全文获取类型
收费全文 | 13276篇 |
免费 | 631篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 154篇 |
综合类 | 5篇 |
化学工业 | 2340篇 |
金属工艺 | 223篇 |
机械仪表 | 343篇 |
建筑科学 | 549篇 |
矿业工程 | 30篇 |
能源动力 | 468篇 |
轻工业 | 1072篇 |
水利工程 | 164篇 |
石油天然气 | 49篇 |
武器工业 | 2篇 |
无线电 | 1177篇 |
一般工业技术 | 2545篇 |
冶金工业 | 2891篇 |
原子能技术 | 57篇 |
自动化技术 | 1863篇 |
出版年
2023年 | 81篇 |
2022年 | 130篇 |
2021年 | 261篇 |
2020年 | 225篇 |
2019年 | 245篇 |
2018年 | 271篇 |
2017年 | 265篇 |
2016年 | 323篇 |
2015年 | 262篇 |
2014年 | 397篇 |
2013年 | 690篇 |
2012年 | 682篇 |
2011年 | 972篇 |
2010年 | 697篇 |
2009年 | 564篇 |
2008年 | 743篇 |
2007年 | 707篇 |
2006年 | 584篇 |
2005年 | 525篇 |
2004年 | 422篇 |
2003年 | 387篇 |
2002年 | 414篇 |
2001年 | 240篇 |
2000年 | 206篇 |
1999年 | 197篇 |
1998年 | 440篇 |
1997年 | 322篇 |
1996年 | 258篇 |
1995年 | 207篇 |
1994年 | 214篇 |
1993年 | 191篇 |
1992年 | 136篇 |
1991年 | 86篇 |
1990年 | 126篇 |
1989年 | 111篇 |
1988年 | 97篇 |
1987年 | 84篇 |
1986年 | 111篇 |
1985年 | 93篇 |
1984年 | 80篇 |
1983年 | 73篇 |
1982年 | 69篇 |
1981年 | 63篇 |
1980年 | 61篇 |
1979年 | 50篇 |
1978年 | 58篇 |
1977年 | 91篇 |
1976年 | 93篇 |
1975年 | 54篇 |
1974年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
141.
A study of mechanical shear bands in liquids at high pressure 总被引:2,自引:2,他引:0
142.
OBJECTIVE: To determine the results peranal excision for rectal carcinoma. DESIGN: Retrospective case series. SETTING: A university-affiliated hospital. PATIENTS: Of 178 patients who presented for curative resection of rectal carcinoma between 1975 and 1993, 19 (10.7%) were deemed suitable for local excision. There were 10 men and 9 women with a mean age of 71.2 years. The follow-up ranged from 13 to 184 months. INTERVENTION: Peranal excision. MAIN OUTCOME MEASURES: Histologic differentiation, gross morphology, depth of invasion and size of the carcinoma, adequacy of margins of excision, complications of operation, rates of recurrence, results of salvage therapy and 5-year survival. RESULTS: There were no intraoperative complications. Postoperative complications included urinary retention (one patient) and bleeding (one patient). There were five local recurrences (26%). Salvage operations were performed in three (60%) patients and were successful in two of them. The 5-year cancer-specific survival rate was 82%. The recurrence rate was higher in patients with inadequate margins of excision and ulcerative lesions. Neither size nor grade of the carcinoma correlated with recurrence. CONCLUSIONS: Local excision of rectal carcinoma can be performed successfully in selected patients. Diligent follow-up is required, because up to 60% of local recurrences can be treated successfully. 相似文献
143.
