全文获取类型
收费全文 | 3635篇 |
免费 | 55篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 437篇 |
金属工艺 | 35篇 |
机械仪表 | 77篇 |
建筑科学 | 119篇 |
矿业工程 | 5篇 |
能源动力 | 66篇 |
轻工业 | 182篇 |
水利工程 | 19篇 |
石油天然气 | 10篇 |
无线电 | 236篇 |
一般工业技术 | 406篇 |
冶金工业 | 1740篇 |
原子能技术 | 47篇 |
自动化技术 | 284篇 |
出版年
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 105篇 |
2012年 | 65篇 |
2011年 | 82篇 |
2010年 | 73篇 |
2009年 | 68篇 |
2008年 | 95篇 |
2007年 | 97篇 |
2006年 | 70篇 |
2005年 | 69篇 |
2004年 | 67篇 |
2003年 | 61篇 |
2002年 | 60篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 98篇 |
1998年 | 459篇 |
1997年 | 297篇 |
1996年 | 215篇 |
1995年 | 117篇 |
1994年 | 106篇 |
1993年 | 121篇 |
1992年 | 50篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 55篇 |
1988年 | 47篇 |
1987年 | 44篇 |
1986年 | 41篇 |
1985年 | 52篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1982年 | 35篇 |
1981年 | 53篇 |
1980年 | 31篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 77篇 |
1976年 | 117篇 |
1975年 | 33篇 |
1974年 | 18篇 |
1973年 | 31篇 |
1972年 | 20篇 |
排序方式: 共有3693条查询结果,搜索用时 21 毫秒
21.
We evaluated the effect of halothane anesthesia on the motility of the sphincter of Oddi and simultaneous transsphincteric flow in Australian Brush-tailed possums (Trichosurus vulpecula). Halothane levels in the range of 0.25 to 2% were administered and decreased transsphincteric flow in a dose-dependent manner. Sphincter of Oddi basal pressure was higher than normal, but not in a dose-dependent manner. Additionally, halothane anesthesia influenced the sphincter of Oddi motility by decreasing the motility index (mean amplitude multiplied by frequency of contractions). This decrease was dose dependent. These findings indicate that sphincter of Oddi basal pressure is a major component of sphincter of Oddi motility responsible for regulating transsphincteric flow in this species. For studies of the sphincter of Oddi motility in anesthetized Australian Brush-tailed possums, we recommend anesthetic induction with ketamine (50 mg/kg, i.m.) and the inspired halothane level should not exceed 0.75% during the study period, as the effects we have demonstrated were most evident at levels greater than 0.75%. If higher halothane levels are required to maintain satisfactory anesthesia, an alternative anesthetic agent should be considered. 相似文献
22.
23.
24.
Steven S Fu Miles McFall Andrew J Saxon Jean C Beckham Timothy P Carmody Dewleen G Baker Anne M Joseph 《Nicotine & tobacco research》2007,9(11):1071-1084
We conducted a systematic review of what is known about the relationship between post-traumatic stress disorder (PTSD) and smoking to guide research on underlying mechanisms and to facilitate the development of evidence-based tobacco treatments for this population of smokers. We searched Medline, PsychINFO, and the Cochrane Central Register of Controlled Trials and identified 45 studies for review that presented primary data on PTSD and smoking. Smoking rates were high among clinical samples with PTSD (40%-86%) as well as nonclinical populations with PTSD (34%-61%). Most studies showed a positive relationship between PTSD and smoking and nicotine dependence, with odds ratios ranging between 2.04 and 4.52. Findings also suggest that PTSD, rather than trauma exposure itself, is more influential for increasing risk of smoking. A small but growing literature has examined psychological factors related to smoking initiation and maintenance and the overlapping neurobiology of PTSD and nicotine dependence. Observational studies indicate that smokers with PTSD have lower quit rates than do smokers without PTSD. Yet a few tobacco cessation treatment trials in smokers with PTSD have achieved quit rates comparable with controlled trials of smokers without mental disorders. In conclusion, the evidence points to a causal relationship between PTSD and smoking that may be bidirectional. Specific PTSD symptoms may contribute to smoking and disrupt cessation attempts. Intervention studies that test behavioral and pharmacological interventions designed specifically for use in patients with PTSD are needed to reduce morbidity and mortality in this population. 相似文献
25.
Most (98%) of the fat in human milk is present as triglycerides. This paper describes the use of a clarification procedure that enables the level of human milk fat to be determined by measurement of glycerol released by enzymic hydrolysis of triglycerides. The method requires only 10-50 microliters milk, thus presenting a possible technique for work with small mammals, and is suitable for use with autoanalysers, permitting rapid sample throughput. 相似文献
26.
A novel method for the crosslinking of poly(ethylene terephthalate) fibers is described using 1,6‐hexanedisulfonyl azide, 1,3‐benzenedisulfonyl azide, and 2,6‐naphthalenedisulfonyl azide. The azides are diffused into poly(ethylene terephthalate) fibers (Dacron) from perchloroethylene solution, and the fibers are heat treated to bring about decomposition of the sulfonyl azide and give rise to crosslinking. A study is made of the mechanical and thermal properties of the resultant fibers, which are changed considerably in comparison to the untreated fiber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1517–1527, 2002 相似文献
27.
