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   3473篇
  免费   1篇
综合类   1篇
化学工业   20篇
机械仪表   2篇
建筑科学   7篇
能源动力   1篇
轻工业   28篇
无线电   7篇
一般工业技术   8篇
冶金工业   3390篇
自动化技术   10篇
  2020年   1篇
  2018年   1篇
  2017年   1篇
  2016年   2篇
  2015年   1篇
  2014年   2篇
  2012年   7篇
  2011年   3篇
  2010年   2篇
  2009年   1篇
  2008年   5篇
  2007年   6篇
  2006年   5篇
  2005年   5篇
  2004年   4篇
  2003年   9篇
  2002年   4篇
  2001年   4篇
  2000年   3篇
  1999年   127篇
  1998年   1155篇
  1997年   593篇
  1996年   414篇
  1995年   197篇
  1994年   190篇
  1993年   176篇
  1992年   40篇
  1991年   33篇
  1990年   44篇
  1989年   44篇
  1988年   40篇
  1987年   36篇
  1986年   34篇
  1985年   39篇
  1984年   1篇
  1983年   5篇
  1982年   13篇
  1981年   13篇
  1980年   17篇
  1979年   4篇
  1978年   6篇
  1977年   52篇
  1976年   125篇
  1975年   3篇
  1972年   2篇
  1971年   1篇
  1969年   2篇
  1964年   1篇
  1955年   1篇
排序方式: 共有3474条查询结果,搜索用时 0 毫秒
981.
The authors present the study of four children with arteritis as vascular complication of acute bacterial meningitis. They report pathophysiological mechanisms involved in vascular lesions, and progress in the understanding of these complications.  相似文献   
982.
The incidental finding of microscopic foci of acantholytic dyskeratosis, reproducing the histological pattern of Darier's disease, has been the subject of a number of papers in the last few years. In contrast, the incidental finding of other types of acantholysis has not been mentioned in the literature. In the last 5 years, we have noticed such a microscopic finding in 14 biopsy specimens (0.15% of our cutaneous specimens). they were from 13 patients (7 men and 6 women); their ages ranged from 37 to 79 years (mean, 63). Three lesions were located on the head, 7 on the trunk, and 4 on the limbs. The histological diagnoses were basal cell carcinoma (6 cases), keratoacanthoma (2 cases), psoriasis (2 cases), elastolytic granuloma, acral arteriovenous angioma, tinea corporis, and leukocytoclastic vasculitis (1 case each). The histological patterns of the acantholytic foci simulated pemphigus vulgaris (9 cases), superficial pemphigus (1 case), Hailey-Hailey disease (3 cases), and unclassifiable acantholysis (1 case). None of the patients had familial or personal history of acantholytic disorders. We propose a classification of the primary acantholytic disorders based on both their acantholytic pattern and their clinical extent.  相似文献   
983.
Early infancy (< 1 year of age), massive tumor cell burden, and extremely poor prognosis are characteristic features of a particular subset of childhood acute leukemias (AL). In these cases, chromosome aberrations at the 11q23 band are the most frequently reported cytogenetic abnormalities. We have recently cloned a genetic locus named ALL-1, in which DNA breakpoints are clustered in leukemic patients with 11q23 aberrations. Analysis of the ALL-1 genomic configuration in DNA from 15 infants with AL showed specific ALL-1 rearrangements in 12 cases (80%), including 5 with normal karyotypes. These findings indicate that a consistent genetic defect underlies this particular leukemic subset.  相似文献   
984.
Trophoblast, the only fetal tissue in direct contact with maternal cells, fails to express the polymorphic HLA class I molecules HLA-A and -B, but does express the nonpolymorphic class I molecule HLA-G. It is thought that HLA-G may provide some of the functions of a class I molecule without stimulating maternal immune rejection of the fetal semiallograft. As a first step in identifying the cis-acting DNA regulatory elements involved in the control of class I expression by extraembryonic tissue, several types of transgenic mice were produced. Two HLA-G genomic fragments were used, 5.7 and 6.0 kb in length. These included the entire HLA-G coding region, 1 kb of 3' flanking sequence, and 1.2 or 1.4 kb of 5' flanking sequence, respectively. A hybrid transgene, HLA-A2/G, was produced by replacing the 5' flanking sequence, first exon, and early first intron of HLA-G with the corresponding elements of HLA-A. Comparison of transgene mRNA expression patterns seen in HLA-A2/G and HLA-G transgenic mice suggests that 5' flanking sequences are largely responsible for the differing patterns of expression typical of the classical class I and HLA-G genes. Studies comparing the extraembryonic HLA-G expression levels of founder embryos transgenic for either the 5.7- or 6.0-kb HLA-G transgene showed that the 6.0-kb transgene directed HLA-G expression far more efficiently than did the 5.7-kb HLA-G transgene, producing extraembryonic HLA-G mRNA levels similar to those seen in human extraembryonic tissues. The results of these studies suggest that the 250-bp fragment present at the extreme 5' end of the 6.0-kb HLA-G transgene and absent from the 5.7-kb HLA-G transgene contains an important positive regulatory element. This 250-bp fragment lies further upstream than any of the previously documented class I regulatory regions and may function as a locus control region.  相似文献   
985.
