全文获取类型
收费全文 | 60325篇 |
免费 | 3091篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 443篇 |
综合类 | 138篇 |
化学工业 | 13217篇 |
金属工艺 | 1226篇 |
机械仪表 | 1258篇 |
建筑科学 | 1859篇 |
矿业工程 | 145篇 |
能源动力 | 1404篇 |
轻工业 | 10455篇 |
水利工程 | 593篇 |
石油天然气 | 357篇 |
武器工业 | 8篇 |
无线电 | 2478篇 |
一般工业技术 | 9856篇 |
冶金工业 | 11687篇 |
原子能技术 | 326篇 |
自动化技术 | 8055篇 |
出版年
2024年 | 125篇 |
2023年 | 545篇 |
2022年 | 1085篇 |
2021年 | 1763篇 |
2020年 | 1283篇 |
2019年 | 1445篇 |
2018年 | 2294篇 |
2017年 | 2258篇 |
2016年 | 2369篇 |
2015年 | 1732篇 |
2014年 | 2232篇 |
2013年 | 4597篇 |
2012年 | 3587篇 |
2011年 | 3521篇 |
2010年 | 2866篇 |
2009年 | 2588篇 |
2008年 | 2448篇 |
2007年 | 2216篇 |
2006年 | 1662篇 |
2005年 | 1352篇 |
2004年 | 1219篇 |
2003年 | 1220篇 |
2002年 | 1058篇 |
2001年 | 853篇 |
2000年 | 749篇 |
1999年 | 796篇 |
1998年 | 3750篇 |
1997年 | 2510篇 |
1996年 | 1650篇 |
1995年 | 976篇 |
1994年 | 777篇 |
1993年 | 828篇 |
1992年 | 335篇 |
1991年 | 317篇 |
1990年 | 239篇 |
1989年 | 263篇 |
1988年 | 269篇 |
1987年 | 246篇 |
1986年 | 218篇 |
1985年 | 236篇 |
1984年 | 218篇 |
1983年 | 146篇 |
1982年 | 183篇 |
1981年 | 213篇 |
1980年 | 229篇 |
1979年 | 123篇 |
1978年 | 115篇 |
1977年 | 367篇 |
1976年 | 770篇 |
1973年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
E Orgnero de Gaisán C Maldonado MF Diaz Gavier A Aoki 《Canadian Metallurgical Quarterly》1997,179(5):453-460
A bioassay system for rapid detection of carcinogenic agents has been developed using male Fischer 344 rats to bridge the gap between long-term carcinogenicity tests and short-term screening assays. The system, called the medium-term liver bioassay, is fundamentally based on the 2-stage hypothesis of tumor production, employing initiation by diethylnitrosamine (200 mg/kg, i.p.) in the first stage and test chemical administration during the second, in combination with two-thirds partial hepatectomy. It requires only 8 wk for animal experimentation and a further few weeks for quantitative analysis of immunohistochemically demonstrated glutathione S-transferase placental form positive hepatic foci. A total of 291 chemicals/substances have already been analyzed in our laboratory. Among 63 chemicals that were proved to be carcinogenic in the liver of rat and/or mouse, 57 (90%) gave positive results irrespective of their mutagenicity. Negative compounds include peroxisome proliferators and tamoxifen. Even nonhepatocarcinogens were positive at a rate of 24%. Eighty-six percent (12/14) of mouse liver carcinogens were also positive. On the other hand, only 2 out of 45 noncarcinogens showed very weak positivity. Thus, the efficacy of the system for hepatocarcinogens has been well established. This bioassay is increasingly regarded as an appropriate alternative test for carcinogenicity risk assessment and is practically used for a rapid evaluation of hepatocarcinogenicity of chemicals. 相似文献
72.
JA Carballido Rodríguez 《Canadian Metallurgical Quarterly》1997,21(7):641-643
A case of a large dentigerous cyst containing a canine tooth in the maxillary antrum is presented. This case is of interest due because of its extensiveness and the presence of a canine tooth in the roof of the maxillary sinus. In addition, this caused a right-sided epiphora. Enucleation of the cyst containing the ectopic tooth was made. 相似文献
73.
A Serrano Pascual C Merino Hernáez R Ochoa Mejías A Escolano Chamois J Golbano Ablanque I Otero Tejero M Sanz Redondo F Román Ruiz 《Canadian Metallurgical Quarterly》1997,21(6):631-635
BACKGROUND AND AIMS OF THE STUDY: Surgical treatment of functional tricuspid regurgitation associated with advanced valvular disease remains controversial, mainly due to the difficulty in choosing between valve replacement or reconstructive surgery. Failure to correct tricuspid regurgitation during valvular surgery carries a poor prognosis, as reoperation may represent a significant risk to the patient. Thus correct tricuspid valve surgery is vital to achieve improved early and long-term clinical results. METHODS: A total of 142 patients underwent concomitant tricuspid annuloplasty with mitral valve replacement and their clinical outcome was assessed. RESULTS: Overall hospital mortality rate was 11.3%. Seven patients died during follow up. The overall actuarial survival rate for 10 years was 74.1 +/- 14.2%. Postoperatively, 75.8% of the patients had no residual tricuspid insufficiency, while 24.2% had first- or second-degree tricuspid insufficiency and were treated medically. All patients were in NHYA functional class I or II postoperatively. CONCLUSION: Clinically, it is important to assess the severity of functional tricuspid insufficiency before and/or during the operation. Bicuspidalization annuloplasty for functional tricuspid insufficiency has provided good results, with a low incidence of reoperation and significant clinical improvement. The technique could be used in most patients with functional tricuspid regurgitation. 相似文献
74.
