全文获取类型
收费全文 | 16598篇 |
免费 | 1720篇 |
国内免费 | 918篇 |
专业分类
电工技术 | 559篇 |
技术理论 | 1篇 |
综合类 | 1643篇 |
化学工业 | 3021篇 |
金属工艺 | 947篇 |
机械仪表 | 597篇 |
建筑科学 | 1300篇 |
矿业工程 | 823篇 |
能源动力 | 807篇 |
轻工业 | 871篇 |
水利工程 | 442篇 |
石油天然气 | 558篇 |
武器工业 | 92篇 |
无线电 | 1142篇 |
一般工业技术 | 1842篇 |
冶金工业 | 1625篇 |
原子能技术 | 191篇 |
自动化技术 | 2775篇 |
出版年
2024年 | 64篇 |
2023年 | 259篇 |
2022年 | 442篇 |
2021年 | 514篇 |
2020年 | 554篇 |
2019年 | 498篇 |
2018年 | 472篇 |
2017年 | 455篇 |
2016年 | 529篇 |
2015年 | 543篇 |
2014年 | 887篇 |
2013年 | 1147篇 |
2012年 | 1013篇 |
2011年 | 1232篇 |
2010年 | 961篇 |
2009年 | 1021篇 |
2008年 | 967篇 |
2007年 | 1099篇 |
2006年 | 966篇 |
2005年 | 830篇 |
2004年 | 724篇 |
2003年 | 612篇 |
2002年 | 559篇 |
2001年 | 448篇 |
2000年 | 359篇 |
1999年 | 313篇 |
1998年 | 229篇 |
1997年 | 188篇 |
1996年 | 176篇 |
1995年 | 157篇 |
1994年 | 131篇 |
1993年 | 116篇 |
1992年 | 125篇 |
1991年 | 89篇 |
1990年 | 66篇 |
1989年 | 58篇 |
1988年 | 33篇 |
1987年 | 27篇 |
1986年 | 22篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1963年 | 18篇 |
1961年 | 17篇 |
1960年 | 19篇 |
1959年 | 23篇 |
1958年 | 16篇 |
1957年 | 19篇 |
1956年 | 21篇 |
1955年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
Young-of-the-year spottail shiners (Notropis hudsonius) were used as biomonitors to determine the spatial distribution (1982/83) and assess trend data for organochlorine and mercury residues. Significantly (p < 0.01) higher PCB residues were found in Detroit River spottail shiners than in collections from southwestern Lake St. Clair and northwestern Lake Erie. The highest PCB residues were found in the west bank collections from Michigan waters (912–2,997ng/g) compared to the mid-stream (96–290 ng/g) and east bank collections (153–316 ng/g). Chlordane residues were found to be elevated in all spottail shiner samples from urbanized areas. Octachlorostyrene and ∑ DDT residues were distributed uniformly within the study area, whereas mercury concentrations were found to be lower in spottail shiners from northwestern Lake Erie than in comparable samples from the Detroit River and southwestern Lake St. Clair. Residues for BHC, heptachlor, aldrin, and chlorinated benzenes were near their detection limits; mirex and chlorinated phenols were not detectable. Recent (1982/83) PCB residue levels in spottail shiners exceeded the IJC aquatic life objective (Great Lakes Water Quality Agreement of 1978) at all the sites sampled, except at Pike Creek in Lake St. Clair. PCB residues in spottail shiners from Pike Creek, Big Creek, and Leamington have declined significantly (p < 0.01) since the mid-seventies. Mercury and chlordane residues have decreased in spottail shiner samples from Leamington, but have remained virtually unchanged at Big Creek and Pike Creek. 相似文献
14.
New mesogenic homologous series having an azo central linkage was synthesized by fixing a rigid 4-methyl phenyl azo group
to resorcinol moiety. The terminal and lateral phenolic -OH groups were esterified, one by one, with 4-n-alkoxybenzoyl and acetyl group, respectively. All the twelve homologues synthesized exhibit mesomorphism. The methoxy ton-decyloxy andn-hexadecyloxy derivatives exhibit monotropic nematic mesophase whereas,n-dodecyloxy andn-tetradecyloxy derivatives exhibit enantiotropic nematic mesophase. The mesogenic properties of the present series was compared
with those of other structurally related mesogenic series.
Paper presented at the 5th National Seminar on Liquid Crystals, University of Jammu, Jammu, December 1997. 相似文献
15.
Yu. Dzyadykevych O. Smiyan 《International Journal of Refractory Metals and Hard Materials》2007,25(5-6):361-366
The results of investigation of initial stage of the tantalum borating as well as the effect of oxygen and hydrogen on it are presented. The scheme of the initial stage of tantalum boron saturation is proposed. 相似文献
16.
Gregory S. Ho Chen Huang Emily A. Carter 《Current Opinion in Solid State & Materials Science》2007,11(5-6):57-61
Orbital-free density functional theory (OF-DFT) can be made to scale linearly with sample size, allowing thousands of atoms to be treated explicitly with quantum mechanics. State-of-the-art kinetic energy density functionals and ion–electron pseudopotentials are used to obtain accurate structural property predictions for nanoparticles, nanowires, extended surfaces, and nanoindentation of simple metals. 相似文献
17.
Interventions for a variety of emotional and behavioral problems are commonly delivered in the context of treatment groups, with many using rolling admission to sustain membership (i.e., admission, dropout, and discharge from group are perpetual and ongoing). The authors present an overview of the analytic challenges inherent in rolling group data and outline commonly used (but flawed) analytic and design approaches to addressing (or sidestepping) these issues. Moreover, the authors propose use of latent class pattern mixture models (LCPMMs) as a statistically and conceptually defensible approach for modeling treatment data from rolling groups. The LCPMM approach is illustrated with rolling group data from a group-based alcoholism pilot treatment trial (N = 128). Different inferences were made with regard to treatment efficacy under LCPMM vs. the commonly used standard group-clustered latent growth model (LGM); coupled with other preliminary findings in this area, inferences from LGMs may be overly liberal when applied to data from rolling groups. Continued work on data analytic difficulties in groups with membership turnover is critical for furthering the ecological validity of research on behavioral treatments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
18.
19.
20.