全文获取类型
收费全文 | 726109篇 |
免费 | 9291篇 |
国内免费 | 2070篇 |
专业分类
电工技术 | 13055篇 |
综合类 | 671篇 |
化学工业 | 110430篇 |
金属工艺 | 28171篇 |
机械仪表 | 21137篇 |
建筑科学 | 17759篇 |
矿业工程 | 3727篇 |
能源动力 | 19229篇 |
轻工业 | 64393篇 |
水利工程 | 7411篇 |
石油天然气 | 13972篇 |
武器工业 | 49篇 |
无线电 | 81209篇 |
一般工业技术 | 141006篇 |
冶金工业 | 140367篇 |
原子能技术 | 15297篇 |
自动化技术 | 59587篇 |
出版年
2021年 | 6266篇 |
2020年 | 4630篇 |
2019年 | 5814篇 |
2018年 | 10144篇 |
2017年 | 9939篇 |
2016年 | 10532篇 |
2015年 | 7279篇 |
2014年 | 11981篇 |
2013年 | 32678篇 |
2012年 | 18996篇 |
2011年 | 26126篇 |
2010年 | 20872篇 |
2009年 | 23416篇 |
2008年 | 23971篇 |
2007年 | 23475篇 |
2006年 | 20673篇 |
2005年 | 19063篇 |
2004年 | 18123篇 |
2003年 | 17776篇 |
2002年 | 17164篇 |
2001年 | 17170篇 |
2000年 | 16030篇 |
1999年 | 16766篇 |
1998年 | 42711篇 |
1997年 | 30482篇 |
1996年 | 23441篇 |
1995年 | 17554篇 |
1994年 | 15387篇 |
1993年 | 15071篇 |
1992年 | 11068篇 |
1991年 | 10559篇 |
1990年 | 10262篇 |
1989年 | 10088篇 |
1988年 | 9557篇 |
1987年 | 8412篇 |
1986年 | 8306篇 |
1985年 | 9378篇 |
1984年 | 8825篇 |
1983年 | 7961篇 |
1982年 | 7456篇 |
1981年 | 7680篇 |
1980年 | 7292篇 |
1979年 | 7109篇 |
1978年 | 6999篇 |
1977年 | 8304篇 |
1976年 | 10932篇 |
1975年 | 6208篇 |
1974年 | 5810篇 |
1973年 | 5880篇 |
1972年 | 4978篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
C Faure M Besnard A Hirsch JF Mougenot M Peuchmaur JP Cezard J Navarro 《Canadian Metallurgical Quarterly》1996,23(4):419-421
N-(phosphonacetyl)-disodium L-aspartic acid (PALA) demonstrates a synergistic antitumor effect when combined with 5-Fluorouracil (5-FU) in in vitro studies. In a Phase II trial, 23 eligible patients with unresectable or metastatic adenocarcinoma of the stomach were treated with weekly i.v. bolus PALA (250 mg/M2) followed 24 hours later by a 24-hour infusion of 5-FU (2600 mg/M2) for an initial period of 8 weeks. No objective responses were noted. PALA and 5-FU is inactive against gastric adenocarcinoma at the doses and schedule used in this trial. 相似文献
992.
G Barbaro G Barbarini W Calderon B Grisorio P Alcini G Di Lorenzo 《Canadian Metallurgical Quarterly》1996,111(5):1169-1177
BACKGROUNDS & AIMS: Contrasting opinions exist about the pharmacological treatment of esophageal candidiasis in patients with acquired immunodeficiency syndrome (AIDS). The aim of this study was to assess the long-term efficacy of fluconazole and itraconazole treatment. METHODS: This study evaluated 2213 human immunodeficiency virus-positive patients at first episode of esophageal candidiasis diagnosed by endoscopy; 1105 received fluconazole and 1108 received itraconazole. The endoscopic and clinical response to treatment was assessed periodically until the end of the follow-up period (1 year). RESULTS: At week 2, endoscopic cure occurred in 81.2% of patients treated with fluconazole and in 65.6% of patients treated with itraconazole (P < 0.001). Clinical cure was observed in 81.5% of patients treated with fluconazole and in 75.2% of patients treated with itraconazole (P < 0.001). At the end of the follow-up period, endoscopic and clinical cure were observed in 96% of patients treated with fluconazole and in 95.6% of patients treated with itraconazole (P = 0.788), with similar differences by intention-to-treat analysis (93.6% vs. 93.3%; P = 0.853). Treatment failure was observed in 22.3% of fluconazole-treated patients and in 26.6% of itraconazole-treated patients (P = 0.022). CONCLUSIONS: Fluconazole and itraconazole are provided with good long-term therapeutic efficacy in the treatment of Candida esophagitis in patients with AIDS. Fluconazole is associated with a higher rate of cure than itraconazole in short-term treatment. 相似文献
993.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
994.
995.
