全文获取类型
收费全文 | 24449篇 |
免费 | 2668篇 |
国内免费 | 2824篇 |
专业分类
电工技术 | 2001篇 |
技术理论 | 1篇 |
综合类 | 2917篇 |
化学工业 | 2153篇 |
金属工艺 | 638篇 |
机械仪表 | 872篇 |
建筑科学 | 10343篇 |
矿业工程 | 1562篇 |
能源动力 | 753篇 |
轻工业 | 784篇 |
水利工程 | 3435篇 |
石油天然气 | 726篇 |
武器工业 | 49篇 |
无线电 | 819篇 |
一般工业技术 | 929篇 |
冶金工业 | 703篇 |
原子能技术 | 252篇 |
自动化技术 | 1004篇 |
出版年
2024年 | 118篇 |
2023年 | 318篇 |
2022年 | 666篇 |
2021年 | 880篇 |
2020年 | 856篇 |
2019年 | 685篇 |
2018年 | 642篇 |
2017年 | 840篇 |
2016年 | 865篇 |
2015年 | 904篇 |
2014年 | 1774篇 |
2013年 | 1421篇 |
2012年 | 1908篇 |
2011年 | 2016篇 |
2010年 | 1611篇 |
2009年 | 1663篇 |
2008年 | 1409篇 |
2007年 | 1867篇 |
2006年 | 1667篇 |
2005年 | 1572篇 |
2004年 | 1273篇 |
2003年 | 1015篇 |
2002年 | 776篇 |
2001年 | 632篇 |
2000年 | 531篇 |
1999年 | 411篇 |
1998年 | 344篇 |
1997年 | 231篇 |
1996年 | 193篇 |
1995年 | 179篇 |
1994年 | 136篇 |
1993年 | 81篇 |
1992年 | 72篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 40篇 |
1988年 | 37篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 36篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Jinsheng Que Qing Wang Jianping Chen Bingfei Shi Qinghui Meng 《Bulletin of Engineering Geology and the Environment》2008,67(4):479-483
The paper describes some geotechnical properties of the soft soils in Guangzhou College City, China, which are difficult to
both sample and test. Laboratory and in situ tests were carried out to assess the physical and mechanical indices of the soils.
The data were statistically analyzed and linear regression undertaken such that equations could be developed by which the
geotechnical properties of the soft soils can be predicted. The statistical validity of the degree of correlation confirmed
that using these equations, the mechanical indices can be estimated from physical indices determined by routine testing.
相似文献
12.
13.
L. Rutigliano D. Fino G. Saracco V. Specchia P. Spinelli 《Journal of Applied Electrochemistry》2008,38(7):1035-1041
This paper describes the results obtained from an electrokinetic treatment of a real soil polluted by lead acetate. Powdered
soil samples were pressed with a consolidometer till 100 kPa to obtain cylindrical specimens with the same characteristics
as a subsoil. Tests were carried out in a Perspex electrochemical cell where soil specimens were introduced with a hollow
punch. A low intensity direct current was applied in order to remove contaminants, due to electrophoresis and electroosmosis
phenomena. The water flow, conductivity, apparent electroosmotic coefficient, as well as other characteristic parameters,
were measured throughout the test. The water content and degree of pore saturation were estimated at the beginning and end
of the test. The soil slab was divided into four slices and the Pb concentration profile determined. The main factor governing
the extraction of contaminant was found to be the pH in the acidic range. Indeed, under these conditions high removal efficiencies
could be reached. These results could lead to the design of a new electrochemical treatment cell equipped with a cationic
membrane to expand the region of favourable pH within the soil. 相似文献
14.
We present a new post processing method of simulating depth of field based on accurate calculations of circles of confusion. Compared to previous work, our method derives actual scene depth information directly from the existing depth buffer, requires no specialized rendering passes, and allows easy integration into existing rendering applications. Our implementation uses an adaptive, two‐pass filter, producing a high quality depth of field effect that can be executed entirely on the GPU, taking advantage of the parallelism of modern graphics cards and permitting real time performance when applied to large numbers of pixels. 相似文献
15.
16.
17.
近年来,国际上标准参考物质的种类与数量急剧增加,一些重要的领域,象地球化学、环境科学、生物学等都有了相应的SRM。国内研制SRM的工作也十分活跃。 标准样品必须均匀,故在分析定值和样品发行前,需要先作均匀性检验。由于均匀性是一个相对的概念,它与各个元素在SRM中的分布紧密相关。取样量直接影响均匀性的好坏。因此,当给出SRM中某元素的均匀性数值时,必须注明相应的取样量。由于仪器中子活化分析法(INAA)具有灵敏度高、不破坏试样、且可同时测定多种元素等特点,因此可在较小的取样量情况下,实现对SRM中多种痕量元素的均匀性检验。 相似文献
18.
Simulation of nitrogen dynamics and biomass production in winter wheat using the Danish simulation model DAISY 总被引:14,自引:0,他引:14
S. Hansen H. E. Jensen N. E. Nielsen H. Svendsen 《Nutrient Cycling in Agroecosystems》1991,27(2-3):245-259
A dynamic simulation model for the soil plant system is described. The model includes a number of main modules, viz., a hydrological model including a submodel for soil water dynamics, a soil temperature model, a soil nitrogen model including a submodel for soil organic matter dynamics, and a crop model including a submodel for nitrogen uptake. The soil part of the model has a one-dimensional vertical structure. The soil profile is divided into layers on the basis of physical and chemical soil characteristics. The simulation model was used to simulate soil nitrogen dynamics and biomass production in winter wheat grown at two locations at various levels of nitrogen fertilization. The simulated results were compared to experimental data including concentration of inorganic nitrogen in soil, crop yield, and nitrogen accumulated in the aboveground part of the crop. Based on this validation it is concluded that the overall performance of the model is satisfactory although some minor adjustments of the model may prove to be necessary. 相似文献
19.
介绍自密封阀的密封原理及其在氨汽提尿素装置中的应用,对其长期运行中出现的泄漏及泄漏原因进行分析,根据不同的泄漏方式分别提出了现场维修的方法. 相似文献
20.
Nguyen Van Nguu 《Nutrient Cycling in Agroecosystems》1987,14(2):135-142
The shortening of fallow period in several areas in tropical Africa has reduced soil fertility and exposed soils to erosion and run-off. Fertilizer application and crop conservation practices are needeed to sustain high crop yield and to conserve the natural resource base for upland crop production in the continent. Field trials were carried out to evaluate the effect of fertilizer application and soil and crop residues management practices on yield of maize (Zea mays L.) planted on a Plinthudult soil at Bertoua, Eastern Cameroon. Maize yields increased significantly with nitrogen and phosphorus fertilizer application. Under the rainfall pattern prevailing in the area, the amount of nitrogen required for maximum yield was higher in the second season. On the other hand, the amount of phosphorus required for maximum yield appeared to decrease with time. The burning of crop residues and weeds prior to planting together with no-till practive gave higher yield of maize than other soil and crop residues management practices. 相似文献