全文获取类型
收费全文 | 1464篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 19篇 |
金属工艺 | 10篇 |
机械仪表 | 7篇 |
建筑科学 | 9篇 |
能源动力 | 4篇 |
轻工业 | 8篇 |
石油天然气 | 2篇 |
无线电 | 6篇 |
一般工业技术 | 34篇 |
冶金工业 | 1344篇 |
原子能技术 | 5篇 |
自动化技术 | 9篇 |
出版年
2022年 | 3篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2013年 | 5篇 |
2012年 | 7篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 4篇 |
1999年 | 33篇 |
1998年 | 452篇 |
1997年 | 276篇 |
1996年 | 143篇 |
1995年 | 89篇 |
1994年 | 62篇 |
1993年 | 79篇 |
1992年 | 13篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 20篇 |
1976年 | 41篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1944年 | 2篇 |
1942年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有1469条查询结果,搜索用时 15 毫秒
51.
The importance of abnormalities of function and epididymis structure in the etiology of male infertility is still not well understood. We studied 52 individuals distributed in five age groups: fetuses, children, adolescents, adults and the elderly. The region of the body of epididymis was obtained by autopsy and immediately fixed by immersion in a solution of 10% buffered formaldehyde, embedded in paraffin and histologically prepared. The samples were observed under an optic microscope. Test-points were counted in 12 random microscopic fields with the M42 test-system. The following stereological parameters were determined: ductal area, volumetric densities (Vv) of the duct, smooth muscle, connective tissue, epithelial duct and blood vessels. The main results distinguished by those whose averages were statistically significant (p < 0.05), showed that the ductal area is 9.7 times greater in the adolescent/adult/elderly group than the children's group. The Vv of the lumen of the epididymis duct occupies 11.7% of the epididymis body in the fetal period, 5.3% in the child and in individuals after puberty this figures reaches more than 15%. The Vv of smooth muscle occupies 28.3% of the body of the epididymis in the fetus and 35.9% in children, but after puberty this figures stays around 22%. The Vv of the connective tissue occupies 26% in prenatal life, 37% in children, and after puberty these figures range from 21 to 27.5%. Comparing the results of the adult group with that of the elderly group there is an increase in the volumetric density of the connective tissue by 18.1%. In conclusion, the epididymal duct area and the Vv of the ductal lumen, smooth muscle and connective tissue were significant comparing the different groups. However, the quantitative relative differences of the duct's epithelium and the blood vessels were not significant comparing these groups. The study of quantitative aspects of the normal human epididymis can increase our knowledge about male fertility. 相似文献
52.
SW Rabkin 《Canadian Metallurgical Quarterly》1994,54(22):1649-1657
The purpose of this study was to examine the roles of brain opioid receptors, using the opioid receptor antagonist naloxone, and brain alpha 2 adrenergic and imidazole receptors, using their agonist clonidine, in the hypertension and tachycardia induced by electrical stimulation of the AHA and PHA area. Unanesthetized and unrestrained Wistar rats 300-400 g that had previously had catheters inserted into the lateral cerebral ventricle and femoral artery and electrodes in AHA or PHA areas received intracerebral (ICV) administration of naloxone or clonidine prior to hypothalamic stimulation. AHA and PHA stimulation with current strength from 0.5 to 2.0 mA produced a significant (p < 0.05) and dose dependent increase in BP and heart rate. Naloxone reduced the increase in BP with AHA stimulation at all but the highest stimulation current intensity. Clonidine also blunted the BP increase to AHA stimulation but to a lesser degree than naloxone. The combination of both naloxone and clonidine completely prevented the increase in BP even at high current intensities. Both naloxone and clonidine prevented the increase in heart rate with AHA stimulation. In contrast to AHA stimulation, naloxone did not alter the BP increase produced by PHA stimulation while clonidine prevented the effects of PHA stimulation. Heart rate did not increase with PHA stimulation. These data suggest that (i) the mechanisms involved in the hypertensive response to AHA are different from that of PHA. (ii) the endogenous opioid system is more operative in mediating the BP elevation produced by AHA but not PHA stimulation (iii) activation of the central alpha adrenergic or imidazole receptors can suppress hypertensive response to both AHA and PHA but is more effective for PHA than AHA stimulation. 相似文献
53.
54.
Many proteins require enzymatic assistance in order to achieve a functional conformation. One rate-limiting step in protein folding is the cis-trans isomerization of prolyl residues, a reaction catalyzed by prolyl isomerases. SurA, a periplasmic protein of Escherichia coli, has sequence similarity with the prolyl isomerase parvulin. We tested whether SurA was involved in folding periplasmic and outer membrane proteins by using trypsin sensitivity as an assay for protein conformation. We determined that the efficient folding of three outer membrane proteins (OmpA, OmpF, and LamB) requires SurA in vivo, while the folding of four periplasmic proteins was independent of SurA. We conclude that SurA assists in the folding of certain secreted proteins. 相似文献
55.
