全文获取类型
收费全文 | 11856篇 |
免费 | 24篇 |
国内免费 | 42篇 |
专业分类
系统科学 | 35篇 |
丛书文集 | 80篇 |
教育与普及 | 30篇 |
理论与方法论 | 42篇 |
现状及发展 | 5127篇 |
研究方法 | 565篇 |
综合类 | 5887篇 |
自然研究 | 156篇 |
出版年
2013年 | 96篇 |
2012年 | 191篇 |
2011年 | 330篇 |
2010年 | 85篇 |
2009年 | 59篇 |
2008年 | 190篇 |
2007年 | 222篇 |
2006年 | 203篇 |
2005年 | 224篇 |
2004年 | 208篇 |
2003年 | 207篇 |
2002年 | 198篇 |
2001年 | 380篇 |
2000年 | 364篇 |
1999年 | 263篇 |
1992年 | 232篇 |
1991年 | 180篇 |
1990年 | 204篇 |
1989年 | 190篇 |
1988年 | 201篇 |
1987年 | 205篇 |
1986年 | 160篇 |
1985年 | 248篇 |
1984年 | 170篇 |
1983年 | 149篇 |
1982年 | 166篇 |
1981年 | 135篇 |
1980年 | 170篇 |
1979年 | 385篇 |
1978年 | 291篇 |
1977年 | 287篇 |
1976年 | 249篇 |
1975年 | 287篇 |
1974年 | 309篇 |
1973年 | 308篇 |
1972年 | 344篇 |
1971年 | 344篇 |
1970年 | 428篇 |
1969年 | 364篇 |
1968年 | 381篇 |
1967年 | 352篇 |
1966年 | 319篇 |
1965年 | 203篇 |
1959年 | 107篇 |
1958年 | 204篇 |
1957年 | 137篇 |
1956年 | 122篇 |
1955年 | 105篇 |
1954年 | 81篇 |
1948年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
872.
1 Introduction Metal, metal oxide and metal compound nanoparticles (NPs) received considerable attention due to their unique properties: catalytic, magnetic, optical, electronic, etc. We believe that for different applications, there are preferable morphologies of NP-stabilizing medium composites. For example, small (1-3 nm) nanoparticles formed in micro/mesoporous hypercrosslinked polystyrene demonstrate excellent catalytic properties in various hydrogenation and oxidation reactions due to high surface... 相似文献
873.
Field trial of an HTS filter system on a CDMA base station 总被引:3,自引:0,他引:3
YIN ZheSheng WEI Bin CAO BiSong WANG Xin GUO XuBo ZHANG XiaoPing GAO LongMa PIAO YunLong ZHU MaFeng LIANG Yong WANG Fan H. PIEL B. AMINOV F. AMINOVA M. GETTA S. KOLESOV A. KNACK N. PUPETER D. WEHLER 《科学通报(英文版)》2007,52(2):171-174
This paper presents the field trial results of a high temperature superconductor filter system (HTSFS) in a code division multiple access (CDMA) mobile communication base station (BTS) in Tangshan, China. The center frequency of the HTSFS is 830 MHz with 1.4% fractional bandwidth. The noise figure (NF) of the HTSFS, including connectors and cables, is 0.8 dB. The field trial results show that after the HTSFS was installed in the receiver front-end of a CDMA base station, the transmitting power of handset was decreased by 3.1 dB on average. Up to now, the HTSFS has been running steadily in the base station for more than 22 months, demonstrating the reliability and stability of the system. 相似文献
874.
了解微量元素经由土壤-植物-人体链的基本、性质与变化过程,大有助于人体健康与环境保护。本书集中过去30多年的知识,提供最新数据及有关食物链的基本内容,附有引证文献资料共有68页(P.451-518)之多。 相似文献
875.
Ionophores consist of molecules which surround and carry positive metal ions and other ions through biological membranes.
One classe of ionophores which we have been developing contains dipeptides which are encouraged to become part of a ring because
of possible hydrogen bond formation between the 2-hydroxy on the phenyl group and carboxyl group (COOH) of the final amide
proline. Formation of a ring should increase the complexation ability of the ionophore. We report that the synthesis of N-(2-hydroxyl-1-phenoxyacetyl)
prolyproline(1), a novel ionophore is prepared from activated 2-acetoxy phenoxyacetic acid (3a) and the appropriate dipeptide
ester using coupling methods such as dicyclohexyl carbodiimide with hydroxyben-ztriazole or carbonyl diimidazole.
Yang Dingqiao: born in 1958, Associate professor 相似文献
876.
It is reported that concanavalin A (conA) and wheat germ agglutinin (WGA) have a differential binding pattern on normal mouse spleen lymphocytes and the surface of Dalton's lymphoma cells. It is suggested that sialic acid on the cell surface controls the expression of lectin binding sites. Further, it has been observed that the increased release of sialic acid from cell surfaces after cis-dichlorodiammine platinum (II) (cis-Platin) treatment is due to the increased activity of sialidase. 相似文献
877.
878.
879.
Coexistence of A- and B-form DNA in a single crystal lattice 总被引:5,自引:0,他引:5
It is well known that DNA can exist in a variety of conformations which can be interconverted by relatively mild changes in conditions. The in vivo conformation of DNA is usually thought to be the B form, but there is recent evidence that other conformations may be important in DNA-protein recognition. Different fragments of DNA crystallized under virtually identical conditions can form A, B or Z helices. A fragment that adopted an A conformation in a crystal was found in the B conformation in solution, whereas NMR spectroscopy of A-DNA films revealed the presence of a substantial amount of disordered B-DNA. Until now, however, a DNA fragment of a given sequence has not been crystallized in more than one global conformation. We report here an X-ray diffraction study of crystals of the DNA octamer dGGBrUABrUACC. In addition to a 'framework' of A-DNA, which gives discrete X-ray reflections, there are partially disordered B-DNA helices, recognized by their diffuse scattering features. 相似文献
880.
Alexey B. Petrovsky 《系统科学与系统工程学报(英文版)》2007,16(1):22-33
There are many practical decision problems where decision makers' preferences may be inconsistent and contradictory. In this paper, new methods for ordering and classifying multi-attribute objects by discordant collective preferences are suggested. These methods are based on the theory of multiset metric spaces. The proposed techniques are applied to ranking companies and a competitive selection of projects, which are estimated by several experts upon multiple qualitative criteria. 相似文献