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   1138篇
  免费   1篇
  国内免费   1篇
电工技术   3篇
化学工业   8篇
金属工艺   1篇
机械仪表   1篇
建筑科学   6篇
能源动力   1篇
轻工业   7篇
无线电   6篇
一般工业技术   7篇
冶金工业   1087篇
自动化技术   13篇
  2016年   1篇
  2015年   1篇
  2014年   3篇
  2011年   1篇
  2010年   1篇
  2009年   5篇
  2008年   3篇
  2007年   3篇
  2006年   3篇
  2005年   2篇
  2004年   1篇
  2003年   3篇
  2002年   4篇
  2001年   2篇
  2000年   3篇
  1999年   21篇
  1998年   351篇
  1997年   152篇
  1996年   123篇
  1995年   80篇
  1994年   65篇
  1993年   58篇
  1992年   6篇
  1991年   8篇
  1990年   12篇
  1989年   15篇
  1988年   18篇
  1987年   13篇
  1986年   11篇
  1985年   16篇
  1982年   4篇
  1981年   8篇
  1980年   8篇
  1978年   3篇
  1977年   39篇
  1976年   84篇
  1975年   3篇
  1974年   2篇
  1972年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有1140条查询结果,搜索用时 0 毫秒
991.
Previous studies from this laboratory have shown evidence of regeneration of long descending spinal motor tracts in rats after spinal cord transection and treatment to modify the animals' immune response. In this study, less extensive surgical lesions were combined with the most favorable drug treatment (75 mg per kilogram of cyclophosphamide in a single dose) in an effort to improve the prospects for regeneration. Less than complete spinal cord transections in the rat were frequently followed by clinical and electrophysiologic evidence of return of function. Such return of function appears to depend on a reorganization of the nervous system that results in the use of the few remaining fibers to transmit motor information rather than on regeneration. Immunosuppressive treatment had no effect on these results.  相似文献   
992.
When 7721 human hepatocarcinoma cells were treated with 100 nM phorbol-12-myristate-13-acetate (PMA), the activity of N-acetylglucosaminyltransferase V(GnT-V) in the cells varied in accordance with the activity of membranous protein kinase C (PKC), but not with that of cytosolic PKC. Quercetin, a non-specific inhibitor of Ser/Thr protein kinase, and D-sphingosine and staurosporine, two specific inhibitors of PKC, blocked the activation of membranous PKC and GnT-V by PMA. Among the three inhibitors, quercetin was least effective. The inhibitory rates of quercetin and staurosporine toward membranous PKC and GnTV were proportional to the concentrations of the two inhibitors. The activities of GnTV and membranous protein kinase A (PKA) were also induced in parallel by dibutyryl cAMP (db-cAMP) and this induction was blocked by a specific PKA inhibitor. When cell free preparations of 7721 cells and human kidney were treated with alkaline phosphatase (ALP) to remove the phosphate groups, the GnTV activities were decreased. These results suggest that GnTV may be activated by membranous PKC or PKA, indirectly or directly, via phosphorylation of Ser/Thr residues.  相似文献   
993.
BACKGROUND AND OBJECTIVE: An inflammatory response produced by excimer laser photorefractive keratectomy (PRK) may be associated with the subsequent corneal haze and regressions in refractive error observed after treatment. Complement-derived anaphylatoxins, potent mediators of inflammation, may have a role in postoperative healing. MATERIALS AND METHODS: Twenty right human donor corneas underwent a 6-D excimer laser PRK treatment. The corresponding left donor corneas served as the controls. After incubation in tissue culture media for 6 hours and elution in phosphate-buffered saline with EDTA for 24 hours, complement-derived anaphylatoxins C3a, C4a, and C5a were measured in corneal eluates by radioimmunoassay. RESULTS: Compared with control corneas, the excimer PRK corneas failed to demonstrate a significant increase in C3a, C4a, or C5a levels (P > .05). CONCLUSIONS: These results suggest that the excimer laser at this dose does not activate significant complement in the cornea.  相似文献   
994.
