全文获取类型
收费全文 | 2721篇 |
免费 | 198篇 |
国内免费 | 121篇 |
专业分类
3040篇 |
出版年
2023年 | 21篇 |
2022年 | 57篇 |
2021年 | 105篇 |
2020年 | 72篇 |
2019年 | 90篇 |
2018年 | 101篇 |
2017年 | 73篇 |
2016年 | 86篇 |
2015年 | 159篇 |
2014年 | 158篇 |
2013年 | 218篇 |
2012年 | 225篇 |
2011年 | 180篇 |
2010年 | 128篇 |
2009年 | 103篇 |
2008年 | 95篇 |
2007年 | 112篇 |
2006年 | 104篇 |
2005年 | 106篇 |
2004年 | 105篇 |
2003年 | 80篇 |
2002年 | 55篇 |
2001年 | 64篇 |
2000年 | 55篇 |
1999年 | 55篇 |
1998年 | 28篇 |
1997年 | 26篇 |
1996年 | 23篇 |
1995年 | 28篇 |
1994年 | 27篇 |
1993年 | 19篇 |
1992年 | 39篇 |
1991年 | 30篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1971年 | 8篇 |
排序方式: 共有3040条查询结果,搜索用时 0 毫秒
11.
Lijuan Chen Yi Zhang Lin Tang Danlian Huang Can Liu Ya Pang Jie Luo 《Analytical biochemistry》2010,407(2):172-179
Picloram, a herbicide widely used for broadleaf weed control, is persistent and mobile in soil and water with adverse health and environmental effects. It is important to develop a sensitive method for accurate detection of trace picloram in the environment. In this article, a type of ordered three-dimensional (3D) gold (Au) nanoclusters obtained by two-step electrodeposition using the spatial obstruction/direction of the polycarbonate membrane is reported. Bovine serum albumin (BSA)-picloram was immobilized on the 3D Au nanoclusters by self-assembly, and then competitive immunoreaction with picloram antibody and target picloram was executed. The horseradish peroxidase (HRP)-labeled secondary antibody was applied for enzyme-amplified amperometric measurement. The electrodeposited Au nanoclusters built direct electrical contact and immobilization interface with protein molecules without postmodification and positioning. Under the optimal conditions, the linear range for picloram determination was 0.001-10 μg/ml with a correlation coefficient of 0.996. The detection and quantification limits were 5.0 × 10−4 and 0.0021 μg/ml, respectively. Picloram concentrations in peach and excess sludge supernatant extracts were tested by the proposed immunosensor, which exhibited good precision, sensitivity, selectivity, and storage stability. 相似文献
12.
13.
Infectious hematopoietic necrosis virus (IHNV) is an important fish pathogen that infects both wild and cultured salmonids. As a species of the genus Novirhabdovirus, IHNV is a valuable model system for exploring the host entry mechanisms of rhabdoviruses. In this study, quantum dots (QDs) were used as fluorescent labels for sensitive, long-term tracking of IHNV entry. Using live-cell fluorescence microscopy, we found that IHNV is internalized through clathrin-coated pits after the virus binds to host cell membranes. Pretreatment of host cells with chlorpromazine, a drug that blocks clathrin-mediated endocytosis, and clathrin light chain (LCa) depletion using RNA interference both resulted in a marked reduction in viral entry. We also visualized transport of the virus via the cytoskeleton (i.e., actin filaments and microtubules) in real time. Actin polymerization is involved in the transport of endocytic vesicles into the cytosol, whereas microtubules are required for the trafficking of clathrin-coated vesicles to early endosomes, late endosomes, and lysosomes. Disrupting the host cell cytoskeleton with cytochalasin D or nocodazole significantly impaired IHNV infectivity. Furthermore, infection was significantly affected by pretreating the host cells with bafilomycin A1, a compound that inhibits the acidification of endosomes and lysosomes. Strong colocalizations of IHNV with endosomes indicated that the virus is internalized into these membrane-bound compartments. This is the first report in which QD labeling is used to visualize the dynamic interactions between viruses and endocytic structures; the results presented demonstrate that IHNV enters host cells via clathrin-mediated endocytic, cytoskeleton-dependent, and low-pH-dependent pathways. 相似文献
14.
Pang J Salim A Lee VJ Hibberd ML Chia KS Leo YS Lye DC 《PLoS neglected tropical diseases》2012,6(5):e1641
Background
Dengue hemorrhagic fever (DHF) is a severe form of dengue, characterized by bleeding and plasma leakage. A number of DHF risk factors had been suggested. However, these risk factors may not be generalized to all populations and epidemics for screening and clinical management of patients at risk of developing DHF. This study explored demographic and comorbidity risk factors for DHF in adult dengue epidemics in Singapore in year 2006 (predominantly serotype 1) and in year 2007–2008 (predominantly serotype 2).Methods
A retrospective case-control study was conducted with 149 DHF and 326 dengue fever (DF) patients from year 2006, and 669 DHF and 1,141 DF patients from year 2007–2008. Demographic and reported comorbidity data were collected from patients previously. We performed multivariate logistic regression to assess the association between DHF and demographic and co-morbidities for year 2006 and year 2007–2008, respectively.Results
Only Chinese (adjusted odds ratio [AOR] = 1.90; 95% confidence interval [CI]: 1.01–3.56) was independently associated with DHF in year 2006. In contrast, age groups of 30–39 years (AOR = 1.41; 95% CI:1.09–1.81), 40–49 years (AOR = 1.34; 95% CI:1.09–1.81), female (AOR = 1.57; 95% CI:1.28–1.94), Chinese (AOR = 1.67; 95% CI:1.24–2.24), diabetes (AOR = 1.78; 95% CI:1.06–2.97), and diabetes with hypertension (AOR = 2.16; 95%CI:1.18–3.96) were independently associated with DHF in year 2007–2008. Hypertension was proposed to have effect modification on the risk of DHF outcome in dengue patients with diabetes. Chinese who had diabetes with hypertension had 2.1 (95% CI:1.07–4.12) times higher risk of DHF compared with Chinese who had no diabetes and no hypertension.Conclusions
Adult dengue patients in Singapore who were 30–49 years, Chinese, female, had diabetes or diabetes with hypertension were at greater risk of developing DHF during epidemic of predominantly serotype 2. These risk factors can be used to guide triaging of patients who require closer clinical monitoring and early hospitalization in Singapore, when confirmed in more studies. 相似文献15.
