全文获取类型
收费全文 | 506280篇 |
免费 | 7395篇 |
国内免费 | 1468篇 |
专业分类
电工技术 | 9611篇 |
综合类 | 437篇 |
化学工业 | 75512篇 |
金属工艺 | 20559篇 |
机械仪表 | 18150篇 |
建筑科学 | 13599篇 |
矿业工程 | 1709篇 |
能源动力 | 12130篇 |
轻工业 | 48823篇 |
水利工程 | 4582篇 |
石油天然气 | 3451篇 |
武器工业 | 18篇 |
无线电 | 62928篇 |
一般工业技术 | 98734篇 |
冶金工业 | 85343篇 |
原子能技术 | 6748篇 |
自动化技术 | 52809篇 |
出版年
2021年 | 3268篇 |
2020年 | 2379篇 |
2019年 | 3047篇 |
2018年 | 13184篇 |
2017年 | 13804篇 |
2016年 | 9733篇 |
2015年 | 4797篇 |
2014年 | 6731篇 |
2013年 | 21232篇 |
2012年 | 14133篇 |
2011年 | 23986篇 |
2010年 | 20044篇 |
2009年 | 20466篇 |
2008年 | 21034篇 |
2007年 | 23278篇 |
2006年 | 13388篇 |
2005年 | 16006篇 |
2004年 | 13811篇 |
2003年 | 13135篇 |
2002年 | 11855篇 |
2001年 | 11424篇 |
2000年 | 10640篇 |
1999年 | 11042篇 |
1998年 | 25420篇 |
1997年 | 18531篇 |
1996年 | 14514篇 |
1995年 | 11363篇 |
1994年 | 10063篇 |
1993年 | 9717篇 |
1992年 | 7254篇 |
1991年 | 6936篇 |
1990年 | 6491篇 |
1989年 | 6215篇 |
1988年 | 5969篇 |
1987年 | 4981篇 |
1986年 | 4918篇 |
1985年 | 6074篇 |
1984年 | 5678篇 |
1983年 | 4893篇 |
1982年 | 4574篇 |
1981年 | 4535篇 |
1980年 | 4292篇 |
1979年 | 4124篇 |
1978年 | 3813篇 |
1977年 | 4711篇 |
1976年 | 6460篇 |
1975年 | 3147篇 |
1974年 | 3048篇 |
1973年 | 2932篇 |
1972年 | 2335篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
OBJECTIVE: To evaluate the efficacy of terazosin, an alpha-blocker, for the treatment of idiopathic oligozoospermia. PATIENTS AND METHODS: Thirty couples with infertility whose only detectable abnormality was male idiopathic subfertility entered the study. The diagnosis of idiopathic subfertility in all males studied, aged 26 to 38 years (mean 28.2 years), was confirmed after exclusion of any iatrogenic, systemic, congenital, infectious, autoimmune or endocrinological cause. In order to start with a baseline value before the study, at least three semen samples were evaluated in accordance with the WHO recommendation. Before initiation of treatment, blood samples were drawn for measurement of FSH, LH, testosterone, prolactin, dihydrotestosterone, and estradiol. Fifteen randomly selected patients (Group A) received 2 mg/d of alpha-blocker (terazosin), while another 15 (Group B) were administered an identically packed placebo tablet. Both groups received therapy for 6 months. RESULTS: The mean seminal volume changed insignificantly between the two groups (4.15 +/- 1.95 vs. 4.10 +/- 1.95). There was a statistically significant increase of the sperm concentration in patients who received the alpha-blocker compared to those receiving placebo (24.76 +/- 9.45 vs. 13.15 +/- 11.55 millions/mL; P < .001). No improvement of the mean percentage of abnormal spermatozoa was observed in the treated patients, nor a statistically significant difference of sperm motility in the treated group compared to the placebo group. Side effects were not observed in the patients receiving terazosin treatment, or were so minimal that therapy was continued. The pregnancy rates did not differ between the two groups to a statistically significant degree. CONCLUSION: The administration of terazosin to patients with idiopathic oligozoospermia has a demonstrably positive effect, especially on sperm concentration. 相似文献
992.
993.
A random sample of patients (n = 43) had been investigated to detect any difference in response of bright light therapy in lithium-treated inpatients (n = 18) suffering from depression. Only 27% of the lithium-based inpatients respond to bright light therapy, but 73% of patients respond who were not treated with lithium. We conclude that lithium therapy reduces the chance of achieving t remission of depression by bright light therapy. 相似文献
994.
JN Vauthey RJ Tomczak T Helmberger P Gertsch C Forsmark J Caridi A Reed MR Langham GY Lauwers P Goffette J Lerut 《Canadian Metallurgical Quarterly》1997,113(4):1390-1401
BACKGROUND & AIMS: Arterioportal fistulas (APFs) are rare vascular disorders of the mesenteric circulation. The aim of this study was to determine the etiology, anatomical location, and main symptom at presentation of APFs, and analyze the various modes of treatment. METHODS: The etiology, clinical presentation, radiographs, and treatment of 12 patients with APFs are reported in detail, and another 76 cases published since 1980 are reviewed. RESULTS: APFs result from trauma (n = 25, 28%), iatrogenic procedures (n = 14, 16%), congenital vascular malformations (n = 13, 15%), tumor (n = 13, 15%), aneurysm (n = 12, 14%), and other causes (n = 11, 12%). The origin of APFs is the hepatic artery in the majority of patients (n = 56, 65%). The main symptoms at presentation are lower or upper gastrointestinal bleeding (n = 29, 33%), ascites (n = 23, 26%), heart failure (n = 4.5%), or diarrhea (n = 4.5%). Radiological intervention provides definitive treatment in 42% (n = 33) of patients, whereas the remainder are treated by surgery alone (n = 27, 31%) or a combination of radiological intervention and surgery (n = 8, 9%). CONCLUSIONS: APFs result in a protean syndrome variously combining portal hypertension and other hemodynamic imbalances (heart failure, intestinal ischemia). Single or multiple interventional radiological procedures using arterial and/or venous approaches allow definitive treatment of most APFs. With increasing technological advances, it is anticipated that surgery will only be indicated in rare instances after failure of radiological intervention(s). 相似文献
995.
