全文获取类型
收费全文 | 1423篇 |
免费 | 91篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 27篇 |
综合类 | 55篇 |
化学工业 | 211篇 |
金属工艺 | 218篇 |
机械仪表 | 58篇 |
建筑科学 | 204篇 |
矿业工程 | 26篇 |
能源动力 | 64篇 |
轻工业 | 83篇 |
水利工程 | 72篇 |
石油天然气 | 58篇 |
武器工业 | 3篇 |
无线电 | 123篇 |
一般工业技术 | 100篇 |
冶金工业 | 94篇 |
原子能技术 | 16篇 |
自动化技术 | 145篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 56篇 |
2021年 | 63篇 |
2020年 | 40篇 |
2019年 | 28篇 |
2018年 | 31篇 |
2017年 | 28篇 |
2016年 | 62篇 |
2015年 | 53篇 |
2014年 | 68篇 |
2013年 | 93篇 |
2012年 | 86篇 |
2011年 | 101篇 |
2010年 | 63篇 |
2009年 | 95篇 |
2008年 | 68篇 |
2007年 | 70篇 |
2006年 | 88篇 |
2005年 | 73篇 |
2004年 | 45篇 |
2003年 | 41篇 |
2002年 | 47篇 |
2001年 | 56篇 |
2000年 | 47篇 |
1999年 | 43篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1982年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有1557条查询结果,搜索用时 31 毫秒
1.
Juliano Henrique Borges Daniel Minutti de Oliveira Sofia Helena Valente de Lemos-Marini Bruno Geloneze Ezequiel Moreira Gonçalves Gil Guerra-Júnior 《Lipids》2021,56(1):101-110
We aimed to compare detailed fat distribution and lipid profile between young adults with congenital adrenal hyperplasia due to 21-hydroxylase enzyme deficiency and a control group. We also verified independent associations of treatment duration and daily hydrocortisone dose equivalent (HDE) with lipid profile within patients. This case–control study included 23 patients (7 male and 16 female) matched by an age range of young adults (18–31 years) with 20 control subjects (8 male and 12 female). Dual energy X-ray absorptiometry was used to measure the fat distribution. Male patients demonstrated elevated indices of fat mass for total (7.7 ± 2.1 vs. 4.5 ± 1.3 kg/m2, p = 0.003), trunk (4.0 ± 1.2 vs. 2.2 ± 0.8 kg/m2, p = 0.005), android (0.63 ± 0.24 vs. 0.32 ± 0.15 kg/m2, p = 0.008), gynoid (1.34 ± 0.43 vs. 0.74 ± 0.24 kg/m2, p = 0.005), arm (0.65 ± 0.16 vs. 0.39 ± 0.10 kg/m2, p = 0.009), and leg regions (2.7 ± 0.8 vs. 1.6 ± 0.4 kg/m2, p = 0.005) than the control group, but not in females. However, female patients demonstrated elevated ratio of low-density lipoprotein cholesterol to high-density lipoprotein cholesterol (1.90 ± 0.46 vs. 1.39 ± 0.47, p = 0.009) than the control group, but not in males. Total fat mass was inversely correlated with total testosterone (r = −0.64, p = 0.014) and positively correlated with leptin in males (r = 0.75, p = 0.002). An elevated daily HDE (β = 0.43, p = 0.038 and β = 0.47, p = 0.033) and trunk to total fat mass ratio (β = 0.46, p = 0.025, and β = 0.45, p = 0.037) were independently correlated with impaired lipid profile markers. Although there is no altered lipid profile, male patients demonstrated an increased fat distribution. However, female patients presented with an impaired lipid profile marker but demonstrated close values of normal fat distribution. Interestingly, the dose of glucocorticoid therapy can have some role in the lipid mechanisms. 相似文献
2.
