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   462篇
  免费   9篇
  471篇
  2023年   2篇
  2022年   7篇
  2021年   9篇
  2020年   9篇
  2019年   7篇
  2018年   12篇
  2017年   11篇
  2016年   20篇
  2015年   12篇
  2014年   19篇
  2013年   37篇
  2012年   41篇
  2011年   36篇
  2010年   11篇
  2009年   19篇
  2008年   29篇
  2007年   32篇
  2006年   42篇
  2005年   25篇
  2004年   30篇
  2003年   14篇
  2002年   15篇
  2001年   3篇
  2000年   3篇
  1999年   4篇
  1998年   3篇
  1997年   1篇
  1996年   3篇
  1995年   4篇
  1994年   3篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1985年   1篇
  1983年   1篇
  1979年   1篇
  1962年   1篇
排序方式: 共有471条查询结果,搜索用时 0 毫秒
461.
Apilarnil is 3–7 days old drone larvae. It is an organic bee product known to be rich in protein. In this study, the biological activities of Apilarnil were determined by its antioxidant and enzyme inhibition effects. Antioxidant activities were determined by Fe3+, Cu2+, Fe3+-TPTZ ((2,4,6-tris(2-pyridyl)-s-triazine), reducing ability and 1,1-diphenyl-2-picrylhydrazyl (DPPH⋅) scavenging assays. Also, its enzyme inhibition effects were tested against carbonic anhydrase I and II isoenzymes (hCA I, hCA II), acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Antioxidant activity of Apilarnil was generally lower than the standard molecules in the applied methods. In DPPH⋅ radical scavenging assay, Apilarnil exhibited higher radical scavenging than some standards. Enzyme inhibition results towards hCA I (IC50: 14.2 μg/mL), hCA II: (IC50: 11.5 μg/mL), AChE (IC50: 22.1 μg/mL), BChE (IC50: 16.1 μg/mL) were calculated. In addition, the quantity of 53 different phytochemical compounds of Apilarnil was determined by a validated method by LC/MS/MS. Compounds with the highest concentrations (mg analyte/g dry extract) were determined as quinic acid (1091.045), fumaric acid (48.714), aconitic acid (47.218), kaempferol (39.946), and quercetin (27.508). As a result, it was determined that Apilarnil had effective antioxidant profile when compared to standard antioxidants.  相似文献   
462.
In our study, we tried to assess the relation between ductus venosus Doppler indices [pulsatility index (PI), resistance index (RI) and S/D] and first-trimester screening markers (MoM of serum pregnancy-associated plasma protein A, pappalysin 1 (PAPP-A), MoM of serum free β-human chorionic gonadotrophin (β-hCG), and nuchal translucency (NT) and second trimester screening markers (MoM of serum α-fetoprotein, MoM of serum total β-hCG and MoM of serum estriol). We analyzed the data of 121 singleton pregnancies. Roche cobas e 601ECLIA (electrochemiluminescence immunoassay) was used to measure MoM of serum PAPP-A and Roche cobas e 602 ECLIA (electrochemiluminescence immunoassay) was used to measure MoM of serum free β-hCG in the first trimester. Beckman Coulter Access 2 Immunoassay was used to measure MoM of serum α-fetoprotein, MoM of serum total β-hCG and MoM of serum estriol in the second trimester. The first author performed all ultrasound screenings and ductus venosus Doppler studies. What we found new in our study is presented as following; MoM of serum α-fetoprotein had a negative correlation with RI of ductus venosus Doppler, MoM of serum estriol had a negative correlation with RI of ductus venosus Doppler and MoM of serum estriol had a negative correlation with S/D of ductus venosus doppler. The results of our study suggest that ductus venosus Doppler can be used to increase the effectiveness of the second trimester screening test.  相似文献   
463.
This study was designed to assess the tolerability of chronomodulated infusion chemotherapy, individualized by the rhythm of peripheral blood cells. Twenty patients with metastatic gastric cancer were randomized to chronotherapy or day-time arms of 5-fluorouracil (FU) (600 mg/m2, 8 h inf.d1-5) and folinic acid (FA) (20 mg/m2, iv, d1-5) in the first cycle and crossed-over to the other arm in the following cycles. Ten of 18 evaluable patients were assigned to chronotherapy arm and eight to day-time in the first cycle. Although there was no significant difference between two arms on enrollment, chronotherapy arm yielded an improvement of 45% of QLQ-C30 scores (p = 0.021) and the day-time arm had 11% improvement (p = 0.575). After the crossing-over, chronotherapy arm, again, had a significant improvement in QLQ-C30 scores, compared to the day-time arm (14% vs. -18%, p = 0.001, respectively). Mucositis/diarrhea was significantly higher in the day-time arm compared to chronotherapy arm (p = 0.015). In conclusion, chronomodulated infusion of 5-FU might improve the quality of life.  相似文献   
464.
