全文获取类型
收费全文 | 2433篇 |
免费 | 37篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 28篇 |
综合类 | 9篇 |
化学工业 | 170篇 |
金属工艺 | 15篇 |
机械仪表 | 24篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 13篇 |
轻工业 | 81篇 |
水利工程 | 14篇 |
石油天然气 | 7篇 |
武器工业 | 1篇 |
无线电 | 120篇 |
一般工业技术 | 148篇 |
冶金工业 | 1685篇 |
原子能技术 | 2篇 |
自动化技术 | 120篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 51篇 |
2012年 | 21篇 |
2011年 | 36篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 46篇 |
2006年 | 34篇 |
2005年 | 60篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 29篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 69篇 |
1998年 | 487篇 |
1997年 | 308篇 |
1996年 | 199篇 |
1995年 | 125篇 |
1994年 | 113篇 |
1993年 | 105篇 |
1992年 | 19篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 39篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 31篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 45篇 |
1976年 | 112篇 |
1975年 | 12篇 |
1973年 | 4篇 |
排序方式: 共有2484条查询结果,搜索用时 15 毫秒
1.
Dr. Laurent David Dr. Mark Wenlock Dr. Patrick Barton Dr. Andreas Ritzén 《ChemMedChem》2021,16(17):2669-2685
Chameleonic properties, i. e., the capacity of a molecule to hide polarity in non-polar environments and expose it in water, help achieving sufficient permeability and solubility for drug molecules with high MW. We present models of experimental measures of polarity for a set of 24 FDA approved drugs (MW 405-1113) and one PROTAC (MW 1034). Conformational ensembles in aqueous and non-polar environments were generated using molecular dynamics. A linear regression model that predicts chromatographic apparent polarity (EPSA) with a mean unsigned error of 10 Å2 was derived based on separate terms for donor, acceptor, and total molecular SASA. A good correlation (R2=0.92) with an experimental measure of hydrogen bond donor potential, Δlog Poct-tol, was found for the mean hydrogen bond donor SASA of the conformational ensemble scaled with Abraham's A hydrogen bond acidity. Two quantitative measures of chameleonic behaviour, the chameleonic efficiency indices, are introduced. We envision that the methods presented herein will be useful to triage designed molecules and prioritize those with the best chance of achieving acceptable permeability and solubility. 相似文献
2.
3.
A theory is presented that explains how the visual system infers the lightness, opacity, and depth of surfaces from stereoscopic images. It is shown that the polarity and magnitude of image contrast play distinct roles in surface perception, which can be captured by 2 principles of perceptual inference. First, a contrast depth asymmetry principle articulates how the visual system computes the ordinal depth and lightness relationships from the polarity of local, binocularly matched image contrast. Second, a global transmittance anchoring principle expresses how variations in contrast magnitudes are used to infer the presence of transparent surfaces. It is argued that these principles provide a unified explanation of how the visual system computes the 3-D surface structure of opaque and transparent surfaces. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
B Conrad E Weidmann G Trucco WA Rudert R Behboo C Ricordi H Rodriquez-Rilo D Finegold M Trucco 《Canadian Metallurgical Quarterly》1994,371(6495):351-355
Insulin-dependent diabetes mellitus (IDDM) is a T-cell-mediated autoimmune disease whose onset is believed to be triggered by unknown environmental factors acting on a predisposing genetic background. Islet-infiltrating T (IIT) cells from two IDDM patients, who had died at the onset of the disease from brain swelling as a complication of ketoacidosis, were analysed. The results provided evidence for the involvement of a pancreatic islet cell membrane-bound superantigen as a diabetes aetiopathogenetic factor. There was a selective expansion of a T-cell receptor (TCR) variable segment of the beta-chain (V beta 7) in these IIT cells in association with unselected V alpha-chain segments; extensive junctional diversity of the TCR V beta 7 chains; and evidence of positive selection, after exposure to diabetic islet cell membrane preparations, of V beta 7+ T-cell clones among peripheral blood lymphocytes from non-diabetic individuals. 相似文献
5.
