全文获取类型
收费全文 | 303031篇 |
免费 | 3396篇 |
国内免费 | 982篇 |
专业分类
化学 | 142751篇 |
晶体学 | 3740篇 |
力学 | 16295篇 |
综合类 | 5篇 |
数学 | 56743篇 |
物理学 | 87875篇 |
出版年
2021年 | 2005篇 |
2020年 | 2259篇 |
2019年 | 2436篇 |
2018年 | 13223篇 |
2017年 | 12925篇 |
2016年 | 10608篇 |
2015年 | 3948篇 |
2014年 | 4745篇 |
2013年 | 11158篇 |
2012年 | 12737篇 |
2011年 | 20641篇 |
2010年 | 12518篇 |
2009年 | 12577篇 |
2008年 | 15853篇 |
2007年 | 18014篇 |
2006年 | 9401篇 |
2005年 | 9466篇 |
2004年 | 8959篇 |
2003年 | 8332篇 |
2002年 | 7219篇 |
2001年 | 7176篇 |
2000年 | 5660篇 |
1999年 | 4287篇 |
1998年 | 3469篇 |
1997年 | 3369篇 |
1996年 | 3284篇 |
1995年 | 2922篇 |
1994年 | 2728篇 |
1993年 | 2633篇 |
1992年 | 2885篇 |
1991年 | 2797篇 |
1990年 | 2696篇 |
1989年 | 2488篇 |
1988年 | 2546篇 |
1987年 | 2550篇 |
1986年 | 2378篇 |
1985年 | 3113篇 |
1984年 | 3339篇 |
1983年 | 2728篇 |
1982年 | 2890篇 |
1981年 | 2840篇 |
1980年 | 2705篇 |
1979年 | 2816篇 |
1978年 | 2890篇 |
1977年 | 2889篇 |
1976年 | 2949篇 |
1975年 | 2727篇 |
1974年 | 2687篇 |
1973年 | 2855篇 |
1972年 | 1798篇 |
排序方式: 共有10000条查询结果,搜索用时 345 毫秒
141.
142.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
143.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes 下载免费PDF全文
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
144.
145.
146.
V. I. Maksimov E. N. Maksimova T. P. Surkova V. D. Parkhomenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):31-41
The real structure of bulk Zn1 – хМхSe (S) crystals of diluted magnetic semiconductors with М = V, Cr, Fe, Co, Ni 3d impurities is characterized by neutron diffraction. These impurities are known to greatly destabilize even the initial lattices of pure zinc chalcogenides. Data on the resulting non-uniform microstrain field induced by atomic displacements are obtained from the structural peaks along the tangential and radial directions on the above crystals within a dopant concentration range of 0.01 ≤ х ≤ 0.10. Additional nodes with q = (1/3 1/3 1/3) 2π/a (q is the wave vector and a is the cubic unit cell) emerging in the reciprocal lattice of the cubic structure are considered as evidence for a pre-transition to the fcc (face-centered cubic)–hcp (hexagonal close-packed) phase state, which implies transitions from the fcc lattice along an 8-ray non-Lifshitz star with the wave vector k5 = μ(b1 + b2 + b3), where b1, b2, b3 are the reciprocal lattice vectors and μ ≈ 1/3. 相似文献
147.
Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films 下载免费PDF全文
Zhe Qiang Maurice L. Wadley Bryan D. Vogt Kevin A. Cavicchi 《Journal of Polymer Science.Polymer Physics》2015,53(15):1058-1064
Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064 相似文献
148.
149.
150.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献