全文获取类型
收费全文 | 1486篇 |
免费 | 0篇 |
专业分类
化学工业 | 13篇 |
机械仪表 | 1篇 |
建筑科学 | 1篇 |
轻工业 | 2篇 |
石油天然气 | 3篇 |
无线电 | 5篇 |
一般工业技术 | 3篇 |
冶金工业 | 1455篇 |
原子能技术 | 1篇 |
自动化技术 | 2篇 |
出版年
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2013年 | 1篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2000年 | 1篇 |
1999年 | 27篇 |
1998年 | 408篇 |
1997年 | 274篇 |
1996年 | 150篇 |
1995年 | 103篇 |
1994年 | 75篇 |
1993年 | 91篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 13篇 |
1980年 | 23篇 |
1978年 | 3篇 |
1977年 | 59篇 |
1976年 | 130篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1486条查询结果,搜索用时 15 毫秒
71.
To evaluate the efficacy and safety of low dose (10 mg) pravastatin in hypercholesterolemic, hypertensive elderly subjects undergoing antihypertensive treatment, a randomized, double-blind, placebo-controlled 6-month trial was conducted. The subjects had a total plasma cholesterol of at least 250 mg/dL and had been, for at least 3 months, consuming a standard lipid-lowering diet (American Heart Association Step 1 Diet). Sixty elderly hypertensive patients randomly received placebo (n = 30) or pravastatin (n = 30) treatment. The dosage consisted of 10 mg of pravastatin daily during the 6-month trial. Over that period, in the pravastatin group, plasma levels of total cholesterol and LDL-cholesterol significantly (P < .01) dropped (-20% and -25%, respectively) compared to the placebo group. The plasma level of HDL-cholesterol increased (+5%) while triglycerides slightly decreased (-8%) (P < .05). No serious side effects occurred, and pravastatin was generally tolerated. Fasting hyperinsulinemia (11.0 +/- 0.8 v 9.3 +/- 0.7 microU/mL; P = .06) also improved, although not significantly, after 6 months of pravastatin therapy. Results from this study confirmed that a low dose (10 mg) of pravastatin daily is a safe and effective method of reducing plasma total and LDL-cholesterol in hypercholesterolemic, hypertensive elderly patients who are on concurrent antihypertensive drug therapy. 相似文献
72.
73.
Skin ulcers are the most common chronic wounds. Current management principles and theories of causation of the most common ulcers--pressure, diabetic, and venous--are described. Issues related to occlusive dressings, compression dressings, topical antimicrobials, debridement, growth factors, grafting, and bioengineered tissue therapy are discussed. Special emphasis is placed on regulatory concerns. 相似文献
74.
Proteins are targeted to the membrane and matrix of peroxisomes by distinct pathways. Recent observations suggest a further route: a subset of peroxisomal membrane proteins might be targeted first to the endoplasmic reticulum, and from there to peroxisomes by vesicle-mediated transport. 相似文献
75.
The present study assesses the endocrinological, endometrial histology and vaginal ultrasound profiles of nomegestrol acetate subdermal implant users at varying times after insertion. Follicle stimulatory hormone, luteinizing hormone, oestradiol, progesterone, vaginal ultrasound assessment of the ovaries and the histological dating of the endometrium were serially assessed for a period of 50 days immediately after the insertion, and after at 6 months and 12 months of use. The endocrinological results of this prospective observational clinical trial indicated that 75% of the cycles across the study period in Uniplant users were anovulatory, 63% showing development of a persistent non-luteinized follicle. Anovulatory cycles devoid of follicular development were seen primarily in the first months after Uniplant insertion. Ovulatory cycles represented 25% of the Uniplant cycles. Inadequate luteal phase or disregulation of follicular growth was a common feature of ovulatory cycles. In conclusion, these findings suggest that the contraceptive mechanisms of a single nomegestrol acetate subdermal implant involve prevention of follicular growth, development of a persistent non-luteinized follicle, inadequate luteal phase and disruption of the endometrial architecture. 相似文献
76.
