全文获取类型
收费全文 | 104395篇 |
免费 | 1864篇 |
国内免费 | 431篇 |
专业分类
电工技术 | 1018篇 |
综合类 | 2334篇 |
化学工业 | 15454篇 |
金属工艺 | 5141篇 |
机械仪表 | 3490篇 |
建筑科学 | 3294篇 |
矿业工程 | 616篇 |
能源动力 | 1722篇 |
轻工业 | 5503篇 |
水利工程 | 1399篇 |
石油天然气 | 407篇 |
武器工业 | 1篇 |
无线电 | 11093篇 |
一般工业技术 | 19745篇 |
冶金工业 | 6774篇 |
原子能技术 | 501篇 |
自动化技术 | 28198篇 |
出版年
2023年 | 163篇 |
2022年 | 325篇 |
2021年 | 494篇 |
2020年 | 376篇 |
2019年 | 414篇 |
2018年 | 14791篇 |
2017年 | 13685篇 |
2016年 | 10392篇 |
2015年 | 1058篇 |
2014年 | 790篇 |
2013年 | 1375篇 |
2012年 | 4064篇 |
2011年 | 10547篇 |
2010年 | 9061篇 |
2009年 | 6384篇 |
2008年 | 7672篇 |
2007年 | 8569篇 |
2006年 | 912篇 |
2005年 | 1866篇 |
2004年 | 1696篇 |
2003年 | 1675篇 |
2002年 | 1037篇 |
2001年 | 467篇 |
2000年 | 560篇 |
1999年 | 501篇 |
1998年 | 1094篇 |
1997年 | 727篇 |
1996年 | 590篇 |
1995年 | 401篇 |
1994年 | 374篇 |
1993年 | 367篇 |
1992年 | 251篇 |
1991年 | 225篇 |
1990年 | 191篇 |
1989年 | 173篇 |
1988年 | 195篇 |
1987年 | 160篇 |
1986年 | 149篇 |
1985年 | 195篇 |
1984年 | 163篇 |
1983年 | 156篇 |
1982年 | 120篇 |
1981年 | 132篇 |
1980年 | 119篇 |
1979年 | 125篇 |
1978年 | 120篇 |
1977年 | 164篇 |
1976年 | 226篇 |
1975年 | 95篇 |
1974年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
D Martin 《Canadian Metallurgical Quarterly》1998,28(7):52-53
A clinical ladder identifies nursing competence, provides recognition and financial reward for bedside nursing practice, promotes responsibility, accountability, project and committee involvement, and enhances self-worth and positive morale. Because of the program's blend of skill levels, it develops a climate for clinical learning while promoting professional growth and confidence. 相似文献
72.
The potential of a gonadotropin-releasing hormone (GnRH) agonist (goserelin acetate), delivered constantly for 28 days via a subcutaneous depot, to induce ovulation in seasonally anestrous mares, was investigated. Two experiments were conducted, in which a range of doses (30 to 240 micrograms/mare/d) was examined. Mares were selected on the basis of lack of substantial follicular development (follicle diameter < 20 mm determined ultrasonically) and low serum concentrations of luteinizing hormone (LH) and progesterone. Constant administration of the GnRH agonist-induced ovulation in anestrous mares, but a dose-response relation was not observed. Furthermore, with identical doses tested in consecutive or alternate years, considerable variation was observed in the ovulatory response. In general, ovulation in all treated mares was accompanied by increased circulating concentrations of LH and a decrease in follicle-stimulating hormone values. Ovulation was preceded by an increase in estradiol and LH concentrations. In mares in which ovulation did not occur, concentration of LH increased during agonist treatment, whereas that of follicle-stimulating hormone either increased or did not change. It was concluded that constant administration of GnRH agonists may induce ovulation in mares during seasonal anestrus; however, percentage of mares ovulating and the lack of reproducibility of effect indicate that this approach is inappropriate for use as a reliable method to manipulate breeding activity in commercial broodmares. 相似文献
73.
74.
D Averill D Blockus B Brabson J Brom C Jung H Ogren DR Rust M Derrick P Kooijman JS Loos B Musgrave LE Price J Repond K Sugano B Cork C Akerlof J Chapman D Errede MT Ken DI Meyer H Neal D Nitz R Thun R Tschirhart S Abachi P Baringer BG Bylsma R DeBonte D Koltick EH Low RL McIlwain DH Miller CR Ng EI Shibata 《Canadian Metallurgical Quarterly》1989,39(1):123-137
75.
By nature, cryptographers tend to be extremely cautious and conservative. From their perspective, spending time getting people to use a new cryptographic algorithm is roughly on par with getting involved in a land war in Asia. In some cases, however, the difficulty involved in developing a new algorithm is worth the effort. This is the case with identity-based encryption (IBE), a new type of public-key algorithm 相似文献
76.
Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for
which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that
is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation
to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and
calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium
sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur
dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this
Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide
pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023
and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique.
The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen
reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity
decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic
of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants.
A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial
pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated
several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification,
combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported
in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part
II. 相似文献
77.
Microbiological denitrification of red beet juice 总被引:1,自引:0,他引:1
Dorota Walkowiak-Tomczak 《European Food Research and Technology》2002,215(5):401-406
The purpose of study was the determination of optimal conditions for red beet juice denitrification by Paracoccus denitrificans bacteria as well as the evaluation of the usefulness of microbiologically treated juice for the production of a natural colouring preparation for foods. Total reduction of nitrates was found during bacterial culturing at 25 and 30 °C, at an initial pH of 7.0-8.0 and juice osmotic pressure of 900-1100 mOsm/kg. Microbiological denitrification procedure affected colour, taste and aroma of the juice. However, the use of juice as food colouring and component was made feasible by acidification and partial evaporation of water together with volatile substances. 相似文献
78.
Steel box sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which can influence their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The welding procedure and the behaviour of the box sections under load has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Modelling has been shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. A design method has been proposed. 相似文献
79.
80.
George Ter-Stepanian 《Bulletin of Engineering Geology and the Environment》2002,61(3):197-205
The paper discusses the postulated suspension force, by which it is possible to explain some enigmatic phenomena observed
in different types of mass movements. This force is generated in thick suspensions as a result of friction between sinking
solid particles and static water. The suspension force is related to the seepage force but they have opposite directions.
Both forces form flow networks. Having explained the suspension force, the paper describes how this influences the movement
of material, particularly in debris flows. Enigmatic features and the mechanism of debris flows and lahars are explained by
virtue of the suspension force.
Electronic Publication 相似文献