全文获取类型
收费全文 | 1821篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
综合类 | 2篇 |
化学工业 | 60篇 |
金属工艺 | 6篇 |
机械仪表 | 4篇 |
建筑科学 | 25篇 |
矿业工程 | 2篇 |
能源动力 | 5篇 |
轻工业 | 30篇 |
水利工程 | 9篇 |
无线电 | 28篇 |
一般工业技术 | 38篇 |
冶金工业 | 1580篇 |
自动化技术 | 37篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 16篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 14篇 |
2007年 | 19篇 |
2006年 | 7篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 55篇 |
1998年 | 510篇 |
1997年 | 280篇 |
1996年 | 167篇 |
1995年 | 92篇 |
1994年 | 91篇 |
1993年 | 93篇 |
1992年 | 23篇 |
1991年 | 28篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 21篇 |
1987年 | 14篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 37篇 |
1976年 | 103篇 |
1975年 | 6篇 |
1968年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1828条查询结果,搜索用时 15 毫秒
91.
Peek DC Butcher MK Shields WJ Yost LJ Maloy JA 《Environmental science & technology》2002,36(8):1671-1675
Drinking water is supplied by individual roof-catchment systems for homes and businesses near a dissolving sulfite pulp mill (now closed) located just north of Ketchikan in southeast Alaska. This study was conducted to determine if polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) found in the sediments of the roof-catchment cisterns resulted from historical deposition of stack emissions from the pulp mill's multi-fuel power boilers. Fly ash from the power boilers had maximum total PCDD/F concentrations of 3.08 x 10(5)-3.10 x 10(6) ng/kg, which resulted from combustion of bleach plant wastewater sludge and saltwater-soaked wood waste. Cistern sediments had maximum total PCDD/F concentrations of 7.71 x 10(4) ng/kg. Potential sources of PCDDs/Fs in the cistern sediments were considered to be automobile exhaust, heating oil combustion, and private trash burning as well as pulp mill boiler emissions. Discriminant analysis was used to analyze differences between profiles of tetra through octa homologue classes of PCDDs/ Fs (defined as proportional contributions to total concentration) from different source terms. Homologue profiles of potential sources from Ketchikan included in this analysis were fly ash collected from the mill's power boilers and soils collected from background areas (areas with similar PCDD/F sources as the residences [e.g., auto exhaust and burn barrels] near the mill but beyond the zone of aerial deposition of emissions from the mill). Profiles for emissions from automobile exhaust, fertilizers, oil heating, residential trash burning, and residential wood heating were also included in the source "training" data set (for the discriminant analysis) using data from published literature. The classification rules developed from the discriminant analysis were applied to the following test media sampled at Ketchikan: roof-catchment cistern sediments and soils collected from areas in the vicinity of the mill's power boilers (i.e., nearby residential or commercial [developed] areas, on the mill property, and nearby forestlands). The homologue profiles of cistern sediment and nearby developed area soil samples were similar to background soils, whereas the profiles for the forestland soil samples (influenced by emissions from the mill but not other anthropogenic sources) closely matched the fly ash pattern. The homologue profiles of the emission sources from published data were more similar to one another than either background soils or fly ash. Soil samples from the mill property were classified as members of all source groups. On the basis of these analyses, the composition of PCDDs/Fs detected in the cistern sediments is typical of Ketchikan background conditions and not reflective of mill emissions. 相似文献
92.
DA Alexander AA Naji SB Pinion J Mollison HC Kitchener DE Parkin DR Abramovich IT Russell 《Canadian Metallurgical Quarterly》1996,312(7026):280-284
OBJECTIVE: To compare in psychiatric and psychosocial terms the outcome of hysterectomy and endometrial ablation for the treatment of dysfunctional uterine bleeding. DESIGN: Prospective randomised controlled trial. SETTING--Obstetrics and gynaecology department of a large teaching hospital. SUBJECTS: 204 women with dysfunctional bleeding for whom hysterectomy would have been the preferred treatment were recruited over 24 months and randomly allocated to hysterectomy (99 women) or to hysteroscopic surgery (transcervical resection (52 women) or laser ablation (53 women). MAIN OUTCOME MEASURES: Mental state, martial relationship, psychosocial and sexual adjustment in assessments conducted before the operation and one month, six months, and 12 months later. RESULTS: Both treatments significantly reduced the anxiety and depression present before the operation, and there were no differences in mental health between the groups at 12 months. Hysterectomy did not lead to postoperative psychiatric illness. Sexual interest after the operation did not vary with treatment. Overall, 46 out of 185 (25%) women reported a loss sexual interest and 50 out of 185 (27%) reported increased sexual interest. Marital relationships were unaffected by surgery. Personality and duration of dysfunctional uterine bleeding played no significant part in determining outcome. CONCLUSIONS: Hysteroscopic surgery and hysterectomy have a similar effect on psychiatric and psychosocial outcomes. There is no evidence that hysterectomy leads to postoperative psychiatric illness. 相似文献
93.
