全文获取类型
收费全文 | 14175篇 |
免费 | 1724篇 |
国内免费 | 1644篇 |
专业分类
化学 | 6873篇 |
晶体学 | 94篇 |
力学 | 549篇 |
综合类 | 99篇 |
数学 | 901篇 |
物理学 | 3038篇 |
综合类 | 5989篇 |
出版年
2024年 | 76篇 |
2023年 | 255篇 |
2022年 | 506篇 |
2021年 | 535篇 |
2020年 | 510篇 |
2019年 | 520篇 |
2018年 | 441篇 |
2017年 | 441篇 |
2016年 | 587篇 |
2015年 | 660篇 |
2014年 | 810篇 |
2013年 | 910篇 |
2012年 | 1037篇 |
2011年 | 1020篇 |
2010年 | 723篇 |
2009年 | 713篇 |
2008年 | 793篇 |
2007年 | 659篇 |
2006年 | 643篇 |
2005年 | 570篇 |
2004年 | 475篇 |
2003年 | 521篇 |
2002年 | 696篇 |
2001年 | 590篇 |
2000年 | 388篇 |
1999年 | 425篇 |
1998年 | 302篇 |
1997年 | 252篇 |
1996年 | 245篇 |
1995年 | 195篇 |
1994年 | 180篇 |
1993年 | 155篇 |
1992年 | 163篇 |
1991年 | 123篇 |
1990年 | 115篇 |
1989年 | 86篇 |
1988年 | 68篇 |
1987年 | 46篇 |
1986年 | 48篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1971年 | 2篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1955年 | 1篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
本文用小角x射线射法法对硒化蓖麻酸多相脂质体的抗癌作用从结构和功能上进行了研究。 相似文献
52.
H. L. Frisch Yongpeng Xue 《Journal of polymer science. Part A, Polymer chemistry》1995,33(12):1979-1985
A hybrid inorganic/organic interpenetrating polymer network (IPN) of a three-dimensional network structure zeolite crystal (13X, powder) and crosslinked or linear polystyrene (PS) was prepared and characterized by differential scanning calorimetry (DSC), solid-state13C-NMR, and scanning electron microscopy (SEM). The size and shape of the crystalline zeolite particles were revealed on SEM micrographs in both the pure zeolite and the IPNs. Solubility tests and the results of DSC with solid-state 13C-NMR confirm that some organic PS chains are incorporated within the internal three-dimensional channels of the zeolite particles. We speculate that the internal PS chains may adopt an extended “one-dimensional” conformation and exhibit no bulk polymer glass transition. These novel hybrid inorganic/organic IPNs are a new kind of IPN structure. © 1995 John Wiley & Sons, Inc. 相似文献
54.
Hui-Zhen Li Cheng-tian Xue Xiang-wen Chen 《International Journal of Infrared and Millimeter Waves》1991,12(12):1425-1436
This paper describes a global optimization design for quasi-optics power combiner of solid-state millimeter-wave sources. The operating frequency is about 100 GHz and the oscillating sources are GaAs Gunn diodes. The source-array plane is a matrix consisting of NxN (N=3,5, ..., 2k+1, where k is positive integer) diodes. The radio frequency power of the combiner is from threefold to sevenfold larger than the sum total of the single diodes power. The global optimums of the array and the location in the cuvity of the suorce-array plane will be given by a global optimizition method. 相似文献
55.
本文描述了利用KTP晶体和腔的基波输出镜构成非线性镜实现1.08μmNd:YAP激光器的被动锁模。实验表明,这种新的锁模技术比用染料作可饱和吸收体的被动锁模技术有很多突出的优点,具有很大的发展潜力。实验测得锁模时基波1.08μm输出2.4mJ,二次谐波0.54μm输出0.5mJ(同样条件下的静态输出为2.5mJ),基波脉冲的平均脉宽为40ps。 相似文献
56.
57.
58.
Xu Zhang Dongfeng Xue Meinan Liu Henryk Ratajczak Dongli Xu 《Journal of Molecular Structure》2005,754(1-3):25-30
On the basis of the crystallographic characteristics of lithium niobate (LN) crystals, Law of Bravais and Pauling's third rule (i.e. Polyhedral Sharing Rule) are employed with the aim to find the relationship between the crystal structure and morphological faces of LN powders. In order to validate our analytical results, we have successfully synthesized LN powders and measured the corresponding X-ray powder diffraction. Our results show that the structural analysis is consistent with the experimental data and is helpful and effective for us to control the single-crystal growth and to design superstructures at the specific plane, starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame. 相似文献
59.
Zhigang Zhang Jianping Deng Weiguo Zhao Jianmin Wang Wantai Yang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):500-508
A novel chiral N‐propargylsulfamide monomer ( 1a ) and its enantiomer ( 1b ) were synthesized and polymerized with (nbd)Rh+B?(C6H5)4 as a catalyst providing poly(1) (poly( 1a ) and poly( 1b )) in high yields (≥99%). Poly(1) could take stable helices in less polar solvents (chloroform and THF), demonstrated by strong circular dichroism signals and UV–vis absorption peaks at about 415 nm and the large specific rotations; but in more polar solvents including DMF and DMSO, poly(1) failed to form helix. Quantitative evaluation with anisotropy factor showed that the helical screw sense had a relatively high thermal stability. These results together with the IR spectra measured in solvents showed that hydrogen bonding between the neighboring sulfamide groups is one of the main driving forces for poly(1) to adopt stable helices. In addition, copolymerization of monomer 1a and monomer 2 was conducted, the solubility of poly(1) was improved drastically. However, the copolymerization had adverse effects on the formation of stable helices in the copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 500–508, 2007 相似文献
60.
The wavelet and harmonic filtering method suggested by Zalevsky and Ouzieli is introduced in this paper and adopted in our volume holographic image recognition system. This composite filter combines several scaled versions of the cascaded wavelet and harmonic filter, obtaining high discrimination ability and wide dynamic range of rotation and scale deformations. Optical experiments are conducted to demonstrate the validity and practicability of the algorithm. To the best of our knowledge, this is the first report of using this algorithm in a volume holographic system. Moreover, the separate correlation approach proposed in this paper greatly simplifies the manufacturing process and reduces the cost of the system. 相似文献