全文获取类型
收费全文 | 555533篇 |
免费 | 7495篇 |
国内免费 | 2006篇 |
专业分类
电工技术 | 10087篇 |
综合类 | 570篇 |
化学工业 | 83005篇 |
金属工艺 | 22163篇 |
机械仪表 | 16146篇 |
建筑科学 | 13328篇 |
矿业工程 | 2383篇 |
能源动力 | 15459篇 |
轻工业 | 48559篇 |
水利工程 | 5469篇 |
石油天然气 | 10253篇 |
武器工业 | 37篇 |
无线电 | 62630篇 |
一般工业技术 | 109288篇 |
冶金工业 | 109148篇 |
原子能技术 | 11054篇 |
自动化技术 | 45455篇 |
出版年
2022年 | 3297篇 |
2021年 | 5126篇 |
2020年 | 3680篇 |
2019年 | 4805篇 |
2018年 | 8234篇 |
2017年 | 8026篇 |
2016年 | 8443篇 |
2015年 | 5942篇 |
2014年 | 9794篇 |
2013年 | 25780篇 |
2012年 | 15543篇 |
2011年 | 21433篇 |
2010年 | 16827篇 |
2009年 | 18963篇 |
2008年 | 19197篇 |
2007年 | 19039篇 |
2006年 | 16515篇 |
2005年 | 15080篇 |
2004年 | 14456篇 |
2003年 | 14145篇 |
2002年 | 13378篇 |
2001年 | 13642篇 |
2000年 | 12516篇 |
1999年 | 13306篇 |
1998年 | 34392篇 |
1997年 | 24133篇 |
1996年 | 18521篇 |
1995年 | 13767篇 |
1994年 | 11846篇 |
1993年 | 11578篇 |
1992年 | 8364篇 |
1991年 | 7822篇 |
1990年 | 7652篇 |
1989年 | 7393篇 |
1988年 | 6763篇 |
1987年 | 6088篇 |
1986年 | 5936篇 |
1985年 | 6552篇 |
1984年 | 6121篇 |
1983年 | 5398篇 |
1982年 | 5102篇 |
1981年 | 5175篇 |
1980年 | 4960篇 |
1979年 | 4839篇 |
1978年 | 4618篇 |
1977年 | 5649篇 |
1976年 | 7454篇 |
1975年 | 4017篇 |
1974年 | 3748篇 |
1973年 | 3866篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
During the 1980s, the ecologic association of conjugated estrogens with endometrial cancer changed from positive to negative in a prepaid health plan. During the same period, use of progestins increased dramatically. We investigated whether the latter increase could explain the reversal of the estrogen-cancer association. Endometrial cancer incidence was estimated from cases recorded in the health plan registry divided by the number of women over age 45 years. Conjugated estrogens usage was measured as milligrams prescribed per woman per year and progestin was measured as tablets per woman per year, both based upon pharmacy records. Graphical and regression methods were used to analyze the resulting ecologic data. In a log-linear regression of incidence on conjugated estrogens and medroxyprogesterone usage, estrogen usage had a strong positive association with incidence, while medroxyprogesterone had a strong negative association with incidence. The change in the direction of the ecologic association between estrogen and endometrial cancer that occurred in 1984 continued until 1993, suggesting that the decline in endometrial cancer incidence and concomitant increase in conjugated estrogens usage since 1984 is explained by the increasing use of progestins. The data are entirely consistent with the hypothesis that progestins can protect against most of the excess risk conferred by conjugated estrogens, although the ecologic nature of the data prohibits drawing further inferences. 相似文献
172.
Application of the polymerase chain reaction (PCR) method for detection of subgenus B adenoviruses (types 3, 7 and 11) was investigated. It is based on a simple (nonnested) PCR using primer pairs specific for the hexon-coding region. The PCR allowed amplification of DNA from subgenus B adenovirus prototype strains (types 3, 7 and 11) and adenovirus isolates (types 3 and 7), whereas it did not amplify DNA from subgenus A (type 31), C (types 1, 2, 5 and 6), D (types 8, 19 and 37), E (type 4) and adenovirus isolates (types 1, 2, 5 and 6). These results suggest that subgenus B adenoviruses (types 3, 7 and 11) are detectable selectively by means of PCR with primer pairs developed in this study. Amplified fragments from adenovirus types 3, 7 and 11 could be differentiated with restriction endonuclease analysis with Rsa I. 相似文献
173.
PURPOSE: To develop risk-based recommendations for mammographic screening for women in their 40s that take into account the woman's age, race, and specific risk factors. METHODS: We assumed that regular mammographic screening is justified for a 50-year-old woman, even one with no risk factors, and that a younger woman with an expected 1-year breast cancer incidence rate as great or greater than that of a 50-year-old woman with no risk factors would benefit sufficiently to justify regular screening. Recommendations under this criterion were based on age- and race-specific breast cancer incidence rates from the National Cancer Institute's (NCI's) Surveillance, Epidemiology, and End Results (SEER) Program; assessments of risk factors from the Breast Cancer Detection and Demonstration Project (BCDDP); and reports in the literature. RESULTS: Two methods, the exact-age procedure (EAP) and the grouped-age procedure (GAP), were developed. The less precise GAP only requires following a flow diagram. The proportion of white women recommended for screening by the EAP ranges from 10% for 40-year-old women to 95% for 49-year-old women, and the corresponding percentages for black women are 16% and 95%. The assumptions that underlie the guidelines are discussed critically. CONCLUSION: For women or physicians who prefer an individualized approach in deciding whether to initiate regular mammographic screening in the age range of 40 to 49 years, the present report offers recommendations based on individualized risk-factor data and clearly stated assumptions that have an empiric basis. These recommendations can be used to facilitate the counseling process. 相似文献
174.