Zhugang Li Lingxia Zhao Guoyin Kai Shunwu Yu Youfang Cao Yongzhen Pang Xiaofen Sun Kexuan Tang 《Plant Physiology and Biochemistry》2004,42(10):789-794
Plant growth and productivity are greatly affected by water stress, such as drought and salinity. Here we report on the cloning and expression analysis of a water stress-induced gene from Brassica oleracea (designated as BoWS, GenBank accession number AY571333) by rapid amplification of cDNA ends (RACE). The full-length cDNA of BoWS consisted of 594 bp and contained a 285 bp open reading frame (ORF) encoding a 95-amino-acid protein. The deduced protein had a calculated molecular mass of 10.53 kDa and an isoelectric point of 6.93. The sequence similarity and comparative analysis showed that BoWS was 84% identical to Arabidopsis thaliana putative water stress-induced protein (GenBank accession number AAM67282). Southern blot analysis indicated that BoWS was a low-copy gene. Northern blot analysis revealed that the expression of BoWS was upregulated by abscisic acid (ABA), mannitol, NaCl, drought, salicylic acid (SA) and hydrogen peroxide (H(2)O(2)). Our results indicate that BoWS is extremely related to the water-deficit stress in B. oleracea. 相似文献
16.
In some clinical development programs, there are potential biomarkers with promising but uncertain predictive effect, while the probability of success in the overall population cannot be readily dismissed. It is risky to focus only on the overall population, or just the biomarker subpopulation. In 2009, Chen and Beckman proposed a Bayesian decision framework to optimize the type I error rate (alpha) allocation in a Phase III clinical study with possible predictive subset effect. The utilization of internal data in this framework is of particular interest because it provides an opportunity to mitigate the potential risk of misspecified study assumptions using an auto-adaptive strategy. In this paper, we examine this auto-adaptive strategy in detail through extensive numerical case studies and provide guidance on the appropriate use of partial current trial (internal) data in this data-driven optimization framework. We show that internal data can be used to inform the alpha allocation to hypothesis testing in the overall population and the subgroup. The resulting adaptive testing strategy is robust with respect to the uncertainty in the predictive subgroup effect and biomarker prevalence. 相似文献
17.
Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats. 相似文献
18.
19.
Direct electrochemistry and electrocatalysis of heme-proteins entrapped in agarose hydrogel films 总被引:5,自引:0,他引:5
Three heme-proteins, including myoglobin (Mb), hemoglobin (Hb) and horseradish peroxidase (HRP), were immobilized on edge-plane pyrolytic graphite (EPG) electrodes by agarose hydrogel. The proteins entrapped in the agarose film undergo fast direct electron transfer reactions, corresponding to FeIII = e- --> FeII. The formal potential (E degrees'), the apparent coverage (Gamma), the electron transfer coefficient (alpha) and the apparent electron transfer rate constant (ks) were calculated by integrating cyclic voltammograms or performing nonlinear regression analysis of square wave voltammetric (SWV) experimental data. The E degrees's are linearly dependent on solution pH (redox Bohr effect), indicating that the electron transfer was proton-coupled. Ultraviolet visible (UV-Vis) and reflection-absorption infrared (RAIR) spectra suggest that the conformation of proteins in the agarose film are little different from that proteins alone, and the conformation changes reversibly in the range of pH 3.0-10.0. Atomic force microscopy (AFM) images of the agarose film indicate a stable and crystal-like structure formed possibly due to the synergistic interaction of hydrogen bonding between N,N-dimethylformamide (DMF), agarose hydrogel and heme-proteins. This suggests a strong interaction between the heme-proteins and the agarose hydrogel. DMF plays an important role in immobilizing proteins and enhancing electron transfer between proteins and electrodes. The mechanisms for catalytic reduction of hydrogen peroxide and nitric oxide (NO) by proteins entrapped in agarose hydrogel were also explored. 相似文献
20.
Qin Zhou Fan Zhao Ze-ping Lv Chen-guang Zheng Wei-dong Zheng Liang Sun Na-na Wang Shenghang Pang Fabiana Michelsen de Andrade Mian Fu Xiang-hua He Juan Hui Wen-yu Jiang Chu-yu Yang Xiao-hong Shi Xiao-quan Zhu Guo-fang Pang Yi-ge Yang Hai-qun Xie Wan-dong Zhang Cai-you Hu Ze Yang 《PloS one》2014,9(1)