全文获取类型
收费全文 | 62284篇 |
免费 | 4209篇 |
国内免费 | 1586篇 |
专业分类
电工技术 | 3693篇 |
综合类 | 5680篇 |
化学工业 | 4431篇 |
金属工艺 | 1901篇 |
机械仪表 | 2285篇 |
建筑科学 | 11281篇 |
矿业工程 | 1538篇 |
能源动力 | 978篇 |
轻工业 | 16543篇 |
水利工程 | 3250篇 |
石油天然气 | 1815篇 |
武器工业 | 224篇 |
无线电 | 3161篇 |
一般工业技术 | 3051篇 |
冶金工业 | 3281篇 |
原子能技术 | 187篇 |
自动化技术 | 4780篇 |
出版年
2024年 | 360篇 |
2023年 | 909篇 |
2022年 | 1519篇 |
2021年 | 1958篇 |
2020年 | 1987篇 |
2019年 | 1649篇 |
2018年 | 1465篇 |
2017年 | 1754篇 |
2016年 | 1847篇 |
2015年 | 2057篇 |
2014年 | 4378篇 |
2013年 | 3547篇 |
2012年 | 4402篇 |
2011年 | 4640篇 |
2010年 | 3631篇 |
2009年 | 3833篇 |
2008年 | 3403篇 |
2007年 | 4099篇 |
2006年 | 3703篇 |
2005年 | 2990篇 |
2004年 | 2591篇 |
2003年 | 2338篇 |
2002年 | 2053篇 |
2001年 | 1489篇 |
2000年 | 1232篇 |
1999年 | 972篇 |
1998年 | 639篇 |
1997年 | 493篇 |
1996年 | 436篇 |
1995年 | 363篇 |
1994年 | 273篇 |
1993年 | 217篇 |
1992年 | 189篇 |
1991年 | 124篇 |
1990年 | 84篇 |
1989年 | 90篇 |
1988年 | 64篇 |
1987年 | 68篇 |
1986年 | 42篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 22篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Monitoring water quality in reservoirs with IRS-1A-LISS-I 总被引:1,自引:1,他引:0
V. K. Choubey 《Water Resources Management》1994,8(2):121-136
An attempt has been made to quantify the relationship between the variation in IRS-IA-LISS-I (Indian Remote Sensing Satellite-1A Linear Imaging Self-Scanning System) radiance data and field measured change in secchi disc depth. Secchi disc depth was measured for 47 predetermined sampling locations on reservoir surface water. At extinction depth (secchi depth), water samples were collected from all the sampling locations. Suspended sediments of eight locations representing various reaches of the reservoir were selected for mineralogical, particle size and optical properties analysis. The LISS-I radiance value in band 1 (0.45–0.52µm) band 2 (0-52–0.59 µm) and band 3 (0.62–0.68 µm) were used in a regression analysis. The absorption infrared band 4 (0.77–0.86 µm) was not included in the analysis. In these, the dependable variable was secchi depth (SD) and the LISS-I-radiance data was the estimator variable. Forty-seven data sets of 20 October 1988 from Tawa reservoir surface water were used to obtain an estimator equation for SD. The verification of the estimator equation was tested by applying it to a data set of 21 measurements of 28 September 1988 for this reservoir. The coefficient of correlation between observed and estimated values for the 28 September 1988 data set wasr=0.92 for SD, indicating that the equation could accurately predict the water clarity (SD) for this reservoir on new occasions from IRS-IA-LISS-I spectral data. It is shown that mineral composition and optical properties of suspended sediments influence the reflected radiance of water quality. It is concluded that IRS-IA-LISS-I data provide a useful means of mapping water quality in reservoir. 相似文献
32.
压力容器材料质量控制的几个重要环节 总被引:2,自引:0,他引:2
针对压力容器材料方面存在的问题,从设计、采购、检验、制造等环节进行了分析,根据实际情况确定材料的质量控制要点。材料使用前要通过各种检测手段,判断材料的真实性,确保所用材料合格;并应从设计、选材、采购、计划、填报内容和选择可靠的供应方等方面加以控制,确保材料的正确使用,为压力容器产品的材料控制提供借鉴。 相似文献
33.
34.
Engineering the surfaces of components to improve the life and performance of parts used in automotive and aerospace engineering is the active area of research. Suitable Thermal/Mechanical/Thermo mechanical surface engineering treatments will produce extensive rearrangement of atoms in metals and alloys and corresponding marked variations in Physical, Chemical and Mechanical properties. Among the more important of these treatments are heat treatment processes such as hardening by Quenching, Induction hardening and Case Carburizing which rely on phase transformations to produce desired changes in mechanical properties. Other processes where phase transformation occur are casting, welding and machining etc. [1] Phase transformation may be homogeneous or heterogeneous. Homogeneous involves rearrangements in the structure of the material taking place simultaneously in all parts of the solid, while the heterogeneous transformation involves structural changes which are more localized. Alternatively they could be called as Isothermal and Nonisothermal transformation. But irrespective of the classification, these transformations alter the structure of the material giving rise to changes in the mechanical and physical properties of the processed material. It is of interest to review some consequences of surface modification in isothermal (Normalizing) and nonisothermal transformations (Machining) of low carbon steels. 相似文献
35.
针对磷酸二铵(DAP)产品养分波动大、含水量偏高、易结块、颜色变化大等缺点,在生产过程中采取了相应的解决措施,如配矿、联产、设备改造、工艺指标调整等,使DAP装置不仅保持了原有的优点,而且产品质量问题也得到了有效解决。养分基本保持在64.0%~64.6%,水分下降到2.1%~2.2%,结块现象较少,颜色也比较统一。 相似文献
36.
37.
Responses ofRhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies to host fruit visual stimuli (apples or models of apples) and chemical stimuli (synthetic apple volatile blend) were studied in semidwarf field-caged apple trees. Three different fruit or model densities (1, 4, or 16 fruit or models/ tree) and two odor release rates [ca. 0.7g/hr (close to the natural release rate of a ripe apple) and ca. 500g/hr (amount of odor released by commercially sold apple maggot traps)] were tested. Individually released flies were followed as they moved within a tree for a maximum of 20 min. We recorded three-dimensional search paths followed by foraging flies and computed such variables as total relative distance traveled before alighting on a fruit or model, track length between individual alightment sites, and directness of flight to fruits or models. Effect of odor on propensity to alight on fruit or models and host-searching behavior prior to alighting on fruit or on models varied according to fruit or model color and density. If the fruit visual stimulus was strong (e.g., red color), odor did not increase the probability of finding fruit or fruit models. As the visual stimulus became progressively weaker (red to green to clear), odor (irrespective of concentration) appeared to aid flies during the fruit-finding process. As density of fruit or models increased, the probability of flies finding a fruit or model also increased (e.g., 50% of flies found a red fruit model at 1 model/tree while 90% found a red model at 16 models/tree; 4% of flies found a clear model with odor at 1 model/tree while 35% found a clear model with odor at 16 models/tree). Findings reported elsewhere indicate thatR. pomonella flies are able to discover a point source of odor (an odor-bearing tree in a patch of trees) by flying upwind (in the tree patch) in response to intermittent exposure to odor. Findings here indicate that after arrival on a host tree (point source), flies discover individual apparent and abundant host fruit on the basis of vision. If fruit are less apparent or scarce, odor appears to interact with vision during the fruit-finding process. 相似文献
38.
39.
预焙阳极的质量已严重制约铝电解技术的发展,必须予以足够的重视.国外在提高阳极质量方面的有效措施,可以供国内阳极工厂技术改造及科研攻关借鉴. 相似文献
40.