175.
E Campagnutta R Cannizzaro M De Cicco G De Piero G Giorda F Sopracordevole A Parin C Scarabelli 《Canadian Metallurgical Quarterly》1998,50(7-8):305-311
BACKGROUND AND AIMS: Intestinal obstruction is a frequent cause of death in patients suffering from gynecological cancer, who have undergone multiple treatment in the form of surgery and/or chemotherapy and/or radiotherapy. The usual form of rescue treatment consists in the use of a nasogastric tube to administer support and analgesic treatment. Surgical gastrostomy is not a viable proposition in these extremely weak patients with large masses compressing and displacing the stomach. Percutaneous endoscopic gastrostomy (PEG), a technique first introduced for nutritional purposes, can be beneficially used to achieve decompression in these patients. METHODS: PEG was performed in a total of 67 patients who had already undergone multiple treatment for abdominal-pelvic neoplasia with upper gastrointestinal obstruction, who could no longer be operated and who had a life expectancy of less than sixty days. In three cases positioning was not possible owing to the lack of transillumination of the gastric and abdominal wall. 54/64 patients had previously undergone at least two operations. RESULTS: Esophagogastric lesions were found in 29% of patients, some of which were attributed to the nasogastric tube. Symptomatic wellbeing was obtained in 76.5% a few days after PEG. PEG remained in situ from 4 to 472 days. Slight peristomal infection was observed in 9% of cases. In seven cases it was necessary to add octreotide owing to the reappearance of symptoms. CONCLUSIONS: PEG is relatively easy to use and allows obstructive symptoms to be resolved in the majority of patients. Special medical skills are not required and the patient may be easily managed at home together with support therapy and pain management. Once PEG has been performed, it is possible to take fluids and semi-liquid foods, offering the patient a chance to taste flavours which have often been forgotten. PEG enables neoadjuvant chemotherapy to be performed in patients with previously untreated intestinal obstruction. 相似文献
176.
R Feldman M Bacher N Campbell A Drover A Chockalingam 《Canadian Metallurgical Quarterly》1998,89(5):I16-I18
Adherence to pharmacologic therapy of hypertension is low (in the range of 50-70%) and has important implications both for blood pressure control and cardiovascular complications. Based on a review of the literature using the levels of evidence grading technique, determinants of adherence to the pharmacologic therapy of hypertension have been assessed. Additionally, interventions to improve compliance were evaluated. Patient-centred, health care provider-centred and drug-specific factors have all been shown to affect adherence rates. We conclude that the extent of adherence to pharmacologic therapy is modifiable. Measurable improvements in adherence can be obtained from simplified medication regimens and a combination of behaviour strategies, including the tailoring of pill-taking to patients' daily habits and rituals, the advocacy of self-monitoring of pills and blood pressure, and the institution of reward systems. 相似文献
177.
178.
179.
MA Steller KJ Gurski M Murakami RW Daniel KV Shah E Celis A Sette EL Trimble RC Park FM Marincola 《Canadian Metallurgical Quarterly》1998,4(9):2103-2109
Human papillomavirus (HPV) infection has been causally associated with cervical cancer. We tested the effectiveness of an HLA-A*0201-restricted, HPV-16 E7 lipopeptide vaccine in eliciting cellular immune responses in vivo in women with refractory cervical cancer. In a nonrandomized Phase I clinical trial, 12 women expressing the HLA-A2 allele with refractory cervical or vaginal cancer were vaccinated with four E786-93 lipopeptide inoculations at 3-week intervals. HLA-A2 subtyping was also performed, and HPV typing was assessed on tumor specimens. Induction of epitope-specific CD8+ T-lymphocyte (CTL) responses was analyzed using peripheral blood leukapheresis specimens obtained before and after vaccination. CTL specificity was measured by IFN-gamma release assay using HLA-A*0201 matched target cells. Clinical responses were assessed by physical examination and radiographic images. All HLA-A*0201 patients were able to mount a cellular immune response to a control peptide. E786-93-specific CTLs were elicited in 4 of 10 evaluable HLA-A*0201 subjects before vaccination, 5 of 7 evaluable HLA-A*0201 patients after two vaccinations, and 2 of 3 evaluable HLA-A*0201 cultures after all four inoculations. Two of three evaluable patients' CTLs converted from unreactive to reactive after administration of all four inoculations. There were no clinical responses or treatment toxicities. The ability to generate specific cellular immune responses is retained in patients with advanced cervical cancer. Vaccination with a lipidated HPV peptide epitope appears capable of safely augmenting CTL reactivity. Although enhancements of cellular immune responses are needed to achieve therapeutic utility in advanced cervical cancer, this approach might prove useful in treating preinvasive disease. 相似文献
180.