全文获取类型
收费全文 | 126783篇 |
免费 | 21830篇 |
国内免费 | 7736篇 |
专业分类
156349篇 |
出版年
2024年 | 214篇 |
2023年 | 1328篇 |
2022年 | 3008篇 |
2021年 | 5275篇 |
2020年 | 5182篇 |
2019年 | 7341篇 |
2018年 | 7389篇 |
2017年 | 6721篇 |
2016年 | 7932篇 |
2015年 | 9922篇 |
2014年 | 10709篇 |
2013年 | 11743篇 |
2012年 | 11187篇 |
2011年 | 9664篇 |
2010年 | 8052篇 |
2009年 | 6274篇 |
2008年 | 6037篇 |
2007年 | 5130篇 |
2006年 | 4541篇 |
2005年 | 3989篇 |
2004年 | 3457篇 |
2003年 | 3074篇 |
2002年 | 2625篇 |
2001年 | 2155篇 |
2000年 | 1976篇 |
1999年 | 1799篇 |
1998年 | 1005篇 |
1997年 | 918篇 |
1996年 | 892篇 |
1995年 | 833篇 |
1994年 | 735篇 |
1993年 | 518篇 |
1992年 | 752篇 |
1991年 | 587篇 |
1990年 | 526篇 |
1989年 | 397篇 |
1988年 | 338篇 |
1987年 | 319篇 |
1986年 | 246篇 |
1985年 | 243篇 |
1984年 | 151篇 |
1983年 | 163篇 |
1982年 | 101篇 |
1981年 | 88篇 |
1980年 | 54篇 |
1979年 | 89篇 |
1977年 | 51篇 |
1974年 | 57篇 |
1973年 | 63篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Canran Liu 《植被学杂志》2001,12(3):411-416
Abstract. The behaviour of five statistics (extensions of Pielou's, Clark and Evansapos;, Pollard's, Johnson & Zimmer's, and Eberhardt's statistics, which are denoted as Pi, Ce, Po, Jz and Eb respectively) that involve the distance from a random point to its jth nearest neighbour were examined against several alternative patterns (lattice‐based regular, inhomogeneous random, and Poisson cluster patterns) through Monte Carlo simulation to test their powers to detect patterns. The powers of all the five statistics increase as distance order j increases against inhomogeneous random pattern. They decrease for Pi and Ce and increase for Po, Jz, and Eb against regular and Poisson cluster patterns. Po, Jz, and Eb can reach high powers with the third or higher order distances in most cases. However, Po is recommended because no extra information is needed, it can reach a high power with the second or third distance even though the sample size is not large in most cases, and the test can be performed with an approximate χ2 distribution associated with it. When a regular pattern is expected, Jz is recommended because it is more sensitive to lattice‐based regular pattern than Po and Eb, especially for the first distance. However, simulation tests should be used because the speed of convergence of Jz to normal distribution is very slow. 相似文献
992.
The XbaI-BlnI-CeuI genomic cleavage map of Salmonella enteritidis shows an inversion relative to Salmonella typhimurium LT2 总被引:10,自引:0,他引:10
We have established the genomic cleavage map of Salmonella enteritidis strain SSU7998 using pulsed-field gel electrophoresis. The chromosome of 4600kb was analysed by XbaI (16 fragments), I-CeuI (7 fragments) and BlnI (12 fragments); the genome also contains a plasmid of 60 kb. Cleavage sites of I-CeuI, in the large subunit ribosomal RNA gene, are conserved from Salmonella typhimurium and Escherichia coli K-12, and the XbaI and BinI sites in glt-tRNA are also conserved, but other sites are less conserved. Transposon Tn10, located at 60 different positions in the chromosome of S. typhimurium, was transduced by bacteriophage P22 into S. enteritidis and the insertion mapped using the XbaI and BlnI sites on Tn10. Gene order in S. enteritidis is identical to S. typhimurium LT2 and similar to E. coli K-12 except for an inversion of 815 kb, which covers the terminus region including T1 and T2. Endpoints are in the NDZs, or non-divisible zones, in which inversion endpoints were not detected in experiments in E. coli K-12 and S. typhimurium LT2. This inversion resembles the inversion between S. typhimurium and E. coli, but is longer at both ends. 相似文献
993.
