全文获取类型
收费全文 | 30357篇 |
免费 | 2392篇 |
国内免费 | 2087篇 |
专业分类
34836篇 |
出版年
2024年 | 67篇 |
2023年 | 440篇 |
2022年 | 1017篇 |
2021年 | 1704篇 |
2020年 | 1042篇 |
2019年 | 1343篇 |
2018年 | 1279篇 |
2017年 | 932篇 |
2016年 | 1272篇 |
2015年 | 1858篇 |
2014年 | 2210篇 |
2013年 | 2474篇 |
2012年 | 2768篇 |
2011年 | 2460篇 |
2010年 | 1481篇 |
2009年 | 1279篇 |
2008年 | 1507篇 |
2007年 | 1312篇 |
2006年 | 1156篇 |
2005年 | 942篇 |
2004年 | 794篇 |
2003年 | 664篇 |
2002年 | 597篇 |
2001年 | 535篇 |
2000年 | 471篇 |
1999年 | 483篇 |
1998年 | 269篇 |
1997年 | 290篇 |
1996年 | 292篇 |
1995年 | 282篇 |
1994年 | 253篇 |
1993年 | 179篇 |
1992年 | 276篇 |
1991年 | 185篇 |
1990年 | 151篇 |
1989年 | 151篇 |
1988年 | 92篇 |
1987年 | 85篇 |
1986年 | 60篇 |
1985年 | 68篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Xiaofei Feng Kangxian Li Fangming Tan Mei Zhu Jieyi Zhou Yongjun Lai Lingfeng Zeng Yingting Ye Jing Huang Xiaosong Wu Shasha Li 《Biochemistry and Biophysics Reports》2018
ObjectiveThe objective of the present study was to investigate the hepatoprotective role of Radix Fici Hirtae on acute alcohol-induced liver injury in mice.MethodsThe component of Radix Fici Hirtae was extracted using petroleum ether, chloroform, ethyl acetate and n-butanol and divided into three dose groups of high, medium and low according to the clinical man's normal dose of the 50 g crude drug/d (0.83 g/kg body weight). Saline in concentration of 10 mg/mL, 5 mg/mL and 2.5 mg/mL and a dose of mouse lavage (0.2 mL/10 g mouse body weight) were added to the solution. Histopathlogical analysis of liver was performed. Finally, liver protection was validated by examining the effect of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (AKP), and lactate dehydrogenase (LDH) on the hepatic function of mice in alcohol-induced liver injury model.ResultsExcept for group with saturated n-butyl alcohol, for the rest of the groups, pathological changes of hepatic lipid and inflammatory cells infiltration were alleviated and liver sinus was normal. As compared to model group, the concentrations of AST, ALT, AKP and LDH in chloroform groups and ethyl acetate groups were significantly decreased.ConclusionsExtracts of Radix Fici Hirtae are effective for the prevention of alcohol-induced hepatic damage in mice. The results revealed that extracts of Radix Fici Hirtae could be used as hepatoprotective agent. 相似文献
92.
Joe Carver Domingos Ng Michelle Zhou Peggy Ko Dejin Zhan Mandy Yim David Shaw Brad Snedecor Michael W. Laird Steven Lang Amy Shen Zhilan Hu 《Biotechnology progress》2020,36(4):e2967
Historically, therapeutic protein production in Chinese hamster ovary (CHO) cells has been accomplished by random integration (RI) of expression plasmids into the host cell genome. More recently, the development of targeted integration (TI) host cells has allowed for recombination of plasmid DNA into a predetermined genomic locus, eliminating one contributor to clone-to-clone variability. In this study, a TI host capable of simultaneously integrating two plasmids at the same genomic site was used to assess the effect of antibody heavy chain and light chain gene dosage on antibody productivity. Our results showed that increasing antibody gene copy number can increase specific productivity, but with diminishing returns as more antibody genes are added to the same TI locus. Random integration of additional antibody DNA copies in to a targeted integration cell line showed a further increase in specific productivity, suggesting that targeting additional genomic sites for gene integration may be beneficial. Additionally, the position of antibody genes in the two plasmids was observed to have a strong effect on antibody expression level. These findings shed light on vector design to maximize production of conventional antibodies or tune expression for proper assembly of complex or bispecific antibodies in a TI system. 相似文献
93.