The classical shortest route problem in networks assumes deterministic arc weights and a utility (or cost) function that is linear over path weights for route evaluation. When the environment is stochastic and the “traveler's” utility function for travel attributes is nonlinear, we define “optimal paths” that maximize the expected utility.We review the concepts of temporary and permanent preferences for comparing a traveler's preference for available subpaths. It has been shown before that when the utility function is linear or exponential, permanent preferences prevail and an efficient Dijkstra-type algorithm [3] is available that determines the optimal path.In this paper an exact procedure is developed for determining an optimal path when the utility function is quadratic—a case where permanent preferences do not always prevail. The algorithm uses subpath comparison rules to establish permanent preferences, when possible, among subpaths of the given network. Although in the worst case the algorithm implicitly enumerates all paths (the number of operations increasing exponentially with the size of the network), we find, from the computational experience reported, that the number of potentially optimal paths to evaluate is generally manageable.  相似文献   
995.
996.
This study evaluated the effect of dosage on severity of cyclosporin-A (CSA) induced gingival overgrowth. Eighty (80) male Sprague-Dawley rats were randomly distributed into 4 groups. Rats in each group daily received CSA in mineral oil by gastric feeding at dosages of 0 (control), 3, 10, and 30 mg/kg, respectively, for 6 weeks. Stone models of the mandibular incisal region were obtained biweekly and were used for analysis of the gingival dimensions. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluations. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluation Gingival overgrowth including bucco-lingual and mesio-distal width and vertical height were significantly increased with increasing CSA dosage. Furthermore, the gingival dimensions displayed a positive linear relation to dosage and treatment duration. The histopathologic evaluation revealed a granulomatous tissue wedging the tooth-gingival interface in the 3 mg/kg group. This tissue had reached exuberant size in the 10 and 30 mg/kg groups. In summary, the analysis of gingival dimensions the histopathologic evaluation shows a dose-dependent effect on the severity of CSA-induced gingival overgrowth.  相似文献   
997.
998.
Increased production of PTH-related protein (PTHrP) and PTH is frequently responsible for hypercalcemia and its associated morbidity. However, it is unclear whether these peptides produce identical effects on cells in the osteoclast lineage in vivo. To examine the effects of continuous in vivo exposure to these factors on both the osteoclast precursors and mature osteoclasts, we inoculated Chinese hamster ovarian cells expressing PTH-(1-84), PTHrP-(1-141), or nontransfected Chinese hamster ovarian cells into nude mice. The effects of these tumors on blood ionized calcium, plasma PTH and PTHrP concentrations, and osteoclast formation were then determined. PTH and PTHrP tumor-bearing mice became hypercalcemic (1.90 +/- 0.04 and 1.97 +/- 0.16 mmol/liter, respectively) compared with control mice (1.29 +/- 0.015 mmol/liter). After 4 days of hypercalcemia, mice were killed, and bone marrow cells were harvested to examine cells at three discrete stages of osteoclast development: multipotent osteoclast precursors, the granulocyte/macrophage colony-forming unit; more committed marrow mononuclear osteoclast precursors; and mature osteoclasts. Neither PTH nor PTHrP had an effect on granulocyte/macrophage colony-forming unit, but similarly increased the number of more committed mononuclear osteoclast progenitors as well as mature osteoclasts in the calvaria. No differences were detected between the effects of PTH and PTHrP on cells in the osteoclast lineage in vivo. Thus, PTH and PTHrP appear to affect only more differentiated cells in the osteoclast lineage, and the differences in osteoclastic bone resorption between primary hyperparathyroidism and humoral hypercalcemia of malignancy are probably due to mechanisms other than effects on osteoclast precursor cells in vivo.  相似文献   
999.
Cellular aspects of the immunomodulating activity of a proprietary mistletoe extract (Eurixor) standardized for mistletoe lectin-1 (ML-1) were investigated in patients suffering from mammary carcinoma (n = 20). Regular subcutaneous injections of the different dosages (0.5 and 1.0 ng ML-1/kg body weight, twice a week, for 5 weeks) yielded statistically significant increases of defined peripheral blood lymphocyte subsets (helper T-cells, natural killer (NK)-cells) which are generally believed to be involved in antitumor activity. Moreover, administration of either ML-1 concentration resulted in enhanced expression of activation markers such as interleukin-2 receptors and HLA/DR-antigens on peripheral blood T-lymphocytes. This study suggests that regular subcutaneous administration of both ML-1 concentrations (0.5 and 1.0 ng/kg body weight) can efficiently stimulate the cellular immune system of cancer patients.  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