全文获取类型
收费全文 | 103008篇 |
免费 | 10359篇 |
国内免费 | 6736篇 |
专业分类
化学 | 63564篇 |
晶体学 | 1288篇 |
力学 | 6090篇 |
综合类 | 517篇 |
数学 | 11903篇 |
物理学 | 36741篇 |
出版年
2023年 | 1413篇 |
2022年 | 1902篇 |
2021年 | 2497篇 |
2020年 | 2793篇 |
2019年 | 2690篇 |
2018年 | 2622篇 |
2017年 | 2302篇 |
2016年 | 3556篇 |
2015年 | 3327篇 |
2014年 | 4160篇 |
2013年 | 6212篇 |
2012年 | 7135篇 |
2011年 | 7699篇 |
2010年 | 5304篇 |
2009年 | 5238篇 |
2008年 | 5608篇 |
2007年 | 5194篇 |
2006年 | 4852篇 |
2005年 | 4196篇 |
2004年 | 3534篇 |
2003年 | 2814篇 |
2002年 | 2565篇 |
2001年 | 2744篇 |
2000年 | 2307篇 |
1999年 | 2292篇 |
1998年 | 1892篇 |
1997年 | 1712篇 |
1996年 | 1704篇 |
1995年 | 1524篇 |
1994年 | 1429篇 |
1993年 | 1238篇 |
1992年 | 1216篇 |
1991年 | 1116篇 |
1990年 | 1001篇 |
1989年 | 887篇 |
1988年 | 805篇 |
1987年 | 767篇 |
1986年 | 670篇 |
1985年 | 738篇 |
1984年 | 669篇 |
1983年 | 516篇 |
1982年 | 528篇 |
1981年 | 486篇 |
1980年 | 400篇 |
1979年 | 447篇 |
1978年 | 434篇 |
1977年 | 446篇 |
1976年 | 439篇 |
1975年 | 399篇 |
1973年 | 390篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
Guangrui Chen Yuxing Yan Dr. Jie Wang Prof. Yong Sik Ok Guiyuan Zhong Prof. Bu Yuan Guan Prof. Yusuke Yamauchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19831-19836
Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition. 相似文献
112.
In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC4H3X ( 1 X ), SiC4H2X2 ( 2 X ), SiC4HX3 ( 3 X ), and SiC4X4 ( 4 X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔEs-t, a possible indication of stability), and band gap (ΔEH-L) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X . Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F . The trend of divalent angle () for each X is 4 X > 1 X > 3 X > 2 X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔEs-t and ΔEH-L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry. 相似文献
113.
The sunset diagram of λφ4 theory is evaluated numerically in cutoff scheme and a nonzero finite term(in accordance with dimensional regularization (DR) result) is found in contrast to published calculations. This findingdramatically reduces the critical couplings for symmetry breaking in the two-loop effective potential discussed in ourprevious work. 相似文献
114.
115.
ON A PAIR OF NON-ISOMETRIC ISOSPECTRAL DOMAINS WITH FRACTAL BOUNDARIES AND THE WEYL-BERRY CONJECTURE
ONAPAIROFNONISOMETRICISOSPECTRALDOMAINSWITHFRACTALBOUNDARIESANDTHEWEYLBERRYCONJECTURESLEEMAN,B.D.CHENHUAManuscriptrec... 相似文献
116.
117.
在氢化丁苯共聚物13C-NMR谱脂肪碳部分谱带归属的基础上,根据各谱带的主要来源,推导出六个二单元浓度的计算公式。计算出二单元、一单元的相对含量,各结构单元的数均序列长度、嵌段含量和其它结构参数。加氢前后的1H-和13C-NMR谱的组成计算结果基本一致。初步探讨了作为粘度指数改进剂的氢化丁苯共聚物微观结构与性能的关系,为合成提供了依据。 相似文献
118.
Palladium and molybdenum polycrystalline layers (clusters) have been deposited in a stainless steel UHV system onto a layer of alumina (Al2O3). This layer has been prepared by high temperature oxidation of an aluminium layer. The interaction of this system with nitrogen has been investigated at room temperature by an FEM technique. Under these conditions nitrogen spillover from molybdenum to palladium has been observed. 相似文献
119.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
120.
V. D. Orlov Z. Kaluski N. P. Borob'eva E. Figas A. A. Tishchenko F. G. Yaremko 《Chemistry of Heterocyclic Compounds》1994,30(8):964-971
We have measured the PMR spectra of 5, 7-diaryl-1, 4-diazabicyclo[4. ].O]hept-4-enes. We have studied the structure of the 5-(4-nitrophenyl)-7-phenyl derivative by x-ray diffraction. We show that the six-membered heterocycle has the half-chair form. The 6-H and 7-H protons of the aziridine ring are trans, while the 7-aryl is exo relative to the six-membered ring. Introduction of substituents into the aromatic ring has practically no effect on the geometry of the bicycle.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1124, August, 1994.For Communication 11, see [1]. 相似文献