全文获取类型
收费全文 | 6764篇 |
免费 | 176篇 |
国内免费 | 18篇 |
专业分类
化学 | 4492篇 |
晶体学 | 70篇 |
力学 | 76篇 |
综合类 | 1篇 |
数学 | 267篇 |
物理学 | 1434篇 |
无线电 | 618篇 |
出版年
2022年 | 44篇 |
2021年 | 72篇 |
2020年 | 86篇 |
2019年 | 80篇 |
2018年 | 65篇 |
2017年 | 54篇 |
2016年 | 102篇 |
2015年 | 102篇 |
2014年 | 112篇 |
2013年 | 269篇 |
2012年 | 267篇 |
2011年 | 333篇 |
2010年 | 162篇 |
2009年 | 182篇 |
2008年 | 319篇 |
2007年 | 337篇 |
2006年 | 338篇 |
2005年 | 355篇 |
2004年 | 339篇 |
2003年 | 241篇 |
2002年 | 246篇 |
2001年 | 216篇 |
2000年 | 199篇 |
1999年 | 122篇 |
1998年 | 68篇 |
1997年 | 87篇 |
1996年 | 109篇 |
1995年 | 90篇 |
1994年 | 99篇 |
1993年 | 112篇 |
1992年 | 133篇 |
1991年 | 123篇 |
1990年 | 98篇 |
1989年 | 107篇 |
1988年 | 98篇 |
1987年 | 67篇 |
1986年 | 73篇 |
1985年 | 108篇 |
1984年 | 114篇 |
1983年 | 66篇 |
1982年 | 66篇 |
1981年 | 60篇 |
1980年 | 66篇 |
1979年 | 72篇 |
1978年 | 68篇 |
1977年 | 80篇 |
1976年 | 52篇 |
1975年 | 48篇 |
1974年 | 48篇 |
1973年 | 51篇 |
排序方式: 共有6958条查询结果,搜索用时 15 毫秒
201.
E. Miyoshi T. Iura Y. Sakai H. Tochihara S. Tanaka H. Mori 《Journal of Molecular Structure》2003,630(1-3):225-232
We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T1), bridge (B2), and 3-fold filled (T4) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent. 相似文献
202.
Mori M Saito N Tanaka D Takimoto M Sato Y 《Journal of the American Chemical Society》2003,125(19):5606-5607
Novel alkenylative cyclization of enyne was developed using Cp*RuCl(cod) under ethylene gas at room temperature. 相似文献
203.
204.
205.
Kiyokawa T Kanaori K Tajima K Kawaguchi M Mizuno T Oku J Tanaka T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(14):3548-3554
The alpha-helical coiled coils have a representative amino acid sequence of (abcdefg)(n) heptad repeats. We previously reported that two peptides named IZ-2A and IZ-2W formed an (IZ-2A)(2)/IZ-2W heterotrimer with an Ala-Ala-Trp interaction in the hydrophobic core. In this paper, we describe the selective formation of AAB- and ABC-type heterotrimers. To increase the selectivity of the AAB-type heterotrimeric formation, Lys residues at the f position were mutated to either an Ala or a Gln residue to form IZ-2A(fA) or IZ-2W(fQ). Separately, both IZ-2A(fA) and IZ-2W(fQ) have a random structure at pH 7 and 20 degrees C. However, together IZ-2A(fA) and IZ-2W(fQ) form a 2:1 complex with a thermal transition midpoint (Tm) of 48 degrees C. This procedure was applied to prepare the ABC-type heterotrimer, in which two sets of Ala-Ala-Trp interactions were designed in the hydrophobic core. Interhelical interaction between the e and g positions and the alpha-helical propensity of the amino acid at the f position were also considered in the design. The resultant three peptides selectively formed the ABC-type heterotrimer with a Tm of 51 degrees C. Other peptide combinations had random coil properties. 相似文献
206.
Determination of chemical form of antimony in contaminated soil around a smelter using X-ray absorption fine structure. 总被引:1,自引:0,他引:1
Masaki Takaoka Satoshi Fukutani Takashi Yamamoto Masato Horiuchi Naoya Satta Nobuo Takeda Kazuyuki Oshita Minoru Yoneda Shinsuke Morisawa Tsunehiro Tanaka 《Analytical sciences》2005,21(7):769-773
Only limited information is available about the behavior of antimony (Sb) in contaminated soils. However, understanding the behavior of Sb in contaminated soils is important, because the toxicity or solubility of this element depends on its chemical state. In this study, we investigated the levels of Sb and the chemical forms of Sb in the soil around a smelter using X-ray absorption fine structure (XAFS) spectra. The highest Sb concentration in the contaminated soil was 2900 mg/kg dry soil. According to Sb-K edge X-ray absorption near edge (XANE) spectra, the Sb in the soil was in the form of Sb(V) compounds. The similarity of extended XAFS (EXAFS) spectra suggests that Sb speciation was independent of the sampling site, which indicates that Sb or Sb2O3 emitted from the smelter was converted into Sb(V) compounds in the soil. 相似文献
207.
208.
Angle-resolved photoelectron spectra were measured for a single-domain monolayer film of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTCDA) prepared on a cleaved GeS(0 0 1) surface using synchrotron radiation. The observed photoelectron angular distributions were analyzed by a calculation using the single-scattering approximation combined with molecular orbital calculation. With the help of the low-energy electron diffraction pattern, the structure of the NTCDA monolayer on GeS(0 0 1) was estimated quantitatively. 相似文献
209.
Mitomycin C, an anti-neoplastic agent, was covalently attached to bovine serum albumin through various kinds of spacers such as glutaryl, succinyl, trans-aconityl, methylsuccinyl and the trimellityl group. The prior acylation of albumin not only prevented protein polymerization in the presence of carbodiimide, but also increased the extent of conjugation of the drug. The conjugate of mitomycin C-glutarylated albumin showed the best properties among the conjugates prepared in meeting the requirements for a high yield of nonpolymerized product with an adequately high mitomycin C content and stability as a macromolecular prodrug. 相似文献
210.
Hiroyuki Hayakawa Hiromichi Tanaka Keiko Sasaki Kazuhiro Haraguchi Takafumi Saitoh Fumi Takai Tadashi Miyasaka 《Journal of heterocyclic chemistry》1989,26(1):189-192
Several 8-substituted cordycepins were prepared via LDA lithiation of 2′,5′-bis-O-(t-butyldimethylsilyl)-cordycepin and successive reactions of its C-8 lithiated species with various types of electrophiles. Wittig reaction of the 8-formyl derivative was also examined. 相似文献