“Study of a Numerically Modeled Severe Storm” is a well known animation within the scientific visualization community. The visualization is among the best of its genre, featuring full storyboarding, well chosen representations, high quality rendering, and professional narration. We recently revisited the thunderstorm to consider what we would do differently if we were to make that video again. We wanted to demonstrate several principles of effective information presentation, drawing from the fields of graphic design and visual perception. Our purpose was not to find fault with bad visualization. Rather, we wanted to study how to make a good thing better. The original video was produced using the modeling, animation, and rendering capabilities of Wavefront's Advanced Visualizer. To facilitate comparison, we did most of the current work with the same software. However, many points discussed here apply to interactive visualization tools as well. The original visualization and our revised version are both based on data generated by a simulation run on a Cray supercomputer at NCSA. The simulation models the genesis and lifetime of a severe storm by solving a set of time dependent equations over a collection of regularly spaced grid points in a three dimensional rectangular space 相似文献
28.
OBJECTIVE: To evaluate the use and efficacy of electroconvulsive therapy (ECT) in refractory major depression according to DSM-III-R criteria, and to look for factors predicting response in the acute phase and the occurrence of relapse or recurrence after recovery. DESIGN: Retrospective. SETTING: University Hospital Rotterdam, The Netherlands. METHODS: Of all patients who received ECT between January 1988 and July 1993 data were collected by study of clinical records and of information by treating physicians after discharge. Every patient was visited once, or received an outpatient department appointment, to obtain informed consent, take a follow-up history and evaluate social functioning by scoring Global Assessment of Functioning and Sickness Impact Profile rating scales. RESULTS: 35 patients received ECT. In clinical practice, the guidelines of the Netherlands Psychiatric Association were not violated; most patients had received adequate pharmacological pretreatment before the decision to start ECT was made. Two patients died in hospital (not from ECT). In the acute phase 25 of the 33 patients still alive upon discharge showed good recovery. Seven of these suffered relapse within six months. The number of patients with a return of depressive symptoms rose to 12 by the end of the first year of follow-up. Sociodemographic variables and treatment characteristics did not appear to influence the result of treatment in the acute phase, nor the occurrence of relapse or recurrence. With less intensive pre- and post-ECT drug treatment the chances of relapse were increased. CONCLUSIONS: ECT is an effective treatment in the acute phase of a depression. Results after a longer period of follow-up are less satisfactory. 相似文献
29.
Mechanisms for the abnormal copper (Cu) accumulation in the liver of LEC rats were examined using primary cultured liver parenchymal cells prepared from mutant LEC rats and those from control LEA rats (original strain). The Cu and metallothionein (MT) mRNA levels in the liver of LEC rats were caused to decrease to the same levels as those of LEA rats by removing Cu in vivo selectively with tetrathiomolybdate. Cu was taken up by LEC rat cells to the same extent as LEA rat cells by exposure to low medium Cu and to a higher extent by exposure to high medium Cu, while the MT mRNA level in LEC rat cells increased dose-dependently at a much higher rate than that in LEA rats. MT mRNA levels in both cells were comparable by exposure to cadmium, zinc and dexamethasone. The results indicate that expression of MT mRNA is selectively enhanced by Cu in LEC cells despite the fact that uptake of Cu is comparable with normal cells. 相似文献
30.
B van Hout D Gagnon E Souêtre S Ried C Remy G Baker P Genton H Vespignani P McNulty 《Canadian Metallurgical Quarterly》1997,38(11):1221-1226
PURPOSE: The relationship between seizure frequency and both health care costs and quality of life (QOL) was investigated in a retrospective, cross-sectional, multicenter study in France, Germany, and the United Kingdom. METHODS: Three hundred outpatients with stable partial epilepsy were approximately evenly distributed among five seizure-frequency groups, ranging from seizure-free in the last 3 months (group 1) to daily seizures (group 5). Economic data, obtained through patient interviews and record abstraction, comprised direct medical costs, direct nonmedical costs, and indirect costs for the preceding 3 months. Total societal costs in the three countries were pooled and converted to United States dollar equivalents. QOL was assessed through a self-administered questionnaire, the Functional Status Questionnaire (FSQ). RESULTS: Mean total costs increased from $780 in group 1 to $2,171 in group 5 (p = 0.0001), with significant increases in each cost category as seizure frequency increased. Greater seizure frequency also significantly (p = 0.0270) correlated with lower employment rates, which ranged from 57% in group 1 to 30% in group 5. QOL declined as seizure frequency increased. Particularly affected were basic and intermediate activities of daily living (ADL), mental health, social activity, and feeling about health. CONCLUSIONS: The study results show that higher seizure frequencies are associated with higher direct and indirect costs and with reduced QOL for patients with epilepsy. 相似文献