全文获取类型
收费全文 | 6558篇 |
免费 | 57篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 19篇 |
综合类 | 3篇 |
化学工业 | 412篇 |
金属工艺 | 30篇 |
机械仪表 | 81篇 |
建筑科学 | 135篇 |
矿业工程 | 3篇 |
能源动力 | 66篇 |
轻工业 | 241篇 |
水利工程 | 14篇 |
石油天然气 | 3篇 |
无线电 | 304篇 |
一般工业技术 | 410篇 |
冶金工业 | 4563篇 |
原子能技术 | 29篇 |
自动化技术 | 305篇 |
出版年
2021年 | 23篇 |
2019年 | 30篇 |
2018年 | 29篇 |
2017年 | 31篇 |
2016年 | 35篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 112篇 |
2012年 | 64篇 |
2011年 | 90篇 |
2010年 | 67篇 |
2009年 | 61篇 |
2008年 | 94篇 |
2007年 | 87篇 |
2006年 | 80篇 |
2005年 | 80篇 |
2004年 | 60篇 |
2003年 | 70篇 |
2002年 | 76篇 |
2001年 | 60篇 |
2000年 | 64篇 |
1999年 | 193篇 |
1998年 | 1310篇 |
1997年 | 792篇 |
1996年 | 519篇 |
1995年 | 323篇 |
1994年 | 266篇 |
1993年 | 301篇 |
1992年 | 76篇 |
1991年 | 99篇 |
1990年 | 89篇 |
1989年 | 105篇 |
1988年 | 113篇 |
1987年 | 89篇 |
1986年 | 68篇 |
1985年 | 79篇 |
1984年 | 41篇 |
1983年 | 38篇 |
1982年 | 60篇 |
1981年 | 62篇 |
1980年 | 57篇 |
1979年 | 31篇 |
1978年 | 39篇 |
1977年 | 149篇 |
1976年 | 205篇 |
1975年 | 37篇 |
1974年 | 29篇 |
1973年 | 17篇 |
1971年 | 19篇 |
1970年 | 20篇 |
排序方式: 共有6618条查询结果,搜索用时 3 毫秒
1.
Karim Gharbi Louise Matthews James Bron Ron Roberts Alan Tinch Michael Stear 《Journal of the Royal Society Interface》2015,12(110)
Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis, the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of lice numbers within this time window was moderately high at 0.3, confirming that selective breeding is viable. We combined an epidemiological model of sea lice infection and control on a salmon farm with genetic variation in susceptibility among individuals. We simulated 10 generations of selective breeding and examined the frequency of treatments needed to control infection. Our model predicted that substantially fewer chemical treatments are needed to control lice outbreaks in selected populations and chemical treatment could be unnecessary after 10 generations of selection. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production. 相似文献
2.
This paper describes techniques for the on-chip measurement of high-frequency and/or high-bandwidth electrical phenomena in ultra large-scale integration environments. The techniques rely on the integration of multiple compact and robust electronic test devices, or cores, at various locations within an integrated circuit. The cores consist primarily of signal generators that approximate the output of a sigma-delta modulator using finite repetitious bit patterns and a small set of highly robust analog components. They are capable of digitizing on-chip signals at gigahertz rates even using low-cost manufacturing processes. Simple communication between the multiple cores enables the migration of many "board-level" type measurements down to the chip level. 相似文献
3.
