全文获取类型
收费全文 | 110145篇 |
免费 | 6621篇 |
国内免费 | 5262篇 |
专业分类
化学 | 63430篇 |
晶体学 | 1317篇 |
力学 | 6092篇 |
综合类 | 387篇 |
数学 | 13638篇 |
物理学 | 37164篇 |
出版年
2023年 | 855篇 |
2022年 | 1348篇 |
2021年 | 2057篇 |
2020年 | 2603篇 |
2019年 | 2800篇 |
2018年 | 3119篇 |
2017年 | 3081篇 |
2016年 | 3885篇 |
2015年 | 2781篇 |
2014年 | 3928篇 |
2013年 | 5678篇 |
2012年 | 5952篇 |
2011年 | 6425篇 |
2010年 | 4973篇 |
2009年 | 4986篇 |
2008年 | 5266篇 |
2007年 | 4955篇 |
2006年 | 4483篇 |
2005年 | 3968篇 |
2004年 | 3571篇 |
2003年 | 3145篇 |
2002年 | 3080篇 |
2001年 | 2835篇 |
2000年 | 2192篇 |
1999年 | 1753篇 |
1998年 | 1667篇 |
1997年 | 1431篇 |
1996年 | 1413篇 |
1995年 | 1203篇 |
1994年 | 1304篇 |
1993年 | 1216篇 |
1992年 | 1167篇 |
1991年 | 1215篇 |
1990年 | 1221篇 |
1989年 | 1110篇 |
1988年 | 998篇 |
1987年 | 969篇 |
1986年 | 943篇 |
1985年 | 1010篇 |
1984年 | 983篇 |
1983年 | 893篇 |
1982年 | 848篇 |
1979年 | 836篇 |
1978年 | 847篇 |
1977年 | 851篇 |
1976年 | 962篇 |
1975年 | 852篇 |
1974年 | 892篇 |
1973年 | 891篇 |
1972年 | 770篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
JETP Letters - The electronic and transport properties of new hybrid 2D–1D–2D structures of carbon atoms, which are graphene sheets continuously connected through a fragment of a... 相似文献
42.
Chinese Annals of Mathematics, Series B - In the present article, the authors find and establish stability of multiplier ideal sheaves, which is more general than strong openness. 相似文献
43.
Gaineev A. M. Galkina I. V. Davletshin R. R. Davletshina N. V. Kuznetsov N. O. Grishaev D. Yu. Shulayeva M. P. Pozdeev O. K. 《Russian Journal of General Chemistry》2022,92(7):1208-1213
Russian Journal of General Chemistry - Aminophosphabetaines, i.e., isobutyl {[alkyl(dimethyl)ammonio]methyl}phosphonates with higher alkyl substituents at the nitrogen atom, were obtained by a... 相似文献
44.
Pasyukov D. V. Chernenko A. Yu. Lavrentev I. V. Baydikova V. A. Minyaev M. E. Starovoytova O. A. Chernyshev V. M. 《Russian Chemical Bulletin》2022,71(5):993-1008
Russian Chemical Bulletin - The reaction of 1,4-disubstituted thiosemicarbazides with N,N-dimethylformamide dimethyl acetal afforded 1,4-disubstituted 1,2,4-triazolium-3-thiolates. Heating of the... 相似文献
45.
46.
Complex Study of the Spearhead Superficial Crust from Burial Mound no. 1 near Novosvobodnaya Village
Loboda A. Yu. Kolobylina N. N. Veligzhanin A. A. Zubavitchus Y. V. Tereshchenko E. Yu. Shishlina N. I. Yatsishina E. B. Kashkarov P. K. 《Crystallography Reports》2018,63(2):295-301
A complex study of a spearhead dated back to IV mill. BC from burial mound no. 1 near Novosvobodnaya village (collection of the State Historical Museum) and, in particular, the material of spearhead superficial crust has been performed. The elemental and phase composition of the metal of spearhead and the superficial crust on its surface have been determined by scanning electron microscopy, jointly with energydispersive X-ray microanalysis and X-ray phase analysis. A comparative analysis of the results of studying the spearhead superficial crust and similar crusts on other artifacts from the mounds near Novosvobodnaya village suggest natural origin of the crust on copper?arsenic artifacts.
相似文献47.
对硫化镉反蛋白石结构光子晶体薄膜进行了可控合成,用巯基乙酸修饰的纳米晶和P(St-MMA-SPMAP)高分子小球共组装,成功地构筑了反蛋白石结构并用于可见光光解水产氢。结果表明,在可见光(λ≥420 nm)照射下,Cd S-310反蛋白石结构薄膜的光解水产氢性能比硫化镉纳米颗粒提高了一倍。这主要是因为等级孔结构反蛋白石光子晶体特性对催化剂的光催化性能的提升:首先,反蛋白石的周期性结构增加了光子在材料中的传播,提高了催化剂对太阳光的利用率;同时,大孔孔壁是由纳米颗粒堆积而成的,在反应中提供了更多的反应活性位点;此外,孔结构有利于物质的传输和分子的吸附。 相似文献
48.
Ajay Gupta Fillip Kumar Sarkar Rajib Sarkar Ramen Jamatia Chang Yeon Lee Gajendra Gupta Amarta Kumar Pal 《应用有机金属化学》2020,34(9):e5782
Magnetically retrieval CuFe2O4@MIL-101(Cr) metal–organic framework was successfully prepared from easily available starting materials and characterized using various spectroscopic and analytical techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, elemental mapping, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, vibrating sample magnetometer, and inductively coupled plasma optical emission spectroscopy. The catalyst was then used in the synthesis of benzodiazepines containing a triazole moiety in water. The advantages of this protocol include high yields, reusability of the catalyst, and gram-scale synthesis. 相似文献
49.
Dr. Zhoulong Fan Katherine L. Bay Dr. Xiangyang Chen Zhe Zhuang Han Seul Park Dr. Kap-Sun Yeung Prof. Dr. K. N. Houk Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4800-4807
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process. 相似文献
50.
Peter T. Smith Younghoon Kim Dr. Bahiru Punja Benke Prof. Kimoon Kim Prof. Christopher J. Chang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4932-4937
We report a supramolecular strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. We utilized cobalt tetraphenylporphyrin (Co-TPP), an oxygen reduction reaction (ORR) catalyst with highly variable product selectivity, as a building block to assemble the permanently porous supramolecular cage Co-PB-1(6) bearing six Co-TPP subunits connected through twenty-four imine bonds. Reduction of these imine linkers to amines yields the more flexible cage Co-rPB-1(6). Both Co-PB-1(6) and Co-rPB-1(6) cages produce 90–100 % H2O2 from electrochemical ORR catalysis in neutral pH water, whereas the Co-TPP monomer gives a 50 % mixture of H2O2 and H2O. Bimolecular pathways have been implicated in facilitating H2O formation, therefore, we attribute this high H2O2 selectivity to site isolation of the discrete molecular units in each supramolecule. The ability to control reaction selectivity in supramolecular structures beyond traditional host–guest interactions offers new opportunities for designing such architectures for a broader range of catalytic applications. 相似文献