The mammalian cell cycle is important in controlling normal cell proliferation and the development of various diseases. Cell cycle checkpoints are well regulated by both activators and inhibitors to avoid cell growth disorder and cancerogenesis. Cyclin dependent kinase 20 (CDK20) and p21Cip1/Waf1 are widely recognized as key regulators of cell cycle checkpoints controlling cell proliferation/growth and involving in developing multiple cancers. Emerging evidence demonstrates that these two cell cycle regulators also play an essential role in promoting cell survival independent of the cell cycle, particularly in those cells with a limited capability of proliferation, such as cardiomyocytes. These findings bring new insights into understanding cytoprotection in these tissues. Here, we summarize the new progress of the studies on these two molecules in regulating cell cycle/growth, and their new roles in cell survival by inhibiting various cell death mechanisms. We also outline their potential implications in cancerogenesis and protection in heart diseases. This information renews the knowledge in molecular natures and cellular functions of these regulators, leading to a better understanding of the pathogenesis of the associated diseases and the discovery of new therapeutic strategies. 相似文献
3.
A strongly electron deficient and high triplet energy host for blue emitters was developed by decorating a dibenzofuran modified biphenyl backbone structure with multiple CN units. Two hosts, 6,6′-bis(6-cyanodibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-3,3′-dicarbonitrile(CNDBF1) and 2,2′-bis(6-cyanodibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-4,4′-dicarbonitrile(CNDBF2), were derived from the CN decoration strategy for application in blue organic light-emitting diodes requiring high triplet energy host. They showed high triplet energy above 2.79 eV and acted as the electron transport type host based on the strong electron deficiency. The mixture of the CNDBF1 and CNDBF2 hosts with a hole transport type 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl host performed as the exciplex host of a blue phosphor and accomplished high external quantum efficiency of 22.7% in the blue phosphorescent organic light-emitting diodes. 相似文献
4.
基于实际井眼轨迹的抽油杆柱API设计方法 总被引:3,自引:0,他引:3
目前的抽油杆柱设计方法大都基于设计井眼轨迹或经验公式,因此设计的抽油杆柱与井眼的匹配性并没有达到最优,结果可能影响了抽油杆柱的受力特性和寿命。概述了目前现有的抽油杆柱设计方法,提出了基于实际井眼轨迹的抽油杆柱API设计方法,即考虑到在三维空间中井下粘滞阻力及动载的影响,利用微单元分析方法计算出轴向载荷与轴向应力,然后在此基础上进行杆柱组合设计,并给出了设计流程。以江苏油田永21-3井为例,对几种设计方法的设计结果进行了对比分析,结果表明,江苏油田目前采用的抽油杆柱设计方法包含了人为经验因素,并不是最优的杆柱设计结果,有待进一步改进。 相似文献
5.
介绍了数字信号处理器ADSP21XX芯片的特点以及实现FFT(快速离散付里叶变换)的方法,给出了ADSP21XX的C和汇编混合编程的特点及技巧。 相似文献
6.
Abhijit Majumdar Puneet Mishra Jürgen Meichsner 《Surface & coatings technology》2007,201(14):6437-6444
Carbon nitride films have been deposited by dielectric barrier discharge with a CH4/N2 gas mixture at different conditions. Fourier Transform Infrared (FTIR) spectroscopy, X-ray photo electron spectroscopy (XPS), Raman spectroscopy, Atomic force microscopy (AFM) and ellipsometry were used to systematically study chemical composition, bond structure and surface morphology of deposited films. Various bonds between carbon, nitrogen, hydrogen, and also oxygen were observed. 相似文献
7.
LIU Jianchao GUO Yunyi XING Zhongshu SHI Changxu Institute of Metal Research Academia Sinica Shenyang China LIANG Wubiao No. Automobile Factory Shiyan Hubei China Professor Institute of Metal Research Academia Sinica Shenyang China 《金属学报(英文版)》1989,2(3):168-173
Effects of 650℃ aging for 1—1000 h on structure and hydrogen embrittlement susceptibility(HES)of steel Cr21Ni6Mn9N have been investigated.The results show that M_(23)C_6 typecarbide precipitates at grain boundaries and Cr-depletive region appears beside them duringaging.The precipitates grow and connect each other as the aging time prolongs.Meanwhile,the degree of Cr-depletion aggravates first and then recovers gradually while the aging time isvery long,i.e.,1000 h.The HES of the steel increases with increasing aging time but does notreduce with the recovery of Cr content at the Cr-depletive region.That implies that the ex-isting of carbides at grain boundaries might be the main reason which promotes the HES ofsteel during aging. 相似文献
8.
