全文获取类型
收费全文 | 36223篇 |
免费 | 907篇 |
国内免费 | 801篇 |
专业分类
化学 | 15661篇 |
晶体学 | 355篇 |
力学 | 1791篇 |
综合类 | 58篇 |
数学 | 9593篇 |
物理学 | 10473篇 |
出版年
2023年 | 124篇 |
2022年 | 232篇 |
2021年 | 321篇 |
2020年 | 292篇 |
2019年 | 279篇 |
2018年 | 1387篇 |
2017年 | 1648篇 |
2016年 | 1005篇 |
2015年 | 823篇 |
2014年 | 820篇 |
2013年 | 1177篇 |
2012年 | 3786篇 |
2011年 | 2955篇 |
2010年 | 2261篇 |
2009年 | 1946篇 |
2008年 | 1061篇 |
2007年 | 1028篇 |
2006年 | 998篇 |
2005年 | 4771篇 |
2004年 | 4202篇 |
2003年 | 2534篇 |
2002年 | 724篇 |
2001年 | 444篇 |
2000年 | 211篇 |
1999年 | 288篇 |
1998年 | 209篇 |
1997年 | 148篇 |
1996年 | 126篇 |
1995年 | 113篇 |
1994年 | 89篇 |
1993年 | 74篇 |
1992年 | 218篇 |
1991年 | 205篇 |
1990年 | 161篇 |
1989年 | 130篇 |
1988年 | 121篇 |
1987年 | 76篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 36篇 |
1976年 | 80篇 |
1975年 | 39篇 |
1974年 | 41篇 |
1973年 | 52篇 |
1972年 | 41篇 |
1970年 | 40篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Marijana ?aković Zora Popović 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):m507-m509
In the title compound, [Ni(N3)2(C6H6N2O)2], the NiII atom lies on an inversion centre. The distorted octahedral nickel(II) coordination environment contains two planar trans-related N,O-chelating picolinamide ligands in one plane and two monodentate azide ligands perpendicular to this plane. Molecules are linked into a three-dimensional framework by N—H...N hydrogen bonds. 相似文献
92.
NIKITIN S.; PR?TZEL-WOLTERS D. 《IMA Journal of Mathematical Control and Information》1991,8(4):431-439
In 1983 Morse proved, for unknown scalar one-dimensional linearsystems, the nonexistence of rational or polynomial universalstabilizers (UAS). In 1983, Nussbaum gave an example of an analyticUAS. In our paper, it is shown that there exist time-invariantpolynomial UAS's with multidimensional gain adaptation. Thedesign procedure is developed for linear, minimum-phase systemsof relative degree one. Convergence of the closed-loop systemis proved. Some numerical simulations are provided. 相似文献
93.
Ivica ?ilovi Dubravka Matkovi‐alogovi Ivan Kos Mladen Biru Milena Jadrijevi‐Mladar Taka
《Acta Crystallographica. Section C, Structural Chemistry》2007,63(1):o45-o47
In the crystal structures of two cyclic trihydroxamic acid derivatives containing the same substructure unit, viz. 1,3,5‐trihydroxy‐1,3,5‐triazinane‐2,4,6‐trione dihydrate, C3H3N3O6·2H2O, (I), and 1,3,5‐benzyloxy‐1,3,5‐triazinane‐2,4,6‐trione, C24H21N3O6, (II), there is no significant difference in the geometric parameters. In (I), there are 11 hydrogen bonds of the O—H⋯O type interconnecting the molecules in a three‐dimensional network, while in (II) there are only two weak C—H⋯O hydrogen bonds. The results of IR spectroscopic analysis are in good agreement with the crystallographic study. 相似文献
94.
95.
Suoyuan Lian Lei Gao Zhenhui Kang Di Wu Yang Lan Lin Xu 《Solid State Communications》2004,132(6):375-378
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed. 相似文献
96.
对一类遗传程序设计问题,提出了简单等长的分布式染色体,取代复杂变长的树结构染色体,使演化算子操作更方便,个体复杂度得到有效控制.用该染色体形式解决割草问题,分析了分布式染色体带来的一些性质,并给出了很好的计算结果. 相似文献
97.
Katalin E. Kövér Dušan Uhr?&#x;n Victor J. Hruby 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):162-168
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time. 相似文献
98.
Georgia Benkart Seok-Jin Kang Duncan Melville 《Transactions of the American Mathematical Society》1998,350(8):3297-3319
We construct quantum deformations of enveloping algebras of Borcherds superalgebras, their Verma modules, and their irreducible highest weight modules.
99.
超重元素(新核素)合成研究进展情况分析和展望 总被引:2,自引:0,他引:2
本文在介绍和分析国际、国内在超重元素(新核素)合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素(核)合成研究工作提出一些看法和建议,提供讨论。 相似文献
100.
E.Y. Kang Yoon B. Kim K.Y. Kim Y.H. Chung H.K. Baik 《Journal of magnetism and magnetic materials》2006
FeSiBNb amorphous powder cores were prepared with the amorphous powder by gas atomization and subsequent hot pressing of resulting powder after creating oxide layers on the amorphous powder. Fully amorphous FeSiBNb powders with good soft magnetic properties were successfully obtained in the particle size range below 100 μm. FeSiBNb amorphous powder cores exhibit stable permeability up to 10 MHz, showing excellent high-frequency characteristics. 相似文献