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   425篇
  免费   3篇
综合类   2篇
化学工业   13篇
金属工艺   5篇
机械仪表   5篇
建筑科学   3篇
能源动力   2篇
轻工业   13篇
石油天然气   3篇
无线电   7篇
一般工业技术   13篇
冶金工业   348篇
原子能技术   7篇
自动化技术   7篇
  2022年   2篇
  2021年   2篇
  2020年   1篇
  2018年   2篇
  2017年   1篇
  2016年   2篇
  2014年   3篇
  2013年   4篇
  2012年   2篇
  2011年   12篇
  2010年   1篇
  2009年   2篇
  2008年   5篇
  2007年   3篇
  2006年   4篇
  2005年   2篇
  2004年   4篇
  2003年   2篇
  2002年   3篇
  2000年   2篇
  1999年   9篇
  1998年   106篇
  1997年   57篇
  1996年   42篇
  1995年   34篇
  1994年   19篇
  1993年   14篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   3篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1982年   4篇
  1981年   1篇
  1980年   3篇
  1979年   3篇
  1978年   2篇
  1977年   17篇
  1976年   30篇
  1975年   1篇
  1973年   2篇
  1967年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有428条查询结果,搜索用时 15 毫秒
111.
The protochordate allorecognition system has long invited comparison with the vertebrate major histocompatibility complex (MHC). In the colonial species Botryllus schlosseri, a rapid fusion or rejection response resembling graft acceptance or rejection in vertebrates is controlled by a single highly polymorphic genetic region. Because linkage between heat shock protein 70 (HSP70) genes and the MHC appears to be conserved within the vertebrate lineage, linkage relationships between two HSP70 genes (HSP70.1 and HSP70.2) and the historecognition locus (FuHC) have been analyzed in B. schlosseri. Segregation patterns of restriction fragment length polymorphisms located in the 3' flanking regions of HSP70.1 and HSP70.2 were determined for progeny of defined crosses. These progeny were also analyzed for fusibility type by an in vivo cut colony assay. No close linkage was detected between any of the three loci. These results do not support the hypothesis that the allorecognition response in B. schlosseri is determined by an MHC homologue. However, it remains a possibility that orthologues of other MHC-linked genes will be linked to the B. schlosseri FuHC.  相似文献   
112.
HIV-1 RNA dimerization involves at least two key regions, one located upstream from the splice donor (SD) site, and the other located downstream from the SD site. To determine the precise location and the mechanism of action of the downstream region, we constructed a model system using a synthetic HIV-1 RNA fragment (HXB2, 455-1146), which dimerized at relatively low salt concentrations (100 mM KCl, 1 mM MgCl2). We tested in this system antisense DNAs that are complementary to both the upstream and downstream regions of HIV-1 RNA for their possible inhibitory effects on dimerization. Antisense DNAs complementary to nucleotides 773-789 located downstream from the SD site effectively inhibited dimerization of HIV-1 RNA. These inhibitory antisense DNAs hybridized with the dimer form of HIV-1 RNA, and dissociated the dimer into monomers. However, antisense DNAs complementary to the region upstream from the SD site did not hybridize with the dimer, although they inhibited RNA dimerization and also dissociated the preformed dimer.  相似文献   
113.
STUDY DESIGN: A population-based evaluation including cross-sectional comparisons of eight simple function tests (mobility and strength) and answers on questions concerning lifestyle factors, work environment, and health. The study population was randomly selected among people 35-45 years old. OBJECTIVES: To construct a simple, self-administered surveillance system to test musculoskeletal function to be mailed to a sample population along with a questionnaire. SUMMARY OF BACKGROUND DATA: A surveillance system should be easy to use, detect treatable symptoms at an early stage, and detect change of function or symptoms. METHOD: Questionnaires, which also contained instructions in performing the eight tests of musculoskeletal function, were sent to a randomly selected sample population. The questionnaire covered type and level of musculoskeletal problems, and lifestyle and occupational factors. RESULTS: The questionnaire and the self-administered test were completed by 834 people. The test movements could be performed and the questions answered by the study population. The tests discriminated between those with and without moderate or severe problems. Performance of physically heavy work did not significantly correlate with the test results. The results of the physical function test discriminated significantly between those with different levels of fear of movement (odds ratio, 2.2) and the degree of current somatic distress (odds ratio, 5.9). CONCLUSION: The test of physical function could be performed and the questionnaire completed by this randomly selected cohort, and the results discriminated significantly between groups.  相似文献   
114.