通过超声辅助NaBH4还原法制备了3%Ru/CN催化剂(Ru的质量分数),该催化剂用于对苯二甲酸二甲酯(DMT)加氢制备1,4-环己烷二甲酸二甲酯(DMCD)。采用Raman、SEM、TEM、N2吸脱附、XRD、XPS等对载体和催化剂的组成、表面性质进行表征,结果表明,氮元素成功掺入碳骨架中且氮掺杂碳材料为介孔结构。研究了催化剂的用量、反应温度、H2 压力、反应时间等对催化剂加氢性能的影响。结果表明,当反应物用量为1.00 g,催化剂(含载体)用量为0.05 g,反应温度140 ℃,反应压力5.0 MPa,反应时间1 h时,DMT转化率为100%,DMCD选择性为99.3%。3%Ru/CN-1000催化剂循环使用5次后,催化剂催化性能未见明显下降,DMT转化率为98.8%,DMCD选择性为99.7%。 相似文献
9.
This study utilizes a two‐dimensional hydrodynamic model to calibrate and validate an inundation model for the Brisbane River estuary in Queensland, Australia. The bathymetry data used in the hydraulic model are derived from one arc second (1 s) shuttle radar topography mission digital elevation model, and the two‐dimensional hydraulic model is parameterized using the generated bathymetry with four open boundaries with water level observations and roughness coefficients. The calibration performance is evaluated by comparing the simulated results with the digitized records during the January 2013 flood event (a low magnitude event) at three gauging stations. The calibrated model is validated with water level data and available discharge data during the January 2011 flood (a large magnitude event) at four gauging stations located along the Brisbane River. Different performance indices are applied to demonstrate that the developed model performs well during calibration and validation. A sensitivity analysis is presented to assess the influence of riverbed elevation changes on the model because the main uncertainty of the model is the bathymetry data. The proposed model with the shuttle radar topography mission digital elevation model‐derived riverbed elevation for the Brisbane estuary is able to predict the flood inundation extent at an accuracy of 66.9% which is higher than or comparable with the accuracies of the existing studies. However, it is expected that the accuracy will increase if some improved bathymetry data become available in the future. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
10.
The popular Natural Resources Conservation Service Curve Number (NRCS-CN) (earlier known as Soil Conservation Service Curve Number (SCS-CN) method of rainfall-runoff modeling has often faced the criticism of exhibiting quantum jumps in runoff computations because of the sudden jumps appearing in CN-values derived from NEH-4 tables for three antecedent moisture conditions (AMC), viz., AMC-I, AMC-II, and AMC-III valid for dry, normal, and wet conditions, respectively. The variability of antecedent soil moisture within an AMC category is responsible for the abrupt jump and other deficiencies in the CN method for runoff estimation. This paper suggests a novel procedure to account for the antecedent moisture (M), preventing quantum jumps and eliminating deficiencies in determination of CN and, in turn, estimation of direct runoff. Its validity was verified utilizing the observed rainfall (P)-runoff (Q) events from 36 US watersheds, four sub-catchments of the Godavari basin, and small agricultural plots at Roorkee, India. The performance of the proposed model (M5) for runoff prediction was compared with the existing NRCS-CN (M1), Mishra and Singh (2002) (M2), Singh et al. (2015) (M3), and Verma et al. (2021) (M4) model using various performance indices. Using the CNs derived from observed events, model M5 was seen to have performed better than M1-M4 in terms of Nash Sutcliffe Efficiency (NSE), Root Mean Square Error (RMSE), and Percent Bias (PBIAS) for the data of US watersheds, and CN-P correlation improved as the coefficient of determination (R2) enhanced. Similarly, using the RS & GIS-based CNs on natural watersheds of the Godavari basin and considering AMC-I, the performance of M5 was again better than M1-M4 in terms of RMSE, Mean Bias Error (mBIAS), Mean Absolute Error (MAE), and Normalized-Nash Sutcliffe Efficiency (NNSE). Interestingly, there existed a significant (p < 0.05) relationship between the in-situ water content (w) measured for the experimental plots of Roorkee and the model input variable antecedent moisture (M), offering a physical touch to the conceptual model. 相似文献