全文获取类型
收费全文 | 708篇 |
免费 | 24篇 |
国内免费 | 51篇 |
专业分类
系统科学 | 19篇 |
丛书文集 | 25篇 |
教育与普及 | 18篇 |
理论与方法论 | 4篇 |
现状及发展 | 2篇 |
研究方法 | 1篇 |
综合类 | 714篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 21篇 |
2012年 | 26篇 |
2011年 | 24篇 |
2010年 | 25篇 |
2009年 | 19篇 |
2008年 | 34篇 |
2007年 | 30篇 |
2006年 | 22篇 |
2005年 | 30篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 22篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 43篇 |
1998年 | 40篇 |
1997年 | 43篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 24篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 3篇 |
排序方式: 共有783条查询结果,搜索用时 156 毫秒
101.
本文以三叶草为样本,研究其含根量分别为0.0 g/60 cm3、0.1 g/60 cm3、0.3 g/60 cm3、0.5 g/60 cm3、0.7 g/60 cm3和1.0 g/60 cm3的根—土复合体抗剪切强度,试验中对三叶草根-土复合体进行了法向应力分别为100 kPa、200 kPa、300 kPa及400 kPa下的抗剪强度。结果表明:三叶草根系增加了土体的抗剪强度;根—土复合体在同一含根量下,其抗剪强度均随着法向应力的增加而增加;在同一法向应力下,随着含根量的增大,根—土复合体的抗剪强度、粘聚力和内摩擦角均呈现出先增大后减小的趋势,均在含根量为0.5 g/60 cm3时出现最大值。三叶草含根量为0.5-0.7 g/60 cm3时护坡效果最好。 相似文献
102.
HaiTao Zong XinYu Zhang LiXin Li LinYan Bian ShunXing Liang ChunLin Tan 《科学通报(英文版)》2012,57(11):1219-1222
The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson’s ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys. 相似文献
103.
The amorphous Fe78Si9B13 alloy was used as a heterogeneous Fenton catalyst in the process of phenol degradation.The influences of main operating parameters such as reaction temperature,catalyst amount,hydrogen peroxide dosage and initial pH of solution on phenol degradation rate were investigated.The maximum mineralization of phenol was achieved at 60°C,6 g/L Fe78Si9B13, 0.31 mol/L hydrogen peroxide,with an initial pH of 2.5.More than 99%of phenol was completely removed under the optimum conditions within 10 min for a solution containing 1000 mg/L of phenol.Batch experiments for solutions containing phenol con- centrations ranging from 50 to 2000 mg/L were investigated under the above conditions and the same excellent degradation rate was obtained.The Fe78Si9B13 showed better catalytic activity than iron powder and Fe 2+ .Addition of n-butannol(hydroxyl radical scavenger)decreased the degradation rate of phenol,which demonstrates that hydroxyl radicals were mainly responsible for the removal of phenol.We demonstrated that phenol may be degraded by hydroxyl radicals decomposed by hydrogen peroxide on the surface of Fe78Si9B13 and illustrated the reaction mechanism for this process.This amorphous alloy exhibited high stability in recycling experiments and showed excellent reuse performance even after continuous operations of 8 cycles. 相似文献
104.
An in vitro feasibility study of the use of poly(ethylene carbonate) (PEC) as a
biodegradable coating material for drug-eluting stents is reported, and the performance of PEC
is compared with that of poly(lactic-co-glycolic acid) (PLGA). Scanning electron microscopy
(SEM) images of PEC and PLGA discs after treatment with an alkaline KO2 solution as a
superoxide source showed that the PEC maintained its integrity whereas holes and small particles
appeared during the treatment of PLGA. Sirolimus and paclitaxel were loaded into PEC and
PLGA in order to study drug release performance. Attenuated total reflectance–infrared (ATR–
FTIR) spectroscopy of sirolimus, PEC and the sirolimus-loaded PEC coating showed that no
chemical reaction occurred between sirolimus and PEC. The results of atomic force microscopy
(AFM) revealed that the mean roughness (Ra) values of the bare metal stent (BMS) and the drugeluting
stent (DES) were 2.3 nm and 1.0 nm, respectively. After balloon expansion experiments, no
delamination or destruction of the PEC coating was observed. The drug release profile of sirolimus
was different from that of paclitaxel when PEC was employed as the drug carrier, and the release curves of sirolimus were different when PEC and PLGA were used as drug carriers. All the
experimental results demonstrated that PEC was one of the best potential stent-coating materials. 相似文献
105.
