全文获取类型
收费全文 | 1009篇 |
免费 | 57篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 31篇 |
综合类 | 42篇 |
化学工业 | 186篇 |
金属工艺 | 78篇 |
机械仪表 | 50篇 |
建筑科学 | 84篇 |
矿业工程 | 19篇 |
能源动力 | 18篇 |
轻工业 | 44篇 |
水利工程 | 19篇 |
石油天然气 | 76篇 |
武器工业 | 7篇 |
无线电 | 87篇 |
一般工业技术 | 111篇 |
冶金工业 | 126篇 |
原子能技术 | 17篇 |
自动化技术 | 90篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 45篇 |
2020年 | 35篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 44篇 |
2016年 | 32篇 |
2015年 | 37篇 |
2014年 | 41篇 |
2013年 | 37篇 |
2012年 | 55篇 |
2011年 | 61篇 |
2010年 | 66篇 |
2009年 | 51篇 |
2008年 | 48篇 |
2007年 | 54篇 |
2006年 | 43篇 |
2005年 | 42篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 20篇 |
1998年 | 40篇 |
1997年 | 27篇 |
1996年 | 14篇 |
1995年 | 24篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1972年 | 3篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1085条查询结果,搜索用时 33 毫秒
121.
以网络极限承载能力为突破口,对两种无线资源利用率算法进行浅析,研究在网络极限能力下的实际运行效率,并将两种算法联合分析,通过两种建模,给出判定高效小区的初步方法。 相似文献
122.
123.
对山东铝业公司第二氧化铝厂的能源消耗情况进行了简略分析,并阐述了通过科技进步降低能源消耗的主要措施及效果。 相似文献
124.
P Menéndez O Redondo A Rodriguez MC Lopez-Berges G Ercilla A López A Durán J Almeida JA Pérez-Simón JF San Miguel JW Gratama A Orfao 《Canadian Metallurgical Quarterly》1998,34(6):264-271
The flow cytometric enumeration of CD34+ hemopoietic precursor cells (HPC) present in samples used for transplantation of HPC has proven to be the most powerful single parameter for prediction of engraftment. At present, several different methodological approaches are used for the flow cytometric enumeration of CD34+ HPC. In the present study we have compared two of these methods as regards enumeration of CD34+ HPC and their CD34+/CD19- and CD34+/CD19+ subsets: a lyse-non-wash procedure based on the use of a recently commercialized red cell lysing solution (Quicklysis, Cytognos, Salamanca, Spain) and a lyse-and-then-wash method in which the Becton Dickinson (San Jose, CA) FACS Lysing Solution was used. For that purpose a total of 52 samples corresponding to 20 G-CSF mobilized peripheral blood (PB) samples and 21 PB-derived leucapheresis products from patients undergoing autologous PB stem cell harvest, together with 11 bone marrow (BM) samples from healthy volunteers were analyzed. Our results show that for each of the three types of samples analyzed the use of the lyse-and-then-wash method is associated with significantly lower numbers of both total CD34+ HPC (P < or = 0.003) and its major CD34+/CD19- subset (P < or = 0.01) while no significant changes are detected in the number of CD34+/CD19+ HPC in BM samples (P > 0.05). The use of an internal standard (reference beads) added just prior to data acquisition, showed that the differences between both methods are due to a selective loss of CD34+ HPC and its major CD34+/CD19- subset in BM (P=0.002 and P=0.003), PB (P < 0.0001 and P < 0.0001) and PB-derived leucapheresis products (P < 0.0001 and P=0.0001). Finally, addition of a centrifugation and washing step to a group of 11 leucapheresis samples lysed with Quicklysis showed that they did not significantly affect the overall number of total CD34+, CD34+/CD19- and CD34+/CD19+ HPC obtained. In line with these findings elimination of centrifugation and washing steps when FACS Lysing Solution was used to lyse mature red cells almost corrected for the selective loss of CD34+ HPC. In spite of these differences a significant degree of correlation (r > 0.83 in all cases) was found between both methods regarding the total number of CD34+, CD34+/CD19- and CD34+/CD19+ HPC present in the BM, PB and PB-derived leucapheresis samples analyzed in this study. 相似文献
125.
The co-administration of nonsteroidal anti-inflammatory drugs (NSAIDs) and antihypertensive agents often, but not always, results in blunting of the effect of antihypertensive therapy. Although NSAIDs have no detectable pressor effects in normal subjects or untreated hypertensive people, they seem to antagonize the action of the majority of antihypertensive agents, making it necessary to increase their dosage, and often preventing proper control of blood pressure, particularly in black and elderly patients. The mechanism of this pharmacodynamic interaction is not completely understood, but may involve inhibition of vascular and renal prostaglandin (PG) synthesis, with resulting vasoconstriction and impaired renal excretion of Na+ and water. Also, suppression of a possible intermediary action of PG in the antihypertensive action of agents such as angiotensin converting enzyme inhibitors has been proposed. Certain antihypertensive drugs, such as Ca(2+)-channel blockers, centrally acting alpha agonists, and diuretics seem less sensitive to antagonism by NSAIDs. Aspirin and sulindac seem to be devoid of pressor effects, and thus provide a safe alternative in patients at risk for this interaction. These compounds may, in selected circumstances, even potentiate the effects of antihypertensive medications. Studies are underway to evaluate the hemodynamic effects of more selective blockers of arachidonate metabolism, such as thromboxane synthase inhibitors and selective inhibitors of PGH synthase-2. 相似文献
126.
