全文获取类型
收费全文 | 7425篇 |
免费 | 1062篇 |
国内免费 | 498篇 |
专业分类
化学 | 1443篇 |
晶体学 | 43篇 |
力学 | 1180篇 |
综合类 | 194篇 |
数学 | 3202篇 |
物理学 | 2923篇 |
出版年
2024年 | 22篇 |
2023年 | 61篇 |
2022年 | 187篇 |
2021年 | 176篇 |
2020年 | 236篇 |
2019年 | 227篇 |
2018年 | 226篇 |
2017年 | 233篇 |
2016年 | 298篇 |
2015年 | 230篇 |
2014年 | 360篇 |
2013年 | 593篇 |
2012年 | 407篇 |
2011年 | 460篇 |
2010年 | 371篇 |
2009年 | 440篇 |
2008年 | 434篇 |
2007年 | 434篇 |
2006年 | 413篇 |
2005年 | 433篇 |
2004年 | 367篇 |
2003年 | 324篇 |
2002年 | 310篇 |
2001年 | 218篇 |
2000年 | 223篇 |
1999年 | 171篇 |
1998年 | 175篇 |
1997年 | 156篇 |
1996年 | 113篇 |
1995年 | 118篇 |
1994年 | 105篇 |
1993年 | 67篇 |
1992年 | 62篇 |
1991年 | 56篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 26篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 3篇 |
1982年 | 24篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有8985条查询结果,搜索用时 15 毫秒
111.
邢凤鸣 《中国科学B辑(英文版)》1991,(11)
It is considered that the early Jinning period granitoids from southern Anhui Province belong to the continental crust transformation (S) type and have their own characteristics which are different from those for general continental crust transformation type granitoids. They were formed at the early stage of the late Proterozoic era when that region was at an island-arc stage of the continental margin environment. By that time the continental crust was just formed and had a nature of juvenile crust. It is this juvenile crust that determined a series of characteristics of that type granitoids and made them a relatively independent rock type. They are the products formed by the continental crust in a certain stage of development. 相似文献
112.
113.
114.
On the plastic deformation of bulk syndiotactic polypropylene 总被引:1,自引:0,他引:1
The plastic deformation of syndiotactic polypropylene (sPP) bulk samples has been investigated. A structural comparison of
the initial states before and after plastic deformation by necking is carried out by X-ray diffraction observations. Independent
of the initial states (amorphous, semi-crystalline with different crystal phases), only the planar all-trans crystal form of sPP is present in the deformed samples after necking. Form these results, molecular mechanisms of the plastic
deformation in the neck zone of semi-crystalline polymers will be discussed.
Received: 11 February 1997 Accepted: 15 August 1997 相似文献
115.
116.
Multiple-locus variable number tandem repeats analysis for genetic fingerprinting of pathogenic bacteria 总被引:1,自引:0,他引:1
Lindstedt BA 《Electrophoresis》2005,26(13):2567-2582
DNA fingerprinting has attracted considerable interest as means for identifying, tracing and preventing the dissemination of infectious agents. Various methods have been developed for typing of pathogenic bacteria, which differ in discriminative power, reproducibility and ease of interpretation. During recent years a typing method, which uses the information provided by whole genome sequencing of bacterial species, has gained increased attention. Short sequence repeat (SSR) motifs are known to undergo frequent variation in the number of repeated units through cellular mechanisms most commonly active during chromosome replication. A class of SSRs, named variable number of tandem repeats (VNTRs), has proven to be a suitable target for assessing genetic polymorphisms within bacterial species. This review attempts to give an overview of bacterial agents where VNTR-based typing, or multiple-locus variant-repeat analysis (MLVA) has been developed for typing purposes, together with addressing advantages and drawbacks associated with the use of tandem repeated DNA motifs as targets for bacterial typing and identification. 相似文献
117.
X. Bokhimi A. Morales E. Ortíz T. López R. Gómez J. Navarrete 《Journal of Sol-Gel Science and Technology》2004,29(1):31-40
Sol-gel titania was sulfated by using sulfuric acid as hydrolysis catalyst, or by impregnating with ammonium sulfate fresh samples prepared with nitric acid or ammonium hydroxide as hydrolysis catalyst. Samples were characterized with X-ray powder diffraction, infrared spectroscopy, thermogravimetry and atomic absorption spectroscopy. Sulfate ions were found anchored to brookite and anatase phases, because they have short O—O atomic bond lengths slightly larger than the largest O—O bond length of sulfate ion. Since the shortest O—O atomic bond in anatase is smaller than the one in brookite, the sulfate ions are then less deformed when they are anchored to anatase, and consequently more stable. Therefore when the sample temperature is raised, the brookite with sulfate ions was transformed mainly to anatase and not into rutile, which is the most probably transformation when these ions are not involved. Sulfate ions also hindered anatase and brookite crystallite growing and stabilized the crystalline structure of anatase. When the sulfate ions are lost the crystalline anatase phase is transformed into rutile, leaving a large number of vacancies that favored atom diffusion and consequently the growing of rutile crystallites. The crystalline evolution of the samples as a function of the annealing temperature is almost independent of the sulfating method. 相似文献
118.
119.
Yuichi Michiue 《Journal of solid state chemistry》2006,179(8):2578-2583
Phase relations of rutile, freudenbergite, and hollandite structures were examined in the pseudobinary system NaCrO2-TiO2 (i.e., NaxCrxTi8−xO16) at 1350 °C. The hollandite structure was obtained in the composition range 1.7?x?2.0. The symmetry of the samples at room temperature was tetragonal for x=1.7 and 1.75, and monoclinic for x=1.8 and above. Single crystals of monoclinic hollandite Na2Cr2Ti6O16 were grown and the structure refinement has been carried out using an X-ray diffraction technique. The space group was I2/m and cell parameters were a=10.2385(11), b=2.9559(9), c=9.9097(11)Å, and β=90.545(9)° with Z=1. The Na ion distribution in the tunnel was markedly deformed from that in the tetragonal form. It was suggested that Cr/Ti ratios were different between the two framework metal sites. 相似文献
120.
Rational drug design involves finding solutions to large combinatorial problems for which an exhaustive search is impractical. Genetic algorithms provide a novel tool for the investigation of such problems. These are a class of algorithms that mimic some of the major characteristics of Darwinian evolution. LEA has been designed in order to conceive novel small organic molecules which satisfy quantitative structure-activity relationship based rules (fitness). The fitness consists of a sum of constraints that are range properties. The algorithm takes an initial set of fragments and iteratively improves them by means of crossover and mutation operators that are related to those involved in Darwinian evolution. The basis of the algorithm, its implementation and parameterization, are described together with an application in de novo molecular design of new retinoids. The results may be promising for chemical synthesis and show that this tool may find extensive applications in de novo drug design projects. 相似文献