全文获取类型
收费全文 | 670943篇 |
免费 | 7395篇 |
国内免费 | 2092篇 |
专业分类
化学 | 334632篇 |
晶体学 | 9554篇 |
力学 | 33051篇 |
综合类 | 19篇 |
数学 | 107936篇 |
物理学 | 195238篇 |
出版年
2021年 | 4264篇 |
2020年 | 4858篇 |
2019年 | 5193篇 |
2018年 | 20617篇 |
2017年 | 20872篇 |
2016年 | 17538篇 |
2015年 | 7790篇 |
2014年 | 10121篇 |
2013年 | 24851篇 |
2012年 | 24432篇 |
2011年 | 39373篇 |
2010年 | 25281篇 |
2009年 | 25277篇 |
2008年 | 33429篇 |
2007年 | 37427篇 |
2006年 | 20097篇 |
2005年 | 24042篇 |
2004年 | 20289篇 |
2003年 | 18655篇 |
2002年 | 16254篇 |
2001年 | 16178篇 |
2000年 | 12480篇 |
1999年 | 9748篇 |
1998年 | 8227篇 |
1997年 | 7942篇 |
1996年 | 7879篇 |
1995年 | 7052篇 |
1994年 | 6769篇 |
1993年 | 6655篇 |
1992年 | 7357篇 |
1991年 | 7405篇 |
1990年 | 7057篇 |
1989年 | 6954篇 |
1988年 | 6922篇 |
1987年 | 6867篇 |
1986年 | 6479篇 |
1985年 | 8470篇 |
1984年 | 8717篇 |
1983年 | 7013篇 |
1982年 | 7368篇 |
1981年 | 7225篇 |
1980年 | 6842篇 |
1979年 | 7234篇 |
1978年 | 7535篇 |
1977年 | 7227篇 |
1976年 | 7198篇 |
1975年 | 6720篇 |
1974年 | 6623篇 |
1973年 | 6803篇 |
1972年 | 4659篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
S. Venkatesan S. Suresh P. Ramu M. Kandasamy J. Arumugam S. Thambidurai K.M. Prabu N. Pugazhenthiran 《印度化学会志》2022,99(5):100436
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications. 相似文献
42.
Satyanarayana A. V. S. Rao M. Jagannadha Mouli K. Chandra 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(3):1509-1513
Journal of Radioanalytical and Nuclear Chemistry - 相似文献
43.
44.
In a 2:2 reaction with silver(I) chloride or bromide, 1,5-bis(1-phospholano)pentane ( 1a ) afforded frame-like macrocyclic structures, with intra- ( 2 , Cl) or intermolecular ( 3 , Br) halido bridges. In contrast, 1,7-bis(1-phospholano)heptane ( 1b ) formed coordination polymers 4a (Cl) and 4b (Br) with bridging bis-phospholane and halido ligands. A unique paddle wheel-type metallacryptand structure 5 was obtained from 1a and silver(I) bromide in a 2:3 reaction (M:L). All complexes were fully characterized by NMR, IR spectroscopy, mass spectrometry, and X-ray crystallography. 相似文献
45.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
46.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
47.
ABSTRACTThe Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle. 相似文献
48.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. 相似文献
49.
50.
Knyazev A. A. Karyakin M. E. Krupin A. S. Galyametdinov Yu. G. 《Russian Journal of General Chemistry》2015,85(12):2806-2812
Russian Journal of General Chemistry - Hybrid liquid crystal systems with different ratios of the components have been prepared on the basis of 5,5′-di(heptadecyl)-2,2′-bipyridine... 相似文献