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   2892篇
  免费   141篇
  国内免费   3篇
  2023年   32篇
  2022年   61篇
  2021年   122篇
  2020年   74篇
  2019年   80篇
  2018年   110篇
  2017年   84篇
  2016年   135篇
  2015年   171篇
  2014年   191篇
  2013年   245篇
  2012年   295篇
  2011年   255篇
  2010年   144篇
  2009年   114篇
  2008年   123篇
  2007年   105篇
  2006年   105篇
  2005年   109篇
  2004年   85篇
  2003年   79篇
  2002年   59篇
  2001年   31篇
  2000年   29篇
  1999年   19篇
  1998年   12篇
  1997年   6篇
  1996年   8篇
  1995年   7篇
  1994年   13篇
  1993年   9篇
  1992年   17篇
  1991年   13篇
  1990年   9篇
  1989年   6篇
  1988年   4篇
  1986年   9篇
  1985年   8篇
  1984年   4篇
  1983年   3篇
  1982年   6篇
  1981年   4篇
  1980年   5篇
  1978年   6篇
  1977年   3篇
  1976年   4篇
  1975年   5篇
  1973年   2篇
  1972年   6篇
  1971年   2篇
排序方式: 共有3036条查询结果,搜索用时 31 毫秒
91.
Breast cancer recurrence (BCR) is a common treatment outcome despite curative-intent primary treatment of non-metastatic breast cancer. Currently used prognostic and predictive factors utilize tumor-based markers, and are not optimal determinants of risk of BCR. Germline-based copy number aberrations (CNAs) have not been evaluated as determinants of predisposition to experience BCR. In this study, we accessed germline DNA from 369 female breast cancer subjects who received curative-intent primary treatment following diagnosis. Of these, 155 experienced BCR and 214 did not, after a median duration of follow up after breast cancer diagnosis of 6.35 years (range = 0.60–21.78) and 8.60 years (range = 3.08–13.57), respectively. Whole genome CNA genotyping was performed on the Affymetrix SNP array 6.0 platform. CNAs were identified using the SNP-Fast Adaptive States Segmentation Technique 2 algorithm implemented in Nexus Copy Number 6.0. Six samples were removed due to poor quality scores, leaving 363 samples for further analysis. We identified 18,561 CNAs with ≥1 kb as a predefined cut-off for observed aberrations. Univariate survival analyses (log-rank tests) identified seven CNAs (two copy number gains and five copy neutral-loss of heterozygosities, CN-LOHs) showing significant differences (P<2.01×10−5) in recurrence-free survival (RFS) probabilities with and without CNAs.We also observed three additional but distinct CN-LOHs showing significant differences in RFS probabilities (P<2.86×10−5) when analyses were restricted to stratified cases (luminal A, n = 208) only. After adjusting for tumor stage and grade in multivariate analyses (Cox proportional hazards models), all the CNAs remained strongly associated with the phenotype of BCR. Of these, we confirmed three CNAs at 17q11.2, 11q13.1 and 6q24.1 in representative samples using independent genotyping platforms. Our results suggest further investigations on the potential use of germline DNA variations as prognostic markers in cancer-associated phenotypes.  相似文献   
92.
A reason for much pessimism about the environmental benefits of today's biofuels, essentially corn and sugarcane ethanol, is the so‐called indirect land‐use change (ILUC) emissions associated with expanding biofuel production. While there exist several simulation‐based estimates of indirect emissions, the empirical basis underlying key input parameters to such simulations is not beyond doubt, while empirical verification of indirect emissions is hard. Regardless, regulators have adopted global warming intensity ratings for biofuels based on those simulations and in some case are holding regulated firms accountable for (some forms of) leakage. Suffice to say that both the estimates of and the approach to regulating leakage are controversial. The objective of this study is therefore to review a wider economic in order to identify a broader set of policy options for mitigating emissions leakage. We find that controlling leakage by affixing responsibility to regulated firms lacks support in the broader literature, which emphasizes alternative approaches.  相似文献   
93.
94.
BackgroundObesity has become a major global health challenge due to its increasing prevalence, and the associated health risk. It is the main cause of various metabolic diseases including diabetes, hypertension, cardiovascular disease, stroke and certain forms of cancer.

Methods and Results

In the present study we evaluated the anti-obesity property of Daesiho-tang (DSHT), an herbal medicine, using high fat diet (HFD)-induced obese mice as a model. Our results showed that DSHT ameliorated body weight gain, decreased total body fat, regulated expression of leptin and adiponectin genes of adipose tissue and exerted an anti-diabetic effect by attenuating fasting glucose level and serum insulin level in HFD-fed animals. In addition, DSHT-treatment significantly reduced total cholesterol (TC), triglycerides (TG) and increased high density lipoprotein-cholesterol (HDL), glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) levels in serum and reduced deposition of fat droplets in liver. DSHT treatment resulted in significantly increased relative abundance of bacteria including Bacteroidetes, Bacteroidetes/Firmicutes ratio, Akkermansia Bifidobacterium., Lactobacillus, and decreased the level of Firmicutes. Using RT2 profiler PCR array, 39 (46%) genes were found to be differentially expressed in HFD-fed mice compared to normal control. However, normal gene expressions were restored in 36 (92%) genes of HFD-fed mice, when co-exposed to DSHT.

