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   2703篇
  免费   140篇
  国内免费   2篇
  2845篇
  2023年   40篇
  2022年   46篇
  2021年   58篇
  2020年   59篇
  2019年   48篇
  2018年   108篇
  2017年   106篇
  2016年   118篇
  2015年   87篇
  2014年   106篇
  2013年   174篇
  2012年   198篇
  2011年   198篇
  2010年   128篇
  2009年   88篇
  2008年   124篇
  2007年   133篇
  2006年   109篇
  2005年   153篇
  2004年   147篇
  2003年   145篇
  2002年   107篇
  2001年   51篇
  2000年   56篇
  1999年   32篇
  1998年   14篇
  1997年   14篇
  1996年   7篇
  1995年   6篇
  1994年   6篇
  1992年   12篇
  1991年   9篇
  1990年   11篇
  1989年   5篇
  1988年   7篇
  1987年   6篇
  1986年   6篇
  1985年   10篇
  1984年   6篇
  1983年   4篇
  1982年   6篇
  1981年   4篇
  1979年   7篇
  1978年   5篇
  1976年   4篇
  1975年   13篇
  1974年   8篇
  1973年   6篇
  1971年   5篇
  1969年   4篇
排序方式: 共有2845条查询结果,搜索用时 0 毫秒
51.
Perovskite solar cells (PSC) have shown that under laboratory conditions they can compete with established photovoltaic technologies. However, controlled laboratory measurements usually performed do not fully resemble operational conditions and field testing outdoors, with day‐night cycles, changing irradiance and temperature. In this contribution, the performance of PSCs in the rooftop field test, exposed to real weather conditions is evaluated. The 1 cm2 single‐junction devices, with an initial average power conversion efficiency of 18.5% are tracked outdoors in maximum power point over several weeks. In parallel, irradiance and air temperature are recorded, allowing us to correlate outside factors with generated power. To get more insight into outdoor device performance, a comprehensive set of laboratory measurements under different light intensities (10% to 120% of AM1.5) and temperatures is performed. From these results, a low power temperature coefficient of ?0.17% K?1 is extracted in the temperature range between 25 and 85 °C. By incorporating these temperature‐ and light‐dependent PV parameters into the energy yield model, it is possible to correctly predict the generated energy of the devices, thus validating the energy yield model. In addition, degradation of the tested devices can be tracked precisely from the difference between measured and modelled power.  相似文献   
52.
BackgroundGluconeogenesis and renal glucose excretion in kidneys both play an important role in glucose homeostasis. Sodium-glucose cotransporter (SGLT2), coded by the SLC5A2 gene is responsible for reabsorption up to 99% of the filtered glucose in proximal tubules. SLC5A2 genetic polymorphisms were suggested to influence glucose homeostasis. We investigated if common SLC5A2 rs9934336 polymorphism influences glycemic control and risk for macro or microvascular complications in Slovenian type 2 diabetes (T2D) patients.MethodsAll 181 clinically well characterized T2D patients were genotyped for SLC5A2 rs9934336 G>A polymorphism. Associations with glycemic control and T2D complications were assessed with nonparametric tests and logistic regression.ResultsSLC5A2 rs9934336 was significantly associated with increased fasting blood glucose levels (P<0.001) and HbA1c levels under the dominant genetic model (P=0.030). After adjustment for T2D duration, significantly higher risk for diabetic retinopathy was present in carriers of at least one polymorphic SLC5A2 rs9934336 A allele compared to non-carriers (OR=7.62; 95%CI=1.65-35.28; P=0.009).ConclusionsOur pilot study suggests an important role of SLC5A2 polymorphisms in the physiologic process of glucose reabsorption in kidneys in T2D patients. This is also the first report on the association between SLC5A2 polymorphism and diabetic retinopathy.  相似文献   
53.
Molecular Biology Reports - Heat shock protein 90 (Hsp90) is a key chaperone that is abnormally expressed in cancer cells, and therefore, designing novel compounds to inhibit chaperone activities...  相似文献   
54.

Ischemic infarctions occur under the influence of genetic and environmental factors. In our study, the role of ischemia-modified albumin and thiol balance, which are new markers in determining oxidative damage together with MTHFR gene polymorphisms and homocysteine levels, in the development of SBI was investigated. White matter lesions in the magnetic resonance imaging (MRI) results of the patients were evaluated according to the Fazekas scale and divided into groups (Grade 0, 1, 2, and 3). Homocysteine, folate, B12, IMA, total thiol, and native thiol were measured by biochemical methods. The polymorphisms in MTHFR genes were investigated by the RT-PCR method. According to our results, a significant difference was found between the groups in age, homocysteine, folate, IMA, total thiol, and native thiol parameters (p?<?0.05). When we compared the groups in terms of genotypes of the C677T gene, we found a significant difference in TT genotype between grades 0/3 and 1/3 (p?<?0.05). We determined that homocysteine and IMA levels increased and folate levels decreased in CC/TT and CT/TT genotypes in the C677T gene (p?<?0.05). Considering our results, the observation of homocysteine and IMA changes at the genotype level of the MTHFR C677T gene and between the groups, and the deterioration of thiol balance between the groups suggested that these markers can be used in the diagnosis of silent brain infarction.

  相似文献   
55.
Cytotechnology - Six extracts were obtained from plant species Hypericum perforatum L., collected at Samsun in Turkey. The aim of this study was to examine the mechanisms of the anticancer activity...  相似文献   
56.

