全文获取类型
收费全文 | 827篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
综合类 | 2篇 |
化学工业 | 14篇 |
金属工艺 | 4篇 |
轻工业 | 6篇 |
石油天然气 | 1篇 |
无线电 | 1篇 |
一般工业技术 | 2篇 |
冶金工业 | 796篇 |
自动化技术 | 4篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2007年 | 1篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 22篇 |
1998年 | 267篇 |
1997年 | 158篇 |
1996年 | 86篇 |
1995年 | 46篇 |
1994年 | 35篇 |
1993年 | 50篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 31篇 |
1976年 | 54篇 |
1951年 | 1篇 |
1947年 | 3篇 |
排序方式: 共有830条查询结果,搜索用时 15 毫秒
101.
102.
103.
S Shefer G Salen A Honda AK Batta LB Nguyen GS Tint YA Ioannou R Desnick 《Canadian Metallurgical Quarterly》1998,39(12):2471-2476
The mechanism for the catalytic reduction of the double bond at C-7, 8 in 7-dehydrocholesterol by 3beta-hydroxysterol Delta7-reductase was investigated by testing structurally related sterols as substrates and potential inhibitors. The hepatic smooth endoplasmic reticulum was identified as the site of enzyme activity. All putative substrates contained 27 carbons, but differed from 7-dehydrocholesterol by the addition of either an ethyl substituent at C-24 (7-dehydrositosterol), a double bond at C-22 with a methyl substituent at C-24 (ergosterol), epimerization of the hydroxyl from the 3beta- to 3alpha-configuration (7-dehydroepicholesterol), or a saturated double bond at C-5,6 (lathosterol). Two non-steroidal compounds that inhibit 3beta-hydroxysterol Delta7-reductase in vivo (AY 9944 and BM 15.766) were also tested. Ergosterol, 7-dehydrositosterol, and 7-dehydroepicholesterol were reduced at C-7, 8 to form brassicasterol, sitosterol, and epicholesterol, respectively, but 75% less efficiently than 7-dehydrocholesterol. Increasing concentrations of these sterols competitively inhibited 3beta-hydroxysterol Delta7-reductase activity. The double bond at C-7,8 in lathosterol was not reduced. AY 9944 and BM 15.766 inhibited 3beta-hydroxysterol Delta7-reductase activity non-competitively. 3beta-Hydroxysterol-Delta7-reductase activity declined after microsomes were exposed to alkaline phosphatase, and enzyme activity was increased by phosphorylation with Mg2+, and ATP. These results demonstrate that the reduction of the double bond at C-7,8 requires binding of the enzyme protein with the B-ring of the sterol substrate that contains a double bond at C-5,6. The reaction is hindered by substituents located on the apolar side-chain and epimerization of the hydroxyl group in ring A to a 3alpha-configuration. 3beta-Hydroxysterol Delta7-reductase exists in two forms: an active phosphorylated form and an inactive dephosphorylated form. 相似文献
104.
AIM OF STUDY: Intrathecal sufentanil has recently been used in labour as part of a combined spinal epidural technique. This study was conducted to compare its use in combination with bupivacaine for caesarean section with fentanyl added to bupivacaine and bupivacaine alone. METHODS: Sixty ASA I and II patients for non-emergency caesarean section under spinal anaesthesia were divided into three groups to receive 15 micrograms fentanyl added to 7.5 mg bupivacaine, 10 micrograms sufentanil added to 7.5 mg bupivacaine and 7.5 mg bupivacaine. Onset time of sensory blockade, side effects, surgical conditions, neonatal outcome and quality of the anaesthetic was assessed. On the first postoperative day, duration of effective analgesia, side effects and patient satisfaction were noted. RESULTS: The duration of effective analgesia of bupivacaine alone was prolonged with the addition of sufentanil and fentanyl by 358% and 256% respectively. No patient in the sufentanil and fentanyl groups required additional intra-operative analgesics compared with 17.6% of patients in the bupivacaine alone group. There was an increase in incidence of desaturation in the sufentanil group (45%) and fentanyl group (5.6%) compared with the bupivacaine only group (0%). The incidence of pruritus was 35% with sufentanil, 27.8% with fentanyl against 0% with bupivacaine alone. CONCLUSION: The addition of 10 micrograms of sufentanil and 15 micrograms of fentanyl to 7.5 mg of bupivacaine prolonged the duration of effective analgesia and improved intra-operative analgesia. However, the incidence of pruritus and episodes of desaturation were increased more with 10 micrograms sufentanil than with 15 micrograms fentanyl. 相似文献
105.