The objectives of this study were to investigate the moisture-induced protein aggregation of whey protein powders and to elucidate
the relationship of protein stability with respect to water content and glass transition. Three whey protein powder types
were studied: whey protein isolate (WPI), whey protein hydrolysates (WPH), and beta-lactoglobulin (BLG). The water sorption
isotherms were determined at 23 and 45°C, and they fit the Guggenheim–Andersson–DeBoer (GAB) model well. Glass transition
was determined by differential scanning calorimeter (DSC). The heat capacity changes of WPI and BLG during glass transition
were small (0.1 to 0.2 Jg−1 °C−1), and the glass transition temperature (T
g) could not be detected for all samples. An increase in water content in the range of 7 to 16% caused a decrease in T
g from 119 down to 75°C for WPI, and a decrease from 93 to 47°C for WPH. Protein aggregation after 2 weeks’ storage was measured
by the increase in insoluble aggregates and change in soluble protein fractions. For WPI and BLG, no protein aggregation was
observed over the range of 0 to 85% RH, whereas for WPH, ∼50% of proteins became insoluble after storage at 23°C and 85% RH
or at 45°C and ≥73% RH, caused mainly by the formation of intermolecular disulfide bonds. This suggests that, at increased
water content, a decrease in the T
g of whey protein powders results in a dramatic increase in the mobility of protein molecules, leading to protein aggregation
in short-term storage. 相似文献
94.
Liming Yan Yiqi Luo Rebecca A. Sherry Jesse E. Bell Xuhui Zhou Jianyang Xia 《Global Change Biology Bioenergy》2014,6(5):556-565
The efficiency of a terrestrial ecosystem to use rainfall in production is critical in regulating the ecological functions of the earth system under global change. However, it remains unclear how rain use efficiency (RUE) will be altered by changes in climate and human activities such as biofuel harvest. In this study, we used RUE data from a long‐term experiment in a tallgrass prairie to analyze the effects of warming and biofuel harvest (clipping). From 2000 to 2011, experimental warming enhanced RUE in most years, with larger positive effects in normal and wet than dry hydrological years. Clipping decreased RUE in dry and normal hydrological years, but had no impact on RUE in wet years. The observed RUE responses resulted from treatment‐induced changes in both biologically ineffective (i.e., runoff and soil evaporation) and effective (i.e., transpiration) parts of precipitation. For example, litter cover was increased in warming plots, but reduced by clipping, leading to negative and positive effects on runoff and soil evaporation, respectively. The dominance of C4 species, which usually have higher water use efficiency than C3 species, was enhanced by warming, but reduced by clipping. Moreover, RUE was positively correlated with ratios of rainfall in the late growing season (June–August), when the growth of C4 plants was most active, relative to that in the other seasons. Our results indicate that RUE is positively influenced by climate warming, but negatively affected by biofuel harvest in tallgrass prairie of the Great Plains. These findings highlight the important roles of plant community structure and temporal distribution of precipitation in regulating ecosystem RUE. 相似文献
95.
Guang-Jin Zhou Yue Zhang Jian Wang Jin-Hu Guo Jun Ni Zhao-Ming Zhong Li-Qun Wang Yong-Jun Dang Jian-Feng Dai Long Yu 《DNA sequence》2004,15(3):219-224
Present work reported the cloning and characterization of a human novel RNA binding gene Partner of NOB1 (PNO1), with a length of 1637bp and a putative open reading frame of 759 bp, isolated from human kidney. It is composed of seven exons and is localized on chromosome 2p14. Western blot showed that the molecular weight of PNO1 is about 35kDa. RT-PCR results in 16 human tissues indicated that PNO1 is expressed mainly in liver, lung, spleen and kidney, slightly in thymus, testis, ovary, respectively, but not in heart, brain, skeletal muscle, placenta, pancreas, prostate, small intestine, colon and peripheral blood leukocytes. GFP fusion expression in mammalian cells exhibited its localization in the nucleus, especially in nucleoli. Subcellular localization of thirteen GFP fusion PNO1 deletion proteins showed that the region of 92-230 aa is solely responsible for its nucleolar retention, and KH domain alone is not sufficient for nucleolar retention. The PNO1 family shows significant conservation in both eukaryotes and prokaryotes. 相似文献
96.
Zhou HL Yang HJ Li YM Wang Y Yan L Guo XL Ba YC Liu S Wang TH 《Neurochemical research》2008,33(5):927-937
Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the
spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords
following transection injury (T9–T10) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that
hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion
function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral
horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in
astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent
a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with
the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX.
No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique.
No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested
that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is
involved in the regulation of local circuitry in transected spinal cords of adult rats. 相似文献
97.
