全文获取类型
收费全文 | 35076篇 |
免费 | 2866篇 |
国内免费 | 1891篇 |
专业分类
39833篇 |
出版年
2024年 | 68篇 |
2023年 | 389篇 |
2022年 | 933篇 |
2021年 | 1633篇 |
2020年 | 1036篇 |
2019年 | 1250篇 |
2018年 | 1226篇 |
2017年 | 866篇 |
2016年 | 1325篇 |
2015年 | 2029篇 |
2014年 | 2365篇 |
2013年 | 2550篇 |
2012年 | 3092篇 |
2011年 | 2769篇 |
2010年 | 1724篇 |
2009年 | 1438篇 |
2008年 | 1677篇 |
2007年 | 1525篇 |
2006年 | 1360篇 |
2005年 | 1153篇 |
2004年 | 1028篇 |
2003年 | 866篇 |
2002年 | 748篇 |
2001年 | 679篇 |
2000年 | 683篇 |
1999年 | 657篇 |
1998年 | 389篇 |
1997年 | 336篇 |
1996年 | 360篇 |
1995年 | 334篇 |
1994年 | 325篇 |
1993年 | 216篇 |
1992年 | 351篇 |
1991年 | 271篇 |
1990年 | 307篇 |
1989年 | 257篇 |
1988年 | 189篇 |
1987年 | 172篇 |
1986年 | 152篇 |
1985年 | 137篇 |
1984年 | 122篇 |
1983年 | 96篇 |
1982年 | 77篇 |
1981年 | 62篇 |
1979年 | 75篇 |
1978年 | 55篇 |
1977年 | 54篇 |
1975年 | 59篇 |
1974年 | 47篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
A strain of Paenibacillus sp., OSY-SE, was isolated from soil and found to produce a novel lipopeptide antibiotic. The antibiotic, paenibacterin, is active against Gram-negative and Gram-positive bacterial pathogens. Paenibacterin is biosynthesized by a nonribosomal peptide synthetase pathway. Here we report the draft genome sequence of Paenibacillus sp. OSY-SE. 相似文献
192.
193.
Jinmei Xu Jianxiong Lu Fucheng Bao Robert Evans Geoffrey Downes Rongfeng Huang Youke Zhao 《Trees - Structure and Function》2012,26(3):1007-1016
Microfibril angle (MFA) is an important factor in determining the mechanical properties of individual cells and wood as a whole. While some studies have described the variation of MFA within trees, little work has been done on the extent to which MFA is influenced by climate, despite it being known to respond to climatic events. Year-to-year variation in MFA and ring width was measured at high resolution by SilviScan-3? on 30 dated Picea crassifolia trees growing in the northeastern Tibetan plateau. The climate signals registered in MFA and ring width were analyzed using dendroclimatological methods. The response function of MFA accounted for 67% of total variance, of which 60% was explained by climate elements. The response function of ring width explained 57% total variance, 37% of which was explained by climate variables. MFA significantly responded to July–August temperatures, and to precipitation in March, May and September. Over the period 1987–2009 temperatures generally increase and appeared to have a greater influence on MFA. A decrease in the strength of the relationship between MFA and ring width over the period 1987–2009 was also observed. MFA offers the potential to build robust climate proxies. The strong climate sensitivity of MFA to increasing temperature or the observed changes in the MFA–ring width relationship may contribute to resolving the “divergence problem” in temperature reconstructions. As far as we are aware, this study is the first to show a strong climate response in MFA and suggests that it might be a useful climate proxy. 相似文献
194.
Y S Huang D F Horrobin M S Manku 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1985,178(2):209-214
Weanling female rats raised on a fat-free diet for 8 weeks were then given the same diet supplemented with 0, 0.25, 0.5, or 1% by weight of cholesterol in addition to 10% of safflower oil for 3 days. Fatty acid compositions of cholesteryl esters (CE), triglycerides (TG), and phospholipids (PL) in liver and plasma were examined. Cholesterol feeding increased plasma and liver cholesterol contents and also affected the patterns of n-6 polyunsaturated fatty acids. There were no consistent changes in either plasma and liver TG which contained little 20:3n-6 and 20:4n-6. The levels of 20:3n-6 increased in plasma and liver PL, while proportions of 20:4n-6 decreased in liver and plasma CE. However, the absolute amount of 20:4n-6 in cholesteryl esters increased because of a threefold rise in cholesteryl ester levels. The changes might be attributable to an increased utilization of 20:4n-6 for cholesterol transport and/or an inhibition of delta 5-desaturation of n-6 fatty acids by cholesterol feeding. 相似文献
195.