以12根抗拔桩承载力为研究对象,利用4参数的贝塔分布拟合出抗拔桩承载力试计比(承载力实测值和计算值的比)的概率分布.通过K-S检验法检验指出:贝塔分布的拟合精度优于常见的正态分布、对数正态分布和极值I型分布.利用蒙特卡罗法计算出抗拔桩承载力的可靠度指标,计算结果表明:承载力试计比的均值、荷载组合、荷载比和安全系数对可靠度有显著的影响.最后利用荷载抗力系数设计法给出了抗拔桩的抗力系数. 相似文献
106.
针对小基高比立体匹配中的"黏合"现象和深度精度问题,提出一种小基高比立体匹配方法.该方法通过将自适应窗口技术和多窗口策略相结合为参考图像确定匹配窗口;然后根据规范化互相关函数和"胜者全取"策略计算整数级视差;再以整数级视差为基础利用基于二分法的亚像素匹配方法计算亚像级视差;最后采用基于图像分割的迭代传播方法以获得稠密视差图.实验结果表明:该立体匹配算法减少了小基高比匹配中的"黏合"现象,同时获得了稠密的高精度亚像素级视差,其亚像素精度可优于1/20个像元. 相似文献
107.
Bian Hongwei~ Jin Zhihua~ & Tian Weifeng~ . Dept. of Information Measurement Technology Instruments Shanghai Jiaotong Univ. Shanghai P. R. China . Dept. of Electrical Engineering of Naval Univ. of Engineering Wuhan ) 《系统工程与电子技术(英文版)》2006,17(3):502-508
1 .INTRODUCTIONInertial navigation system(INS) and Global posi-tioning system ( GPS) are two major navigationsystems now widely usedfor marine applications a-round the world. Considering both systems pos-sess complementary working characteristics , abooming attention is focused on finding effectivemethods to combine the two different systems toconstituteintegrated navigation system with higheraccuracy and better performance .Information likeGPS position and velocity are often chosen as… 相似文献
108.
基于GIS和USLE模型的巢湖流域土壤侵蚀评价 总被引:3,自引:0,他引:3
土壤侵蚀是全世界都关心的土地资源与环境保护问题。巢湖作为中国第五大淡水湖,近年来由于水体富营养化产生的水华现象引起多方重视,对巢湖流域土壤侵蚀评估对于环境保护战略与土地规划政策具有重要的意义。基于GIS平台,采用通用土壤流失方程(USLE)来评估巢湖流域14县/区2000年到2010年土壤侵蚀空间分布变化趋势。研究表明:(1)巢湖流域土壤侵蚀严重区域主要分布在金安区、舒城县、居巢区以及含山县的丘陵地区,即杭埠河-丰乐河流域、裕溪河流域与柘皋河流域的上游地区;(2)从2000年到2010年,土壤微度侵蚀、强度侵蚀、极强度侵蚀和剧烈侵蚀区域占巢湖流域总面积比例分别减少了0.5%、0.05%、0.21%和0.23%,而轻度侵蚀、中度侵蚀区域所占比例分别增加了0.98%和0.01%,总体呈现土壤强度侵蚀、极强度侵蚀与剧烈侵蚀区域向轻、中度侵蚀转移的趋势。(3)植被覆盖度变化是巢湖流域土壤侵蚀分级发生变化的主要原因,总体上,2000~2010年研究区由于植被覆盖度的波动性增加呈现土壤侵蚀分级波动性降低的趋势。 相似文献
109.
本文利用化学方法从油莎豆中提取出了蛋白蛋、脂肪和糖,并进行了定性和定量分析,为大面积推广种植油莎豆、开发利用其相应产品提供了科学依据。 相似文献
110.
提出了在FTP(文件传输协议)方式下,客户机/服务器工作方式下的MIS(管理信息系统),在改变数据库口令和应用时能自动更新客户端应用的有效方法。 相似文献