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   4369篇
  免费   7篇
电工技术   2篇
综合类   1篇
化学工业   68篇
金属工艺   12篇
机械仪表   6篇
建筑科学   30篇
矿业工程   3篇
能源动力   15篇
轻工业   41篇
水利工程   6篇
石油天然气   2篇
无线电   28篇
一般工业技术   95篇
冶金工业   4000篇
原子能技术   7篇
自动化技术   60篇
  2022年   5篇
  2021年   3篇
  2020年   5篇
  2019年   3篇
  2017年   4篇
  2016年   4篇
  2015年   12篇
  2014年   7篇
  2013年   12篇
  2012年   20篇
  2011年   22篇
  2010年   13篇
  2009年   11篇
  2008年   22篇
  2007年   22篇
  2006年   14篇
  2005年   15篇
  2004年   14篇
  2003年   26篇
  2002年   15篇
  2001年   30篇
  2000年   17篇
  1999年   119篇
  1998年   1201篇
  1997年   734篇
  1996年   473篇
  1995年   235篇
  1994年   237篇
  1993年   223篇
  1992年   22篇
  1991年   50篇
  1990年   44篇
  1989年   44篇
  1988年   36篇
  1987年   45篇
  1986年   52篇
  1985年   39篇
  1984年   5篇
  1983年   16篇
  1982年   19篇
  1981年   26篇
  1980年   52篇
  1979年   3篇
  1978年   9篇
  1977年   113篇
  1976年   259篇
  1975年   9篇
  1964年   2篇
  1955年   5篇
  1954年   2篇
排序方式: 共有4376条查询结果,搜索用时 15 毫秒
991.
Trichomonas vaginalis harbors a double-stranded (ds)-RNA virus, and the presence of virus is related to upregulated expression and phenotypic variation of a prominent immunogen (Khoshnan A, Alderete JF (1994) J Virol 68: 4035-4038). To further test the influence of virus on T. vaginalis, virus-infected (V+) isolates were compared to virus-free (V-), agar-cloned progeny trichomonads derived from the parental isolates for accumulation of total proteins and cysteine proteinases. Comparative high resolution two dimensional (2D)-SDS-PAGE was performed of trichomonads grown in a chemostat under identical conditions. At least 47 proteins were identified as specifically expressed by representative V+ isolate 347, and approximately 41 spots were specific to the corresponding V- progeny, showing an association between virus and the presence and absence of parasite proteins. Qualitatively and quantitatively dissimilar cysteine proteinase patterns were detected from numerous V+ isolates and the V- progeny. A 2D analysis for isolate 347 showed the appearance of unique proteinase activities for parental parasites and presence of at least one proteinase in the V- progeny. Finally, the V+ T. vaginalis isolate 347, but not the V- isolate 347 progeny nor other V+ isolates, underwent fluctuations in density during chemostat growth allowing for purification of virus particles from the V+ isolate 347 supernatants during decreased parasite density.  相似文献   
992.
This study compares the efficacy of two time-limited group psychotherapies for depression and functional disability in late life. Goal-focused group psychotherapy (GFGP) utilized focused psychoeducation and skills training to assist each patient in the achievement of individualized goals. Reminiscence therapy (RT) emphasized individual life review to facilitate discussion. Subjects (N = 13), ages 55 and above, with major depression were randomly assigned to one of the two groups. Most were receiving antidepressant treatment. All had failed to achieve full remission. Whereas both treatment groups improved in depressed mood and disability, GFGP subjects had a far greater change in depressive symptomatology and also improved in the areas of hope, hopelessness, anxiety and social functioning.  相似文献   
993.
Capillary zone electrophoresis (CZE) was utilized to identify a synaptobrevin-thioredoxin fusion protein (TSB-51). TSB-51 is a substrate for cleavage by botulinum toxin B at the Q(76)-F(77) site. TSB-51 was derivatized with a fluorophore, CBQCA [3-(4-carboxy-benzoyl)-2-quinoline-carboxaldehyde], for 4 h at room temperature. Optimal conditions for CZE separation of the TSB-51-CBQCA complex were determined: buffer (sodium borate), pH (9.0), applied voltage (25 kV), temperature (25 degrees C) and forward polarity. SDS-PAGE showed that TSB-51 had a molecular mass of approximately 19 kDa. The protein was transferred to PVDF membrane and sequenced by the Edman degradation method verifying the first twelve amino acids as SDKIIHLTDDSF. TSB-51 was also collected during CZE separation and subsequently sequenced yielding the first three amino acids as SDK. This CZE-LIF method coupled with the CBQCA derivatization, fraction collection and Edman sequencing allowed for identification of the recombinant protein, a fast separation run time and utilization of small volumes of peptide (1.5 ng protein/23.6 nl injection). This method will be used for monitoring the endopeptidase activity of botulinum toxin B on TSB-51.  相似文献   
994.
