全文获取类型
收费全文 | 19140篇 |
免费 | 1409篇 |
国内免费 | 1515篇 |
专业分类
22064篇 |
出版年
2024年 | 48篇 |
2023年 | 329篇 |
2022年 | 658篇 |
2021年 | 1088篇 |
2020年 | 670篇 |
2019年 | 905篇 |
2018年 | 802篇 |
2017年 | 558篇 |
2016年 | 876篇 |
2015年 | 1153篇 |
2014年 | 1456篇 |
2013年 | 1519篇 |
2012年 | 1808篇 |
2011年 | 1565篇 |
2010年 | 989篇 |
2009年 | 847篇 |
2008年 | 942篇 |
2007年 | 809篇 |
2006年 | 658篇 |
2005年 | 578篇 |
2004年 | 484篇 |
2003年 | 436篇 |
2002年 | 387篇 |
2001年 | 285篇 |
2000年 | 290篇 |
1999年 | 303篇 |
1998年 | 195篇 |
1997年 | 199篇 |
1996年 | 188篇 |
1995年 | 151篇 |
1994年 | 136篇 |
1993年 | 96篇 |
1992年 | 140篇 |
1991年 | 114篇 |
1990年 | 100篇 |
1989年 | 77篇 |
1988年 | 52篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 41篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
采用全基因分段合成和补丁连接相结合的方法构建了人甲状旁腺素 (hPTH) (1~ 34)肽基因 ,并利用GST融合表达系统 ,在大肠杆菌中克隆和可溶性表达了hPTH(1~ 34)肽基因。融合蛋白表达量占菌体总蛋白质的 2 5 %以上 ,经高密度发酵、亲和纯化后 ,在每升发酵液中得到了 10 g融合蛋白。融合蛋白经肠激酶一步加工并亲合纯化和反相脱盐后 ,最终可以得到约 0 .6g /L人甲状旁腺素 (1~ 34)肽纯品 ,样品的理论回收值达到了4 8.75 %。产物的纯度和性质经HPLC、毛细管电泳、质谱分析、N端测序等得到证明 ,并与化学合成产物的结果相吻合。兔肾皮质细胞测活表明 ,重组产物与化学合成人甲状旁腺素 (1~ 34)肽具有相近的腺苷酸环化酶激活活性。 相似文献
42.
Zhang?Lijuan Jifu?Liu Hao?Zhang Shanshan?Wu Lingyun?Huang Dacheng?He Xueyuan?XiaoEmail author 《中国科学C辑(英文版)》2005,48(6):641-647
There are multiple reports of autoimmune response in patients with lung cancer. To investigate whether a novel autoantibody
is present in patients with lung cancer and evaluate its clinical diagnostic and prognostic value, sera from 10 patients with
lung cancer and 10 normal individuals were analyzed using immunofluorescence and Western blotting. It was found that one serum
sample from the patients with squamous carcinoma gave a fine speckled pattern staining in nucleus and had a high titer antinuclear
autoantibody which could recognize 31 kD of nuclear protein isolated from both cancer cells and normal cells. The same patient’s
serum was further used to immunoprecipitate the target antigen. The protein bands were excised from the SDS-PAGE gels and
were analyzed with a Qstar Pulser I Quadrupole time-flight mass spectrometer, and the 31 kD target antigen was identified
as U1-AsnRNP. To test the prevalence of anti-U1-AsnRNP antibody, sera from 93 patients including 36 squmaous carcinomas (SCC),
26 adenocarcinomas (Ad), and 31 small cell carcinomas (SCLC) were screened by Western blotting. The results demonstrated that
anti-U1-A snRNP antibody was present in 50% of SCC sera, 26.9% of Ad sera and 54.8% of SCLC sera. In this paper, we report
for the first time that anti-U1-AsnRNP antibody could be detected in the patients with lung cancer. 相似文献
43.
44.
Wang-Shan Zheng Yao-Xi He Chao-Ying Cui Ouzhuluobu Dejiquzong Yi Peng Cai-Juan Bai Duojizhuoma Gonggalanzi Bianba Baimakangzhuo Yong-Yue Pan Qula Kangmin Cirenyangji Baimayangji Wei Guo Yangla Hui Zhang Xiao-Ming Zhang Yong-Bo Guo Shu-Hua Xu Hua Chen Sheng-Guo Zhao Yuan Cai Shi-Ming Liu Tian-Yi Wu Xue-Bin Qi Bing Su 《动物学研究》2017,38(3)
The genetic adaptation of Tibetans to high altitude hypoxia likely involves a group of genes in the hypoxic pathway,as suggested by earlier studies.To test the adaptive role of the previously reported candidate gene EP300 (histone acetyltransferase p300),we conducted resequencing of a 108.9 kb gene region of EP300 in 80 unrelated Tibetans.The allele-frequency and haplotype-based neutrality tests detected signals of positive Darwinian selection on EP300 in Tibetans,with a group of variants showing allelic divergence between Tibetans and lowland reference populations,including Han Chinese,Europeans,and Africans.Functional prediction suggested the involvement of multiple EP300 variants in gene expression regulation.More importantly,genetic association tests in 226 Tibetans indicated significant correlation of the adaptive EP300 variants with blood nitric oxide (NO) concentration.Collectively,we propose that EP300 harbors adaptive variants in Tibetans,which might contribute to high-altitude adaptation through regulating NO production. 相似文献
45.