94.
S Fletcher RG Jones HC Rayner P Harnden LD Hordon JE Aaron B Oldroyd AM Brownjohn JH Turney MA Smith 《Canadian Metallurgical Quarterly》1997,75(4):412-419
Bone biopsies were studied in 73 patients to determine if a two-site radioimmunometric assay for serum bone alkaline phosphatase (BAP), total serum alkaline phosphatase (ALP), serum intact parathyroid hormone (iPTH), hand X-rays, regional bone mineral density (BMD) measurements and parathyroid enlargement detected by ultrasonography could accurately predict renal osteodystrophy. In the patients studied 57 had hyperparathyroid bone disease, 4 mixed renal osteodystrophy, 3 adynamic bone disease, 1 osteomalacia and 8 normal histology. Serum BAP, ALP and iPTH correlated positively with mineral apposition rate, osteoblastic, osteoid and eroded surface. In the diagnosis of hyperparathyroid bone disease serum iPTH was the most sensitive investigation, detecting 81% of patients at a level > 100 pg/ml but with a specificity of only 66%. Serum BAP was more sensitive, 70% at a level of > 10 ng/ml, than serum total ALP, 30% at a level of 300 IU/l, with similar specificities, 92 and 100%, respectively. Ultrasound detection of an enlarged parathyroid gland had a sensitivity of 64% and a specificity of 100% for the diagnosis of hyperparathyroid bone disease. Hand X-rays had a poor sensitivity, 47%, but a high specificity, 92%, for the detection of hyperparathyroid bone disease. The majority of patients had regional BMD values within the normal reference range and this test was of poor discriminatory value. The non-invasive markers were unable to distinguish between patients with low turnover, mild hyperparathyroidism and patients with normal histology. In conclusion the measurement of serum iPTH is a useful screening tool for the detection of hyperparathyroid bone disease which can be confirmed by the finding of a raised serum BAP or parathyroid enlargement. For definitive diagnosis, however, the gold standard remains bone biopsy and at present one cannot recommend any non-invasive method as an adequate substitute. 相似文献
95.
María L Auad Tara Richardson William J Orts Eliton S Medeiros Luiz HC Mattoso Mirna A Mosiewicki Norma E Marcovich Mirta I Aranguren 《Polymer International》2011,60(5):743-750
Segmented polyurethanes exhibiting shape memory properties were modified by the addition of polyaniline (PANI)‐coated cellulose nanofibrils (CNFs). The two‐phase structure of the polymer is responsible for the material's ability to ‘remember’ and autonomously recover its original shape after being deformed in response to an external thermal stimulus. PANI was grown on the surface of the CNFs via in situ polymerization. Modified nanocrystals were added to the segmented polyurethane in concentrations ranging from 0 to 15 wt%. The changes in the material properties associated with the percolation of the coated fibrils appear at higher concentrations than previously observed for non‐modified CNFs, which suggests that fibril agglomeration is occurring due to the PANI coating. The shape memory behavior of the composites is maintained at about the same level as that of the unfilled polyurethane only up to 4 wt% of fibrils. At higher concentrations, the rigidity of the nanofibrils as well as their interaction with the hard‐segment phase and the increasing difficulty of dispersing them in the polymer collaborate to produce early breakage of the specimens when stretched at temperatures above the melting point of the soft segments. Copyright © 2010 Society of Chemical Industry 相似文献
96.
