全文获取类型
收费全文 | 118639篇 |
免费 | 9914篇 |
国内免费 | 14443篇 |
专业分类
化学 | 90151篇 |
晶体学 | 2070篇 |
力学 | 4480篇 |
综合类 | 1091篇 |
数学 | 13963篇 |
物理学 | 31241篇 |
出版年
2024年 | 130篇 |
2023年 | 894篇 |
2022年 | 1666篇 |
2021年 | 2566篇 |
2020年 | 3357篇 |
2019年 | 3104篇 |
2018年 | 2780篇 |
2017年 | 3738篇 |
2016年 | 4330篇 |
2015年 | 3780篇 |
2014年 | 4785篇 |
2013年 | 9521篇 |
2012年 | 7941篇 |
2011年 | 6865篇 |
2010年 | 5805篇 |
2009年 | 7466篇 |
2008年 | 7779篇 |
2007年 | 7981篇 |
2006年 | 7280篇 |
2005年 | 6206篇 |
2004年 | 5827篇 |
2003年 | 4941篇 |
2002年 | 5985篇 |
2001年 | 3682篇 |
2000年 | 3428篇 |
1999年 | 3132篇 |
1998年 | 2703篇 |
1997年 | 2157篇 |
1996年 | 1834篇 |
1995年 | 1731篇 |
1994年 | 1510篇 |
1993年 | 1255篇 |
1992年 | 1186篇 |
1991年 | 821篇 |
1990年 | 699篇 |
1989年 | 631篇 |
1988年 | 499篇 |
1987年 | 404篇 |
1986年 | 383篇 |
1985年 | 304篇 |
1984年 | 318篇 |
1983年 | 177篇 |
1982年 | 261篇 |
1981年 | 192篇 |
1980年 | 211篇 |
1979年 | 204篇 |
1978年 | 158篇 |
1977年 | 98篇 |
1976年 | 81篇 |
1973年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
从患罗氏沼虾幼苗肌肉白浊病的幼虾体内分离到两种病毒颗粒,诺达病毒(MrNV)和直径只有15nm的小病毒颗粒(extrasmallvirus,XSV),本文通过建立病毒cDNA文库获得XSV基因组的部分序列,在此基础上合成探针,用从病虾组织中提取的总PNA进行Northern杂交,结果表明XSV基因组至少包括两条RNA片段.利用不同的方法对XSV的两端序列进行克隆和测定,分别得到了872、831和662bp3个相互重叠的序列片段,这3个序列的阅读框编码一个相同的大小在17×103左右的蛋白. 相似文献
993.
994.
Conventionally, surface roughness is predominantly determined through the use of stylus instruments. However, there are certain limitations involved in the method, particularly when a test specimen, such as a silicon wafer, has a smooth mirror-like surface. Hence, it is necessary to explore alternative non-contact techniques. Light scattering has recently been gaining popularity as an optical technique to provide prompt and precise inspection of surface roughness. In this paper, the total integrated scattering (TIS) model is modified to retrieve parameters on surface micro-topography through light scattering. The applicability of the proposed modified TIS model is studied and compared with an atomic force microscope. Experimental results obtained show that the proposed technique is highly accurate for measuring surface roughness in the nanometer range. 相似文献
995.
研究了阳离子表面活性剂十六烷基三甲基溴化铵 (CTAB)对四 ( 4 N 甲基吡啶 )卟啉 (H2 TMPyP)及其银配合物 (AgTMPyP)在Ag胶中的表面增强拉曼散射 (SERS)谱的影响 .SERS光谱表明 ,吸附于Ag胶粒的H2 TMPyP与衬底银原子结合形成AgTMPyP ,加入CTAB后 ,部分AgTMPyP表面络合物还原为H2 TMPyP .相似的去金属化反应也出现在AgTMPyP/Ag胶 /CTAB体系中 .CTAB的加入使SERS谱带强度明显增加 .AgTMPyP的去金属化被认为是由于CTAB的存在使Ag胶颗粒表面附近微环境发生改变 相似文献
996.
N. A. A. Rossi R. G. Jones S. J. Holder 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):30-40
ABA block copolymers of methyl methacrylate and methylphenylsilane were synthesized with a methodology based on atom transfer radical polymerization (ATRP). The reaction of samples of α,ω‐dihalopoly(methylphenylsilane) with 2‐hydroxyethyl‐2‐methyl‐2‐bromoproprionate gave suitable macroinitiators for the ATRP of methyl methacrylate. The latter procedure was carried out at 95 °C in a xylene solution with CuBr and 2,2‐bipyridine as the initiating system. The rate of the polymerization was first‐order with respect to monomer conversion. The block copolymers were characterized with 1H NMR and 13C NMR spectroscopy and size exclusion chromatography, and differential scanning calorimetry was used to obtain preliminary evidence of phase separation in the copolymer products. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 30–40, 2003 相似文献
997.
The paper analyzes new publications on the brittle fracture mechanics of prestressed materials. It is found out that new scientific results published in the International Journal of Solids and Structures in 2002 are a particular case of the results obtained at the Institute of Mechanics 20 years ago 相似文献
998.
999.
Two new polyacid derivative ligands of thienyl-substituted terpyridine analogues, N,N,N1,N1-[4′-(2?-thienyl)-2,2′:6′,2″-terpyridine-6,6″-diyl]bis(methylenenitrilo) tetrakis(acetic acid) (TTTA) and N,N,N1,N1-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-(2″-thienyl)pyridine] tetrakis(acetic acid) (BTTA), were synthesized, and the luminescence properties of their Eu3+ and Tb3+ chelates were investigated. The Eu3+chelates of the two ligands are strongly luminescent having luminescence quantum yields of 0.150 (TTTA-Eu3+) and 0.114 (BTTA-Eu3+), and lifetimes of 1.284 ms (TTTA-Eu3+) and 1.352 ms (BTTA-Eu3+), whereas their Tb3+ chelates are weakly luminescent. The TTTA-Eu3+ chelate was used for streptavidin (SA) labeling, and the labeled SA was used for time-resolved fluoroimmunoassay of insulin in human sera. The method gives the detection limits of 33 pg ml−1. 相似文献
1000.
Monica Sorescu L Diamandescu D Tarabasanu-Mihaila 《Journal of Physics and Chemistry of Solids》2004,65(10):1719-1725
α-Fe2O3-In2O3 mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1−x)Fe(NO3)3·9H2O·xIn(NO3)3·5H2O aqueous solution (x=0-1). X-ray diffraction and Mössbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the α-Fe2O3-In2O3 nanoparticle system together with the solubility limits of In3+ ions in the hematite lattice and of Fe3+ ions in the cubic In2O3 structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given. 相似文献