全文获取类型
收费全文 | 754784篇 |
免费 | 10616篇 |
国内免费 | 2127篇 |
专业分类
电工技术 | 14226篇 |
综合类 | 895篇 |
化学工业 | 110433篇 |
金属工艺 | 31598篇 |
机械仪表 | 24674篇 |
建筑科学 | 18133篇 |
矿业工程 | 3615篇 |
能源动力 | 19455篇 |
轻工业 | 62302篇 |
水利工程 | 7824篇 |
石油天然气 | 12791篇 |
武器工业 | 100篇 |
无线电 | 87896篇 |
一般工业技术 | 147995篇 |
冶金工业 | 141622篇 |
原子能技术 | 14615篇 |
自动化技术 | 69353篇 |
出版年
2021年 | 6171篇 |
2020年 | 4537篇 |
2019年 | 5895篇 |
2018年 | 15267篇 |
2017年 | 15554篇 |
2016年 | 13430篇 |
2015年 | 7425篇 |
2014年 | 11894篇 |
2013年 | 32280篇 |
2012年 | 20486篇 |
2011年 | 31454篇 |
2010年 | 25788篇 |
2009年 | 27624篇 |
2008年 | 28237篇 |
2007年 | 29342篇 |
2006年 | 20736篇 |
2005年 | 21315篇 |
2004年 | 19594篇 |
2003年 | 19077篇 |
2002年 | 17546篇 |
2001年 | 17107篇 |
2000年 | 16172篇 |
1999年 | 16895篇 |
1998年 | 42834篇 |
1997年 | 30133篇 |
1996年 | 23213篇 |
1995年 | 17551篇 |
1994年 | 15367篇 |
1993年 | 15068篇 |
1992年 | 11144篇 |
1991年 | 10401篇 |
1990年 | 10128篇 |
1989年 | 9725篇 |
1988年 | 9123篇 |
1987年 | 8110篇 |
1986年 | 7980篇 |
1985年 | 8983篇 |
1984年 | 8433篇 |
1983年 | 7504篇 |
1982年 | 7087篇 |
1981年 | 7233篇 |
1980年 | 6826篇 |
1979年 | 6661篇 |
1978年 | 6330篇 |
1977年 | 7614篇 |
1976年 | 9775篇 |
1975年 | 5606篇 |
1974年 | 5347篇 |
1973年 | 5483篇 |
1972年 | 4429篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
891.
A 3-wave longitudinal design was used to examine the relationships among emotional restraint, peer drug associations, and gateway drug use in a sample of 1,256 middle school students. Structural equation modeling was used to compare 3 models: (1) One model viewed drug use as a consequence of emotional restraint and peer variables; (2) 1 viewed drug use as a cause of restraint and peer variables; and (3) 1 included reciprocal effects. All 3 models fit the data fairly well. However, the reciprocal model fit the data significantly better than either of the others. Within this model, low emotional restraint was significantly related to subsequent increases in gateway drug use among boys. In contrast, peer drug models and peer pressure were not related to subsequent changes in gateway drug use. Changes in peer drug models were, however, predicted by previous levels of gateway drug use. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
892.
893.
894.
Butyl, hexyl, and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl)-2,2-dichloroethene, hexyl and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl) ketone, and the hexyl diester of 1,1-bis(5-carboxyl-2-furyl)methane were synthesized from furfural and evaluated for their plasticizing abilities toward PVC, by the application of dynamic mechanical thermal analysis and [di(2-ethylhexyl) phthalate] as a standard of reference. © 1995 John Wiley & Sons, Inc. 相似文献
895.
In the last 2 years (1994-95), two symposium volumes and three reviews have been published that were fully devoted to peptide antibiotics (antibacterial peptides or antimicrobial peptides). Since the field has been growing rapidly, this review is largely a follow-up of new results published in the last 2 years. Sequencing of the 16S RNA of the small ribosomal subunit indicate that the microbial world is much larger than generally appreciated. The importance of the natural flora is stressed and its effect on the evolution of peptide antibiotics and immunity in general is discussed. 相似文献
896.
