全文获取类型
收费全文 | 22325篇 |
免费 | 1535篇 |
国内免费 | 1030篇 |
专业分类
24890篇 |
出版年
2024年 | 53篇 |
2023年 | 299篇 |
2022年 | 635篇 |
2021年 | 1021篇 |
2020年 | 680篇 |
2019年 | 905篇 |
2018年 | 892篇 |
2017年 | 680篇 |
2016年 | 963篇 |
2015年 | 1341篇 |
2014年 | 1520篇 |
2013年 | 1762篇 |
2012年 | 1963篇 |
2011年 | 1831篇 |
2010年 | 1031篇 |
2009年 | 923篇 |
2008年 | 1025篇 |
2007年 | 942篇 |
2006年 | 861篇 |
2005年 | 734篇 |
2004年 | 638篇 |
2003年 | 537篇 |
2002年 | 478篇 |
2001年 | 311篇 |
2000年 | 323篇 |
1999年 | 285篇 |
1998年 | 177篇 |
1997年 | 163篇 |
1996年 | 185篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 102篇 |
1992年 | 152篇 |
1991年 | 150篇 |
1990年 | 124篇 |
1989年 | 97篇 |
1988年 | 98篇 |
1987年 | 101篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 50篇 |
1983年 | 53篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1975年 | 29篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Man Zhang Su-Su Li Qiao-Mei Xie Jian-Hua Xu Xiu-Xiu Sun Fa-Ming Pan Sheng-Qian Xu Sheng-Xiu Liu Jin-Hui Tao Shuang Liu Jing Cai Pei-Ling Chen Long Qian Chun-Huai Wang Chun-Mei Liang Hai-Liang Huang Hai-Feng Pan Hong Su Yan-Feng Zou 《Genes & genomics.》2018,40(10):1069-1079
Although the current glucocorticoids (GCs) treatment for systemic lupus erythematosus (SLE) is effective to a certain extent, the difference in therapeutic effect between patients is still a widespread problem. Some patients can have repeated attacks that greatly diminish their quality of life. This study was conducted to investigate the relationship between HSP90AA2 polymorphisms and disease susceptibility, GCs efficacy and health-related quality of life (HRQoL) in Chinese SLE patients. A case–control study was performed in 470 SLE patients and 470 normal controls. Then, 444 patients in the case group were followed up for 12 weeks to observe efficacy of GCs and improvement of HRQoL. Two single nucleotide polymorphisms (SNPs) of HSP90AA2 were selected for genotyping: rs1826330 and rs6484340. HRQoL was assessed using the SF-36 questionnaire. The minor T allele of rs1826330 and the TT haplotype formed by rs1826330 and rs6484340 showed associations with decreased SLE risk (T allele: PBH?=?0.022; TT haplotype: PBH?=?0.033). A significant association between rs6484340 and improvement of HRQoL was revealed in the follow-up study. Five subscales of SF-36 were appeared to be influenced by rs6484340: total score of SF-36 (additive model: PBH?=?0.026), physical function (additive model: PBH?=?0.026), role-physical (recessive model: PBH?=?0.041), mental health (dominant model: PBH?=?0.047), and physical component summary (additive model: PBH?=?0.026). No statistical significance was found between HSP90AA2 gene polymorphisms and GCs efficacy. These results revealed a genetic association between HSP90AA2 and SLE. Remarkably, HSP90AA2 has an impact on the improvement of HRQoL in Chinese population with SLE. 相似文献
952.
Xumiao Chen Xiaozhong Hu Xiaofeng Lin Khaled A.S. Al-Rasheid Honggang Ma Miao Miao 《European journal of protistology》2013,49(4):611-622
This paper investigates the morphology, ontogenesis and small subunit (SSU) rRNA gene-based phylogeny of a new urostylid ciliate, Bakuella subtropica sp. n., discovered from the estuary of the Pearl River in Guangzhou, southern China. The new species is diagnosed by its elongate body, one buccal and one parabuccal cirrus, midventral complex comprised of 9–23 midventral pairs and one or two midventral rows extending to four fifths of body length, yellow-brown to yellow-greenish cortical granules and an estuary habitat. Its main ontogenetic features are: (1) in the proter, the parental adoral zone of membranelles is completely renewed by new structures and old midventral pairs join the formation of frontal-midventral-transverse cirral anlagen (FVT-anlagen); (2) in the opisthe, the oral primordium originates apokinetally, FVT-anlagen are formed besides and some old midventral cirri join the formation; (3) the anlagen for marginal rows and dorsal kineties develop intrakinetally; and (4) the numerous macronuclear nodules fuse into a single mass before dividing. Based on the SSU rDNA sequences, phylogenetic analyses show a close relationship between Bakuella subtropica sp. n., Apobakuella and Neobakuella, forming a clade separated from the other genera in the family Bakuellidae. Available morphological and ontogenetic data challenge the monophyly of Bakuellidae. 相似文献
953.