6.
7.
JA McCrohon WA Walters JT Robinson RJ McCredie L Turner MR Adams DJ Handelsman DS Celermajer 《Canadian Metallurgical Quarterly》1997,29(7):1432-1436
OBJECTIVES: We sought to assess whether high dose estrogen treatment is associated with enhanced arterial reactivity in genetic males. BACKGROUND: Although estrogens have been shown to enhance arterial reactivity in women, and are thereby thought to confer cardiovascular benefit, the vascular effects of long-term estrogen therapy in genetic males is unknown. METHODS: We studied the arterial physiology of 30 genetic males--15 male to female transsexuals receiving long-term high dose estrogen therapy and 15 healthy male control subjects matched for age, smoking history and vessel size. Using external vascular ultrasound, brachial artery diameter was measured at rest, after flow increase (causing endothelium-dependent dilation [EDD]) and after nitroglycerin (GTN), an endothelium-independent dilator. Blood pressure, cholesterol and testosterone levels were also measured in each subject. RESULTS: Total testosterone and free testosterone index levels were lower in the transsexuals compared with the control subjects (p < 0.001). In contrast, EDD was significantly higher in the transsexuals than in the control males (mean [+/-SD] 7.1 +/- 3.1% vs. 3.2 +/- 2.8%, p = 0.001), as was the GTN response (21.2 +/- 6.7% vs. 14.6 +/- 3.3%, p = 0.002). Total and high density lipoprotein cholesterol, blood pressure levels and baseline vessel size were similar in the two groups. On multivariate analysis, enhanced EDD was associated independently with estrogen therapy (p = 0.02) and with low total cholesterol (p = 0.04). An enhanced GTN response was also significantly associated with estrogen therapy (p = 0.03). CONCLUSIONS: Long-term treatment with high dose estrogens is associated with enhanced arterial reactivity in genetic males, which may be due to the effects of estrogen excess or androgen deprivation, or both. 相似文献
8.
A new sub-class of binding protein-dependent transporter with specificity for a broad range of polar amino acids has been identified by sequence comparison, in Rhizobium leguminosarum, Rhodobacter capsulatus, Escherichia coli and Pseudomonas fluorescens. Southern blotting and PCR analysis has shown that transporters from this new sub-class are widely distributed in Gram-negative bacteria, including, in addition to the above, Citrobacter freundii, Erwinia carotovorum and Rhizobium meliloti. ABC transporters of polar amino acids can be divided into two groups: those with narrow solute specificity and the newly identified sub-class with broad solute specificity. The binding and inner membrane proteins from transporters with a broad solute specificity are larger by approximately 30% than those with a narrow solute specificity. Multiple alignment of the inner membrane proteins from all sequenced polar amino acid transporters indicates there is an N-terminal conserved region that may be involved in solute specificity. A conserved arginine or lysine at residue 30 of this region is changed to glutamate in arginine transporters. Residue 53 also has a strong correlation with the charge on the transported solute, with basic amino acid transporters replacing an aliphatic amino acid at this position with a negatively charged amino acid. The general amino acid permease from R. leguminosarum, which will transport aliphatic as well as basic and acidic amino acids, juxtaposes two prolines at residues 52 and 53 of the N-terminal conserved region. 相似文献
9.
SL Tannheimer SL Barton SP Ethier SW Burchiel 《Canadian Metallurgical Quarterly》1997,18(6):1177-1182
A method was developed to determine in eggs 2 components [4,6-dimethyl-2-hydroxypyrimidine and 1,3-bis(4-nitrophenyl)urea] of the anticoccidial drug nicarbazin, used to treat poultry. Samples were extracted with acetonitrile, and the extracts were washed with hexane and evaporated to dryness before analysis by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization. By switching from positive to negative ion monitoring and using gradient elution, both components were measured within one run. The limit of quantitation of the assay was 10 ng/g for each component. The results of a preliminary feeding trial in which chickens were fed contamination levels of the drug are also reported. 相似文献
10.