全文获取类型
收费全文 | 704549篇 |
免费 | 8698篇 |
国内免费 | 1539篇 |
专业分类
电工技术 | 13379篇 |
综合类 | 558篇 |
化学工业 | 107553篇 |
金属工艺 | 28244篇 |
机械仪表 | 22099篇 |
建筑科学 | 15489篇 |
矿业工程 | 4731篇 |
能源动力 | 17785篇 |
轻工业 | 55160篇 |
水利工程 | 8051篇 |
石油天然气 | 16188篇 |
武器工业 | 45篇 |
无线电 | 79726篇 |
一般工业技术 | 141944篇 |
冶金工业 | 130263篇 |
原子能技术 | 16747篇 |
自动化技术 | 56824篇 |
出版年
2021年 | 6238篇 |
2019年 | 6033篇 |
2018年 | 10423篇 |
2017年 | 10597篇 |
2016年 | 11109篇 |
2015年 | 6978篇 |
2014年 | 11881篇 |
2013年 | 31710篇 |
2012年 | 18502篇 |
2011年 | 25095篇 |
2010年 | 20176篇 |
2009年 | 22717篇 |
2008年 | 23219篇 |
2007年 | 22974篇 |
2006年 | 20115篇 |
2005年 | 18368篇 |
2004年 | 17671篇 |
2003年 | 17252篇 |
2002年 | 16716篇 |
2001年 | 16561篇 |
2000年 | 15749篇 |
1999年 | 15992篇 |
1998年 | 39483篇 |
1997年 | 27875篇 |
1996年 | 21525篇 |
1995年 | 16369篇 |
1994年 | 14608篇 |
1993年 | 14391篇 |
1992年 | 10714篇 |
1991年 | 10424篇 |
1990年 | 10235篇 |
1989年 | 9946篇 |
1988年 | 9411篇 |
1987年 | 8321篇 |
1986年 | 8207篇 |
1985年 | 9303篇 |
1984年 | 8358篇 |
1983年 | 7882篇 |
1982年 | 7143篇 |
1981年 | 7378篇 |
1980年 | 6911篇 |
1979年 | 6917篇 |
1978年 | 6811篇 |
1977年 | 7664篇 |
1976年 | 9743篇 |
1975年 | 6069篇 |
1974年 | 5846篇 |
1973年 | 5858篇 |
1972年 | 5062篇 |
1971年 | 4661篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
Several different lines of evidence have demonstrated that inherited susceptibility to rheumatoid arthritis (RA) is associated with the DRB1 genes encoding the HLA-DR4 and HLA-DR1 molecules. A contrasting hypothesis has recently been proposed, suggesting that, in general, the DRB1 locus is associated with protection to RA and that the RA-associated DRB1 alleles are not responsible for the primary disease association but merely permissive for the susceptibility conferred by the HLA-DQ alleles with which they are in linkage disequilibrium. We have performed a critical review of the literature on the HLA association in RA with special emphasis on studies in which both an HLA-DR and -DQ association has been investigated. Our analyses provide strong evidence against the hypothesis that HLA-DQ molecules play a major role in the general susceptibility to RA. Thus, the strongest association in rheumatoid arthritis is with DRB1 genes rather than DQB1 genes. 相似文献
992.
A King 《Canadian Metallurgical Quarterly》1997,48(4):576-593
By using a 'cultural' definition of 'postmodernism' (derived from Jameson and Martin) in which postmodernism is regarded as the transgression of modern boundaries, this article traces the emergence of postmodern aspects to violent male fandom at football games since the 1960s. It is argued that at games, male fans have created imaginary masculine and national boundaries by which they have affirmed their identities but that in fighting they have sought to breach these boundaries in postmodern fashion. 相似文献
993.
The mycobacterial embCAB operon encodes arabinosyl transferases, putative targets of the antimycobacterial agent ethambutol (EMB). Mutations in embB lead to resistance to EMB in Mycobacterium tuberculosis. The basis for natural, intrinsic resistance to EMB in nontuberculous mycobacteria (NTM) is not known; neither is the practical implication of resistance to EMB in the absence of embB mutations in M. tuberculosis well understood. The conserved embB resistance-determining region (ERDR) of a collection of 13 strains of NTM and 12 EMB-resistant strains of M. tuberculosis was investigated. Genotypes were correlated with drug susceptibility phenotypes. High-level natural resistance to EMB (MIC, . or =64 microg/ml) was associated with a variant amino acid motif in the ERDR of M. abscessus, M. chelonae, and M. leprae. Transfer of the M. abscessus emb allele to M. smegmatis resulted in a 500-fold increase in the MICs. In M. tuberculosis, embB mutations were associated with MICs of > or =20 microg/ml while resistance not associated with an ERDR mutation generally resulted in MICs of < or =10 microg/ml. These data further support the notion that the emb region determines intrinsic and acquired resistance to EMB and might help in the reassessment of the current recommendations for the screening and treatment of infections with EMB-resistant M. tuberculosis and NTM. 相似文献
994.
