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   951篇
  免费   1篇
电工技术   1篇
化学工业   13篇
金属工艺   3篇
建筑科学   15篇
能源动力   5篇
轻工业   18篇
无线电   44篇
一般工业技术   22篇
冶金工业   807篇
原子能技术   3篇
自动化技术   21篇
  2020年   1篇
  2018年   1篇
  2017年   2篇
  2016年   2篇
  2014年   2篇
  2013年   8篇
  2012年   9篇
  2011年   7篇
  2010年   4篇
  2009年   3篇
  2008年   6篇
  2007年   7篇
  2006年   3篇
  2005年   3篇
  2004年   5篇
  2003年   5篇
  2002年   4篇
  2001年   5篇
  2000年   5篇
  1999年   29篇
  1998年   262篇
  1997年   144篇
  1996年   76篇
  1995年   55篇
  1994年   33篇
  1993年   62篇
  1992年   10篇
  1991年   18篇
  1990年   12篇
  1989年   15篇
  1988年   13篇
  1987年   18篇
  1986年   8篇
  1985年   11篇
  1984年   2篇
  1983年   5篇
  1982年   5篇
  1981年   5篇
  1980年   4篇
  1978年   1篇
  1977年   17篇
  1976年   60篇
  1975年   1篇
  1974年   2篇
  1972年   1篇
  1964年   1篇
排序方式: 共有952条查询结果,搜索用时 15 毫秒
131.
BACKGROUND: Meningeal hemangiopericytoma is an uncommon neoplasm with a high propensity for recurrence. The purpose of this study was to analyze the efficacy of different treatment options in patients with recurrent disease. METHODS: The records of all patients with recurrent meningeal hemangiopericytoma treated at the study institution between 1976 and 1996 were reviewed. RESULTS: Thirty-four consecutive patients were studied. The mainstay of treatment was brain surgery in 21 patients (62%); the median time to recurrence from surgery was 12 months. Ten patients (29%) had 20 recurrent central nervous system (CNS) lesions treated by stereotactic radiosurgery. Of these, 3 previously nonirradiated patients (all with lesion size < 25 mm) achieved a complete response, which persisted at a median of 3 years. In 14 lesions (70%) a partial response (PR) occurred with a median duration of 12 months, whereas 3 lesions (15%) remained stable. Two patients with inoperable CNS lesions received external beam radiation therapy and both had PRs lasting 14 and 24 months, respectively. Nine patients (26%) received radiation therapy for metastatic disease. Of these, seven patients remained stable with good symptomatic relief, and two patients experienced tumor progression. Chemotherapy with doxorubicin-containing regimens was administered in 7 patients (21%); there was only 1 PR that lasted 8 months. The median survival from first recurrence was 4.6 years. CONCLUSIONS: Surgical management is important for the successful treatment of patients with recurrent meningeal hemangiopericytoma. Radiosurgery plays a definite role in the treatment of smaller recurrent CNS lesions. Radiation therapy is helpful in the management of inoperable tumors. More effective chemotherapeutic agents are needed.  相似文献   
132.
Incubation of mock-transfected PC12 rat pheochromocytoma cells (PC12) for 2 h with increasing concentrations of glutamate caused progressive loss of viability (e.g., 67% with 15 mM glutamate). In contrast, the viability of bcl-2-transfected cells (PC12/bcl-2) was unaffected by glutamate. Neither PC12 nor PC12/bcl-2 cells showed a significant incidence of apoptosis in response to glutamate. Conventional phospholipid analysis by high-performance TLC and phosphorous determination showed no significant changes in the phospholipid composition of either cell line incubated with 5 mM glutamate. The peroxyl radical initiator 2,2'-azobis(2,4-dimethylvaleronitrile) caused a pronounced loss of all major phospholipid classes in PC12 cells, but no loss of cell viability. No phospholipid peroxidation was detected in PC12/bcl-2 cells incubated with 相似文献   
133.
134.
