首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   728546篇
  免费   13669篇
  国内免费   5281篇
电工技术   15102篇
技术理论   3篇
综合类   6763篇
化学工业   105507篇
金属工艺   31456篇
机械仪表   24127篇
建筑科学   20717篇
矿业工程   4730篇
能源动力   19279篇
轻工业   57851篇
水利工程   7910篇
石油天然气   14067篇
武器工业   576篇
无线电   85214篇
一般工业技术   137922篇
冶金工业   124307篇
原子能技术   12190篇
自动化技术   79775篇
  2022年   5235篇
  2021年   7803篇
  2020年   5781篇
  2019年   6556篇
  2018年   23454篇
  2017年   22460篇
  2016年   19573篇
  2015年   9029篇
  2014年   13364篇
  2013年   30876篇
  2012年   22689篇
  2011年   35328篇
  2010年   28852篇
  2009年   28544篇
  2008年   30049篇
  2007年   30571篇
  2006年   21192篇
  2005年   20114篇
  2004年   18580篇
  2003年   18102篇
  2002年   16563篇
  2001年   16256篇
  2000年   15187篇
  1999年   16227篇
  1998年   39808篇
  1997年   27836篇
  1996年   21541篇
  1995年   15952篇
  1994年   13813篇
  1993年   13248篇
  1992年   9480篇
  1991年   8865篇
  1990年   8575篇
  1989年   8135篇
  1988年   7448篇
  1987年   6451篇
  1986年   6375篇
  1985年   6998篇
  1984年   6530篇
  1983年   5694篇
  1982年   5446篇
  1981年   5471篇
  1980年   5120篇
  1979年   4977篇
  1978年   4720篇
  1977年   5747篇
  1976年   7704篇
  1975年   4043篇
  1974年   3776篇
  1973年   3864篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
A high-performance liquid chromatographic (HPLC) assay has been developed for thimerosal and some of its degradation products: thiosalicylic and 2,2'-dithiosalicylic acids. Using this method, the influence of formulation factors as: isotonic agent, initial concentration, addition of tromethamine, pH and container material, over thimerosal stability was studied.  相似文献   
962.
Isolation of Salmonella from the feces of impounded dogs was carried out to make clear the recent microbiological condition of dogs introduced into our facilities. Salmonella was isolated from 10 out of 283 samples (3.5%). Inparticular, during the first week after introduction, Salmonella was isolated from nine out of 74 dogs (12.2%). The isolation rate during the first week after introduction was significantly higher than that for dogs introduced later. No isolates were detected from dogs reared for more than 3 weeks after introduction. This study indicates that impounded dogs had the highest risk of infecting a person with Salmonella during the first week after introduction into our laboratory animal facilities, and that we need to pay attention to this fact when handling them.  相似文献   
963.
964.
Two mobilizable cloning vectors, designated pABW1 and pAWB2, were constructed basing on the E. coli vector pBGS18 and oriT originating from RK2. In pABW2 the kanamycin resistance gene was replaced by a novel tetracycline resistance cassette derived from Tn1721. Both vectors, specific for E. coli, allow to perform the cloning steps in E. coli and then to efficiently transfer the constructs by conjugation to the host of choice. A vector which cannot propagate in the given host can be applied for identification of the host specific plasmid replicator regions. With the use of pABW2 we defined the minimal replicator region of pTAV202-a mini-derivative of the large pTAV1 plasmid of P. versutus. We also proved that RepC' encoded on this fragment is the principal initiator replication protein and that oriV is located along its coding sequence.  相似文献   
965.
966.
An off-line handwritten word recognition system is described. Images of handwritten words are matched to lexicons of candidate strings. A word image is segmented into primitives. The best match between sequences of unions of primitives and a lexicon string is found using dynamic programming. Neural networks assign match scores between characters and segments. Two particularly unique features are that neural networks assign confidence that pairs of segments are compatible with character confidence assignments and that this confidence is integrated into the dynamic programming. Experimental results are provided on data from the U.S. Postal Service.  相似文献   
967.
