全文获取类型
收费全文 | 6081篇 |
免费 | 206篇 |
国内免费 | 34篇 |
专业分类
化学 | 4523篇 |
晶体学 | 36篇 |
力学 | 139篇 |
数学 | 840篇 |
物理学 | 783篇 |
出版年
2023年 | 34篇 |
2022年 | 21篇 |
2021年 | 52篇 |
2020年 | 84篇 |
2019年 | 83篇 |
2018年 | 57篇 |
2017年 | 50篇 |
2016年 | 153篇 |
2015年 | 130篇 |
2014年 | 140篇 |
2013年 | 283篇 |
2012年 | 376篇 |
2011年 | 424篇 |
2010年 | 215篇 |
2009年 | 185篇 |
2008年 | 386篇 |
2007年 | 421篇 |
2006年 | 452篇 |
2005年 | 381篇 |
2004年 | 341篇 |
2003年 | 304篇 |
2002年 | 272篇 |
2001年 | 71篇 |
2000年 | 39篇 |
1999年 | 42篇 |
1998年 | 38篇 |
1997年 | 68篇 |
1996年 | 74篇 |
1995年 | 63篇 |
1994年 | 63篇 |
1993年 | 98篇 |
1992年 | 55篇 |
1991年 | 53篇 |
1990年 | 70篇 |
1989年 | 50篇 |
1988年 | 40篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 70篇 |
1984年 | 55篇 |
1983年 | 37篇 |
1982年 | 66篇 |
1981年 | 57篇 |
1980年 | 47篇 |
1979年 | 47篇 |
1978年 | 44篇 |
1977年 | 27篇 |
1976年 | 40篇 |
1975年 | 23篇 |
1974年 | 19篇 |
排序方式: 共有6321条查询结果,搜索用时 15 毫秒
81.
Victoria E. Wright Fernando Castro-Gómez Ewa Jurneczko James C. Reynolds Andrew Poulton Steven D. R. Christie Perdita Barran Carles Bo Colin S. Creaser 《International Journal for Ion Mobility Spectrometry》2013,16(1):61-67
Collision cross sections (CCS) have been measured for three salen ligands, and their complexes with copper and zinc using travelling-wave ion mobility-mass spectrometry (TWIMS) and drift tube ion mobility-mass spectrometry (DTIMS), allowing a comparative size evaluation of the ligands and complexes. CCS measurements using TWIMS were determined using peptide and TAAH calibration standards. TWIMS measurements gave significantly larger CCS than DTIMS in helium, by 9 % for TAAH standards and 3 % for peptide standards, indicating that the choice of calibration standards is important in ensuring the accuracy of TWIMS-derived CCS measurements. Repeatability data for TWIMS was obtained for inter- and intra-day studies with mean RSDs of 1.1 % and 0.7 %, respectively. The CCS data obtained from IM-MS measurements are compared to CCS values obtained via the projection approximation, the exact hard spheres method and the trajectory method from X-ray coordinates and modelled structures using density functional theory (DFT) based methods. 相似文献
82.
Steven A. Barker Jimo Borjigin Izabela Lomnicka Rick Strassman 《Biomedical chromatography : BMC》2013,27(12):1690-1700
We report a qualitative liquid chromatography–tandem mass spectrometry (LC/MS/MS) method for the simultaneous analysis of the three known N,N‐dimethyltryptamine endogenous hallucinogens, their precursors and metabolites, as well as melatonin and its metabolic precursors. The method was characterized using artificial cerebrospinal fluid (aCSF) as the matrix and was subsequently applied to the analysis of rat brain pineal gland‐aCSF microdialysate. The method describes the simultaneous analysis of 23 chemically diverse compounds plus a deuterated internal standard by direct injection, requiring no dilution or extraction of the samples. The results demonstrate that this is a simple, sensitive, specific and direct approach to the qualitative analysis of these compounds in this matrix. The protocol also employs stringent MS confirmatory criteria for the detection and confirmation of the compounds examined, including exact mass measurements. The excellent limits of detection and broad scope make it a valuable research tool for examining the endogenous hallucinogen pathways in the central nervous system. We report here, for the first time, the presence of N,N‐dimethyltryptamine in pineal gland microdialysate obtained from the rat. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
83.
84.
Steven J. Wittenberger Andrew Tasker Bryan K. Sorensen B. Gregory Donner 《合成通讯》2013,43(22):3231-3248
The facile preparation of 2-butyl-4-iodoimidazole-5-carboxaldehyde 1 is described. The versatility of this intermediate in the synthesis of highly tunctionalized imidazoles is demonstrated with the synthesis of two potent and selective angiotensin II receptor antagonists. 相似文献
85.
We give an overview of some remarkable connections between symmetric informationally complete measurements (SIC-POVMs, or SICs) and algebraic number theory, in particular, a connection with Hilbert’s 12th problem. The paper is meant to be intelligible to a physicist who has no prior knowledge of either Galois theory or algebraic number theory. 相似文献
86.
By gluing together the sides of eight copies of an all-right angled hyperbolic six-dimensional polytope, two orientable hyperbolic six-manifolds with Euler characteristic ?1 are constructed. They are the first known examples of orientable hyperbolic six-manifolds having the smallest possible volume. 相似文献
87.
Oriented closed curves on an orientable surface with boundary are described up to continuous deformation by reduced cyclic
words in the generators of the fundamental group and their inverses. By self-intersection number one means the minimum number
of transversal self-intersection points of representatives of the class. We prove that if a class is chosen at random from
among all classes of m letters, then for large m the distribution of the self-intersection number approaches the Gaussian distribution. The theorem was strongly suggested
by a computer experiment with four million curves producing a very nearly Gaussian distribution. 相似文献
88.
89.
Molecular and morphological characterization of midblock‐sulfonated styrenic triblock copolymers 下载免费PDF全文
Kenneth P. Mineart Justin J. Ryan Byeongdu Lee Steven D. Smith Richard J. Spontak 《Journal of Polymer Science.Polymer Physics》2017,55(6):490-497
Midblock‐sulfonated triblock copolymers afford a desirable opportunity to generate network‐forming amphiphilic materials that are suitable for use in a wide range of emerging technologies as fuel‐cell, water‐desalination, ion‐exchange, photovoltaic, or electroactive membranes. Employing a previously reported synthetic strategy wherein poly(p‐tert‐butylstyrene) remains unreactive, we have selectively sulfonated the styrenic midblock of a poly(p‐tert‐butylstyrene‐b‐styrene‐b‐p‐tert‐butylstyrene) (TST) triblock copolymer to different extents. Comparison of the resulting sulfonated copolymers with results from our prior study provides favorable quantitative agreement and suggests that a shortened reaction time is advantageous. An ongoing challenge regarding the morphological development of charged block copolymers is the competition between microphase separation of the incompatible blocks and physical cross‐linking of ionic clusters, with the latter often hindering the former. Here, we expose the sulfonated TST copolymers to solvent‐vapor annealing to promote nanostructural refinement. The effect of such annealing on morphological characteristics, as well as on molecular free volume, is explored. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 490–497 相似文献
90.