M Suda K Tanaka K Natsui T Usui I Tanaka M Fukushima C Shigeno J Konishi S Narumiya A Ichikawa N Nakao 《Canadian Metallurgical Quarterly》1996,137(5):1698-1705
PGE2 is one of the key molecules in the osteoblast. It is the major prostanoid in the bone, and its production is under the control of both systemic and local factors. PGE2 has been reported to have multiple actions in the osteoblast, such as growth promotion and cell differentiation. To better understand the action of PGE2 in the osteoblast, we determined the PGE receptor subtypes in MC3T3-E1, an osteoblastic cell line derived from the normal mouse calvaria. Northern blot analysis revealed that EP1 and EP4 subtypes are expressed in MC3T3-E1. In contrast, EP3 subtype was not detected by either Northern blot analysis or RT-PCR. The contribution of each subtype was evaluated by studying the effects of subtype-specific analogs on osteoblastic function at confluency and 5 days after confluency. An EP1 agonist, 17-phenyl-omega-trinor PGE2, increased DNA synthesis and decreased alkaline phosphatase activity. 11-Deoxy-PGE1, and EP2 and EP4 agonist, decreased DNA synthesis and increased alkaline phosphatase activity at both stages. Butaprost, an EP2-selective agonist, showed effects similar to those of 11-deoxy-PGE1 only at confluency. Another and more differentiated osteoblastic marker, osteocalcin production, was detectable and was stimulated by 11-deoxy-PGE1 only 5 days after confluency. The exposure of these cells to EP1 agonist changed the cell shape to a more fibroblastic appearance. These results indicate that EP1, EP4, and probably EP2 are present in MC3T3-E1 cells; EP1 promotes cell growth, and EP2 and EP4 mediate differentiation of the osteoblast. Furthermore, the decreased response to EP2-specific agonist 5 days after confluency suggests that the expression of PGE receptor subtype is dependent on the stage of osteoblastic differentiation. This is the first report to determine PGE receptor subtypes in the bone. 相似文献
996.
997.
S Tetali E Abrams S Bakshi M Paul N Oyaizu S Pahwa 《Canadian Metallurgical Quarterly》1996,12(8):669-675
The relationship of virus load to clinical disease progression in HIV-infected children remains to be elucidated. In this study, HIV-1 proviral DNA load was determined in peripheral blood mononuclear cells (PBMCs) by the quantitative competitive DNA polymerase chain reaction assay (QC-PCR) in 47 HIV-infected children subdivided by age (group I, < or = 2 years; group II, > or = 5 years), who were further categorized to include 12 rapid progressors (RP, age < or = 2 years, Centers for Disease Control [CDC] defined clinical category C and/or immune category 3, or death before age 2 years) and slow progressors (SP, age > or = 5 years, excluding CDC categories C and/or immune category 3). Significantly higher mean proviral copies/10(3) PBMCs were detected in group I versus group II (75.4 +/- 104.3 and 13.0 +/- 17.8 respectively, p < 0.0001) and in RP (158.0 +/- 118.2) as compared to either SP (11.8 +/- 18.8, p < 0.0001) or other age-matched infected children (20.3 +/- 38.8, p < 0.0001). Thus HIV-infected children appear to have a higher cell-associated virus load early in life, especially in association with rapid disease progression. 相似文献
998.
Amador F.G. Berman D. Borning A. DeRose T. Finkelstein A. Neville D. Notkin D. Salesin D. Salisbury M. Sherman J. Sun Y. Weld D.S. Winkenbach G. 《Knowledge and Data Engineering, IEEE Transactions on》1993,5(4):611-618
The electronic encyclopedia exploratorium (E3) is a vision of a future computer system-an electronic book describing how thing work. Typical articles in E3 will describe such mechanisms as compression refrigerators, engines, telescopes, and mechanical linkages. Each article will provide simulations, three-dimensional animated graphics that the user can manipulate, laboratory areas that allow a user to modify the device or experiment with related artifacts, and a facility for asking questions and receiving customized, computer-generated English-language explanations. Some of the foundational technology is discussed, focusing on topics in artificial intelligence, graphics, and user interfaces. The initial prototype system and the technical lessons learned from it, as well as the second prototype currently under construction, are described 相似文献
999.
For multiuser packet communications with unpredictable user demands (e.g., in a local or metropolitan area network), coordination and control of access to the frequency-division multiplexing (FDM) channels are difficult. B. Glance (J. Lightwave Technol., vol.10, pp.1323-1328, Sep 1992) proposed using a simple protection-against-collision (PAC) circuit to solve this media access problem and achieve full optical connectivity. The PAC system has the potential to interconnect hundreds of ports, each transmitting at several gigabits per second. Performance aspects of the PAC optical packet network are discussed here. The delay-throughout performance of this network is analyzed for uniform traffic patterns. The results show that in geographically distributed applications the maximum achievable throughput (normalized to the transmission rate) is typically between 0.4 and 0.5 per channel. In a centralized switch the (normalized) maximum achievable throughput can approach 0.8 per channel 相似文献
1000.