Few investigations have been made concerning hormonal changes and dyspareunia in fertile aged women with alcoholics experiencing sexual dysfunction. Twenty-seven Japanese woman with alcoholics under 40 years of age excluded with liver cirrhosis were studied to describe alcohol drinking related to sexual dysfunction. Among 21 sexually active women, 20(95.2%) had both symptoms of dyspareunia and vaginal dryness, and only one had neither symptom. Most of patients have lower estradiol levels and 92.0% of patients have the moderately elevated prolactin levels. Eleven of them were having the second grade amenorrhea associated with hyperprolactinemia and hypergonadotropic hypogonadism and 14 were having the first grade amenorrhea. In this study alcoholic abuse women may have deeply related to the hyperprolactinemia, dyspareunia, amenorrhoea, vaginal dryness, ovarian dysfunction and fetal alcohol syndrome.  相似文献   
968.
Twenty-two children with chronic hepatitis serologically positive for hepatitis C virus (HCV) were treated with interferon-alpha (IFN-alpha). Liver biopsy showed chronic active hepatitis in 13 and chronic persistent hepatitis in 9 patients. A sustained clearance of HCV was observed in 8/22 children 12 months after the administration of IFN-alpha for 26 weeks, associated with normalization of HCV core antibody. Of these eight patients six had HCV genotype III and two HCV genotype II or IV. Hepatitis relapsed in seven other patients after completion of IFN-alpha with an increase in HCV core antibody titre, five with HCV genotype II, and two with HCV genotype III or IV. A second course of IFN-alpha suppressed the reactivation of HCV in all seven patients. Three of seven responders who relapsed after the first course remained negative for HCV RNA 12 months after their second course of IFN-alpha. However, the remaining four patients with HCV genotype II again relapsed after completing their second course of IFN-alpha. Seven children with the HCV genotype II resistant to IFN, including 8 weeks of IFN-beta administration, and showed no significant reduction in HCV core antibody titre. CONCLUSION: The genotype of HCV (III) and a reduction in the core antibody titre appear to be useful parameters for predicting the response to IFN-alpha therapy.  相似文献   
969.
Indocyanine green (ICG; absorption peak in human plasma 805 nm) was investigated for ICG-mediated phototherapy in vitro. The cellular uptake of ICG (1 microM-50 microM) into HaCaT keratinocytes after an incubation period of 24 h increased up to an intracellular ICG concentration of 12.1 +/- 1.3 nmol per 10(6) cells. To examine dose dependent phototoxic effects in vitro, keratinocytes were incubated with 0 microM-50 microM ICG for 24 h and irradiated by a diode laser (805 nm) with different energy densities (0, 12, 24, 48 J cm-2). All applied ICG concentrations except for 5 microM yielded a cell killing effect in combination with irradiation depending significantly on ICG concentration and light dose. Cell viability for dark control and cells incubated with 50 microM ICG and irradiated with 48 J cm-2 was 0.82 +/- 0.15 and 0.07 +/- 0.02, respectively. Sodium azide (100 mM), a quencher of reactive oxygen species, inhibited significantly the cell killing using 50 microM ICG and 24 J cm-2. Taken together, photoactivation of ICG by irradiation with a diode laser was shown to induce effectively cell killing of HaCaT keratinocytes. Moreover, this effect was inhibited by sodium azide, thus irradiation of ICG might induce a photodynamic reaction.  相似文献   
970.
To further investigate the process of amyloid beta-protein (Abeta) deposition, we determined, using sensitive enzyme immunoassays, the levels of Abeta40 and Abeta42 (Abetas) in the soluble and insoluble fractions of the leptomeninges (containing arachnoid mater and leptomeningeal vessels) and cerebral cortices from elderly control subjects showing various stages of Abeta deposition and from patients affected by Alzheimer's disease (AD). In both locations, insoluble Abeta levels were higher by orders of magnitude than soluble Abeta levels. Soluble Abeta levels in cortices were much lower than those in leptomeninges. In insoluble Abeta in the cortex, Abeta42 was by far the predominant species, and Abeta42 in AD cortices was characterized by the highest degree of modifications in the amino terminus. In contrast, this Abeta42 predominance was not observed in insoluble Abeta in the leptomeninges, which were found to be able to accumulate Abetas to an extent similar to that in the cortex, on a weight basis. The levels of insoluble Abeta in the leptomeninges or cortex generally correlated with the degree of cerebral amyloid angiopathy or the abundance of senile plaque, respectively. However, the presence of plaque-free cortical samples showing significant levels of insoluble Abeta42 suggests that biochemically detectable Abeta accumulation precedes immunocytochemically detectable Abeta deposition in the cortex.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号