Reactive oxygen species may participate in development of neurological toxicity resulting from hyperbaric oxygen exposure. To explore the possibility that increased reactive O2 metabolite generation may result in oxidative modification of lipids and proteins, rats were exposed to five atmospheres (gauge pressure) of O2 until development of an electroencephalographic seizure. Lipid peroxidation (as thiobarbituric acid-reactive substances) and protein oxidation (as 2,4-dinitrophenyl-hydrazones) were measured in five brain regions. Oxidized and reduced glutathione were also determined because of their role in regulating lipid peroxidation. Lipid peroxidation was confined to the frontal cortex and hippocampus, while protein oxidation (in both cytoplasmic and membranous fractions) and increased oxidized glutathione was evident throughout the brain. These results support a role for formation of reactive O2 metabolites from hyperbaric O2 exposure and suggest that protein oxidation, especially in soluble proteins, may be one of the most sensitive measures. 相似文献
897.
T P?usa P Górski H Frank-Piskorska M Kowalski J Kruszewski P Kuna M Kurek R Kurzawa W Silny E Zawisza 《Canadian Metallurgical Quarterly》1996,1(4):292-293
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre. 相似文献
898.
S Fong SJ Hamill M Proctor SM Freund GM Benian C Chothia M Bycroft J Clarke 《Canadian Metallurgical Quarterly》1996,264(3):624-639
The NMR solution structure of an immunoglobulin superfamily module of twitchin (Ig 18') has been determined and the kinetic and equilibrium folding behaviour characterised. Thirty molecular coordinates were calculated using a hybrid distance geometry-simulated annealing protocol based on 1207 distance and 48 dihedral restraints. The atomic rms distributions about the mean coordinate for the ensemble of structures is 0.55( +/- 0.09) A for backbone atoms and 1.10( +/- 0.08) A for all heavy atoms. The protein has a topology very similar to that of telokin and the titin Ig domains and thus it falls into the I set of the immunoglobulin superfamily. The close agreement between the predicted and observed structures of Ig 18' demonstrates clearly that the I set profile can be applied in the structure prediction of immunoglobulin-like domains of diverse modular proteins. Folding studies reveal that the protein has relatively low thermodynamic stability, deltaG(H2O)U-F = 4.0 kcal mol(-1) at physiological pH. Unfolding studies suggest that the protein has considerable kinetic stability, the half life of the unfolding is greater than 40 minutes in the absence of denaturant. 相似文献
899.
JP Larsen H Odegaard E Tandberg A H?dneb? D Aarsland 《Canadian Metallurgical Quarterly》1996,9(4):157-163
As hypersensitivity to natural rubber latex (NRL) has become an increasingly recognized problem in children, identification of all groups at risk seems important. In this study hypersensitivity to NRL was evaluated in 337 children with potential risk factors. We identified by questionnaire children's underlying diseases, history of surgical procedures, evidence of atopy and patient's history of NRL-specific reactions. Hypersensitivity to NRL and other allergens relevant in the Düsseldorf area was evaluated by skin prick test and specific IgE. In 9.2% of all children hypersensitivity to NRL was observed. Significant risk factors for hypersensitivity to NRL were, among the underlying diseases, spina bifida (odds ratio 29.2), hydrocephalus internus (10.1), gastrointestinal malformation (5.2) and atopy (2.2). Surgical procedures with significant risk were the implantation of a ventriculo-peritoneal shunt (15.7) and surgery of the gastrointestinal tract (3.1). Frequency of surgical procedures correlated (p < 0.001) with risk of hypersensitivity. Frequent surgery and atopy were found to have an additional effect on the risk of hypersensitivity. Information about previous NRL-specific reactions obtained by questionnaire was of little predictive value when performing multivariate analysis. For children at high risk for hypersensitivity to NRL preoperative evaluation and, in case of hypersensitivity, preventive measures seem to be advised. 相似文献
900.
V. M. Yakovenko M. V. Burtyka I. V. Yakovenko 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(3):559-568
The theory of interaction of charged particle beams with 2D electron gas, located in the field of the delta-like potential wallU(y) =U oδ(y) has been developed. The kinetic equation for plasmons in 2D electron gas was obtained; the conditions of arising of their instability are given and the corresponding expressions for the increment of plasmons are found. 相似文献