A detection error mechanism termed delay ambiguity is identified as one of the main causes of the irreducible bit error rate observed for data detection over fast fading communication channels. A periodic sequence of phase rotations applied to the phase shift keyed (PSK) transmit data symbols is proposed to prevent this type of detection error 相似文献
996.
A chromosomally integrated Bradyrhizobium japonicum hoxA mutant is unable to oxidize hydrogen in free-living conditions. Derepressing conditions that induce hydrogenase activity in free-living, wild-type B. japonicum cells cannot induce expression of the hydrogenase structural genes in the hoxA mutant. The DNA-binding capacity of HoxA at the hup promoter region was studied by means of gel retardation. Both heterotrophically growing cells and cells induced to express hydrogenase activity contain a protein that specifically binds to the hup promoter region. Crude protein extracts isolated from a B. japonicum hoxA mutant do not contain this binding compound. The HoxA protein was overexpressed in E. coli and isolated in the form of a maltose-binding protein (MBP)-HoxA fusion. The MBP-HoxA hybrid protein specifically bound to a 50 bp region of the hupSL promoter known to be important for regulation of hupSL expression. 相似文献
997.
J Weber P Majer J Litera J Urban M Soucek J Vondrásek J Konvalinka P Novek J Sedlácek P Strop HG Kr?usslich I Pichová 《Canadian Metallurgical Quarterly》1997,341(1):62-69
The results of investigation of haptoglobin (Hp) types in 596 donor blood samples in some towns of Ukraine (Dnepropetrovsk, Kharkov, Odessa, Kiev, Uzhgorod, Zhitomir) are presented. Three normal Hp types (Hp1-1, Hp2-1 and Hp2-2) have been found. The reliable interpopulation differences in the Hp types frequency were not found. On the whole the Hp types frequency in the type Hp1-1 comprised 12.7%. In the type Hp2-1-48.1% and in the type Hp2-2-36.5%. The frequency of the gene Hp1 is 0.38. The frequency of the Hp types and of the gene Hpl in Ukraine is similar to that in population of Eastern Europe and European Part of Russia. 相似文献
998.
S. Vaynman R. S. Guico M. E. Fine S. J. Manganello 《Metallurgical and Materials Transactions A》1997,28(5):1274-1276
999.
Wernicke encephalopathy is considered a complication of dialytic therapy, but there are few reports of this complication. We report a 57 years old man and a 45 years old woman, with grade IV renal failure, who after acute peritoneodialysis and chronic hemodialysis respectively, had a confusional syndrome that responded to the administration of thiamine. CT scans in both patients discarded abnormal blood collections or new cerebrovascular episodes. The man bad two previous cerebrovascular episodes, a severe anemia that was corrected, angina and an episode of arrhythmia during the dialytic procedure previous to the confusional episode. The woman had an acute uremic syndrome and a concomitant urinary tract infection during the confusional episode. Wernicke encephalopathy must be suspected in patients in dialysis with confusional episodes. 相似文献
1000.
E Espinosa-Huerta A Robles-Páramo L Viniegra-Velázquez 《Canadian Metallurgical Quarterly》1997,49(6):469-474
PURPOSE: To compare the response rates, toxicities and survival durations of elderly patients (70 years of age or more) with those of younger patients (less than 70 years of age) with non-small-cell lung cancer (NSCLC) treated with cisplatin-based chemotherapy. PATIENTS AND METHODS: We analyzed retrospectively the data of 203 assessable patients entered on a prospective randomized trial of cisplatin-based combination chemotherapy. Chemotherapy consisted of three dosage regimens: (1) vindesine and cisplatin (VP); (2) mitomycin, vindesine and cisplatin (MVP); or (3) etoposide and cisplatin alternating with vindesine and mitomycin (EP/VM). RESULTS: A greater proportion of elderly patients had localized disease and more squamous cell carcinoma than non-elderly patients. The overall response rates were 44% in the elderly group and 28% in the non-elderly group. In the EP/VM arm, the response rate was significantly better in the elderly group than in the non-elderly group. The frequency of grade 4 leukocytopenia in the MVP and EP/VM arms in the elderly group was significantly greater than in the non-elderly group (P < 0.05). No differences were found in nonhematological toxicities between the two groups. There was no difference in overall survival between the groups. CONCLUSION: Elderly patients treated with mitomycin-containing regimens have higher hematologic toxicities than younger patients. The results of this study are consistent with the previously reported pharmacologic data on mitomycin suggesting altered pharmacokinetics in elderly patients. The improved response rate in the elderly patients was probably because more elderly patients had earlier disease, squamous cell carcinoma and better performance status. Cisplatin-based chemotherapy was tolerable for most elderly NSCLC patients with good performance status. 相似文献