全文获取类型
收费全文 | 793篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 604篇 |
晶体学 | 17篇 |
力学 | 10篇 |
数学 | 106篇 |
物理学 | 86篇 |
出版年
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 41篇 |
2012年 | 34篇 |
2011年 | 58篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 33篇 |
2007年 | 50篇 |
2006年 | 43篇 |
2005年 | 40篇 |
2004年 | 29篇 |
2003年 | 35篇 |
2002年 | 40篇 |
2001年 | 20篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1926年 | 2篇 |
排序方式: 共有823条查询结果,搜索用时 15 毫秒
111.
112.
Shi R Cutler A Werker J Cruickshank M 《The Journal of the Acoustical Society of America》2006,119(6):EL61-EL67
High-frequency functors are arguably among the earliest perceived word forms and may assist extraction of initial vocabulary items. Canadian 11- and 8-month-olds were familiarized to pseudo-nouns following either a high-frequency functor the or a low-frequency functor her versus phonetically similar mispronunciations of each, kuh and ler, and then tested for recognition of the pseudo-nouns. A preceding the (but not kuh, her, ler) facilitated extraction of the pseudo-nouns for 11-month-olds; the is thus well-specified in form for these infants. However, both the and kuh (but not her-ler) facilitated segmentation for 8-month-olds, suggesting an initial underspecified representation of high-frequency functors. 相似文献
113.
Surface strain plays a major role in determining the rate limiting step and catalytic activity of platinum for CO oxidation. 相似文献
114.
Del Bene JE Elguero J Alkorta I Yañez M Mó O 《The journal of physical chemistry. A》2006,110(32):9959-9966
Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond (11)B-(15)N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on (13)C-(13)C coupling constants for benzene. 相似文献
115.
Karplus-type equations are derived for the variation of one-bond X-Y coupling constants 1J(X-Y) as a function of dihedral angle for molecules HmX-YHn, for X, Y, = 15N, 17O, 31P, and 33S. Coupling constants were obtained from ab initio EOM-CCSD calculations, with all terms evaluated. The relative orientation of lone pairs appears to be a primary factor determining the dependence of 1J(X-Y) on the dihedral angle. 相似文献
116.
Bence Paul Kai Kysenius James B. Hilton Michael W. M. Jones Robert W. Hutchinson Daniel D. Buchanan Christophe Rosty Fred Fryer Ashley I. Bush Janet M. Hergt Jon D. Woodhead David P. Bishop Philip A. Doble Michelle M. Hill Peter J. Crouch Dominic J. Hare 《Chemical science》2021,12(30):10321
Tumours are abnormal growths of cells that reproduce by redirecting essential nutrients and resources from surrounding tissue. Changes to cell metabolism that trigger the growth of tumours are reflected in subtle differences between the chemical composition of healthy and malignant cells. We used LA-ICP-MS imaging to investigate whether these chemical differences can be used to spatially identify tumours and support detection of primary colorectal tumours in anatomical pathology. First, we generated quantitative LA-ICP-MS images of three colorectal surgical resections with case-matched normal intestinal wall tissue and used this data in a Monte Carlo optimisation experiment to develop an algorithm that can classify pixels as tumour positive or negative. Blinded testing and interrogation of LA-ICP-MS images with micrographs of haematoxylin and eosin stained and Ki67 immunolabelled sections revealed Monte Carlo optimisation accurately identified primary tumour cells, as well as returning false positive pixels in areas of high cell proliferation. We analysed an additional 11 surgical resections of primary colorectal tumours and re-developed our image processing method to include a random forest regression machine learning model to correctly identify heterogenous tumours and exclude false positive pixels in images of non-malignant tissue. Our final model used over 1.6 billion calculations to correctly discern healthy cells from various types and stages of invasive colorectal tumours. The imaging mass spectrometry and data analysis methods described, developed in partnership with clinical cancer researchers, have the potential to further support cancer detection as part of a comprehensive digital pathology approach to cancer care through validation of a new chemical biomarker of tumour cells.Digital pathology and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging reveals a unique elemental signature of colorectal cancer. 相似文献
117.
Shannon P. O'Grady Lindsey E. Enright Janet E. Barnette Thure E. Cerling James R. Ehleringer 《Isotopes in environmental and health studies》2013,49(4):476-483
The isotope ratio analysis of body water often involves large sample numbers and lengthy sample processing. Here we demonstrate the ability of isotope ratio infrared spectroscopy (IRIS) to rapidly and accurately analyse the isotope ratios of water in urine. We analysed water extracted from human urine using traditional isotope ratio mass spectrometry (IRMS) and compared those values with IRIS-analysed extracted water and un-extracted urine. Regression analyses for δ2H and δ18O values between (1) extracted water analysed via IRMS and IRIS and (2) urine and extracted water analysed via IRIS were significant (R 2=0.99). These results indicate that cryogenic distillation of urine was not required for an accurate estimate of the isotopic composition of urine when using IRIS. 相似文献
118.
Nicole M. Else-Quest Janet S. Hyde Ahalya Hejmadi 《Mathematical Thinking and Learning》2013,15(1):5-35
Mathematics is often thought of as a purely intellectual and unemotional activity. Recently, researchers have begun to question the validity of this approach, arguing that emotions and cognition are intertwined. The emotions expressed during mathematics work may be linked to mathematics achievement. We used behavioral measures to identify the emotions expressed by U.S. mothers and their 11-year-old children while solving pre-algebra tasks in the home. The most notable positive emotions displayed by mothers and children included positive interest, affection, joy, and pride, whereas the most notable negative emotions expressed included tension, frustration, and distress. Reflecting the social aspects of doing homework together, mothers' and children's emotions were highly correlated. Independent of pre-existing differences in knowledge, children's emotions were associated with their performance on a mathematics post-test: tension was linked to poorer performance while positive interest, humor, and pride were linked to better performance. We found no evidence of gender differences in the emotions while working the tasks, although boys responded with more tension following an incorrect solution than did girls. 相似文献
119.
Martin PichetteDrapeau Janet Bahri Dominik Lichte Lukas J. Gooßen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):902-906
In the presence of a bimetallic Pd/Cu system with 1,10‐phenanthroline as the ligand and either air or N‐methylmorpholine N‐oxide as the oxidant, electron‐deficient benzoic acids undergo oxidative decarboxylative coupling with unprotected amines. This operationally simple aniline synthesis is widely applicable with respect to the amine and gives good yields, even on multigram scale. The orthogonality of this reaction to other Pd‐catalyzed cross‐couplings allows the concise synthesis of multisubstituted arenes by sequential C?C, C?Cl, and C?N functionalizations. Mechanistic investigations suggest the intermediacy of a hypervalent Pd species. 相似文献