全文获取类型
收费全文 | 1466篇 |
免费 | 15篇 |
国内免费 | 13篇 |
专业分类
化学 | 863篇 |
晶体学 | 5篇 |
力学 | 19篇 |
综合类 | 1篇 |
数学 | 298篇 |
物理学 | 186篇 |
无线电 | 122篇 |
出版年
2021年 | 11篇 |
2020年 | 8篇 |
2018年 | 13篇 |
2016年 | 22篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 72篇 |
2012年 | 61篇 |
2011年 | 70篇 |
2010年 | 39篇 |
2009年 | 32篇 |
2008年 | 66篇 |
2007年 | 70篇 |
2006年 | 70篇 |
2005年 | 73篇 |
2004年 | 67篇 |
2003年 | 54篇 |
2002年 | 65篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 21篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 41篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 27篇 |
1978年 | 30篇 |
1977年 | 24篇 |
1976年 | 24篇 |
1975年 | 27篇 |
1974年 | 22篇 |
1973年 | 19篇 |
1972年 | 14篇 |
1971年 | 8篇 |
1968年 | 9篇 |
排序方式: 共有1494条查询结果,搜索用时 281 毫秒
91.
92.
93.
Dr. Rebeca Arevalo Dr. Ramón López Prof. Larry R. Falvello Dr. Lucía Riera Dr. Julio Perez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):379-389
The reactions of [Re(N-N)(CO)3(PMe3)]OTf (N-N=2,2′-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt3 have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt3 reacted with [Re(bipy)(CO)3(PMe3)]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral ReI products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to ReI complexes containing bipy- and phen-derived chelates with several C(sp3) centers. 相似文献
94.
Peter Alfeld Larry L. Schumaker Tatyana Sorokina 《Advances in Computational Mathematics》2010,32(4):381-391
A variant of the classical C
1 Powell-Sabin-12 macro-element is defined that has the same approximation power, but has fewer degrees of freedom and only
requires vertex data. The same idea is then applied to a related C
1 trivariate macro-element. 相似文献
95.
Govindarajan Muralidharan Kanth Kurumaddali Andrew K. Kercher Larry Walker Scott G. Leslie 《Journal of Electronic Materials》2013,42(2):240-248
There is a need for next-generation, high-performance power electronic packages and systems utilizing wide-band-gap devices to operate at high temperatures in automotive and electricity transmission applications. Sn-3.5Ag solder is a candidate for use in such packages with potential maximum operating temperatures of about 200°C. However, there is a need to understand the thermal cycling reliability of Sn-3.5Ag solders subject to such high-temperature operating conditions. The results of a study on the damage evolution occurring in large-area Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates with Au/Ni-P metallization subject to thermal cycling between 200°C and 5°C are presented in this paper. Interface structure evolution and damage accumulation were followed using high-resolution X-ray radiography, cross-sectional optical and scanning electron microscopies, and X-ray microanalysis in these joints for up to 3000 thermal cycles. Optical and scanning electron microscopy results showed that the stresses introduced by the thermal cycling result in cracking and delamination at the copper–intermetallic compound interface. X-ray microanalysis showed that stresses due to thermal cycling resulted in physical cracking and breakdown of the Ni-P barrier layer, facilitating Cu-Sn interdiffusion. This interdiffusion resulted in the formation of Cu-Sn intermetallic compounds underneath the Ni-P layer, subsequently leading to delamination between the Ni-rich layer and Cu-Sn intermetallic compounds. 相似文献
96.
Daniel J. Tao Dr. Mikko Muuronen Yuriy Slutskyy Alexander Le Prof. Filipp Furche Prof. Larry E. Overman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8786-8790
The stereochemical outcome of reactions of chiral nucleophilic trisubstituted acetonide radicals with electron‐deficient alkenes is dictated by a delicate balance between destabilizing non‐bonding interactions and stabilizing hydrogen‐bonding between substituents on the α and β carbons. 相似文献
97.
Valentina Simonetti Jason Y. Park Nicholas J. Panaro Larry J. Kricka 《Journal of nanoparticle research》2008,10(2):365-368
Nylon nanorods and nanotubes (200 nm diameter) were fabricated by the membrane wetting technique (solvent and melt wetting)
from a range of nylons (6; 6,6; 6,9; 6,10; 6,12; 11; 12, 6(3)T) and nylon blended with different dyes (Nylon Cast Blue, Nylon
6/6 Black) or with molybdenum disulfide (Nylon cast MDS). The 65-μm long nylon nanotubes and nanorods were characterized by
scanning electron microscopy. The nanoscale nylon 6,6 served as an effective high surface area alternative to a nylon membrane
as a solid support in a chemiluminescent assay for nylon-bound biotinylated nucleic acids based on streptavidin- alkaline
phosphatase and chemiluminescent detection of the bound alkaline phosphatase label with the dioxetane substrate, CDP-Star.
Layer-by-layer deposition of the cationic polymer (Sapphire-II™; Tropix) onto the nylon 6,6 nanostructures prior to UV-cross-linking
with biotinylated DNA resulted in further enhancement of binding and detection of biotinylated DNA. 相似文献
98.
Summary. We derive error bounds for bivariate spline interpolants which are calculated by minimizing certain natural energy norms.
Received March 28, 2000 / Revised version received June 23, 2000 / Published online March 8, 2002
RID="*"
ID="*" Supported by the National Science Foundation under grant DMS-9870187
RID="**"
ID="**" Supported by the National Science Foundation under grant DMS-9803340 and by the Army Research Office under grant DAAD-19-99-1-0160 相似文献
99.
VanNieuwenhze MS Mauldin SC Zia-Ebrahimi M Winger BE Hornback WJ Saha SL Aikins JA Blaszczak LC 《Journal of the American Chemical Society》2002,124(14):3656-3660
Bacterial peptidoglycan is composed of a network of beta-[1,4]-linked glyan strands that are cross-linked through pendant peptide chains. The final product, the murein sacculus, is a single, covalently closed macromolecule that precisely defines the size and shape of the bacterial cell. The recent increase in bacterial resistance to cell wall active agents has led to a resurgence of activity directed toward improving our understanding of the resistance mechanisms at the molecular level. The biosynthetic enzymes and their natural substrates can be invaluable tools in this endeavor. While modern experimental techniques have led to isolation and purification of the biosynthetic enzymes utilized in peptidoglycan biosynthesis, securing useful quantities of their requisite substrates from natural substrates has remained problematic. In an effort to address this issue, we report the first total synthesis of lipid II (4), the final monomeric intermediate utilized by Gram positive bacteria for peptidoglycan biosynthesis. 相似文献
100.
Larry D. Merkle 《Solid State Communications》1984,52(3):299-302
Two recent theories of pressure dependent impurity optical spectra are tested by constraining the configurational coordinate parameters using crystal field theory. It is found that the theory of Drickamer, Frank and Slichter is more consistent with crystal field behavior and with experimental evidence than that of Curie, Berry and Williams. 相似文献