全文获取类型
收费全文 | 2906篇 |
免费 | 53篇 |
国内免费 | 19篇 |
专业分类
化学 | 1794篇 |
晶体学 | 19篇 |
力学 | 87篇 |
数学 | 491篇 |
物理学 | 587篇 |
出版年
2021年 | 22篇 |
2020年 | 25篇 |
2018年 | 30篇 |
2016年 | 44篇 |
2015年 | 29篇 |
2014年 | 42篇 |
2013年 | 124篇 |
2012年 | 98篇 |
2011年 | 146篇 |
2010年 | 80篇 |
2009年 | 75篇 |
2008年 | 126篇 |
2007年 | 140篇 |
2006年 | 145篇 |
2005年 | 166篇 |
2004年 | 151篇 |
2003年 | 118篇 |
2002年 | 117篇 |
2001年 | 63篇 |
2000年 | 45篇 |
1999年 | 28篇 |
1998年 | 35篇 |
1997年 | 29篇 |
1996年 | 54篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 45篇 |
1992年 | 34篇 |
1991年 | 35篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 34篇 |
1987年 | 27篇 |
1986年 | 23篇 |
1985年 | 65篇 |
1984年 | 42篇 |
1983年 | 30篇 |
1982年 | 49篇 |
1981年 | 54篇 |
1980年 | 50篇 |
1979年 | 36篇 |
1978年 | 36篇 |
1977年 | 31篇 |
1976年 | 39篇 |
1975年 | 36篇 |
1974年 | 38篇 |
1973年 | 39篇 |
1972年 | 27篇 |
1971年 | 15篇 |
1968年 | 16篇 |
排序方式: 共有2978条查询结果,搜索用时 15 毫秒
101.
Syntheses of 1b-d is described using 1-chloro-2-deoxy-3,5-di-p-toluoyl-D-erythro-pentosyl chloride. 相似文献
102.
103.
Two efficient syntheses of 3-chloro-7-[(chlorocarbonyl)methoxy]-4-methylcoumarin are described, one utilizing traditional chemistry starting from 3-chloro-7-hydroxy-4-methylcoumarin, while the other uses a novel reagent, sulfuryl chloride/thionyl chloride, in a one-pot reaction starting from 7-(carboxymethoxy)-4-methylcoumarin. 相似文献
104.
J. F. Lawrence R. W. Frei 《International journal of environmental analytical chemistry》2013,93(4):317-325
The fluorigenic labelling of several N-methyl carbamates is carried out using 1-dimethyl-aminonaphthalene-5-sulfonyl chloride (dansyl chloride). Prior to chromatography the carbamates are reacted in aqueous solution with the dansyl chloride. The derivative is extracted from the solution with n-hexane and subsequently spotted on a thin-layer plate for chromatography. For each N-methyl carbamate, two highly fluorescent spots are obtained. One is common to all N-methyl carbamates studied, whereas the other is characteristic of each individual carbamate. N.m.r. and infrared spectroscopic data indicate that the common spot is the methylamine derivative, and the second spot is the derivative from the phenyl moiety of each carbamate. The sensitivity of the method is less than one nanogram and has been successfully applied to the analysis of natural water samples. 相似文献
105.
Kätchen K. Lachmayr Charlotte M. Wentz Prof. Lawrence R. Sita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1537-1542
“One-component” soft material Frank–Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self-reconfiguration and close packing of an initial assembly of identical “deformable” spheres into two or more size- or shape-distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid-state assembly, and low thermodynamic stability. Here we show that a readily-accessible sugar–polyolefin conjugate quantitatively produces an exceptionally stable solid-state FK A15 phase through a rapid and irreversible thermotropic order–order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non-equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar–polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems. 相似文献
106.
Saikat Banerjee Waqas Rasheed Ruixi Fan Dr. Apparao Draksharapu Dr. Williamson N. Oloo Prof. Dr. Yisong Guo Prof. Dr. Lawrence Que Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9608-9613
The [FeIV(O)(Me3NTB)]2+ (Me3NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, 1H NMR spectroscopy was used to determine that 1 does not have C3-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme FeIV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 FeIV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the FeIV=O center to rationalize nonheme oxoiron(IV) reactivity. 相似文献
107.
Prof. Dr. Jevgenij A. Raskatov Dr. Scott Virgil Dr. Hsiau-Wei Lee Dr. Lawrence M. Henling Ka Chan Ariel J. Kuhn Alejandro R. Foley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4467-4470
Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO2 chromatography and allows obtaining both diastereomers in purities exceeding 99 %. 1H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol−1, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides. 相似文献
108.
109.
110.
ANKA is a relatively new synchrotron radiation facility at the Forschungszentrum Karlsruhe, a large government research center in the southwest of Germany. The acronym stands for Angstrom Source Karlsruhe. The electron storage ring is 110.4 m in circumference and stores a 2.5 GeV electron beam at a typical current of 200 mA. The facility has been open for users since March 2003. 相似文献