全文获取类型
收费全文 | 202643篇 |
免费 | 1960篇 |
国内免费 | 588篇 |
专业分类
化学 | 101632篇 |
晶体学 | 2859篇 |
力学 | 9286篇 |
综合类 | 5篇 |
数学 | 22468篇 |
物理学 | 68941篇 |
出版年
2021年 | 1647篇 |
2020年 | 1797篇 |
2019年 | 1998篇 |
2018年 | 2699篇 |
2017年 | 2600篇 |
2016年 | 3764篇 |
2015年 | 2304篇 |
2014年 | 3614篇 |
2013年 | 9084篇 |
2012年 | 7239篇 |
2011年 | 8733篇 |
2010年 | 6040篇 |
2009年 | 5908篇 |
2008年 | 7911篇 |
2007年 | 8079篇 |
2006年 | 7722篇 |
2005年 | 6889篇 |
2004年 | 6424篇 |
2003年 | 5650篇 |
2002年 | 5491篇 |
2001年 | 6424篇 |
2000年 | 4931篇 |
1999年 | 3794篇 |
1998年 | 3038篇 |
1997年 | 3045篇 |
1996年 | 2790篇 |
1995年 | 2613篇 |
1994年 | 2462篇 |
1993年 | 2337篇 |
1992年 | 2690篇 |
1991年 | 2588篇 |
1990年 | 2523篇 |
1989年 | 2324篇 |
1988年 | 2388篇 |
1987年 | 2386篇 |
1986年 | 2221篇 |
1985年 | 2912篇 |
1984年 | 3179篇 |
1983年 | 2589篇 |
1982年 | 2758篇 |
1981年 | 2715篇 |
1980年 | 2592篇 |
1979年 | 2695篇 |
1978年 | 2787篇 |
1977年 | 2803篇 |
1976年 | 2864篇 |
1975年 | 2651篇 |
1974年 | 2626篇 |
1973年 | 2755篇 |
1972年 | 1743篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
91.
Dr. Christopher R. Opie Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki Dr. Naoya Kumagai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4648-4653
The B3NO2 six-membered heterocycle (1,3-dioxa-5-aza-2,4,6-triborinane=DATB), comprising three different non-carbon period 2 elements, has been recently demonstrated to be a powerful catalyst for dehydrative condensation of carboxylic acids and amines. The tedious synthesis of DATB, however, has significantly diminished its utility as a catalyst, and thus the inherent chemical properties of the ring system have remained virtually unexplored. Here, a general and facile synthetic strategy that harnesses a pyrimidine-containing scaffold for the reliable installation of boron atoms is disclosed, giving rise to a series of Pym-DATBs from inexpensive materials in a modular fashion. The identification of a soluble Pym-DATB derivative allowed for the investigation of the dynamic nature of the B3NO2 ring system, revealing differential ring-closing and -opening behaviors depending on the medium. Readily accessible Pym-DATBs proved their utility as efficient catalysts for dehydrative amidation with broad substrate scope and functional-group tolerance, offering a general and practical catalytic alternative to reagent-driven amidation. 相似文献
92.
93.
Vovchenko E. D. Kozlovskij K. I. Shikanov A. E. Karimov A. R. Rashchikov V. I. Shatokhin V. L. Isaev A. A. Deryabochkin O. V. 《Physics of Particles and Nuclei Letters》2020,17(4):498-502
Physics of Particles and Nuclei Letters - The collective acceleration of laser plasma ions in a rapidly increasing magnetic field (108 T/s) excited by a powerful current pulse in a low-inductive... 相似文献
94.
95.
96.
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
97.
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
98.
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
99.
100.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献