Rui-Fang Li Xin-Xin Wang Liu Wu Li Huang Qi-Jian Qin Jia-Li Yao Guang-Tao Lu Ji-Liang Tang 《Molecular Plant Pathology》2020,21(3):360-375
Xanthomonas campestris pv. campestris (Xcc) controls virulence and plant infection mechanisms via the activity of the sensor kinase and response regulator pair HpaS/hypersensitive response and pathogenicity G (HrpG). Detailed analysis of the regulatory role of HpaS has suggested the occurrence of further regulators besides HrpG. Here we used in vitro and in vivo approaches to identify the orphan response regulator VemR as another partner of HpaS and to characterize relevant interactions between components of this signalling system. Bacterial two-hybrid and protein pull-down assays revealed that HpaS physically interacts with VemR. Phos-tag SDS-PAGE analysis showed that mutation in hpaS reduced markedly the phosphorylation of VemR in vivo. Mutation analysis reveals that HpaS and VemR contribute to the regulation of motility and this relationship appears to be epistatic. Additionally, we show that VemR control of Xcc motility is due in part to its ability to interact and bind to the flagellum rotor protein FliM. Taken together, the findings describe the unrecognized regulatory role of sensor kinase HpaS and orphan response regulator VemR in the control of motility in Xcc and contribute to the understanding of the complex regulatory mechanisms used by Xcc during plant infection. 相似文献
196.
Kuo Huang Ling Bai Jiun Chen Yun Wen Peng Shih Chong Tsai Fu Chuo Peng Chung Kuang Yang 《Mycotoxin Research》1987,3(2):58-64
The chemical reaction of cleavaging territrem B to give 3,4,5-trimethoxy benzoic acid by alkaline hydrogen peroxide was investigated. The method was applied for confirmation of the chemical structure of the aromatic moiety of territrem A, A’, B, and B’. The physicochemical properties of the aromatic cleavage product of territrem Aindicated the structure as 3,4-methylendioxy, 5-methoxy benzoic acid (or 4-methoxy, 6-carboxy, 1, 3-benzodioxole). The experiment also gave the evidences that territrem A and A’, on the other hand territrem B and B’ have the identical aromatic moieties on their structures. 相似文献
197.
AGAT, GAMT and CT1, three creatine synthesis and transport‐related molecules, have been widely studied in mammals. To explore their homologous genes in adult zebrafish Danio rerio, the gene expression patterns of these three genes in D. rerio were investigated. The results reveal that AGAT, GAMT and CT1 are expressed widely in diverse tissues of D. rerio where the homologous genes in mammals are also expressed. 相似文献
198.
Mason HA Rakowiecki SM Raftopoulou M Nery S Huang Y Gridley T Fishell G 《Development (Cambridge, England)》2005,132(19):4247-4258
Numerous lines of evidence suggest that Notch signaling plays a pivotal role in controlling the production of neurons from progenitor cells. However, most experiments have relied on gain-of-function approaches because perturbation of Notch signaling results in death prior to the onset of neurogenesis. Here, we examine the requirement for Notch signaling in the development of the striatum through the analysis of different single and compound Notch1 conditional and Notch3 null mutants. We find that normal development of the striatum depends on the presence of appropriate Notch signals in progenitors during a critical window of embryonic development. Early removal of Notch1 prior to neurogenesis alters early-born patch neurons but not late-born matrix neurons in the striatum. We further show that the late-born striatal neurons in these mutants are spared as a result of functional compensation by Notch3. Notably, however, the removal of Notch signaling subsequent to cells leaving the germinal zone has no obvious effect on striatal organization and patterning. These results indicate that Notch signaling is required in neural progenitor cells to control cell fate in the striatum, but is dispensable during subsequent phases of neuronal migration and differentiation. 相似文献
199.
200.
Kateryna Raykova Melina V. Jones Hwa Huang Paul F. Hoffman Michael Levy 《Journal of visualized experiments : JoVE》2015,(99)
The rat optic nerve is a useful model for stem cell regeneration research. Direct injection into the rat optic nerve allows delivery into the central nervous system in a minimally-invasive surgery without bone removal. This technique describes an approach to visualization and direct injection of the optic nerve following minor fascial dissection from the orbital ridge, using a conjunctival traction suture to gently pull the eye down and out. Representative examples of an injected optic nerve show successful injection of dyed beads. 相似文献