catalyst. This method has the advantages of easier work‐up, mild reaction condition, high yields, shorter reaction time, and environmentally benign procedure. 相似文献
957.
Tian‐hao Huang Ying‐hui Wang Zhi‐hui Kang Jin‐bo Yao Ran Lu Han‐zhuang Zhang 《Photochemistry and photobiology》2014,90(1):29-34
The effects of π‐spacer and electron donor groups on the photophysical behaviors of fluorenone‐based linear conjugated oligomers have been systemically investigated. Solvent‐dependent steady‐state measurements exhibit that the fluorene vinylene (FV) spacer and the electron‐donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength. 相似文献
958.
Ying‐Hui Wang Lu Zou Zhi‐Hui Kang Cheng Qian Fuyin Wang Yu‐Guang Ma Ran Lu Hong Ji Han‐Zhuang Zhang 《Photochemistry and photobiology》2014,90(1):45-50
We study the photophysical characters of two oligofluorenes‐functionalized anthracenes molecules with different fluorine‐vinylene (FV) units, which exhibits that “excimer” state appears in the solution after photoexcitation. The dynamic data shows that two mechanisms are responsible for the generation of “excimer”. The fast one is controlled by the arene‐arene interaction between molecules and the slow one is influenced by the diffusion motion of molecules. Increasing the number of FV units may suppress the DM‐dependent “excimer” and enhance the yield of intrinsic fluorescence, which finally improves the fluorescence property of molecules in solution. 相似文献
959.
Mn3O4资源丰富、结构稳定,具有较高的理论电容,是一种较有潜力的超级电容器材料,但其较差的导电性却阻碍了其在这方面应用。本论文以实心ε-MnO2微米粉体和具有亲水性的GO粉体为原料,在去离子水中通过磁力搅拌和冷冻干燥制备出具有良好接触的MnO2/GO复合粉体。然后经一步氢气还原处理,使实心ε-MnO2和GO同步转化为具有纳米多孔结构的多孔Mn3O4和RGO,从而获得分散均匀、具有高比表面积和优良导电性的高性能Mn3O4/RGO复合粉体。经电化学测试可知,Mn3O4/RGO复合粉体在2 mV/s的扫描速率下的比电容为25.2 F/g且具有较好的电容留存率。 相似文献
960.
Dr. Man‐Sheng Chen Xiong‐Wen Tan Dr. Chun‐Hua Zhang Dai‐Zhi Kuang 《无机化学与普通化学杂志》2011,637(9):1220-1223
A new three‐dimensional (3D) porous framework [Zn(INAIP)] · DMA · H2O ( 1 ) [INAIP = 5‐(isonicotinamido)isophthalate, DMA = N,N′‐dimethylacetamide] was synthesized by solvothermal methods and characterized by single‐crystal and powder X‐ray diffraction, as well as thermogravimetric analysis. The results of X‐ray diffraction analyses revealed that complex 1 has an unusual 3D architecture with the (3,6)‐connected rutile ( rtl ) topology. The adsorption behavior shows that compound 1 exhibits selective adsorptions of CO2 over N2 after the removal of the solvent molecules within the pores. 相似文献