OBJECTIVE: To create a neovagina using a combined laparoscopic and ultrasonographic technique in Mayer-Rokitansky-Kuster-Hauser syndrome by modification of Vecchietti's operation. DESIGN: Case report. SETTING: Division of Physiopathology of Reproduction, University of Palermo, Palermo, Italy. MAIN OUTCOME MEASURE(S): The advancement of the needle from the pseudohymen, through the vesicorectal space using a triple contrast ultrasonographic technique. RESULT(S): The ultrasonographic scanning guides the accurate transit from external genitalia to the peritoneal cavity. CONCLUSION(S): This original approach allowed a safe and rapid creation of a neovagina in a case of Mayer-Rokitansky-Kuster-Hauser syndrome.  相似文献   
115.
OBJECTIVE: Alterations in cortical benzodiazepine receptor density have been described in postmortem and in vivo studies of alcoholic subjects. The authors attempted to replicate these findings using single photon emission computed tomography and the benzodiazepine receptor radiotracer [123I]iomazenil. METHOD: They measured the distribution volume of benzodiazepine receptors in 11 recently detoxified patients with type II alcoholism and 11 healthy comparison subjects. The tracer was given as a bolus followed by a continuous infusion to achieve sustained binding equilibrium at the benzodiazepine receptors. Data were analyzed by using a region of interest method (regions of interest were identified on coregistered magnetic resonance imaging scans) and by a pixel-by-pixel method (distribution volume maps were analyzed with statistical parametric mapping for between-group differences). RESULTS: The region of interest analysis revealed that alcoholic patients had significantly lower benzodiazepine distribution volume than comparison subjects in the frontal, anterior cingulate, and cerebellar cortices. Statistical parametric mapping revealed two large excursions in which the distribution volume in alcoholic patients was significantly lower than in comparison subjects: the anterior cingulate, extending into the right middle frontal gyrus, and the left occipital cortex. CONCLUSIONS: Benzodiazepine receptor distribution volume is significantly lower in several cortical regions and the cerebellum in alcoholic subjects than in healthy comparison subjects. These results are consistent with previous reports and might indicate either a toxic effect of alcoholism on benzodiazepine receptors or a vulnerability factor for developing alcoholism.  相似文献   
116.
We isolated hematopoietic stem cells (HSC) from mice treated with cyclophosphamide (CY) and granulocyte colony-stimulating factor (G-CSF). All mobilized multipotent progenitor activity was contained in two populations: Thy-1(lo) Sca-1+ Lin- Mac-1- CD4- c-kit+ long-term reconstituting progenitors and Thy-1(lo) Sca-1+ Lin- Mac-1(lo) CD4- transiently reconstituting progenitors. CY/G-CSF treatment drove both long-term and transient multipotent progenitors into cycle, leading to a more than 12-fold expansion in the number of long-term self-renewing HSC prior to mobilization. After CY and 2 days of G-CSF treatment the number of bone marrow HSC began to decline and the number of blood and splenic HSC increased. HSC continued to proliferate in the bone marrow and spleen through 8 days of G-CSF treatment, but HSC released into the blood tended to be in G0/G1 phase. Mobilized multipotent progenitors isolated from the spleen were less efficient than normal bone marrow multipotent progenitors in engrafting irradiated mice but did not differ in colony forming unit-spleen (CFU-S) activity or single cell in vitro assays of primitive progenitor activity. The data suggest that mobilized HSC isolated from the spleen are less efficient at homing to and engrafting the bone marrow of irradiated recipient mice.  相似文献   
117.
