全文获取类型
收费全文 | 3407篇 |
免费 | 2篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 145篇 |
金属工艺 | 11篇 |
机械仪表 | 23篇 |
建筑科学 | 59篇 |
矿业工程 | 6篇 |
能源动力 | 27篇 |
轻工业 | 147篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 77篇 |
一般工业技术 | 132篇 |
冶金工业 | 2611篇 |
原子能技术 | 15篇 |
自动化技术 | 135篇 |
出版年
2021年 | 15篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 24篇 |
2013年 | 71篇 |
2012年 | 27篇 |
2011年 | 34篇 |
2010年 | 31篇 |
2009年 | 27篇 |
2008年 | 42篇 |
2007年 | 42篇 |
2006年 | 33篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 25篇 |
2002年 | 30篇 |
2001年 | 18篇 |
2000年 | 26篇 |
1999年 | 104篇 |
1998年 | 834篇 |
1997年 | 441篇 |
1996年 | 281篇 |
1995年 | 179篇 |
1994年 | 143篇 |
1993年 | 171篇 |
1992年 | 42篇 |
1991年 | 46篇 |
1990年 | 39篇 |
1989年 | 39篇 |
1988年 | 44篇 |
1987年 | 45篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 9篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 38篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 40篇 |
1976年 | 125篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有3409条查询结果,搜索用时 15 毫秒
91.
92.
Psychiatric workers facing redeployment completed questionnaire measures of stressors, resources (locus of control and perceived social support), coping, well-being, and negative affectivity, at baseline (N = 109) and 1 year later (loss of 7 participants). Regression analyses of the baseline data suggested that as stressors increased, so did avoidance coping, but less so for those high in internality or perceived social support. Problem-focused coping was bolstered by internality and emotion-focused coping by perceived social support. Other regression analyses, with a longitudinal aspect, suggested that stressors had a deleterious effect on well-being. Problem- and emotion-focused coping had beneficial effects, whereas avoidance coping had a (delayed) deleterious effect. These effects of coping were predominantly main and not buffering effects. 相似文献
93.
94.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
95.
96.
M Higashiyama O Doi K Kodama H Yokouchi M Adachi CL Huang T Taki T Kasugai S Ishiguro S Nakamori M Miyake 《Canadian Metallurgical Quarterly》1997,74(2):205-211
STUDY OBJECTIVE: To determine the effect of adding the nebulized anticholinergic drug ipratropium bromide to standard therapy compared with standard therapy alone for acute severe asthma (peak expiratory flow rate [PEFR] < 50% of predicted) in children presenting to the emergency department. METHODS: Ninety children aged 6 to 18 years were randomly assigned to two groups in a prospective, double-blind, placebo-controlled study performed in the ED of an urban children's hospital. All children received nebulized albuterol solution (.15 mg/kg) every 30 minutes, and all received oral steroids with the second dose of albuterol. Children in group 1 received ipratropium bromide (500 micrograms/dose) with the first and third dose of albuterol those in group 2 received saline placebo instead of ipratropium. Pulmonary functions (PEFR and 1-second forced expiratory volume [FEV1]) and physiologic measurements were assessed every 30 minutes up to 120 minutes. By chance, the baseline values for percent of predicted PEFR and FEV1 differed between the two groups. Therefore a multivariate model accounting for both time and baseline effects was used to compare the response between groups. RESULTS: On average, and adjusting for baseline measures, children in the ipratropium group had a significantly greater improvement in percent of predicted PEFR than did children in the placebo group at 60 minutes (P = .02), 90 minutes (P = .002), and 120 minutes (P < .0001). The improvement in percent predicted FEV1 was significantly greater for children in the ipratropium group only at 120 minutes (P = .013). Nine children (20%) from the ipratropium group and 14 (31.1%) from the control group were admitted (P = .33, chi 2). There were no significant adverse effects attributable to the ipratropium, and there was no relation between ipratropium use and changes in pulse, respiratory rate, blood pressure, or oxygen saturation. CONCLUSION: We detected significant improvement in pulmonary function studies over 120 minutes in children with severe asthma who were given nebulized ipratropium combined with albuterol and oral steroids, compared with children who received the standard therapy. Further study is needed to determine whether early use of ipratropium decreases the need for hospitalization. 相似文献
97.
The purpose of this experiment was to investigate the functional contributions of various limbic structures to locomotion and stereotypy induced by dopaminergic drugs. Female rats were randomly assigned to one of 5 groups (n = 10-14 rats/group) that received either a lesion of the hippocampus (colchicine + kainic acid), basolateral amygdala (quinolinic acid), frontal cortex (aspiration), nucleus accumbens (ibotenic acid), or served as unoperated controls. Beginning at least 2 weeks following surgery locomotion (measured as photocell beam breaks) elicited by D-amphetamine (0.0, 0.32, 1.0 and 3.2 mg/kg), SKF 82958 (0.0, 0.04, 0.08 and 0.16 mg/kg) or quinpirole (0.0, 0.25, 0.1 and 0.5 mg/kg) was determined. In agreement with previous results rats with hippocampal lesions were hyperactive in response to amphetamine. In comparison to these changes in drug-induced locomotion, lesions of the basolateral amygdala, and frontal cortex had only minor effects on drug-induced locomotion. Lesions of the nucleus accumbens produced consistent hyperactivity that was suppressed by doses of amphetamine or quinpirole that elicited behavioral stereotypy. These results provide evidence suggesting that, in comparison to other limbic structures that have substantial inputs to the nucleus accumbens, the hippocampus play a relatively prominent role in the modulation of drug-induced locomotion. 相似文献
98.