The subgroup II luteovirus barley yellow dwarf virus-RPV (BYDV-RPV) acts as a helper virus for a satellite RNA (satRPV RNA). The subgroup II luteovirus beet western yellows virus (BWYV) and the ST9-associated RNA (ST9a RNA), a BWYV-associated RNA that encodes a polymerase similar to those of subgroup I luteoviruses, were assayed for their ability to support replication of satRPV RNA. SatRPV RNA was replicated in tobacco protoplasts in the presence of BWYV RNA or a mixture of BWYV plus the ST9a RNA, but not in the presence of ST9a RNA alone. ST9a RNA stimulated BWYV RNA accumulation which, in turn, increased the accumulation of satRPV RNA. SatRPV RNA was encapsidated in BWYV capsids primarily as circular monomers, which differs from the linear monomers found in BYDV (RPV + PAV) particles. SatRPV RNA was transmitted to Capsella bursa-pastoris plants by aphids only in the presence of BWYV and ST9a RNA. SatRPV RNA reduced accumulation of both BWYV helper and ST9a nonhelper RNAs in plants but did not affect symptoms. The replication of satRPV RNA only in the presence of subgroup II luteoviral RNAs but not in the presence of RNAs with subgroup I-like polymerase genes, in both monocotyledonous and dicotyledonous hosts, suggests that the specificity determinants of satRPV RNA replication are contained within the polymerase genes of supporting viruses rather than in structural genes or host plants.  相似文献   
135.
A 17-year-old girl with unilateral congenital glaucoma who had undergone trabeculectomy and peripheral iridectomy in infancy developed apparent exfoliation syndrome (XFS) in the eye that underwent the surgical procedures. A conjunctival biopsy was performed and the specimen was fixed in 2.5% glutaraldehyde, embedded in epoxy resin (Epon-Araldite, Electron Microscopy Sciences, Fort Washington, Pa), and processed for routine electron microscopy and immunostaining for elastin. Results of ultrastructural study showed scattered fibrillar aggregates compatible with those of XFS in an older adult, differing chiefly in sparsity of granular interfibrillar matrix. The XFS fibers were closely associated with elastic fibers and microfibrils. Elastosis of the actinic-aging type was somewhat greater than expected for age. To our knowledge, this is the youngest patient described with characteristic ocular findings of XFS to date, supporting others who have suggested an association between iris surgery in youth and early onset XFS. Electron microscopy was essential in ruling out the possibility of a clinically similar entity caused by ultrastructurally different material.  相似文献   
136.
We report two cases of massive, solitary, plexiform schwannoma. One was a 9-cm subcutaneous lesion on the hip of a 72-year-old man who had become aware of the slow-growing tumor 50 years earlier; the other is the first reported plexiform schwannoma to arise in a visceral organ: it arose in the ascending colon of a 54-year-old man and exhibited a dumbbell configuration with submucosal and subserosal components. Neither patient had neurofibromatosis or schwannomatosis. Both tumors were well-circumscribed and multinodular, and both showed a plexiform architecture. Microscopically, the nodules were composed primarily of Antoni A tissue, replete with nuclear palisading and Verocay bodies. Examination by immunohistochemistry and electron microscopy demonstrated the features of well-differentiated Schwann cells; nodules were surrounded by attenuated, residual perineurium. Both patients followed a benign clinical course, without recurrence or metastasis. Neither the large tumor size nor the unusual locations affected the biologic behavior of these neoplasms. A massive plexiform schwannoma must be distinguished from a malignant peripheral nerve sheath tumor and from a plexiform neurofibroma, a tumor prone to malignant transformation.  相似文献   
137.
A 56-year-old female with rheumatoid arthritis was admitted because of bilateral hip pain. In a few months of her hospitalization, a relatively abrupt renal dysfunction was emerged besides complement breakdown, and renal biopsy revealed crescentic glomerulonephritis. Immunofluorescence study showed peripheral granular deposits of IgG, IgM, and C3 in the glomeruli. Cresents were predominantly composed of macrophages and glomerular epithelial cells. Amyloid nephropathy, renal vasuculitis, and association of other collagen vascular diseases were negligible for the causative factor. It was suggested that immune complexes were formed in the glomeruli, in which both humoral and cellular immune responses were to be induced, that brought cescents formation in the lesions. Crescentic glomerulonephritis in patients with rheumatoid arthritis is rare and a possible pathogenetic mechanisms involved in the development of renal dysfunction are discussed with the special reference to immune complex-induced inflammation.  相似文献   
138.