Agriculture is the most intensive form of environmental exploitation performed by mankind. It involves replacing the natural ecosystem with an artificial plant community comprising one or more crop species, and weeds can invade the cleared land. Initially, the adoption of agriculture did not necessarily imply an improvement in standard of living (there is, in fact, evidence to the contrary), but as agricultural efficiency improved, surpluses were generated on top of mere subsistence levels. It may take many years of labor in order to obtain a crop that has all of the desired traits. It is not possible to control which genes are transferred from the parents to the offspring, and the results are often uncertain. In comparison, the utilization of genetic engineering to improve crops can be a faster and more precise approach. Unlike traditional breeding, genetic engineering makes it possible to select the specific traits desired and insert the genes that code for them into the plant.  相似文献   
465.
Eighteen prostacyclin injections (19.4±1.5 μg/kg) were performed in five chronically instrumented, intact fetal lambs in order to study the effects on pulmonary blood flow. These resulted in a brief period of bradycardia followed by a more prolonged period of increased pulmonary blood flow. In this latter phase, pulmonary blood flow increased from a baseline value of 49±4 ml/(kg min) to 122±10 ml/(kg min). Systolic/diastolic pulmonary arterial pressure simultaneously fell from to mm Hg. Flow through the ductus arteriosus was unchanged and right ventricular output increased to account for the increased pulmonary blood flow. Thus, prostacyclin causes pulmonary vasodilation in intact fetal lambs and may participate in the control of fetal pulmonary blood flow and the circulatory adjustments to extra-uterine life.  相似文献   
466.
Our extension of the AM1 semiempirical molecular orbital technique, AM1*, has been parameterized for the elements V and Cr. The basis sets for both metals contain one set each of s-, p- and d-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Cu, Zn, Br, Zr, Mo and I. The performance and typical errors of AM1* are discussed for V and Cr and compared with available NDDO Hamiltonians. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
467.
Secondary infections related to neutropenia and functional defects of phagocytes are common consequences in patients treated for cancer. The hematopoietic colony-stimulating factors (CSF) have been introduced into clinical practice as additional supportive measures that can reduce the incidence of infectious complications in patients with cancer and neutropenia. The aim of this study was to determine the role of␣granuolcyte/macrophage(GM)-CSF and granulocyte(G)-CSF in enhancing in vivo human neutrophil function. A luminol-dependent chemiluminescence assay was developed to evaluate whether the repair in neutropenia accompanies the ability of neutrophils to function. A dose of 5 μg G-CSF kg−1 day−1 [recombinant human (rHu) G-CSF; filgrastim] or 250 μg GM-CSF m−2 day−1 (rHu GM-CSF; molgramostim) was administered subcutaneously once daily to 12 metastatic cancer patients being treated with different cytotoxic regimens. All injections of CSF were given after the initiation of neutropenia and continued until the occurrence of an absolute neutrophil recovery. rHu GM-CSF and rHu G-CSF, administered once daily at the 250 μg m−2 day−1 and 5 μg kg−1 day−1 level, were effective in increasing the absolute neutrophil count and neutrophil function, as measured by an automated chemiluminescence system. Received: 26 February 1998 / Accepted: 21 May 1998  相似文献   
468.
Circadian variations in superoxide dismutase (SOD) activity were determined in liver homogenates of Balb-C mice that were synchronized under controlled environmental conditions with 12 h light: 12 h dark. The activity of hepatic SOD exhibited a significant circadian rhythm, with a minimum at 01:00 h and maximum at 10:00-13:00 h. It is concluded that fluctuations in hepatic SOD activity render mice more susceptible to the toxic effects of reactive oxygen radicals at particular times of the day.  相似文献   
469.
470.
Abstract

Volatile organic compounds (VOCs) are some of the most important pollutants that have adverse effects on human health. In this study, simultaneous indoor and outdoor air samples were collected from four types of microenvironments (restaurants, photocopy centers, dry cleaners, and auto paint shops) in Kocaeli, Turkey in both winter and summer. Twenty-four VOCs were detected using gas chromatography and a flame ionization detector. The aim of the study was to determine the VOC concentrations in various workplaces and investigate associated health risks. Results show that the highest mean total VOC concentrations are in auto paint shops (14,066 µg/m3 in winter, 3441 µg/m3 in summer) followed by dry cleaners, restaurants, and photocopy centers. Total cancer risk was approximately 310 times greater than the acceptable limit in auto paint shops, 44 times greater in restaurants, 42 times greater in dry cleaners, and 17 times greater in photocopy centers. Total hazard quotients were also greater than the acceptable limit in all microenvironments.  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