首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3660篇
  免费   179篇
  国内免费   46篇
化学   2572篇
晶体学   41篇
力学   141篇
综合类   2篇
数学   444篇
物理学   685篇
  2024年   38篇
  2023年   69篇
  2022年   384篇
  2021年   325篇
  2020年   202篇
  2019年   188篇
  2018年   165篇
  2017年   139篇
  2016年   211篇
  2015年   142篇
  2014年   156篇
  2013年   287篇
  2012年   231篇
  2011年   250篇
  2010年   148篇
  2009年   129篇
  2008年   146篇
  2007年   126篇
  2006年   100篇
  2005年   81篇
  2004年   56篇
  2003年   48篇
  2002年   46篇
  2001年   24篇
  2000年   18篇
  1999年   11篇
  1998年   13篇
  1997年   9篇
  1996年   12篇
  1995年   10篇
  1994年   6篇
  1993年   6篇
  1992年   8篇
  1991年   8篇
  1989年   6篇
  1988年   8篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1984年   5篇
  1983年   4篇
  1982年   5篇
  1981年   8篇
  1980年   5篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1976年   8篇
  1973年   3篇
  1970年   2篇
排序方式: 共有3885条查询结果,搜索用时 15 毫秒
71.
Cellulose - The sustainable development of oil–gas and petrochemical industries necessitates the development of cost-effective and eco-friendly technologies to treat mass-produced oily...  相似文献   
72.
Cellulose - This study focuses on the synergistic effects of hydroxide based nanoparticles namely aluminum trihydrate (ATH) and zirconium hydroxide (ZHO) on the mechanical characteristics, thermal...  相似文献   
73.
Journal of Thermal Analysis and Calorimetry - Nanofluids have recently attracted attention of many researchers due to their growing potential applications in heat transfer devices. They possess...  相似文献   
74.
Medicinal plants have been traditionally used to treat cancer in Ethiopia. However, very few studies have reported the in vitro anticancer activities of medicinal plants that are collected from different agro-ecological zones of Ethiopia. Hence, the main aim of this study was to screen the cytotoxic activities of 80% methanol extracts of 22 plants against human peripheral blood mononuclear cells (PBMCs), as well as human breast (MCF-7), lung (A427), bladder (RT-4), and cervical (SiSo) cancer cell lines. Active extracts were further screened against human large cell lung carcinoma (LCLC-103H), pancreatic cancer (DAN-G), ovarian cancer (A2780), and squamous cell carcinoma of the esophagus (KYSE-70) by using the crystal violet cell proliferation assay, while the vitality of the acute myeloid leukemia (HL-60) and histiocytic lymphoma (U-937) cell lines was monitored in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) microtiter assay. Euphorbia schimperiana, Acokanthera schimperi, Kniphofia foliosa, and Kalanchoe petitiana exhibited potent antiproliferative activity against A427, RT-4, MCF-7, and SiSo cell lines, with IC50 values ranging from 1.85 ± 0.44 to 17.8 ± 2.31 µg/mL. Furthermore, these four extracts also showed potent antiproliferative activities against LCLC-103H, DAN-G, A2780, KYSE-70, HL-60, and U-937 cell lines, with IC50 values ranging from 0.086 to 27.06 ± 10.8 µg/mL. Hence, further studies focusing on bio-assay-guided isolation and structural elucidation of active cytotoxic compounds from these plants are warranted.  相似文献   
75.
Drought poses a serious threat to oilseed crops by lowering yield and crop failures under prolonged spells. A multi-year field investigation was conducted to enhance the drought tolerance in four genotypes of Camelina and canola by selenium (Se) application. The principal aim of the research was to optimize the crop yield by eliciting the physio-biochemical attributes by alleviating the adverse effects of drought stress. Both crops were cultivated under control (normal irrigation) and drought stress (skipping irrigation at stages i.e., vegetative and reproductive) conditions. Four different treatments of Se viz., seed priming with Se (75 μM), foliar application of Se (7.06 μM), foliar application of Se + Seed priming with Se (7.06 μM and 75 μM, respectively) and control (without Se), were implemented at the vegetative and reproductive stages of both crops. Sodium selenite (Na2SeO3), an inorganic compound was used as Se sources for both seed priming and foliar application. Data regarding physiochemical, antioxidants, and yield components were recorded as response variables at crop maturity. Results indicated that WP, OP, TP, proline, TSS, TFAA, TPr, TS, total chlorophyll contents, osmoprotectant (GB, anthocyanin, TPC, and flavonoids), antioxidants (APX, SOD, POD, and CAT), and yield components (number of branches per plant, thousand seed weight, seed, and biological yields were significantly improved by foliar Se + priming Se in both crops under drought stress. Moreover, this treatment was also helpful in boosting yield attributes under irrigated (non-stress) conditions. Camelina genotypes responded better to Se application as seed priming and foliar spray than canola for both years. It has concluded that Se application (either foliar or priming) can potentially alleviate adverse effects of drought stress in camelina and canola by eliciting various physio-biochemicals attributes under drought stress. Furthermore, Se application was also helpful for crop health under irrigated condition.  相似文献   
76.
Journal of Thermal Analysis and Calorimetry - In the present study, the thermal efficiency, convective heat transfer and friction factor analysis are investigated for a flat plate solar collector...  相似文献   
77.
Journal of Thermal Analysis and Calorimetry - This paper provides a theoretical study of 3D nanofluid flow with zero nanoparticles mass and constant heat fluxes conditions. An incompressible...  相似文献   
78.
Journal of Thermal Analysis and Calorimetry - The unsteady thermal behavior of a porous longitudinal fin in a fully wet circumstance in the existence of convection as well as radiation effect is...  相似文献   
79.
Journal of Thermal Analysis and Calorimetry - The thermal performance of an isothermal horizontal cylinder with different selected cross sections in cross-flow was investigated numerically. These...  相似文献   
80.
This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH4 + CO2 hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH4 + CO2 hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号