全文获取类型
收费全文 | 2314篇 |
免费 | 1篇 |
专业分类
化学工业 | 6篇 |
建筑科学 | 1篇 |
轻工业 | 5篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 1篇 |
一般工业技术 | 4篇 |
冶金工业 | 2290篇 |
自动化技术 | 6篇 |
出版年
2020年 | 1篇 |
2019年 | 2篇 |
2017年 | 1篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2006年 | 2篇 |
2004年 | 2篇 |
2003年 | 3篇 |
1999年 | 89篇 |
1998年 | 757篇 |
1997年 | 463篇 |
1996年 | 267篇 |
1995年 | 155篇 |
1994年 | 133篇 |
1993年 | 122篇 |
1992年 | 13篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 11篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1978年 | 2篇 |
1977年 | 37篇 |
1976年 | 79篇 |
1975年 | 2篇 |
1964年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2315条查询结果,搜索用时 0 毫秒
971.
972.
Adipose tissue is known to consist of at least two compartments, the adipocytes and the non-lipid filled cells. During normal growth and development of the rat epididymal fat pad, these two compartments changed in different manners. From 12 to 35 days of age, the DNA contained in both compartments increased linearly, indicative of hyperplastic growth. From 35 to 70 days of age, the DNA in the non-lipid filled cells continued to increase linearly; DNA in the adipocyte fraction increased more slowly. From 70 to 182 days of age, DNA accretion continued in the non-lipid filled cells while remaining unchanged in adipocytes. From 35 to 70 days of age, an abrupt change in the rate of tissue lipid accumulation occurred, shown both by a tripling of fat cell size and a markedly increased slope in the accumulation of lipid per pad. These data confirm that adipose tissue growth proceeds as suggested by radioactive thymidine incorporation studies and further suggest that a critical period for the onset of lipid filling may begin around 35 days of age. 相似文献
973.
R Vanhoof MP Vanderlinden R Dierickx S Lauwers E Yourassowsky JP Butzler 《Canadian Metallurgical Quarterly》1978,14(4):553-556
The activity of 29 antimicrobial agents was tested against 95 strains of Campylobacter fetus subsp. jejuni isolated from human stools. Furazolidone and gentamycin were the most active agents. The tetracyclines, erythromycin, and chloramphenicol were very active against most of the strains, but with each antibiotic a few resistant strains were found. The penicillins were relatively inactive, and the cephalosporins tested were only active against occasional strains. 相似文献
974.
975.
A survey in fifteen communities and nationwide of consumers' opinions about changes in their local health care system reveals that Americans are surprisingly positive about recent changes in their personal access to and quality of care and consistently negative about changes in the cost of care. Although many consumers think that changes in the system are making things worse, they are optimistic about the trend toward managed care. Subgroup analysis shows that uninsured persons and persons with health problems reported high rates of concern about many of the health system issues we explored, while Medicaid recipients, Hispanics, and African Americans reported positive changes in their access to and quality of care. 相似文献
976.
G Cheng C Cassissi PG Drexler SB Vogel CA Sninsky MP Hocking 《Canadian Metallurgical Quarterly》1996,171(1):85-8; discussion 88-9
BACKGROUND: Previously, we demonstrated that ketorolac, a nonsteroidal antiinflammatory drug (NSAID), prevented postoperative small bowel ileus in a rodent model. The aim of this study was to evaluate the effect of salsalate, an NSAID without antiplatelet effect, on postoperative ileus alone or in combination with morphine. METHODS: Forty-eight rats underwent placement of duodenal catheters and were then randomly assigned to one of eight groups (n = 6). Four groups had standardized laparotomy following drug administration, whereas 4 groups underwent the same treatment without laparotomy: control and morphine animals received 0.1 mL alcohol via the catheter, whereas salsalate and salsalate-plus-morphine animals received salsalate (15 mg/kg) dissolved in 0.1 mL alcohol. The animals also received 0.5 mg/kg morphine (morphine and salsalate plus morphine) or the same volume of saline (control and salsalate) subcutaneously. Transit was measured following the injection of a nonabsorbed marker via the duodenal catheter and is defined as the geometric center (GC) of distribution. An additional 20 rats had serosal electrodes placed on the jejunum, and were assigned to one of four treatment groups (control, salsalate, morphine, and salsalate plus morphine; n = 5 each group). Myoelectric activity was recorded until the reappearance of the migrating myoelectric complex (MMC) following laparotomy. RESULTS: Laparotomy and morphine independently reduced small bowel transit (P = 0.0006 and 0.006, respectively, by three-way analysis of variance [ANOVA]; GC 4.3 +/- 0.2 control versus 2.2 +/- 0.3 laparotomy versus 3.6 +/- 0.4 morphine), but morphine did not further worsen postoperative transit (GC 2.4 +/- 0.4; P = 0.42). Although salsalate did not alter baseline transit, pretreatment improved postoperative transit (P = 0.0002; GC 3.6 +/- 0.4). This effect was lost with the addition of morphine (GC 2.7 +/- 0.2; P = 0.21). The MMCs returned earlier after laparotomy in salsalate-pretreated rats (63 +/- 18 minutes salsalate versus 160 +/- 12 minutes laparotomy; P < 0.01, one-way ANOVA). However, this effect was also lost in animals receiving morphine (106 +/- 16 min; P > 0.05). CONCLUSION: Salsalate improves postoperative small bowel motility in a rodent model; however, this effect is masked by morphine. 相似文献
977.
