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   7724篇
  免费   1356篇
  国内免费   939篇
化学   5540篇
晶体学   114篇
力学   440篇
综合类   53篇
数学   1127篇
物理学   2745篇
  2024年   11篇
  2023年   165篇
  2022年   197篇
  2021年   230篇
  2020年   301篇
  2019年   295篇
  2018年   247篇
  2017年   258篇
  2016年   418篇
  2015年   400篇
  2014年   529篇
  2013年   589篇
  2012年   749篇
  2011年   770篇
  2010年   502篇
  2009年   453篇
  2008年   510篇
  2007年   401篇
  2006年   406篇
  2005年   371篇
  2004年   323篇
  2003年   237篇
  2002年   213篇
  2001年   183篇
  2000年   118篇
  1999年   182篇
  1998年   118篇
  1997年   89篇
  1996年   107篇
  1995年   111篇
  1994年   91篇
  1993年   57篇
  1992年   58篇
  1991年   57篇
  1990年   67篇
  1989年   45篇
  1988年   29篇
  1987年   22篇
  1986年   28篇
  1985年   14篇
  1984年   14篇
  1983年   14篇
  1982年   8篇
  1981年   10篇
  1979年   3篇
  1976年   2篇
  1975年   2篇
  1974年   2篇
  1973年   2篇
  1928年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
This paper is dedicated to studying the following Schrödinger–Poisson system Δ u + V ( x ) u K ( x ) ϕ | u | 3 u = a ( x ) f ( u ) , x 3 , Δ ϕ = K ( x ) | u | 5 , x 3 . Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions.  相似文献   
22.
The success of intracellular protein therapy demands efficient delivery and selective protein activity in diseased cells. Therefore, a cascaded nanozymogen consisting of a hypoxia-activatable pro-protein, a hypoxia-inducing protein, and a hypoxia-strengthened intracellular protein delivery nanovehicle was developed. RPAB, an enzymatically inactive pro-protein of RNase, reversibly caged with hypoxia-cleavable azobenzene, was delivered with glucose oxidase (GOx) using hypoxia-responsive nanocomplexes (NCs) consisting of azobenzene-cross-linked oligoethylenimine (AOEI) and hyaluronic acid (HA). Upon NC-mediated delivery into cancer cells, GOx catalyzed glucose decomposition and aggravated tumoral hypoxia, which drove the recovery of RPAB back to the hydrolytically active RNase and expedited the degradation of AOEI to release more protein cargoes. Thus, the catalytic reaction of the nanozymogen was self-accelerated and self-cycled, ultimately leading to a cooperative anti-cancer effect between GOx-mediated starvation therapy and RNase-mediated pro-apoptotic therapy.  相似文献   
23.
In the present research, field-amplified sample injection–CZE (FASI–CZE) coupled with a diode array detector was established to determine trace level sulfa antibiotic. Sulfathiazole, sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfisoxazole were selected as analytes for the experiments. The background electrolyte solution consisted of 70.0 mmol/L borax and 60.0 mmol/L boric acid (including 10% methanol, pH 9.1). The plug was 2.5 mmol/L borax, which was injected into the capillary at a pressure of 0.5 psi for 5 s. Then the sample was injected into the capillary at an injection voltage of –10 kV for 20 s. The electrophoretic separation was carried out under a voltage of +19 kV. The capillary temperature was maintained at 20˚C throughout the analysis, and six sulfonamides were completely separated within 35 min. Compared with pressure injection-CZE, the sensitivity of FASI-CZE was increased by 6.25–10.0 times, and the LODs were reduced from 0.2–0.5 to 0.02–0.05 μg/mL. The method was applied to the determination of sulfonamides in river water and particulate matter samples. The recoveries were 78.59–106.59%. The intraday and interday precisions were 2.89–7.35% and 2.77–7.09%, respectively. This provides a simpler and faster method for the analysis of sulfa antibiotic residues in environmental samples.  相似文献   
24.
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation.  相似文献   
25.
A rapid and useful approach for screening potential bioactive components in Ginkgo biloba extract (GBE) with preventive effect against diabetic nephropathy (DN) was developed using mesangial cells extraction coupled with high‐performance liquid chromatography tandem mass spectrometry (LC‐MS/MS) analysis. Mesangial cells were first divided into two groups according to their treatments with high glucose or high glucose plus GBE. After incubation for 4, 8, 12, 16, 24 and 48 h, the cells were harvested and extracted with 40% acetic acid in water before LC‐MS/MS analysis. Then, 19 compounds and five metabolites were found to selectively combine with mesangial cells. Notably, compounds including quercetin and rutin were identified or tentatively characterized according to the results of retention time and MS spectra, which is highly consistent with our previous reports that quercetin and rutin are potent protective agents against glomerulosclerosis in DN. Therefore, all these results indicate that target cell extraction coupled with LC‐MS/MS analysis can be successfully applied for predicting the bioactive components in GBE with preventive effect against DN. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
26.
27.
28.
This study is concerned with a new,explicit approach by means of which forms of the large strain elastic potential for multiaxial rubberlike elasticity may be obtained based on data for a single deformation mode.As a departure from usual studies,here for the first time errors may be estimated and rendered minimal for all possible deformation modes and,furthermore,failure behavior may be incorporated.Numerical examples presented are in accurate agreement with Treloar's well-known data.  相似文献   
29.
30.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  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