主要介绍了我国压力容器用中厚板生产情况、主要钢种、执行标准及生产厂家等状况;简要介绍了各钢种的工艺工序和特殊性能以及我国压力容器用钢板的发展趋势。  相似文献   
986.
[Correction Notice: An erratum for this article was reported in Vol 12(1) of Review of General Psychology (see record 2008-02668-007). On page 389, right column, last paragraph, the second to last sentence should read "The goal now, however, will be to improve students' success, faculty's scholarship, and the future of their communities". On page 386, right column, third paragraph, line six, "psychologist-administrators" should appear as "psychologist administrators". On page 390, right column, the Logue 2006 reference should read "[Survey of fields of Middle States Commission accredited New York State institutions of higher education chief academic officers and presidents]".] Higher education is currently facing many serious challenges. These challenges derive from the effects of globalization, massification (the wide availability of higher education), competition, expanding technology, regulation, litigation, and tuition increases that are outpacing student aid. Many psychologists possess the skills to overcome these challenges: to facilitate the learning, creativity, and performance of each student, faculty member, and staff member; foster productive group relations; analyze human behavior qualitatively, quantitatively, and experimentally; and generate and steward funds for their institutions. Psychologists are well prepared to lead institutions of higher education through and beyond their 21st-century challenges. Relatively few higher education leaders are psychologists, however. Psychologists should be encouraged to choose administrative career paths and thus greatly benefit our colleges and universities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
987.
Genomic alterations and abnormal expression of the FHIT gene at 3p14.2 have been observed in cell lines and primary tumors of the lung. To correlate FHIT locus DNA and RNA lesions with effects on Fhit protein expression, we have analyzed 11 lung cancer cell lines, 15 small cell lung carcinomas, and 38 pairs of non-small cell primary tumors and bronchial mucosa specimens by molecular genetic and immunocytochemical methods. Using specific antibodies against the Fhit protein, we observed concordance between RNA abnormalities and lack of Fhit protein expression in lung tumors and cell lines. In addition, absence of Fhit protein in some precancerous dysplastic lesions suggested that FHIT inactivation may occur at an early phase of lung carcinogenesis.  相似文献   
988.
INTRODUCTION: This review was performed to evaluate the outcome of patients undergoing pancreaticoduodenectomy (PD) for isolated metastatic or locally advanced nonperiampullary tumors at a single institution over a 13-year period. METHODS: Between 1983 and 1996, patients undergoing PD for metastatic or locally advanced nonperiampullary malignancies were identified. Medical records were reviewed and outcome factors and survival data analyzed. RESULTS: Eighteen patients were identified. The primary tumor histopathology included colon (n = 7), gastric (n = 4), renal cell (n = 3), lung (n = 2), bladder (n = 1), and melanoma (n = 1). The median length of hospital stay was 15 days (6 to 48) with one perioperative death (5.5%). The median tumor size was 5.5 cm (0.8 to 11.5), and 7 patients had positive peripancreatic lymph nodes. The median survival was 40 months, with a 5-year survival of 35%. CONCLUSIONS: Pancreaticoduodenectomy for nonperiampullary malignancy is infrequently indicated. However, in the absence of widely metastatic disease, PD should be considered for locally advanced tumors or isolated metastatic malignancy.  相似文献   
989.
Cell-cell adhesion mediated by E-cadherin is often lost or disturbed in human carcinomas. For regular adhesive function, E-cadherin has to form complexes with peripheral cytoplasmic catenins which are multifunctional proteins that are also involved in signal transduction and growth regulation. We have analyzed the expression levels of the genes encoding alpha-catenin, beta-catenin and plakoglobin in correlation to the E-cadherin expression levels in cell lines derived from human cervical carcinomas. Reduced mRNA and protein levels were detected for plakoglobin, whereas alpha- and beta-catenin showed only reduced protein (but not mRNA) levels. The alterations in catenin gene expression were often associated with absent or reduced E-cadherin. The findings indicate that a reduction of catenin gene expression may contribute to the development of cervical carcinomas.  相似文献   
990.
Tissue ingrowth into porous-coated orthopedic and dental implants is commonly used as a means to achieve long-term fixation of these prostheses. However, the degree of tissue ingrowth is often inadequate and inconsistent. If the pores of these implants are impregnated with a controlled drug release system delivering relevant growth factors, then it might be possible to stimulate more tissue ingrowth. The present study introduces such a system based on biodegradable polymers and investigates its protein release profile and polymer degradation characteristics. Porous coated titanium implants were impregnated with a mixture of a 50%-50% polylactic acid-polyglycolic acid copolymer and a model protein, soybean trypsin inhibitor. Control implants contained only the polymer and no protein. The implants were subjected to hydrolytic degradation in phosphate buffered saline at 37 degrees C for periods of 3, 6, and 11 weeks. The protein release and the mass and molecular weight of the polymer were monitored. The results indicate that the protein is released in three distinct phases and the polymer loses almost all its mass and molecular weight by 11 weeks. There was a significant difference in the polymer degradation characteristics between the control and test implants, which might be the result of some complex polymer-protein interactions.  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