Conclusion/Major Findings

The results of this study demonstrated that DSHT is an effective herbal formulation in attenuation of obesity in HFD-fed mice through alteration of gene expressions and modulation of intestinal microbiota.  相似文献   
95.
Among hydrocarbon pollutants, diesel oil is a complex mixture of alkanes and aromatic compounds which are often encountered as soil contaminants leaking from storage tanks and pipelines or as result of accidental spillage. One of the best ecofriendly approaches is to restore contaminated soil by using microorganisms able to degrade those toxic compounds in a bioremediation process. In the present study, nineteen bacteria were isolated by enrichment culture technique from diesel spilled soil collected from electric generator shed of NBAIM, Mau. All the isolates were subjected to screening for lipase production and twelve isolates were found to be positive for lipase. When the isolates were screened for biosurfactant production using CTAB-methylene blue agar plates, only one isolate viz. 2NBDSH3 was found positive which was found to be phylogenetically closely related with Bacillus flexus. Despite having low emulsification index, the bacterium could degrade 88.6% of diesel oil in soil. Biosurfactant from the isolate was extracted and characterized through infra-red spectroscopy which indicated its possible lipopeptide nature which was further supported by strong absorption in UV range in the UV-Vis spectrum. The results of the present study indicated that the isolate either does not produce any bioemulsifier or produces very low amount of emulsifier rather it produces a lipopeptide biosurfactant which helps in degradation of diesel oil by lowering the surface tension. The bacterium thus isolated and characterized can serve as a promising solution for ecofriendly remediation of bacterium diesel contaminated soils.  相似文献   
96.
97.
98.

Objectives

Betulin (BT) is an abundant triterpene found predominantly in the bark of Himalayan birch. It is difficult to deliver it in vivo because of its low aqueous solubility. We have therefore developed novel formulations of BT for improving its solubility, bioavailability and therapeutic efficacy.

Results

Poly-d,l-lactide nanovectors (PLA NVs) were synthesized using poly(vinyl alcohol) and Lonicera japonica leaf extract (LE) as a stabiliser and named as PLA-1 NVs and PLA-2 NVs. PLA-1 NVs and PLA-2 NVs were used for the encapsulation of betulin (BT) and named as BT-En-1 and BT-En-2 NVs. The encapsulation efficiency of BT-En-1 and BT-En-2 NVs were 99.3 and 100 % respectively. Prepared nanoformulations were physically stable. An in vitro study revealed 45 % BT was released over 24 h. BT had a prolonged release from BT-En-2 NVs as compared to BT-En-1 NVs. BT-En-2 NVs had better anticancerous activity against SiHa cells than BT-En-1 NVs.

Conclusions

Developed BT-EN-2 NVs had better biocompatibility, excellent stability and enhanced release characteristics than BT-En-1 NVs.
  相似文献   
99.
100.

Aim

The aim of this study is to evaluate performance of ArcCHECK diode array detector for the volumetric modulated arc therapy (VMAT) patient specific quality assurance (QA). VMAT patient specific QA results were correlated with ion chamber measurement. Dose response of the ArcCHECK detector was studied.

Background

VMAT delivery technique improves the dose distribution. It is complex in nature and requires proper QA before its clinical implementation. ArcCHECK is a novel three dimensional dosimetry system.

Materials and methods

Twelve retrospective VMAT plans were calculated on ArcCHECK phantom. Point dose and dose map were measured simultaneously with ion chamber (IC-15) and ArcCHECK diode array detector, respectively. These measurements were compared with their respective TPS calculated values.

Results

The ion chamber measurements are in good agreement with TPS calculated doses. Mean difference between them is 0.50% with standard deviation of 0.51%. Concordance correlation coefficient (CCC) obtained for ion chamber measurements is 0.9996. These results demonstrate a strong correlation between the absolute dose predicted by our TPS and the measured dose. The CCC between ArcCHECK doses and TPS predictions on the CAX was found to be 0.9978. In gamma analysis of dose map, the mean passing rate was 98.53% for 3% dose difference and 3 mm distance to agreement.

Conclusions

The VMAT patient specific QA with an ion chamber and ArcCHECK phantom are consistent with the TPS calculated dose. Statistically good agreement was observed between ArcCHECK measured and TPS calculated. Hence, it can be used for routine VMAT QA.  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