全文获取类型
收费全文 | 6453篇 |
免费 | 256篇 |
国内免费 | 45篇 |
专业分类
化学 | 4763篇 |
晶体学 | 24篇 |
力学 | 207篇 |
数学 | 882篇 |
物理学 | 878篇 |
出版年
2023年 | 63篇 |
2022年 | 71篇 |
2021年 | 126篇 |
2020年 | 118篇 |
2019年 | 148篇 |
2018年 | 91篇 |
2017年 | 82篇 |
2016年 | 197篇 |
2015年 | 165篇 |
2014年 | 205篇 |
2013年 | 369篇 |
2012年 | 465篇 |
2011年 | 500篇 |
2010年 | 271篇 |
2009年 | 240篇 |
2008年 | 424篇 |
2007年 | 436篇 |
2006年 | 391篇 |
2005年 | 361篇 |
2004年 | 338篇 |
2003年 | 299篇 |
2002年 | 249篇 |
2001年 | 84篇 |
2000年 | 80篇 |
1999年 | 65篇 |
1998年 | 56篇 |
1997年 | 60篇 |
1996年 | 74篇 |
1995年 | 49篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 34篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 18篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 39篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 37篇 |
1976年 | 27篇 |
1975年 | 28篇 |
1974年 | 16篇 |
1973年 | 18篇 |
排序方式: 共有6754条查询结果,搜索用时 15 毫秒
991.
High‐Frequency Fe–H Vibrations in a Bridging Hydride Complex Characterized by NRVS and DFT
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Vladimir Pelmenschikov Dr. Leland B. Gee Dr. Hongxin Wang Dr. K. Cory MacLeod Sean F. McWilliams Dr. Kazimer L. Skubi Prof. Dr. Stephen P. Cramer Prof. Dr. Patrick L. Holland 《Angewandte Chemie (International ed. in English)》2018,57(30):9367-9371
High‐spin iron species with bridging hydrides have been detected in species trapped during nitrogenase catalysis, but there are few general methods of evaluating Fe?H bonds in high‐spin multinuclear iron systems. An 57Fe nuclear resonance vibrational spectroscopy (NRVS) study on an Fe(μ‐H)2Fe model complex reveals Fe?H stretching vibrations for bridging hydrides at frequencies greater than 1200 cm?1. These isotope‐sensitive vibrational bands are not evident in infrared (IR) spectra, showing the power of NRVS for identifying hydrides in this high‐spin iron system. Complementary density functional theory (DFT) calculations elucidate the normal modes of the rhomboidal iron hydride core. 相似文献
992.
Patrick Headley 《Journal of Algebraic Combinatorics》1997,6(4):331-338
Let be an irreducible crystallographic rootsystem in a Euclidean space V, with + theset of positive roots. For ,
, let
be the hyperplane
. We define a set of hyperplanes
. This hyperplane arrangement is significant inthe study of the affine Weyl groups. In this paper it is shown that thePoincaré polynomial of
is
, where n is the rank of and h is the Coxeter number of the finiteCoxeter group corresponding to . 相似文献
993.
Patrick Chiu 《Proceedings of the American Mathematical Society》1997,125(3):723-730
Relations between the height and the determinant of the Laplacian on the space of -dimensional flat tori and the classical formulas of Kronecker and Epstein are established. Extrema of the height are shown to exist, and results for a global minimum for 2-d tori and a local minimum for 3-d tori are given, along with more general conjectures of Sarnak and Rankin.
994.
The matrix elements of the exponential of a finite difference realization of the one-dimensional Laplacian are found exactly. This matrix is used to formulate an efficient algorithm for the numerical solution to the time-dependent quantum mechanical scattering of a single particle from a time-independent potential in one-space and one-time dimension. The method generalizes to higher spatial dimensions, as well as to multiparticle problems. 相似文献
995.
