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   1571篇
  免费   3篇
  国内免费   1篇
电工技术   2篇
化学工业   24篇
金属工艺   1篇
建筑科学   3篇
矿业工程   1篇
能源动力   4篇
轻工业   13篇
无线电   21篇
一般工业技术   14篇
冶金工业   1471篇
原子能技术   2篇
自动化技术   19篇
  2023年   1篇
  2018年   2篇
  2017年   3篇
  2013年   5篇
  2012年   3篇
  2011年   2篇
  2009年   2篇
  2008年   4篇
  2007年   1篇
  2006年   8篇
  2005年   3篇
  2004年   4篇
  2003年   7篇
  2002年   3篇
  2001年   5篇
  2000年   5篇
  1999年   49篇
  1998年   478篇
  1997年   272篇
  1996年   174篇
  1995年   96篇
  1994年   79篇
  1993年   91篇
  1992年   11篇
  1991年   19篇
  1990年   16篇
  1989年   22篇
  1988年   12篇
  1987年   12篇
  1986年   14篇
  1985年   13篇
  1984年   2篇
  1983年   7篇
  1982年   7篇
  1981年   10篇
  1980年   9篇
  1979年   1篇
  1978年   4篇
  1977年   26篇
  1976年   82篇
  1975年   5篇
  1971年   1篇
  1969年   1篇
  1967年   1篇
  1965年   1篇
  1955年   1篇
  1940年   1篇
排序方式: 共有1575条查询结果,搜索用时 15 毫秒
991.
The presence and role of the c-kit protein were examined in mature sperm of the mouse. Monoclonal antibodies (mAbs) against the c-kit protein were used to perform immunohistochemical staining, electron microscopy studies, and Western blot analysis. The acrosomal region of both fixed and unfixed noncapacitated sperm stained with the antibodies. No acrosomal staining was noted in acrosome-reacted (AR) sperm. Electron microscopy studies demonstrated immunogold label on the plasma membrane of the acrosome and confirmed the lack of binding following the acrosome reaction. Proteins corresponding to 33 kDa, 48 kDa, and 150 kDa were detected by the antibodies utilizing Western blot analysis. The 48-kDa and 150-kDa proteins were released into the media during sperm capacitation, and release from the acrosome was dependent upon the acrosome reaction. The mAbs significantly inhibited the acrosome reaction and increased sperm agglutination. Monoclonal antibody ACK1 significantly inhibited the motility of the sperm, whereas mAbs ACK2 and NCL-ckit did not. These results suggest that c-kit-related proteins are present in mature sperm and may play a role in capacitation and/or the acrosome reaction.  相似文献   
992.
993.
994.
Cell and tissue concentrations of NO2- and NO3- are important indicators of nitric oxide synthase activity and crucial in the regulation of many metabolic functions, as well as in nonenzymatic nitric oxide release. We adapted the capillary electrophoresis technique to quantify NO2- and NO3- levels in single identified buccal neurons and ganglia in the opisthobranch mollusc Pleurobranchaea californica, a model system for the study of the chemistry of neuron function. Neurons were injected into a 75-microm separation capillary and the NO2- and NO3- were separated electrophoretically from other anions and detected by direct ultraviolet absorbance. The limits of detection for NO2- and NO3- were <200 fmol (<4 microM in the neurons under study). The NO2- and NO3- levels in individual neurons varied from 2 mM (NO2-) and 12 mM (NO3-) in neurons histochemically positive for NADPH-diaphorase activity down to undetectable levels in many NADPH-diaphorase-negative cells. These results affirm the correspondence of histochemical NADPH-diaphorase activity and nitric oxide synthase in molluscan neurons. NO2- was not detected in whole ganglion homogenates or in hemolymph, whereas hemolymph NO3- averaged 1.8 +/- 0.2 x 10(-3) M. Hemolymph NO3- in Pleurobranchaea was appreciably higher than values measured for the freshwater pulmonate Lymnaea stagnalis (3.2 +/- 0.2 x 10(-5) M) and for another opisthobranch, Aplysia californica (3.6 +/- 0.7 x 10(-4) M). Capillary electrophoresis methods provide utility and convenience for monitoring NO2-/NO3- levels in single cells and small amounts of tissue.  相似文献   
995.