Xiao-long Tang Feng Yue Jian-zheng He Ning-bo Wang Ming Ma Jia-run Mo Qiang Chen 《Zoology (Jena, Germany)》2013,116(6):331-335
A viviparous lizard, Eremias multiocellata, was used to investigate the possible sexual and ontogenetic effects on selected body temperature, thermal tolerance range and the thermal dependence of locomotor performance. We show that adults are sexually dimorphic and males have larger bodies and heads than females. Adults selected higher body temperatures (34.5 vs. 32.4 °C) and could tolerate a broader range of body temperatures (8.1–46.8 vs. 9.1–43.1 °C) than juveniles. The sprint speed and maximum sprint distance increased with temperature from 21 °C to 33 °C, but decreased at 36 °C and 39 °C in both juveniles and adults. Adults ran faster and longer than juveniles at each tested temperature. Adult locomotor performance was not correlated with snout–vent length (SVL) or sex, and sprint speed was positively correlated with hindlimb length. Juvenile locomotor performance was positively correlated with both SVL and hindlimb length. The ontogenetic variation in selected body temperature, thermal tolerance and locomotor performance in E. multiocellata suggests that the effects of morphology on temperature selection and locomotor performance vary at different ontogenetic stages. 相似文献
954.
Uroplakins and cytokeratins in the regenerating rat urothelium after sodium saccharin treatment 总被引:5,自引:2,他引:5
A sodium saccharin (NaSac) diet was used to induce cell damage and regeneration in the urothelium of the male rat urinary
bladder. Foci of terminally differentiated superficial cell exfoliation were detected after 5 weeks and their number increased
after 10 and 15 weeks of the diet. At the sites of superficial cell loss, regenerative simple hyperplasia developed. Within
5 weeks of NaSac removal, regeneration re-established normal differentiated urothelium. In order to follow urothelial differentiation
during regeneration we studied the expression of uroplakins and cytokeratins by means of immunocytochemistry and immunohistochemistry,
respectively. Normal urothelium was characterised by terminally differentiated superficial cells which expressed uroplakins
in their luminal plasma membrane and cytokeratin 20 (CK20) in the cytoplasm. Basal and intermediate cells were CK20 negative
and cytokeratin 17 (CK17) positive. In hyperplastic urothelium all cells synthesised CK17, but not CK20. Differentiation of
the superficial layer was reflected in three successive cell types: cells with microvilli, cells with rounded microridges
and those with a rigid-looking plasma membrane on the luminal surface. The cells with microvilli did not stain with anti-uroplakin
antibody. When the synthesis of uroplakins was detected rounded microridges were formed. With the elevated expression of uroplakins
the luminal plasma membrane becomes rigid-looking which is characteristic of asymmetric unit membrane of terminally differentiated
cells. During differentiation, syn-thesis of CK17 ceased in superficial cells while the synthesis of CK20 started. These results
indicate that during urothelial regeneration after NaSac treatment, specific superficial cell types develop in which the switch
to uroplakin synthesis and transition from CK17 to CK20 synthesis are crucial events for terminal differentiation.
Accepted: 19 August 1997 相似文献
955.
Jing Han Hua Liang Jianhua Yi Wuhong Tan Shulan He Sen Wang Feng Li Xiaofang Wu Jing Ma Xiaowei Shi Xiong Guo Chuanyi Bai 《Biological trace element research》2017,175(2):396-404
The effects of selenium (Se)-deficient diet on the liver were evaluated by using growing rats which were fed with normal and Se-deficient diets, respectively, for 109 days. The results showed that rats fed with Se-deficient diet led to a decrease in Se concentration in the liver, particularly among male rats from the low-Se group. This causes alterations to the ultrastructure of hepatocytes with condensed chromatin and swelling mitochondria observed after low Se intake. Meanwhile, pathological changes and increased fibrosis in hepatic periportal were detected by hematoxylin and eosin and Masson’s trichrome staining in low-Se group. Furthermore, through immunohistochemistry (IHC) staining, higher expressions of metalloproteinases (MMP1/3) and their tissue inhibitors of metalloproteinases (TIMP1/3) were observed in the hepatic periportal of rats from the low-Se group. However, higher expressions of MMP1/3 and lower expressions of TIMP1/3 were detected in hepatic central vein and hepatic sinusoid. In addition, upregulated expressions of MMP1/3 and downregulated expressions of TIMP1/3 at the messenger RNA (mRNA) and protein levels also appeared to be relevant to low Se intake. In conclusion, Se-deficient diet could cause low Se concentration in the liver, alterations of hepatocyte ultrastructure, differential expressions of MMP1/3 and TIMP1/3 as well as fibrosis in the liver hepatic periportal. 相似文献
956.