T Reck F K?ckerling C Schneider W Hohenberger 《Canadian Metallurgical Quarterly》1997,122(10):914-918
Morgagni hernias are the least common form of diaphragmatic hernias. Although they are congenital, most of them are not diagnosed until later in life. The indication for surgery is based on the patient's symptoms or on the radiological evidence of incarcerated tissue, and until quite recently involved a laparotomy or thoracotomy. Laparoscopy not only permits the suspected diagnosis to be confirmed--which is otherwise often difficult--but also makes it possible to close the hernia site by suturing. For improved security, the hernia site is augmented by fixing in place a non-absorbable mesh. The operative technique employed is described. 相似文献
995.
M Kanazawa M Yano C Namchai S Yamamoto A Ohtake M Takayanagi M Mori H Niimi 《Canadian Metallurgical Quarterly》1997,239(2):580-584
cDNAs for green fluorescent protein (GFP) and for a GFP fusion protein containing the presequence of human ornithine transcarbamylase (pOTC-GFP) were transfected into cultured human fibroblasts. GFP cDNA gave diffuse fluorescence throughout the cytoplasm and the nucleus, whereas pOTC-GFP cDNA gave mitochondria-associated fluorescence. Fluorescent mitochondrial structures could be classified into five patterns: thread-like mitochondria, fine thread-like ones, rod-like ones, granular ones, and granular ones with weak cytosolic fluorescence. pOTC-GFP mutants resulted in a loss of mitochondrial fluorescence and an appearance of weak fluorescence throughout the cytoplasm. pOTC-GFP cDNA was transfected into fibroblasts from patients with various mitochondrial diseases. Higher ratios of fibroblasts with granular mitochondria and those with fine thread-like ones were observed in a patient with Reye's syndrome and a patient with Kearns-Sayre syndrome. Weak cytosolic fluorescence was sometimes observed in fibroblasts from these patients. This method will be useful to analyze mitochondrial structural alterations and disorders of mitochondrial protein import. 相似文献
996.
997.
Sixty-two women (mean age 68.7 +/- 0.9 yr) with postmenopausal spinal osteoporosis were treated with cyclical etidronate therapy (400 mg for 2 weeks alternating with 12 weeks of 1 gm elemental calcium and 400 IU Vitamin D3) for a minimum of 2 yr. Bone mineral density (BMD) of the lumbar spine (g/cm2) increased significantly (p < 0.0001) after yr 1 (4.1 +/- 0.5 per cent) and yr 2 compared with yr 1 (2.2 +/- 0.5 per cent). The response rate was 89 per cent after yr 1 and 84 per cent after yr 2. BMD of the hip (30 patients) increased by 1.5 +/- 0.9 per cent after yr 1 and 5.5 +/- 1.1 per cent (p < 0.0001) after yr 2 when compared with baseline. The response rate was 63 per cent after yr 1 and 80 per cent after yr 2. Smaller numbers of patients continued with treatment up to 4 yr with no adverse long-term effects. 相似文献
998.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
999.
P Klein R Béliard A Glacet S Moitel T Ducrot D Bourel 《Canadian Metallurgical Quarterly》1997,8(1):17-25
The aim of this study was to investigate how intrauterine growth retardation affects body proportions in VLBW infants. The cohort consisted of 135 surviving and 80 deceased preterm infants weighing less than 1250 grams at birth. Gestational age varied between 24 and 36 weeks (mean age 29.7 and 27.5 weeks, respectively). Birth weight was more than 2 SD below the mean birth standard values in 32% of the surviving, and in 27% of the deceased infants. Reduction of weight, length and head circumference at birth was analysed using Z scores based on Swedish birth standards. Z scores of weight, length and head circumference were highly correlated in the surviving and the deceased infants (r = 0.78 to 0.94 and 0.65 to 0.97, respectively). Length was significantly more affected by growth retardation than weight. Weight and head circumference were proportionately reduced. Intrauterine growth retardation influences body proportions in VLBW infants differently than in larger preterm and term infants. 相似文献
1000.