Vascular endothelium is an important target for gene transfer in atherosclerosis. In this study, we examined gene transfer to normal and atherosclerotic blood vessels from two species, using an organ culture method. Using normal aorta, we determined optimal dose, duration of exposure to adenovirus, and duration of incubation of vessels in tissue culture. Aortas from normal and atherosclerotic monkeys were cut into rings and incubated for 2 hours with a recombinant adenovirus, carrying the reporter gene for beta-galactosidase driven by a cytomegalovirus (CMV) promoter. After 20 hours of incubation, transgene expression was assessed with a morphometric method after histochemical staining and a chemiluminescent assay of enzyme activity. Expression of beta-galactosidase after histochemical staining, expressed as percentage of total cells, was similar in adventitial cells of normal monkeys (21 +/- 4%, mean +/- SE%) and atherosclerotic monkeys (25 +/- 12%). Transgene expression in endothelium was higher in atherosclerotic than in normal vessel (53 +/- 3% versus 27 +/- 7%, P < .05). Chemiluminescent assay indicated greater beta-galactosidase activity (2.5 +/- 0.6 mU/mg of protein) in the intima and media of atherosclerotic than normal vessels (0.6 +/- 0.2 mU/mg of protein, P < .05). Aortas from normal (n = 6) and atherosclerotic (n = 5) rabbits also were examined. Transgene expression (after histochemical staining) in endothelium was much greater in atherosclerotic than normal rabbits (39 +/- 3% versus 9 +/- 2%, P < .05) and expression in adventitial cells was similar (normal 23 +/- 2%, atherosclerotic 24 +/- 4%). Chemiluminescent assay indicated greater beta-galactosidase activity (1.2 +/- 0.4 mU/mg of protein) in the intima and media of atherosclerotic than normal vessels (0.2 +/- 0.1 mU/mg protein, P < .05). These findings suggest that an adenoviral vector with a CMV promoter provides similar transgene expression in adventitia of both normal and atherosclerotic vessels. Gene transfer to the endothelium was much more effective in atherosclerotic than in normal vessels. Thus it may be possible to achieve greater transgene expression in atherosclerotic than in normal arteries.  相似文献   
996.
The mechanisms by which monocytes from patients infected with human immunodeficiency virus (HIV) have reduced growth inhibitory activity against Cryptococcus neoformans was examined. Monocyte-enriched peripheral blood mononuclear cells from 12 HIV-seropositive donors with CD4 cell counts of 10-210 cells/mm3 (median, 85) and HIV-seronegative donors were compared in assays to determine the binding and phagocytosis of C. neoformans and the respiratory burst and degranulation in response to C. neoformans and zymosan. Monocytes from HIV-infected and uninfected persons bound and ingested C. neoformans equally well; however, generation of hydrogen peroxide and specific release of beta-glucuronidase in response to C. neoformans was significantly reduced in monocyte-enriched cells from the HIV-infected donors. The impaired anticryptococcal activity of monocytes from persons with HIV may be related to defects in both oxidative and nonoxidative effector pathways that occur after the binding and internalization of the organism.  相似文献   
997.
998.
OBJECTIVES: The NHANES I Epidemiologic Followup Study (NHEFS) is a longitudinal study that uses as its baseline those adult persons 25-74 years of age who were examined in the first National Health and Nutrition Examination Survey (NHANES I). NHEFS was designed to investigate the association between factors measured at baseline and the development of specific health conditions. The three major objectives of NHEFS are to study morbidity and mortality associated with suspected risk factors, changes over time in participants' characteristics, and the natural history of chronic disease and functional impairments. METHODS: Tracing and data collection in the 1992 Followup were undertaken for the 11,195 subjects who were not known to be deceased in the previous surveys. No additional information was collected in the 1992 NHEFS for the 3,212 subjects who were known to be deceased before the 1992 NHEFS data collection period. RESULTS: By the end of the 1992 NHEFS survey period, 90.0 percent of the 11,195 subjects in the 1992 Followup cohort had been successfully traced. Interviews were conducted for 9,281 subjects. An interview was conducted for 8,151 of the 8,687 surviving subjects; 551 interviews were administered to a proxy respondent because the subject was incapacitated. A proxy interview was conducted for 1,130 of the 1,392 decedents identified in the 1992 NHEFS. In addition, 10,535 facility stay records were collected for 4,162 subjects reporting overnight facility stays. Death certificates were obtained for 1,374 of the 1,392 subjects who were identified as deceased since last contact. Approximately 32 percent of the NHEFS cohort is known to be deceased with a death certificate available for 98 percent of the 4,604 NHEFS decedents.  相似文献   
999.
The majority of immunogenic CTL epitopes bind to MHC class I molecules with high affinity. However, peptides longer or shorter than the optimal epitope rarely bind with high affinity. Therefore, identification of optimal CTL epitopes from pathogens may ultimately be critical for inducing strong CTL responses and developing epitope-based vaccines. The SIV-infected rhesus macaque is an excellent animal model for HIV infection of humans. Although a number of CTL epitopes have been mapped in SIV-infected rhesus macaques, the optimal epitopes have not been well defined, and their anchor residues are unknown. We have now defined the optimal SIV gag CTL epitope restricted by the rhesus MHC class I molecule Mamu-A*01 and defined a general peptide binding motif for this molecule that is characterized by a dominant position 3 anchor (proline). We used peptide elution and sequencing, peptide binding assays, and bulk and clonal CTL assays to demonstrate that the optimal Mamu-A*01-restricted SIV gag CTL epitope was CTPYDINQM(181-189). Mamu-A*01 is unique in that it is found at a high frequency in rhesus macaques, and all SIV-infected Mamu-A*01-positive rhesus macaques studied to date develop an immunodominant gag-specific CTL response restricted by this molecule. Identification of the optimal SIV gag CTL epitope will be critical for a variety of studies designed to induce CD8+ CTL responses specific for SIV in the rhesus macaque.  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