全文获取类型
收费全文 | 3124篇 |
免费 | 22篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 132篇 |
金属工艺 | 3篇 |
机械仪表 | 24篇 |
建筑科学 | 28篇 |
矿业工程 | 1篇 |
能源动力 | 10篇 |
轻工业 | 48篇 |
水利工程 | 16篇 |
石油天然气 | 5篇 |
无线电 | 50篇 |
一般工业技术 | 109篇 |
冶金工业 | 2656篇 |
自动化技术 | 53篇 |
出版年
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 8篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2014年 | 7篇 |
2013年 | 21篇 |
2012年 | 18篇 |
2011年 | 26篇 |
2010年 | 27篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 12篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 94篇 |
1998年 | 775篇 |
1997年 | 453篇 |
1996年 | 287篇 |
1995年 | 163篇 |
1994年 | 163篇 |
1993年 | 165篇 |
1992年 | 38篇 |
1991年 | 48篇 |
1990年 | 51篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 47篇 |
1986年 | 36篇 |
1985年 | 31篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 28篇 |
1979年 | 6篇 |
1978年 | 13篇 |
1977年 | 59篇 |
1976年 | 121篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有3146条查询结果,搜索用时 15 毫秒
41.
Although long-term clinical studies have shown no excessive risk of lymphoma in rheumatoid arthritis (RA) patients treated with methotrexate (MTX), an increasing number of reports of this association continue to appear. We describe two cases, review the cases in the world's literature, and summarize their important characteristics. Possible oncogenic mechanisms are discussed. Most lymphoproliferation cases presented here have features of immunosuppression-associated lymphoma. The immunosuppressed state is attributable to a combination of factors, such as RA itself and the actions of MTX. The risk factors for RA patients to develop lymphoma while on MTX include severe disease, intense immunosuppression, genetic predisposition, and an increased frequency of latent infection with prooncogenic viruses such as Epstein-Barr virus (EBV). The spontaneous remission of lymphomas in eight RA patients after MTX was stopped highlights the likely causative role of the drug in the development of these malignancies. If the clinical situation permits, a period of observation for spontaneous remission after MTX is stopped is advisable. The physicians caring for RA patients on MTX should maintain a high surveillance for signs and symptoms suggestive of lymphoma. 相似文献
42.
Variation in repeated nucleotide sequences (RNSs) at the level of entire families assayed by Southern blot hybridization is remarkably low within species and is a powerful tool for scrutinizing the origin of allopolyploid taxa. Thirty-one clones from RNSs isolated from different Triticeae genera were used to investigate the genome constitution of South American Elymus. One of these clones, pHch2, preferentially hybridized with the diploid H genome Hordeum species. Hybridization of this clone with a worldwide collection of Elymus species with known genome formulas showed that pHch2 clearly discriminates Elymus species with the H genome (StH, StHH, StStH, and StHY) from those with other genome combinations (StY, StStY, StPY, and StP). Hybridization with pHch2 indicates the presence of the H genome in all South American Elymus species except Elymus erianthus and Elymus mendocinus. Hybridization with additional clones that revealed differential restriction fragments (marker bands) for the H genome confirmed the absence of the H genome in these species. Differential restriction fragments for the Ns genome of Psathyrostachys were detected in E. erianthus and E. mendocinus and three species of Leymus. Based on genome constitution, morphology, and habitat, E. erianthus and E. mendocinus were transferred to the genus Leymus. 相似文献
43.
The surface-crack-in-flexure (SCF) method uses a Knoop indenter to create small, semielliptical surface precracks in beam specimens. Lateral cracks may interfere with the primary median crack and cause errors of up to 10% in determination of fracture toughness, particularly for materials for which the fracture toughness is ∼3 MPa·m1/2 or less. Although the residual-stress-damage zone is ground or polished away by hand by removing 4.5–5 times the indentation depth, this amount may not be sufficient to completely remove the lateral cracks in low-fracture-toughness materials. A series of tests were conducted on sintered alpha silicon carbide with different amounts of material removed after indentation. Once the lateral cracks were fully removed, the SCF results concurred with single-edged-precracked-beam and chevron-notched-beam data collected in accordance with ASTM Designation C1421. A simple remedy for the SCF method is to examine the outer ground surface for remnants of lateral cracks before fracture and to remove more material if necessary. 相似文献
44.
45.
46.