957.
Zhang Y Ju J Peng H Gao F Zhou C Zeng Y Xue Y Li Y Henrissat B Gao GF Ma Y 《The Journal of biological chemistry》2008,283(46):31551-31558
An intracellular mannanase was identified from the thermoacidophile Alicyclobacillus acidocaldarius Tc-12-31. This enzyme is particularly interesting, because it shows no significant sequence similarity to any known glycoside hydrolase. Gene cloning, biochemical characterization, and structural studies of this novel mannanase are reported in this paper. The gene consists of 963 bp and encodes a 320-amino acid protein, AaManA. Based on its substrate specificity and product profile, AaManA is classified as an endo-beta-1,4-mannanase that is capable of transglycosylation. Kinetic analysis studies revealed that the enzyme required at least five subsites for efficient hydrolysis. The crystal structure at 1.9 angstroms resolution showed that AaManA adopted a (beta/alpha)8-barrel fold. Two catalytic residues were identified: Glu151 at the C terminus of beta-stand beta4 and Glu231 at the C terminus of beta7. Based on the structure of the enzyme and evidence of its transglycosylation activity, AaManA is placed in clan GH-A. Superpositioning of its structure with that of other clan GH-A enzymes revealed that six of the eight GH-A key residues were functionally conserved in AaManA, with the exceptions being residues Thr95 and Cys150. We propose a model of substrate binding in AaManA in which Glu282 interacts with the axial OH-C(2) in-2 subsites. Based on sequence comparisons, the enzyme was assigned to a new glycoside hydrolase family (GH113) that belongs to clan GH-A. 相似文献
958.
A crucial issue in limb development is how a correct set of precisely shaped digits forms in the digital plate. This process relies on patterning across the anterior-posterior axis of the limb bud, which is under the control of Sonic hedgehog emanating from the zone of polarizing activity. Recently, Sonic hedgehog function in the limb bud has been shown to have a dual character controlling both growth and patterning of the digital field. This finding has prompted the proposal of new models of how these two functions are achieved, and this will be discussed in this review. 相似文献
959.
To study influence of wheat straw returning mode on CH4 emission from paddy soils, a field experiment was conducted at Jurong, Jiangsu Province, China in 2006. Five treatments, no wheat straw applied (CK), wheat straw evenly incorporated into the topsoil (WI), wheat straw buried in ditches (WD), wheat straw strip-mulched onto the field surface (WM) and wheat straw burned in-situ (WB), were laid out in a randomized block design. Results showed that seasonal CH4 emissions ranged from 6.9 to 28.1 g CH4 m?2. Wheat straw incorporation significantly increased CH4 emission. No significant difference was observed between Treatments WI and WD in total CH4 emission. Compared with Treatment WI, Treatment WM reduced total CH4 emission by 32% and Treatment WB by 42%. Treatment WM was about 27% higher than Treatment CK in grain yield. Based on the findings, the best management of wheat straw prior to rice cultivation is strip-mulching wheat straw onto the field surface, which largely reduced CH4 emission from rice fields with no decrease in rice yield. 相似文献
960.
Hypoxia inducible factor 1 (HIF-1) plays a pivotal role in cellular responses to hypoxia. Prolyl hydroxylase 3 (PHD3) degrades HIF-1α under normoxic conditions through the hydroxylation of HIF-1α for proteolysis. Inhibiting PHD3 activity is crucial for up-regulating HIF-1α, thereby acting as a potential target for treating hypoxia-related diseases. In this study, two proline analogues (PA1 and PA2) were screened as PHD3 inhibitors with apparent EC50 values of 1.53 and 3.17 µM respectively, indicating good inhibition potency. Nine proteins, significantly regulated by PA1, were identified using 2-DE coupled with MALDI-TOF/TOF MS. Pyruvate kinase isozymes M1/M2 (PKM) and alpha-enolase 1 (ENO1), which are key modulators of glycolysis, are directly regulated by HIF-1α. Moreover, VEGF, a signal protein stimulating angiogenesis, was strongly promoted by PA1. Our findings suggest that PA1 stabilized HIF-1α as well as up-regulated glycolysis and angiogenesis proteins. Herein, for the first time, we systematically studied proline analogue PA1 as a PHD3 inhibitor, which provides innovative evidence for the treatment of HIF-related diseases. 相似文献