H. B. Li W. Yan G. R. Liu S. M. Wen C. J. Liu 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2011,122(2):395-403
Tan spot, caused by Pyrenophora tritici-repentis, is a foliar disease of wheat, and it can inflict serious reduction in grain yield and quality. The bread wheat variety Ernie
was found to be immune to this disease in Australia, and its genetic control was investigated by quantitative trait loci (QTL)
analysis using a doubled haploid population. Eight QTL were identified in this population from three independent trials, and
four of them were derived from the parent Ernie. The most significant QTL was located on chromosome arm 2BS, explaining 38.2,
29.8 and 36.2% of the phenotypic variance, respectively, in these trials. The effects of the 2BS QTL were further validated
in four additional populations. The presence of this single QTL reduced disease severity by between 29.2 and 67.1% with an
average of 50.5%. The significant effects of this QTL and its consistent detection across all the trials with different genetic
backgrounds make it an ideal target for breeding programmes as well as for its further characterization. Data from this study
also showed that neither plant height nor heading date significantly affects tan spot resistance. 相似文献
994.
995.
996.
Tai‐An Chiang Yu‐Lin Yang Ya‐Ying Yang Min‐Hsiu Hu Pei‐Fen Wu Shu‐Fen Liu Ruay‐Ming Huang Tung‐Nan Liao Chien‐Ya Hung Tsung‐Jen Hung Tao‐Chen Lee 《Journal of cellular biochemistry》2010,109(4):663-671
Hyperosmolarity plays an essential role in the pathogenesis of diabetic tubular fibrosis. However, the mechanism of the involvement of hyperosmolarity remains unclear. In this study, mannitol was used to evaluate the effects of hyperosmolarity on a renal distal tubule cell line (MDCK). We investigated transforming growth factor‐β receptors and their downstream fibrogenic signal proteins. We show that hyperosmolarity significantly enhances the susceptibility to exogenous transforming growth factor (TGF)‐β1, as mannitol (27.5 mM) significantly enhanced the TGF‐β1‐induced increase in fibronectin levels compared with control experiments (5.5 mM). Specifically, hyperosmolarity induced tyrosine phosphorylation on TGF‐β RII at 336 residues in a time (0–24 h) and dose (5.5–38.5 mM) dependent manner. In addition, hyperosmolarity increased the level of TGF‐β RI in a dose‐ and time‐course dependent manner. These observations may be closely related to decreased catabolism of TGF‐β RI. Hyperosmolarity significantly downregulated the expression of an inhibitory Smad (Smad7), decreased the level of Smurf 1, and reduced ubiquitination of TGF‐β RI. In addition, through the use of cycloheximide and the proteasome inhibitor MG132, we showed that hyperosmolarity significantly increased the half‐life and inhibited the protein level of TGF‐β RI by polyubiquitination and proteasomal degradation. Taken together, our data suggest that hyperosmolarity enhances cellular susceptibility to renal tubular fibrosis by activating the Smad7 pathway and increasing the stability of type I TGF‐β receptors by retarding proteasomal degradation of TGF‐β RI. This study clarifies the mechanism underlying hyperosmotic‐induced renal fibrosis in renal distal tubule cells. J. Cell. Biochem. 109: 663–671, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
997.
Chick embryos grown in ex ovo culture by the modified Cornish pasty method reported in Nagai, Lin and Sheng in this issue. 相似文献
998.
999.
Achieving a thorough explanation of the behavior of metal sites in the formation of native metalloprotein structures is an exciting challenge in the biochemistry of metallobiomacromolecules. This study presents a personal insight into the subject. It is proposed that a metal center and its exogenous ligand compose a template. A template may impose a clear stereochemical preference on the loose peptide chains, and organize them into natural stereospecificity via the metal-ligand interaction, a long-range and strong interaction. Therefore, the stable peptide conformation induced by the template effect surrounding a template polyhedron could be called a template-mediated structural motif (TMSM). 相似文献
1000.