H Nakai RW Herzog JN Hagstrom J Walter SH Kung EY Yang SJ Tai Y Iwaki GJ Kurtzman KJ Fisher P Colosi LB Couto KA High 《Canadian Metallurgical Quarterly》1998,91(12):4600-4607
Recombinant adeno-associated virus vectors (AAV) were prepared in high titer (10(12) to 10(13) particles/mL) for the expression of human factor IX after in vivo transduction of murine hepatocytes. Injection of AAV-CMV-F.IX (expression from the human cytomegalovirus IE enhancer/promoter) into the portal vein of adult mice resulted in no detectable human factor IX in plasma, but in mice injected intravenously as newborns with the same vector, expression was initially 55 to 110 ng/mL. The expression in the liver was mostly transient, and plasma levels decreased to undetectable levels within 5 weeks. However, long-term expression of human F.IX was detected by immunofluorescence staining in 0.25% of hepatocytes 8 to 10 months postinjection. The loss of expression was likely caused by suppression of the CMV promoter, because polymerase chain reaction data showed no substantial loss of vector DNA in mouse liver. A second vector in which F.IX expression was controlled by the human EF1alpha promoter was constructed and injected into the portal vein of adult C57BL/6 mice at a dose of 6.3 x 10(10) particles. This resulted in therapeutic plasma levels (200 to 320 ng/mL) for a period of at least 6 months, whereas no human F.IX was detected in plasma of mice injected with AAV-CMV-F.IX. Doses of AAV-EF1alpha-F. IX of 2.7 x 10(11) particles resulted in plasma levels of 700 to 3, 200 ng/mL. Liver-derived expression of human F.IX from the AAV-EF1alpha-F.IX vector was confirmed by immunofluorescence staining. We conclude that recombinant AAV can efficiently transduce hepatocytes and direct stable expression of an F.IX transgene in mouse liver, but sustained expression is critically dependent on the choice of promoter. 相似文献
106.
BACKGROUND: Respiratory syncytial virus immunoglobulin intravenous (RSV-IGIV) has been shown to reduce the risk of lower respiratory illness (LRI) hospitalization in preterm infants and infants with bronchopulmonary dysplasia (BPD). The purpose of this analysis was to estimate the economic costs and benefits of prophylaxis with RSV-IGIV in these groups. METHODS: The analysis was performed from a payer's perspective and therefore included only costs and cost savings that would be realized by an insurer. Estimates of the direct costs of prophylaxis and the risk and cost of LRI hospitalization were based on data about preterm very low birth weight infants cared for at our medical center. Estimates of the reduction in risk of LRI hospitalization associated with RSV-IGIV were based on data from a randomized trial (the PREVENT Study). RESULTS: The range of cost for a five-dose course of RSV-IGIV was estimated to be $3280 to $8800 for infants weighing 1.2 to 10.0 kg at the time of the initial dose. Risks of LRI hospitalization were estimated to be 12, 17 and 28%, respectively, for preterm infants without BPD, with mild BPD and with moderate to severe BPD. Estimates of duration and per diem cost of LRI hospitalizations were, respectively, 5 days and $971. The estimated net cost of prophylaxis per infant ranged between $5415 for a 6-kg infant without BPD to $1689 for an infant with BPD and age < or =3 months. CONCLUSIONS: The cost of RSV-IGIV typically exceeds the cost of hospitalizations prevented by several thousand dollars. Cost minus benefit is lower for infants with BPD and infants 3 months of age or younger. 相似文献
107.
This study was designed to determine what effect physical training has on heart rate and stroke volume responses to exercise stress and to determine if exercise altered the distribution of uterine blood flow. Measurements were made in ten pregnant ewes at rest and immediately following exercise on a treadmill. Five ewes underwent physical training for 3 wk prior to measurement. An increase in heart rate with no change in stroke volume was observed following exercise in both trained and untrained ewes. Total uterine blood flow was not changed following exercise, but distribution was altered in favor of the placenta. Blood flow was evenly distributed within the placenta before and after exercise. The redistribution of flow to the placenta that occurs after exercise. tphe redistribution of flow to the placenta that occurs after exercise might represent a compensatory mechanism for the fetus. 相似文献
108.
LB Simper 《Canadian Metallurgical Quarterly》1976,138(29):1757-1758
109.
110.
Cells of nasal placode of chick embryos were studied with thymidine H3 and autoradiography. Our results shown, that the nuclei in the nasal placode synthesize DNA in the outer zone, then migrate toward the inner zone to undergo division and subsequently return to the outer zone. 相似文献