Rheological Property and Stress Development during Drying of Tape-Cast Ceramic Layers 总被引:1,自引:0,他引:1
Jennifer A. Lewis Kimberly A. Blackman rea L. Ogden James A. Payne Lorraine F. Francis 《Journal of the American Ceramic Society》1996,79(12):3225-3234
Rheological property and stress development of tape-cast ceramic layers derived from nonaqueous alumina (A12 O3 )-poly(vinyl butyral) (PVB) suspensions were observed during drying. Casting suspensions exhibited strong shear-thinning behavior, with a low shear Newtonian plateau apparent viscosity >102 Pa. s. The apparent suspension viscosity displayed a power-law dependence on the A12 O3 volume fraction during the initial stage of drying (<30% solvent loss). Stress development, measured by a cantilever deflection method, and parallel weight loss measurements were performed during the drying of tape-cast layers and pure binder coatings. Maximum drying stresses (σmax ) of 1.37-0.77 MPa were observed for plasticized tapes cast at gap heights of 150-400 μm. In contrast, nonplasticized tapes of similar thickness displayed a more gradual stress increase, with σmax values approximately an order of magnitude higher than their plasticized counterparts. The stress histories of the corresponding binder coatings were quite similar to the tape-cast layers, albeit slightly lower σ max values were observed. Stresses decayed beyond σmax with a logarithmic time dependence to an almost constant value of 0.2-0.4 MPa for the plasticized tapes. Based on these observations, process methodologies have been offered to minimize stress development and retention in tape-cast ceramic layers 相似文献
144.
Six cows were exposed during milkings to electrical current to assess its effects on behavior, health, milking performance, and endocrine responses. Three treatments (0, 4, and 8 mA) were applied in a changeover design over three consecutive 1-wk periods. A cow received the same current treatment during 14 consecutive milkings, beginning with the evening milking (d 1) and ending with the morning milking (d 8). Treatments began 5 min before milking and continued until milking unit removal. Treatments consisted of 60 Hz square wave current of 5-s duration applied every 30 s from udder to hooves. Milk accumulation curves provided information about milk yields, milking times, peak milk flow rates, and times of peak milk flow. Residual milk yields also were measured. Milk was analyzed for protein, fat, and somatic cells. Blood samples from 60 min before to 60 min after treatment were collected, and oxytocin, prolactin, and cortisol concentrations were measured. Behavioral responses to current decreased with time. Changes of milking performance and milk composition were not significant. Changes of milking related cortisol responses during 8-mA current stimulation were significant. Oxytocin release was delayed during 8-mA treatments. Current treatments did not affect prolactin. 相似文献
145.
Examined the use of an intervention for reducing unawareness of memory deficits in 3 male adults (aged 20–25 yrs) with brain injury. High predicted test scores on a brief multiparametric memory test, relative to actual test scores, were considered underestimations of symptom severity (unawareness). An estimation technique, feedback, and explicit positive reinforcement for decreases in discrepancies between predicted and actual scores were used to reduce unawareness. Differences between Ss' predicted and actual scores decreased over time following treatment for all Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
146.
147.
Life table studies were performed in 1996 with Aedes aegypti (L.) during the low (cool/dry) and high (hot/rainy) dengue virus transmission seasons in Puerto Rico. Mated adult females from field-collected pupae were placed individually in cages and divided into 2 treatment groups: one was fed only human blood and the other human blood plus a 10% sucrose solution. Survival and number of eggs laid were recorded daily for each female. During both seasons, age specific survivorship was higher for the blood plus sugar group, groups fed only human blood had higher reproductive outputs (mx), and net replacement rates (Ro) for blood only groups were higher than for those fed blood plus sugar. Intrinsic rates of growth (r) were the same for both treatments during the low (cool/dry) transmission season, but higher for the blood-only treatment during the high (hot/rainy) transmission season. Our results indicate that feeding on only human blood provides an evolutionary advantage to Ae. aegypti females in Puerto Rico. These results are similar to those from an earlier study carried out with Ae. aegypti in Thailand; the advantage of feeding on human blood does not seem to be restricted to a particular geographic region. We also found that the benefits associated with human feeding persist through epidemiologically different times of the year. We conclude that feeding on human blood is reproductively beneficial for Ae. aegypti, which may increase their contact with human hosts, and therefore may influence their vectorial capacity for dengue viruses through frequent feeding on blood. 相似文献
148.