BACKGROUND AND OBJECTIVES: To evaluate the benefit of measuring the intraocular pressure (IOP) on the first postoperative day after argon laser trabeculoplasty (ALT). PATIENTS AND METHODS: We retrospectively reviewed 407 ALT procedures with perioperative apraclonidine performed on 226 patients between January 1991 and December 1993. Data analyzed included type of glaucoma, extent of treatment, whether the procedure was initial or repeat, laser parameters, and IOP preoperatively and at 1 hour, 1 day, and 1 month postoperatively. RESULTS: The percentage of patients with an IOP rise of greater than 3 mm Hg at 1 hour, 1 day, and 1 month following ALT was 11.3%, 4.2%, and 5.2% respectively. The incidence of IOP elevations greater than 10 mm Hg was 2.2%, 1.0%, and 1.5% at 1 hour, 1 day and 1 month, respectively. Of 17 cases with an IOP elevation greater than 3 mm Hg at 1 day, four eventually required a trabeculectomy. However, there were no consistent factors that distinguished which cases with elevated IOP at 1 day ultimately needed further therapy, nor did the 1-day postoperative examination predict which patients would have IOP elevation at 1 month. CONCLUSION: IOP 1 day after ALT is rarely elevated and does not correlate with IOP elevation at 1 month. Therefore, an IOP check at 1 day is not felt to be necessary for most patients. 相似文献
97.
Reconceptualized the distinction between those situations in which one can and cannot expect to observe hypnotic hypermnesia using the levels-of-processing theory of memory, as proposed by F. I. Craik and R. S. Lockhart (see record 1973-20189-001). In Study 1, 20 hypnotized Ss (high hypnotizables), relaxed/motivated Ss (high hypnotizables), and 20 simulating Ss (low hypnotizables) processed lists of words matched for meaningfulness and imagery value at "deep" or "shallow" levels. As predicted, the hypnotized group recalled more deeply but not more shallowly processed stimuli than the control groups. In Study 2, these findings were replicated with 30 undergraduates using improved experimental procedures and were extended to a recognition situation. In neither study was the observed hypnotic enhancement accompanied by an increment in errors. It is concluded that cognition at the time of processing is critical in rendering a stimulus amenable to hypnotic hypermnesia. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
This study was based on 192 patients treated surgically for 228 metastatic lesions of the long bones from 1986 through 1995. The survival rate was 0.3 at 1 year after surgery. The surgical treatment consisted of resection and reconstruction of the involved bone (18), intralesional curettage (133), or stabilization only (77). Reconstruction was achieved by an endoprosthesis in 54 cases, by an osteosynthetic device in 162, by cement only in 10. In two cases no reconstruction was performed. The local failure rate was 11% and the median time to failure was 8 months. Local failure was most frequent in patients with kidney cancer (24%) and in diaphyseal and distal femoral lesions (20%). Among 162 operations involving osteosynthetic devices, 22 (14%) were failures as compared with one of 54 (2%) endoprostheses. Sixty percent of the patients received preoperative or postoperative radiotherapy. Five of the six patients who had surgery for local tumor progression had not received radiotherapy. Eight of 10 nonunions and all five patients who developed a stress fracture had been treated with radiotherapy. It is concluded that endoprosthetic reconstructions are preferable to osteosynthetic devices. The skeletal complications associated with radiotherapy may be circumvented by the use of endoprostheses. 相似文献
99.
HN Nguyen D Frank S Handt HC Rieband N Maurin HG Sieberth S Matern 《Canadian Metallurgical Quarterly》1999,94(1):232-235
Intense immunosuppressive therapy is used frequently for treatment of systemic vasculitides, collagenoses, rapidly progressive glomerulonephritis, and after organ transplantation. Numerous serious treatment-related side effects include localized or disseminated opportunistic infections, and require careful monitoring of immunosuppressed patients. Gastrointestinal infections with Mycobacterium avium complex (MAC) or other nontuberculous mycobacteria have been previously identified in HIV seropositive patients only. We now report the first case of an HIV seronegative patient who received immunosuppressive therapy for rapidly progressive glomerulonephritis. The patient presented with severe lower gastrointestinal bleeding and was diagnosed to have ulcerative colitis due to infection with MAC. The patient recovered promptly after administration of antimycobacterial therapy. MAC infection should be included in the differential diagnosis of gastrointestinal bleeding in all immunodeficient patients. The significance of repeated colonoscopy to obtain multiple biopsy specimens with histological examination for foam cells and specific staining for acid-fast organisms is emphasized. 相似文献
100.