56.
57.
1. Colchicine poisoning, which is relatively rare, is associated with significant morbidity and mortality. Whilst a new treatment modality, in the form of colchicine-specific Fab fragments is on the horizon, currently available therapy is largely supportive. 2. The elimination of colchicine occurs primarily by hepatic metabolism, following a first-order process, with significant enterohepatic circulation. Renal extraction is responsible for approximately 20% of colchicine elimination. 3. We report a case of colchicine intoxication, complicated by the presence of co-ingestants, in which serum colchicine concentrations remained quasi-constant over the 3 days of the patient's survival, consistent with marked alterations both in metabolism and excretion. The initial presentation was relatively benign but the subsequent course was one of severe colchicine poisoning, resulting in death. 4. Severe colchicine toxicity appears to have resulted in a vicious cycle of progressive organ dysfunction and impaired elimination. 5. Josamycin, one of the co-ingestants and an inhibitor of P-glycoprotein, the membrane pump responsible for multidrug resistance, may have played a significant role in impeding the cellular and biliary elimination of colchicine. Co-ingested opioid and anticholinergic compounds may have altered colchicine absorption and gastrointestinal transit. 6. This case serves as a reminder of the need for attention to co-ingested drugs, to early aggressive therapy, and if available, to consideration of immunotherapy. 相似文献
58.
The activity of a new photosensitizer, mono-L-aspartyl chlorin e6 (Npe6), was assessed in an ascending dose Phase I study for patients with superficial tumor. Eleven patients, with a total of 14 tumor sites, were treated with photodynamic therapy (PDT) using Npe6. Lesions included recurrent adenocarcinoma of the breast, basal cell carcinoma, and squamous cell carcinoma. The phototherapy protocol consisted of a single i.v. injection of 0.5-3.5 mg/kg Npe6, followed 4 h later by 25-100 j/cm2 at 664 nm of light. PDT using Npe6 caused no significant toxicity with the exception of temporary generalized skin photosensitivity. In all cases, light treatment caused immediate tissue blanching, followed by a marked necrosis of the tumor mass. Regression of tumor occurred over 24-48 h after the light treatment and was followed by the formation of a heavy eschar over the tumor site. Tumor regression was short-lived at Npe6 doses of 1.65 mg/kg and below. In two of three patients, tumor regression was either incomplete or tumors recurred within the 12-week observation period. Increasing the Npe6 dose to 2.5 or 3.5 mg/kg combined with 100 J/cm2 of light energy resulted in better control of tumor regrowth with 66% (6/9) of sites remaining tumor-free through 12 weeks observation. This increased tumor response came at the expense of the tissue selectivity observed at Npe6 doses of 1.65 mg/kg and below. There was no apparent selectivity for destruction of tumor compared with normal skin at Npe6 doses of 2.5 mg/kg and above. These data demonstrate that Npe6 is both an effective and safe photosensitizer for use in PDT and provide the impetus for continued study in Phase II clinical trials. 相似文献
59.
60.
A Borrelia burgdorferi N40 genomic expression library was screened with serum from actively infected mice to identify gene products that elicit protective immunity. A clone that contained a putative bicistronic operon containing two genes that encoded 20- and 22-kDa lipoproteins was identified and sequenced. These genes showed homology with the genes encoding decorin binding proteins DbpB and DbpA, respectively, of B. burgdorferi 297 and B31. N40-dbpA DNA hybridized with B. burgdorferi N40 DNA on a single 48-kb linear plasmid. Homologous genes could be amplified under various degrees of stringency by PCR or hybridized by Southern blotting from B. burgdorferi sensu stricto N40 and B31, and from B. burgdorferi sensu lato PBi and 25015, but not PKo. Recombinant N40-DbpB and N40-DbpA were reactive with antibody in serum from infected mice, and serum was more reactive against N40-DbpA than against B. burgdorferi N40 recombinant P39, OspC, or OspA. Sera from mice infected with B. burgdorferi sensu lato strains PKo and PBi were weakly reactive against N40-DbpB and N40-DbpA, and sera from mice infected with 25015 were moderately reactive, compared to sera from mice infected with B. burgdorferi N40. Hyperimmunization of mice with N40-DbpA, but not N40-DbpB, induced protective immunity against syringe challenge with cultured B. burgdorferi N40. DbpA may therefore be one of the antigens responsible for eliciting protective antibody known to exist in serum from infected mice. DNA amplification and serology suggest that DbpB and DbpA are likely to have homologs throughout the B. burgdorferi sensu lato family, but they are likely to be heterogeneous. 相似文献