全文获取类型
收费全文 | 28407篇 |
免费 | 4723篇 |
国内免费 | 3587篇 |
专业分类
化学 | 20912篇 |
晶体学 | 467篇 |
力学 | 1546篇 |
综合类 | 223篇 |
数学 | 3016篇 |
物理学 | 10553篇 |
出版年
2024年 | 106篇 |
2023年 | 612篇 |
2022年 | 1129篇 |
2021年 | 1274篇 |
2020年 | 1360篇 |
2019年 | 1280篇 |
2018年 | 1093篇 |
2017年 | 1039篇 |
2016年 | 1451篇 |
2015年 | 1534篇 |
2014年 | 1750篇 |
2013年 | 2364篇 |
2012年 | 2665篇 |
2011年 | 2667篇 |
2010年 | 1855篇 |
2009年 | 1764篇 |
2008年 | 2023篇 |
2007年 | 1654篇 |
2006年 | 1476篇 |
2005年 | 1259篇 |
2004年 | 963篇 |
2003年 | 743篇 |
2002年 | 679篇 |
2001年 | 542篇 |
2000年 | 478篇 |
1999年 | 466篇 |
1998年 | 321篇 |
1997年 | 240篇 |
1996年 | 309篇 |
1995年 | 238篇 |
1994年 | 211篇 |
1993年 | 189篇 |
1992年 | 152篇 |
1991年 | 133篇 |
1990年 | 120篇 |
1989年 | 100篇 |
1988年 | 80篇 |
1987年 | 63篇 |
1986年 | 67篇 |
1985年 | 60篇 |
1984年 | 41篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1971年 | 7篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Rui-Jia Chen Jun-Jie Wang Li Han Yu-Cheng Gu Zhi-Ping Xu Jia-Gao Cheng Xu-Sheng Shao Xiao-Yong Xu Zhong Li 《Journal of heterocyclic chemistry》2021,58(7):1429-1436
A series of diamide derivatives containing α-amino acids were designed and synthesized. These compounds were evaluated for their insecticidal activities against Plutella xylostella, Mythimna separate, Myzus persicae, and Tetranychus cinnabarinus. Most of the title compounds containing an l -phenylglycine skeleton were endowed with good activities at the concentration of 500 mg·L−1. Compounds ( R)-A6 showed a potential value for further optimization as an insecticidal lead with the LC50 value of 86.8 mg·L−1. 相似文献
992.
Sun Mingxia Han Lijuan Li Aijuan Zhu Xunzhen Wu Wenjun Zhang Jiwen 《Chemistry of Natural Compounds》2021,57(6):1081-1085
Chemistry of Natural Compounds - A series of novel L-pyroglutamate containing 1,2,3-triazole ring substructures was synthesized and characterized by adopting an appropriate synthetic scheme. The... 相似文献
993.
Chemical Characteristic of Bioactive Polysaccharides Isolated from Ornithogalum caudatum Ait. 总被引:3,自引:0,他引:3
SHILei LIJuan LIUWen-Xiang WANGYong LIUZhi-qiang LIUShu-ying 《高等学校化学研究》2003,19(3):286-289
A water-soluble crude extract prepared from Ornithogalum caudatum Ait. (()CA) showing a high immunomodulating activitiy was isolated and characterized by virtue of gel filtration and column chromatography. The presence of the monosaccharides has been established by the chemical analysis. The quantitative analysis of the alditol acetate derivatives of them showed the ratios of the monosaccharides analyzed by means of GC respectively. The concentrations of protein(280 nm) and carbohydrate(496 nm) were detected respectively. The information of the molecular weight from the pure polysaccharide was obtained by several standard Dextrans from the Sephadex chromatography. 相似文献
994.
Yonggyu Han 《Journal of organometallic chemistry》2003,679(1):48-58
Nine thermally stable complexes (η5-Cp*)[η5-(C5H4)CMe2CB10H10CR]MCl2 (R=H and Me) and (η5-Cp*)[η5; η1-(C5H4)CMe2(CB10H10C)]MCl have been prepared via metathesis reactions of Cp*MCl3 (M=Ti, Zr and Hf, Cp*=pentamethylcyclopentadienyl) with monolithium salts of (C5H5)CMe2(CB10H10CR) (R=H and Me) and with dilithium salt of (C5H5)CMe2(CB10H10CH), respectively. These compounds have been fully characterized by various spectroscopic methods and elemental analyses. All of the compounds except (η5-Cp*)[η5-(C5H4)CMe2CB10H10CMe]HfCl2 were additionally characterized by a single crystal X-ray diffraction study, establishing their monomeric bent metallocene structural feature with carborane acting as a substituent or an ancillary ligand. The titanium and zirconium complexes produce high-density polyethylenes with the activity range of about 103-104 g PE per mol of M bar h in the presence of modified methylaluminoxane cocatalyst. 相似文献
995.