PJ Colletier AS Garden WH Morrison H Goepfert F Geara KK Ang 《Canadian Metallurgical Quarterly》1998,20(8):674-681
BACKGROUND: This retrospective study assesses the outcomes and patterns of failure in patients with squamous cell carcinoma metastatic to cervical lymph nodes from an unknown primary site treated with combined surgery and postoperative radiotherapy. METHODS: One hundred thirty-six patients with squamous cell carcinoma metastatic to cervical lymph nodes from an unknown primary source were treated postoperatively with radiotherapy at the University of Texas M. D. Anderson Cancer Center between the years 1968 and 1992. Stage distribution was: N1, 31 patients; N2a, 49; N2b, 25; N2c, 3; N3, 18; and Nx, 10. Thirty-nine patients had excisional biopsies only, 64 patients underwent modified neck dissections, and 33 had radical neck dissections. Extracapsular extension was present in 87 cases. Fifty-nine patients had multiple nodes involved. The median duration of follow-up for surviving patients was 8.7 years. RESULTS: Twelve patients, all with extracapsular nodal disease, developed regional relapse. The 5-year actuarial rates of regional relapse in patients with and without extracapsular nodal disease were 16% and 0%, respectively (p = .004). Nine patients (22%) with extracapsular disease and multiple nodes relapsed compared with three patients (7%) with extracapsular disease and a solitary node (p = .02). None of the patients treated with excisional biopsy and radiotherapy relapsed regionally. No statistically significant relationship between dose, treatment duration, time interval between surgery, and the start of radiotherapy and relapse was detected. The 2-, 5-, and 10-year actuarial disease-specific survival rates were 82%, 74%, and 68%, respectively. Fourteen patients developed cancers in head and neck mucosal sites; six of these cancers were located in unirradiated tissues. CONCLUSIONS: Relapse occurred infrequently in patients treated with excisional biopsies and postoperative radiotherapy. Extracapsular extension and multiple nodes were associated with worse regional control and disease-specific survival. These results appear consistent with those expected for patients with advanced neck disease and a known primary site, and the absence of a primary site should not exclude patients from studies aiming to improve outcomes in patients with extensive neck disease from a head and neck squamous cell cancer. We continue to recommend radiation to the necks and pharyngeal axis for patients suspected of having residual microscopic disease following surgery for squamous cell carcinoma metastatic to the neck from an unknown primary site. 相似文献
77.
Molecular models of an oligodeoxynucleotide-peptide conjugate complexed to an RNA hairpin loop were constructed to assess the effect of stereoisomerism at the point of attachment of the peptide to the oligodeoxynucleotide on the affinity of the conjugate for an RNA target. The peptide portion of the oligodeoxynucleotide-peptide conjugate, (L-lysine)8, was covalently attached to the N-allyl group of (D)- or (L)-aspartic alcohol that was incorporated into the interior of an antisense oligodeoxynucleotide. The stereocenter in the oligodeoxynucleotide interior originates from either (D)- or (L)-aspartic alcohol. The oligodeoxynucleotide portion of the oligodeoxynucleotide-peptide conjugate forms Watson-Crick base pairs with the single-stranded RNA that flanks the RNA hairpin loop. The positively charged peptide makes specific electrostatic contacts with the negatively charged phosphate backbone of the RNA hairpin loop when attached to the N-allyl of (D)-aspartic alcohol but does not have the proper orientation to make these electrostatic contacts when attached to the N-allyl of (L)-aspartic alcohol. This modelling study emphasizes the importance of stereocontrol at the point of branching in synthesizing oligodeoxynucleotide-peptide conjugates for binding of RNA hairpin loops. 相似文献
78.
79.
LE Pyle WH Sawyer Y Fujiwara A Mitchell NH Fidge 《Canadian Metallurgical Quarterly》1996,35(37):12046-12052
Utilizing the Escherichia coli/pGex vector expression system incorporating a thrombin cleavage site, full-length (residues -6-243) and truncated forms of proapolipoprotein AI (proapoAI), terminating at amino acid residues 222, 210, 150, and 135, were purified to levels of at least 5 mg/L, after thrombin cleavage. Assessed by circular dichroism, the helical contents of L-alpha-dimyristoylphosphatidylcholine-associated forms of human plasma-derived apolipoprotein AI (apoAI) and recombinant proapoAI were comparable, being 69% and 65%, respectively. Circular dichroism measurements of the lipid-associated complexes of the truncated forms showed that between the sequence of residues 150-222 no additional helicity was gained until the carboxyl-terminal sequence was present in the molecule, indicating that the carboxyl terminus of the protein is required for the formation of helix within this central region. While tryptophan residues were more than 86% accessible, as assessed by iodide quenching, in the two truncated forms, proapoAI-6-135 and proapoAI-6-150, for both free and complexed protein, this figure fell to about 50% for full-length recombinant proapoAI, further indicating the influence of the carboxyl terminus on the structure of the whole protein. While cross-linking human plasma apoAI in solution with dithiobis-(succinimidyl propionate) revealed high molecular weight oligomers by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, recombinant proapoAI did not strongly form complexes larger than trimers. None of the truncated proapoAI molecules formed oligomers larger than trimers. The shortest form, proapoAI-6-135, only dimerized. Initial results from lecithin:cholesterol acyltransferase activation (apoAI peptide concentration 0.2 microM) indicated that truncation of the 21 carboxy-terminal amino acids resulted in a drop of approximately 53% in activation and 33 residues a drop of 67% relative to the full-length protein. Overall these results indicate the important influence of the carboxyl terminus on the structure of apoAI. 相似文献
80.