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   12418篇
  免费   579篇
  国内免费   12篇
电工技术   109篇
综合类   14篇
化学工业   2828篇
金属工艺   278篇
机械仪表   320篇
建筑科学   449篇
矿业工程   27篇
能源动力   606篇
轻工业   1407篇
水利工程   72篇
石油天然气   50篇
武器工业   1篇
无线电   599篇
一般工业技术   1977篇
冶金工业   2263篇
原子能技术   151篇
自动化技术   1858篇
  2024年   35篇
  2023年   99篇
  2022年   247篇
  2021年   354篇
  2020年   254篇
  2019年   221篇
  2018年   416篇
  2017年   434篇
  2016年   478篇
  2015年   327篇
  2014年   546篇
  2013年   1067篇
  2012年   598篇
  2011年   707篇
  2010年   591篇
  2009年   603篇
  2008年   480篇
  2007年   465篇
  2006年   398篇
  2005年   292篇
  2004年   260篇
  2003年   238篇
  2002年   209篇
  2001年   162篇
  2000年   165篇
  1999年   139篇
  1998年   691篇
  1997年   414篇
  1996年   295篇
  1995年   194篇
  1994年   169篇
  1993年   178篇
  1992年   79篇
  1991年   69篇
  1990年   70篇
  1989年   58篇
  1988年   62篇
  1987年   38篇
  1986年   38篇
  1985年   79篇
  1984年   65篇
  1983年   38篇
  1982年   44篇
  1981年   72篇
  1980年   47篇
  1979年   48篇
  1978年   31篇
  1977年   83篇
  1976年   134篇
  1975年   34篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
Diphtheria antitoxin was determined in serum from 44 pregnant women, of whom 26 had received one injection of diphtheria toxoid during pregnancy. Their infants were vaccinated with a combined diphtheria-tetanus vaccine at 3, 5 and 12 months of age. This vaccination schedule has been used in Sweden since 1986, replacing the old schedule of vaccination at 3, 4.5 and 6 months of age originally designed for diphtheria-tetanus-pertussis vaccine, which had not been used after cessation of general vaccination against pertussis in 1979. Serum samples from the infants were obtained at 3, 7 and 18 months of age. After 2 injections infants of mothers with high antitoxin titers, > or = 0.1 IU/ml, tended to have lower antitoxin titers than infants of mothers with low antitoxin concentrations (P = 0.067). All children had, however, antitoxin above the minimum protective level of 0.01 IU/ml. Median antitoxin titers were 1.6 IU/ml in both groups after the third booster injection. Four infants of mothers who had been vaccinated during pregnancy and who had titers of > or = 0.4 IU/ml did not reach the 0.1 IU/ml level after 2 injections: all 4 responded with high antitoxin titers after the third dose. Thus all infants were primed by 2 doses of vaccine, irrespective of maternal antibody concentration. The repressive effect of maternal antibody on titers noted after 2 doses was no longer observed after the third, booster dose.  相似文献   
104.
The purpose of this study was to examine the relationship of job satisfaction to job difficulty and worthiness, reported by the clinical psychologists who worked at medical institutions. A mail survey of 748 clinical psychologists working at hospital and clinics revealed the following results. First, job satisfaction was related more to job situation than job content. Also, job satisfaction was low among those who worked at non-university psychiatric or geriatric hospitals, who did not practice psychotherapy, and who were not in education, research, or management. In addition, compared to the high job satisfaction group, the low group perceived more incongruity between institutional climate and their psychological work, felt being less valued by other professionals, were less able to function fully as a practicing psychologist, and experienced more role ambiguity as a clinical psychologist in a hospital setting.  相似文献   
105.
A chromosomally encoded 66-kDa protein (P66) of Borrelia spp. that cause Lyme disease has previously been shown to be associated with the spirochetal outer membrane. A topological model of P66 predicts a surface-exposed fragment which links the N- and C-terminal intramembranous domains of the protein (J. Bunikis, L. Noppa, and S. Bergstr?m, FEMS Microbiol. Lett. 131:139-145, 1995). In the present study, an immunogenic determinant of P66 was identified by a comparison of the immunoreactivities of different fragments of P66 generated either by proteolytic treatment of intact spirochetes or as recombinant proteins expressed in Escherichia coli. The immune response to P66 during natural infection was found to be directed against the predicted surface domain which comprises amino acids at positions 454 through 491. A sequence comparison revealed considerable polymorphism of the surface domains of P66 proteins of different Lyme disease-causing Borrelia species. Five sequence patterns of this domain were observed in the B. garinii strains studied. In contrast, sequences of the relevant part of P66 of the B. afzelii and B. burgdorferi sensu stricto isolates studied were identical within the respective species. In immunoblotting, 5 of 17 (29.4%) sera from North American patients with early disseminated or persistent Lyme disease reacted against P66 of B. burgdorferi sensu stricto B31. These sera, however, failed to recognize P66 of B. afzelii and B. garinii, as well as an analog of P66 in the relapsing fever agent, B. hermsii. In conclusion, the topological model of P66 is supported by the demonstration of an apparent surface localization of an immunoreactive domain of this protein. Furthermore, analogous to the plasmid-encoded borrelial outer surface proteins, the predicted surface-exposed portion of chromosomally encoded P66 appears to be antigenically heterogenous.  相似文献   
106.