STUDY OBJECTIVES: To determine whether disease specific characteristics, reflecting clinical disease severity, add to the explanation of mobility limitations in patients with specific chronic diseases. DESIGN AND SETTING: Cross sectional study of survey data from community dwelling elderly people, aged 55-85 years, in the Netherlands. PARTICIPANTS AND METHODS: The additional explanation of mobility limitations by disease specific characteristics was examined by logistic regression analyses on data from 2830 community dwelling elderly people. MAIN RESULTS: In the total sample, chronic non-specific lung disease, cardiac disease, peripheral atherosclerosis, diabetes mellitus, stroke, arthritis and cancer (the index diseases), were all independently associated with mobility limitations. Adjusted for age, sex, comorbidity, and medical treatment disease specific characteristics that explain the association between disease and mobility mostly reflect decreased endurance capacity (shortness of breath and disturbed night rest in chronic non-specific lung disease, angina pectoris and congestive heart failure in cardiac disease), or are directly related to mobility function (stiffness and lower body complaints in arthritis). For atherosclerosis and diabetes mellitus, disease specific characteristics did not add to the explanation of mobility limitations. CONCLUSIONS: The results provide evidence that, to obtain more detailed information about the differential impact of chronic diseases on mobility, disease specific characteristics are important to take into account.  相似文献   
139.
BACKGROUND: Alveolar macrophages are thought to play an important part in regulating lung immune responses. While it is clear that human alveolar macrophages suppress T cell proliferation in vitro, the mechanisms by which this is achieved are not clear, nor is it known whether alveolar macrophages also inhibit other aspects of T cell function. METHODS: Peripheral blood mononuclear cells were stimulated with phytohaemagglutinin or house dust mite allergen, and cultured with variable numbers of autologous alveolar macrophages obtained by bronchoalveolar lavage from 20 normal subjects. RESULTS: Alveolar macrophages induced a reversible inhibition of T cell proliferation in response to both mitogen and allergen stimulation, with the latter being considerably more susceptible to inhibition. This was achieved via heterogenous mechanisms, involving both soluble factors derived from alveolar macrophages and cell-cell contact. Despite inhibiting proliferation, alveolar macrophages had little or no effect on T cell calcium flux, the characteristic changes in CD3, CD2, CD28 and interleukin-2 (IL-2) receptor expression which accompany normal T cell activation, and IL-2 and interferon gamma secretion. In contrast, alveolar macrophages inhibited the tyrosine phosphorylation of proteins which may be involved in IL-2 receptor-associated signal transduction. CONCLUSIONS: The immunoregulatory properties of alveolar macrophages are relatively selective, allowing T cell activation and cytokine secretion while inhibiting T cell proliferation within the lung.  相似文献   
140.
Hexose oxidase from the red seaweed, Chondrus crispus was purified to homogeneity. The enzyme appeared to be encapsulated in particles obtained after mechanical disintegration of the fronds. Liberation of the enzyme in soluble form required either waiting for the spontaneous development of a suitable microbial flora in the suspension, or treatment with a mixture of proteases (pronase). As deduced from (SDS/)PAGE, the enzyme has a molecular mass of 87 kDa and probably consists of subunits of 36 kDa and 25 kDa. The low isoelectric point of 2.8 and the presence of 25% (by mass) sugars indicate that the enzyme is a strongly acidic glycoprotein. The absorption spectrum of isolated enzyme minus that of the substrate-reduced enzyme, and the EPR spectrum of the free radical observed in the reduced enzyme revealed the presence of a flavin. This cofactor is probably covalently bound since flavins were not released upon denaturation of the enzyme by heat or acid treatment. Taking free FAD as a reference compound, the enzyme contains 1 mol flavin/mol enzyme. EPR spectroscopy of the purified preparation showed the presence of Cu2+. However, since the amount was substoichiometric, substrate addition did not affect the signal, and the addition of chelator or Cu2+ did not affect the activity, the presence of this metal ion seems adventitious. It is concluded that the large discrepancies between the presently and the previously reported [Sullivan, J. D. & Ikawa, M. (1973) Biochim. Biophys. Acta 309, 11-22] characteristics of the enzyme probably originate from the characterization of a contaminating protein in the latter case.  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