全文获取类型
收费全文 | 4490篇 |
免费 | 111篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 35篇 |
综合类 | 2篇 |
化学工业 | 280篇 |
金属工艺 | 20篇 |
机械仪表 | 40篇 |
建筑科学 | 70篇 |
矿业工程 | 3篇 |
能源动力 | 35篇 |
轻工业 | 129篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 308篇 |
一般工业技术 | 394篇 |
冶金工业 | 2958篇 |
原子能技术 | 23篇 |
自动化技术 | 289篇 |
出版年
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 26篇 |
2019年 | 30篇 |
2018年 | 36篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 47篇 |
2014年 | 37篇 |
2013年 | 119篇 |
2012年 | 49篇 |
2011年 | 78篇 |
2010年 | 57篇 |
2009年 | 42篇 |
2008年 | 72篇 |
2007年 | 58篇 |
2006年 | 56篇 |
2005年 | 55篇 |
2004年 | 62篇 |
2003年 | 53篇 |
2002年 | 51篇 |
2001年 | 38篇 |
2000年 | 47篇 |
1999年 | 137篇 |
1998年 | 926篇 |
1997年 | 562篇 |
1996年 | 336篇 |
1995年 | 207篇 |
1994年 | 165篇 |
1993年 | 205篇 |
1992年 | 57篇 |
1991年 | 39篇 |
1990年 | 63篇 |
1989年 | 45篇 |
1988年 | 34篇 |
1987年 | 40篇 |
1986年 | 50篇 |
1985年 | 45篇 |
1984年 | 23篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 36篇 |
1980年 | 46篇 |
1978年 | 22篇 |
1977年 | 80篇 |
1976年 | 145篇 |
1975年 | 16篇 |
1974年 | 12篇 |
1972年 | 13篇 |
1970年 | 14篇 |
排序方式: 共有4608条查询结果,搜索用时 15 毫秒
1.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine. 相似文献
2.
3.
MG McInnis A Chakravarti J Blaschak MB Petersen V Sharma D Avramopoulos JL Blouin U K?nig C Brahe TC Matise 《Canadian Metallurgical Quarterly》1993,16(3):562-571
A genetic linkage map of human chromosome 21q (HC21q) containing 43 markers genotyped by the polymerase chain reaction in the CEPH pedigrees is presented. The markers placed on this map are highly polymorphic with an average heterozygosity of 61%. The average interval size of the markers localized at 1000:1 odds is 2.5 cM. The map has a total length of 65.5 cM, with male and female lengths of 47.7 and 83.3 cM, respectively. The genotypes used in the construction of this map were subjected to rigorous error checking, which is reflected in the shorter map length compared to previous maps; the estimated error rate in genotyping is less than 0.04%. As noted in previous linkage maps there is increased recombination in females on proximal HC 21q and in the male in a region near the telomere. This map of HC 21 represents a highly informative and dense meiotic linkage map and will be useful in linking disease phenotypes to loci on this chromosome. 相似文献
4.
Anguilla is a UK overseas (non-independent) territory in the Caribbean. It is a small middle-income island with a population of 13 000, and recent statistics indicate that it is more dependent on tourism than any other country or territory in the world. Rapid population growth and development have placed more emphasis on the need for human health and environmental protection. For the first time, a systematic water-quality monitoring programme has been developed, based on the realities of the local situation, e.g. low resource base, limited capabilities, dependence on household rainwater catchment, storage cisterns, and a poor water-supply network. Development of the programme incorporated the key themes of pragmatic, realistic, incremental, responsive, and consultative approaches. 相似文献
5.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration. 相似文献
6.
7.
8.
The current, most frequently employed, commercial route to produce hydroxyapatite prosthetic coatings is plasma spraying. However, this has several important limitations especially for textured surfaces. Low temperature methods of coating fabrication such as cathodic electrodeposition are attractive alternatives. However, quantitative characterisation of the phase composition of thin electrodeposited coatings can be problematic. An X-ray diffraction method, which provides quantitative compositional information without reference to external or internal standards, is introduced and validated. The method can also be applied when Bragg peaks from the supporting substrate are apparent within the data and preferred orientation can be tolerated. This method has been used to examine in detail the microstructure of electrodeposited coatings which are compared directly with those formed by a commercial plasma spraying process.We show that, unlike the plasma sprayed coatings, the electrodeposited material consists of a single crystalline phase (hydroxyapatite) and a significantly reduced amorphous phase. The electrodeposited coatings also possess significantly more microstrain and a smaller crystallite size than the corresponding plasma sprayed material. 相似文献
9.
Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles. 相似文献
10.
MG Newman 《Canadian Metallurgical Quarterly》1997,2(1):180-198
The design and implementation of clinical trials (CTs) carried out to evaluate antimicrobial and anti-infective drugs and devices are one of the most difficult challenges in contemporary periodontal research and product development. The overwhelming amount of evidence which has established a microbial etiology for periodontitis is the basis for developing and testing antimicrobial treatments. Well-designed antimicrobial CTs start with a carefully crafted hypothesis and a protocol which explicitly integrates the requirements of the patient, the clinician, the sponsor, and regulatory authorities. Surrogate variables for effectiveness must be clinically relevant, scientifically sound, and statistically valid. Currently, clinical attachment level measurements and alveolar bone assessments are accepted as proof of effectiveness. Indication and claim support of the antimicrobial product guide the design and implementation of the CT. Adverse microbiologic consequences, such as lack of antimicrobial susceptibility, wrong spectrum, incorrect dosage, non-compliance, and drug interference, must be monitored. Successful CTs balance a large group of variables used to screen, randomize, and assign subjects to experimental and control groups to ensure that prognostic and risk factors are properly accounted for. 相似文献