全文获取类型
收费全文 | 2378篇 |
免费 | 24篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 21篇 |
综合类 | 10篇 |
化学工业 | 170篇 |
金属工艺 | 22篇 |
机械仪表 | 25篇 |
建筑科学 | 61篇 |
矿业工程 | 4篇 |
能源动力 | 16篇 |
轻工业 | 126篇 |
水利工程 | 7篇 |
石油天然气 | 6篇 |
武器工业 | 1篇 |
无线电 | 61篇 |
一般工业技术 | 98篇 |
冶金工业 | 1680篇 |
原子能技术 | 13篇 |
自动化技术 | 97篇 |
出版年
2021年 | 11篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 41篇 |
2012年 | 26篇 |
2011年 | 21篇 |
2010年 | 34篇 |
2009年 | 35篇 |
2008年 | 24篇 |
2007年 | 36篇 |
2006年 | 19篇 |
2005年 | 57篇 |
2004年 | 15篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 62篇 |
1998年 | 485篇 |
1997年 | 293篇 |
1996年 | 198篇 |
1995年 | 104篇 |
1994年 | 99篇 |
1993年 | 100篇 |
1992年 | 17篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 28篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 16篇 |
1983年 | 24篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 25篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 56篇 |
1976年 | 121篇 |
1975年 | 22篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1971年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有2418条查询结果,搜索用时 15 毫秒
21.
RB Hudson 《Canadian Metallurgical Quarterly》1994,34(6):743-748
The analysis of genomic DNA fragment patterns has revealed as a powerful tool for strain discrimination in Staphylococcus aureus; for use as an epidemiological marker, stability during the course of an outbreak is an essential prerequisite. Genomic DNA fragment patterns (SmaI restriction, pulsed-field electrophoresis) of four different epidemic MRSA strains were compared along with intra- and interhospital and country-wide spread over more than 12 months in Germany. Strain I was isolated from infections in 8 hospitals. In one hospital a subclone arised which differed from the original strain by 4 fragments. Strain II was spread among 4 hospitals, isolates from three of these hospitals exhibited a variability of one to three fragments in the 150-200 kb range. Two hospitals in the Hannover-area were affected by strain III; in 17 isolates of this strain a variability up to three fragments was found in the 170-200 kb range. Strain IV was isolated from 19 cases of infections in 3 hospitals in Berlin. The fragment patterns were completely stable. When S. aureus strains are typed by genomic DNA fragment patterns, a variability in a definite range of molecular masses during the course of an epidemic should be taken into consideration. 相似文献
22.
23.
WA Cafruny SE Bradley A Brunick DM Nelson RF Nelson 《Canadian Metallurgical Quarterly》1996,59(1-2):83-89
An animal model of dental virus transmission was developed using the lactate dehydrogenase-elevating virus (LDV) of mice to study cross infection. Mouse-to-mouse cross-infection was carried out by scaling the teeth of LDV-infected donor mice with dental instruments, immediately prior to using the contaminated instruments on the teeth of recipient indicator mice. The level of donor viremia was found to correlate with the rate of virus cross-infection, with a viremia threshold level of 10(7.5) ID50/ml observed for dental cross-infection. The blood volume transferred during dental cross-infection was approximately 10(-4) to 10(-5) ml, demonstrating the inefficiency of virus cross-infection, since deposition of about 1000 virions on dental instruments was associated with the threshold limit. Virus transferred during dental cross-infection rapidly entered the blood circulation, showing that dental cross-infection was not dependent on an oral infection. The results from these model studies predict the general inefficiency of dental instrument virus cross-infection, and a further reduced likelihood of dental cross-infection with appropriately cleaned instruments. 相似文献
24.
Deletion of PHR1, a pH-regulated gene of Candida albicans, results in pH-conditional defects in growth, morphogenesis, and virulence evident at neutral to alkaline pH but absent at acidic pH. Consequently, we searched for a functional homolog of PHR1 active at low pH. This resulted in the isolation of a second pH-regulated gene, designated PHR2. The expression of PHR2 was inversely related to that of PHR1, being repressed at pH values above 6 and progressively induced at more acidic pH values. The predicted amino acid sequence of the PHR2 protein, Phr2p, was 54% identical to that of Phr1p. A PHR2 null mutant exhibited pH-conditional defects in growth and morphogenesis analogous to those of PHR1 mutants but manifest at acid rather than alkaline pH values. Engineered expression of PHR1 at acid pH in a PHR2 mutant strain and PHR2 at alkaline pH in a PHR1 mutant strain complemented the defects in the opposing mutant. Deletion of both PHR1 and PHR2 resulted in a strain with pH-independent, constitutive growth and morphological defects. These results indicate that PHR1 and PHR2 represent a novel pH-balanced system of functional homologs required for C. albicans to adapt to environments of diverse pH. 相似文献
25.