Two dodecachlorinated porphyrins, 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetra(4-chlorophenyl)porphyrin free base (TCl12PPH2) and its nickel compound (TCl12PPNi), have been synthesized. Single-crystal X-ray diffraction analysis shows that porphyrin rings are heavily distorted and exhibit saddled conformations. The Soret and Q bands of two compounds are red-shifted compared to their non-chlorinated counterparts. Theoretical calculations reveal that the optical band gap of TCl12PPH2 is reduced, whereas that of TCl12PPNi remains almost the same as to its non-chlorinated nickel compound due to the concurrent lowering of HOMO and LUMO energy levels. The frontier molecular orbitals are degenerated due to the decrease of symmetry of the molecules. 相似文献
46.
Sun HG Ruszczycky MW Chang WC Thibodeaux CJ Liu HW 《The Journal of biological chemistry》2012,287(7):4602-4608
UDP-galactopyranose mutase (UGM) requires reduced FAD (FAD(red)) to catalyze the reversible interconversion of UDP-galactopyranose (UDP-Galp) and UDP-galactofuranose (UDP-Galf). Recent structural and mechanistic studies of UGM have provided evidence for the existence of an FAD-Galf/p adduct as an intermediate in the catalytic cycle. These findings are consistent with Lewis acid/base chemistry involving nucleophilic attack by N5 of FAD(red) at C1 of UDP-Galf/p. In this study, we employed a variety of FAD analogues to characterize the role of FAD(red) in the UGM catalytic cycle using positional isotope exchange (PIX) and linear free energy relationship studies. PIX studies indicated that UGM reconstituted with 5-deaza-FAD(red) is unable to catalyze PIX of the bridging C1-OP(β) oxygen of UDP-Galp, suggesting a direct role for the FAD(red) N5 atom in this process. In addition, analysis of kinetic linear free energy relationships of k(cat) versus the nucleophilicity of N5 of FAD(red) gave a slope of ρ = -2.4 ± 0.4. Together, these findings are most consistent with a chemical mechanism for UGM involving an S(N)2-type displacement of UDP from UDP-Galf/p by N5 of FAD(red). 相似文献
47.
He M Horuk R Moochhala SM Bhatia M 《American journal of physiology. Gastrointestinal and liver physiology》2007,292(4):G1173-G1180
Sepsis is a complex clinical syndrome resulting from a harmful host inflammatory response to infection. Chemokines and their receptors play a key role in the pathogenesis of sepsis. BX471 is a potent nonpeptide CC chemokine receptor-1 (CCR1) antagonist in both human and mouse. The aim of the present study was to evaluate the effect of prophylactic and therapeutic treatment with BX471 on cecal ligation and puncture-induced sepsis in the mouse and to investigate the underlying mechanisms. In sepsis induced by cecal ligation and puncture, treatment with BX471 significantly protected mice against lung and liver injury by attenuating MPO activity, an indicator of neutrophil recruitment in lungs and livers and attenuating lung and liver morphological changes in histological sections. Blocking CCR1 by BX471 also downregulated ICAM-1, P-selectin, and E-selectin expression at mRNA and protein levels in lungs and livers compared with placebo-treated groups. These findings suggest that blockage of CCR1 by specific antagonist may represent a promising strategy to prevent disease progression in sepsis. 相似文献
48.
鼎湖山自然林豆科固氮植物资源的调查研究 总被引:2,自引:1,他引:2
本文在调查鼎湖山自然林木本豆科植物结瘤固氮的基础上,参阅了国内外有关豆科植物结瘤固氮的主要文献,研究了鼎湖山自然林木本豆科植物的固氮资源。结果得出鼎湖山自然林中常见的木本豆科植物共有41种,其中乔木15种,灌木6种,木质藤本20种;有结瘤固氮特性的26种,其中乔木11种,灌木5种,木质藤本10种;经初步调查未见根瘤的6种,其中乔木2种,灌木1种,木质藤本3种;未调查的9种,其中乔木2种,木质藤本7种。本研究结果为鼎湖山木本豆科固氮植物资源的保护、管理和开发利用提供了科学论据,在理论和应用方面均有重要意义。 相似文献
49.
50.