Since the seminal remark by Pecora and Carroll [Phys. Rev. Lett. 64, 821 (1990)] that one can synchronize chaotic systems, the main example in the related literature has been the Lorenz equations. Yet this literature contains a mixture of true and false, and of justified and unsubstantiated claims about the synchronization properties of the Lorenz equations. In this note we clarify some of the confusion. (c) 1997 American Institute of Physics. 相似文献
996.
Forman Mark A. Zanoni Brian C. Chopko Emily C. Carroll Patrick J. 《Structural chemistry》1998,9(1):27-32
The synthesis and X-ray crystal structure of the p-bromoanilide derivative of bicyclo[2.2.0]hexane-l-carboxylic acid (1), N-(4-bromophenyl)-bicyclo[2.2.0]hexane-l-carboxamide (2), is reported. N-(4-Bromophenyl)-bicyclo[2.2.0]hexane-l-carboxamide is synthesized in good yield via the DCC coupling of bicyclo[2.2.0]hexane-l-carboxylic acid (1) with p-bromoaniline. Low-temperature X-ray analysis of 2 reveals that the
bonds of the bicyclo[2.2.0]hexane skeleton vicinal to the amide group show a slight lengthening due to conjugative interaction with the -accepting amide group. Ab initio calculations at the 6-31G* level of theory on bicyclo[2.2.0]hexane-l-carboxamide, a model for 2, and for other 1-substituted bicyclo[2.2.0]hexanes are also reported. 相似文献
997.
Patrick A. Wayman 《Europhysics News》1998,28(5-6):159-160
George Johstone Stony, th man who maned the electron, was led to the concept of a fundamental unit of electic charge by combining electro-chemistry with the kinetic theory of gases. But his understanding was incomplete (so the discovery of the electron is associated wit JJ Thomsons determination of its charge to mass ratio in October 1897) 相似文献
998.
Friebele EJ Putnam MA Patrick HJ Kersey AD Greenblatt AS Ruthven GP Krim MH Gottschalck KS 《Optics letters》1998,23(3):222-224
We report ultrahigh-sensitivity static strain sensing (noise equivalent strain =1.5n rms) by two fiber etalon cavities made from silica and fluoride fibers. The anomalous thermo-optic coefficient of fluoride glass fibers allows for determination of thermal and laser drift. This sensor is also capable of simultaneous strain and temperature measurement, with errors in strain and temperature of 6.4% and 0.68%, respectively. 相似文献
999.
A Li-Na-containing borosilicate glass was submitted to aqueous corrosion in static mode in tritiated solutions of various pH at room temperature and 90 °C. Tritium counting, β-autoradiography, scanning electron microscopy (SEM) and ion beam analysis (IBA) techniques have been used to investigate the composition variations of the leached glass surfaces. In an acidic medium, the glass surface is covered by a thick hydrated silica layer; mobile elements like Li, Na and B and transition elements like Fe and Mo are strongly depleted. Near pH 7, relative enrichments of aluminium and iron are shown together with strong Li, Na and B depletions. In a basic medium, the glass surface exhibits iron and molybdenum enrichments whereas mobile elements seem to be kept at their nominal concentration level at the glass surface. The tritium activity and distribution on the leached glass surface is shown to depend strongly on the pH of the tritiated solutions. These observations are correlated with the observed changes of the surface morphology and chemistry characterized by IBA and SEM analysis. Elemental solubility versus pH of various chemical species have been calculated for comparison purpose with the experimental observations. 相似文献
1000.
Lohier JF Foucoin F Jaffrès PA Garcia JI Sopková-de Oliveira Santos J Perrio S Metzner P 《Organic letters》2008,10(6):1271-1274
A straightforward and high-yielding access to various [2.2]paracyclophanes possessing a sulfur-based functional group is reported, the key step being a SEAr reaction mediated by a sulfonium salt. The versatility of the methodology was exemplified by an original application in sulfenate salt chemistry, from which a remarkable chirality transfer was observed. 相似文献