The visna-maedi lentivirus can induce an interstitial pneumonitis in sheep, and provides a convenient example to study natural or experimental lentiviral pathology. We wanted to determine whether high resolution computed tomography (HRCT) is able to detect early morphological changes following lentiviral infection in the lungs. Spontaneously infected adult sheep (n=3) and experimentally infected lambs (n=5) were compared to uninfected controls (n=4). The HRCT scans generally showed abnormal features in infected animals, including: increased parenchymal density; alveolar oedema; thickened interlobular septa; and increased density in peribronchiolar areas. HRCT was more sensitive than chest radiography for the early diagnosis of interstitial pneumonitis, although one sheep with advanced disease and radiographic and histopathological abnormalities had a paradoxically normal scan. One control animal showed minor abnormalities on scanning, which were probably due to the procedure used for anaesthesia. The HRCT observations were confirmed by postmortem histological examination of the lungs. In conclusion, high resolution computed tomography provides a noninvasive means of following the development of lung pathology in a natural ovine model of lentiviral disease.  相似文献   
995.
Lipoblastoma is a rare benign pediatric soft tissue tumor that may be difficult to distinguish from a myxoid liposarcoma clinically or histologically. The authors present a case of a progressively growing, locally invasive soft tissue tumor in a child. Tissue culture for cytogenetic study showed a breakpoint in the long arm of chromosome 8. A review of the literature showed seven case reports of lipoblastoma karyotype, six of which had a similar breakpoint in chromosome 8. This distinguishes it from the histologically alike myxoid liposarcoma, the karyotype of which typically contains the clonal anomaly t(12;16)(q13:p11). The authors recommend that when performing a biopsy of a childhood adipose tumor with unusual features, such as progressive or invasive growth, that fresh tissue be submitted for cell culture. The tumor karyotype will, in most cases, aid in differentiating lipoblastoma from myxoid liposarcoma.  相似文献   
996.
997.
OBJECTIVE: Familial occurrence of Bartter's syndrome is well known, but the simultaneous occurrence of hypokalemia/hypomagnesemia and chondrocalcinosis in one family has not been described. We present the clinical, laboratory and radiological findings of a family, in which 7 members were affected by disease. METHODS: A total of 43 members of the family could be interviewed concerning their general health, past diseases and joint complaints. Serum potassium and magnesium were determined in all and radiographic studies were performed in those who had hypokalemia and hypomagnesemia or those with merely articular complaints. Urinary excretion of potassium, magnesium and calcium were determined in the affected persons. RESULTS: Seven patients were found with hypokalemia and hypomagnesemia. Urinary potassium and magnesium excretion was inappropriately high when compared to the serum levels of these electrolytes. All patients had hypocalciuria and extensive chondrocalcinosis, mainly in the knees, elbows and shoulders. In one patient, most probably as a result of magnesium supplementation, a striking reduction of chondrocalcinosis was observed during a followup of 10 years. CONCLUSION: A family with familial hypokalemia/hypomagnesemia and chondrocalcinosis is described. The reduction of chondrocalcinosis, after years of magnesium supplementation in one patient, suggests that hypomagnesemia is an important factor in the pathogenesis of chondrocalcinosis in these patients.  相似文献   
998.
Indirect fluorescent-antibody (IFA) staining methods with Ehrlichia equi (MRK or BDS strains) and Western blot analyses containing a human granulocytic ehrlichiosis (HGE) agent (NCH-1 strain) were used to confirm probable human cases of infection in Connecticut during 1995 and 1996. Also included were other tests for Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis (HME), Babesia microti, and Borrelia burgdorferi. Thirty-three (8.8%) of 375 patients who had fever accompanied by marked leukopenia or thrombocytopenia were serologically confirmed as having HGE. Western blot analyses of a subset of positive sera confirmed the results of the IFA staining methods for 15 (78.9%) of 19 seropositive specimens obtained from different persons. There was frequent detection of antibodies to a 44-kDa protein of the HGE agent. Serologic testing also revealed possible cases of Lyme borreliosis (n = 142), babesiosis (n = 41), and HME (n = 21). Forty-seven (26.1%) of 180 patients had antibodies to two or more tick-borne agents. Therefore, when one of these diseases is clinically suspected or diagnosed, clinicians should consider the possibility of other current or past tick-borne infections.  相似文献   
999.
Correlation analysis of the findings suggests that in March an increase of the glucose level is induced by the thyroid hormones in humans living on Spitsbergen Archipelago. A liability of functional interactions among thyroid hormones, insulin, and glucose seems to be caused bias alterations in the air temperature as contrast to photoperiodicity.  相似文献   
1000.
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