107.
Catalytic chlorination of methane was studied over SO 4 2– /ZrO2, Pt/SO 4 2– /ZrO2, and Fe/Mn/SO 4 2– /ZrO2 solid superacid catalysts. The reactions were carried out in a continuous flow reactor under atmospheric pressure, at temperatures below 240°C, with a gaseous hourly space velocity of 1000 ml/g h and a methane to chlorine ratio of 4 to 1. At 200°C with 30% chlorine converted the selectivity in methyl chloride exceeds 90%. At more elevated temperatures, the selectivity decreases but stays above 80% in methyl chloride at 225°C using the sulfated zirconia catalysts. The selectivity can be enhanced by adding platinum to sulfated zirconia catalysts. An iron and manganese-doped catalyst exhibited excellent selectivities at somewhat lower conversions. Methyl chloride is obtained at 235°C in selectivities greater than 85%. No chloroform or carbon tetrachloride is formed. The electrophilic insertion involves electron-deficient metal-coordinated chlorine into the methane C-H bond.Catalysis by solid superacids, 29. For part 28 see ref. [14].  相似文献   
108.
109.
Summary Surface morphology and molecular arrangement have been recorded by atomic force microscopy (AFM) on polytetrafluoroethylene (PTFE) and on polycarbonate (PC) films. In a thin layer of PTFE deposited by rubbing polymer on hot glass substrate unidirectional orientation of polymer has been revealed. Individual polymer chains have been visualized. An interchain distance of .53 nm and several periodicities along the chain contours have been found-.44 nm, .62 nm and .82 nm-in accordance with a 13/6 helix.The monitoring of surface changes during thermal treatment of amorphous-bis-phenol A-PC film has been realized by AFM. Different types of surface morphology were revealed. Spherulites are formed during polymer crystallization. In most cases, however, numerous nanocrystallites appeared after thermal treatment. On their surfaces well-ordered atomic scale AFM images have been received. The arrangement of AFM patterns can be characterized by periodicities of .50 nm and .52 nm in the orthogonal directions. Polycarbonate oligomers-as the product of surface degradation-effectively might form the observed nanocrystallites.Prof. Dr. G. Zachmann zum 60. Geburtstag herzlichst gewidmetThese results were given by us first in a lecture in Baltimore, at the 5th ISPAC Symposium on May 31, 1991, and in a lecture in Santa Barbara, at the Nanoscope Users Meeting on June 25, 1991  相似文献   
110.
One hundred and eighty-one consecutive patients with standard-risk leukaemia were transplanted with HLA-identical sibling grafts depleted of lymphocytes using counter-flow centrifugation. In 116 patients, standard conditioning was intensified by the addition of anthracyclines. Multivariate analysis revealed significantly more acute GVHD > or = grade 2 and a trend towards more chronic GVHD in patients conditioned with the addition of anthracyclines. For all patients the risk for chronic GVHD, but not for acute GVHD increased with a higher number of T cells in the graft. The projected 5-year probability of relapse was significantly lower in the group of patients conditioned with anthracyclines; 26% versus 52% (P = 0.015). In multivariate analysis the addition of anthracyclines to the conditioning regimen was the only significant factor contributing to a lower probability of relapse. The projected 5-year probability of leukaemia-free survival [LFS] in the patients conditioned with and without the addition of anthracyclines was 56% and 36%, respectively (P = 0.004). In multivariate analysis the addition of anthracyclines to the conditioning regimen correlated significantly with a lower number of mixed chimaeras in patients at 6 and 12 months after BMT. Mixed chimaerism at 6 months after transplantation did not significantly correlate with a higher incidence of relapse in further follow-up. In contrast, mixed chimaerism at 12 months after BMT was significantly associated with higher relapse rate. We conclude that the addition of anthracyclines to the conditioning regimen improves outcome of BMT using T-cell-depleted grafts.  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