This study compared the conceptual foci and methodological characteristics of research projects which tested the effects of nursing interventions, published in four general nursing research journals with predominantly North American, and two with predominantly European/International authorship and readership. Dimensions and variables of comparison included: nature of subjects, design issues, statistical methodology, statistical power, and types of interventions and outcomes. Although some differences emerged, the most striking and consistent finding was that there were no statistically significant differences (and thus similarities) in the content foci and methodological parameters of the intervention studies published in both groups of journals. We conclude that European/International and North American nursing intervention studies, as reported in major general nursing research journals, are highly similar in the parameters studied, yet in need of overall improvement. Certainly, there is no empirical support for the common (explicit or implicit) ethnocentric American bias that leadership in nursing intervention research resides with and in the United States of America.  相似文献   
118.
This work deals with the problem of relationship between the molecular parameters of group A meningococcal polysaccharide and its immunological effectiveness for laboratory animals and humans. The depolymerization of group A polysaccharide contained in the vaccine leads to a decrease in its capacity of inducing the production of hemagglutinating (19S and 7S) and bactericidal IgA antibodies in humans, as well as inducing an increase in the number of cells producing IgA antibodies in the spleen of immunized mice and the appearance of circulating IgA antibodies in their sera. As shown in this investigation, fully developed immune response to group A meningococcal vaccine may be achieved in humans only if the content of group A high-molecular polysaccharide in the vaccine is not less than 70%. Mice have been recommended as an experimental model for the prognostication of the effectiveness of meningococcal polysaccharide vaccines and for their control in the process of manufacture instead of currently used titration of bacteriolysins in the sera of immunized humans.  相似文献   
119.
The so-called TCR-delta-deleting elements, deltaRec and psiJ alpha, flank the major part of the TCR-delta gene complex. By rearranging to each other, the deltaRec and psiJ alpha gene segments delete the TCR-delta gene complex and prepare the allele for subsequent TCR-alpha rearrangement. This intermediate rearrangement is thought to be a specific rearrangement event. In our studies on TCR-delta deletion mechanisms, we identified several T cell acute lymphoblastic leukemias (T-ALL) with continuous activity of the deltaRec-psiJ alpha rearrangement process. Extensive Southern blot, PCR, and sequencing analyses on the coding joints as well as the signal joints of the deltaRec-psiJ alpha rearrangements in these patients allowed us to prove that this continuous rearrangement activity occurred in the leukemic cells and that these cells, therefore, represent a polyclonal subpopulation within the otherwise monoclonal T-ALL. In additional studies, we also identified a T cell line (DND41) with continuous activity of the deltaRec-psiJ alpha rearrangement process. Our data suggest that the ongoing deltaRec-psiJ alpha gene rearrangements predominantly occur in T cells that cannot express a functional TCR-gammadelta, due to biallelic out-of-frame TCR-delta and/or TCR-gamma gene rearrangements. The described T-ALL and the T cell line can serve as an experimental model in further studies on the regulatory elements involved in the specific deletion of the TCR-delta gene complex.  相似文献   
120.
BACKGROUND: To determine the efficacy, safety and tolerability of antidepressants in depressed elderly patients. METHODS: Search for randomized controlled double-blind studies evaluating atypical antidepressants (ATYPs), reversible inhibitors of monoamine oxidase-A, selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants in moderate/severe depressed patients > or = 60 years for > or = four weeks. The random effects model (single-arm; comparative) was used to aggregate efficacy, safety and dropout. RESULTS: No difference in single-arm aggregation of outcomes for four antidepressant classes. Comparative analyses showed no statistical difference between outcomes, except SSRIs had a higher response rate than ATYPs. CONCLUSION: Elderly show no differences in antidepressant class outcomes. LIMITATIONS: Heterogeneity and lack of power. CLINICAL RELEVANCE: There is little advantage for antidepressant classes over another in the aged.  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