全文获取类型
收费全文 | 111805篇 |
免费 | 8135篇 |
国内免费 | 4194篇 |
专业分类
电工技术 | 5842篇 |
技术理论 | 11篇 |
综合类 | 6591篇 |
化学工业 | 18949篇 |
金属工艺 | 5815篇 |
机械仪表 | 6673篇 |
建筑科学 | 8624篇 |
矿业工程 | 3076篇 |
能源动力 | 3099篇 |
轻工业 | 6624篇 |
水利工程 | 1714篇 |
石油天然气 | 6218篇 |
武器工业 | 692篇 |
无线电 | 13965篇 |
一般工业技术 | 14240篇 |
冶金工业 | 5894篇 |
原子能技术 | 1237篇 |
自动化技术 | 14870篇 |
出版年
2024年 | 432篇 |
2023年 | 1751篇 |
2022年 | 2885篇 |
2021年 | 3987篇 |
2020年 | 3050篇 |
2019年 | 2592篇 |
2018年 | 2985篇 |
2017年 | 3372篇 |
2016年 | 2935篇 |
2015年 | 3855篇 |
2014年 | 4887篇 |
2013年 | 6254篇 |
2012年 | 6554篇 |
2011年 | 7178篇 |
2010年 | 6244篇 |
2009年 | 6161篇 |
2008年 | 6162篇 |
2007年 | 5751篇 |
2006年 | 6042篇 |
2005年 | 5418篇 |
2004年 | 3698篇 |
2003年 | 3197篇 |
2002年 | 2850篇 |
2001年 | 2753篇 |
2000年 | 2871篇 |
1999年 | 3380篇 |
1998年 | 2911篇 |
1997年 | 2547篇 |
1996年 | 2287篇 |
1995年 | 1922篇 |
1994年 | 1551篇 |
1993年 | 1219篇 |
1992年 | 965篇 |
1991年 | 738篇 |
1990年 | 600篇 |
1989年 | 501篇 |
1988年 | 390篇 |
1987年 | 295篇 |
1986年 | 206篇 |
1985年 | 176篇 |
1984年 | 108篇 |
1983年 | 81篇 |
1982年 | 87篇 |
1981年 | 57篇 |
1980年 | 46篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
171.
In order to find out rapidly the causes of the liver diseases suffered by patients with negative hepatitis B surface antigen (HBsAg), nested polymerase chain reaction (PCR) and multiple cloned antibody capture PCR techniques were established to examine serum hepatitis B virus (HBV) DNA. By using both techniques along with the examination of hepatitis C virus (HCV) infection, the causes of chronic liver diseases with negative HBsAg were studied. It is found that nested-PCR can increase the sensitivity of single PCR more than 1,000 fold and multiple cloned antibody capture-PCR can detect concentration of HBV DNA as low as 0.1-0.01 pg/L. HBV DNA positive patients were found in 45.5%, 30.8%, 13.3% and 100% respectively of the patients suffering from liver cirhosis with negative HBsAg (group A, 22 cases), chronic hepatitis with negative HBsAg (group B, 13 cases), normal subjects with negative HBsAg and positive hepatitis B core antibody (HBcAb, group C, 30 cases) and liver cirhosis with positive HBsAg and negative HBeAg (group D, 12 cases). HBV DNA can be also found in the serum of HBsAb positive patients and subjects supposed to be healthy, 81.8% and 53.8% of the patients were infected with HBV and/or HCV in group A and group B respectively. All these results suggest that nested-PCR and multiple cloned antibody capture-PCR are rapid and highly sensitive methods for detection of serum HBV DNA. HBV infection is an important cause of chronic liver diseases in patients with negative HBsAg. The causes of most of the HBsAg-negative chronic liver diseases are related with infection of viruses. The clinical significance of serum HBsAb in naturally infected patients should be reconsidered. 相似文献
172.
Since the late 1980s, the eight-component model of the comprehensive school health program (CSHP), has been adopted widely in the United States and internationally. While it is acknowledged that the eight program elements should be delivered in a coordinated, interactive manner, numerous issues regarding how this integration best can be achieved, including who at the school level should have this responsibility and how the eight components relate conceptually and logistically, have not been addressed adequately. In essence, a CSHP transforms several solo performers into an orchestra. This article proposes the school health coordinator as an essential element in the eight-component model of the CSHP--the maestro, without whom there can be no symphony. The coordinator's principal responsibilities include administration, integration of personnel and programs, evaluation, and direct intervention. Three program elements--staff wellness, healthy environment, and community/family involvement--are subsumed within the coordinator's role, effectively reducing the number of program elements from eight to five. Potential benefits in addition to issues regarding feasibility of the SHC, are discussed and studies examining the effectiveness of the SHC model are recommended. 相似文献
173.
174.
K Okano S Wu X Huang CJ Pirola H Juppner AB Abou-Samra GV Segre K Iwasaki JA Fagin TL Clemens 《Canadian Metallurgical Quarterly》1994,135(3):1093-1099
175.
176.
J.Z. Wu S.H. Yoo T. Aytug A. Gapud B.W. Kang S. Wu W. Zhou 《Journal of Superconductivity》1998,11(1):169-171
The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates. 相似文献
177.
The tail-flick (TF) technique was used to assess the antinociceptive properties of nifedipine (NIF) given intraperitoneally (i.p.). First, the most suitable intensity of the noxious stimulus (temperature of the bulb) has been ascertained and used in the main study. Male Sprague-Dawley rats received NIF, dissolved in dimethyl sulfoxide (DMSO) at the doses of 0.0, 0.5, 2, 5, 10 and 15 mg/kg, or control with no injection. For the main study, the noxious stimulus was limited to 15 sec (cut-off time) and TF latencies were recorded up to 120 min. The antinociceptive response was expressed as the area under the curve for each rat and analyzed by one-way ANOVA. The antinociceptive response to the lower doses of NIF (0.5 and 2 mg/kg) did not differ from control (no injection) and DMSO alone. Significance was found at 5, 10 and 15 mg NIF with no difference among the doses. However, there was an increasing tendency of the mean values from 0.5 to 15 mg NIF resulting in a positive correlation. The correlation coefficient was 0.32483 (p = 0.015) and regression equation Y = (19.37) x dose + 1320. Our data suggest that spinal mechanisms are involved in NIF-induced antinociception. 相似文献
178.
179.
吴连生 《理化检验(物理分册)》1998,34(1):15-19
简叙了电站装备失效分析程序、失效原因及其失效机理。大量的各种各样的失效,常常涉及一种或多种的失效机理。在众机理中,主要是:腐蚀失效、环境断裂失效、变形失效和断理解失效。 相似文献
180.
RH Rau YL Chan HI Chuang CR Cheng KL Wong KH Wu TT Wei 《Canadian Metallurgical Quarterly》1997,35(2):113-118
While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid. 相似文献