全文获取类型
收费全文 | 8189篇 |
免费 | 537篇 |
国内免费 | 4篇 |
专业分类
8730篇 |
出版年
2024年 | 9篇 |
2023年 | 23篇 |
2022年 | 105篇 |
2021年 | 157篇 |
2020年 | 87篇 |
2019年 | 119篇 |
2018年 | 163篇 |
2017年 | 156篇 |
2016年 | 231篇 |
2015年 | 432篇 |
2014年 | 432篇 |
2013年 | 516篇 |
2012年 | 721篇 |
2011年 | 626篇 |
2010年 | 401篇 |
2009年 | 367篇 |
2008年 | 487篇 |
2007年 | 511篇 |
2006年 | 457篇 |
2005年 | 393篇 |
2004年 | 386篇 |
2003年 | 326篇 |
2002年 | 285篇 |
2001年 | 249篇 |
2000年 | 230篇 |
1999年 | 165篇 |
1998年 | 62篇 |
1997年 | 55篇 |
1996年 | 35篇 |
1995年 | 34篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 40篇 |
1991年 | 49篇 |
1990年 | 39篇 |
1989年 | 46篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1981年 | 9篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1974年 | 12篇 |
1973年 | 14篇 |
1972年 | 11篇 |
1971年 | 7篇 |
排序方式: 共有8730条查询结果,搜索用时 0 毫秒
851.
852.
853.
A laboratory-scale Bardenpho process was established to investigate the proper nitrogen loading rate (NLR) when modified spent caustic (MSC) is applied as electron donor and alkalinity source for denitrification. MSC injection induced autotrophic nitrogen removal with sulfur as electron donor and heterotrophic denitrification. The nitrogen removal rate (NRR) did not increase proportionally to NLR. Based on the total nitrogen concentration in the effluent observed in the trials with MSC, the NLR in the influent should not exceed 0.15 kg N/m3 d in order to satisfy water quality regulations. Microbial communities in the anoxic reactors were characterized by pyrosequencing of 16S rRNA gene sequences amplified by the polymerase chain reaction of DNA extracted from sludge samples. Microbial diversity was lower as MSC dosage was increased, and the injection of MSC caused an increase in SOB belonging to the genus Thiobacillus which is responsible for denitrification using sulfur. 相似文献
854.
X.?NirmalaEmail author S.?R.?Olson T.?C.?Holler K.?H.?Cho A.?M.?Handler 《BioControl》2011,56(3):333-340
Field population surveillance of a targeted insect pest species is critical in evaluating management programs such as the
sterile insect technique. Fluorescent powder dyes currently used to distinguish released tephritids from the field population
are not optimal in terms of reliability and human health issues. Genetically transformed tephritid species present the possibility
of using fluorescent transgenes for marking. Here we studied the stability of DsRed fluorescence in transgenic flies maintained
in aqueous torula yeast borax and propylene glycol. DsRed was stable in both solutions for three weeks by visual microscopic
observations and could be used to unambiguously distinguish them from non-fluorescent wild type flies. To compensate for any
potential ambiguity in visual identification a diagnostic PCR was developed that could specifically amplify the exotic heterologous
marker gene. Therefore, the use of sterile transgenic insect strains carrying stably integrated fluorescent protein marker
genes in biologically-based control programs could greatly improve released fly identification in pest management programs. 相似文献
855.
A novel one-step electrochemical method for DNA detection is described. The procedure utilizes a reaction catalyzed by a peroxidase-mimicking DNAzyme to produce a product, which forms an insoluble precipitation layer on the surface of an electrode. A rationally designed forward primer, conjugated with a peroxidase DNAzyme complementary sequence at its 5′-end, is used for PCR amplification of target DNA. As a result, the DNAzyme sequence is produced by amplification only when the target DNA is present in the sample. The PCR product is then subjected to the precipitation reaction on the electrode surface using an electrolyte assay buffer containing 4-chloronaphthol, hydrogen peroxide, ferrocenemethanol, hemin, and 5′-lambdaexonuclease. Finally, analysis is carried out using Faradaic impedance spectroscopy. The impedance value was found to greatly increase when target DNA is present owing to the formation of a precipitation layer on the electrode surface caused by the catalytic action of the DNAzyme. In contrast, no impedance increase is observed when a control sample not containing target DNA is utilized. By employing this strategy, target DNA from Chlamydia trachomatis was reliably detected within a 10 min period following precipitation without the need for complicated secondary procedures. This effort has led to the development of a highly convenient electrochemical one-step method for DNA detection that utilizes a peroxidase-mimicking DNAzyme, which is specifically designed to undergo amplification during PCR of target DNA. 相似文献
856.