M Beksa? MS Beksa? VB Tipi HA Duru MU Karakás AN Cakar 《Canadian Metallurgical Quarterly》1997,30(3):145-150
The endothelium participates actively in homeostatic mechanisms such as the regulation of vascular tone and maintenance of a nonthrombotic environment, as well as directing biological responses such as leukocyte trafficking to inflammatory sites. Disruption of these processes leads to disease. In the antiphospholipid antibody syndrome autoantibodies provoke the endothelium to develop a prothrombotic surface. In systemic vasculitides associated with presence of antineutrophil cytoplasm antibodies, it is likely that the autoantibodies incite premature neutrophil activation, disrupted neutrophil-endothelium interactions and endothelial damage. This review considers how normal endothelial functions may be subverted in disease and how active endothelial responses may contribute to disease. 相似文献
75.
The hypothesis of Geisler (Brain Res. 212 (1981) 198-201), in which the different spontaneous-rate classes of primary auditory neurons were accounted for by the different sizes of uniquantal EPSPs relative to the gap between resting membrane and threshold potentials, was represented with an expanded model which included relative refractory effects. The spike rates generated by the expanded model, when plotted vs. estimated sound level, are qualitatively similar to those of experimentally obtained rate-level curves. The hypothesis is also consistent with recent ultrastructural data which suggest that average quantal-release rates for any particular primary auditory neuron are inversely related to its spontaneous rate. The model's recovery processes following spike generation (hazard functions) are also similar to those observed experimentally. 相似文献
76.
77.
78.
We have analyzed the compositional properties of coding (protein encoding) and non-coding sequences of Plasmodium falciparum, a unicellular parasite characterized by an extremely AT-rich genome. GC% levels, base and dinucleotide frequencies were studied. We found that among the various factors that contribute to the properties of the sequences analyzed, the most relevant are the compositional constraints which operate on the whole genome. 相似文献
79.
J Weber P Majer J Litera J Urban M Soucek J Vondrásek J Konvalinka P Novek J Sedlácek P Strop HG Kr?usslich I Pichová 《Canadian Metallurgical Quarterly》1997,341(1):62-69
The results of investigation of haptoglobin (Hp) types in 596 donor blood samples in some towns of Ukraine (Dnepropetrovsk, Kharkov, Odessa, Kiev, Uzhgorod, Zhitomir) are presented. Three normal Hp types (Hp1-1, Hp2-1 and Hp2-2) have been found. The reliable interpopulation differences in the Hp types frequency were not found. On the whole the Hp types frequency in the type Hp1-1 comprised 12.7%. In the type Hp2-1-48.1% and in the type Hp2-2-36.5%. The frequency of the gene Hp1 is 0.38. The frequency of the Hp types and of the gene Hpl in Ukraine is similar to that in population of Eastern Europe and European Part of Russia. 相似文献
80.
E Espinosa-Huerta A Robles-Páramo L Viniegra-Velázquez 《Canadian Metallurgical Quarterly》1997,49(6):469-474
PURPOSE: To compare the response rates, toxicities and survival durations of elderly patients (70 years of age or more) with those of younger patients (less than 70 years of age) with non-small-cell lung cancer (NSCLC) treated with cisplatin-based chemotherapy. PATIENTS AND METHODS: We analyzed retrospectively the data of 203 assessable patients entered on a prospective randomized trial of cisplatin-based combination chemotherapy. Chemotherapy consisted of three dosage regimens: (1) vindesine and cisplatin (VP); (2) mitomycin, vindesine and cisplatin (MVP); or (3) etoposide and cisplatin alternating with vindesine and mitomycin (EP/VM). RESULTS: A greater proportion of elderly patients had localized disease and more squamous cell carcinoma than non-elderly patients. The overall response rates were 44% in the elderly group and 28% in the non-elderly group. In the EP/VM arm, the response rate was significantly better in the elderly group than in the non-elderly group. The frequency of grade 4 leukocytopenia in the MVP and EP/VM arms in the elderly group was significantly greater than in the non-elderly group (P < 0.05). No differences were found in nonhematological toxicities between the two groups. There was no difference in overall survival between the groups. CONCLUSION: Elderly patients treated with mitomycin-containing regimens have higher hematologic toxicities than younger patients. The results of this study are consistent with the previously reported pharmacologic data on mitomycin suggesting altered pharmacokinetics in elderly patients. The improved response rate in the elderly patients was probably because more elderly patients had earlier disease, squamous cell carcinoma and better performance status. Cisplatin-based chemotherapy was tolerable for most elderly NSCLC patients with good performance status. 相似文献