全文获取类型
收费全文 | 16066篇 |
免费 | 416篇 |
国内免费 | 107篇 |
专业分类
化学 | 11626篇 |
晶体学 | 149篇 |
力学 | 327篇 |
数学 | 2202篇 |
物理学 | 2285篇 |
出版年
2023年 | 75篇 |
2021年 | 144篇 |
2020年 | 204篇 |
2019年 | 197篇 |
2018年 | 146篇 |
2017年 | 133篇 |
2016年 | 291篇 |
2015年 | 295篇 |
2014年 | 354篇 |
2013年 | 707篇 |
2012年 | 865篇 |
2011年 | 1126篇 |
2010年 | 544篇 |
2009年 | 459篇 |
2008年 | 998篇 |
2007年 | 1067篇 |
2006年 | 1100篇 |
2005年 | 1087篇 |
2004年 | 922篇 |
2003年 | 787篇 |
2002年 | 757篇 |
2001年 | 202篇 |
2000年 | 184篇 |
1999年 | 188篇 |
1998年 | 207篇 |
1997年 | 218篇 |
1996年 | 276篇 |
1995年 | 176篇 |
1994年 | 166篇 |
1993年 | 171篇 |
1992年 | 138篇 |
1991年 | 115篇 |
1990年 | 101篇 |
1989年 | 102篇 |
1988年 | 101篇 |
1987年 | 102篇 |
1986年 | 93篇 |
1985年 | 160篇 |
1984年 | 171篇 |
1983年 | 101篇 |
1982年 | 141篇 |
1981年 | 136篇 |
1980年 | 142篇 |
1979年 | 118篇 |
1978年 | 102篇 |
1977年 | 98篇 |
1976年 | 81篇 |
1975年 | 94篇 |
1974年 | 87篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
41.
It is well known from work of Bruhat and Tits that an affinebuilding has a spherical building at infinity. The paper studiesthe structure at infinity for an affine twin building. It isshown that the twinning restricts the structure at infinityin a natural way, producing two smaller spherical buildingsthat are canonically isomorphic to one another. In the processit is shown that to each wall and panel of these buildings atinfinity is attached a twin tree. 相似文献
42.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献
43.
Motivated by the central limit problem for convex bodies, we study normal approximation of linear functionals of high-dimensional
random vectors with various types of symmetries. In particular, we obtain results for distributions which are coordinatewise
symmetric, uniform in a regular simplex, or spherically symmetric. Our proofs are based on Stein’s method of exchangeable
pairs; as far as we know, this approach has not previously been used in convex geometry. The spherically symmetric case is
treated by a variation of Stein’s method which is adapted for continuous symmetries.
This work was done while at Stanford University. 相似文献
44.
The Meyerhoff Program is an intensive, multicomponent program focused on enhancing the success of talented African-American students in science and engineering at a predominantly white, medium-sized university. The program components, taken together, address the four primary factors emphasized in the research literature as limiting minority student performance and persistence in science: knowledge and skills, motivation and support, monitoring and advising, and academic and social integration. Outcome analyses indicated that the first three cohorts of Meyerhoff students (total N=69) achieved an overall GPA (mean=3.5) significantly greater than that of an African-American historical comparison sample (mean=2.8) of comparably talented science students at the university. This difference was even greater for first year science GPA (means of 3.4 and 2.4, respectively), and in specific science and mathematics courses. Observational and questionnaire data indicated that the Meyerhoff program study groups, peerbased community, financial scholarships, summer bridge program and staff appear to be especially important contributors to student success. Implications of the findings for enhancing the success of African-American and other underrepresented populations in science are discussed. 相似文献
45.
Applied Biochemistry and Biotechnology - In summary, it appears that the microbial reduction process is clearly not competitive with conventional SO2-reduction techniques when glucose (DE95 corn... 相似文献
46.
Mark Jerrum 《Random Structures and Algorithms》1995,7(2):157-165
A fully polynomial randomized approximation scheme is presented for estimating the number of (vertex) k-colorings of a graph of maximum degree Δ, when k ≥ 2Δ + 1. © 1995 John Wiley & Sons, Inc. 相似文献
47.
Eric Gifford Mark Johnson Chun-che Tsai 《Journal of computer-aided molecular design》1991,5(4):303-322
Summary The metabolic pathways of medazepam, oxazepam, and diazepam were modeled using graph-theoretic transforms which are incorporable into computer-assisted metabolic analysis programs. The information, represented in the form of a graph-theoretic transform kit, which was obtained from these pathways was then used to predict the metabolites of other benzodiazepine compounds. The transform kits gave statistically significant predictions with respect to a statistical method for evaluating the performance of the transform kits. 相似文献
48.
Christopher A. Luckhurst Ian Millichip Beth Parker James Reuberson Mark Furber 《Tetrahedron letters》2007,48(50):8878-8882
A one-pot reaction of carboxylic acids with sulfonamides to afford sulfonylureas is described. 相似文献
49.
Val M. Runge Mark A. Osborne Michael L. Wood Samuel M. Wolpert Eddie Kwan Dean M. Kaufman 《Magnetic resonance imaging》1987,5(6):421-430
The angle between the straight axial plane and the orbito-meatal line was measured in 156 consecutive magnetic resonance examinations. Inconsistent head positioning caused this angle to vary by as much as 44 degrees. Careful positioning of the patient by the technologist can minimize this variability, leading potentially to improved image interpretation. To assess the merit of a standardized orientation for MR examinations of the head, straight axial and tilted axial MR scans were compared in 34 patients. The tilted images were obtained parallel to the orbito-meatal line and were found to be superior for visualization of the cerebellum. When correlative x-ray CTs are available or when an abnormality in the posterior fossa is suspected, tilted axial MR scans should be employed. 相似文献
50.
Mark Pollicott 《Topology and its Applications》2007,154(12):2365-2375
We study lifts of the stable foliation of a pseudo-Anosov diffeomorphism to abelian covers. Under certain conditions, we show that it is ergodic but not uniquely ergodic and describe the ergodic measures. 相似文献