全文获取类型
收费全文 | 821233篇 |
免费 | 7047篇 |
国内免费 | 2317篇 |
专业分类
电工技术 | 14949篇 |
综合类 | 884篇 |
化学工业 | 122570篇 |
金属工艺 | 29772篇 |
机械仪表 | 23152篇 |
建筑科学 | 21307篇 |
矿业工程 | 2936篇 |
能源动力 | 22408篇 |
轻工业 | 75429篇 |
水利工程 | 7556篇 |
石油天然气 | 10707篇 |
武器工业 | 49篇 |
无线电 | 97746篇 |
一般工业技术 | 154086篇 |
冶金工业 | 160147篇 |
原子能技术 | 14270篇 |
自动化技术 | 72629篇 |
出版年
2021年 | 7000篇 |
2020年 | 5498篇 |
2019年 | 6884篇 |
2018年 | 10310篇 |
2017年 | 10147篇 |
2016年 | 10976篇 |
2015年 | 7883篇 |
2014年 | 12919篇 |
2013年 | 37879篇 |
2012年 | 21089篇 |
2011年 | 29566篇 |
2010年 | 23177篇 |
2009年 | 26065篇 |
2008年 | 27119篇 |
2007年 | 27036篇 |
2006年 | 23928篇 |
2005年 | 21991篇 |
2004年 | 21197篇 |
2003年 | 20900篇 |
2002年 | 19962篇 |
2001年 | 19970篇 |
2000年 | 18537篇 |
1999年 | 19776篇 |
1998年 | 49548篇 |
1997年 | 35181篇 |
1996年 | 27178篇 |
1995年 | 20769篇 |
1994年 | 18217篇 |
1993年 | 17782篇 |
1992年 | 12858篇 |
1991年 | 12254篇 |
1990年 | 11798篇 |
1989年 | 11448篇 |
1988年 | 10788篇 |
1987年 | 9391篇 |
1986年 | 9243篇 |
1985年 | 10802篇 |
1984年 | 10096篇 |
1983年 | 8866篇 |
1982年 | 8305篇 |
1981年 | 8385篇 |
1980年 | 7940篇 |
1979年 | 7733篇 |
1978年 | 7337篇 |
1977年 | 8892篇 |
1976年 | 11969篇 |
1975年 | 6291篇 |
1974年 | 5988篇 |
1973年 | 5977篇 |
1972年 | 4870篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Conclusions 1. In engineering-geologic explorations, it is necessary to investigate the engineering-geologic morphology to a depth of 15–18 m: lenses and interlayers of weak soils - unevenly compacted silty-sand fills, peat, slime, etc.2. Open unwatering of pits in the vicinity (10–15 m) of existing structures is impermissible, since it leads to removal of fine soil fractions because of piping, and to large and impermissible deformations of the load-bearing elements of the structures. In such cases, deep groundwater lowering by means of wellpoints should be used.In the case described in this article, the industrial structure underwent a mean settlement of about 20 cm, a tilt of 0.015, and a wall deflection of 0.002. By using deep groundwater lowering, such deformations could have been prevented.3. The development of settlements with time was due to the presence of weak soils - peat lenses and thin slime interlayers - in the foundation bed of the shop.4. An effective means for stopping the settlement of the industrial structure was the construction, under the walls, of two rows of cast-in-place piles with cantilever beams to which the wall loads were transmitted.Scientific-Research Institute of Foundations. GIPROLESKhIM. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 5–7, January–February, 1975. 相似文献
52.
A short-term study of a commercially-available physical—chemical waste treatment plant is reported. Results indicate that an excellent quality of effluent can be consistently obtained despite wide fluctuations of influent wastewater characteristics. Physical, chemical, and biological parameters were monitored. The short-term data obtained offer some evidence of superior treatment efficiency in terms of COD, color, turbidity, and phosphorus removals when compared to more conventional treatment methods. 相似文献
53.
焦五一 《建筑科学与工程学报》1989,(2)
本文用弦线模量计算了营业楼地基的压缩变形和湿陷变形,以及由它们引起的差异沉降值和局部倾斜。计算结果和楼房的裂缝情况吻合。计算湿陷变形时考虑地基浸水后的含水量为30.00%,这是由实测情况确定。根据浸水的实际状况计算建筑物的湿陷变形,分析工程事故在文献中似未见到。 相似文献
54.
Bacterial epiphytes on the surface of the fresh-water plant Alisma plantago-aquatica collected from a polluted river were found to be a major factor in contributing to the total metal concentrations of the plant. The removal of epiphytes from the leaf surface resulted in significant reductions in the concentrations of Cr (reduced by 15–50%), Cu (30–35%), Fe, Pb, and Zn (10–50%). While numbers of epiphytes and concentrations of heavy metals increased in samples collected from polluted water compared with from unpolluted water, the fraction of metals held by the epiphytes appeared to remain similar for all samples. 相似文献
55.
Munschy C Héas-Moisan K Tixier C Boulesteix L Morin J 《The Science of the total environment》2011,409(21):4618-4627
Brominated flame retardants (BFRs) were investigated in juvenile common sole from nursery zones situated along the French coast in 2007, 2008 and 2009. Extensive identification was performed with regard to PBDEs, novel BFRs 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and decabromodiphenylethane (DBDPE), and other non-PBDE BFRs, namely, hexabromobenzene (HBB) and 2,2′,4,4′,5,5′-hexabromobiphenyl (BB-153). Polybrominated diphenyl ether (PBDE) concentrations (Σ 14 congeners) ranged from 0.01 ng/g to 0.16 ng/g wet weight (ww) in muscle, and 0.07 ng/g to 2.8 ng/g ww in liver. Concentrations were in the lower range of those reported in the literature in other European locations. Lower PBDE concentrations, condition indices and lipid contents were observed in the Seine estuary in 2009, possibly in relation to a lower water flow. The PBDE patterns and ratios we observed suggested that juvenile sole have a relative high metabolic degradation capacity. Non-PBDE BFRs were detected at lower levels than PBDEs, i.e., within the < method detection limit - 0.005 ng/g ww range in muscle, and < method detection limit - 0.2 ng/g ww range in liver. The data obtained is of particular interest for the future monitoring of these compounds in the environment. 相似文献
56.