MR Workman PG Wall P Tearle M O'Mahony WA Brunton 《Canadian Metallurgical Quarterly》1995,5(4):R54-R56
In microbiology laboratories highly infectious material is handled alongside complex and potentially dangerous equipment, and staff are therefore at risk of infections and accidents. Acts of parliament and regulations exist to protect staff in the workplace, including those exposed to biological agents. The current monitoring of health and safety in laboratories seeks to ensure that employers and employees comply with existing regulations, but this form of passive surveillance is of limited value because it does not highlight shortcomings in techniques, equipment, premises, or personnel. We propose a scheme for the surveillance of health and safety in microbiology laboratories that will actively seek information about laboratory incidents and practices, in order to enable appropriate preventive measures to be instituted. 相似文献
26.
27.
Most (98%) of the fat in human milk is present as triglycerides. This paper describes the use of a clarification procedure that enables the level of human milk fat to be determined by measurement of glycerol released by enzymic hydrolysis of triglycerides. The method requires only 10-50 microliters milk, thus presenting a possible technique for work with small mammals, and is suitable for use with autoanalysers, permitting rapid sample throughput. 相似文献
28.
29.
CG Tankersley RS Fitzgerald RC Levitt WA Mitzner SL Ewart SR Kleeberger 《Canadian Metallurgical Quarterly》1997,82(3):874-881
The purpose of the present study was to determine the genetic control of baseline breathing pattern by examining the mode of inheritance between two inbred murine strains with differential breathing characteristics. Specifically, the rapid, shallow phenotype of the C57BL/6J (B6) strain is consistently distinct from the slow, deep phenotype of the C3H/HeJ (C3) strain. The response distributions of segregant and nonsegregant progeny were compared with the two progenitor strains to determine the mode of inheritance for each ventilatory characteristic. The BXH recombinant inbred (RI) strains derived from the B6 and C3 progenitors were examined to establish strain distribution patterns for each ventilatory trait. To establish the mode of inheritance, baseline breathing frequency (f), tidal volume, and inspiratory time (TI) were measured five times in each of 178 mature male animals from the two progenitor strains and their progeny by using whole body plethysmography. With respect to f and TI, the two progenitor strains were consistently distinct, and segregation analyses of the inheritance pattern suggest that the most parsimonious genetic model for response distributions of f and TI is a two-loci model. In similar experiments conducted on 82 mature male animals from 12 BXH RI strains, each parental phenotype was represented by one or more of the RI strains. Intermediate phenotypes emerged to confirm the likelihood that parental strain differences in f and TI were determined by more than one locus. Taken together, these studies suggest that the phenotypic difference in baseline respiratory timing between male B6 and C3 mice is best explained by a genetic model that considers at least two loci as major determinants. 相似文献
30.
MJ Hickey Y Wilson JV Hurley WA Morrison 《Canadian Metallurgical Quarterly》1998,101(5):1296-304; discussion 1305-6
This study, using 62 rabbits, examines the rate and pattern of vascular outgrowth from a subcutaneously implanted vascular pedicle, how the newly formed vessels connect to preexisting skin vessels, and whether local application of basic fibroblast growth factor can accelerate the angiogenic process. When the femoral artery and vein of rabbits are implanted beneath the skin, angiogenesis from both the pedicle and small blood vessels within the adjacent skin begins within 3 days. Perfusion with India ink reveals connections between the pedicle and dermal vessels as early as 5 days after implantation of the pedicle. Provided the pedicle does not thrombose, skin flaps based on it may survive completely when elevated as early as 2 weeks after implantation. Flap survival depends on the development of a small number of vascular connections between vessels arising from the pedicle and preexisting dermal vessels. If elevation is delayed until 4 weeks after implantation a flap may survive even if its pedicle has thrombosed. Prolonged release of basic fibroblast growth factor adjacent to the pedicle significantly increases the survival of flaps elevated 1 week after implantation but does not alter the survival of flaps elevated at 2 and 4 weeks. 相似文献