Dam Go Junghwan Lee Ji‐Ae Choi Soo‐Na Cho Seon‐Hwa Kim Sang‐Hun Son Chang‐Hwa Song 《Cellular microbiology》2019,21(12)
Mycobacterium avium, a slow‐growing nontuberculous mycobacterium, causes fever, diarrhoea, loss of appetite, and weight loss in immunocompromised people. We have proposed that endoplasmic reticulum (ER) stress‐mediated apoptosis plays a critical role in removing intracellular mycobacteria. In the present study, we investigated the role of the regulated IRE1‐dependent decay (RIDD) pathway in macrophages during M. avium infection based on its role in the regulation of gene expression. The inositol‐requiring enzyme 1 (IRE1)/apoptosis signal‐regulating kinase 1 (ASK1)/c‐Jun N‐terminal kinase (JNK) signalling pathway was activated in macrophages after infection with M. avium. The expression of RIDD‐associated genes, such as Bloc1s1 and St3gal5, was decreased in M. avium‐infected macrophages. Interestingly, M. avium‐induced apoptosis was significantly suppressed by pretreatment with irestatin (inhibitor of IRE1α) and 4μ8c (RIDD blocker). Macrophages pretreated with N‐acetyl cysteine (NAC) showed decreased levels of reactive oxygen species (ROS), IRE1α, and apoptosis after M. avium infection. The expression of Bloc1s1 and St3gal5 was increased in NAC‐pretreated macrophages following infection with M. avium. Growth of M. avium was significantly increased in irestatin‐, 4μ8c‐, and NAC‐treated macrophages compared with the control. The data indicate that the ROS‐mediated ER stress response induces apoptosis of M. avium‐infected macrophages by activating IRE1α‐RIDD. Thus, activation of IRE1α suppresses the intracellular survival of M. avium in macrophages. 相似文献
857.
The primary objective of this study was to assess the in vitro melanogenesis inhibitory effects of methanolic extracts of the edible and medicinal lichens, Umbilicaria (Gyrophora) esculenta and Usnea longissima. The quantities of the total phenolic compounds of methanolic extract of the two lichen extracts were determined to be 1.46% and 2.62%, respectively. In order to evaluate the antioxidative effects of the extracts, we also measured electron donating abilities (EDA) and lipid peroxidation rates. The EDA values measured by the reduction of 1.1'-diphenyl-2-picrylhydrazyl (DPPH) were 72.8% and 80.7% for the extracts, with SC50 (median scavenging concentration) values of 1.29+/-0.05 mg/ml and 1.03+/-0.06 mg/ml, respectively. The rates of inhibition of lipid peroxidation using linoleic acid were 92.1% and 97.3% for the extracts, with IC50 (median inhibitory concentration) values of 0.57+/-0.05 mg/ml and 0.53+/-0.06 mg/ml, respectively. The inhibitory rates of the extracts against tyrosinase were 67.4% and 84.8%, respectively. The extracts were shown to reduce melanin formation in human melanoma cells. Melanin contents in the samples treated with 0.01% and 0.1% U. esculenta were 47.1% and 31.2%, respectively, and those treated with 0.01% and 0.1% Usnea longissima were 51.1% and 34.9%, respectively, whereas a value of 54.0% was registered when ascorbic acid was utilized as a positive control. In addition to direct tyrosinase inhibition, it was determined that the lichen extracts affected the activity of tyrosinase via the inhibition of tyrosinase glycosylation. As a result, the methanolic extracts of U. esculenta and Usnea longissima evidenced melanogenesis inhibitory effects, which occurred via multiple routes. 相似文献
858.
859.
Jang SW Cho MK Park MK Kang SA Na BK Ahn SC Kim DH Yu HS 《The Korean journal of parasitology》2011,49(3):245-254
Many immune down-regulatory molecules have been isolated from parasites, including cystatin (cystain protease inhibitor). In a previous study, we isolated and characterized Type I cystatin (CsStefin-1) of the liver fluke, Clonorchis sinensis. To investigate whether the CsStefin-1 might be a new host immune modulator, we induced intestinal inflammation in mice by dextran sodium sulfate (DSS) and treated them with recombinant CsStefin-1 (rCsStefin-1). The disease activity index (DAI) increased in DSS only-treated mice. In contrast, the DAI value was significantly reduced in rCsStefin-1-treated mice than DSS only-treated mice. In addition, the colon length of DSS only-treated mice was shorter than that of rCsStefin-1 treated mice. The secretion levels of IFN-γ and TNF-α in the spleen and mesenteric lymph nodes (MLNs) were significantly increased by DSS treatment, but the level of TNF-α in MLNs was significantly decreased by rCsStefin-1 treatment. IL-10 production in both spleen and MLNs was significantly increased, and IL-10(+)F4/80(+) macrophage cells were significantly increased in the spleen and MLNs of rCsStefin-1 treated mice after DSS treatment. In conclusion, rCsStefin-1 could reduce the intestinal inflammation occurring after DSS treatment, these effects might be related with recruitment of IL-10 secreting macrophages. 相似文献
860.
Background: We hypothesize that pH difference between acid‐secreting corpus and non‐secreting antrum might influence the activity of H. pylori’s urease and/or related genes. We therefore measured urease activity and the expression of amiE whose encoded protein that hydrolyzes short‐chain amides to produce ammonia. Materials and Methods: Fifty‐four patients were recruited into this study. Each gastroscopic biopsy specimen collected from the antrum and body of each patient was immediately used to measure urease activity using serial changes of urease activity (ammonia levels) during 60 minutes. Probe specific for amiE was labeled with a biotin nick‐translation kit and was used to detect expression of these genes (mRNA) in fresh‐frozen gastroscopic biopsy specimens using fluorescent in situ hybridization (FISH). Results: Urease activity at 60 minutes from the gastric antrum and body of all patients infected with H. pylori was 399.5 ± 490.5 and 837.9 ± 1038.9 μg/dL, respectively (p = .004). Urease activity in the antrum was correlated with H. pylori density. Urease activity or H. pylori density in the antrum was significantly correlated with chronic active inflammation; in contrast, this correlation was not found in the gastric body. The expression level of amiE was 1.5 times higher (p < .05) in the gastric body compared with the antrum. Conclusion: Topographically, the urease activity in body was much higher than in antrum. The expression level of amiE was higher in the gastric body compared with the antrum. 相似文献