S Natsch YA Hekster A Keyser CL Deckers H Meinardi WO Renier 《Canadian Metallurgical Quarterly》1997,17(4):228-240
In the last few years a number of new anticonvulsants have been introduced into clinical practice mainly as add-on therapy in patients who do not become seizure-free while receiving established anticonvulsants. Up to now, no single drug has been shown to be more effective at controlling seizures of a particular type than another, so other factors such as mechanism of action, pharmacokinetics, dosage regimens or the spectrum of adverse drug reactions and interactions are used when making a choice between one agent and another. The mechanism of action of tiagabine and vigabatrin is very specific; both agents increase gamma-aminobutyric acid (GABA) levels through inhibition of reuptake and catabolism respectively. However, the mechanism of action of gabapentin is unknown and those of felbamate, lamotrigine and topiramate are not sufficiently clarified as yet, and may be multiple. Great advances have been made in improving the pharmacokinetic characteristics of these newer anticonvulsants. Gabapentin and vigabatrin exhibit relatively ideal pharmacokinetic properties as they are not bound to proteins, are excreted mostly unchanged in the urine and show linear pharmacokinetics. Lamotrigine possesses a highly variable elimination half-life depending on the co-medication. Tiagabine is highly protein bound and zonisamide shows nonlinear pharmacokinetics; both these drugs are extensively metabolised. Problematic drug interactions between newer anticonvulsants and other drugs in general occur rarely when these agents are given concomitantly. However, in common with most new drugs, there are very few data on the use of the newer anticonvulsants in women of childbearing age. Studies done so far on interactions with oral contraceptives used low anticonvulsant dosages for a very short time. The newer anticonvulsants elicit adverse reactions that, while not being unique, are particularly associated with that drug. For example, felbamate may cause aplastic anaemia and fulminant liver failure, lamotrigine is prone to cause skin rash, and oxcarbazepine may cause symptomatic hyponatraemia. Topiramate and zonisamide cause kidney stones, and vigabatrin may induce psychiatric syndromes. Although highly diverse in structure and activity, these newer drugs offer new possibilities for treating refractory epilepsy. However, since no single factor can dictate the choice of drug nor predict the success of treatment, prescribing of these rather expensive drugs has to depend upon careful consideration of the aims of treatment, the characteristics of the drug and the needs of the individual patient. 相似文献
99.
CL Zani E Chiari AU Krettli SM Murta ML Cunningham AH Fairlamb AJ Romanha 《Canadian Metallurgical Quarterly》1997,5(12):2185-2192
Naphtho[2,3-b]thiophen-4,9-quinone and five derivatives were prepared using the Friedel-Crafts reaction and tandem-lithiation of aromatic diethylamides. These quinones were evaluated for their trypanocidal and anti-plasmodial activities by their effects on: (1) growth of epimastigote forms of Trypanosoma cruzi in vitro, (2) lysis of trypomastigote forms of T. cruzi in murine blood, (3) growth of Plasmodium falciparum in vitro, and (4) inhibition of the recombinant enzyme trypanothione reducatase. The parent compound, naphtho[2,3-b]thiophen-4,9-quinone (3a), was among the most active quinone tested in vitro against P. falciparum at 0.2 microM. However, it was inactive against P. berghei-infected mice treated with 2.3 mmol/kg daily for 5 days. Most of the quinones prepared were active against T. cruzi epimastigotes in culture but exhibited weak activity at 4 degrees C against trypomastigotes in murine blood as well against the enzyme trypanothione reducatase. Further structural modifications will be necessary to improve the in vivo activity of the naphthothiophenquinones. 相似文献
100.
MJ Concannon B Gainor GF Petroski CL Puckett 《Canadian Metallurgical Quarterly》1997,100(6):1452-1458
In recent years, electrodiagnostic studies have become an expected component in the work up and evaluation of carpal tunnel syndrome. We conducted a retrospective review of 460 carpal tunnel decompressions to determine whether the accuracy of diagnosis and the prediction of therapeutic outcome could be related to the positivity and severity of findings on preoperative electrical studies. The 349 patients (460 hands) were divided into two groups: group 1 consisted of hands with the clinical diagnosis of carpal tunnel syndrome but with normal electrodiagnostic studies (n = 62); in group 2 the hands had a clinical diagnosis of carpal tunnel syndrome with confirmatory electrodiagnostic studies (n = 398). The number and distribution of signs and symptoms of carpal tunnel syndrome were not statistically different between these two groups. There was not a statistically significant difference in the success rate of surgery or the incidence of complications. The similarities between these two groups suggests that the distinction between them (the positivity of electrodiagnostic studies) is an artificial one and that the clinical diagnosis of carpal tunnel syndrome is sufficient to predict the presence of the disease, as well as outcome of surgery. On the basis of these data, strict adherence to electrodiagnostic studies to confirm the diagnosis will exclude 13 percent of the patients with legitimate carpal tunnel syndrome from receiving appropriate therapy. 相似文献