Roland J. Caubergs Han H. Asard Jan A. DeGreef Frans J. Leeuwerik Fred L. Oltmann 《Photochemistry and photobiology》1986,44(5):641-649
Sucrose density gradient centrifugation of a microsomal membrane fraction of cauliflower inflorescences showed a strong correlation between a blue light mediated cytochrome b reduction (LIAC) and an ion stimulated nitrate-insensitive but a vanadate-sensitive ATPase activity at 38-40% sucrose. LIAC activity and vanadate-sensitive ATPase might be assigned to the same type of membrane different from ER, Golgi, tonoplast and mitochondria. The Mg2+ -dependent ATP-hydrolytic activity obtained after purification of the microsomal fraction on an aqueous polymer two phase system was partially characterized. Temperature optimum (40°C), pH optimum (pH 7.0), vanadate inhibition (I50 at 20 μ M ), substrate kinetics ( K m = 1.37 m M Mg.ATP) and inhibitor studies all point to the presence of the frequently described plasma membrane ATPase. Potassium and Na+ stimulated the enzyme activity (20-40%). In general our data arc strongly in favour of the hypothesis that LIAC activity is localized on the plant plasma membrane. The cytochrome b involved in the light reaction has a midpoint potential near +150 mV. This cytochrome which has been previously shown in a cauliflower microsomal fraction is a constituent of the plasma membrane. 相似文献
996.
Arthur A. Santilli Dong Han Kim Stephen V. Wanser 《Journal of heterocyclic chemistry》1971,8(3):445-453
A novel method for the preparation of esters and amides of thieno[2,3-d]pyrimidine-6-carb-oxylic acids was described. A typical example was the direct formation of ethyl 5-amino-2-methylthiothieno[2,3-d]pyrimidine-6-earboxylate(IIIa) from 4-chloro-2-methylthio-5-pyrimidine-carbonitrile (Ia) and ethyl mercaptoacetate in refluxing ethanol containing sodium carbonate. Displacement of the methylthio group in IIIa by various amines gave the corresponding amino derivatives. The reactions of IIIa and related compounds with acetylating agents such as acetic anhydride or chloroacetyl chloride gave various products. Treatment of 5-carbethoxy-4-chloro-2-phenylpyrimidine(IV) with methyl mercaptoacetate afforded the dechloro intermediate diester Va, which cyclized on reaction with sodium ethoxide to form methyl 5-hydroxy-2-phenylthieno-[2,3-d]pyrimidine-6-carboxylate (Vla). The synthesis was expanded to include the preparation of various new 2,4,5-trisubstituted thieno[2,3-d]pyrimidine-6-carboxylic acid esters and amides (Charts I-V). 相似文献
997.
A highly sensitive nanomechanical cantilever sensor assay based on an electrical measurement has been developed for detecting activated cyclic adenosine monophosphate (cyclic AMP)-dependent protein kinase (PKA). Employing a peptide derived from the heat-stable protein kinase inhibitor (PKI), a magnetic bead system was first selected as a vehicle to immobilize the PKI-(5-24) peptide for capturing PKA catalytic subunit and the activity assay was applied for indirectly assessing the binding. Synergistic interactions of adenosine triphosphate (ATP) and the peptide inhibitor with the kinase were then investigated by a solution phase capillary electrophoretic assay, and by surface plasmon resonance technology which involved immobilization of the peptide inhibitor. After systemically evaluated by a homogeneous direct binding assay, the ATP-dependent recognition of the catalytic subunit of PKA by PKI-(5-24) was successfully transferred on to the nanomechanical cantilevers at protein concentrations of 6.6 pM-66 nM, exhibiting much higher sensitivity and wider dynamic range than the conventional activity assay. Thus, direct assessment of activated kinases using the cantilever sensor system functionalized with specific peptide inhibitors holds great promise in analytical applications and clinical medicine. 相似文献
998.
Formation of ternary complexes between a macrotricyclic host and hetero-guest pairs: an acid-base controlled selective complexation process 总被引:1,自引:0,他引:1
A triptycene-based cylindrical macrotricyclic host can include diquat and electron-rich aromatics simultaneously to form stable ternary complexes, which is stabilized not only by a charge-transfer (CT) interaction between electron-rich and electron-deficient guests but also by the face to face pi-stacking interactions between the host and the guests. Moreover, a selective complexation process between a ternary complex containing benzidine and a binary complex can be effectively controlled by the use of acid and base. 相似文献
999.
Lei Wang Pinhua Li Jianhui Chen Jincan Yan 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1807-1813
Tellurium metal in near-critical water (275°;C) provides a novel and efficient method for the reduction of azides, producing amines in good yields. 相似文献
1000.