全文获取类型
收费全文 | 20496篇 |
免费 | 4143篇 |
国内免费 | 3163篇 |
专业分类
化学 | 15375篇 |
晶体学 | 404篇 |
力学 | 1112篇 |
综合类 | 246篇 |
数学 | 2105篇 |
物理学 | 8560篇 |
出版年
2024年 | 56篇 |
2023年 | 497篇 |
2022年 | 696篇 |
2021年 | 926篇 |
2020年 | 1131篇 |
2019年 | 1082篇 |
2018年 | 903篇 |
2017年 | 887篇 |
2016年 | 1158篇 |
2015年 | 1202篇 |
2014年 | 1438篇 |
2013年 | 1827篇 |
2012年 | 2078篇 |
2011年 | 2119篇 |
2010年 | 1539篇 |
2009年 | 1406篇 |
2008年 | 1510篇 |
2007年 | 1230篇 |
2006年 | 1065篇 |
2005年 | 862篇 |
2004年 | 706篇 |
2003年 | 526篇 |
2002年 | 448篇 |
2001年 | 374篇 |
2000年 | 302篇 |
1999年 | 313篇 |
1998年 | 229篇 |
1997年 | 177篇 |
1996年 | 203篇 |
1995年 | 146篇 |
1994年 | 138篇 |
1993年 | 110篇 |
1992年 | 85篇 |
1991年 | 97篇 |
1990年 | 71篇 |
1989年 | 58篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1969年 | 2篇 |
1959年 | 2篇 |
1957年 | 7篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
151.
JIN Fenga b FENG Xiao-Juna TIAN Leia WU Jie-Yinga ZHOU Hong-Pinga TIAN Yu-Penga c a 《结构化学》2005,24(6):645-650
A new compound 1,1‘-bis(3-pyridyl)-propylene(3,7-diformyl-N-ethylphenothiazinyl)ketone (C30H23N3O2S, Mr = 489.4) has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction method. The crystal is of orthorhombic, space group Ima2 with a = 27.491 (5), b = 11.942(2), c = 7.389(2) A, V = 2425.8(7) A^3, Z = 8, Dc =1.340 g/cm^3,μ = 0,167 mm ^1, F(000) = 1024, the final R = 0.0363 and wR = 0.0869 for 2054 unique reflections with Rint = 0.0254. The structural determination shows that the molecule assumes a butterfly configuration with nearly planar wings. In addition, the electrochemical study indicates that there is a high electronic delocalization in the molecule. 相似文献
152.
Meng F. Q. Lu M. K. Yang Z. H. Zeng H. 《Journal of Thermal Analysis and Calorimetry》1998,52(2):609-613
The thermal behavior of two new non-linear optical (NLO) materials, urea-(D) tartaric acid (UDT) and urea-(DL) tartaric acid
(UDLT) were studied by using DSC, TG and TMA. The results show that: 1) The two crystals have different melting points but
similar decomposition temperatures due to the influences of intermolecular forces, which is attributed to the stereo effects
of (D)-tartaric and (DL)-tartaric acid molecules; 2) There was only thermal expansion and no thermal contraction when the
UDT and UDLT crystals were heated; 3) There was no phase transition within the measured temperature range; 4) The thermal
expansion of the UDT and UDLT crystals shows a small anisotropy; 5) The specific heats of UDT and UDLT change linearly with
temperature in the measured temperature range and the value for UDT is 1.321 J g-1 K-1 at 320 K while the specific heat of
UDLT is 1.357 J g-1 K-1 at the same temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
153.
154.
Fa‐Yan Meng Xu‐Qing Liu Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):m341-m342
The terephthalate dianion and the bis(imidazolyl)benzene ligand of the title compound, {[Zn(C8H4O4)(C20H14N4)]·C2H6O}n, each bridges two adjacent zinc centers, resulting in a layer‐type coordination polymer; the zinc center shows tetrahedral coordination. The disordered ethanol solvent molecules occupy the spaces between the layers and are hydrogen bonded to the layers. The two symmetry‐independent dianions lie on different inversion sites. 相似文献
155.
We reported controllable synthesis of ZnS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as
a polymer matrix. In a typical run, the appropriate amounts of zinc chloride (ZnCl2) and sodium sulfide (Na2S) in the presence of 2-mercaptoethanol (ME) as the organic ligand were well dispersed in H2O/dimethylformamide solution without any aggregation. In addition, the Mn-doped ZnS nanocrystals (NCs) were synthesized with
similar method. Then, ZnS-PMMA hybrids were obtained via free radical polymerization in situ by using ZnS NCs functionalized
with methacryloxypropyltrimethoxysilane (MPS). FT-IR characterization indicates the formation of robust bonding between ZnS
NCs and the organic ligand. The TEM images show that ZnS NCs are well dispersed in PMMA matrix, and particle size of as-prepared
ZnS NCs is about 2.6 nm, in agreement with the computing results of Brus’s model and Debye–Scherrer formula. The photoluminescence
measurements present that ZnS NCs, Mn-doped ZnS NCs, and ZnS/PMMA hybrid show good optical properties. 相似文献
156.
157.
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
158.
THE NECESSARY AND SUFFICIENT CONDITIONS FOR THE SOLVABILITY OF A CLASS OF THE MATRIX INVERSE PROBLEM
Censider the solutions of the matrix inverse problem, which are symmetric positive semide finite on a subspace. Necessary and sufficient conditions for the solvability, as well as the general solution are obtained. The best approximate solution by the above solution set is given. Thus the open problem in [1] is solved. 相似文献
159.
本文把文[1]、[2]的变换技巧推广到变系数线性系统(i=1,…,n),用函数方法,研究了n=2、3时零解的稳定性,得到了零解稳定的若干判据.有关系数a_(ij)(t)不必都限制为有界. 相似文献
160.