L García Menéndez J Galende del Canto J Valentín Cid MA Orejas García 《Canadian Metallurgical Quarterly》1998,198(1):48-49
OBJECTIVE: This was a pilot teleradiology project connecting two secondary KwaZulu-Natal hospitals' radiography departments to a central Durban teaching hospital. The purpose of the study was to assess the usefulness of same-day teleradiology reports to the medical staff and whether such a service changed patient management. DESIGN: After 1 month's service at each hospital, the first 200 teleradiology reports, original radiographs and patients' case notes were reviewed to determine whether any errors in interpretation of the radiographs had been made and whether the reports had changed patient management. RESULTS: The service changed patient management in 10% of cases. Undetected pathology was recognised by the radiologist in 20 patients--pulmonary tuberculosis in 10, spinal tuberculosis in 3, miliary tuberculosis in 2 and fractures in 5. Problems were encountered with transmission of data using the current telephone network, loss of data at the receiving station and the increased workload of the radiographer transmitting the data. CONCLUSIONS: Teleradiology services do make a positive impact on patient management in rural hospitals. However, there are many technical pitfalls that must be avoided in order to establish an effective service. 相似文献
127.
OBJECTIVE: To describe the style and effectiveness (adaptability) of the leadership of coordinators of an autonomous community according to the model of leadership on the ground, analysing its relationship with the work environment. DESIGN: Observational crossover study. SETTING: All the functioning teams in this community. PARTICIPANTS: Medical and nursing coordinators. MEASUREMENTS AND MAIN RESULTS: Hersey and Blanchard's questionnaire on leadership on the ground was employed. This identifies 1) the predominant style (scoring for style 0-12). On the approach of the coordinator to personal relationships and/or task development, it identifies 4 points: direction, persuasion, participation, delegation. 2) Adaptability of the manager (ranging from +24 to -24), based on that the best choice between different options depends on the maturity of the group. To contrast work environment and leadership, a validated questionnaire, adapted to our milieu, was used. Overall reply rate (51 coordinators) was 89.4%. Analysis of styles was: persuasive 5.05 points (SD = 1.25), participatory 4.74 (SD 1.76), directive 1.2 (SD 1.11) and delegating 0.34 (SD 0.68). Adaptability scored 8.38 points (SD = 4.67), and was greater for the nursing coordinators (p < 0.002) without differences for type, place or teaching qualifications. The work environment, both overall and by dimensions, correlated with adaptability, although no relationship was found with leaders' styles. CONCLUSIONS: Leadership adaptability was quite high and greater in nursing. The most prevalent styles were the persuasive and the participatory, more efficacious in teams of average maturity. Theoretical effectiveness was positively related to a better work environment. 相似文献
128.
129.
我国典型天然气藏输导体系研究——以鄂尔多斯盆地苏里格气田为例 总被引:9,自引:1,他引:8
前陆盆地褶皱-冲断带气藏和裂谷盆地气藏油气输导体系以断裂为主,天然气运移方向以垂向为主,运移距离短,输导效率高;而克拉通盆地岩性气藏和前陆盆地斜坡带气藏油气输导体系以砂体为主,油气运移方向为侧向、垂向,运移距离较长,输导效率低。苏里格气田属克拉通盆地岩性气藏,输导体系主要类型为砂体型,也有少量断裂型、砂体-断裂型。砂体型又可进一步分为厚层带状砂体、薄层带状砂体与透镜状砂体等类型。输导体系的输导能力随时间而变化。在200~150 Ma溶蚀作用和断层活动最强,输导体系的输导能力增大到顶峰。在成藏关键时刻(J3—K1),输导体系格架产状西高东低、北高南低,主要输导体系为砂体、断层与裂缝,油气向西北方向运移,输导效率高。在成藏后调整期(K2—Q),输导体系格架大部为东高西低、北高南低,主要输导体系为砂体与裂缝。油气运移效率较低,运移不太明显。 相似文献
130.
《建筑地基基础工程施工质量验收规范》(GB50202-2002)实施要点 总被引:1,自引:0,他引:1
《建筑地基基础工程施工质量验收规范)(GB50202-2002)内容包括总则及基本规定;地基;桩基础;土方与基坑工程等,规范共设强制性条款7条,应严格遵照执行,并注重规范中涉及的要点,以适应建筑施工技术的发展。 相似文献