全文获取类型
收费全文 | 2416篇 |
免费 | 77篇 |
国内免费 | 9篇 |
专业分类
化学 | 1851篇 |
晶体学 | 26篇 |
力学 | 36篇 |
数学 | 233篇 |
物理学 | 356篇 |
出版年
2023年 | 12篇 |
2022年 | 32篇 |
2021年 | 53篇 |
2020年 | 48篇 |
2019年 | 52篇 |
2018年 | 33篇 |
2017年 | 28篇 |
2016年 | 75篇 |
2015年 | 59篇 |
2014年 | 63篇 |
2013年 | 113篇 |
2012年 | 160篇 |
2011年 | 205篇 |
2010年 | 94篇 |
2009年 | 71篇 |
2008年 | 179篇 |
2007年 | 161篇 |
2006年 | 159篇 |
2005年 | 122篇 |
2004年 | 115篇 |
2003年 | 91篇 |
2002年 | 94篇 |
2001年 | 29篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 26篇 |
1995年 | 33篇 |
1994年 | 22篇 |
1993年 | 26篇 |
1992年 | 16篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 13篇 |
1974年 | 7篇 |
1972年 | 7篇 |
1969年 | 6篇 |
排序方式: 共有2502条查询结果,搜索用时 15 毫秒
1.
Elizabeth S. Senger 《School science and mathematics》1997,97(3):139-149
Thirteen fifth graders were given an assignment to invent their own numeration systems, following a unit on bases and a look at early events in the history of numbers. The task presented options that required the students to make decisions (such as whether to use a base, which base to use, design of symbols, etc.), and build a rationale for the elements of their system. Analyses of patterns embedded in their invented systems provided an assessment of student understanding of numeration. The progression of more and less complex thinking related to the student's choice of a base other than 10, consistency of logic throughout the system in words and symbols, rationale for change, and perception of real life examples that would change if the system was adopted. The invention task is presented as another way to make connections. 相似文献
2.
Accreditation and Quality Assurance - 相似文献
3.
Elizabeth Wulcan 《Arkiv f?r Matematik》2007,45(1):157-178
With a given holomorphic section of a Hermitian vector bundle, one can associate a residue current by means of Cauchy–Fantappiè–Leray
type formulas. In this paper we define products of such residue currents. We prove that, in the case of a complete intersection,
the product of the residue currents of a tuple of sections coincides with the residue current of the direct sum of the sections. 相似文献
4.
Experts were interviewed to identify criteria for evaluation of vocal performance. A scale was then constructed and inter- and intrajudge reliability assessed. Experts listened to 19 different performances, plus 6 presented a second time. Interjudge reliability for one judge was modest, but increased dramatically as the size of the judge panel increased. The most reliable items were overall score and intonation accuracy. Diction was less reliable than other items. Intrajudge reliability was higher for overall score than for any other item. A factor analysis on the test items yielded factors labelled intrinsic quality, execution, and diction. Another factor analysis, using the experts as variables, revealed two underlying evaluative dimensions. It was found that 13 experts were primarily influenced by execution, and that 8 were mainly affected by intrinsic quality. Interjudge and intrajudge reliabilities of these two groups differed. 相似文献
5.
Gisha Elizabeth Luckachan C. K. S. Pillai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(10):3250-3260
Novel multiblock poly(ester amide)s containing poly(L ‐lactide) and cycloaliphatic amide segments were synthesized from telechelic oligomer of α,ω‐hydroxyl terminated poly(L ‐lactide), 1,3‐cyclohexylbis(methylamine), and sebacoylchloride by the “two‐step” interfacial polycondensation method. The blocky nature of PEAs was established by FTIR and 1H NMR spectroscopies. The effect of relative content of ester and amide segments on the crystallization nature of PEAs was investigated by WAXD and DSC analyses. PEAs having lower content of PLLA, PEA 1 and PEA 2, showed a crystallization pattern analogous to polyamides, whereas PEA 3, having higher content of PLLA, showed two crystalline phases characterized by polyester and polyamide segments. Random nature of PEAs was observed from single Tg values. Biodegradation studies using the enzyme lipase from Candida Cylindracea showed higher degradation rate for PEA 3 than that for PEA 1 and PEA 2. FTIR, 1H NMR, and DSC analyses of the degraded products indicated the involvement of ester linkages in the degradation process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3250–3260, 2006 相似文献
6.
Two problems in projectiles are discussed which generate interestingloci. 相似文献
7.
We show that the isotropy types of the singularities of Riemannian orbifolds are not determined by the Laplace spectrum. Indeed,
we construct arbitrarily large families of mutually isospectral orbifolds with different isotropy types. Finally, we show
that the corresponding singular strata of two isospectral orbifolds may not be homeomorphic.
Received: 6 October 2005 相似文献
8.
Elizabeth M. Holt Balawant S. Joshi Dilip H. Gawad S. William Pelletier 《Journal of chemical crystallography》1990,20(3):261-264
The crystal and molecular structure of 1-ethyl-4-methoxy-9H-pyrido[3,4b]indole (crenatine) carbonate C14H14N2O·H2CO3, (MS, m/z 226)M
R
288.3, a-carboline alkaloid, has been determined from X-ray diffraction data. The compound crystallizes in the space group Pbca with cell parameters:a=11.616(4),b=18.450(8),c=12.992(5)Å,V=2784(2)Å3,Z=8,D
calc=1.375 g cm–3, (MoK)=0.71069Å,(Mo K)=0.94 cm–1,F(000)=1216,R/R
w
=8.2/10.3% for 1099 reflections. The ring system of the-carboline nucleus is planar. The title compound shows a two center hydrogen bond between the indole N-H group and the oxygen atom of a carbonate group. The structure does not display hydrogen bonding between-carboline groups but rather a bonding network involving the carbonate group. 相似文献
9.
Recent highlights in stationary phase design for open-tubular capillary electrochromatography 总被引:1,自引:0,他引:1
This review examines the most recent innovations made to achieve high performance in open-tubular capillary electrochromatography (OT-CEC) separations, focusing on the ingenious chemical and physical solutions made to increase the surface area and equip the stationary phase with exploitable selectivity. Among the approaches taken are chemically bonded ligands, etching with chemical bonding, sol-gels, molecularly imprinted polymers, porous layers, physically attached or adsorbed phases, and nanoparticle coatings. Particularly noteworthy are modern developments with macrocyclic receptor ligands, nanoparticles and open channel electrochromatography on-chip. 相似文献
10.
We show that, for any Jordan domain J in R2, harmonic measureis supported by a Borel set of packing dimension 1. We alsoobtain incomplete analogs to the results of Makarov, which connectthe almost everywhere behavior of the derivative near the boundaryfor the conformal mapping function from the unit disk J withthe Hausdorff measure properties of sets supporting the harmonicmeasure. 相似文献