Longitudinal studies often feature incomplete response and covariate data. Likelihood-based methods such as the expectation-maximization algorithm give consistent estimators for model parameters when data are missing at random (MAR) provided that the response model and the missing covariate model are correctly specified; however, we do not need to specify the missing data mechanism. An alternative method is the weighted estimating equation, which gives consistent estimators if the missing data and response models are correctly specified; however, we do not need to specify the distribution of the covariates that have missing values. In this article, we develop a doubly robust estimation method for longitudinal data with missing response and missing covariate when data are MAR. This method is appealing in that it can provide consistent estimators if either the missing data model or the missing covariate model is correctly specified. Simulation studies demonstrate that this method performs well in a variety of situations. 相似文献
98.
Although hydrogen peroxide (H2O2) and nitric oxide (NO) can act as an upstream signaling molecule to modulate the dynamic microtubule cytoskeleton during the defense responses to Verticillium dahliae (VD) toxins in Arabidopsis, it is not known the relationship between these two signaling molecules. Here, we show that VD-toxin-induced NO accumulation was dependent on prior H2O2 production, NO is downstream of H2O2 in the signaling process, and that H2O2 acted synergistically with NO to modulate the dynamic microtubule cytoskeleton responses to VD-toxins in Arabidopsis. 相似文献
99.
Yujie Yang Chengshi Huang Zuguo Ge Bengeng Zhou Guangju Su Chunling Liu Yongjun Fei 《Phyton》2022,91(1):129-148
Drought stress negatively impacts growth and physiological processes in plants. The foliar application of glycine betaine (GB) is an effective and low-cost approach to improve the drought tolerance of trees. This study examined the effect of exogenously applied GB on the cell membrane permeability, osmotic adjustment, and antioxidant enzyme activities of Phoebe hunanensis Hand.-Mazz under drought stress. Two levels (0 and 800 mL) of water irrigation were tested under different applied GB concentrations (0, 50, 100, and 200 mM). Drought stress decreased the relative water content by 58.5% while increased the electric conductivity, malondialdehyde, proline, soluble proteins, soluble sugars, and antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase) by up to 62.9%, 42.4%, 87.0%, 19.1%, 60.5%, 68.3%, 71.7%, and 83.8%, respectively, on the 25th day. The foliar application of GB, especially at 100 mM, increased the relative water content of P. hunanensis leaves under drought stress. The concentration of GB from 50 to 100 mM effectively alleviated the improvement of cell membrane permeability and inhibited the accumulation of membrane lipid peroxidation products. Under drought stress, the concentrations of proline, soluble proteins, and soluble sugars in the leaves of P. hunanensis increased as the applied GB concentration was increased and the water stress time was prolonged. Exogenously applied GB decreased oxidative stress and improved antioxidant enzyme activities as compared with treatments without GB application. Furthermore, the physiological and biochemical indexes of P. hunanensis showed a certain dose effect on exogenous GB concentration. These results suggest that GB helps maintain the drought tolerance of P. hunanensis. 相似文献
100.
Man Liu Hongxia Zhang Lu Zhang Xin Liu Simin Zhou Xiaoyi Wang Weilong Zhong Jie Zhang Bangmao Wang Jingwen Zhao Lu Zhou 《International journal of biological sciences》2022,18(1):199
Autoimmune hepatitis (AIH) is an immune-mediated chronic inflammatory liver disease, and its pathogenesis is not fully understood. Our previous study discovered that receptor interacting protein kinase 3 (RIP3) is correlated with serum transaminase levels in AIH patients. However, its role and underlying mechanism in AIH are poorly understood. Here, we detected the increased expression and activation of RIP3 in livers of patients and animal models with AIH. The inhibition of RIP3 kinase by GSK872 prevented concanavalin A (ConA)-induced immune-mediated hepatitis (IMH) by reduced hepatic proinflammatory cytokines and immune cells including Th17 cells and macrophages. Further experiments revealed that RIP3 inhibition resulted in an increase in CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs) with immunoregulatory properties in the liver, spleen, and peripheral blood. Moreover, the depletion of Gr-1+ MDSCs abrogated the protective effect and immune suppression function of GSK872 in ConA-induced IMH. Altogether, our data demonstrate that RIP3 blockade prevents ConA-induced IMH through promoting MDSCs infiltration. Inhibition of RIP3 kinase may be a novel therapeutic avenue for AIH treatment. 相似文献