CONTEXT: Although the long-term health benefits of good glycemic control in patients with diabetes are well documented, shorter-term quality of life (QOL) and economic savings generally have been reported to be minimal or absent. OBJECTIVE: To examine short-term outcomes of glycemic control in type 2 diabetes mellitus (DM). DESIGN: Double-blind, randomized, placebo-controlled, parallel trial. SETTING: Sixty-two sites in the United States. PARTICIPANTS: A total of 569 male and female volunteers with type 2 DM. INTERVENTION: After a 3-week, single-blind placebo-washout period, participants were randomized to diet and titration with either 5 to 20 mg of glipizide gastrointestinal therapeutic system (GITS) (n = 377) or placebo (n = 192) for 12 weeks. MAIN OUTCOME MEASURES: Change from baseline in glucose and hemoglobin A1c (HbA1c) levels and symptom distress, QOL, and health economic indicators by questionnaires and diaries. RESULTS: After 12 weeks, mean (+/-SE) HbA1c and fasting blood glucose levels decreased with active therapy (glipizide GITS) vs placebo (7.5% 0.1% vs 9.3%+/-0.1% and 7.0+/-0.1 mmol/L [126+/-2 mg/dL] vs 9.3+/-0.2 mmol/L [168+/-4 mg/ dL], respectively; P<.001). Quality-of-life treatment differences (SD units) for symptom distress (+0.59; P<.001), general perceived health (+0.36; P= .004), cognitive functioning (+0.34; P=.005), and the overall visual analog scale (VAS) (+0.24; P=.04) were significantly more favorable for active therapy. Subscales of acuity (+0.38; P=.002), VAS emotional health (+0.35; P=.003), general health (+0.27; P=.01), sleep (+0.26; P=.04), depression (+0.25; P=.05), disorientation and detachment (+0.23; P= .05), and vitality (+0.22; P=.04) were most affected. Favorable health economic outcomes for glipizide GITS included higher retained employment (97% vs 85%; P<.001), greater productive capacity (99% vs 87%; P<.001), less absenteeism (losses = $24 vs $115 per worker per month; P<.001), fewer bed-days (losses = $1539 vs $1843 per 1000 person-days; P=.05), and fewer restricted-activity days (losses = $2660 vs $4275 per 1000 person-days; P=.01). CONCLUSIONS: Improved glycemic control of type 2 DM is associated with substantial short-term symptomatic, QOL, and health economic benefits. 相似文献
47.
48.
IM Boier Martin DC Marinescu RE Lynch TS Baker 《Canadian Metallurgical Quarterly》1997,120(2):146-157
Interferon-gamma (IFN-gamma) has the most potent immunomodulatory activity of all the interferons. This phase II-B study was performed to define time- and dose-dependent immunomodulatory effects mediated by IFN-gamma in a subset of patients with melanoma treated in the dose-seeking therapeutic trial conducted by the Eastern Cooperative Oncology Group E4687 (13). The effects of IFN-gamma (Genentech, San Francisco, CA) were evaluated for phenotype and function of peripheral blood lymphocytes obtained twice prestudy, and on days 2, 9, and 29 of IFN-gamma therapy for 50 patients. Early significant increases in CD4/CD8 ratio (p = 0.001) were noted, largely due to a rise in CD4+ and fall in CD8+ T-cell populations sustained through day 29 at only the lowest dosage. Increased natural killer cell (NK) activity (p = 0.001 on day 9; p = 0.01 on day 29) was accompanied by durable increases in circulating activated NK cells (CD56+DR+% p = 0.001, day 9; p = 0.001, day 29). After initial depression of CD56+ and CD16+ cells on day 2, the total percent of CD56+ and CD16+ cells increased significantly by day 29. Increases in NK cell activity were maximal at doses > or =0.1 mg. Monocyte CD14+ expression of DQ+ rose early (p = 0.011 and 0.001 on days 2 and 9), accompanied by elevation in CD14+DR+ cells that was less significant. Immunomodulatory effects of IFN-gamma reported in this trial have major implications for interpretation of past and current clinical trials, and the design of future trials. This is the first trial in which IFN-gamma has been shown to have significant effects on the T-cell compartment of the immune system. 相似文献
49.
50.
Localization of putative tumor suppressor loci by genome-wide allelotyping in human pancreatic endocrine tumors 总被引:1,自引:0,他引:1
DC Chung SB Brown F Graeme-Cook LG Tillotson AL Warshaw RT Jensen A Arnold 《Canadian Metallurgical Quarterly》1998,58(16):3706-3711
Only two tumor suppressor gene loci, one on 3p25 and the MEN1 gene on 11q13, have thus far been implicated in the pathogenesis of sporadic human pancreatic endocrine tumors (PETs). A genome-wide allelotyping study of 28 human PETs was undertaken to identify other potential tumor suppressor gene loci. In addition to those on chromosomes 3p and 11q, frequent allelic deletions were identified on 3q (32%), 11p (36%), 16p (36%), and 22q (29%). Finer deletion mapping studies localized the smallest regions of common deletion to 3q27, 11p13, and 16p12.3-13.11. Potential candidate genes at these loci include WT1 (11p13), TSC2 (16p13), and NF2 (22q12), but no known tumor suppressor gene localizes to 3q27. The mean fractional allelic loss among these human PETs is 0.126, and no correlation was observed between allelic loss and clinical parameters, including age, sex, hormonal subtype, and disease stage. These findings highlight novel locations of tumor suppressor gene loci that contribute to the pathogenesis of human PETs, and several of these on 3p, 3q, and 22q are syntenic with loci on mouse chromosomes 9 and 16 that are implicated in a murine transgenic model of PETs. 相似文献