OA al-Swayeh MS al-Humayyd AA Mustafa AS al-Tuwaijri RS al-Rashed AT Ali 《Canadian Metallurgical Quarterly》1997,12(7):481-489
Recent evidence suggests that oxygen-derived free radicals are involved in mediating gastric microvascular and parenchymal cell injuries induced by ischaemia and reperfusion. Therefore, the effect of the locally acting anti-ulcer drug, sucralfate, was studied on ischaemia and reperfusion (e.g. induced gastric lesions, intraluminal bleeding, changes in vascular permeability and non-protein sulfhydryl levels in the rat stomach). Allopurinol was used as a known standard antioxidant drug. Rats were subjected to 30 min of gastric ischaemia in the presence of 100 mmol/L hydrochloric acid and reperfusion periods of 15, 30 or 60 min duration. The gastric lesions were assessed microscopically under an inverted microscope. The vascular permeability was quantified by measuring the extravasated Evans blue in the stomach. There were significantly greater numbers of gastric lesions, intraluminal bleeding and leakage of Evans blue during all reperfusion periods as compared with those of ischaemia, with maximum effects occurring at 60 min following reperfusion. Pretreatment with sucralfate (31.25-250 mg/kg, p.o.) or allopurinol (12.5-50 mg/kg, i.p.) 30 min before the procedure, dose-dependently reduced the gastric lesions, intraluminal bleeding, and decreased the vascular permeability induced by ischaemia and reperfusion. Furthermore, sucralfate dose-dependently reverses the ischaemia and reperfusion-induced depletion of mucosal non-protein sulfhydryl levels and inhibited the superoxide radical production in both cell-free xanthine-xanthine oxidase and in the stimulated polymorphonuclear cellular systems. These results suggest that the protection produced by sucralfate against gastric injury may be due to its antioxidant effects. 相似文献
4.
5.
The tet(M) genes were characterized from 84 isolates of 10 different bacterial species isolated from the periodontal pockets of 16 patients with periodontal disease. A 740 bp polymerase chain reaction product from the hypervariable region of the tet(M) structural gene was cleaved with the restriction enzymes AluI and HinfI. Three different restriction patterns were identified for each of the two enzymes. By DNA sequencing, using a direct solid-phase automated sequencing method, the isolates could be grouped into 3 different clusters of tet(M) subtypes. The internal DNA homology within each subtype was 98-100%; the homology between clusters was 89-94%. Two different subtypes were identified in 9 of 10 bacterial species, and the remaining species had 3 different subtypes. One of the subtypes (M3) was seen mainly in the anaerobic isolates. This subtype was different from all earlier sequenced structural tet(M) genes present in the Genbank. Most patients had two different subtypes of tet(M), and a third subtype was seen in the 3 patients who exhibited the greatest variety of tetracycline-resistant bacterial species. It appears that the presence of one subtype of the tet(M) gene within a patient or bacterial species does not prevent the acquisition of another subtype of the same gene. This study identified a new subtype of the tet(M) gene and grouped it into 3 distinct yet highly homologous genetic subtypes. 相似文献
6.
Rolandic discharge (RD), noted in the electroencephalography (EEG) of patients with benign epilepsy in childhood with centrotemporal spikes (BECCT) has several unique features. One feature is that the amount or frequency of RDs does not correlate well with the incidence of seizures in BECCT although it is a key finding in the diagnosis of this epileptic syndrome. In this study, we examined the efficacy of antiepileptic drugs focusing on the disappearance of RDs in relationship with seizure control. Forty patients with BECCT who were not medically treated prior to this study were randomly sorted into three groups. Twenty patients were assigned for clonazepam (CZP) treatment, 10 patients for valproate (VPA) and the remaining 10 patients for carbamazepine (CBZ). Each drug was administered for 4 consecutive weeks. EEGs were recorded twice during the study, before and 4 weeks after the medication trial. The effects of each treatment on RDs were assessed. RDs disappeared in 15 of the 20 cases treated with CZP (75%) within 4 weeks while the same was observed in only one of the 10 cases treated with VPA (10%). CBZ failed to demonstrate any effect on RD. In the group treated with CZP, there were no differences in seizure incidence, seizure type and blood concentration of CZP between the patients whose RDs disappeared and those whose RDs remained. 相似文献
7.
Vascular injuries may occur as complications of elbow dislocation and usually involve the brachial artery. A case report is presented in which only the radial artery was compromised as a result of the dislocation. 相似文献
8.
9.
10.
V Kumar PM Carabateas JA Dority WG Earley JP Mallamo C Subramanyam LD Aimone B Ault DL DeHaven Hudkins MS Miller 《Canadian Metallurgical Quarterly》1995,38(10):1826-1830
Replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with thiazolium (4a and 4b) and N-methylimidazolium (4c and 4d) resulted in equipotent compounds in the [3H]TCP binding assay. The corresponding N-methyl-1,2,4-triazolium analogs were less potent in this assay. The thiazolium derivative 4b, with a Ki = 2.9 nM, is being evaluated as a possible neuroprotective N-methyl-D-aspartic acid (NMDA) antagonist. 相似文献