Oligoribonuclease, a 3'-to-5' exoribonuclease specific for small oligoribonucleotides, was purified to homogeneity from extracts of Escherichia coli. The purified protein is an alpha2 dimer of 40 kDa. NH2-terminal sequence analysis of the protein identified the gene encoding oligoribonuclease as yjeR (o204a), a previously reported open reading frame located at 94 min on the E. coli chromosome. However, as a consequence of the sequence information, the translation start site of this open reading frame has been revised. Cloning of yjeR led to overexpression of oligoribonuclease activity, and interruption of the cloned gene with a kanamycin resistance cassette eliminated the overexpression. On the basis of these data, we propose that yjeR be renamed orn. Orthologs of oligoribonuclease are present in a wide range of organisms, extending up to humans. 相似文献
978.
Putidaredoxin is a di-iron protein whose paramagnetic region is not well characterized by 1H detected NMR. We have studied the structure of this region in greater detail by directly observed 15N NMR of oxidized and reduced putidaredoxin preparations in which the six cysteine residues are selectively labeled with 15N. A new method for preparation of a stable form of reduced putidaredoxin has been developed for use in NMR. The 15N NMR spectra of the oxidized and reduced forms are characteristically different, and we have measured and compared 15N chemical shifts, spin-lattice relaxation times (T1), and chemical shift/temperature dependences for both forms. Evidence for localized valencies of the iron atoms in the reduced form is presented. From the 15N T1 values of the oxidized form, reduced distances of the cysteine backbone 15N nuclei from the center of the Fe2S2 cluster have been calculated. These distances are consistent with those calculated from X-ray crystal structure data for five ferredoxins, and confirm the structural similarity of the Fe2S2 clusters in putidaredoxin and in these ferredoxins in the oxidized state. 相似文献
979.
AT Natarajan SJ Santos F Darroudi V Hadjidikova S Vermeulen S Chatterjee M Berg M Grigorova ET Sakamoto-Hojo F Granath AT Ramalho MP Curado 《Canadian Metallurgical Quarterly》1998,400(1-2):299-312
The radiation accident in focus here occurred in a section of Goiania (Brazil) where more than a hundred individuals were contaminated with 137Cesium on September 1987. In order to estimate the absorbed radiation doses, initial frequencies of dicentrics and rings were determined in 129 victims [A.T. Ramalho, PhD Thesis, Subsidios a tecnica de dosimetria citogenetica gerados a partir da analise de resultados obtidos com o acidente radiologico de Goiania, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, 1992]. We have followed some of these victims cytogenetically over the years seeking for parameters that could be used as basis for retrospective radiation dosimetry. Our data on translocation frequencies obtained by fluorescence in situ hybridization (FISH) could be directly compared to the baseline frequencies of dicentrics available for those same victims. Our results provided valuable information on how precise these estimates are. The frequencies of translocations observed years after the radiation exposure were two to three times lower than the initial dicentrics frequencies, the differences being larger at higher doses (>1 Gy). The accuracy of such dose estimates might be increased by scoring sufficient amount of cells. However, factors such as the persistence of translocation carrying lymphocytes, translocation levels not proportional to chromosome size, and inter-individual variation reduce the precision of these estimates. 相似文献
980.
Resting L1210 cells were treated with nimustine (ACNU), a bifunctional alkylating anticancer agent, for 2 h in a nutrient-depleted medium. The cells were then transferred to a fresh medium and incubated for a further 48 h. Functions of the cells thus prepared were examined in terms of the dye-exclusion of the membrane, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl] -2H-tetrazolium hydroxide, inner salt, sodium salt (XTT)-reducing ability of the mitochondria, and heat generation due to vital metabolism as the measure of cell viability. The cells treated with ACNU were functioning normally in all the cell functions examined but were completely devoid of proliferating capacity. These results suggest the possibility that ACNU might impair the proliferative capacity of the resting cell population inside a solid tumor without causing such impairment to the cells of normal organs and tissues composed of intrinsically non-proliferative cells. 相似文献