Osteoarthritis (OA) is a common condition that impacts many people worldwide and involves weight-bearing joints, resulting in chronic pain. In this study, we aimed to compare the effectiveness of inpatient and outpatient physical therapy modalities and spa combination treatments on pain and functional status in patients with knee osteoarthritis. Seventy-four patients diagnosed with primary knee osteoarthritis were included in this study. The patients were randomized into two groups, inpatient (n?=?37) and outpatient (n?=?37) physical therapy. All patients received a physical therapy program (superficial heater + deep heater + transcutaneous electrical nerve stimulation) for 2 weeks and spa therapy. All cases were evaluated clinically, laboratory, and radiographically. In order to evaluate pain and functional status, the Visual Analogue Scale (VAS), Western Ontario and McMaster Universities osteoarthritis index (WOMAC), and Timed Up and Go (TUG) test were used before and after treatment. There was no significant difference between the two groups in the TUG test and WOMAC scores (p?>?0.05). However, a significant difference was found in VAS scores in favor of the outpatient group (p?<?0.05). As a result, although there was a significant improvement in pain scores in the outpatient group, multicenter studies with larger patient groups may provide more evidence.

  相似文献   
57.
International Journal of Biometeorology - Epidemiological studies have suggested an association between particulate air pollution, increased temperatures, and morbidity related to pregnancy...  相似文献   
58.
Nanocarriers for encapsulation and sustained release of agrochemicals such as auxins have emerged as an attractive strategy to provide enhanced bioavailability and efficacy for improved crop yields and nutrition quality. Here, a comparative study was conducted on the effectiveness of chitosan-as a biopolymeric nanocarrier- and silver-as a metallic nanocarrier- on in vitro adventitious rooting potential of microcuttings in apple rootstocks, for the first time. Auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) loaded silver (nAg) or chitosan nanoparticles (nChi) were synthesized. Scanning electron microscopy and transmission electron microscopy studies showed the spherical shape of the nanoparticles. The average particle size of IAA-nChi was 167.5 ± 0.1 nm while that of IBA-nChi was 123.2 ± 2.6 nm. The hydrodynamic diameter of the nAg-IAA and nAg-IBA particles were measured as 93.66 ± 5 nm and 71.41 ± 3 nm, respectively. Fourier transform infrared spectroscopy analyses confirmed the encapsulation of IAA or IBA in the chitosan nanoparticles. Meanwhile, the characteristic peaks of IAA or IBA were detected on silver nanoparticles. In-vitro adventitious rooting of microcuttings of Malling Merton 106 (MM 106) was significantly higher both in chitosan and silver nanoparticles loaded with IAA or IBA (91.7%–62.5%) compared to free IAA or IBA applications (50.0%–33.3%), except for 2.0 mg L–1 IBA (66.7%). However, the application of 2 mg L–1 IBA and IBA-nChi at all concentrations caused an undesirable large callus development.  相似文献   
59.
Therapies that utilize immune checkpoint inhibition work by leveraging mutation-derived neoantigens and have shown greater clinical efficacy in tumors with higher mutational burden. Whether tumors with a low mutational burden are susceptible to neoantigen-targeted therapy has not been fully addressed. To examine the feasibility of neoantigen-specific adoptive T-cell therapy, the authors studied the T-cell response against somatic variants in five patients with myelodysplastic syndrome (MDS), a malignancy with a very low tumor mutational burden. DNA and RNA from tumor (CD34+) and normal (CD3+) cells isolated from the patients’ blood were sequenced to predict patient-specific MDS neopeptides. Neopeptides representing the somatic variants were used to induce and expand autologous T cells ex vivo, and these were systematically tested in killing assays to determine the proportion of neopeptides yielding neoantigen-specific T cells. The authors identified a total of 32 somatic variants (four to eight per patient) and found that 21 (66%) induced a peptide-specific T-cell response and 19 (59%) induced a T-cell response capable of killing autologous tumor cells. Of the 32 somatic variants, 11 (34%) induced a CD4+ response and 11 (34%) induced a CD8+ response that killed the tumor. These results indicate that in vitro induction of neoantigen-specific T cells is feasible for tumors with very low mutational burden and that this approach warrants investigation as a therapeutic option for such patients.  相似文献   
60.
The antioxidant and mutagenic/antimutagenic activities of the fixed oils from Nigella sativa (NSO) and Nigella damascena (NDO) seeds, obtained by cold press-extraction from the cultivar samples, were comparatively investigated for the first time. The antimutagenicity test was carried out using classical and modified Ames tests. The fatty acid composition of the fixed oils was characterized by gas chromatography–mass spectrometry (GC-MS) while the quantification of thymoquinone in the fixed oils was determined by UPC2. The main components of the NSO and NDO were found to be linoleic acid, oleic acid, and palmitic acid. The results of the Ames test confirmed the safety of NSO and NDO from the viewpoint of mutagenicity. The results of the three antioxidant test methods were correlated with each other, indicating NDO as having a superior antioxidant activity, when compared to the NSO. Both NSO and NDO exhibited a significant protective effect against the mutagenicity induced by aflatoxin B1 in Salmonella typhimurium TA98 and TA100 strains. When microsomal metabolism was terminated after metabolic activation of the mycotoxin, a significant increase in antimutagenic activity was observed, suggesting that the degradation of aflatoxin B1 epoxides by these oils may be a possible antimutagenic mechanism. It is worthy to note that this is the first study to assess the mutagenicity of NSO and NDO according to the OECD 471 guideline and to investigate antimutagenicity of NDO in comparison to NSO against aflatoxin.  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