BG Hattler C Madia C Johnson JM Armitage RL Hardesty RL Kormos SM Pham DN Payne BP Griffith 《Canadian Metallurgical Quarterly》1994,58(5):1348-1352
In an era of progressive cost containment and public scrutiny, the wisdom of aggressive surgical therapy for high-risk candidates has been questioned. At our center in the previous 24 months, 728 patients with coronary artery disease were entered into The Society of Thoracic Surgeons national database, and the hospital outcomes plus length of stay were analyzed. Patients were separated according to the predicted mortality based on the groupings in The Society of Thoracic Surgeons database: 0 to 5% (453 patients); 5% to 10% (126 patients); 10% to 20% (96 patients); 20% to 30% (17 patients); and 30% and greater (36 patients). There was a close correlation with the predicted rates of mortality. Importantly, the preoperative risk stratification demonstrated a strong correlation with the significant morbidity and excessive length of stay in the highest-risk groups (predicted risk of 20% to > or = 30%). The incidences of the most common complications in the group with the highest predicted risk (> or = 30%) were 28%, renal failure; 33%, ventilator dependence; and 17%, cardiac arrest. In addition, at short-term follow-up (6 to 8 months), a 24.3% mortality was identified in patients with a predicted mortality that exceeded 20%. These data quantify the risks and morbidities associated with the care of seriously ill patients with coronary artery disease and demonstrate the need for professional and public discussions focusing on the association of a high preoperative risk status and the consumption of resources. 相似文献
149.
Cleyo Harris Travis O. Brenden Chris S. Vandergoot Matthew D. Faust Seth J. Herbst Charles C. Krueger 《Journal of Great Lakes research》2021,47(1):48-58
Infrequent captures of invasive, non-native grass carp (Ctenopharyngodon idella) have occurred in Lake Erie over the last 30+ years, with recent evidence suggesting wild reproduction in the lake’s western basin (WB) is occurring. Information on grass carp movements in the Laurentian Great Lakes is lacking, but an improved understanding of large-scale movements and potential areas of aggregation will help inform control strategies and risk assessment if grass carp spread to other parts of Lake Erie and other Great Lakes. Twenty-three grass carp captured in Lake Erie’s WB were implanted with acoustic transmitters and released. Movements were monitored with acoustic receivers deployed throughout Lake Erie and elsewhere in the Great Lakes. Grass carp dispersed up to 236 km, with approximately 25% of fish dispersing greater than 100 km from their release location. Mean daily movements ranged from <0.01 to 2.49 km/day, with the highest daily averages occurring in the spring and summer. The Sandusky, Detroit, and Maumee Rivers, and Plum Creek were the most heavily used WB tributaries. Seventeen percent of grass carp moved into Lake Erie’s central or eastern basins, although all fish eventually returned to the WB. One fish emigrated from Lake Erie through the Huron-Erie Corridor and into Lake Huron. Based on our results, past assessments may have underestimated the potential for grass carp to spread in the Great Lakes. We recommend focusing grass carp control efforts on Sandusky River and Plum Creek given their high use by tagged fish, and secondarily on Maumee and Detroit Rivers. 相似文献
150.
Caihua Liu Didar Zowghi Matthew Kearney Muneera Bano 《Journal of Computer Assisted Learning》2021,37(1):1-23
Recent years have seen a growing call for inquiry-based learning in science education, and mobile technologies are perceived as increasingly valuable tools to support this approach. However, there is a lack of understanding of mobile technology-supported inquiry-based learning (mIBL) in secondary science education. More evidence-based, nuanced insights are needed into how using mobile technologies might facilitate students' engagement with various levels of inquiry and enhance their science learning. We, therefore, conducted a robust systematic literature review (SLR) of the research articles on mIBL in secondary school science education that have been published from 2000 to 2019. We reviewed and analysed 31 empirical studies (34 articles) to explore the types of mIBL, and the benefits and constraints of mIBL in secondary school science education. The findings of this SLR suggest new research areas for further exploration and provide implications for science teachers' selection, use and design of mIBL approaches in their teaching. 相似文献