全文获取类型
收费全文 | 68323篇 |
免费 | 7951篇 |
国内免费 | 10911篇 |
专业分类
化学 | 47314篇 |
晶体学 | 3741篇 |
力学 | 1241篇 |
综合类 | 340篇 |
数学 | 2525篇 |
物理学 | 16684篇 |
无线电 | 15340篇 |
出版年
2024年 | 185篇 |
2023年 | 896篇 |
2022年 | 1560篇 |
2021年 | 1759篇 |
2020年 | 2177篇 |
2019年 | 2111篇 |
2018年 | 1803篇 |
2017年 | 2438篇 |
2016年 | 2721篇 |
2015年 | 2584篇 |
2014年 | 3607篇 |
2013年 | 5802篇 |
2012年 | 4217篇 |
2011年 | 4686篇 |
2010年 | 4077篇 |
2009年 | 4519篇 |
2008年 | 4608篇 |
2007年 | 4708篇 |
2006年 | 4618篇 |
2005年 | 4178篇 |
2004年 | 3747篇 |
2003年 | 3058篇 |
2002年 | 2514篇 |
2001年 | 2019篇 |
2000年 | 1855篇 |
1999年 | 1585篇 |
1998年 | 1345篇 |
1997年 | 1188篇 |
1996年 | 1160篇 |
1995年 | 1049篇 |
1994年 | 951篇 |
1993年 | 784篇 |
1992年 | 674篇 |
1991年 | 466篇 |
1990年 | 259篇 |
1989年 | 219篇 |
1988年 | 189篇 |
1987年 | 130篇 |
1986年 | 104篇 |
1985年 | 111篇 |
1984年 | 80篇 |
1983年 | 54篇 |
1982年 | 59篇 |
1981年 | 63篇 |
1980年 | 60篇 |
1979年 | 53篇 |
1978年 | 40篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
62.
《Magnetic resonance in chemistry : MRC》2003,41(9):660-670
Reduced forms of iso‐α‐acids (isohumulones), used in modern beer brewing were separated and characterized by 1H and 13C NMR spectroscopy. Components from mixtures of rho‐iso‐α‐acids, tetrahydro‐iso‐α‐acids, and hexahydro‐iso‐α‐acids were isolated using high‐performance liquid chromatography (HPLC) and analyzed by use of one‐ and two‐dimensional NMR experiments. The data presented assign the identities of the main peaks in the HPLC traces for the reduced iso‐α‐acids. Previous tentative assignments regarding the cis and trans configurations and the structures of the acyl residues of the reduced iso‐α‐acids were confirmed and extensive NMR assignments were made. Furthermore, the previously unknown stereochemistry in the C‐4 side‐chain of the rho‐ and hexahydro‐iso‐α‐acids was assigned. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
63.
Martin A. Bos Bertus Dunnewind Ton van Vliet 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):95-105
Interfacial rheological properties and their suitability for foam production and stability of two vegetable proteins were studied and compared to β-casein. Proteins used ranged from flexible to rigid/globular in the order of β-casein, gliadin and soy glycinin. Experiments were performed at pH 6.7. Network forming properties were characterised by the surface dilational modulus (determined with the ring trough) and the critical falling film length (Lstill) at which a stagnant protein film will break. Gliadin had the highest dilational modulus, followed by glycinin and β-casein, whereas glycinin formed the strongest film against fracture in the overflowing cylinder. The rate of decrease in the surface tension was studied at the air–water (Wilhelmy plate method) and the oil–water interface (bursting membrane) and the dynamic surface tension during compression and expansion in the caterpillar. Gliadin had the lowest equilibrium interfacial tensions and β-casein the lowest dynamic surface tension during expansion. Hardly any foam could be formed at a concentration of 0.1 g/l by shaking. At a concentration of 1.4 g/l most foam was formed by β-casein, followed by gliadin and glycinin. It seems that in the first place the rate of adsorption is important for foam formation. For the vegetable proteins, adsorption was slow. This resulted in lower foamability, especially for glycinin. 相似文献
64.
65.
综合介绍了LED显示技术的现状,详细叙述了全色LED显示的关键技术和主要性能,对LED在室内,室外的应用前景作出评述。 相似文献
66.
67.
续竞存 《固体电子学研究与进展》1996,16(3):254-258
用电荷控制及热电子弹道运动模型计算InAs/InP0.7Sb0.3热电子晶体管的截止频率fT及最高振荡频率fmax。结果表明,fT、fmax分别达到280GHz及600GHz。并指出,通过生长GaSb中间层,InAs/InP0.7Sb0.3HET可在GaAs衬底上实现单片集成。 相似文献
68.
This Review discusses the synthesis and characterization by our Group of new antibiotics belonging to the class of penicillins, cephalosporins and rifamycins with ferrocenyl and 1, 1′-ferrocenilene residues in the molecule. As reactants for 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA) the following were used: 1, 1-bis(chlorocarbonyl)ferrocene, ferrocenyl sulfochloride, 1, 1′-ferrocenylenedisulfochloride and thioglycolic acids S-modified with ferrocene. In the synthesis of rifamycins, the hydrazides of the thioglycolic acids, S-modified with ferrocene, were employed as nucleophilic agents. The synthesized intermediates were characterized by elemental analysis, TLC, IR, UV and 1H NMR spectra. The characterization of new antibiotics was made by TLC, IR and UV spectral analysis. Biological activity was tested on Gram-negative and Gram-positive bacteria. Good activity is reported towards Gram-positive bacteria in the case of derivatives containing residues of thioglycolic acid S-modified with ferrocene, the antibacterial activity being similar to that of amoxicillin, carbenicillin and cephalothin. All compounds are inactive towards Gram-negative bacteria. 相似文献
69.
以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃~45℃,无光损伤。 相似文献
70.
多传感器数据融合技术已在军事领域受到广泛重视,并逐步走向实际应用,本文简要介绍它的一般组成、特点以及在军事C^3I系统应用中的主要功效。 相似文献