The introduction of ionic additives, such as KCN, or acidic comonomer units, such as methacrylic acid, which change the nature of the mechanism of nitrile oligomerization reaction from radical to ionic and cause its initiation at lower temperature, allows the level of obscurity and the total amount of smoke production, both in smouldering and flaming conditions to be decreased. An opposite result is obtained if diphenylpicrylhydrayl (DPPH) radicals in polyacrylonitrile is introduced; DPPH retards the initiation of the radical nitrile oligomerization reaction. The acrylonitrile-methacrylic acid copolymers have a limiting oxygen index, which increases with the methacrylic acid content. Owing to the increased amount of NH3 produced during pyrolysis, the copolymers have a swelling behavior during the combustion test. 相似文献
57.
Coagulation dynamics of fractal flocs induced by enmeshment and electrostatic patch mechanisms 总被引:2,自引:0,他引:2
The size and structure of flocs during floc formation were monitored for various coagulation mechanisms. Two distinctive mechanisms, namely, enmeshment and electrostatic patch, govern the dynamics of kaolin particles coagulation by polyaluminum chloride (PACl). They were investigated by small angle static light scattering (SASLS) and solid-state 27Al NMR. In addition, a novel wet SEM (WSEM) was used in-situ to image the morphology of the aggregate in aqueous solution. Synthetic suspended particles were coagulated by two PACl products, a commercial product (PACl) and one laboratory product (PACl-E). The PACl-E contained more than 60% Al13 while the PACl contained only 7% Al13, with large percentage of colloidal Al. For coagulation by PACl at neutral pH and high dosage where the strong repulsion between particles occurs, the enmeshment ruled by reaction-limited aggregation (RLA) results in larger sweep flocs as well as higher fractal dimensional structure. For coagulation by PACl-E at alkaline pH and low dosage, the flocs were coagulated predominately by electrostatic patch with Al13 aggregates. At such condition, it is likely that diffusion-limited aggregation (DLA) predominately rule PACl-E coagulation. The fractal dimension (Ds) values of PACl and PACl-E flocs formed at enmeshment and electrostatic patch increased with dosage, respectively. When breakage of flocs occurs, the breakage rate of PACl-E flocs is slower than that of sweep flocs. By WSEM imaging, the adsorption of spherical Al precipitates onto the particles was observed to form sweep flocs with a rough and ragged contour, while the PACl-E flocs were formed with a smooth and glossy structure. 相似文献
58.
Theoretical analyses are presented for the linear free vibration of a clamped-free cylindrical shell partially filled with an incompressible, inviscid liquid. For the vibration of the shell itself, the dynamic version of the Donnell equations was used and the problem was solved with the modified Galerkin procedure, taking the effect of the axisymmetric deformation due to the static liquid pressure into consideration. Concerning the vibration relevant to the liquid motion, the solution for the velocity potential was assumed as a sum of two sets of linear combinations of the suitable harmonic function, the unknown parameters of which were imposed to satisfy both boundary conditions along the wetted shell wall and the free liquid surface in a sense of appropriate series expansions. The procedure stated in the foregoing leads to a determinantal equation for the determination of the natural frequencies of the present shell-liquid system. To compare with the experimental results which will be stated in a companion paper,14 detailed numerical results will be presented in another companion paper13 on the free vibration characteristics of the two test cylinders partially filled with water. 相似文献
59.
Abstract: A generally applicable mathematical model, tailored for use on a Personal Computer, as the design tool to simulate unsteady flood flow in a network of interconnected rivers has been developed and applied to the Sham Chun River along the border between Hong Kong and the People's Republic of China. The effect on the improved Sham Chun River due to the proposed river training in the River Indus, one of its tributaries, is evaluated. The one-dimensional unsteady flow model itself is broadly applicable to a wide range of hydrologic conditions and varying field situations. It incorporates real hydraulic features including branched channels and 'tidal flats' flooding and drying. The time history of water stages and discharges are computed at any desired location throughout the connected essentially one-dimensional channel network subject to initial and boundary conditions. Details are given of techniques adapted in using the computational scheme to quantify the unsteady flow condition and the means to assure an efficient numerical solution as well as to verify the accuracy of the computed outputs by subjection to carefully selected schematic simplified test cases and real prototype cases with numerical solution method is a useful predictive engineering tool in river design. 相似文献
60.
Nearly 1500 spot urine samples were collected in the winter of 1987-1988 from women of seven farming prefectures located throughout Japan. Samples were analyzed for copper by flameless atomic absorption spectrometry. The copper content of the urine samples (Cu-U) distributed log-normally with a geometric mean (geometric standard deviation) of 36.9 (1.47) micrograms/l after adjustment for the specific gravity of urine of 1.016. The 95% confidence range was 17.1-79.7 micrograms/l. Neither alcohol consumption nor smoking habit affected the Cu-U. A literature survey showed that the observed level appears to be somewhat higher than previously reported values. 相似文献